Conducting polyamic acid membranes for sensing and site-directed immobilization of proteins.

A biosensor platform based on polyamic acid (PAA) is reported for oriented immobilization of biomolecules. PAA, a functionalized conducting polymer substrate that provides electrochemical detection and control of biospecific binding, was used to covalently attach biomolecules, resulting in a significant improvement in the detection sensitivity. The biosensor sensing elements comprise a layer of PAA antibody (or antigen) composite self-assembled onto gold (Au) electrode via N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) linking. The modified PAA was characterized by Fourier transform infrared (FTIR), (1)H nuclear magnetic resonance (NMR), and electrochemical techniques. Cyclic voltammetry and impedance spectroscopy experiments conducted on electrodeposited PAA on Au electrode using ferricyanide produced a measurable decrease in the diffusion coefficient compared with the bare electrode, indicating some retardation of electron transfer within the bulk material of the PAA. Thereafter, the modified PAA surface was used to immobilize antibodies and then to detect inducible nitric oxide synthase and mouse immunoglobulin G (IgG) using enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and amperometric techniques. ELISA results indicated a significant amplified signal by the modified PAA, whereas the SPR and amperometric biosensors produced significant responses as the concentration of the antigen was increased. Detection limits of 3.1×10(-3)ng/ml and 2.7×10(-1)ng/ml were obtained for SPR and amperometric biosensors, respectively.

Spectroelectrochemical characterization of pain biomarkers.

This article reports the first electrochemical characterization of pain biomarkers that include arachidonic acid (AA), prostaglandin G(2) (PGG(2)), and cyclooxygenase 2 (COX-2). These biomarkers are mediators of pathophysiology of pain, inflammation, and cell proliferation in cancer. The article also reports the development of an electrochemical immunosensor for monitoring these pain biomarkers. The results revealed that direct electron transfer between AA metabolites and the electrode could be easily monitored and that an enzyme-modified electrode dramatically enhanced bioelectrocatalytic activity toward AA. Cyclic voltammetric analysis of AA revealed a concentration-dependent anodic current with a slope of 2.37 and a limit of detection (LOD) of 0.25nM. This unique AA/gold electrode electron transfer provides a good electrochemical sensing platform for prostaglandin H(2) (PGH(2)) as the basis for quantitation of pain. An amperometric signal intensity of a COX-2 antibody-modified gold electrode was linear with COX-2 concentration in the range of 0.1-0.5microg/ml and an LOD of 0.095microg/ml. The results also revealed a linear correlation of the concentration of PGG(2) with an LOD of 0.227microM.

Tuning the surfaces of palladium nanoparticles for the catalytic conversion of Cr(VI) to Cr(III).

This work reports the feasibility of using Pd nanoparticles as innovative catalysts in the conversion of reducible contaminants from toxic to benign forms. Cr(VI) is a known carcinogen while the trivalent chromium salts are believed to be non-toxic. The ability of Pd nanoparticles to catalyze the rapid reduction of Cr(VI) to Cr(III) using reactive sulfur intermediates produced in situ was therefore studied. Using a microchamber set at 130 degrees C, the reduction mixture consists of palladium nanoparticles and sulfur (PdNPs/S), which generated highly reducing sulfur intermediates that effected the reduction of Cr(VI) to Cr(III) by 1st order reaction kinetics. UV-visible spectroscopy and cyclic voltammetry were employed to monitor the reduction process. The results showed that 99.8% of 400 microM Cr(VI) was reduced to Cr(III) by PdNPs/S in one hour compared to 2.1% by a control experiment consisting of sulfur only. The rate of Cr(VI) reduction was found to be dependent on temperature and pH and was greatly enhanced by the addition of PdNPs. Subsequent application of this approach in the reduction of Cr(VI) in soil and aqueous media was conducted. In contrast to the control experiments with and without PdNPs or sulfur, greater than 92% conversion rate was obtained in the presence of PdNPs/S within 1 hour. This represents over a 500-fold improvement in conversion rate compared to current microbial approaches. XPS analysis provided the confirmation regarding the oxidation states of Cr(VI), Cr(III) and the nature of the reactive intermediates. This work offers PdNPs/S as a new interface for the reduction of high oxidation state heavy metal pollutants.