Use of surface-enhanced Raman spectroscopy for the detection of human integrins

Cancer Cell Targeting, Magnetic Sorting, and SERS Detection through Cell Surface Receptors

Integrins are cellular surface receptors responsible for the activation of many cellular pathways in cancer. These integrin proteins can be specifically targeted by small peptide sequences that offer the potential for the differentiation of cellular subpopulations by using magnetically assisted cellular sorting techniques. By adding a gold shell to the magnetic nanoparticles, these integrin-peptide interactions can be differentiated by surface-enhanced Raman spectroscopy (SERS), providing a quick and reliable method for on-target binding. In this paper, we demonstrate the ability to differentiate the peptide-protein interactions of the small peptides CDPGYIGSR and cyclic RGDfC functionalized on gold-coated magnetic nanoparticles with the integrins they are known to bind to using their SERS signal. SW480 and SW620 colorectal cancer cells known to have the integrins of interest were then magnetically sorted using these functionalized nanoparticles, suggesting differentiation between the sorted populations and integrin populations among the two cell lines.

Cell Theranostics on Mesoporous Silicon Substrates

The adhesion, proliferation, and migration of cells over nanomaterials is regulated by a cascade of biochemical signals that originate at the interface of a cell with a substrate and propagate through the cytoplasm to the nucleus. The topography of the substrate plays a major role in this process. Cell adhesion molecules (CAMs) have a characteristic size of some nanometers and a range of action of some tens of nanometers. Controlling details of a surface at the nanoscale-the same dimensional over which CAMs operate-offers ways to govern the behavior of cells and create organoids or tissues with heretofore unattainable precision. Here, using electrochemical procedures, we generated mesoporous silicon surfaces with different values of pore size (PS≈11 nm and PS≈21 nm), roughness (Ra≈7 nm and Ra≈13 nm), and fractal dimension (Df≈2.48 and Df≈2.15). Using electroless deposition, we deposited over these substrates thin layers of gold nanoparticles. Resulting devices feature (i) nanoscale details for the stimulation and control of cell assembly, (ii) arrays of pores for drug loading/release, (iii) layers of nanostructured gold for the enhancement of the electromagnetic signal in Raman spectroscopy (SERS). We then used these devices as cell culturing substrates. Upon loading with the anti-tumor drug PtCl (O,O'-acac)(DMSO) we examined the rate of adhesion and growth of breast cancer MCF-7 cells under the coincidental effects of surface geometry and drug release. Using confocal imaging and SERS spectroscopy we determined the relative importance of nano-topography and delivery of therapeutics on cell growth-and how an unbalance between these competing agents can accelerate the development of tumor cells.

Direct Surface Enhanced Raman Spectroscopic Detection of Cortisol at Physiological Concentrations

Cortisol is an important steroid hormone in human physiology. Variations or abnormalities in the physiological cortisol levels control acute and chronic stress response, as well as contribute to diseases and syndromes including Addison's disease and Cushing syndrome. The ability to monitor cortisol levels in the physiological range is key in diagnosis and monitoring of these conditions, where current methodology for determination of cortisol levels relies on instrumentation that requires extensive sample preparation, long run times, and is destructive to the sample. Raman spectroscopy provides rapid sample analysis with relatively simple instrumentation; however, Raman spectroscopy is an inherently weak technique. To provide an enhanced Raman signal, we use surface enhanced Raman spectroscopy (SERS) which utilizes oscillating electric fields of metal nanoparticles, enhancing the overall electric field and therefore resulting in an enhanced signal. We demonstrate SERS-based detection of cortisol in the physiologically relevant range using colloidal silver nanoparticles in ethanolic solutions and bovine serum albumin. The SERS spectra obtained in an ethanol matrix demonstrate a sigmoidal concentration response over the physiologically relevant concentration range, with a limit of detection established at 177 nM. Analysis of cortisol solutions in a complex matrix (bovine serum albumin in phosphate buffered saline) is also demonstrated through the use of principal components analysis, a multivariate technique, which shows the separation of cortisol in a linear fashion with respect to cortisol concentration.

Bioanalytical applications of surface-enhanced Raman spectroscopy: de novo molecular identification

Surface enhanced Raman scattering (SERS) has become a powerful technique for trace analysis of biomolecules. The use of SERS-tags has evolved into clinical diagnostics, the enhancement of the intrinsic signal of biomolecules on SERS active materials shows tremendous promise for the analysis of biomolecules and potential biomedical assays. The detection of the de novo signal from a wide range of biomolecules has been reported to date. In this review, we examine different classes of biomolecules for the signals observed and experimental details that enable their detection. In particular, we survey nucleic acids, amino acids, peptides, proteins, metabolites, and pathogens. The signals observed show that the interaction of the biomolecule with the enhancing nanostructure has a significant influence on the observed spectrum. Additional experiments demonstrate that internal standards can correct for intensity fluctuations and provide quantitative analysis. Experimental methods that control the interaction at the surface are providing for reproducible SERS signals. Results suggest that combining advances in methodology with the development of libraries for SERS spectra may enable the characterization of biomolecules complementary to other existing methods.

Detection of Hepatitis B virus antigen from human blood: SERS immunoassay in a microfluidic system

A highly sensitive immunoassay utilizing surface-enhanced Raman scattering (SERS) has been developed with a new Raman reporter and a unique SERS-active substrate incorporated into a microfluidic device. An appropriately designed Raman reporter, basic fuchsin (FC), gives strong SERS enhancement and has the ability to bind both the antibody and gold nanostructures. The fuchsin-labeled immuno-Au nanoflowers can form a sandwich structure with the antigen and the antibody immobilized on the SERS-active substrate based on Au-Ag coated GaN. Our experimental results indicate that this SERS-active substrate with its strong surface-enhancement factor, high stability and reproducibility plays a crucial role in improving the efficiency of SERS immunoassay. This SERS assay was applied to the detection of Hepatitis B virus antigen (HBsAg) in human blood plasma. A calibration curve was obtained by plotting the intensity of SERS signal of FC band at 1178cm(-1) versus the concentration of antigen. The low detection limit for Hepatitis B virus antigen was estimated to be 0.01IU/mL. The average relative standard deviation (RSD) of this method is less than 10%. This SERS immunoassay gives exact results over a broad linear range, reflecting clinically relevant HBsAg concentrations. It also exhibits high biological specificity for the detection of Hepatitis B virus antigen.

The development of surface-enhanced Raman scattering as a detection modality for portable in vitro diagnostics: progress and challenges

This perspective provides an overview of the diverse surface-enhanced Raman scattering (SERS)-based sensor platforms that have been developed for in vitro diagnostic applications. To provide focus, protein and nucleic acid detection assays based on the principle of extrinsic SERS sensing are emphasized, as well as their potential for translation to fully integrated point-of-care (POC) test platforms. The development of intrinsic SERS sensors, which are predicated on the direct detection of analytes by laser excitation, entails unique opportunities and challenges deserving of their own attention. As the robust sensing of disease pathogens and cancers in both clinical facilities and limited resource settings is the targeted objective of many next-generation biosensors, the majority of the research progress summarized here centers on SERS sensors developed for the rapid, sensitive and selective detection of disease-causing pathogens and biomarkers. In our effort to communicate a realistic assessment of the progress that has been made and the challenges that lie ahead, we avoid an overtly optimistic appraisal of the current status of SERS diagnostics that does not tacitly acknowledge the difficulties inherent in aligning SERS-based technologies alongside ELISA and PCR technologies as a complementary method for bioanalyte detection possessing unique advantages.

Surface-enhanced Raman scattering: an emerging label-free detection and identification technique for proteins

The detection and identification of biologically important molecules has critical importance in several fields such as medicine, biotechnology, and pharmacology. Surface-enhanced Raman scattering (SERS) is a powerful emerging vibrational spectroscopic technique that allows not only for the characterization, but also for the identification and detection of biomacromolecules in a very short time. In this review, efforts to utilize SERS for label-free protein detection and identification is summarized after a short introduction of proteins and the technique.

Bio-imaging, detection and analysis by using nanostructures as SERS substrates

Surface-enhanced Raman scattering (SERS) is a phenomenon that occurs on nanoscale-roughed metallic surface. The magnitude of the Raman scattering signal can be greatly enhanced when the scatterer is placed in the very close vicinity of the surface, which enables this phenomenon to be a highly sensitive analytical technique. SERS inherits the general strongpoint of conventional Raman spectroscopy and overcomes the inherently small cross section problem of a Raman scattering. It is a sensitive and nondestructive spectroscopic method for biological samples, and can be exploited either for the delivery of molecular structural information or for the detection of trace levels of analytes. Therefore, SERS has long been regarded as a powerful tool in biomedical research. Metallic nanostructure plays a key role in all the biomedical applications of SERS because the enhanced Raman signal can only be obtained on the surface of a finely divided substrate. This review focuses on progress made in the use of SERS as an analytical technique in bio-imaging, analysis and detection. Recent progress in the fabrication of SERS active nanostructures is also highlighted.

Differentiation of healthy brain tissue and tumors using surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a powerful technique for characterization of biological samples. SERS spectra from healthy brain tissue and tumors are obtained by sudden freezing of tissue in liquid nitrogen and crashing and mixing it with a concentrated silver colloidal suspension. The acquired spectra from tissues show significant spectral differences that can be used to identify whether it is from a healthy region or tumor. The most significant change on SERS spectra from the healthy/peripheral brain tissue to tumor is the increase of the ratio of the peaks at around 723 to 655 cm(-1). In addition, the spectral changes indicate that the protein content in tumors increases compared to the peripheral/healthy tissue as observed with tumor invasion. The preliminary results show that SERS spectra can be used for a quick diagnosis due to the simplicity of the sample preparation and the speed of the spectral acquisition.

Ultrasensitive protein detection in blood serum using gold nanoparticle probes by single molecule spectroscopy

A one-step rapid and ultrasensitive immunoassay capable of detecting proteins in blood serum is developed using gold nanoprobes and fluorescence correlation spectroscopy (FCS). In this approach we take advantage of the inherent photoluminescence property of gold nanoparticles (GNPs) to develop a fluorophore-free assay to observe binding entities by monitoring the diffusion of bound versus unbound molecules in a limited confocal volume. 40-nm GNPs conjugated separately with rabbit anti-IgG (Fc) and goat anti-IgG (Fab) when incubated in blood serum containing IgG forms a sandwich structure constituting dimers and oligomers that can be differentiated by to detect IgG in blood serum at a limit of detection (LOD) of 5 pgml. The novelty of integrating GNPs with FCS to develop a sensitive blood immunoassay brings single molecule methods one step closer to the clinic.

Surface-enhanced Raman scattering of rat tissues

Surface-enhanced Raman scattering (SERS) is proven to be a powerful tool for investigation of biological structures. In this study, tissues obtained from different rat organs are examined using SERS. The tissue samples are crushed with a pestle after sudden freezing in liquid nitrogen and mixed with a concentrated colloidal silver nanoparticle suspension. The reproducibility of SERS spectra acquired from several tissue samples from different organs is demonstrated. The collected spectra are comparatively evaluated based on the physiological function of the organ from which the tissue is obtained. The spectra from the tissues show significant differences and indicate that they can be used for tissue characterization and differentiation. The identification of the origins of the bands on the spectra is also attempted. This study suggests that SERS can be used to monitor the changes at the molecular level during metabolic changes in an organ or tissue as a result of a disease or another cause.

Strategies for label-free optical detection

A large number of methods using direct detection with label-free systems are known. They compete with the well-introduced fluorescence-based methods. However, recent applications take advantage of label-free detection in protein-protein interactions, high-throughput screening, and high-content screening. These new applications require new strategies for biosensors. It becomes more and more obvious that neither the transduction principle nor the recognition elements for the biomolecular interaction process alone determine the quality of the biosensor. Accordingly, the biosensor system has to be considered as a whole. This chapter focuses on strategies to optimize the detection platform and the biomolecular recognition layer. It concentrates on direct detection methods, with special focus on optical transduction. Since even this restriction still leaves a large number of methods, only microrefractometric and microreflectometric methods using planar transducers have been selected for a detailed description and a listing of applications. However, since many review articles on the physical principles exist, the description is kept short. Other methods are just mentioned in brief and for comparison. The outlook and the applications demonstrate the future perspectives of direct optical detection in bioanalytics.

Characterization of cellular chemical dynamics using combined microfluidic and Raman techniques

The integration of a range of technologies including microfluidics, surface-enhanced Raman scattering and confocal microspectroscopy has been successfully used to characterize in situ single living CHO (Chinese hamster ovary) cells with a high degree of spatial (in three dimensions) and temporal (1 s per spectrum) resolution. Following the introduction of a continuous flow of ionomycin, the real time spectral response from the cell was monitored during the agonist-evoked Ca²⁺ flux process. The methodology described has the potential to be used for the study of the cellular dynamics of a range of signalling processes.

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Experimental parameters influencing surface-enhanced Raman scattering of bacteria

Surface-enhanced Raman scattering (SERS) is a powerful technique for the analysis of a variety of molecules and molecular structures. Due to its great complexity, the acquisition of detailed molecular information from biological organizations such as bacteria is still a challenging task. SERS can provide valuable information once silver or gold surfaces can be brought in close contact with the biological organization. Because several experimental parameters can affect SERS spectra of bacteria, the experimental conditions must be well defined for comparable and reproducible results. The influence of experimental parameters, such as the type of noble metal, size, and aggregation properties of nanoparticles, and the wavelength of the laser light on the SERS of E. coli and B. megaterium are examined. It is demonstrated that the impact of these parameters could be enormous and a standard protocol must be developed depending on the goal of the study.

S-Nitrosylation of Platelet αIIbβ3 As Revealed by Raman Spectroscopy

The exact mechanisms regulating conformational changes in the platelet-specific integrin alphaIIbbeta3 are not fully understood. However, a role exists for thiol/disulfide exchange in integrin conformational changes leading to altered disulfide bonding patterns, via its endogenous thiol isomerase activity. Nitric oxide (NO) accelerates this intrinsic enzymatic activity and, in doing so, reverses the activational state of the integrin on the platelet surface toward a more unactivated one. We propose that it is an S-nitrosylation-induced "shuffling" of thiol/disulfide exchange that regulates this reversal of the activated state of the integrin. In this study, we use Raman spectroscopy to explore S-nitrosylation of purified alphaIIbbeta3. Using S-nitrosoglutathione (GSNO) as a model system, we identify Raman markers which show a direct interaction between NO and the thiol groups of the integrin and reveal many of the structural changes that occur in alphaIIbbeta3 in the course of not only its activation but also its deactivation. Key conformational changes are detected within the integrin when treated with manganese (Mn2+), occurring mainly in the cysteine and disulfide regions of the protein, confirming the importance of thiol/disulfide exchange in integrin activation. These changes are subsequently shown to be reversed in the presence of NO.

Probing Intrinsic and Extrinsic Components in Single Osteosarcoma Cells by Near-Infrared Surface-Enhanced Raman Scattering

We report on the capabilities of near-infrared surface-enhanced Raman scattering (SERS) using gold nanoparticles to obtain detailed chemical information with high spatial resolution from within single cancer cells, living or fixed. Colloidal gold particles, 60 nm in size, were introduced into live human osteosarcoma cells by endocytosis by adding them to the growth medium. Rapid SERS mapping of cells indicated that not only could rich vibrational spectra be obtained from intrinsic cellular constituents both in the cytoplasm and nucleus and but also the distribution of extrinsic molecules introduced into the cells, in this case, rhodamine 6G could be characterized, suggesting that the intracellular distribution of chemotherapeutic agents could potentially be measured by this technique. We show that the SERS signal intensity from the cellular components increases and more spectral detail is acquired from dried cells when compared with hydrated cells in buffer. The data also show spectral fluctuations, mainly in intensity but also in peak position, which are dependent upon the intensity of the excitation light and are probably due to diffusion of molecules on the surface of the gold nanoparticles. A detailed understanding of the origins of these effects is still not complete, but the ability to acquire very sensitive SERS inside living cancer cells indicates the potential of this technique as a useful tool in biomedicine.