Photophysics and luminescence spectroelectrochemistry of [Tc(dmpe)3](+/2+) (dmpe = 1,2-bis(dimethylphosphino)ethane).

The ligand-to-metal charge transfer (LMCT) excited state luminescence of [Tc(dmpe)3](2+) (dmpe is 1,2-bis-(dimethylphosphino)ethane) has been measured in solution at room temperature and is compared to its Re analogue. Surprisingly, both [M(dmpe)3](2+)* (M = Re, Tc) species have extremely large excited-state potentials (ESPs) as oxidants, the highest for any simple coordination complex of a transition metal. Furthermore, this potential is available using a photon of visible light (calculated for M = Tc; E°'* = +2.

Electronic and molecular structures of trans-dioxotechnetium(V) polypyridyl complexes in the solid state.

The structures of novel Tc(V) complexes trans-[TcO(2)(py)(4)]Cl·2H(2)O (1a), trans-[TcO(2)(pic)(4)]Cl·2H(2)O (2a), and trans-[TcO(2)(pic)(4)]BPh(4) (2b) were determined by X-ray crystallography, and their spectroscopic characteristics were investigated by emission spectroscopy and atomic scale calculations. The cations adopt a tetragonally distorted octahedral geometry, with a trans orientation of the apical oxo groups. trans-[TcO(2)(pic)(4)]BPh(4) has an inversion center located on technetium; however, for trans-[TcO(2)(py)(4)]Cl·2H(2)O and trans-[TcO(2)(pic)(4)]Cl·2H(2)O, a strong H bond formed by only one of the oxo substituents introduces an asymmetry in the structure, resulting in inequivalent trans Tc-N and Tc═O distances.

Spectroelectrochemical sensing of pyrene metabolites 1-hydroxypyrene and 1-hydroxypyrene-glucuronide.

Spectroelectrochemical sensing in an optically transparent thin layer electrode (OTTLE) cell was used for detecting the polycyclic aromatic hydrocarbon (PAH) biomarkers 1-hydroxypyrene (1-pyOH) and 1-hydroxypyrene-glucuronide (1-pyOglu) in phosphate buffer and artificial urine. This approach uses selective electrochemical modulation of a fluorescence signal by sequentially oxidizing the analytes in an OTTLE cell to distinguish between their overlapping fluorescence spectra. This technique allows for complete oxidation and signal modulation in approximately 15 min for each analyte; a mixture of 1-pyOH and its glucuronic acid conjugate can be analyzed in 30 min.

Luminescence-based spectroelectrochemical sensor for [Tc(dmpe)3]2+/+ (dmpe = 1,2-bis(dimethylphosphino)ethane) within a charge-selective polymer film.

A spectroelectrochemical sensor consisting of an indium tin oxide (ITO) optically transparent electrode (OTE) coated with a thin film of partially sulfonated polystyrene-blockpoly(ethylene-ran-butylene)-block-polystyrene (SSEBS) was developed for [Tc(dmpe)(3)](+) (dmpe = 1,2-bis(dimethylphosphino)ethane). [Tc(dmpe)(3)](+) was preconcentrated by ion-exchange into the SSEBS film after a 20 min exposure to aqueous [Tc(dmpe)(3)](+) solution, resulting in a 14-fold increase in cathodic peak current compared to a bare OTE. Colorless [Tc(dmpe)(3)](+) was reversibly oxidized to colored [Tc(dmpe)(3)](2+) by cyclic voltammetry.

Fluorescence spectroelectrochemical sensor for 1-hydroxypyrene.

A spectroelectrochemical sensor was demonstrated for an organic compound whose oxidation proceeds through an electron transfer-chemical reaction-electron transfer (ECE) mechanism to generate new chemical species that are used for detection by fluorescence. The polycyclic aromatic hydrocarbon 1-hydroxypyrene (1-PyOH) served as a representative model analyte. The spectroelectrochemical properties of 1-PyOH in solution were explored with an optically transparent thin layer electrode.

Parallel separations using capillary electrophoresis on a multilane microchip with multiplexed laser-induced fluorescence detection.

Parallel separations using CE on a multilane microchip with multiplexed LIF detection is demonstrated. The detection system was developed to simultaneously record data on all channels using an expanded laser beam for excitation, a camera lens to capture emission, and a CCD camera for detection. The detection system enables monitoring of each channel continuously and distinguishing individual lanes without significant crosstalk between adjacent lanes.

Effect of some physico-chemical conditions on an immunoassay for viable Escherichia coli.

Viable Escherichia coli can be detected by an immunoassay in which live bacteria captured on antibody-coated paramagnetic beads are induced to synthesize the enzyme beta-galactosidase, which catalyzes the hydrolysis of the slightly fluorescent substrate 4-methyl umbelliferyl-beta-D-galactoside to the highly fluorescent product 7-hydroxy-4-methylcoumarin for detection. The effects of bacterial strain, presence of dead bacteria, and some environmental stresses on assay performance were evaluated.

Simultaneous detection of two analytes using a spectroelectrochemical sensor.

Spectroelectrochemical sensors developed in our group achieve three modes of selectivity by combining electrochemistry, spectroscopy, and a chemically selective membrane in a single device. Analyte detection is based upon a change in the optical response due to the conversion of the analyte between two oxidation states that results from the cycling or stepping of the applied potential. We have demonstrated a novel approach to simultaneously detect two metals by combining optical stripping voltammetry for one metal (Pb(2+)) and the in situ ligand complexation in a film for the other metal (Fe(2+)).

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 21. Selective chemical sensing using sulfonated polystyrene-block-poly(ethylene-ran-butylene)block-polystyrene thin films.

Spectroelectrochemical sensors combine three modes of selectivity in a single device (electrochemistry, spectroscopy, and selective partitioning). A thin polymer film is coated onto the sensing platform in order to facilitate chemically selective transport to the electrode. The film is an essential part of the sensor because it provides an increase in selectivity and sensitivity by selectively preconcentrating the analyte.

Inertial microfluidics for sheath-less high-throughput flow cytometry.

Flow cytometer is a powerful single cell analysis tool that allows multi-parametric study of suspended cells. Most commercial flow cytometers available today are bulky, expensive instruments requiring high maintenance costs and specially trained personnel for operation. Hence, there is a need to develop a low cost, portable alternative that will aid in making this powerful research tool more accessible.

Characterization of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene thin films for spectroelectrochemical sensing.

The spectroelectrochemical sensor uses thin, solid polyelectrolyte films as an essential element in its operation. In this work we explored the potential of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS) thin polymer films for chemical sensing. Spectroscopic ellipsometry was used to measure optical and surface properties of the air-dried and hydrated material.

Determination of viable Escherichia coli using antibody-coated paramagnetic beads with fluorescence detection.

A rapid and convenient assay system was developed to detect viable Escherichia coli in water. The target bacteria were recovered from solution by immunomagnetic separation and incubated in tryptic soy broth with isopropyl-beta-D-thiogalactopyranoside, which induces formation of beta-galactosidase in viable bacteria. Lysozyme was used to lyse E.

Simultaneous multiselective spectroelectrochemical sensing of the interaction between protein and its ligand using the redox dye Nile blue as a label.

A new binding assay for a protein and its ligand based on a spectroelectrochemical method was demonstrated using avidin-biotin and 17beta-estradiol-antiestradiol antibody. The sensor consists of a selective film coated on an optically transparent electrode (OTE) consisting of indium tin oxide (ITO). Attenuated total reflection (ATR) was used for optical detection.

Investigations of the optical properties of thin, highly absorbing films under attenuated total reflection conditions: Leaky waveguide mode distortions.

Spectra of thin highly absorbing Nafion films doped with Ru(bpy)(3)(2+) on SF11 glass substrates were studied by internal reflection spectroscopy using a single reflection configuration. For the system under study, two modes of light interaction with the film are available: attenuation due to evanescent wave penetration and light propagation within the absorbing film. Unlike evanescent wave spectroscopy, light propagation within the film causes distortions in the measured spectra due to leaky waveguide propagation modes.

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 20. Detection of metal ions in different oxidation states.

Spectroelectrochemical sensing a metal in two different oxidation states, both of which are weakly absorbing in the visible wavelength range, was demonstrated with ferrous and ferric ion. The sensor consisted of an indium tin oxide optically transparent electrode (ITO OTE) coated with a thin film of Nafion preloaded with the ligand 2,2'-bipyridine (bipy). Fe2+ in the sample partitioned into the film where it reacted with bipy to form Fe(bipy)3(2+), which absorbs strongly at 520 nm.

Characterization and performance of injection molded poly(methylmethacrylate) microchips for capillary electrophoresis.

Injection molded poly(methylmethacrylate) (IM-PMMA), chips were evaluated as potential candidates for capillary electrophoresis disposable chip applications. Mass production and usage of plastic microchips depends on chip-to-chip reproducibility and on analysis accuracy. Several important properties of IM-PMMA chips were considered: fabrication quality evaluated by environmental scanning electron microscope imaging, surface quality measurements, selected thermal/electrical properties as indicated by measurement of the current versus applied voltage (I-V) characteristic and the influence of channel surface treatments.

Highly oxidizing excited states of Re and Tc complexes.

Like the Re analogue, the ligand-to-metal charge transfer (LMCT) excited-state of [Tc(dmpe)3]2+ (dmpe is bis-1,2-(dimethylphosphino)ethane) is luminescent in solution at room temperature. Surprisingly, both [M(dmpe)3]2+* species have extremely large excited-state potentials (ESPs) as oxidants-the highest for any simple coordination complex of a transition metal. Furthermore, this potential is available using a photon of visible light (calculated for M = Re(Tc); E1/2* = +2.

Dynamic in situ spectroscopic ellipsometry of the reaction of aqueous iron(II) with 2,2'-bipyridine in a thin Nafion film.

Dynamic in situ spectroscopic ellipsometry studies of the chemical reaction between ferrous ion and 2,2'-bipyridine (bpy) in a thin Nafion film are presented. A simple prototype system composed of a thin Nafion film on a glass substrate was used throughout the work. The reaction was detected by optically monitoring the formation of the strongly absorbing complex ion, Fe(bpy)3(2+) (epsilon 520 = 7.

Analytical performance of polymer-based microfluidic devices fabricated by computer numerical controlled machining.

A study comparing the electrophoretic separation performance attainable from microchips molded by masters fabricated using conventional CNC machining techniques with commercial microchips, wire imprinted microchips, and microchips from LIGA molding devices is presented. An electrophoresis-based detection system using fluorescence microscopy was used to determine the analytical utility of these microchips. The separation performance of CNC microchips was comparable to commercially available microchips as well as those fabricated from LIGA masters.

An online fiber-optic UV-visible detector for continuous free-flow electrophoresis.

A PC-controlled, scanning online UV detector for continuous free-flow electrophoresis (CFFE) was designed to allow for single UV wavelength monitoring across a 1-D array of 48 longitudinal flow cells interfaced to a CFFE apparatus. In the detection scheme, the UV light is sequentially passed through each of the flow cells. The design integrates online acquisition of absorbance spectra of components separated by CFFE.

The autofluorescence of plastic materials and chips measured under laser irradiation.

Plastic materials have the potential to substitute for glass substrates used in microfluidic and microTAS systems adding flexibility in materials' choices. Optical quality plastic materials with a low autofluorescence are crucial for optimal detection by fluorescence and laser induced fluorescence techniques. This paper summarizes a series of optical investigations on commercially available plastic chip materials (PMMA, COC, PC, PDMS) and chips made from those materials.

Luminescence from the trans-dioxotechnetium(V) chromophore.

The luminescence of trans-[TcO2(L)4]+ (L = pyridine (py) or picoline (pic)) and trans-[TcO2(CN)4]3- at room and low temperature is described and represents the first example of room temperature excited-state luminescence observed for Tc complexes. At room temperature, the complexes exhibited broad luminescence with emission maxima ranging from 745 to 780 nm. Analogous to the Re complexes (emission at 635-655 nm), the low-temperature emission spectra of microcrystalline samples of [TcO2(py)4]BPh4 and [TcO2(pic)4]BPh4 display the characteristic progressions of the symmetric O=Tc=O and Tc-L stretching modes.

Estimation of pK(a) values using microchip capillary electrophoresis and indirect fluorescence detection.

Microchip capillary electrophoresis (CE), coupled with indirect fluorescence detection was investigated for estimating the pK(a) values of non-fluorescent compounds. The CE method is based on the differences in electrophoretic mobility of the analyte as a function of the pH of the running buffer. Nine compounds were tested, including several of pharmaceutical importance, with pK(a) values from 10.

Amperometric determination of live Escherichia coli using antibody-coated paramagnetic beads.

Detecting and enumerating fecal coliforms, especially Escherichia coli, as indicators of fecal contamination, are essential for the quality control of supplied and recreational waters. We have developed a sensitive, inexpensive, and small-volume amperometric detection method for E. coli beta-galactosidase by bead-based immunoassay.

Estimation of logP(ow) values for neutral and basic compounds by microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (muMEEKC-IFD).

Microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (muMEEKC-IFD) was used to obtain logP octanol/water (logP(ow)) values for neutral and basic compounds. Six compounds, with logP(ow) values between 0.38 and 5.