COVID-19 electrochemical immunosensor with Ag-MOF: Rapid and high-selectivity nasal swab testing for effective detection.

Early detection of the coronavirus is acknowledged as a crucial measure to mitigate the spread of the pandemic, facilitating timely isolation of infected individuals, and disrupting the transmission chain. In this study, we leveraged the properties of synthesized Ag-MOF, including high porosity and increased flow intensity. Electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to develop an economical and portable sensor with exceptional selectivity for COVID-19 detection. The methodology involves the deposition of Ag-MOF onto the surface of a Glassy Carbon Electrode (GCE), which resulted in a progressive augmentation of electric current. Subsequently, the targeted antibodies were applied, and relevant tests were conducted. The sensor demonstrated the capacity to detect the virus within a linear range of 100 fM to 10 nM, boasting a noteworthy Limit of Detection (LOD) of 60 fM. The entire detection process could be completed in a brief duration of 20 min, exhibiting high levels of accuracy and precision, outperforming comparable techniques in terms of speed and efficacy.

New application of bimetallic Ag/Pt nanoplates in a colorimetric biosensor for specific detection of E. coli in water.

A fast and sensitive aptasensor was developed using nanoplates with peroxidase activity as a novel approach. E. coli detection is described using a silver/platinum nanoplate (Ag/Pt NPL) that interacts with an oligonucleotide aptamer as a bioreceptor. The size of the Ag/Pt NPLs was about 42 nm according to the FE-SEM images. The EDS result indicates that a thin layer of Pt ions was coated on the surface of the Ag NPLs. This nanobiosensor has the ability to specifically bind to E. coli, increasing the peroxidase activity of the apt-Ag/Pt NPL. Finally, the blue color of the solution in the contaminated water samples was increased in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) as a substrate and H2O2. The assay can be completed in 30 min and the presence of E. coli levels can be distinguished with the naked eye. The absorbance at 652 nm is proportional to pathogen concentration from 10 to 108 CFU·mL-1, with a detection limit of 10 CFU·mL-1. The percent recovery for the water samples spiked with E. coli is 95%. The developed assay should serve as a general platform for detecting other pathogenic bacteria which affect water and food quality. The proposed E. coli detection strategy has appealing characteristics such as high sensitivity, simple operation, short testing time, and low cost.

Smart fluorescence aptasensor using nanofiber functionalized with carbon quantum dot for specific detection of pathogenic bacteria in the wound.

We developed for the first time a novel and smart nanofiber (NF) network with the electrospinning method to create an amplified fluorescent biosensing platform for the detection of Staphylococcus aureus (S. aureus) bacteria in wound. The sensing platform is constructed based on surface modification of NFs by carbon quantum dots (CQDs) on the NF membrane surface, leading to large fluorescence signal amplification. CQDs synthesis was done from orto-phenylenediamine (OPD) with yellow emission fluorescence. Incorporation of CQDs leads to the uniform fluorescence of modified NFs. The proposed biosensing platform can also be applied to detect S. aureus bacteria with high sensitivity and selectivity via a specific aptamer. The linear sensing range for different S. aureus concentration from 10 to 108 CFU/mL and the detection limit of 10 CFU/mL was attained. For the first time these scaffolds were designed for the detection of specific pathogenic bacteria in wound using fluorescence signal of NFs, which can be seen by the naked eye under UV lamp. Enhancing in the fluorescence intensity after putting the modified NFs on skin wounds of mice for 2 h showed the successful application of this novel aptasensor.

Sensitive colorimetric aptasensor based on g-C3N4@Cu2O composites for detection of Salmonella typhimurium in food and water.

A new colorimetric aptasensor equipped with a novel composite of graphitic carbon nitride (g-C3N4) nanosheets and copper oxide(I) (Cu2O) nanocrystals is presented for Salmonella typhimurium (S .typhimurium). The dual-purpose structure of this composite simultaneously contributes to superb peroxidase-like activity and interaction with a label-free aptamer. Although g-C3N4@Cu2O effectively creates a visible blue color following the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in presence of hydrogen peroxide (H2O2), this catalytic activity of the composite severely decreases after the interaction with aptamers. In the presence of S. typhimurium in sample, aptamers bound to their specific target. Subsequently, g-C3N4@Cu2O catalytic activity was enhanced in proportion to S. typhimurium concentration. Under optimized conditions, this aptasensor exhibited an excellent detection performance in a range from 1.5 × 101 to 1.5 × 105 CFU/ml, with a detection limit of 15 CFU/ml. Besides, portable detection of S. typhimurium by paper-based model of this method operated successfully in just 6 min. Analysis of spiked milk samples revealed high potential of this method as a sensitive, rapid, and label-free promising tool for S. typhimurium detection. A novel composite of g-C3N4 nanosheets and Cu2O nanocrystals was constructed through this study, which represented a collection of significant properties for designing an aptasensor. The simultaneous capability of this composite for peroxidase-like activity and interaction with aptamer led to design a fast accurate biosensor for detecting as low as 15 CFU/ml Salmonella typhimurium as one of the most important foodborne pathogens which is a persistent burden for societies.