Detection of Glutamate in Optically Trapped Single Nerve Terminals by Raman Spectroscopy

Drug-Coformer Loaded-Mesoporous Silica Nanoparticles: A Review of the Preparation, Characterization, and Mechanism of Drug Release

Drug-coformer systems, such as coamorphous and cocrystal, are gaining recognition as highly effective strategies for enhancing the stability, solubility, and dissolution of drugs. These systems depend on the interactions between drug and coformer to prevent the conversion of amorphous drugs into the crystalline form and improve the solubility. Furthermore, mesoporous silica (MPS) is also a promising carrier commonly used for stabilization, leading to solubility improvement of poorly water-soluble drugs. The surface interaction of drug-MPS and the nanoconfinement effect prevent amorphous drugs from crystallizing. A novel method has been developed recently, which entails the loading of drug-coformer into MPS to improve the solubility, dissolution, and physical stability of the amorphous drug. This method uses the synergistic effects of drug-coformer interactions and the nanoconfinement effect within MPS. Several studies have reported successful incorporation of drug-coformer into MPS, indicating the potential for significant improvement in dissolution characteristics and physical stability of the drug. Therefore, this study aimed to discuss the preparation and characterization of drug-coformer within MPS, particularly the interaction in the nanoconfinement, as well as the impact on drug release and physical stability.

A novel ratiometric fluorescent probe for detection of l-glutamic acid based on dual-emission carbon dots

In this article, we report for the first time the use of a dual-emission carbon dots (CDs) with orange-yellow fluorescence for the detection of l-glutamic acid (L-Glu). The CDs was synthesized through a facile strategy of one-pot hydrothermal route using o-phenylenediamine (oPD) and oxalic acid. The CDs exhibit two fluorescence emission peaks around 453 nm and 560 nm when the excitation wavelength is at 390 nm. In the existence of L-Glu the fluorescence at 560 nm was decreased, whereas the fluorescence at 453 nm was constant. The fluorescence intensity ratio at 560 nm and 453 nm (F₅₆₀/F₄₅₃) expressed two great linear relationships in the L-Glu concentration range from 0 to 200 μM and 200-400 μM, respectively, with a detection limit (LOD) of about 0.085 μM. In addition, it was used to analyze L-Glu in fetal bovine serum samples successfully, which recoveries were ranging from 97.07 to 103.7%. Those results demonstrate CDs can be further explored in biomedicine studies.

Detection of Glutamate Encapsulated in Liposomes by Optical Trapping Raman Spectroscopy

The transmission of neuronal information is propagated through synapses by neurotransmitters released from presynapses to postsynapses. Neurotransmitters released from the presynaptic vesicles activate receptors on the postsynaptic membrane. Glutamate acts as a major excitatory neurotransmitter for synaptic vesicles in the central nervous system. Determining the concentration of glutamate in single synaptic vesicles is essential for understanding the mechanisms of neuronal activation by glutamate in normal brain functions as well as in neurological diseases. However, it is difficult to detect and quantitatively measure the concentration of glutamate in single synaptic vesicles owing to their small size, i.e., ∼40 nm. In this study, to quantitatively evaluate the concentrations of the contents in small membrane-bound vesicles, we developed an optical trapping Raman spectroscopic system that analyzes the Raman spectra of small objects captured using optical trapping. Using artificial liposomes encapsulating glutamate that mimic synaptic vesicles, we investigated whether spontaneous Raman scattered light of glutamate can be detected from vesicles trapped at the focus using optical forces. A 575 nm laser beam was used to simultaneously perform the optical trapping of liposomes and the detection of the spontaneous Raman scattered light. The intensity of Raman scattered light that corresponds to lipid bilayers increased with time. This observation suggested that the number of liposomes increased at the focal point. The number of glutamate molecules in the trapped liposomes was estimated from the calibration curve of the Raman spectra of glutamate solutions with known concentration. This method can be used to measure the number of glutamate molecules encapsulated in synaptic vesicles in situ.

Raman Spectroscopy of Pharmaceutical Cocrystals in Nanosized Pores of Mesoporous Silica

The Raman spectroscopy of pharmaceutical cocrystals based on caffeine and oxalic acid in nanosized pores of mesoporous silica has been demonstrated at various molar amounts. The Raman peak shifts of caffeine molecules express the existence of pharmaceutical cocrystals in mesoporous silica. The molar amount dependence of the peak shifts describes that caffeine and oxalic acid cocrystallized on the surface of the nanosized pores and piled up layer by layer. This is the first report that shows the Raman spectroscopy is a powerful tool to observe the synthesis of pharmaceutical cocrystals incorporated in the nanosized pores of mesoporous silica. The results indicate a way to control the size of cocrystals on a nanometer scale, which will provide higher bioavailability of pharmaceuticals.

Confocal Raman Microscopy for pH-Gradient Preconcentration and Quantitative Analyte Detection in Optically Trapped Phospholipid Vesicles

The ability of a vesicle membrane to preserve a pH gradient, while allowing for diffusion of neutral molecules across the phospholipid bilayer, can provide the isolation and preconcentration of ionizable compounds within the vesicle interior. In this work, confocal Raman microscopy is used to observe (in situ) the pH-gradient preconcentration of compounds into individual optically trapped vesicles that provide sub-femtoliter collectors for small-volume samples. The concentration of analyte accumulated in the vesicle interior is determined relative to a perchlorate-ion internal standard, preloaded into the vesicle along with a high-concentration buffer. As a guide to the experiments, a model for the transfer of analyte into the vesicle based on acid-base equilibria is developed to predict the concentration enrichment as a function of source-phase pH and analyte concentration. To test the concept, the accumulation of benzyldimethylamine (BDMA) was measured within individual 1 μm phospholipid vesicles having a stable initial pH that is 7 units lower than the source phase. For low analyte concentrations in the source phase (100 nM), a concentration enrichment into the vesicle interior of (5.2 ± 0.4) × 10(5) was observed, in agreement with the model predictions. Detection of BDMA from a 25 nM source-phase sample was demonstrated, a noteworthy result for an unenhanced Raman scattering measurement. The developed model accurately predicts the falloff of enrichment (and measurement sensitivity) at higher analyte concentrations, where the transfer of greater amounts of BDMA into the vesicle titrates the internal buffer and decreases the pH gradient. The predictable calibration response over 4 orders of magnitude in source-phase concentration makes it suitable for quantitative analysis of ionizable compounds from small-volume samples. The kinetics of analyte accumulation are relatively fast (∼15 min) and are consistent with the rate of transfer of a polar aromatic molecule across a gel-phase phospholipid membrane.

Spatial filtering of a diode laser beam for confocal Raman microscopy

With the development of single-longitudinal mode diode lasers, there has been an increase in using these sources for Raman spectroscopy. This is largely due to the cost-effectiveness of diode lasers, which offer savings not only in initial capital cost, but also electrical, cooling, and replacement costs over time, when compared with ion lasers. The use of diode-lasers in confocal Raman microscopy has remained a challenge, however, due to poor transverse beam quality. In this work, we present the design and implementation of a simple spatial filter capable of adapting a single-mode diode laser source to confocal Raman microscopy, yielding comparable spatial resolution as a gas-ion laser beam for profiling and optical-trapping applications. For profiling applications, spatial filtering improved x,y resolution of the beam by a factor 10, which in turn increased optical-trapping forces by ~90 times and yielded sevenfold greater Raman scattering signal intensity from an optically trapped phospholipid vesicle.

Analysis of the developing neural system using an in vitro model by Raman spectroscopy

We developed an in vitro model of early neural cell development.

Raman microspectroscopy: a noninvasive tool for studies of individual living cellsin vitro

There is an increasing need for noninvasive methods that are able to monitor individual live cells in vitro, including in vitro testing of chemicals and pharmaceuticals, monitoring the growth of engineered tissues and the development of cell-based biosensors. Raman spectroscopy is a pure optical technique based on inelastic scattering of laser photons by molecular vibrations of biopolymers, which provide a chemical fingerprint of cells or organelles without fixation, lysis or the use of labels and other contrast-enhancing chemicals. Changes in cells during the cell cycle, cell death, differentiation or during the interaction with various chemicals or materials involve biochemical changes that can be measured with high spatial ( approximately 300 nm) and temporal (seconds to minutes) resolution. The latest technological developments, especially high-sensitivity charged coupled detectors and high-power near-infrared lasers, have spurred the growth of Raman microspectroscopy towards being a well established analytical tool. This review covers the recent applications of this technique, including studies of individual cells, both pro- and eukaryotes, and emphasizes the potential impact on modern scientific endeavors, such as tissue engineering and drug discovery.

Identification of motor and sensory fascicles in peripheral nerve trunk using immunohistochemistry and micro-Raman spectroscopy

OBJECTIVE

To explore a time-efficient method of identifying motor and sensory fascicles in peripheral nerve trunk.

METHODS

Thirty Wistar rats were selected to obtain whole spine. The spinal dorsal roots and ventral roots, and sciatic nerve were harvested as sensor, motor, and mixed samples, annexin V and agrin specificities were observed with Western blot and immunohistochemistry. A total of 32 New Zealand rabbits were selected and killed. The roots of spinal nerves were exposed under an operating microscope, and the ventral and dorsal roots, ∼3 mm to 5 mm, were dissociated, and frozen as transverse sections of 30-μm thickness. The sections were examined by micro-Raman spectroscopy.

RESULTS

The annexin V and agrin were special substances of sensory and motor nerves, respectively, and can act as specific antigens for identifying different nerve fascicles. Sections of the same type of nerve fascicles showed reproducibility with similar spectral features. Significant differences in the spectral properties, such as the intensity and breadth of the peak, were found between motor and sensory fascicles in the frequency regions of 1,088 cm(-1), 1,276 cm(-1), 1,439 cm(-1), 1,579 cm(-1), and 1,659 cm(-1). With the peak intensity ratio of 1.06 (I(1276)/I(1439)) as a standard, we could identify motor fascicles with a sensitivity of 88%, specificity of 94%, positive predictive value of 93%, and negative predictive value of 88%. In the range of 2,700 cm(-1) to 3,500 cm(-1), the half-peak width of the motor fascicles was narrow and sharp, whereas that of the sensory fascicles was relatively wider. A total of 91% of the peak features were in accordance with the identification standard.

CONCLUSION

Motor and sensory fascicles exhibit different characteristics in Raman spectra, which are constant and reliable. Therefore, it is more effective than immunohistochemistry method in identifying different nerve fascicles according to the specific spectrum, and it possesses feasibility for clinical application.

Confocal Raman microscopy of pH-gradient-based 10 000-fold preconcentration of compounds within individual, optically trapped phospholipid vesicles

A stable pH gradient established across the membrane of phospholipid vesicle can induce the accumulation of ionizable compounds from bulk solution into the vesicle interior. This pH-gradient vesicle loading process has previously been utilized to encapsulate drugs in pharmaceutical liposomal formulations. In the present work, this process is exploited to preconcentrate dilute analytes from free solution into phospholipid vesicles, which are then detected by optically trapping individual vesicles and measuring their contents using confocal Raman microscopy. The theory of accumulation, based on the acid-base ionization equilibria of the analyte, is developed to account for depletion of the source phase and the finite buffering capacity of the vesicle interior. The model predicts that, under appropriate conditions, enrichment factors of more than 4 orders of magnitude can be realized. To test the concept, experiments were performed measuring the accumulation of benzyldimethylamine into 600-nm phospholipid vesicles. Manipulation of vesicles by optical trapping allows accumulation within an individual vesicle to be characterized while varying the external solution conditions. A more than 10 000-fold enrichment of the analyte concentration inside the vesicle relative to the source phase is reported. The results suggest that pH-gradient loading could be exploited as a powerful preconcentration scheme for trace analysis using either Raman microscopy or other microspectroscopy techniques.

Oxygen-inducible glutamate oxaloacetate transaminase as protective switch transforming neurotoxic glutamate to metabolic fuel during acute ischemic stroke

This work rests on our previous report (J Cereb Blood Flow Metab 30: 1275-1287, 2010) recognizing that glutamate (Glu) oxaloacetate transaminase (GOT) is induced when brain tissue hypoxia is corrected during acute ischemic stroke (AIS). GOT can metabolize Glu into tricarboxylic acid cycle intermediates and may therefore be useful to harness excess neurotoxic extracellular Glu during AIS as a metabolic substrate. We report that in cultured neural cells challenged with hypoglycemia, extracellular Glu can support cell survival as long as there is sufficient oxygenation. This effect is abrogated by GOT knockdown. In a rodent model of AIS, supplemental oxygen (100% O(2) inhaled) during ischemia significantly increased GOT expression and activity in the stroke-affected brain tissue and prevented loss of ATP. Biochemical analyses and in vivo magnetic resonance spectroscopy during stroke demonstrated that such elevated GOT decreased Glu levels at the stroke-affected site. In vivo lentiviral gene delivery of GOT minimized lesion volume, whereas GOT knockdown worsened stroke outcomes. Thus, brain tissue GOT emerges as a novel target in managing stroke outcomes. This work demonstrates that correction of hypoxia during AIS can help clear extracellular neurotoxic Glu by enabling utilization of this amino acid as a metabolic fuel to support survival of the hypoglycemic brain tissue. Strategies to mitigate extracellular Glu-mediated neurodegeneration via blocking receptor-mediated excitotoxicity have failed in clinical trials. We introduce the concept that under hypoglycemic conditions extracellular Glu can be transformed from a neurotoxin to a survival factor by GOT, provided there is sufficient oxygen to sustain cellular respiration.

Confocal Raman microscopy of optical-trapped particles in liquids

The in situ analysis of small, dispersed particles in liquids is a challenging problem, the successful solution to which influences diverse applications of colloidal particles in materials science, synthetic chemistry, and molecular biology. Optical trapping of small particles with a tightly focused laser beam can be combined with confocal Raman microscopy to provide molecular structure information about individual, femtogram-sized particles in liquid samples. In this review, we consider the basic principles of combining optical trapping and confocal Raman spectroscopy, then survey the applications that have been developed through the combination of these techniques and their use in the analysis of particles dispersed in liquids.

Computer augmented modelling studies of Pb(II), Cd(II), Hg(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of L-glutamic acid in 1,2-propanediol-water mixtures

Chemical speciation of Pb(II), Cd(II), Hg(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of L-glutamic acid was studied at 303 K in 0-60 vol. % 1,2-propanediol-water mixtures, whereby the ionic strength was maintained at 0.16 mol dm-3. The active forms of the ligand are + LH3, LH2 and LH-. The predominant detected species were ML, ML2, MLH, ML2H and ML2H2. The trend of the variation in the stability constants with changing dielectric constant of the medium is explained based on the cation stabilizing nature of the co-solvents, specific solvent-water interactions, charge dispersion and specific interactions of the co-solvent with the solute. The effect of systematic errors in the concentrations of the substances on the stability constants is in the order alkali > > acid > ligand > metal. The bioavailability and transportation of metals are explained based on distribution diagrams and stability constants.

Raman spectroscopic analysis of biochemical changes in individual triglyceride-rich lipoproteins in the pre- and postprandial state

Individual triglyceride-rich lipoprotein (TGRL) particles derived from human volunteers are nondestructively analyzed by laser tweezers Raman microspectroscopy, and information on their composition and distribution is obtained. The Raman signature of single optically trapped very low-density lipoproteins (VLDL), a subclass of TGRL, which play an important role in cardiovascular disease, exhibits distinct peaks associated with molecular vibrations of fatty acids, proteins, lipids, and structural rearrangements of lipids. Our analysis of pre- and postprandial VLDL exhibits the signature of biochemical changes in individual lipoprotein particles following the consumption of meals. Interaction of VLDL with endothelium leads to the breakdown of complex triacylglycerols and the formation of a highly ordered core of free saturated fatty acids in the particle. A particle distribution analysis reveals trends in the degree to which this process has occurred in particles at different times during the postprandial period. Differences in particle distributions based on the different ratios of polyunsaturated to saturated fats in the consumed meals are also easily discerned. Individual lipoprotein particles hydrolyzed in vitro through addition of lipoprotein lipase (LpL) exhibit strikingly similar changes in their Raman spectra. These results demonstrate the feasibility of monitoring the dynamics of lipid metabolism of individual TGRL particles as they interact with LpL in the endothelial cell wall using Raman spectroscopy.

Monitoring dynamic protein expression in livingE. coli. Bacterial cells by laser tweezers Raman spectroscopy

BACKGROUND

Laser tweezers Raman spectroscopy (LTRS) is a novel, nondestructive, and label-free method that can be used to quantitatively measure changes in cellular activity in single living cells. Here, we demonstrate its use to monitor changes in a population of E. coli cells that occur during overexpression of a protein, the extracellular domain of myelin oligodendrocyte glycoprotein [MOG(1-120)].

METHODS

Raman spectra were acquired from individual E. coli cells suspended in solution and trapped by a single tightly focused laser beam. Overexpression of MOG(1-120) in transformed E. coli Rosetta-Gami (DE3)pLysS cells was induced by addition of isopropyl thiogalactoside (IPTG). Changes in the peak intensities of the Raman spectra from a population of cells were monitored and analyzed over a total duration of 3 h. Data were also collected for concentrated purified MOG(1-120) protein in solution, and the spectra compared with that obtained for the MOG(1-120) expressing cells.

RESULTS

Raman spectra of individual, living E. coli cells exhibit signatures due to DNA and protein molecular vibrations. Characteristic Raman markers associated with protein vibrations, such as 1,257, 1,340, 1,453, and 1,660 cm(-1), are shown to increase as a function of time following the addition of IPTG. Comparison of these spectra and the spectra of purified MOG protein indicates that the changes are predominantly due to the induction of MOG protein expression. Protein expression was found to occur mostly within the second hour, with a 470% increase relative to the protein expressed in the first hour. A 230% relative increase between the second and third hour indicates that protein expression begins to level off within the third hour.

CONCLUSION

It is demonstrated that LTRS has sufficient sensitivity for real-time, nondestructive, and quantitative monitoring of biological processes, such as protein expression, in single living cells. Such capabilities, which are not currently available in flow cytometry, open up new possibilities for analyzing cellular processes occurring in single microbial and eukaryotic cells.

Real-Time Detection of Kinetic Germination and Heterogeneity of SingleBacillusSpores by Laser Tweezers Raman Spectroscopy

Germination is the process by which a dormant spore returns to its vegetative state when exposed to suitable conditions. We report on the real-time detection of kinetic germination and heterogeneity of single Bacillus thuringiensis spores in an aqueous solution by monitoring the calcium dipicolinate (CaDPA) biomarker with laser tweezers Raman spectroscopy (LTRS). A single B. thuringiensis spore was optically trapped in a focused laser beam, and its Raman spectra were recorded sequentially in time after exposure to a nutrient-rich medium, so that the CaDPA amount inside the trapped spore was monitored during the dynamic germination process. The CaDPA content in an individual spore was observed to remain almost constant in the first period and then decrease very rapidly due to its release into the medium (within approximately 2 min). The time-to-germination (t(germ)), defined as the time required for the CaDPA band intensity to decrease to the midpoint from its initial value, was found to be stochastic for individual spores with a typical value of approximately 30 min under the experimental conditions. The distribution of the time-to-germination was measured from a time lapse measurement of a population of spores. The results demonstrated that LTRS can be used to noninvasively detect the kinetic germination process at the single-cell level and explore cellular heterogeneity.

Neuro-oncological applications of optical spectroscopy

Advances in optics and molecular imaging have occurred rapidly in the past decade. One technique poised to take advantage of these developments is optical spectroscopy (OS). All optical spectroscopic techniques have in common tissue interrogation with light sources ranging from the ultraviolet (UV) to the infrared (IR) ranges of the spectrum, and collection of information on light reflected (reflectance spectroscopy) or light interactions with tissue and emergence at different wavelengths (fluorescence and Raman spectroscopy). OS can provide information regarding intrinsic tissue optical properties such as tissue structure, nuclear density, and the presence or absence of endogenous or exogenous fluorophores. Among other applications, this information has been used to distinguish tumor from normal brain tissues, to detect tumor margins in intrinsic, infiltrating gliomas, to identify radiation damage to tissues, and to assess tissue viability and predict the onset of apoptosis in vitro and in vivo. Potential applications of OS include detection of specific central nervous system (CNS) structures, such as brain nuclei, identification of cell types by the presence of specific neurotransmitters, and the detection of optically labeled cells or drugs during therapeutic interventions. All have potential utility in neuro-oncology, have been investigated in our laboratories, and will be the subject of this review.

Monitoring neurotransmitter release using surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is a promising tool to monitor neurotransmitter release at the single-cell level: it is a sensitive technique that provides structural information of the released compounds and spatial information about their release sites. In this study we demonstrate that depolarization-evoked catecholamine secretion by rat phaeochromocytoma (PC12) cells can be spatially resolved by SERS using silver colloids. A suitable SERS substrate was created by adding silver colloids to the cell culture medium. Nomarski-DIC microscopy combined with reflection confocal laser scanning microscopy showed that the colloids were primarily present on top of the cell membrane. The SERS spectra were successfully corrected for the contribution of cell constituents. Dopamine and noradrenaline were localized by examining the correlation coefficient between spectra and reference catecholamine spectra. Potential improvements of the temporal resolution of the technique are discussed.

Studies on Stress-Induced Changes at the Subcellular Level by Raman Microspectroscopic Mapping

Raman microspectroscopic mapping enables one to study the chemical composition and molecular structure of subcellular components in individual cells without the need for labeling. Lung fibroblast cells were prepared under normal conditions and under stress, which was induced by 24 h of exposure to glyoxal. Raman microspectroscopic maps were recorded from fixed cells with 785-nm excitation and with 1-microm step width. Cluster analysis was applied to generate pseudocolor images of the cell morphology. Raman maps revealed that the cell nucleus shrinks in stressed cells, called pyknosis, which refers to an early stage of apoptosis. The intensity of nucleic acid bands decreased in cluster-averaged Raman spectra of the nucleus and cytoplasm, which is consistent with degradation and conformational changes of DNA and RNA. During a later stage of apoptosis, Raman maps indicate a rounding of cells, a further intensity decrease of nucleic acids bands, fragmentation of the nucleus, disappearance of lipid bodies, and formation of blisters at the cell surface. Whereas the peripheral membrane of the undisturbed cell is composed of lipids and cholesterol, the blisters have a higher protein content with nucleic acids incorporated. The results demonstrate that Raman spectroscopic mapping might become a powerful tool in cell biology for single cell analysis.

Detection of Drug−Membrane Interactions in Individual Phospholipid Vesicles by Confocal Raman Microscopy

Optical-trapping confocal Raman microscopy is developed as a method to study the interactions of drugs or other compounds with the membranes of individual phospholipid vesicles. This technique allows membrane disorder, permeability, and drug localization to be assessed without the need for labeling of the membrane or the compounds of interest. We have applied this technique to study the interactions of two nonsteroidal antiinflammatory drugs, salicylate and ibuprofen, with vesicles prepared from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The results show that both salicylate and ibuprofen increase membrane disorder, as determined from increases in the Raman scattering from gauche conformers in the phospholipid acyl chains. By monitoring the Raman scattering of the drug molecules in optically trapped DMPC vesicles, the membrane permeability and partitioning of the drugs could be determined; the spatial distributions of the drugs were also measured by scanning the laser focus through surface-adhered 1,2-dipalmitoyl-sn-glycero-3-phosphocholine vesicles, producing a profile of the vesicle and its contents. Though the membrane is permeable to both drugs, ibuprofen preferentially accumulates in the membrane, whereas salicylate does not. The measured ibuprofen accumulation agrees quantitatively with the water/octanol partition coefficient of the drug and the estimated volume of the lipid membrane. The results suggest that ibuprofen localizes in the hydrophobic acyl chain region of the membrane, whereas salicylate weakly associates with the phospholipid headgroups.

Surface-enhanced Raman spectroscopy biosensors: excitation spectroscopy for optimisation of substrates fabricated by nanosphere lithography

In the 28 years since its discovery, surface-enhanced Raman scattering (SERS) has progressed from model system studies of pyridine on a roughened silver electrode to state-of-the-art surface science studies and real-world sensing applications. Each year, the number of SERS publications increases as nanoscale material design techniques advance and the importance of trace analyte detection increases. To achieve the lowest limits of detection, both the relationship between surface nanostructure and laser excitation wavelength and the analyte-surface binding chemistry must be carefully optimised. This work exploits the highly tunable nature of nanoparticle optical properties to establish the optimisation conditions. Two methods are used to study the optimised conditions of the SERS substrate: plasmon-sampled and wavelength-scanned surfaced Raman excitation spectroscopy (SERES). The SERS enhancement condition is optimised when the energy of the localised surface plasmon resonance of the nanostructures lies between the energy of the excitation wavelength and the energy of the vibration band of interest. These optimised conditions enabled the development of SERS-based sensors for the detection of a Bacillus anthracis biomarker and glucose in a serum-protein matrix.

Real-Time Detection of Hyperosmotic Stress Response in Optically Trapped Single Yeast Cells Using Raman Microspectroscopy

Living cells survive environmentally stressful conditions by initiating a stress response. We monitored changes in the Raman spectra of optically trapped Saccharomyces cerevisiae yeast cell under normal, heat-treated, and hyperosmotic stress conditions. It is shown that when glucose was used to exert hyperosmotic stress, two chemical substances-glycerol and ethanol-can be monitored in real time in a single cell.