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Aims: Molecular insights into the analyte-bioreceptor interactions play a vital role in the efficacy of designing biosensors. Biosensors that utilize aptamers as bioreceptors are highly efficient with high specificity and reusability. Aptasensors can be used in a variety of conditions of in vivo or in vitro. The aim of this study was to study the changes in the solvent conditions of the binding of MUC1-G peptide and the anti-MUC1 aptamer.
Materials and Methods: The molecular dynamics simulation method has been used to investigate the change of molecular interactions due to selective variations in solvent conditions. The results can be used to reflect a variety of environments, in which the aptasensor utilizes anti-MUC1 S2.2 aptamer as a bioreceptor and MUC1–G peptide as a biomarker.
Findings: Based on the calculated binding energies, the medium containing 0.10M NaCl and anti-MUC1 S2.2 aptamer demonstrates the highest affinity toward the MUC1-G peptide among the studied concentrations of NaCl, and the arginine amino acid has a key role in the aptamer–peptide binding. Conclusion: The results of MD simulation indicated that the increase in the concentration of NaCl in the interaction environment leads to a decrease in binding energies; therefore, the binding affinity of the anti-MUC1 aptamer to MUC1-G peptide decreases. Insights from present modeling demonstrate the selectiveness and sensitivity to solvent conditions, which should be considered in the development of biosensors.

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Aptamers, DNA or RNA single-stranded sequences, have different applications in biological investigations, such as apatsensors, due to their many advantages including high specificity and affinity, cost-effectiveness and easy synthesis. In this study, an aptasensor was designed based on the changes in the SPR spectra of gold nanoparticle, in order to detect carcinoembryonic antigen (CEA) cancer indicator as a marker for breast cancer. In the presence of aptamer, gold nanoparticles were stable, SPR spectrum of gold nanoparticle was unchanged after adding NaCl. However, in the presence of CEA as a cancer marker, aptamer binds to the target molecule and by adding NaCl consequently the SPR spectrum of gold nanoparticles is changed. The results of this study showed that the designed aptasensor enables the detection of CEA over a range of 50 ng ml^-1. The limit of detection was about 22.75 ng ml^-1. It seems this aptasensor can be used in detection of carcinoembryonic antigen cancer marker.

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Quantitative detection of drug residues in animal food stuffs is very important. Excessive use of veterinarian veterinarians, like antibiotics are a serious threat to consumers, due to the residence of livestock products such as meat, milk, eggs. Rapid detection of antibiotics is essential by using an efficient, fast, affordable, and specific tool for risk reduction and food safety control. In the present study, an aptasensor based on pencil graphite electrode modified with nanomaterial including grapheme and gold, for rapid detection of tetracycline antibiotic was developed in milk samples. Cycle voltammetry and differential pulse voltammetry (DPV) techniques were used for response evaluation of aptasensor. In order to modification the graphite pencil electrode, the scanrate (40 mV/s) and the number of cycles (10) and immobilization time of graphene (90 min) were optimized. Under optimum conditions, using differential pulse voltammetry technique was found to increase linearly in the range of 1 × 10^-12 to 1 × 10^-5 M, with increasing concentration (R² = 0.985). The detection limit of the aptasensor was found to be 1.4× 10^-13 M. A review of functional characteristics including repeatability, reproducibility, satability, and selectivity suggests acceptable performance for aptasensor. Overall, the fabricated aptasensor has efficiency required to detect tetracycline in milk samples.

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Milk, from its production to consumption, is exposed to a variety of microbial and chemical contaminants. Aflatoxin M1 (AFM1) is one of the most important contaminants in milk, which has always received attention due to its carcinogenic and destructive effects on the consumer. Accordingly, the rapid, sensitive, and cost-effective identification of AFM1 in milk is essential. In the present paper, an electrochemical aptasensor based on screen printed electrode (SPE) modified with magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) was proposed to identify AFM1 in cow milk samples. SPE was activated by applying a potential within the range of -1.5 to +1 V versus the reference electrode at a scan rate of 200 mV/s for 5 continuous cycles in the 0.5 M sulfuric acid and 0.1 M potassium chloride solution. Changes of the electrode surface at different stages of preparation were assessed using cyclic voltammetry (CV) technique. Using CV in optimal conditions, it was found that the aptasensor presents a concentration range of 100-700 ng/l and a limit of detection (LOD) of 50 ng/l.  There was a linear relationship between changes of the current peak (∆I) and analyte concentration. This relationship follows the regression equation of ∆I=0.0209C+2.14 (R²=0.9897). Calculation of the relative standard deviation (RSD=3.2%) indicated the acceptable repeatability of the electrochemical aptasensor. The current peak was obtained to be 7.4% in the investigation of RSD reproducibility, indicating the good reproducibility of the electrochemical aptasensor. The obtained results showed that the aptasensor response after 8 days has only reduced by 7% compared to the first day, indicating the desirable stability of the aptasensor. The recovery percentage range for cow milk samples at concentrations of 100 and 200 ng/l was obtained to be 86.5 and 93%, respectively, showing the acceptable recovery percentage of the electrochemical aptasensor.