Part-Per-Billion Level Chemical Sensing with a Gold-Based SERS-Active Substrate.

We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix.

Selective detection of 1000 B. anthracis spores within 15 minutes using a peptide functionalized SERS assay.

A surface-enhanced Raman spectroscopy (SERS) assay has been designed to detect Bacillus anthracis spores. The assay consists of silver nanoparticles embedded in a porous glass structure that have been functionalized with ATYPLPIR, a peptide developed to discriminately bind B. anthracis versus other species of Bacillus.

Detection of drugs of abuse in saliva by surface-enhanced Raman spectroscopy (SERS).

Eighty drugs of abuse and metabolites were successfully measured by surface-enhanced Raman spectroscopy (SERS) using gold- and silver-doped sol-gels immobilized in glass capillaries. A method was developed that provided consistent detection of 50 ppb cocaine in saliva in a focused study. This general method was successfully applied to the detection of a number of additional drugs in saliva, such as amphetamine, diazepam, and methadone.

Rapid detection and identification of overdose drugs in saliva by surface-enhanced Raman scattering using fused gold colloids.

The number of drug-related emergency room visits in the United States doubled from 2004 to 2009 to 4.6 million. Consequently there is a critical need to rapidly identify the offending drug(s), so that the appropriate medical care can be administered.

Surface-enhanced Raman spectral measurements of 5-fluorouracil in saliva.

The ability of surface-enhanced Raman spectroscopy (SERS) to measure 5-fluorouracil (5-FU) in saliva is presented. The approach is based on the capacity of Raman spectroscopy to provide a unique spectral signature for virtually every chemical, and the ability of SERS to provide microg/mL sensitivity. A simple sampling method, that employed 1-mm glass capillaries filled with silver-doped sol-gels, was developed to isolate 5-FU from potential interfering chemical components of saliva and simultaneously provide SERSactivity.

Understanding the origin of metal-sulfur vibrations in an oxo-molybdenum dithiolene complex: relevance to sulfite oxidase.

X-ray crystallography and resonance Raman (rR) spectroscopy have been used to further characterize (Tp*)MoO(qdt) (Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate and qdt is 2,3-quinoxalinedithiolene), which represents an important benchmark oxomolybdenum mono-dithiolene model system relevant to various pyranopterin Mo enzyme active sites, including sulfite oxidase. The compound (Tp*)MoO(qdt) crystallizes in the triclinic space group, P1, where a = 9.8424 (7) A, b = 11.

Surface-enhanced Raman spectra of VX and its hydrolysis products.

Detection of chemical agents as poisons in water supplies not only requires microg/L sensitivity, but also requires the ability to distinguish their hydrolysis products. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect chemical agents at these concentrations. Here we expand these studies and present the SERS spectra of the nerve agent VX (ethyl S-2-diisopropylamino ethyl methylphosphonothioate) and its hydrolysis products, ethyl S-2-diisopropylamino methylphosphonothioate, 2(diisopropylamino) ethanethiol, ethyl methylphosphonic acid, and methylphosphonic acid.

Investigation of metal-dithiolate fold angle effects: implications for molybdenum and tungsten enzymes.

Gas-phase photoelectron spectroscopy and density functional theory have been used to investigate the interactions between the sulfur pi-orbitals of arene dithiolates and high-valent transition metals as minimum molecular models of the active site features of pyranopterin MoW enzymes. The compounds (Tp*)MoO(bdt) (compound 1), Cp(2)Mo(bdt) (compound 2), and Cp(2)Ti(bdt) (compound 3) [where Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, bdt is 1,2-benzenedithiolate, and Cp is eta(5)- cyclopentadienyl] provide access to three different electronic configurations of the metal, formally d(1), d(2), and d(0), respectively. The gas-phase photoelectron spectra show that ionizations from occupied metal and sulfur based valence orbitals are more clearly observed in compounds 2 and 3 than in compound 1.

Probing the electronic structure of [MoOS(4)](-) centers using anionic photoelectron spectroscopy.

Using photodetachment photoelectron spectroscopy (PES) in the gas phase, we investigated the electronic structure and chemical bonding of six anionic [Mo(V)O](3+) complexes, [MoOX(4)](-) (where X = Cl (1), SPh (2), and SPh-p-Cl (3)), [MoO(edt)(2)](-) (4), [MoO(bdt)(2)](-) (5), and [MoO(bdtCl(2))(2)](-) (6) (where edt = ethane-1,2-dithiolate, bdt = benzene-1,2-dithiolate, and bdtCl(2) = 3,6-dichlorobenzene-1,2-dithiolate). The gas-phase PES data revealed a wealth of new electronic structure information about the [Mo(V)O](3+) complexes. The energy separations between the highest occupied molecular orbital (HOMO) and HOMO-1 were observed to be dependent on the O-Mo-S-C(alpha) dihedral angles and ligand types, being relatively large for the monodentate ligands, 1.

Freeze-Quench Magnetic Circular Dichroism Spectroscopic Study of the "Very Rapid" Intermediate in Xanthine Oxidase.

Freeze-quench magnetic circular dichroism spectroscopy (MCD) has been used to trap and study the excited-state electronic structure of the Mo(V) active site in a xanthine oxidase intermediate generated with substoichiometric concentrations of the slow substrate 2-hydroxy-6-methylpurine. EPR spectroscopy has shown that the intermediate observed in the MCD experiment is the "very rapid" intermediate, which lies on the main catalytic pathway. The low-energy (< approximately 30 000 cm(-1)) C-term MCD of this intermediate is remarkably similar to that of the model compound LMoO(bdt) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdt = 1,2-benzenedithiolate), and the MCD bands have been assigned as dithiolate S(ip) --> Mo d(xy) and S(op) --> Mo d(xz,yz) LMCT transitions.