Direct electrochemical oxidation of DNA on polycrystalline gold electrodes

Electrochemical CV and SWV studies were performed with double stranded DNA from salmon testes (dsDNA) and single stranded DNAs, containing 25 nucleotides (ssDNA) directly adsorbed at polycrystalline An electrodes. A distinct oxidation peak at + 730 mV (SWV, scan rate 0.248 V s(-1)) or at + 730 - + 780 mV (CV, scan rate from 0.3 to 1 V s(-1)) was obtained with DNA-modified Au electrodes after a time-dependent prepolarization step at a positive potential value, i.e., at + 500 mV (vs. Ag AgCl), performed with the DNA-modified Au electrodes dipped in a blank buffer solution. No electrochemical activity was detected when ssDNA, containing no guanines, was used for adsorptive modification of the Au electrodes. Electrochemical impedance measurements registered a possible reorganization of the adsorbed DNA layer in the course of the prepolarization, accompanied by decreasing in-phase impedance. ne results enable us to relate the oxidation process observed at the DNA-modified Au electrodes with the oxidation of guanine residues in DNA

Bioelectrocatalytic detection of theophylline at theophylline oxidase electrodes

Bioelectrocatalytic oxidation of theophylline was studied at gold and graphite electrodes modified with microbial theophylline oxidase (ThOx), a multi-cofactor redox enzyme capable of selective oxidation of theophylline. Gold electrodes were additionally modified with self-assembled monolayers (SAMs) of (-OH)- and (-NH2)-terminated alkanethiols of different chain lengths, to achieve compatibility between ThOx and the electrode surface. On graphite, ThOx was either physically co-adsorbed with a surfactant didodecyldimethylammonium bromide (DDAB), or entrapped within an Os-redox-polymer film. At all electrodes, ThOx was bioelectrocatalytically active; direct electrochemistry of ThOx in the absence of theophylline was followed only at the SAM-modified gold electrodes. Direct electrochemistry of ThOx correlated with redox transformations of the heme domain of ThOx, with a E-o/ of - 110 +/- 2 mV versus Ag vertical bar AgCl, at pH 7. Bioelectrocatalytic oxidation of theophylline was optimal at mixed (-OH)/(-NH2)-terminated SAMs; co-adsorption of ThOx with DDAB improved the bioelectrocatalytic performance of the ThOx-electrode. In both cases, the response to theophylline was within the mM range. Alternatively, a reagentless ThOx-electrode based on ThOx cross-linked within the Os-redox-polymer matrix demonstrated a linear response to theophylline within the physiologically important 0.02-0.6 mM (3.6-72 mg I-1) concentration range with a sensitivity of 52.1 +/- 7.8 mA cm(-2) m(-1). (c) 2006 Elsevier B.V. All rights reserved

Design Strategies for Electrochemical Aptasensors for Cancer Diagnostic Devices

Improved outcomes for many types of cancer achieved during recent years is due, among other factors, to the earlier detection of tumours and the greater availability of screening tests. With this, non-invasive, fast and accurate diagnostic devices for cancer diagnosis strongly improve the quality of healthcare by delivering screening results in the most cost-effective and safe way. Biosensors for cancer diagnostics exploiting aptamers offer several important advantages over traditional antibodies-based assays, such as the in-vitro aptamer production, their inexpensive and easy chemical synthesis and modification, and excellent thermal stability. On the other hand, electrochemical biosensing approaches allow sensitive, accurate and inexpensive way of sensing, due to the rapid detection with lower costs, smaller equipment size and lower power requirements. This review presents an up-to-date assessment of the recent design strategies and analytical performance of the electrochemical aptamer-based biosensors for cancer diagnosis and their future perspectives in cancer diagnostics

Electrochemical Assay for a Total Cellulase Activity with Improved Sensitivity

Electrochemical methods allow fast and inexpensive analysis of enzymatic activities. Here, we report a simple and yet efficient electrochemical assay for the total activity of cellulase, a hydrolytic enzyme widely used in food and textiles industries, and for production of bioethanol. The assay exploits the difference in electrochemical signals from a soluble redox indicator, ferricyanide, on nitrocellulose films treated by cellulases. Ferricyanide electrochemistry is totally inhibited on graphite electrodes modified with an insulating nitrocellulose film and is evoked after the cellulase treatment. Ferricyanide voltammetric responses correlate with the increased permeability of the films and electrochemically active surface area of electrodes becoming accessible to the ferricyanide reaction after nitrocellulose digestion by cellulase. Trichoderma and Aspergillus niger cellulases activities were determined in a 5 min assay with a sensitivity of 10^–8 U per assay, being 10³–10⁴-fold more sensitive than the standard commercially available optical assays. That makes the developed electrochemical approach the most prospective cost-effective alternative both for research and automated industrial applications