The aim of this work was to develop a simple, selective and sensitive APTASENSOR for detection of Pb2+ based on hairpin structure of complementary strand (CS) of aptamer (Apt). Screen printed carbon electrode (SPCE) was electrodeposited by gold nanoparticles to be used as the substrate for the immobilization of Apt-CS. Moreover, gold nanoparticles (AuNPs) and thionine were added to increase the sensitivity of the APTASENSOR. The morphology of SPCE and AuNPs modified SPCE was investigated using scanning electron microscopy (SEM). The SEM results exhibited that the AuNPs were homogeneously distributed on the surface of SPCE. The electrochemical performance of APTASENSOR was evaluated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. The electrochemical results indicated that peak current due to the hairpin structure formation of CS decreased in the presence of Pb2+. However, in the absence of Pb2+, peak current was enhanced because of combination of thionine/AuNPs-CS. The designed APTASENSOR showed a high selectivity toward Pb2+, wide linear range (1-40 nM), low detection limit (374 pM), acceptable reproducibility and good long-term stability.

A label-free electrochemical nucleic acid APTASENSOR for the detection of methamphetamine (MA) by the immobilization of thiolated self-assembled DNA sequences on a gold nanoparticles-chitosan modified electrode is constructed. When MA was complexed specifically to the aptamer, the configuration of the nucleic acid aptamer switched to a locked structure and the interface of the biosensor changed, resulting in a variation of the corresponding peak current of an electrochemical probe ([Fe(CN)6]3-/4-). Two different methods of cyclic voltammetry (CV) and microcantilever were employed to determine MA detection limit. Under the optimized experimental conditions, the presented sensor exhibits a nice specificity towards MA. The detection limits for MA in electrode and microcantilever were obtained 10 and 0. 7 nM. The proposed APTASENSOR can be easily regenerated by the denaturalization of aptamer-target complexes in a heated water bath at 80-90 ° C. Besides, this biosensor has a high reproducibility and selectivity, which can be a promising method to detect MA in real samples.

Detection of methylphosphonic acid (MPA) is important as several nerve agents can be hydrolysed to MPA after a certain period of their applications. Given the need for simple and rapid MPA detection, the colorimetric method is considered the most suitable sensor. To enhance the selectivity of this sensor, DNA or RNA aptamers, which can bind to a target molecule with high affinity and specificity, can be integrated. In this study, the optimum conditions for detection of MPA was determined using an aptamer-citrate capped gold nanoparticle (Apt-cit-AuNPs) colorimetric assay. The optimum conditions of the detection based on color change were: 300 µL of cit-AuNPs and 1 µL of 1 µM of DNA aptamer. Under the optimised experimental conditions, the colorimetric response is linearly proportional to MPA concentration range from 5.0 to 30.0 mM, with a detection limit of 0.3 mM. These values are much lower than the LD50 for MPA, indicating the practicability of the sensor. In addition, the APTASENSOR was successfully applied for the determination of MPA in lake and tap water samples, showing great potential for on-site detection of MPA.

Background: In this work, an aptamer-based biosensor was successfully developed based on the salt-induced gold nanoparticle (AuNP) aggregation phenomenon for the detection of carbohydrate antigen 125 (CA125), which is an important tumor marker for ovarian cancer. Materials and Methods: Citrate-coated AuNPs are relatively highly dispersed NPs. In the presence of different salts, the electrostatic stability of NPs is reduced, and depending on the type of salt and its concentration, different degrees of aggregation occur. On the other hand, the aptamer is easily adsorbed on the AuNP surface and can prevent salt-induced AuNP aggregation. This phenomenon was used in this study to develop a simple biosensor for the detection of CA125. Results: In the presence of CA125, the aptamer was desorbed from the AuNP surface to bind to its antigen due to the higher affinity, leading to the aggregation of AuNPs and a change in the absorption spectra of the solution. Under the optimum condition, the fabricated APTASENSOR showed a linear range of 15-160 U/mL with a limit of detection (LOD) of 14.41 U/mL. Conclusion: The APTASENSOR exhibited good repeatability with notable selectivity with regard to CA125 detection, even in human serum samples, as compared to the enzyme-linked immunosorbent assay (ELISA). In conclusion, the engineered APTASENSOR can serve as a promising tool for the simple, rapid, and cost-effective detection of CA125.

Accurate identification and quantification of foodborne pathogens from environmental and clinical samples require techniques with high sensitivity and specificity. Additionally, Vibrio cholerae is prevalent among humans and animals and can harm individuals. The purpose of this research is to optimize Gold NanoParticles (GNPs) for nano bio probe design using an anti-V. cholerae aptamer selected by in silico tools. For this, a library of new aptamer sequences for detecting V. cholerae with higher sensitivity and specificity was designed. Then, using bioinformatics tools and molecular docking, the binding aptamers to the surface protein of V. cholerae (OmpU) were examined. The sequences Apt-Ch30 were proposed as final candidates for constructing the V. cholerae diagnostic APTASENSOR. The correlation between the volume fraction of GNPs and NaCl concentration was investigated using Design Expert software with the Response Surface Method (RSM). The results indicate that this model not only helps determine optimal process variable conditions but also accurately examines process variable interactions. The magnitude of R2 confirms satisfactory compliance of experimental data with the second-order model. The optimal conditions of the process were the volume fraction of GNPs 90% (v/v) and the concentration of NaCl 14 mM. The chosen aptamer sequence was meticulously synthesized and employed to functionalize the surface of the Gold Nanoparticle (GNP). The effectiveness of the optimized APTASENSOR for detecting bacteria was evaluated by monitoring the aggregation or dispersion of the GNPs in the presence of sodium chloride (NaCl). Finally, a high-sensitivity APTASENSOR was designed for more precise and rapid detection of V. cholerae.

Background: Current study is aimed at designing and producing gold-nanoparticle based APTASENSOR for colorimetric detection of tri-nitro toluene (TNT).Materials and Methods: Gold-nanoparticles have a wide range of application in designing biosensors for their special and highly sensitive plasmonic characteristics. In the present study, TNT molecule has been detected by designing and producing gold nanoparticle based APTASENSOR. After synthesizing gold nanoparticles and functionalizing them by ssDNA aptamer having 52 nucleotides, APTASENSOR performance for detecting target molecule was evaluated. Techniques such as dynamic light scattering (DLS), transmission electron micro-scope and UV-Vis spectrophotometer were used to characterize the size and shape of nanoparticles, functionalizing them by aptamer, and also their sensitivity to detect target.Results: UV-Vis spectrophotometer, DLS, and TEM microscopy tests indicated that gold nanoparticles were synthesized with excel-lent quality and average size of 40 nm. TNT molecule was colorimetric detected with sensitivity of 15 nanomolar using gold nanoparticle based APTASENSOR.Conclusion: According to the results it can argue that the strategy promises a novel method in detection due to wide range of such APTASENSORs detection. .