Robert C. Corcoran

Surface-Enhanced Raman Scattering Detection of Amphetamine and Methamphetamine by Modification with 2-Mercaptonicotinic Acid

We have demonstrated the use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of the phenylalkylamines amphetamine and methamphetamine. This work can be viewed as the first phase of development toward a one-step drug detection method with a selective reactive coating on a SERS substrate. This work involves a fairly complicated coupling reaction prior to surface derivatization. Future efforts will be directed at creating a reactive coating directly on the surface. The amines were derivatized by a coupling reaction with 2-mercaptonicotinic acid (2-MNA) with the use of dicyclohexylcarbodiimide (DCC) as the coupling reagent to form the amide compounds AMNA [N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide] and MMNA [N-methyl-N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide]. The amides were qualitatively identified from SERS spectra. Quantification of the amides was accomplished by adding the internal standard pentachlorothiophenol (PCTP) and measuring the intensity of Raman bands of the analyte relative to a Raman band of the internal standard. Calibration curves were plotted of the relative peak intensity ratios as a function of analyte concentration. Detection limits of 19 ppm and 17 ppm were found for amphetamine/2-MNA (AMNA) amide and methamphetamine/2-MNA (MMNA) amide, respectively.

Surface-enhanced Raman assays (SERA): measurement of bilirubin and salicylate

Results of a study to detect bilirubin and salicylate using SERS and a reactive coating are presented. The motivation for this work was to devel to develop an assay that would simplify an analysis by detecting the analyte in a whole blood sample. This would remove the risks and time associated with preparing a serum sample. Quantitative analysis was performed using partial least-squares. The results are that one can detect bilirubin and salicylate in whole blood at levels below the normal or therapeutic levels using a coating based on an argentiphilic diazonium molecule. The sharp Raman bands associated with the analyte–coating adduct are sufficiently resolved to allow the analyte to be detected in the presence of a complex matrix such as whole blood. Copyright

Sodium silicate based sol-gel structures for generating pressure-driven flow in microfluidic channels.

In this article, we report the design of a microchip based hydraulic pump that employs a sodium silicate derived sol-gel structure for generating pressure-driven flow within a microfluidic network. The reported sol-gel structure was fabricated in a chosen location of our device by selectively retaining sodium silicate solution within a sub-micrometer deep segment via capillary forces, and then providing the precursor material appropriate thermal treatment. It was shown that while the molecular weight cut-off for these membranes is at least an order of magnitude smaller than their photo-polymerized counterparts, their electrical conductance is significant. Moreover, unlike their polymeric counterparts these structures were found to be capable of blocking electroosmotic flow, thereby generating a pressure-gradient around their interface with an open microchannel upon application of an electric field across the microchannel-membrane junction. In this work, a fraction of the resulting hydrodynamic flow was successfully guided to an electric field-free analysis channel to implement a pressure-driven assay. Our experiments show that the pressure-driven velocity produced in the analysis channel of our device varied linearly with the voltage applied across the sol-gel membrane and was nearly independent of the cross-sectional dimensions of the membrane and the microfluidic channels. With our current design pressure-driven velocities up to 1.7 mm/s were generated for an applied voltage of 2 kV, which easily covers the range of flow speeds that can minimize the plate height in most microfluidic separations. Finally, the functionality of our device was demonstrated by implementing a reverse phase chromatographic separation in the analysis channel of our device using the pressure-driven flow generated on-chip.

Multiplex ELISA in a single microfluidic channel

In this article, we demonstrate a novel approach to implementing multiplex enzyme-linked immunosorbent assay (ELISA) in a single microfluidic channel by exploiting the slow diffusion of the soluble enzyme reaction product across the different assay segments. The functionality of the reported device is realized by creating an array of ELISA regions within a straight conduit that are selectively patterned with chosen antibodies/antigens via a flow-based method. The different analytes are then captured in their respective assay segments by incubating a 5-μL aliquot of sample in the analysis channel for an hour under flow conditions. Once the ELISA surfaces have been prepared and the enzyme substrate introduced into the analysis channel, it is observed that the concentration of the soluble enzyme reaction product (resorufin) at the center of each assay region grows linearly with time. Further, the rate of resorufin generation at these locations is found to be proportional to the concentration of the analyte being assayed in that segment provided that the ELISA reaction time in the system (τR) is kept much shorter than that required by the resorufin molecules to diffuse across an assay segment (τD). Under the operating condition τR << τD, the reported device has been shown to have a 35% lower limit of detection for the target analyte concentration compared with that on a commercial microtiter plate using only a twentieth of the sample volume.

Concentration effects in chelation controlled reactions

Abstract The diastereo selcctivities of addition reactions of allyltrimethylsilane to an α-benzyloxyaldehyde were found to be relatively insensitive to the amount of added TiCl 4 , and to the absolute concentration of the 1:1 aldehyde/TiCl 4 , complex. In contrast, diastereoselectivities of similar additions to a structurally related β-benzyloxyaldehyde were highly dependent on these variables.