Conformational change-based fluorometric aptasensor for sensitive cadmium(II) detection in fruits and vegetables

Cadmium (Cd2+) is a highly toxic heavy metal that can accumulate in the human body through contaminated food and water, posing great health risks. In this study, a label-free fluorescent aptasensor based on SYBR Green I (SGI) for the rapid and sensitive detection of Cd2+ in food samples was designed. The aptasensor utilizes a Cd2+-specific aptamer (Cd-(21)) and its complementary strand (CSCd-(21)) to form a double-stranded DNA (dsDNA) structure in the absence of Cd2+. SGI intercalates into the dsDNA, resulting in a strong fluorescence signal. In the presence of Cd2+, the aptamer undergoes a conformational change, preventing the formation of dsDNA and leading to a decrease in fluorescence intensity. Under optimized conditions, the aptasensor exhibited a linear response to Cd2+ concentrations ranging from 0.11 to 157.37 ng mL-1, with a limit of detection (LOD) of 0.07 ng mL-1. The aptasensor demonstrated high specificity and was successfully applied to detect Cd2+ in fruits and vegetables, with satisfactory recovery rates (95-111%). The proposed aptasensor provides a promising tool for the rapid and sensitive detection of Cd2+ in food.

Preparation of Molecularly Imprinted Cysteine Modified Zinc Sulfide Quantum Dots Based Sensor for Rapid Detection of Dopamine Hydrochloride

By combining surface molecular imprinting technology with cysteine-modified ZnS quantum dots, an elegant, molecularly imprinted cysteine-modified Mn²⁺: ZnS QDs (MIP@ZnS QDs) based fluorescence sensor was successfully developed. The constructed fluorescence sensor is based on a molecularly imprinted polymer (MIP) coated on the surface cysteine-modified ZnS quantum dots and used for rapid fluorescence detection of dopamine hydrochloride. The MIP@ZnS quantum dots possess the advantages of rapid response, high sensitivity, and selectivity for the detection of dopamine hydrochloride molecules. Experimental results show that the adsorption equilibrium time of MIP@ZnS QDs for dopamine hydrochloride molecules is 12 min, and it can selectively capture and bind dopamine in the sample with an imprinting factor of 29.5. The fluorescence quenching of MIP@ZnS QDs has a good linear (R² = 0.9936) with the concentration of dopamine hydrochloride ranged from 0.01 to 1.0 μM, and the limit of detection is 3.6 nM. In addition, The MIP@ZnS QDs demonstrate good recyclability and stability and are successfully employed for detection of dopamine hydrochloride in urine samples with recoveries was 95.2% to 103.8%. The proposed MIP@ZnS QDs based fluorescent sensor provides a promising approach for food safety detection and drug analysis.

Surfactant-Assisted Label-Free Fluorescent Aptamer Biosensors and Binding Assays

Using DNA staining dyes such as SYBR Green I (SGI) and thioflavin T (ThT) to perform label-free detection of aptamer binding has been performed for a long time for both binding assays and biosensor development. Since these dyes are cationic, they can also adsorb to the wall of reaction vessels leading to unstable signals and even false interpretations of the results. In this work, the stability of the signal was first evaluated using ThT and the classic adenosine aptamer. In a polystyrene microplate, a drop in fluorescence was observed even when non-binding targets or water were added, whereas a more stable signal was achieved in a quartz cuvette. Equilibrating the system can also improve signal stability. In addition, a few polymers and surfactants were also screened, and 0.01% Triton X-100 was found to have the best protection effect against fluorescence signal decrease due to dye adsorption. Three aptamers for Hg²⁺, adenosine, and cortisol were tested for their sensitivity and signal stability in the absence and presence of Triton X-100. In each case, the sensitivity was similar, whereas the signal stability was better for the surfactant. This study indicates that careful control experiments need to be designed to ensure reliable results and that the reliability can be improved by using Triton X-100 and a long equilibration time.

A label-free aptasensor for clenbuterol detection based on fluorescence resonance energy transfer between graphene oxide and rhodamine B

A label-free aptasensor for clenbuterol was developed through the fluorescence resonance energy transfer mechanism by using an aptamer as the recognition element, rhodamine B as the fluorescence probe and graphene oxide as the fluorescence quencher.