Optimization of an electrochemical DNA assay by using a 48-electrode array and redox amplification studies by means of scanning electrochemical microscopy.

Sensible DNA: An electrochemical DNA assay based on specific Salmonella spp. capture probes and enzyme labeling with alkaline phosphatase was optimized by using a 48-electrode microarray and scanning electrochemical microscopy (SECM). SECM was further used to evaluate potential amplification strategies due to redox cycling. Due to insufficient detection limits and selectivity, electrochemical DNA sensors are not yet used as everyday tools in diagnostics. Here, we present an electrochemical DNA assay that is based on specific Salmonella spp. capture probes. Our optimization strategies and the specific features of related electrochemical DNA sensor arrays, which are comprised of a chip with 48 gold electrodes, are also described. A ssDNA monolayer is formed by chemisorption of the thiol-modified capture strand on the different gold electrodes of the array after spotting with a needle spotter. The assay parameters were optimized for the use of minimum amounts of sample and reagents and short assay times. Scanning electrochemical microscopy (SECM) has been used to visualize the local activity of an enzyme label used for amplified hybridization detection at high lateral resolution. The potential of SECM to further amplify the sensor signal by means of redox cycling is demonstrated by using single-stranded DNA capture probe modified gold microelectrodes as SECM tips. The detection limit of the proposed DNA sensor is shown to be in the femtomolar range without redox cycling amplification.