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1IntroductionSequence-specific detection of DNAt argets has become increasingly important in molecular diagnostics.I nt hese years,e lectrochemical DNAb iosensors have been widely proposed for the rapid and inexpensive diagnosis of biological samples due to their prominent advantages such as simple,p ortable,r apid, precise,s ensitive and inexpensive.Atypical electrochemical DNAb iosensor is made of as olid electrode with immobilized short single-stranded DNAp robe on it and electroactive hybridization indicators.T he hybridization event between DNAp robes and complementary sequences influences the performance of the DNAb iosensors.T his is dependent on the selection of the probes and on the conditions of the hybridization. Therefore,d esign chemicalg enosensors relies on the kind of the parameters of the hybridization and on the generation of the electrochemical signal [1][2][3][4][5][6].Thee lectrochemical assays for detection of DNAh ybridization are divided into two main groups.T he first strategy is direct (or label free) method. Direct methods are mainly related to the intrinsic electrochemical activity of the nucleobases such as guanine and adenine [7][8][9].The second strategy is indirect protocol which is based on using label or indicator [10][11][12][13][14][15][16].The changes in the electrochemical response of these labels are monitored to detect DNAh ybridization events.T he background interference can reduce the sensitivity of the electrochemical DNAd etection and it is ap roblem with this assay.I nt he last decade,u sing the surface of paramagnetic beads,o r magnetic nanoparticles,f or hybridization event and enzyme-linked immunoassay have been proposed to overcome this problem by some researchers [17,19].D etection of microarray-hybridized oligonucleotides with magnetic beads was studied by Shlyapnikov et al. Also,a sm entioned above,t he kind of hybridization has an important role in the genosensors.I nt he sandwich hybridization mode,t he target sequence hybridizes with ac apture probe and as ignaling probe.R ecently,t his method has been widely used because of good selectivity Abstract:T he development of an electrochemical genosensor involving DNAb iotinylated capture probe immobilized on streptavidin coated paramagnetic beads and microfluidic based platform for the detection of P53 gene PCR product is reported. Then ovelty of this work is the combination of as ensitive electrochemical platform and ap roper microfluidic system with as imple and effective enzyme signal amplification technology,E LISA, for detection of target DNAs equence and single nucleotide mutation in p53 tumor suppressor gene sequence.T he biosensor has been applied to detect the PCR amplified samples and the results shows that it can discriminate successfully perfect matched DNAf rom mutant form.

A new electrochemical PNA hybridization biosensor for detection of a 15‐mer sequence unique to p53 using indigo carmine (IC) as an electrochemical detector is described in this work. This genosensor is based on the hybridization of target oligonucleotide with its complementary probe immobilized on the gold electrode by self‐assembled monolayer formation. Because this label is electroactive in acidic medium, the interaction between IC and short sequence of p53 is studied by differential pulse voltammety (DPV) in 0.1 M H2SO4. The results of electrochemical impedance spectroscopy and cyclic voltammetry in the solution of [Fe(CN)6]3−/4− shows no breakage in PNA‐DNA duplex. A decrease in the voltammetric peak currents of IC is observed upon hybridization of the probe with the target DNA. The influence of probe concentration on effective discrimination against non‐complementary oligonucleotides is investigated and a concentration of 10−7 M is selected. The diagnostic performance of the PNA sensor is described and the detection limit is found to be 4.31×10−12 M.

Abstract:In this article, it is shown that the efficiency of an electrochemical aptasensing device is influenced by the use of different nanoparticles (NPs) such as gold nanoparticles (Au), silver nanoparticles (Ag), hollow gold nanospheres (HGN), hollow silver nanospheres (HSN), silver-gold core shell (Ag@Au), gold-silver core shell (Au@Ag), and silver-gold alloy nanoparticles (Ag/Au). Among these nanomaterials, Ag@Au core shell NPs are advantageous for aptasensing applications because the core improves the physical properties and the shell provides chemical stability and biocompatibility for the immobilization of aptamers. Self-assembly of the NPs on a cysteamine film at the surface of a carbon paste electrode is followed by the immobilization of thiolated aptamers at these nanoframes. The nanostructured (Ag@Au) aptadevice for Escherichia coli as a target shows four times better performance in comparison to the response obtained at an aptamer modified planar gold electrode. A comparison with other (core shell) NPs is performed by cyclic voltammetry and differential pulse voltammetry. Also, the selectivity of the aptasensor is investigated using other kinds of bacteria. The synthesized NPs and the morphology of the modified electrode are characterized by UV-Vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, and electrochemical impedance spectroscopy.

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Because of the biocompatible properties of gelatine and the good affinity of aptamers for their targets, the combination of aptamer and gelatine type B is reported as promising for the development of biosensing devices. Here, an aptamer for chloramphenicol (CAP) is mixed with different types of gelatine and dropped on the surface of disposable gold screen printed electrodes. The signal of the CAP reduction is investigated using differential pulse voltammetry. The diagnostic performance of the sensor is described and a detection limit of 1.83 × 10−10 M is found. The selectivity and the stability of the aptasensor are studied and compared to those of other CAP sensors described in literature.