Search

A reusable and label-free supersandwich biosensor was constructed for sensitive DNA detection by immobilizing target-triggered DNA concatamers with redox-active intercalators on ternary self-assembled monolayer (TSAM). Interestingly, the target DNA (T-DNA) could hybridize with the inert dumbbell-shaped DNA (D-DNA) to form a duplex DNA containing two sticky termini. The duplex DNA was then hybridized with the capture DNA (C-DNA) and the DNA concatamer reaction proceeded. The ternary self-assembly method was chosen to obtain the low-density C-DNA without reciprocal winding on the gold electrode for high-efficient concatamers hybridization. Hexaammineruthenium chloride was herein used as an electrochemical probe and could intercalate into the groove of double-helix DNA via electrostatic effect. The resultant supersandwich biosensor showed a high sensitivity for the T-DNA detection and a linear dependence between the reduction peak currents and logarithm of T-DNA concentrations in the range of 100.0 fM–10.0 nM with a relatively low detection limit of 30.0 fM. Moreover, the proposed biosensor exhibited favorable specificity and regenerability, and provided a new alternative to detect various target analytes by changing the sequence of capture probe and dumbbell probes, holding great potential for early diagnosis in gene-related diseases.

A highly sensitive and label-free impedimetric biosensor is achieved based on an adjunct probe attached nearby the capture probe. In this work, the adjunct probe was co-assembled on the surface of gold electrode with the capture probe hybridized with the reporter probe, and then 6-mercapto-1-hexanol was employed to block the nonspecific binding sites. When target DNA was added, the adjunct probe functioned as a fixer to immobilize the element of reporter probe displaced by the target DNA sequences and made the reporter probe approach the electrode surface, leading to effective inhibition of charge transfer. The increase in charge transfer resistance is related to the quantity of the target DNA in a wide range. The linear range for target DNA with specific sequences was from 0.1 nM to 0.5 μM with a good linearity ( R = 0.9988) and a low detection limit of 6.3 pM. This impedimetric biosensor has the advantages of simplicity, sensitivity, good selectivity, and large dynamic range.

This paper reports a simple method to immediately functionalize ssDNA onto gold electrodes using a low pH-induced and high salt concentration solution route. Electrochemical impedance spectroscopy, cyclic voltammetry, and chronocoulometry were used to characterize the ssDNA self-assembled monolayer (SAM). The effects of pH, ionic strength, and ssDNA sequences for DNA adsorption were investigated. It was found that thiolated ssDNA can be attached to gold electrodes using a low pH-induced route in a high salt concentration solution. A synergistic effect between pH and the salt has been suggested by studying the fundamental kinetics. The surface coverage of 3.054 × 1013 molecules/cm2 in pH 3.4 buffer was higher than that of 4.574 × 1012 molecules/cm2 in pH 7.4 buffer. The ssDNA on the gold surface was functional and was able to recognize complementary DNA strands.