Design And Application Study Of Signal-enhanced Electrochemical Sensor Based On Nanomaterials In DNA Hybridization And Explosive Detection

A wide range of cadmium sulphide (CdS) 3-D polycrystalline walnut-like nanocrystals were prepared by solvothermal method with polyvinylpyrrolidone (PVP) as stabilizer. The reaction conditions influencing the synthesis of these 3D CdS nanocrystals such as reaction time, reaction temperatures, and the dosages of PVP were studied and optimized. The morphology, structure, and phase composition of the as-prepared CdS nanoparticles were examined by using various techniques (X-ray diffraction (XRD), field-emission microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED),as well as The room-temperature the photoluminescence (PL). The mechanisms for the PVP-assisted synthesis of CdS 3-D nanostructures and the growth process of CdS nanoparticles were proposed based on the results, which may pave the way to shape-controlled synthesis of inorganic nanocrystals with 3D complex structures. The CdS nanospheres with special walnut-like surface are prepared by solvothermal method and characterized first, then the mercapto group-linked probe DNA was covalently immobilized onto the CdS layer and exposed to ODN target for hybridization. Sensitive electrical readouts coupled with Cyclic Voltammogram (CV) and Differential Pulse Voltammogram (DPV) techniques show significant increased responses. The sensor is able to robustly discriminate the DNA hybridization responses with good sensitivity and stability and the selectivity of the sensor is tested using a series of matched and certain-point mismatched sequence with concentration grads ranging from 10-6μM to 101μM. The peak values are almost linear with the minus logarithm of target DNA concentrations with detection limit < 1pM. The optimized target DNA concentration at 101μM for the signal amplification is obvious. A novel electrochemical sensor based on Single-Wall Carbon Nanotubes (SWCNTs) modified glass carbon electrode (GCE) for the kind of explosive molecules which has nitro aromatic groups is constructed and characterized coupled with Linear Sweep Voltammetry (LSV) and Adsorptive Stripping Voltammetry (AdSV) for the qualitative and quantitative analysis via obvious signal amplification. In AdSV, operational parameters such as accumulation time (600s) and accumulation potential (0.0V) have been optimized for higher sensitivity and lower detection limit (～1ppb) comparing with traditional electrodes. The concentration dependence of the sensor was tested using a series TNT concentration grads ranging from 100μg·L-1 to 1000μg·L-1. The related peak current signals are in good linear (>99%) relationship with the TNT concentrations. Due to great surface properties of SWCNTs which provide better sensing unit with more receptor sites to promote the adsorption of TNT-dimethylformamide (P-πconjugate) Meisenheimer complex on SWCNTs, the sensor was able to robustly discriminate sub-μg·L-1concentration level in a safer experimental environment with good stability. TNT electrochemical behavior model is put forward as the cathode Adsorptive Stripping VoltammetryⅡ, which is judged from its characters above. The results are helpful for a further interpretation of sensitive mechanism of TNT ultra-trace level of electrochemical detection.