No abstract

This paper reports a simple electrochemical approach for the detection of the ubiquitous protein lysozyme using aptamer-modified electrodes. Anti-lysozyme DNA aptamers were immobilized on gold surfaces by means of self-assembly, for which the surface density of aptamers was determined by cyclic voltammetric (CV) studies of redox cations (e.g., [Ru(NH3)6]3+) bound to the surface via electrostatic interaction with the DNA phosphate backbone. Upon incubation of the electrode with a solution containing lysozyme, the CV response of surface-bound [Ru(NH3)6]3+ changed substantially, and the relative decrease in the integrated charge of the reduction peak can be tabulated as a quantitative measure of the protein concentration. It is significant that the on-chip protein/aptamer binding constant and the optimized surface density to achieve the best detection limit can be evaluated. This biosensor is label-free and offers an alternative, sensitive, and versatile method for protein detection, which is beneficial to the ever-growing interests of fabricating portable bioanalytical devices with simple electrical readout protocols.

Colloidal gold modified carbon paste electrodes were prepared by mixing 24‐nm‐diameter colloidal Au particles with carbon paste. The modified electrodes displayed a low charging current and a favorable electrochemical response of hexacyanoferrate (III). The direct electrochemical behavior of a horse‐heart cytochrome c (cyt.c) adsorbed on this electrode surface is described. It showed a surface‐controlled electrode process with the electron transfer rate constant of (1.21±0.08) s−1 and α of 0.67. Cyclic voltammograms showed small peak‐to‐peak separations at low scan rates. The adsorbed cyt.c maintained its activity and could also electrocatalyze the reduction of hydrogen peroxide. Since this behavior was quite pronounced the electrode was used for H2O2 detection. The KMapp value for this sensor was found to be 2.28±0.17 mM, allowing measurements down to 0.01 mM H2O2.

The sensing principle of a new class of DNA conformational switches (deoxyribosensors) is based on the incorporation of an aptamer as the receptor, whose altered conformation upon analyte binding switches on the conductivity of an adjacent helical conduction path, leading to an increase in the measured electrical signal through the sensor. We report herein the rational design and biochemical testing of candidate deoxyribosensors for the detection and quantitation of a plasma protein, thrombin, followed by surface immobilization of the optimized sensor and its electrochemical testing in both a near-physiological buffer solution and in diluted blood serum. The very high detection sensitivity (in the picomolar range) and specificity, as well as the adaptability of deoxyribosensors for the detection of diverse molecular analytes both small and macromolecular, make this novel sensing methodology an extremely promising one. Such synthetic and robust DNA-based electronic sensors should find broad application in the rapid, miniaturized, and automated on-chip detection of many biomedically relevant substances (such as metabolites, toxins, and disease and tumor markers) as well as of environmental contaminants.

No abstract