Oligonucleotide probes functionalization of nanogap electrodes.

Nanogap electrodes have attracted a lot of consideration as promising platform for molecular electronic and biomolecules detection. This is mainly for their higher aspect ratio, and because their electrical properties are easily accessed by current-voltage measurements. Nevertheless, application of standard current-voltages measurements used to characterize nanogap response, and/or to modify specific nanogap electrodes properties, represents an issue. Since the strength of electrical fields in nanoscaled devices can reach high values, even at low voltages. Here, we analyzed the effects induced by different methods of surface modification of nanogap electrodes, in test-voltage application, employed for the electrical detection of a desoxyribonucleic acid (DNA) target. Nanogap electrodes were functionalized with two antisymmetric oligo-probes designed to have 20 terminal bases complementary to the edges of the target, which after hybridization bridges the nanogap, closing the electrical circuit. Two methods of functionalization were studied for this purpose; a random self-assembling of a mixture of the two oligo-probes (OPs) used in the platform, and a selective method that controls the position of each OP at selected side of nanogap electrodes. We used for this aim, the electrophoretic effect induced on negatively charged probes by the application of an external direct current voltage. The results obtained with both functionalization methods where characterized and compared in terms of electrode surface covering, calculated by using voltammetry analysis. Moreover, we contrasted the electrical detection of a DNA target in the nanogap platform either in site-selective and in randomly assembled nanogap. According to our results, a denser, although not selective surface functionalization, is advantageous for such kind of applications.

Nanoprobes for enhanced electrochemical DNA sensors.

Biosensors, small devices enabling selective bioanalysis because of properly assembled biological recognition molecules, represent the fortuitous results of years of interdisciplinary and complementary investigations in different fields of science. The ultimate role of a biosensor is to provide coupling between the recognition element and the analyte of interest, bringing a quantitative value of its concentrations into a complex sample matrix. They offer many advantages. Among them, portability, low cost with fast response times, and the possibility to operate in situ without the need for sample preparation are certainly the most important. Among biosensors, a large space is occupied by DNA biosensors. Screening genomic DNA is of fundamental importance for the development of new tools available to physicians during the clinical process. Sequencing of individual human genomes, accomplished principally by microarrays with optical detection, is complex and expensive for current clinical protocols. Efforts in research are focused on simplifying and reducing the cost of DNA biosensors. For this purpose, other transduction techniques are under study to make more portable and affordable DNA biosensors. Compared with traditional optical detection tools, electrochemical methods allow the same sensitivity and specificity but are less expensive and less labor intensive. Scalability of electrochemical devices makes it possible to use the advantages introduced by nanosized components. The involvement of nanomaterials and nanostructures with custom-tailored shapes and properties is expected to rapidly boost the field of electrochemical DNA biosensors and, in general, that of next-generation sequencing technologies.