Zachary D. Schultz

Infrared spectroscopic imaging of latent fingerprints and associated forensic evidence

Fingerprints reflecting a specific chemical history, such as exposure to explosives, are clearly distinguished from overlapping, and interfering latent fingerprints using infrared spectroscopic imaging techniques and multivariate analysis.

Vibrational Spectroscopic and Mass Spectrometric Studies of the Interaction of Bis(3-sulfopropyl)-disulfide with Cu Surfaces

In situ surface enhanced Raman scattering (SERS), infrared-visible sum frequency generation (SFG) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and detailed calculations are used to examine the interaction of bis(3-sulfopropyl)-disulfide (SPS) and mercaptopropylsulfonic acid (MPS) with Cu surfaces both in the absence and presence of chloride. MPS and SPS SERS spectra are similar to each other, and the lack of a specific S-S feature suggests that SPS interacts with Cu as a thiolate. SERS data show a significant shift in the S-O sulfonate region of the SPS or MPS spectra upon the addition of Cl - , a result which is interpreted as arising from CuCI coordination to the SO 3 moiety of these molecules. CuCl association with SPS is also evidenced in the ESI-MS data. The specific spectral shifts are corroborated by density functional theory calculations. In situ SFG measurements provide evidence that SPS and MPS interact with the Cu surface in solutions not containing Cl - at negative potentials. However, there is no evidence in either the SFG or the SERS for SPS or MPS-Cu coordination in the presence of Cl - at any potential. The data suggest that the thiolate moiety in the additives is not an active component for the acceleration behavior observed.

Vibrational spectroscopy of biomembranes.

Vibrational spectroscopy, commonly associated with IR absorption and Raman scattering, has provided a powerful approach for investigating interactions between biomolecules that make up cellular membranes. Because the IR and Raman signals arise from the intrinsic properties of these molecules, vibrational spectroscopy probes the delicate interactions that regulate biomembranes with minimal perturbation. Numerous innovative measurements, including nonlinear optical processes and confined bilayer assemblies, have provided new insights into membrane behavior. In this review, we highlight the use of vibrational spectroscopy to study lipid-lipid interactions. We also examine recent work in which vibrational measurements have been used to investigate the incorporation of peptides and proteins into lipid bilayers, and we discuss the interactions of small molecules and drugs with membrane structures. Emerging techniques and measurements on intact cellular membranes provide a prospective on the future of vibrational spectroscopic studies of biomembranes.

Characterization of hotspots in a highly enhancing SERS substrate

Vapor deposition of silver and gold onto a porous anodized aluminum oxide template is shown to produce a SERS substrate with an average surface enhancement factor of 10(7)-10(8). The high level of enhancement is explored using a combination of dark-field Rayleigh scattering and Raman spectroscopy and imaging. The scattering spectrum of the surface indicates a Plasmon resonance at 633 nm and dark-field imaging shows a relatively uniform scattering intensity at this wavelength. These measurements are consistent with the uniform enhanced Raman intensity observed in Raman maps of the substrate. Scanning electron microscopy shows the surface exhibits heterogeneous nanostructures with diameters of approximately 100 nm, the size of the pores in the template. Our measurements indicate that interactions between adjacent structures forming junctions and crevices likely give rise to a high density of hotspots, which provide the extraordinary SERS enhancement. The advantage of substrates prepared in this way is the reproducibly dense distribution of hotspots across the surface, increasing the likelihood that an analyte will experience the largest enhancement.

Tip-enhanced Raman detection of antibody conjugated nanoparticles on cellular membranes.

Tip enhanced Raman scattering (TERS) microscopy is used to image antibody conjugated nanoparticles on intact cellular membranes. The combination of plasmonic coupling and the resultant electric field obtained from intermediate focusing of a radially polarized source gives rise to Raman images with spatial resolution below 50 nm. Finite element method calculations are used to explain the origins of the observed image resolution and spectroscopic signals. The observed Raman scattering provides information about the biomolecules present near the nanoparticle probes. The results show that aggregates of nanoparticles produce spectroscopic results similar to those reported from other surface enhanced Raman spectroscopies, e.g., shell isolated nanoparticle enhanced Raman spectroscopy (SHINERS) and aggregated nanoparticles; however, TERS enables the detection of isolated nanoparticles on cell membranes where the observed spectra provide information about the interaction of the specific biomolecule conjugated to the nanoparticle probe. These measurements present a new technique for exploring biomolecular interactions on the surface of cells and tissue.

University learning: Improve undergraduate science education

It is time to use evidence-based teaching practices at all levels by providing incentives and effective evaluations, urge Stephen E. Bradforth, Emily R. Miller and colleagues.

Sensing Glucose in Urine and Serum and Hydrogen Peroxide in Living Cells by Use of a Novel Boronate Nanoprobe Based on Surface-Enhanced Raman Spectroscopy

Hydrogen peroxide (H2O2) is known as a key molecule in a variety of biological processes, as well as a crucial byproduct in many enzymatic reactions. Therefore, being able to selectively and sensitively detect H2O2 is not only important in monitoring, estimating, and decoding H2O2 relevant physiological pathways but also very helpful in developing enzymatic-based biosensors for other analytes of interest. Herein, we report a plasmonic probe for H2O2 based on 3-mercaptophenylboronic acid (3-MPBA) modified gold nanoparticles (AuNPs) which is coupled with surface-enhanced Raman scattering (SERS) to yield a limit of detection (LOD) of 70 nM. Our probe quantifies both exogenous and endogenous H2O2 levels in living cells and can further be coupled with glucose oxidase (GOx) to achieve quantitative and selective detection of glucose in artificial urine and human serum.

Protein–ligand binding investigated by a single nanoparticle TERS approach

We report TERS imaging of individual 50 nm, biotin-labeled gold nanoparticles bound to a streptavidin-derivatized glass slide. Individual gold nanoparticles detected by a nanoparticle TERS tip generate Raman enhancements in both the biotin and streptavidin signals. These results indicate that nanoparticles are capable of investigating nanoscale spatial and chemical environments with non-resonant Raman enhancements.

Ultrasensitive Surface-Enhanced Raman Scattering Flow Detector Using Hydrodynamic Focusing

Label-free, chemical specific detection in flow is important for high throughput characterization of analytes in applications such as flow injection analysis, electrophoresis, and chromatography. We have developed a surface-enhanced Raman scattering (SERS) flow detector capable of ultrasensitive optical detection on the millisecond time scale. The device employs hydrodynamic focusing to improve SERS detection in a flow channel where a sheath flow confines analyte molecules eluted from a fused silica capillary over a planar SERS-active substrate. Increased analyte interactions with the SERS substrate significantly improve detection sensitivity. The performance of this flow detector was investigated using a combination of finite element simulations, fluorescence imaging, and Raman experiments. Computational fluid dynamics based on finite element analysis was used to optimize the flow conditions. The modeling indicates that a number of factors, such as the capillary dimensions and the ratio of the sheath flow to analyte flow rates, are critical for obtaining optimal results. Sample confinement resulting from the flow dynamics was confirmed using wide-field fluorescence imaging of rhodamine 6G (R6G). Raman experiments at different sheath flow rates showed increased sensitivity compared with the modeling predictions, suggesting increased adsorption. Using a 50 ms acquisition, a sheath flow rate of 180 μL/min, and a sample flow rate of 5 μL/min, a linear dynamic range from nanomolar to micromolar concentrations of R6G with a limit of detection (LOD) of 1 nM is observed. At low analyte concentrations, rapid analyte desorption is observed, enabling repeated and high-throughput SERS detection. The flow detector offers substantial advantages over conventional SERS-based assays such as minimal sample volumes and high detection efficiency.

The chemical origin of enhanced signals from tip-enhanced Raman detection of functionalized nanoparticles

Here we present results that investigate the origins of signals observed in tip-enhanced Raman (TERS) measurements of functionalized nanoparticles. Surface enhanced Raman scattering (SERS) is known to give the largest enhancements in gap junctions. Similarly, gap-mode TERS also produces significant enhancements. The methodology developed here provides gap-mode like enhancements in TERS measurements without the need for a metal surface. Using a combination of aggregated nanoparticle SERS and TERS detection of functionalized nanoparticles, we assess the chemical origins of the observed peaks and show that molecules outside of gap junctions are also enhanced using our methodology. Our experiments use biotin and streptavidin as a model system for protein-ligand binding. Different size functionalized nanoparticles (20, 50, 80 nm) show changes in intensity in both SERS and TERS measurements. SERS measurements indicate that streptavidin has a larger Raman cross-section than biotin and is preferentially observed. The specific streptavidin peaks observed by TERS vary depending on whether streptavidin is attached to the nanoparticle and located in the gap or bound to the substrate surface. This methodology suggests a route to enhancing TERS signals associated with protein receptors in biological systems that cannot be isolated to a metallic surface.