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In this work, silver nanoparticles decorated onto polyaniline nanowires were synthesized site-specifically onto Pt working electrodes (with only 0.8 mm2 area) using a novel, rapid, and effective electrochemical procedure: electropolymerization of PANi NWs and electrodeposition of AgNPs. The complementary properties of PANi NWs and AgNPs were obtained, including high surface area, high electrochemical activity, high biocompatibility, high chemical stability and good adhesion with the electrode surface. Obtained results showed advantages of the electrosynthesis method compared to traditional methods, which have difficulties in binding between modifying materials with electrode surfaces. The sensor surface modification with the PANi NWs/AgNPs material facilitated the probe DNA immobilization and improved the electrochemical signal of the DNA sensors. The detection limit of the sensors was 2.80 × 10−15 M. The DNA sensors exhibited advantages including direct detection, high sensitivity, good specificity, and potential miniaturization for development of lab-on-a-chip systems.

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A metal-organic framework MIL-53(Fe) was successfully synthesized by a simple hydrothermal method. A synthesized MIL-53(Fe) sample was characterized, and results indicated that the formed MIL-53(Fe) was a single phase with small particle size of 0.8 μm and homogeneous particle size distribution was obtained. The synthesized MIL-53(Fe) has been used to modify a glassy carbon electrode (GCE) by a drop-casting technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the MIL-53(Fe)-modified GCE showed that the MIL-53(Fe) was successfully immobilized onto the GCE electrode surface and the electrochemical behavior of the GCE/MIL-53(Fe) electrode was stable. In addition, several electrochemical parameters of MIL-53(Fe)-modified GCE (GCE/MIL-53(Fe)) including the heterogeneous standard rate constant ( k 0 ) and the electrochemically effective surface area ( A ) were calculated. Obtained results demonstrated that the synthesized MIL-53(Fe) with the small particle size, highly homogeneous particle size, and high electrochemically effective surface area was able to significantly enhance the electrochemical response signal of the working electrode. Therefore, the GCE/MIL-53(Fe) electrode has been used as a highly sensitive electrochemical sensor for cadmium ion (Cd(II)) monitoring in aqueous solution using differential pulse voltammetry (DPV) technique. The response signal of the electrochemical sensor increased linearly in the Cd(II) ion concentration range from 150 nM to 450 nM with the limit of detection (LOD) of 16 nM.

We report here a development of a novel and label-free electrochemical DNA sensor based on a nanostructured electrode of multi-walled carbon nanotubes/manganese dioxide nano-flowers-like/polyaniline nanowires (MWCNTs/MnO2/PANi NWs) nanocomposite. The nanocomposite was synthesized in situ onto the interdigitated platinum microelectrode (Pt) using a novel combined chemical-electrochemical synthesis method: chemical preparation of MWCNTs/MnO2 and electropolymerization of PANi NWs. The fabricated MWCNTs/MnO2/PANi NWs was used for the first time to develop a label-free electrochemical DNA sensor for detection of a specific gene of Escherichia coli (E. coli) O157:H7. The Pt electrode surface modification by the MWCNTs/MnO2/PANi NWs can facilitate the immobilization of probe DNA strands and therefore the electrochemical signal of the DNA sensors has been improved. The electrochemical impedance spectroscopy (EIS) measurements were conducted to investigate the output signals generated by the specific binding of probe and target DNA sequences. The developed electrochemical biosensor can detect the target DNA in the linear range of 5 pM to 500 nM with a low limit of detection (LOD) of 4.42 × 10–13 M. The research results demonstrated that the MWCNTs/MnO2/PANi NWs nanocomposite-based electrochemical DNA sensor has a great potential application to the development of highly sensitive and selective electrochemical DNA sensors to detect pathogenic agents.

In this work, we report a simple electrochemical method to fabricate a label-free and reagentless electrochemical sensor for microRNA detection based on self-assembly of a multifunctional layer on gold nanoparticles-modified glassy carbon electrodes (AuNPs/GCEs).