An electrochemical-DNA (E-DNA) sensor was constructed by using DNA metallization to produce an electrochemical signal reporter in situ and hybridization chain reaction (HCR) as signal amplification strategy. The cyclic voltammetry (CV) technique was used to characterize the electrochemical solid-state Ag/AgCl process. Moreover, the enzyme cleavage technique was introduced to reduce background signals and further improve recognition accuracy. On the basis of these techniques, the as-prepared E-DNA sensor exhibited superior sensing performance for trace ctDNA analysis with a detection range of 0.5 fM to 10 pM and a detection limit of 7 aM. The proposed E-DNA sensor also displayed excellent selectivity, satisfied repeatability and stability, and had good recovery, all of which supports its potential applications for future clinical sample analysis.

the accurate, reliable and specific analysis of foodborne pathogenic bacteria is vital for human health and safety. Staphylococcus aureus (S. aureus), as a common bacterium, is regularly found in food, water, and other biological samples. Herein, a signal-off electrochemical DNA sensor (E-DNA sensor) was designed for the sensitive detection ofS. aureusamplified withthecombination of a dna walker and pb2+-specific dnazyme. In this work, vancomycin functionalized gold nanoclusters (Van@Au NCs) and an aptamer strand as identification units were modified at the termini of two proximity probes. upon the addition of targetS. aureus, a dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pb2+-dependent dnazyme, achieving the conversion of oneS. aureus to many intermediate dna (t) strands. then, the released t strands hybridized with methylene blue-tagged hairpin dna (h-mb) on the electrode. consequently, the conformational alteration of t strands reduced the electron transfer efficiency of mb to the electrodeinterface (signal-off). therefore, sensitive analysis of S. aureus was readily acquired within a range of 10-107 CFU/mL and a low detection limit at 1 CFU/mL. Undoubtedly, dual recognition by aptamer and vancomycin in an integrated scheme brought about a good recognition performance of S. aureus in complex samples, as well as an efficient annihilation of harmful pathogenic bacteria during the experiment.

In this work, we achieved the selective detection of wild and mutated rpoB gene in M. tuberculosis using an electrochemical DNA (E-DNA) sensor based on polypyrrole/Fe3O4 nanocomposite bearing redox naphthoquinone tag on PAMAM (spaNQ/PAMAM/PPy/Fe3O4). The hybridization between a given probe and the complementary DNA target induced a large decrease in the naphthoquinone redox signal as measured by SWV and no cross-hybridization with single nucleotide mismatch DNA target occurred. Thanks to the catalytic properties of iron oxide nanoparticles combined with conducting properties of polypyrrole platform, we demonstrated that the transducing system allowed the detection of 1 fM of DNA target in a 50-µL drop corresponding to 3 × 104 copies of DNA. The sensor was able to detect the rpoB gene in PCR-amplified samples of genomic DNA and could also discriminate between the wild type rpoB gene and a single nucleotide mutated rpoB gene that provides resistance to rifampicin. Furthermore, the sensor could selectively detect the wild and mutant DNA in genomic samples without PCR amplification.

In this work, a sensitive electrochemical DNA sensor based on an avidin modified electrode and a DNA-functionalized Au nanoparticle (DFNP) was developed. The DNA-functionalized Au nanoparticle contained two kinds of DNA, one is hairpin probe DNA with a biotin at the 3\' terminal and a thiol at the 5\' terminal, the other is methylene blue (MB)-labeled linear signal DNA. Without hybridizing with the target DNA, the loop of the hairpin impeded biotin linked with avidin on electrode. However, after target hybridization, the hairpin was opened and biotin was recognized by avidin which resulted in a DNA-functionalized Au nanoparticle brought on the electrode surface. Electrochemical signals of MB bound to signal DNA were measured by differential pulse voltammetry (DPV). Taking advantage of amplification effects of the AuNP and binding specificity of the hairpin probe, this DNA biosensor greatly simplified the electrochemical DNA detection method and displayed high specificity in DNA detection. By using this new method, we demonstrate that this prototype sensor has been able to detect as low as picomolar DNA targets with excellent differentiation ability even for a single mismatch.

In the present study, a gold nanoparticle-modified gold electrode (nanogold electrode) was used to develop a novel fluorescein electrochemical DNA biosensor based on a target-induced conformational change. The nanogold electrode was obtained by electrodepositing gold nanoparticles onto a bare gold electrode. This modification not only immobilized probe oligonucleotides, but also adsorbed fluorescein onto the surface of the gold nanoparticles to form an \"arch-like\" structure. This article compares the electrochemical signal changes caused by the hybridization of \"arch-like\" DNA on nanogold electrode and linear DNA on bare gold electrode. The results showed that the adsorption effect of nanogold can enhance the sensitivity of the sensor. The linear range of target ssDNA is from 2.0 × 10(-9)M to 2.0 × 10(-8)M with a correlation coefficient of 0.9956 and detection limit (3σ) of 7.10 × 10(-10)M. Additionally, the specificity and hybridization response of this simple sensor were investigated.

A signal-on impedimetric electrochemical DNA (E-DNA) sensor using gold nanoparticles (AuNPs) as tag was developed for highly sensitive detection of DNA hybridization. A probe ssDNA (PDNA) was immobilized by forming an amide between the -NH2 moiety at the 5\'-terminus of PDNA and the -COOH group at self-assembled 11-mercaptoundecanoic acid on a gold electrode. Subsequently, AuNPs were attached to the -SH moiety at the 3\'-terminus of the immobilized PDNA by S-Au interaction, and then functionalized with -OH by immersing the electrode in dithiothreitol solution. In the absence of the target DNA, the flexible single-stranded PDNA supports efficient contact between AuNP tag and electrode, ensuring a low electron transfer resistance (Ret) of the E-DNA sensor using the [Fe(CN)6](3-/4-) redox probe. Upon hybridization, a rigid probe-target duplex is formed, which pushes the AuNP tag away from the electrode and increases the distance between AuNP tag and the electrode, thereby increasing the Ret of the E-DNA sensor. Based on hybridization-induced conformational changes, the E-DNA sensor shows an increased Ret response when the target DNA concentration is increased from 5 fM to 500 pM. Furthermore, the E-DNA sensor showed differentiation abilities for single-base mismatch.