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Photonic crystals: emerging biosensors and their promise for point-of-care applicationsHakan Inan, Muhammet Poyraz, [...], and Utkan DemirciAdditional article informationAbstractBiosensors are extensively employed for diagnosing a broad array of diseases and disorders in clinical settings worldwide. The implementation of biosensors at the point-of-care (POC), such as at primary clinics or the bedside, faces impediments because they may require highly trained personnel, have long assay times, large sizes, and high instrumental cost. Thus, there exists a need to develop inexpensive, reliable, user-friendly, and compact biosensing systems at the POC. Biosensors incorporated with photonic crystal (PC) structures hold promise to address many of the aforementioned challenges facing the development of new POC diagnostics. Currently, PC-based biosensors have been employed for detecting a variety of biotargets, such as cells, pathogens, proteins, antibodies, and nucleic acids, with high efficiency and selectivity. In this review, we provide a broad overview of PCs by explaining their structures, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-based biosensors incorporated with emerging technologies, including telemedicine, flexible and wearable sensing, smart materials and metamaterials. Finally, we discuss current challenges associated with existing biosensors, and provide an outlook for PC-based biosensors and their promise at the POC.1. IntroductionBiosensing is an emerging analytical field for the detection of biochemical interactions leveraging electrical, optical, calorimetric, and electrochemical transducing systems.1,2These transduction mechanisms are employed to translate changes and variations within the biological domain into a readable and quantifiable signal (e.g., association, dissociation, and oxidation).3Biosensors are most notably employed for detecting various biological targets, such as cells,4bacteria,5,6viruses,7proteins,8hormones,9enzymes,10and nucleic acids,11to facilitate the diagnosis and prognosis of diseases. Currently, state of the art clinical laboratories require trained personnel to perform sample collection, testing, and analysis using sophisticated biosensing devices in centralized clinical settings (Fig. 1). Staffing the necessary personnel to ensure accurate and reliable readings can be costly, and results are subject to operator error.12,13Although certain automated instrumentation has been used to simultaneously process multiple patient samples at large volumes (e.g., hematology analyzers), technicians are still needed for device oversight and maintenance.14,15Centralized laboratories also perform immunoassays and nucleic amplification strategies, but these methods are time consuming, labor intensive, and expensive. As an example, enzyme-linked immunosorbent assay (ELISA) requires several experimental steps, including antibody immobilization, target binding, labeling, substrate incubation, signal production, and multiple washing steps.16,17Fig. 1Current challenges of biosensing tests for the POC applications. Biosensors face critical impediments at the POC due to large sample volume, transfer of samples to a central site, and being bulky and expensive. These challenges are most obvious at remote ...Recently, substantial research efforts have been devoted to the development of in vitrodiagnostic tests including point-of-care (POC) devices with the market volume estimated to reach US$ 75.1 billion by 2020.18One of the main drivers for these POC technologies is the detection of diseases in resource-limited countries.19–25For example, commercial POC kits have been recently developed to detect human immunodeficiency virus (HIV) and tuberculosis in such settings.26However, there are significant logistical, technical, and social barriers that need to be overcome when performing testing at these sites, and many of these technologies still require the recruitment and training of personnel (Fig. 1).14,27–29,30Thus, there exists a need to develop affordable, sensitive, rapid, portable, label-free, and user-friendly POC diagnostic tools.31–33Incorporation of microfluidics and nanotechnology into biosensing platforms holds great promise to address the aforementioned challenges. Sensitive technologies, such as localized and surface plasmon resonance, electrical sensors, interferometric biosensors, and photonic crystal (PC)-based bio-sensors, have been employed as diagnostic devices (Table 1).34–40PC-based biosensors hold many advantages over other existing competing biosensing technologies, including cost-effective fabrication and short assay time (Table 2). PC structures have been used to detect a wide array of biotargets in biological sample matrices, such as blood, urine, sweat, and tears,41–43and can be fabricated using various inexpensive fabrication methods, such as colloidal self-assembly, hydrogels, and mold-based replica imprinting.44–46Table 1General overview of PC-based biosensorsTable 2Comparison of PC-based biosensors with selected competing technologiesIn this review, recent incorporation of PC structures within emerging label-free biosensing platforms is discussed, including their applications for detecting proteins, nucleic acids, allergens, pathogens, and cancer biomarkers.47–50We will also provide a broad overview of PC structures and PC-based biosensors and their potential utilization as POC diagnostic tools. We describe various aspects of PC-based biosensors, including (i) PC structures and fabrication techniques, (ii) principles of PC-based biosensing, (iii) emerging technologies incorporating PC-based biosensors for potential POC applications, (iv) multi-target detection capability for PC-based biosensors, (v) surface chemistry approaches, (vi) current challenges and limitations for biosensors at the POC, and (vii) future outlook for PC-based biosensors at POC diagnostics.2. Photonic crystal structures and fabrication techniquesPC structures consist of spatially arranged periodic dielectric materials that uniquely interact with light, providing high efficiency reflection at specific wavelengths. There are many examples of PC-type periodically nanostructured surfaces observed in nature.51For instance, the bright iridescent color of the Morpho rhetenor butterfly,52peacock,53Eupholus magnificus insect,54sea mouse55and opals56are all associated with the geometrical arrangement on their surface, where broadband light illuminates and reflects through PC structures (Fig. 2).52In practice, PC structures can be fabricated in one-dimensional (1-D), two-dimensional (2-D) or three-dimensional (3-D) orientations incorporating microcavities,57waveguides,58slabs,59multi-layered thin films,60and porous geometries61(Fig. 3). A diverse range of materials, such as silicon (Si),62glass,63polymers,64colloids,65–68and silk,69–71are used in the fabrication of PC structures (Table 1).Fig. 2PC structures commonly found in the nature. Bright iridescent color of these objects is due to the presence of geometrical periodic elements in their structures. Shown are four types of PC structures: 1. (a and b): 1-D (Morpho rhetenor butterfly), 2. ...Fig. 3Types of photonic crystals. (a) 1-D slab is one of the most exploited PC structures for biosensing applications. Refractive index alternates in one dimension only (in x, or in yaxis) by forming air gaps in between substrate structures.227It also possess ...PC structures are fabricated using various methods, including self-assembly and lithography techniques. For instance, colloids composed of hydrogel polymers,72silica,73or polystyrene74are transferred from solution and self-assembled (viasedimentation, spin coating, or vertical deposition44,75) onto a surface to create PC structures that reflect iridescent color.75–77In addition, hydrogels are utilized in combination with colloidal particles in the fabrication of PC structures. While these self-assembly methods are inexpensive, precisely controlling the dimensions and geometry of the underlying PC structure is difficult. Top-down approaches, including electron beam lithography (e-beam), nanoimprint lithography (NIL), electrochemical etching, and thin film deposition techniques,78,79are alternatives to bottom-up self-assembly methods. Briefly, in the e-beam process, an electron beam is used to write a desired pattern onto a substrate (often silicon), which is previously coated with an electron-sensitive resist. The resist is then developed, and the electron-beam pattern is transferred to the substrate via etching. Performing this method requires e-beam lithography devices, which are large, expensive and require skilled operators. NIL is a rapid, simple, and scalable pattern transfer technique alternative to e-beam lithography.80In NIL, a pattern is initially produced using deep UV/e-beam lithography on a master mold, which can be easily transferred to daughter replicas. The NIL method has been used to mass-produce PC structures rapidly and reliably; however, only a finite number of replicas can be generated from a single mold due to wear.79Electrochemical etching can be used to fabricate porous Si structures that produce a photonic band gap due to formed periodic trenches. Electrochemical etching of Si is inexpensive and can be performed in research labs. Although trenches and channels provide a higher surface area for chemical interactions, large biomolecules may cause aggregation and blocking of the channels (e.g., cells) when using clinical samples.Overall, a wide range of materials and fabrication methods is available for the development of PC structures. Using PC structures for POC applications is highly feasible due to the availability of inexpensive fabrication materials such as hydro-gels and colloidal particles and the scalable production method using NIL. The theoretical background behind the PC phenomenon and how these PC structures are used as biosensors are discussed in the following section.3. Principles of PC-based biosensingA periodic arrangement of dielectric materials creates a photonic band gap when a range of electromagnetic waves cannot propagate due to the destructive interference of incident light with reflections at dielectric boundaries.81PC structures can be produced from a variety of geometries, including Bragg reflectors, slabs, opals, microcavities, and colloids. An optical phenomenon describing most of these structures can be deduced from understanding a simple Bragg structure. A typical Bragg reflector consists of alternating high and low refractive index dielectric thin film layers (Fig. 4a). The optical thicknesses of these layers are designed to be one quarter of the wavelength of incident light (λ) (eqn (1)). Multiple reflections from consecutive layers provide constructive interference and result in total reflection (Fig. 4b). Light at this reflected wavelength resides in a photonic band gap region (Fig. 4c), and cannot propagate at normal incidence.82Fig. 4The design and optical response of simple PCs. (a) A Bragg reflector consisting of alternating low and high refractive index of dielectric layers. At specific wavelengths, reflections from consecutive layers constructively interfere with each other and ...(1)Another common PC structure is comprised of periodically modulated thin films, which are known as 1-D slabs. 1D-PC structures are commonly fabricated from a high refractive index coating layer over a periodically arranged low refractive index grating layer (Fig. 4d). In these PC gratings, only the zeroth order mode is allowed, while higher order modes are restricted at normal incidence, provided that the period of the grating (Λ) is smaller than the wavelength of the incident light (Λ < λ). Gratings of this type are also called subwavelength gratings, and exhibit efficient optical resonances.83Subwavelength PC gratings can be designed to reflect a narrow band of wavelengths and produce a sharp peak in the reflection spectrum (Fig. 4e).84,85Resonance occurs when a diffracted mode from the grating couples to a leaky waveguide mode. Radiation from the leaky mode constructively interferes with the reflected wave and destructively interferes with the transmitted wave, resulting in a resonant reflection.83The resonance wavelength peak is determined by the period (Λ) of PC gratings and the effective refractive index (neff) under resonance conditions (eqn (2)).86λresonance= neffΛ(2)This resonance behavior of PC gratings is highly sensitive to the localized changes in dielectric permittivity on the crystal surface, which makes it suitable for sensing applications. In this regard, PC structures are widely utilized to develop sensing platforms for multiple applications of chemical sensing, environmental sensing, and more specifically, biosensing.87–90Briefly, a biochemical interaction (e.g., binding) on the PC surface causes a change in the effective refractive index, which results in a shift of the resonance wavelength peak, which is proportional to the concentration of the biotarget (Fig. 5). PC structures have gained significant attention as sensitive transducers and have been incorporated into biosensors that capture, detect, and quantify various biological molecules, such as pathogens,7,47,91–96DNA,97–101proteins, enzymes,102,103glucose,42,104–106cells,107,108toxins,109and allergens.110Fig. 5Overall mechanism of biosensing using photonic crystals. (a) An example of the 1-D PC slab surface. (b) Corresponding resonance peak wavelength for this PC slab. (c) Functionalization of the slab surface and biological binding event via antigen–antibody ...4. Emerging technologies incorporating PC-based biosensors for potential POC applicationsRecent advances in microfluidics, telemedicine, flexible materials, and wearable sensing technologies hold promise to provide compact and portable platforms in biosensing applications at POC for the rapid, reliable, accurate, on-site, and label-free detection of biotargets.111–1184.1 MicrofluidicsMicrofluidics technology offers considerable benefits to bio-sensing systems, particularly the POC devices. These advantages include (i) inexpensive fabrication materials (e.g., glass, paper and polymers), (ii) ability to control low sample volume, (iii) ease of integration with optical platforms, and (iv) flexibility in producing multiple channels to allow multiplexed testing platforms.119–121PCs-integrated with microfluidic technologies are emerging as powerful biosensing diagnostic tools with the integration of these features.50,122For instance, integration of 1-D PC slabs within a microfluidic channel network at the bottom of a 96-well plate was used to detect immunoglobulin gamma (IgG).46This microfluidic-integrated platform enabled the concurrent multiplex detection of molecules using only 20 μL of the sample (Fig. 6). In another study using a colloidal polystyrene-based PC structure integrated with microfluidics, IgG molecules were captured and detected down to mg mL−1levels.123PC structures have also been incorporated with polymer microfluidic channels to detect proteins; for example, a slotted PC cavity fabricated from Si was shown to detect 15 nM of avidin protein.124,125Fig. 6PC biosensors integrated with microfluidic platforms for POC applications. (a) Multi-well plate integrated with a network of microfluidic channels with PC-based biosensors at the bottom. Reproduced from ref. 46 with permission from The Royal Society of ...4.2 TelemedicineSmartphones have been increasingly utilized in medical diagnostics and healthcare applications, such as cell counting from whole blood, immunoassay testing, and imaging.111,126,127Smartphones will likely play an important role in the development of new biosensing platforms due to their wide availability, portability, compactness, capacity for data processing, ease of integration with microfluidic devices, and high-resolution optical components.111,128Recently, camera and optical systems in cell-phones have been integrated with microfluidic, microscopy, and photonic crystal technologies for the spectral analyses of bio-sensing applications.126,129–134For instance, a 1-D PC slab was integrated with a smartphone to measure IgG concentration. The phone camera was used as a spectrometer to measure the transmission spectrum from the PC structures.135Although the system produced a reliable dose–response curve, adsorption of biomolecules could only be measured under dry conditions. Thus, further study with aqueous samples is required before this platform could be used to directly analyze clinical samples at the POC. In another study, a 1-D PC slab was integrated with a complementary metal–oxide–semiconductor (CMOS)-based smartphone camera to detect anti-recombinant human protein CD40 (Cluster of Differentiation-40), streptavidin, and anti-EGF antibody (Fig. 7).136Fig. 7PC structure integrated with a smartphone for biosensing applications at the POC. (a) Drawing representing a general scheme of a PC incorporated smartphone. The CCD camera of the phone was utilized as an optical sensing element. (b) Actual image of the ...Smartphone-integrated platforms hold promise to address portability related issues at the POC, though their direct use in clinical applications is challenging because complex specimens, such as blood and tissue, need to be preprocessed before being brought into contact with the device.4.3 Wearable and flexible sensorsWearable sensors and flexible materials have recently gained attention for continuous and real-time monitoring of the physiological parameters and general health status of individuals.137–142For instance, they have been employed to measure the heart rate, skin temperature, blood oxygen levels, and more recently glucose sensing from sweat.143–145Wearable sensors are currently worn as wristbands, skin patches, and fabric patches. From a fabrication perspective, various nanotechnology-based techniques and materials are used for the production of these flexible and wearable sensors. In a recent study, a PC structure was designed with 2-D holes (with a diameter of ~100 nm) to evaluate strain changes.146This flexible sensor could be bent without losing its optical properties (Fig. 8a and b), and provided a sensitivity that was independent of deformation. In another study, colloidal polystyrene spheres were deposited on a flexible polyimide film.147A strain applied over this flexible film resulted in a blue shift in the reflection maxima (Fig. 8c and d).Fig. 8Flexible and wearable PCs in sensing applications. (a) Picture of the Si membrane integrated with a photonic crystal. (b) 2-D holes with a waveguide to couple light into a flexible photonic crystal structure. Reproduced from ref. 146, copyright (2014) ...3-D PC structures have also been incorporated into wearable sensors. For example, 3-D PC structures were investigated under pressure and may conceptually be used for detecting the severity of blast exposure to evaluate traumatic brain injury of soldiers in the battlefield.148,149In this study, 3-D voids were fabricated in an SU-8 resist to create 3-D PC structures that exhibited a color in the visible spectrum. These structures were exposed to varying high pressures (410 to 1090 kPa) to measure blast strength (Fig. 8e), and it was determined that large external forces could be detected by visual inspection (Fig. 8f–h). The PC structure that was exposed to high external forces underwent structural deformation, resulting in a color change. This change was used to estimate the degree of pressure on the PC structure. While this work is promising, using these detectors on soldiers’ uniforms is conceptual and their implementation in this field has not yet been evaluated.4.4 Smart materialsSmart materials are an emerging class of responsive substances that can modify their physical or chemical properties, mostly reversibly, against external stimuli such as pH, temperature, electrical field, and light.150,151Smart materials, such as hydrogels, polyionic liquids, graphene, and carbon nanotubes (CNTs), have been used for various applications, including biosensing. In particular, their incorporation into PC structures holds promise for rapid, sensitive, and reliable biosensing. Hydrogel materials are 3-D nanostructured polymers consisting mostly of water. Hydrogels may be responsive to external stimuli, such as temperature, pH, or bio-stimuli such as antigen–antibody interactions.45,72,152–155For instance, PC structures comprised of hydrogel materials can be used as biosensors for the detection of DNA, proteins, antibodies and enzymes by monitoring the changes in lattice spacing or refractive indices.41,43,156–159In this respect, hydrogel-based PC structures provide either quantitative spectral results or qualitative naked-eye detection of biotarget concentrations.41Hydrogel-based PC structures hold great promise for POC applications owing to their cost-effective fabrication and simple optical detection systems. In a recent study, a hydrogel-based nanoporous PC structure was employed for label-free detection of rotavirus with concentrations ranging from 6.35 μg mL−1to 1.27 mg mL−1(Fig. 9a and b).160Polyionic liquids (PILs) are a class of polymeric materials containing repeating ionic monomeric units, which have recently been demonstrated for sensing applications.161,162In one such study, PIL was used to fabricate a 3-D macroporous PC structure, that exhibited Bragg reflection in the visible wavelength range, to detect a variety of ions.163Fig. 9Smart material- and metamaterial-based PCs for sensing. (a) Hydrogel-based PCs for the detection of rotavirus. (b) SEM image of the hydrogel structure. (a and b are reproduced from ref. 160 with permission from The Royal Society of Chemistry) (c) 3-D ...Hydrogels can also be used in combination with other materials including graphene or carbon nanotubes (CNTs) to produce PC structures. In one such study, graphene oxide was deposited on a silicon wafer and embedded into a hydrogel matrix to detect beta-glucan.164Graphene based-PC structures have also been investigated for enhanced sensitivity biosensing.165In addition, CNTs were incorporated into PC structures that provided a photonic band gap in the visible light spectrum.166Recently, CNT-based PC structures were investigated for optical applications.167–169Smart materials have been studied extensively and have the potential to be utilized as biosensors due to the unique properties of each material. However, they require further validation using clinical matrices.4.5 MetamaterialsRecently, PC structures based on metamaterials have been investigated for various applications, including imaging and biosensing.169–172For instance, a PC metamaterial with a 3-D woodpile geometry was proposed to excite plasmons with high spectral sensitivity.170The proposed structure was a silver-coated woodpile crystal providing a high surface-to-volume ratio with a sensitivity more than 2600 nm per refractive index unit (RIU) (Fig. 9c and d). In another study, a hyperbolic metamaterial biosensor consisting of 16 alternating layers of thin Al2O3(aluminum oxide) and gold layers was demonstrated to detect biotin (Fig. 9e) with very high sensitivity up to 30 000 nm per RIU.171This 1-D multilayer structure supported guided modes ranging from visible to near infrared, enabled optical biosensing at different spectral regions with ultra-high spectral sensitivity, and detected 10 pM biotin in phosphate buffered saline (Fig. 9f). Light coupling was achieved with a 2-D gold diffraction grating on top of the multilayer films, eliminating the need for additional optical elements (e.g., prism). Although metamaterial-based biosensors enable label-free detection with high sensitivity, they require multiple fabrication steps and may not be compatible with clinically relevant matrices (i.e., whole blood, urine, and saliva).Overall, the integration of PC structures with emerging technologies is promising for biosensing applications at POC owing to compact, flexible, and easy-to-use platforms. In particular, PC-based biosensors composed of smart materials may create a new class of flexible and wearable POC sensors with high sensitivity.5. Multi-target detection capability for PC-based biosensorsPC-based biosensors have been employed to detect multiple biological targets, such as pathogens, proteins, nucleic acids, and glucose, for the diagnosis of a broad range of diseases, including diabetes and cancer. Here, we provide a broad perspective of using PC structures to quantify various molecular interactions ranging from biotin–streptavidin to cancer biomarkers.1735.1 Protein detectionPC structures have been used to capture and detect numerous proteins, such as protein A, Immunoglobulin Gamma (IgG), bovine serum albumin (BSA), and Protein G.157,174,175Streptavidin is often used in conjugation with biotin in experiments to validate the sensitivity and detection limit of new PC geometries due to the extraordinary affinity of streptavidin for biotin.123,176,177PC structures have been employed to investigate the substrate specificity and catalytic activity of certain enzymes, such as acetyl cholinesterase, pepsin and other proteases.103,178In one study, a porous Si-based PC structure was developed to evaluate proteolytic activities of pepsin and subtilisin proteases down to 7 pmol and 0.37 pM, respectively. When coupled with a fluorescence assay, a PC surface can significantly amplify the fluorophore intensity, increase the signal-to-noise ratio and reduce the detection limits. For example, a PC structure was coupled with fluorescence-labeled secondary antibody to detect TNF-α concentrations at pg mL−1levels.185The ability of an assay to detect disease targets at low concentrations at an early stage is very important. In this research, imaging of the PC spots was performed for the multiplex detection of different proteins.Colloidal PC structures have also been widely employed for protein detection. For instance, arranged colloidal nanoparticles embedded inside a hydrogel were used to visually monitor a reflectance shift in response to protein concentration.157In this study, silica nanoparticles were embedded within a poly(ethylene glycol)-diacrylate hydrogel to generate a PC structure. This system was able to observe IgG proteins bound to protein A on the surfaces of the embedded nanoparticles. A color change from orange to green was observed after exposure to 10 mg mL−1IgG, and the detection limit in the color shift was at the concentration of 0.5 mg mL−1IgG (Fig. 10). Since this procedure uses a self-assembly deposition method and does not require advanced manufacturing technology, it is cost-effective; however, the concentrations necessary to observe a visual change are high, and thus, may not be compatible with sensitive detection applications.Fig. 10PC biosensor for capturing and quantification of protein molecules. (a) Colloid PC structure was used to capture IgG proteins. (b) IgG bound to the colloid PC surface and changed the reflected color. (c) Image of the PC surface. A color shift was observed ...By coupling with fluorescence-labeled secondary antibodies, PC-based biosensors have also been utilized to capture allergen-specific immunoglobulin (IgE) antibodies.110,179,180PC structures can enhance fluorescence signals when the optical resonance of the PC surface overlaps with either the excitation or emission spectra of a fluorophore. This enhanced excitation and emission yielded ~7500-fold increase in fluorescence signals.181In a recent study, a PC-enhanced fluorescence (PCEF) microarray platform was used to detect low concentrations of IgE in human sera with a limit of detection of 0.02 kU L−1, which was comparable to current blood-based IgE detection methods.110However, current PC-based allergen platforms rely on fluorescence detection, which limits their use at the POC due to the requirements for labeling, additional instrumentation, and multiple assay preparation steps.5.2 Nucleic acid detectionBiosensing of DNA, RNA, and DNA–protein interactions using PC-based platforms has been studied for various applications, including the determination of infectious agents, identification of genetic disorders,182–185and monitoring of DNA–protein interactions.97,173,186For instance, DNA and protein interactions were evaluated using a 1-D PC slab structure with a TiO2layer over a low index material, and DNA was detected down to nanomolar concentrations.173In this study, a panel of 1000 compounds were screened on a microplate-integrated PC-based biosensing platform (Fig. 11a–c). This platform uses multiple fibers, a motorized stage, and a coupled readout system (SRU Biosystems Bind Reader) capable of recording simultaneous readings from 384-wells. This platform has significant potential for drug-screening studies at the POC in resource-constrained settings since it incorporates a disposable and inexpensive 384-well microplate. The platform can further be utilized for the detection of RNA–protein and protein–protein interactions, and may shed light on gene expression at the cellular and molecular levels.187In addition to 1-D PC slab structures, colloid PCs have also been utilized for nucleic acid detection. In this study, self-assembled polystyrene beads were utilized to fabricate a colloidal PC structure that could detect hybridized DNA down to 13.5 fM.188In another study, a planar waveguide was employed for the detection of single-stranded DNA at a concentration of 19.8 nM.98The use of PC structures is a promising alternative to the conventional polymerase chain reaction (PCR) techniques for nucleic acid detection due to their low cost, ease-of-use, rapid response, and high detection capacities.Fig. 11Monitoring DNA–protein interaction using a PC biosensor. (a) Image of a 384-well plate integrated with a PC platform for drug screening. (b) Drug screening for protein–DNA binding inhibition. An outstanding molecule was recorded using ...5.3 Applications in cancerBiosensors are widely employed in the detection of biomarkers for diagnosis and prognosis of cancer. Currently, various bio-markers, such as epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), prostate-specific antigen (PSA), carcinoembryonic antigen (CEA), tumor necrosis factor-α (TNF-α), and calreticulin (CRT), are under clinical study for diagnosis of cancer.189–191Detecting these biomarkers at an early stage of malignancy can contribute to better treatment outcomes and significantly increase the quality of life for cancer patients.Recently, PC-based biosensors have been employed in diagnosis and early detection of cancer.189,192,193In one study, a waveguide integrated with a cavity was employed for the detection of CEA protein for the diagnosis of colon cancer (Fig. 11d–f).192This platform provided a detection limit for CEA protein down to the 0.1 pg mL−1level. In another study, a cavity and a line defect were fabricated on the surface of a silicon substrate to capture lung cancer cells.189In another study, 1-D PC slabs obtained from quartz materials were fabricated via NIL. This PC-based platform was used to detect 21 different cancer biomarkers, including HER2, EGFR, and prostate-specific antigen (PSA) with a detection range from 2.1 pg mL−1to 41 pg mL−1.193This multiplexed cancer biomarker platform can function in both fluorescence and non-fluorescence modes, providing flexibility to work with labelled and non-labelled biotarget sensing.5.4 Pathogen detectionRapid identification and quantification of pathogens, such as bacteria and viruses, is important for diagnosis and prognosis in the POC environments at resource-constrained settings. Recently, PC structures have been deployed at the POC for diagnoses of infectious diseases caused by pathogenic agents and toxins.92,109,194For instance, 2-D PC pillars, fabricated on polymer substrates using NIL, were used for the detection of human influenza virus (H1N1) in human saliva. This platform can detect H1N1 antigens at a concentration as low as 1 ng mL−1.93In another study, polymer-2-D pillar PC structures were used to detect L. pneumophila bacteria down to 200 cells per mL.96PC-based platforms can also be used for the detection of viruses such as rotavirus, HIV-1, and human papilloma virus-like particles.92,94,195To detect HIV-1, a PC surface was functionalized with anti-gp120 antibody for capturing HIV-1 ranging from 104copies per mL to 108copies per mL (Fig. 11g–i). In another study, silica microspheres were used to fabricate colloidal PC structures for the detection of multiple mycotoxins in cereal samples.201Although microspheres are fabricated inexpensively as droplets in water–oil two-phase flow, this system still depends on fluorescence measurements and may be subject to undesirable background variation due to the inherent labelling procedure.1965.5 Glucose sensingDetection of glucose holds significant importance in POC diagnostics for diabetics.197,198Although glucose sensors are globally available as POC tools, there is still a need for non-invasive glucose biosensing using new and advanced technology sensing platforms, including PC-based biosensors.199,200Non-invasive monitoring can be achieved by collecting samples other than blood such as sweat, tear fluid, and urine. For instance, a hybrid photonic structure (1-D Bragg gratings) was fabricated from silver nanoparticles and a hydrogel to detect glucose, fructose, and lactate. This platform was tested with urine samples from diabetes patients with a detection limit of 90 μM.41In another study, the poly(hydroxyethyl methacrylate)-based (pHEMA) matrix was UV cross-linked, and silver nanoparticles were dispersed in this hydrogel. A pulse laser was then used to align the silver particles in confined regions creating a periodic structure, which ultimately provided PC properties.201Furthermore, the platform was also tested in artificial tear fluid for accurate glucose sensing (Fig. 12). This platform is unique because it employs inexpensive hydrogels and can be linked to biomolecules by easy conjugation with carboxylic groups. In this study, PC structures were fabricated from polystyrene colloidal spheres integrated with hydrogel for glucose sensing at 50 μM.Fig. 12Glucose sensing from urine using a PC biosensor. (a) Scheme of Ag incorporated hydrogel PC structure. (b) Simulation of a PWS as a result of the pH change. (c) The PWS at varying pH values and its corresponding observable color code. Reproduced from ref. ...Overall, although PC-based platforms have been employed for the detection of glucose with encouraging results, their widespread utilization for glucose sensing and diabetes diagnosis needs to be evaluated for reliable and accurate sensing.6. Surface chemistry approaches in PC-based biosensing applicationsPC-based biosensing platforms consist of an optically active layer and immobilized binder molecules, such as affibodies, nanobodies, peptides, antibodies, and antibody fragments to ensure biotarget capture.157,158,202Depending on the material type used for the optically active layer, binder molecules can be immobilized using various functionalization strategies, including physical adsorption (physisorption), covalent binding, and affinity-assisted coupling. Furthermore, anti-fouling agents play an important role in reducing the non-specific interactions and improving the sensitivity and specificity. In this section, we discuss surface chemistry approaches for TiO2-, Si-, and SiO2- based PC sensors, as well as anti-fouling agents to minimize non-specific binding.Physical adsorption strategies are used to accumulate bio-targets onto optically active layers via hydrogen bonds and van der Waals interactions. By applying plasma techniques, the net charge on a surface can be changed to increase the surface coverage of a biotarget.203For instance, PC waveguide structures with a Si layer were employed to monitor the physisorption of bovine serum albumin (BSA).35In this study, a BSA solution was directly applied to the PC waveguide surface and non-specific physical adsorption of BSA molecules was monitored. Although physisorption is simple, easy-to-apply, and does not require any wet-chemistry or laborious modification steps, it can interfere with other biomolecules in the detection buffer. Furthermore, physisorption is based on weak interactions between the surface and the biotarget, and is therefore not stable and can easily detach when surface charge is altered by changes in pH, ionic content, and temperature.Covalent binding is one of the standard methods for immobilization approaches using the strong chemical linkage that forms between a sensor surface and binder molecules. TiO2and SiO2surfaces are common substrates for optical sensors; however, performing coupling on these surfaces is laborious since it requires layer-by-layer surface functionalization including surface activation, functional group generation, and binder immobilization. Silane-based molecules with a variety of functional groups are commonly used to immobilize biomolecules onto glass surfaces. A standard protocol for silanizing a surface begins with cleaning the surface using a strong oxidizing agent, such as piranha solution (a mixture of H2O2and H2SO4) to increase the density of silanol groups exposed on a surface, which also increases the hydrophilicity of the sensor surface. Then, a silanization agent, such as (3-aminopropyl)triethoxysilane (APTES) or (3-aminopropyl)trimethoxysilane–tetramethoxysilane (MPTMS or 3-MPS), is applied to generate a self-assembled monolayer (SAM), which consists of hydroxyl groups, alkyl backbone chains, and functional tail groups.204,205Alkyl chains enable the height of captured biotargets to be adjusted from the sensor surface, and can also contain active tail groups, such as amine, carboxyl, and succinimide esters to tether binder molecules (Fig. 13).Fig. 13Surface chemistry approaches for PC-based biosensors. Initially, the PC surface (i.e., TiO2) is treated with piranha solution and/or oxygen plasma to increase the hydrophilicity by exposing polar molecules on the surface. The surface is then immersed ...The latter surface functionalization approach provides affinity-based interactions at specific regions on binders and anchor molecules.206However, clinical samples have a complex composition including proteins, lipids, and sugar units that can non-specifically adhere to a sensor surface. Non-specific binding can occur at active, passivated, and untreated areas on the sensor. Anti-fouling agents, including chemical modifiers, proteins, and polymeric substances, serve to prevent non-specific binding and increase the detection accuracy of target molecules. Furthermore, working with biospecimens requires sample preparation steps to avoid signal fluctuations and inaccuracies, considerably increasing the complexity of biosensing assays.207,2087. Current challenges and limitations for biosensors at the POCIn this section, we discuss a number of emerging technologies with respect to challenges associated with current biosensors at the POC. These criteria include label-free sensing, assay complexity, assay time, multi-target detection, read-out mechanisms, fabrication methods, and applicability for clinical testing. We compare PC-based biosensing platforms with up-to-date bio-sensing technologies: nanomechanical sensors, plasmonics tools, electrical sensing platforms, and magnetosensors (Table 2).7.1 Label-free biosensingLabeling of biotargets, often with fluorescence molecules, has been extensively utilized in biosensing applications to enhance signal readout for improving measurements. However, introducing a label potentially adds complexity, increases experimental errors, and presents additional inefficiencies and uncertainties, such as quenching effects and photobleaching.209Additionally, labeling a biomolecule can significantly alter its characteristic properties (conformation, solubility, and affinity).210Considering the challenges associated with labeling, label-free assays can reduce cost, complexity, and time for POC tests by eliminating the use of labels, dyes, and high-volume of reagents.211–213Therefore, there is a demand for label-free, rapid, sensitive and accurate bio-sensing platforms at the POC, which will address the challenges associated with current label-based biosensor strategies. In this regard, PC structures represent a new class of biosensors that hold promise for label-free biosensing with potential applications at the POC.7.2 Assay timeTo be sustainable, emerging technologies need to provide rapid, inexpensive, and multiplexed solutions over existing assays and methods. Some platforms require filtration-type sample preparation steps to concentrate targets in the sample, which also increases assay complexity and time.214From a POC perspective, biosensing platforms need to be fabricated with inexpensive materials and methods using simple and inexpensive production techniques. For instance, some of the biosensing platforms require clean room facilities and multiple chemical etches for their fabrication, which may significantly increase the total assay cost.214The read-out mechanism is another pivotal criterion to obtain reliable measurements at the POC. For instance, nano-mechanical platforms, including quartz crystal microbalance and piezoelectric sensors, are affected by multiple external parameters such as temperature and vibration and require additional equipment (e.g., vibration insulation and temperature control systems) to minimize these external interferences to ensure reliable measurements.215This additional equipment limits the portability and may also increase the cost, thus not satisfying some of the key requirements for a POC device.7.3 Multiplexing capabilityAn ideal biosensing platform needs to detect multiple targets. This feature will provide a wide window to evaluate different targets on a single platform, increasing its applicability for versatile POC testing. To immobilize various antibodies/binders onto a single sensor surface, PC-based biosensor platforms can benefit from antibody printing technologies (Table 2).1937.4 Clinical validationBiological specimens, such as blood, saliva, urine, and sweat, have distinct characteristics. These matrices have various ionic content, ionic strength, pH, and a diverse makeup comprised of cells, proteins, and lipids. Detecting biotargets in biological matrices constitutes one of the major challenges for biosensing. For instance, electrical-based sensing platforms measure electrical potential via different modalities, such as amperometry, potentiometry, and capacitance read-outs. Most of these platforms require replacing the biological matrix with non-ionic fluids, and therefore multi-step flow or centrifugation is required to minimize or eliminate interfering factors for read-out.115,216Ultimately, biosensors need to undergo extensive clinical validation before they can be used at the POC.8. Future outlook for PC-based biosensors at POC diagnosticsThe global biosensor market is valued at approximately US$ 13 billion in 2013 and projected to grow substantially to US$ 22 billion by 2020.217On-site (bedside) biosensors at the POC are poised to transform the healthcare industry as invaluable tools for the diagnosis and monitoring of diseases, infections, and pandemics worldwide. Advances in flexible, wearable, and implantable sensing technologies integrated with responsive materials can potentially connect patients to the clinic, thus providing continuous monitoring, such as glucose sensing for the patients with diabetes at the point-of-need.218,219Due to their characteristics including flexibility (e.g., hydrogels) and integration capability with smart materials (e.g., CNTs and graphene), PC-based sensors will be an asset to the current wearable continuous monitoring tools and sensors.A color shift that can be observed with the naked eye or with the help of a color legend is valuable at the POC. One interesting potential application for PC-based structures is to dynamically change the optical properties in response to environmental parameters, such as geometry, pH, and temperature. An example can be found in nature as suggested by a recent study on chameleon skin, which revealed the presence of guanine pillar-like nanocrystal PC structures.220When relaxed, crystals were randomly distributed, but changed to a square or hexagonally-packed lattice geometry when excited, thereby changing the skin’s visible colors (Fig. 14). Inspired by this example, PC structures could also be fabricated as simple diagnostic tools to produce a color shift against an external stimulus with a subsequent change in geometry. This method may potentially eliminate the need for large and expensive optical devices for biosensors in the POC applications.Fig. 14Spatial arrangements of PC structures in chameleon’s body. (a) The color change of two male chameleons. The left column indicates the relaxed state; the right column indicates the excited state. (b) TEM images of these two states. In the relaxed ...PC structures with more complicated geometries, such as 2-D PCs, are sensitive to changes in the refractive index in nano-and micro-scale volumes. Large wavelength shifts were experimentally observed after binding single sub-micron sized metallic and polymeric nanoparticles.122,221–224Detection of virus particles using these structures are highly promising, since viruses strongly interact with light, and can be easily captured on top of or inside photonic crystals.34,194However, biological detection of viral particles using 2-D PC structures has been difficult due to the low refractive index contrast between water and biological targets. Recent work with human papillomavirus-like particles spiked into serum has suggested that the detection of biologically relevant particles is possible, with a detection limit in the nanomolar range.929. ConclusionDetection of biomolecules at the POC faces multiple challenges, including the lack of centralized labs, limited technical capabilities, the absence of skilled staff, and poor health care management systems (particularly in resource-limited settings). PC-based biosensors represent a novel class of advanced optical biosensors that readily address these drawbacks. PC structures are used as biosensors for cells, bacteria, viruses, and numerous biomolecules, such as proteins, cancer biomarkers, allergens, DNAs, RNAs, glucose, and toxins. These structures can be manufactured with metals, oxides, plastics, polymers, and glass in mass quantities using NIL technology or wet chemical synthesis of colloidal and polymer structures. Recently, PC structures have been integrated with emerging technologies such as smart-phones, flexible materials, and wearable sensors to enhance their utilization as potential diagnostic tools at the POC. However, clinical specimens may require sample preparation steps such as filtration, which may limit the use of PC-based biosensors at the POC. Additionally, complex biological fluids comprising cells and tissues may interfere with the transducer of biosensors and some of the delicate PC structures might experience challenges with the sensing mechanism including read-out systems. In addition, PC structures have been translated to a few products in biosensing, chemical and humidity sensing. PC-based biosensors represent a new class of advanced technology products that can be good candidates for a wide array of applications at the POC.AcknowledgmentsU. D. is a founder of and has an equity interest in: (i) DxNow Inc., a company that is developing microfluidic and imaging technologies for point-of-care diagnostic solutions, and (ii) Koek Biotech, a company that is developing microfluidic in vitrofertilization (IVF) technologies for clinical solutions. U. D.’s interests were viewed and managed in accordance with the conflict of interest policies. U. D. would like to acknowledge National Institutes of Health (NIH) R01 A1093282, R01 GM108584, R01 DE02497101, NIH R01 AI120683.BiographiesHakan InanHakan Inan is a postdoctoral research fellow at the Canary Cancer Early Detection Center at the Medicine Faculty, Stanford University. He is working on microfluidics and nanotechnology-based diagnostic devices and techniques for cancer diagnosis and prognosis for point-of-care applications. He obtained his Master and PhD degrees in nanotechnology. He joined Professor Utkan Demirci’s lab at Stanford University in 2014 as a visiting graduate student and has performed his research in the same group since then. He has 12 years of teaching experience at high school and undergraduate level, where he taught chemistry and biochemistry.Muhammet PoyrazMuhammet Poyraz is a PhD student in electrical engineering at Stanford University and a graduate researcher at the Canary Center at Stanford for Cancer Early Detection. He received his BS degree from Bilkent University, Turkey, in electrical and electronics engineering. He joined Professor Utkan Demirci’s lab at Stanford University in 2016 as a graduate student. He is currently working on photonic crystal and plasmonic based biosensing technologies for point-of-care applications.Fatih InciFatih Inci received the PhD degree from Istanbul Technical University (Turkey), focusing on biosensor design and development for clinical and pharmaceutical applications. He was then appointed as a Postdoctoral Research Fellow at Harvard Medical School and Stanford University School of Medicine. Dr Inci is currently working as a Basic Life Science Research Scientist at Stanford University School of Medicine, Canary Center at Stanford for Cancer Early Detection. His research is focused on creating point-of-care diagnostic technologies, lab-on-a-chip platforms, nanoplasmonic biosensors, and surface chemistry approaches for medical diagnostics. Dr Inci’s work has been highlighted in the NIH–NIBIB, Boston University, Canary Center at Stanford, Johns Hopkins University, JAMA, Nature Medicine, AIP, Newsweek, and Popular Science.Mark A. LifsonMark Lifson is a biomedical and computer engineer currently working as a postdoctoral research fellow at Stanford. He obtained his Bachelor of Science in computer engineering from the Rochester Institute of Technology, and his Master of Science and Doctorate from the University of Rochester in biomedical engineering. His research interests include developing ultra-sensitive sensors for biomarker detection. He has expertise in photonic crystals, microfluidics, localized surface plasmon resonance, and smart colloidal nanoparticles.Brian T. CunninghamBrian T. Cunningham is the Willett Professor of Engineering in the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign, where he also serves as the Director of the Micro and Nanotechnology Laboratory. His research interests include the development of biosensors and detection instruments for pharmaceutical high throughput screening, disease diagnostics, point-of-care testing, life science research, and environmental monitoring. He has published 160 peer-reviewed journal articles, and is an inventor on 83 patents. Prof. Cunningham was a co-founder of SRU Biosystems in 2000, and founded Exalt Diagnostics in 2012 to commercialize photonic crystal enhanced fluorescence technology for disease biomarker detection. Acoustic MEMS biosensor technology that he developed at the Draper Laboratory has been commercialized by Bioscale, Inc. Prof. Cunningham’s work was recognized with the IEEE Sensors Council Technical Achievement Award and the IEEE Engineering in Medicine and Biology Technical Achievement Award. He is a member of the National Academy of Inventors and a Fellow of IEEE, OSA, and AIMBE.Utkan DemirciUtkan Demirci is an Associate Professor at the School of Medicine, Department of Radiology, Canary Center at Stanford for Cancer Early Detection. His research interests involve the applications of microfluidics, nanoscale technologies and acoustics in medicine, especially portable, inexpensive, disposable technology platforms in resource-constrained settings for global health problems and 3-D biofabrication and tissue models including 3-D cancer and neural cultures. Dr Demirci has published over 120 peer-reviewed publications, over 150 conference abstracts and proceedings, 10 book chapters, and edited four books. His work has been recognized by numerous awards including the NSF Faculty Early Career Development (CAREER) Award and the IEEE-EMBS Early Career Achievement Award. He was selected as one of the world’s top 35 young innovators under the age of 35 (TR-35) by the MIT Technology Review. His patents have been translated into start-up companies including DxNOW and Koek Biotech. Some of these technologies are clinically available across the globe.

This list got out of control haha.*= Pretty sure is true but couldn’t verify.Jidenna applied, was accepted, and attended Stanford University because his guidance counselor said he would never get in. (1)ASAP Rocky invited a college professor who specializes in hallucinogenic drugs to observe him under the influence of psychedelics while recording TESTING. (2)Ludacris’s father was childhood friends with Denzel Washington. (3)Drake wrote nice “Nice For What” during a paused match of NBA 2K. The whole song was complete in about 90 minutes. (4)P. Diddy purchased a $21.1 million painting by Kerry James Marshall, the most ever paid for the work of a living African-American artist. (5)Lil Wayne had his first child at 16 with his then-girlfriend after his mother professed her loneliness because he was often away on tour. (6)According to former professional athlete Chris Simms, Kyle Shanahan, the head coach of the San Francisco 49ers—an American football team, named his son Carter, after Lil Wayne. (7)Due the popularity of his “This Is America” music video and SNL Skit, Childish Gambino’s albums received a 419% sales increase. (8)Big Sean’s mother once shared acting classes with Denzel Washington. (9)Drake wrote “The Calm” off his So Far Gone mixtape after an altercation with his uncle. (10)The Weeknd scrapped an entire album of upbeat music and released My Dear Melancholy instead. (11)Lil Wayne’s favorite band is Nirvana. (12)When Elton John and his partner got their civil union, Eminem sent them two diamond cock rings to celebrate. (13)Bone Thugs-N-Harmony is the only group to work with 2Pac, The Notorious B.I.G., Eazy-E, and Big Pun while all four were still alive. (14)YG’s My Krazy Life was originally titled I’m From Bompton. (15)Preme claims that Drake rewrites some of his rap verses up to 20 times. (16)Anderson .Paak originally performed under the moniker Breezy Lovejoy. (17)*Before Kanye West got signed as a rapper, he would occasionally jump on tables at label meetings and shout that he’s the next Michael Jackson. (18)Before landing on his own album, Tyler, the Creator’s “I Ain’t Got Time” was originally intended for Kanye West and later Nicki Minaj. (19)Kanye West never liked his most successful song to date, “Gold Digger”. He claims he made it because he knew it would make money. (20)Danny Brown is a quarter filipino. (21)Tyler, the Creator’s “Glitter” was originally written for Justin Bieber. (22)Before linking up with film score composer Jon Brion, who altered its musical direction, Kanye West’s Late Registration was about 75% complete by November of 2004—just 9 months after the release of College Dropout. (23)Nine of Post Malone’s songs off his beerbongs & bentleys album landed in the Top 20 of the Billboard Hot 100, breaking the record of six previously set by The Beatles in April of 1964 and tied by J. Cole with KOD. (24)To ensure he did not have a ghostwriter, Eminem only allowed Kendrick Lamar (who showed up with some friends) in the studio to write and record his feature for their collaborative track “Love Game”. (25)Pusha T claims that Kanye West made him write and record his verse on “Runaway” multiple times, stating that he wanted him to sound like a “douchebag”. (26)When Kanye West performed an early version of his Grammy-winning song, “Jesus Walks” to a room of producers and A&Rs, he was mocked and laughed out of the room. (27)Eminem’s first big purchase was a house but he quickly sold it because fans would often pull into his driveway, jump in his pool, and knock on his door. (28)In 2010, 2Pac’s “Dear Mama” was added to the National Recording Registry in the library of Congress. (29)Joey Bada$$ originally attended Edward R. Murrow High School with ambitions of becoming an actor. He decided to focus on music after linking up with the would-be members of Pro Era, some of which were attending the same school. (30)When Kanye West’s mother, Donda West, was just 6 she was arrested for protesting by sitting in at a lunch counter in Oklahoma City. (31)In 2010, Eminem reported that his Donkey Kong arcade video game high score sat at 465,800. This would make him a world-class player, and one of the 30 or so best players on the planet at the time. (32)Pusha T’s favorite cartoon character is Space Ghost. (33)At the request of his grandmother, Common once phoned a then 14-year-old Chance The Rapper and left him words of encouragement. (34)J. Cole’s first thought when he met Jay Z was “Damn, I’m taller than Jay Z”. (35)When Vic Mensa was 17, he had a near-death experience after being struck with 15,000 volts of electricity while trying to sneak into Lollapalooza. (36)Kanye West’s My Beautiful Dark Twisted Fantasy was originally titled Good Ass Job. (37)Vince Staples enjoyed participating in science fairs when he was in middle school. (38)J. Cole attended St. John’s University with intentions of majoring in Computer Science. He quickly switched to Communications after seeing the lonely life of his programmer professor. (39)Some of Denzel Curry’s favorite cartoons includes The Powerpuff Girls, Dragon Ball Z, Samurai Jack, Ed, Edd n Eddy, and Invader Zim. (40)Kanye West made the beat to Jay Z’s “Izzo (H.O.V.A.)” after Jay Z told him to imagine Biggie somersaulting down gold streets in heaven. (41)Boi-1da started working with Drake out of a rat-infested studio. (42)*Kid Cudi was expelled from High School because he threatened to punch his principal. (43)Lil Wayne, arriving to a party late, was once scolded by Stevie Wonder for talking during his piano performance. (44)Anderson .Paak was his class’s prom king. (45)Nas claims that Jay Z’s diss-track, “Takeover” left him so embarrassed that he didn’t move for three days. (46)Frank Ocean wrote the lyrics to his Channel Orange album in two weeks. (47)When he was 12, ScHoolboy Q lost his virginity by having anal sex. (48)Before the success of Outkast, Big Boi planned to study Child Psychology at NYU. (49)The Weeknd wrote the lyrics to “Starboy” in 30 minutes. (50)Logic’s favorite character in Family Guy is Brian. (51)It took Chance The Rapper 7 months to finish “Good Ass Intro”. (52)Eminem recorded “Lose Yourself” in one take. (53)It took Kendrick Lamar 6 months to finish “Alright”. (54)Eminem’s Marshall Mathers LP was nearly titled Amsterdam because a fair portion of it was written there. (55)“I’m iller than standing in front of a gorilla holding a banana” is the lyric Royce Da 5′9 said that caught Eminem’s attention at a Detroit open mic night, leading to their friendship. (56)Eminem has read one book from cover to cover: LL Cool J’s I Make My Own Rules. (57)Despite 808s & Heartbreak being Chance The Rapper’s least favorite Kanye West album, “Streetlights” is his favorite Kanye West song. (58)Because they share a similar tonality, Ghostface Killah initially mistook Action Bronson’s music for his own. (59)Wiz Khalifa said that he did not enjoy his first time smoking marijuana in the slightest. However, he was determined to be a “pothead” so he continued. (60)Drake believes that the best show on television at the moment is Ozark. (61)Saba claims that Chance The Rapper did not remember him until the 3rd or 4th time he was introduced to him. (62)Kanye West believes that 808s & Heartbreak and Yeezus are better than My Beautiful Dark Twisted Fantasy. (63)Snoop Dogg got his name from his mother: Because he watched the show Peanuts so much, she once said to him that he’s starting to look like Snoopy, the dog. (64)Kendrick Lamar claims there was 3 or 4 different versions of good kid, m.A.A.d city. (65)Black Thought’s High School public speaking class developed his impressive breathe control: Students would lay on their backs with an encyclopedia on their chest to learn circular breathing methods. (66)*Outkast originally called themselves “2 Shades Deep” and later “Misfits” but both names were in use. They decided on the unique spelling of “outcast” because it was one of the synonyms for “misfit” in a thesaurus. (67)Mac Miller, born Malcolm McCormick, was named after human rights activist Malcolm X. (68)Comedian Chris Rock believes that Kanye West’s My Beautiful Dark Twisted Fantasy is the best album of the last 50 years. (69)Jay Z’s Reasonable Doubt was originally titled Heir To The Throne. (70)Tyler, the Creator claims he made the “Yonkers” beat in 8 minutes and the whole song was really just a joke. (71)Migos originally performed under the name “Polo Club”. (72)Kendrick Lamar was nearly signed to Jay Z’s Def Jam label when he was 17. (73)Big Sean graduated High School with a 3.7 GPA and was offered a scholarship to attend Michigan State University. He opted out, deciding to focus on music. (74)Saba skipped two grades, graduating High School at 16. (75)*J. Cole graduated High School with a 4.2 GPA. (76)Kanye West’s name originated from a book containing African names. It means “the only one” in Swahili. (An obvious nod to his 2014 single, “Only One”). (77)Inebriated, Chance The Rapper once nearly vomited on Kendrick Lamar at a house party. (78)Chance The Rapper stated that “Same Drugs” off his Coloring Book project was the most difficult song to write and had about 20 versions, including one featuring singer-songwriter Regina Spektor. (79)*Outkast’s “Hey Ya!” music video is a loose parody of The Beatles 1964 performance on the Ed Sullivan Show. (80)Kanye West claims that Drake was the first artist to scare and put pressure on him. (81)The beat to J. Cole’s “Neighbors” is the beat to his “Forbidden Fruit,” backwards. (82)Queen Latifah’s “U.N.I.T.Y.” was the first record Drake ever purchased. (83)Logic claims he currently has several albums finished. (84)As teenagers, Black Thought and Questlove would skip school to listen to NWA’s Straight Outta Compton. (85)ScHoolboy Q claims he could not read until he was nine. (86)Kendrick Lamar originally planned to have minimal, if any input on “Complexion (A Zulu Love)”. It was suppose to feature two verses from Rhapsody and Prince performing the chorus. (87)P. Diddy pays Sting $2,000 every day because he failed formally clear the sample of The Police’s “Every Breathe You Take”. (88)About 120 tracks were recorded for Outkast’s Speakerboxxx/The Love Below. (89)*Paul McCartney knighted Jay Z as “Sir Hova of Brooklyn” in an unofficial ceremony. (90)The Just Blaze-produced beat of Jay Z’s “Girls Girls Girls” was originally intended for Ghostface Killah. (Here’s a video of Ghostface Killah rapping over the beat: Ghostface Killah Freestyle 16 Bars for AOL) (91)*To determine who appeared on each song on the Wu-Tang Clan’s Enter The Wu-Tang 36 Chambers, RZA forced the group members to battle rap each-other. (92)Drake’s Nothing Was The Same has not left the Billboard 200 since its release in 2013. (93)Some of Barack Obama’s favorite songs of 2017 includes “Butterfly Effect” by Travis Scott, “Chanel” by Frank Ocean, “Family Feud” by Jay Z featuring Beyoncé, “HUMBLE.” by Kendrick Lamar, and “Brocken Clocks” by SZA. (94)Guitarist Billy “Spaceman” Patterson stated that Frank Ocean has hours of unreleased Blonde and Endless recordings. (95)In a 2016 interview, Future claimed he had been going to the studio everyday for the last 5 years.Renee Rosenblum-Lowden, Jay Z’s grade-school teacher, stated that he was reading at a 12th grade level in the 6th grade. (97)*Kid Cudi planned on joining the Navy after dropping out of college. He was rejected because of his police record, being arrested for assault when he was 16. He claims he was just an innocent bystander to the assault. (98)J. Cole did not receive his College Diploma until 8 years after his graduation in 2007. He revealed the failure to pay for a library book caused them to withhold it. (99)Black Thought claims that he first met Questlove in their High School principal’s office. He was either about to be suspended or coming back from a suspension, while Questlove was bringing an apple to the principal. (100)Jidenna Talks College and New Album, 'The Chief' (About :15 seconds)A$AP Rocky talks about working with Tyler, The Creator and Frank Ocean in new interviewDenzel Does a Mean Jay-Z Impression on The Queen Latifah Show (About :03 seconds)Drake Wrote "Nice For What" While Playing 'NBA 2K' With Murda BeatzP. Diddy revealed as the buyer of the $21 million Kerry James Marshall paintingThe Life Story of Lil Wayne (Full Movie) (About 12:20)49ers coach Kyle Shanahan named his son after Lil Wayne, according to Chris SimmsChildish Gambino's Album Sales Rise 419% in Wake of 'This Is America' Release and 'SNL' PerformanceGive It All to Me: Big Sean's XXL Cover Story - XXLDrake - My Favourite Verse ("The Calm") | SoulCulture TV (About :15)The Weeknd Talks Fame, Love, & 'My Dear Melancholy' With 'TIME'Lil Wayne Talks 50 Cent, Cocaine & Rock MusicFlashback: Elton John and Eminem UniteN/AYG Interview - What he's afraid of, white people dropping the N bomb, why he's annoyed with Disney. (About 1:00)Preme Says Drake Rewrites His Verses Up To 20 TimesBefore Anderson .Paak - The Complete Guide to Breezy Lovejoy - CentralSauce ♫Couldn’t verify.Tyler, The Creator Wanted Kanye West & Nicki Minaj on "I Ain't Got Time!", Both DeclinedKanye West. Zane Lowe. Full Interview (About 17:45)Who Is Danny Brown?FilipinoTyler, the Creator Wrote 'Glitter' for Justin Bieber & 5 Other Things We Learned From Jerrod Carmichael ChatKanye West And John Mayer Collaborate But Won't ElaboratePost Malone Surpasses The Beatles & J. Cole For The Most Concurrent Top 20 Hits On The Hot 100Eminem Tested Kendrick Lamar to Prove He Didn't Use a Ghostwriter, According to Ed SheeranKanye West: Project Runaway (Cover Story)Kanye West Was Apparently Laughed at While Playing an Early Version of "Jesus Walks"Eminem Interview (MTV, 2002)Tupac Shakur Honored By Library of CongressJoey Bada$$ on "Being His Own Role Model", Lecturing at Harvard/NYU + Kills the 5 Fingers of Death (About 2:30)Kanye West: VH1 Driven (Full Episode) (About 2:13)Eminem's Donkey Kong AmbitionsPUSHA T ✖ MONTREALITY ➥ Interview 2014 (About 3:40)Common left a voicemail for a young fan 10 years ago. That fan is now Chance the RapperJ. Cole Talks Roc Nation, Meeting Jay-Z & 'The Warm Up' MixtapeVic Mensa Almost Died Trying to Sneak Into LollapaloozaKanye West Explains Why He Dropped Good Ass Job Album TitleVince Staples gets politicalJ. 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Cole Reminisces on MTV's 'When I Was 17’ - Rap-UpKanye West: VH1 Driven (Full Episode) (About :38)Nardwuar vs. Chance The Rapper (About 8:10)https://www.reddit.com/r/hiphopheads/comments/4je7ig/hey_this_is_chance_coloringbook_is_out_ask_me/d35w227/ and https://twitter.com/chancetherapper/status/740947189422272512?ref_src=twsrc%5Etfw&ref_url=https%3A%2F%2Fgenius.com%2FChance-the-rapper-same-drugs-lyrics&tfw_site=GeniusCouldn’t verify.Kanye West’s La Dolce Vita [Cover Story Excerpt] - XXLJ. Cole’s “Neighbors” Beat Is “Forbidden Fruit” Reversed | Genius NewsDrake Talks About His First Paycheck , First Kiss, and First Fight In Life!Logic Says He Has “Several Albums That Are Finished”Ice Cube Made His Son Work Hard for a Straight Outta Compton RoleScHoolboy Q Talks How He Got Kanye West on his Song, He Almost Quit Rapping + Couldn't Read Until 9! 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