Fluorescent aptasensor based on magnetic bead-assisted displacement reaction for monitoring vancomycin in plasma

Vancomycin is a glycopeptide antibiotic commonly prescribed for infection by methicillin-resistant Staphylococcus aureus. Due to its narrow therapeutic window and time-dependent bactericidal activity, therapeutic drug monitoring is essential to optimize dosing and minimize toxicity. Immunoassay-based approaches have traditionally been widely used; however, they often require long assay times and are susceptible to matrix interferences, which limit their applicability for rapid clinical use. To enhance the development of point-of-care testing for therapeutic drug monitoring, we developed a fluorescent aptasensor based on a magnetic bead-assisted displacement reaction for the quantification of vancomycin in human plasma.

The sensing mechanism is based on the competition between vancomycin and a complementary single-stranded DNA (cDNA) for binding to a fluorescent aptamer. The cDNA-aptamer complex was immobilized on magnetic beads, and upon addition of vancomycin, the stronger binding affinity between vancomycin and the aptamer displaced the cDNA, releasing the aptamer-vancomycin complex into the supernatant. After magnetic separation, the fluorescence intensity of the supernatant was measured to quantify vancomycin concentration. The optimized experimental conditions were using a 16-mer cDNA and 1 × PBS buffer containing 10 mM MgCl₂ at pH 7.0, with a total reaction time of only 15 min. The aptasensor exhibited a linear response for vancomycin in plasma over the range of 1-25 μM, with a low detection limit of 0.5 μM.

The developed assay was successfully applied to clinical plasma samples, and the results showed good agreement with those obtained by enzyme-linked immunosorbent assay, confirming the accuracy and potential of this aptasensor for clinical application. This aptasensor provides a simple, rapid, and cost-effective strategy for therapeutic drug monitoring of vancomycin in clinical settings.