Raman Spectroscopy Cell-based Biosensors

A characterization of four B16 murine melanoma cell sublines molecular fingerprint and proliferation behavior

Background

One of the most popular and versatile model of murine melanoma is by inoculating B16 cells in the syngeneic C57BL6J mouse strain. A characterization of different B16 modified cell sub-lines will be of real practical interest. For this aim, modern analytical tools like surface enhanced Raman spectroscopy/scattering (SERS) and MTT were employed to characterize both chemical composition and proliferation behavior of the selected cells.

Methods

High quality SERS signal was recorded from each of the four types of B16 cell sub-lines: B164A5, B16GMCSF, B16FLT3, B16F10, in order to observe the differences between a parent cell line (B164A5) and other derived B16 cell sub-lines. Cells were incubated with silver nanoparticles of 50–100 nm diameter and the nanoparticles uptake inside the cells cytoplasm was proved by transmission electron microscopy (TEM) investigations. In order to characterize proliferation, growth curves of the four B16 cell lines, using different cell numbers and FCS concentration were obtained employing the MTT proliferation assay. For correlations doubling time were calculated.

Results

SERS bands allowed the identification inside the cells of the main bio-molecular components such as: proteins, nucleic acids, and lipids. An "on and off" SERS effect was constantly present, which may be explained in terms of the employed laser power, as well as the possible different orientations of the adsorbed species in the cells in respect to the Ag nanoparticles. MTT results showed that among the four tested cell sub-lines B16 F10 is the most proliferative and B164A5 has the lower growth capacity. Regarding B16FLT3 cells and B16GMCSF cells, they present proliferation ability in between with slight slower potency for B16GMCSF cells.

Conclusion

Molecular fingerprint and proliferation behavior of four B16 melanoma cell sub-lines were elucidated by associating SERS investigations with MTT proliferation assay.

Fabrication of reduced graphene oxide and sliver nanoparticle hybrids for Raman detection of absorbed folic acid: a potential cancer diagnostic probe

Reduced graphene oxide (RGO) and silver nanoparticle (AgNP) hybrids (RGO-AgNP) were prepared by a facile one-pot method using Poly (N-vinyl-2-pyrrolidone) as reductant and stabilizer. Folic acid (FA) molecules were attached to the RGO-AgNP by physisorption for targeting specific cancer cells with folate receptors (FRs) and using as Raman reporter molecules. The internalization of the FA loaded RGO-AgNP (RGO-AgNP-FA) inside the FRs-positive cancer cell was confirmed by confocal laser scanning and transmission electron microscopy. The Raman signals of the FA in live cancer cells were detected by confocal Raman spectroscope at 514 nm excitation, indicating that the RGO-AgNP-FA material has great potential as a Raman probe for cancer diagnosis in vitro.

Intracellular SERS nanoprobes for distinction of different neuronal cell types

Distinction between closely related and morphologically similar cells is difficult by conventional methods especially without labeling. Using nuclear-targeted gold nanoparticles (AuNPs) as intracellular probes we demonstrate the ability to distinguish between progenitor and differentiated cell types in a human neuroblastoma cell line using surface-enhanced Raman spectroscopy (SERS). SERS spectra from the whole cell area as well as only the nucleus were analyzed using principal component analysis that allowed unambiguous distinction of the different cell types. SERS spectra from the nuclear region showed the developments during cellular differentiation by identifying an increase in DNA/RNA ratio and proteins transcribed. Our approach using nuclear-targeted AuNPs and SERS imaging provides label-free and noninvasive characterization that can play a vital role in identifying cell types in biomedical stem cell research.

Sensitive and specific discrimination of pathogenic and nonpathogenic Escherichia coli using Raman spectroscopy-a comparison of two multivariate analysis techniques

The determination of bacterial identity at the strain level is still a complex and time-consuming endeavor. In this study, visible wavelength spontaneous Raman spectroscopy has been used for the discrimination of four closely related Escherichia coli strains: pathogenic enterohemorrhagic E. coli O157:H7 and non-pathogenic E. coli C, E. coli Hfr K-12, and E. coli HF4714. Raman spectra from 600 to 2000 cm(-1) were analyzed with two multivariate chemometric techniques, principal component-discriminant function analysis and partial least squares-discriminant analysis, to determine optimal parameters for the discrimination of pathogenic E. coli from the non-pathogenic strains. Spectral preprocessing techniques such as smoothing with windows of various sizes and differentiation were investigated. The sensitivity and specificity of both techniques was in excess of 95%, determined by external testing of the chemometric models. This study suggests that spontaneous Raman spectroscopy with visible wavelength excitation is potentially useful for the rapid identification and classification of clinically-relevant bacteria at the strain level.

Chemical surface modifications for the development of silicon-based label-free integrated optical (IO) biosensors: a review

Increasing interest has been paid to label-free biosensors in recent years. Among them, refractive index (RI) optical biosensors enable high density and the chip-scale integration of optical components. This makes them more appealing to help develop lab-on-a-chip devices. Today, many RI integrated optical (IO) devices are made using silicon-based materials. A key issue in their development is the biofunctionalization of sensing surfaces because they provide a specific, sensitive response to the analyte of interest. This review critically discusses the biofunctionalization procedures, assay formats and characterization techniques employed in setting up IO biosensors. In addition, it provides the most relevant results obtained from using these devices for real sample biosensing. Finally, an overview of the most promising future developments in the fields of chemical surface modification and capture agent attachment for IO biosensors follows.

Peptide-guided surface-enhanced Raman scattering probes for localized cell composition analysis

The ability to control the localization of surface-enhanced Raman scattering (SERS) nanoparticle probes in bacterial cells is critical to the development of analytical techniques that can nondestructively determine cell composition and phenotype. Here, selective localization of SERS probes was achieved at the outer bacterial membrane by using silver nanoparticles functionalized with synthetic hydrophobic peptides.

Monitoring enzymatic degradation of pericellular matrices through SERS stamping

We introduce a surface enhanced Raman spectroscopy (SERS) stamping approach for acquiring cell-surface specific vibrational spectra of individual living cells under physiological conditions. The SERS stamping approach utilizes a nanostructured metal surface on top of a lithographically defined piston that can be translated in 3-dimensions with nanometer resolution to contact living cells in solution with a pristine metal surface. We applied this approach to characterize the chemical composition of the cellular surface of living MCF7 breast cancer cells and to monitor its change upon addition of the enzyme hyaluronidase, which degrades major constituents of the pericellular matrix. Although the cell surface spectra show significant cell-to-cell fluctuations, a statistical barcode analysis of the spectra ensembles reveals systematic changes in the cell surface SERS spectra upon addition of hyaluronidase, which are consistent with a thinning of the pericellular matrix.

Inhibition assay of yeast cell walls by plasmon resonance Rayleigh scattering and surface-enhanced Raman scattering imaging

We report on plasmon resonance Rayleigh scattering (PRRS) and surface enhanced Raman scattering (SERS) imaging for inhibition assay of yeast cell walls. This assay reveals that the proteins having alkali sensitive linkage bound to β1,3 glucan frameworks in cell walls are involved in SERS activity. The result is further confirmed by comparison of genetically modified cells and wild type cells. Finally, we find that PRRS and SERS spots do not appear on cell walls when daughter cells are enough smaller than parent ones, but appear when size of daughter cells are comparable to parent cells. This finding indicates the relationship between expression of the proteins that generate SERS spots and cell division. These results demonstrate that PRRS and SERS imaging can be a convenient and sensitive method for analysis of cell walls.

Real-time sensing and discrimination of single chemicals using the channel of phi29 DNA packaging nanomotor

A highly sensitive and reliable method to sense and identify a single chemical at extremely low concentrations and high contamination is important for environmental surveillance, homeland security, athlete drug monitoring, toxin/drug screening, and earlier disease diagnosis. This article reports a method for precise detection of single chemicals. The hub of the bacteriophage phi29 DNA packaging motor is a connector consisting of 12 protein subunits encircled into a 3.6 nm channel as a path for dsDNA to enter during packaging and to exit during infection. The connector has previously been inserted into a lipid bilayer to serve as a membrane-embedded channel. Herein we report the modification of the phi29 channel to develop a class of sensors to detect single chemicals. The lysine-234 of each protein subunit was mutated to cysteine, generating 12-SH ring lining the channel wall. Chemicals passing through this robust channel and interactions with the SH group generated extremely reliable, precise, and sensitive current signatures as revealed by single channel conductance assays. Ethane (57 Da), thymine (167 Da), and benzene (105 Da) with reactive thioester moieties were clearly discriminated upon interaction with the available set of cysteine residues. The covalent attachment of each analyte induced discrete stepwise blockage in current signature with a corresponding decrease in conductance due to the physical blocking of the channel. Transient binding of the chemicals also produced characteristic fingerprints that were deduced from the unique blockage amplitude and pattern of the signals. This study shows that the phi29 connector can be used to sense chemicals with reactive thioesters or maleimide using single channel conduction assays based on their distinct fingerprints. The results demonstrated that this channel system could be further developed into very sensitive sensing devices.

Metabolic toxicity screening using electrochemiluminescence arrays coupled with enzyme-DNA biocolloid reactors and liquid chromatography-mass spectrometry

New chemicals or drugs must be guaranteed safe before they can be marketed. Despite widespread use of bioassay panels for toxicity prediction, products that are toxic to a subset of the population often are not identified until clinical trials. This article reviews new array methodologies based on enzyme/DNA films that form and identify DNA-reactive metabolites that are indicators of potentially genotoxic species. This molecularly based methodology is designed in a rapid screening array that utilizes electrochemiluminescence (ECL) to detect metabolite-DNA reactions, as well as biocolloid reactors that provide the DNA adducts and metabolites for liquid chromatography-mass spectrometry (LC-MS) analysis. ECL arrays provide rapid toxicity screening, and the biocolloid reactor LC-MS approach provides a valuable follow-up on structure, identification, and formation rates of DNA adducts for toxicity hits from the ECL array screening. Specific examples using this strategy are discussed. Integration of high-throughput versions of these toxicity-screening methods with existing drug toxicity bioassays should allow for better human toxicity prediction as well as more informed decision making regarding new chemical and drug candidates.

Post-synapse model cell for synaptic glutamate receptor (GluR)-based biosensing: strategy and engineering to maximize ligand-gated ion-flux achieving high signal-to-noise ratio

Cell-based biosensing is a “smart” way to obtain efficacy-information on the effect of applied chemical on cellular biological cascade. We have proposed an engineered post-synapse model cell-based biosensors to investigate the effects of chemicals on ionotropic glutamate receptor (GluR), which is a focus of attention as a molecular target for clinical neural drug discovery. The engineered model cell has several advantages over native cells, including improved ease of handling and better reproducibility in the application of cell-based biosensors. However, in general, cell-based biosensors often have low signal-to-noise (S/N) ratios due to the low level of cellular responses. In order to obtain a higher S/N ratio in model cells, we have attempted to design a tactic model cell with elevated cellular response. We have revealed that the increase GluR expression level is not directly connected to the amplification of cellular responses because the saturation of surface expression of GluR, leading to a limit on the total ion influx. Furthermore, coexpression of GluR with a voltage-gated potassium channel increased Ca²⁺ ion influx beyond levels obtained with saturating amounts of GluR alone. The construction of model cells based on strategy of amplifying ion flux per individual receptors can be used to perform smart cell-based biosensing with an improved S/N ratio.

Raman spectroscopy and CARS microscopy of stem cells and their derivatives

The characterisation of stem cells is of vital importance to regenerative medicine. Failure to separate out all stem cells from differentiated cells before therapies can result in teratomas - tumours of multiple cell types. Typically, characterisation is performed in a destructive manner with fluorescent assays. A truly non-invasive method of characterisation would be a major breakthrough in stem cell-based therapies. Raman spectroscopy has revealed that DNA and RNA levels drop when a stem cell differentiates into other cell types, which we link to a change in the relative sizes of the nucleus and cytoplasm. We also used Raman spectroscopy to investigate the biochemistry within an early embryo, or blastocyst, which differs greatly from colonies of embryonic stem cells. Certain cell types that differentiate from stem cells can be identified by directly imaging the biochemistry with CARS microscopy; examples presented are hydroxyapatite - a precursor to bone, and lipids in adipocytes.

Gold nanoparticle-based surface-enhanced Raman scattering for noninvasive molecular probing of embryonic stem cell differentiation

This study reports the use of gold nanoparticle-based surface-enhanced Raman scattering (SERS) for probing the differentiation of mouse embryonic stem (mES) cells, including undifferentiated single cells, embryoid bodies (EBs), and terminally differentiated cardiomyocytes. Gold nanoparticles (GNPs) were successfully delivered into all 3 mES cell differentiation stages without affecting cell viability or proliferation. Transmission electron microscopy (TEM) confirmed the localization of GNPs inside the following cell organelles: mitochondria, secondary lysosome, and endoplasmic reticulum. Using bright- and dark-field imaging, the bright scattering of GNPs and nanoaggregates in all 3 ES cell differentiation stages could be visualized. EB (an early differentiation stage) and terminally differentiated cardiomyocytes both showed SERS peaks specific to metabolic activity in the mitochondria and to protein translation (amide I, amide II, and amide III peaks). These peaks have been rarely identified in undifferentiated single ES cells. Spatiotemporal changes observed in the SERS spectra from terminally differentiated cardiomyocyte tissues revealed local and dynamic molecular interactions as well as transformations during ES cell differentiation.

Raman micro-spectroscopic analysis of cultured HCT116 colon cancer cells in the presence of roscovitine

Raman micro-spectroscopic analysis of cultured HCT116 colon cancer cells in the presence of roscovitine, [seliciclib, 2-(1-ethyl-2-hydroxy-ethylamino)-6-benzylamino-9-isopropylpurine], a promising drug candidate in cancer therapy, has been performed for the first time. The aim of this study was to investigate modulations in colon cancer cells induced by roscovitine. Raman spectra of the cultured HCT116 colon cancer cells treated with roscovitine at different concentrations (0, 5, 10, 25 and 50 μM) were recorded in the range 400-1850 cm(-1). It was shown that the second derivative profile of the experimental spectrum gives valuable information about the wavenumbers and band widths of the vibrational modes of cell components, and it eliminates the appearance of false peaks arising from incorrect baseline corrections. In samples containing roscovitine, significant spectral changes were observed in the intensities of characteristic protein and DNA bands, which indicate roscovitine-induced apoptosis. Roscovitine-induced apoptosis was also assessed by flow cytometry analysis, and analysis of propidium iodide staining. We observed some modifications in amide I and III bands, which arise from alterations in the secondary structure of cell proteins caused by the presence of roscovitine.

On-chip integrated lensless microscopy module for optical monitoring of adherent growing mammalian cells

Lab-on-a-chip systems are increasingly applied in cell-based assays for toxicology and drug testing. In this paper, an on-chip integrated lensless microscopy module using a direct projection method for optical monitoring of the shadow images of adherent growing mammalian cells is presented. The biological cells are conserved and interfaced by a microfabricated cavity chip with a 1 microm thick silicon nitride (Si(3)N(4)) substrate onto the surface of a 5 megapixel CMOS image sensor with 2.2 microm pixel size. The optical resolution of the assembly is estimated by the contact/proximate printing theory from optical lithography. Further characterization is made by imaging microbeads in chips with the Si(3)N(4)-membrane as well as in cavity chips with membranes made from dry film resist (DFR, thickness 20, 40 and 60 microm). The module represents a 3 × optical microscope for cell morphology imaging. The function is demonstrated by the growth monitoring of L929 cells cultured in cavity chips with Si(3)N(4) substrate for 2 days and by checking the colorimetric staining of cells with a compromised membrane.

Modulated Raman spectroscopy for enhanced identification of bladder tumor cells in urine samples

Standard Raman spectroscopy (SRS) is a noninvasive technique that is used in the biomedical field to discriminate between normal and cancer cells. However, the presence of a strong fluorescence background detracts from the use of SRS in real-time clinical applications. Recently, we have reported a novel modulated Raman spectroscopy (MRS) technique to extract the Raman spectra from the background. In this paper, we present the first application of MRS to the identification of human urothelial cells (SV-HUC-1) and bladder cancer cells (MGH) in urine samples. These results are compared to those obtained by SRS. Classification using the principal component analysis clearly shows that MRS allows discrimination between Raman spectra of SV-HUC-1 and MGH cells with high sensitivity (98%) and specificity (95%). MRS is also used to distinguish between SV-HUC-1 and MGH cells after exposure to urine for up to 6 h. We observe a marked change in the MRS of SV-HUC-1 and MGH cells with time in urine, indicating that the conditions of sample collection will be important for the application of this methodology to clinical urine samples.

Lie group study of Raman spectra of the Gurken gradient in Drosophila oogenesis

We carried out a Lie group study of the micro-Raman tissue spectra of the Gurken gradients of Drosophila oogenesis. Matrix representations (2 × 2) resulting from the polarized Raman scattering were employed to assess the roles of the ligand-receptor complexes in follicle cell. It was found that the Gurken expansion caused by overexpressing Dally-like protein (Dlp) revealed an X(1) Lie point symmetry, while the Gurken distribution in the wild-type egg showed an X(23) Lie point symmetry. The correlation between the corresponding continuous symmetry operations and the observed Gurken localization were a corroboration of the significance of the Lie group analysis by means of the reaction-diffusion equation in a prolate spheroidal coordinate system. These investigations suggested that the group-theoretical approach can be applied to characterize the fluctuating asymmetry and the developmental stability in a wide variety of organisms.

Structural changes of human serum albumin in response to a low concentration of heavy ions

Lead ions in solution interact strongly with human serum albumin and modify the properties and function of albumin molecules. In the present study, we used optical spectroscopic techniques to explore the binding sites of lead, present in albumin. Structural and chemical analysis of albumin molecules using fluorescence and Raman spectroscopy, predicted the modification of two major amino acids in albumin due to lead binding. No secondary structural changes are observed in the protein molecule, which is further confirmed using circular dichroism absorption measurements. The results indicate that loss of charge from the binding site of albumin by the charged lead ions, give rise to dipole interaction which acts as the major contributor to promote protein agglomeration.

Raman microspectroscopy of individual algal cells: sensing unsaturation of storage lipids in vivo

Algae are becoming a strategic source of fuels, food, feedstocks, and biologically active compounds. This potential has stimulated the development of innovative analytical methods focused on these microorganisms. Algal lipids are among the most promising potential products for fuels as well as for nutrition. The crucial parameter characterizing the algal lipids is the degree of unsaturation of the constituent fatty acids quantified by the iodine value. Here we demonstrate the capacity of the spatially resolved Raman microspectroscopy to determine the effective iodine value in lipid storage bodies of individual living algal cells. The Raman spectra were collected from three selected algal species immobilized in an agarose gel. Prior to immobilization, the algae were cultivated in the stationary phase inducing an overproduction of lipids. We employed the characteristic peaks in the Raman scattering spectra at 1,656 cm⁻¹ (cis C═C stretching mode) and 1,445 cm⁻¹ (CH₂ scissoring mode) as the markers defining the ratio of unsaturated-to-saturated carbon-carbon bonds of the fatty acids in the algal lipids. These spectral features were first quantified for pure fatty acids of known iodine value. The resultant calibration curve was then used to calculate the effective iodine value of storage lipids in the living algal cells from their Raman spectra. We demonstrated that the iodine value differs significantly for the three studied algal species. Our spectroscopic estimations of the iodine value were validated using GC-MS measurements and an excellent agreement was found for the Trachydiscus minutus species. A good agreement was also found with the earlier published data on Botryococcus braunii. Thus, we propose that Raman microspectroscopy can become technique of choice in the rapidly expanding field of algal biotechnology.

Monitoring human leukocyte antigen class I molecules by micro-Raman spectroscopy at single-cell level

Human leukocyte antigen (HLA) class I molecules are formed by three immunoglobulin-like domains (alpha1, alpha2, and alpha3) once folded by peptide and beta(2)-microglobulin show the presence of two alpha-helix streams and one beta-sheet limiting the pocket for the antigenic peptide. The loss of HLA class I expression in tumors and virus-infected cells, on one hand, prevents T cell recognition, while on the other hand, it leads to natural killer (NK) cell mediated cytotoxicity. We propose the possibility of using Raman spectroscopy to measure the relative expression of HLA class I molecules at the single-cell level. Raman spectra are recorded for three cell lines (K562, T2, and T3) and monomers (HLA class I folded, unfolded and peptide+beta(2)-microlobulin refolded) using 830 nm laser line. Our data are consistent with the hypothesis that in the Raman spectra, ranging from 1600 to 1800 cm(-1), the intensity variation of cells associated with HLA class I molecules could be measured.

BRMS1 expression alters the ultrastructural, biomechanical and biochemical properties of MDA-MB-435 human breast carcinoma cells: an AFM and Raman microspectroscopy study

Restoring BReast cancer Metastasis Suppressor 1 (BRMS1) expression suppresses metastasis in MDA-MB-435 human breast carcinoma cells at ectopic sites without affecting tumor formation at orthotopic site in the body. BRMS1 expression induces many phenotypic alterations in 435 cells such as cell adhesion, cytoskeleton rearrangement, and the down regulation of epidermal growth factor receptor (EGFR) expression. In order to better understand the role of cellular biomechanics in breast cancer metastasis, the qualitative and quantitative detection of cellular biomechanics and biochemical composition is urgently needed. In the present work, using atomic force microscopy (AFM) and fluorescent microscopy we revealed that BRMS1 expression in 435 cells induced reorganization of F-actin and caused alteration in cytoarchitectures (cell topography and ultrastructure). Results from AFM observed increase in biomechanical properties which include cell adhesion, cellular spring constant, and Young's modulus in 435/BRMS1 cells. Raman microspectroscopy showed weaker vibrational spectroscopic bands in 435/BRMS1 cells, implying decrease in concentration of cellular biochemical components in these cells. This was despite the similar spectral patterns observed between 435 and 435/BRMS1 cells. This work demonstrated the feasibility of applying AFM and Raman techniques for in situ measurements of the cellular biomechanics and biochemical components of breast carcinoma cells. It provides vital clues in understanding of the role of cellular biomechanics in cancer metastasis, and further the development of new techniques for early diagnosis of breast cancer.

Raman spectroscopy and related techniques in biomedicine

In this review we describe label-free optical spectroscopy techniques which are able to non-invasively measure the (bio)chemistry in biological systems. Raman spectroscopy uses visible or near-infrared light to measure a spectrum of vibrational bonds in seconds. Coherent anti-Stokes Raman (CARS) microscopy and stimulated Raman loss (SRL) microscopy are orders of magnitude more efficient than Raman spectroscopy, and are able to acquire high quality chemically-specific images in seconds. We discuss the benefits and limitations of all techniques, with particular emphasis on applications in biomedicine--both in vivo (using fiber endoscopes) and in vitro (in optical microscopes).

Potential for Raman spectroscopy to provide cancer screening using a peripheral blood sample

Cancer poses a massive health burden with incidence rates expected to double globally over the next decade. In the United Kingdom screening programmes exists for cervical, breast, and colorectal cancer. The ability to screen individuals for solid malignant tumours using only a peripheral blood sample would revolutionise cancer services and permit early diagnosis and intervention. Raman spectroscopy interrogates native biochemistry through the interaction of light with matter, producing a high definition biochemical 'fingerprint' of the target material. This paper explores the possibility of using Raman spectroscopy to discriminate between cancer and non-cancer patients through a peripheral blood sample. Forty blood samples were obtained from patients with Head and Neck cancer and patients with respiratory illnesses to act as a positive control. Raman spectroscopy was carried out on all samples with the resulting spectra being used to build a classifier in order to distinguish between the cancer and respiratory patients' spectra; firstly using principal component analysis (PCA)/linear discriminant analysis (LDA), and secondly with a genetic evolutionary algorithm. The PCA/LDA classifier gave a 65% sensitivity and specificity for discrimination between the cancer and respiratory groups. A sensitivity score of 75% with a specificity of 75% was achieved with a 'trained' evolutionary algorithm. In conclusion this preliminary study has demonstrated the feasibility of using Raman spectroscopy in cancer screening and diagnostics of solid tumours through a peripheral blood sample. Further work needs to be carried out for this technique to be implemented in the clinical setting.

Detection of drug-induced cellular changes using confocal Raman spectroscopy on patterned single-cell biosensors

We report on a cell-based biosensor application that utilizes patterned single-cell arrays combined with confocal Raman spectroscopy to observe the time-dependent drug response of individual cells in real time. The patterned single-cell platform enables individual cells to be easily located and continuously addressable for Raman spectroscopy characterization of biochemical compositional changes in a non-destructive, quantitative manner so that discrete cellular behavior and cell-to-cell variations are preserved. In this study, human medulloblastoma (DAOY) cells were exposed to the common chemotherapeutic agent etoposide, and Raman spectra from patterned cells were recorded over 48 hours. It was found that 87.5% of the cells monitored exhibited a sharp decrease in DNA and protein associated peaks 48 hours after drug exposure, corresponding to cell death. The remaining 12.5% of the cells showed little to no reduction in key Raman biomarkers, indicating their drug resistance. Furthermore, the patterned cell population showed a very similar response to etoposide as confluent cell cultures, as confirmed by flow cytometry. Finally, patterned cells were assessed with TUNEL assay for apoptosis due to DNA fragmentation after etoposide exposure. The results agree well with those from the Raman spectroscopy analysis. This combined biosensor-Raman platform provides a quick, simple way to assess cell responses to chemical and biological agents with high throughput and can be potentially used for a wide variety of biomedical applications such as pharmaceutical drug discovery, toxin tests, and biothreat detection.