A silver-nanoparticle-based chemosensor for optical detection of captopril

Captopril is an angiotensin-converting enzyme commonly used to treat high blood pressure and to improve survival after a heart attack. Considering the importance of the assay of this drug, the authors propose a simple and cost-effective colorimetric technique for its quantitative determination. The detection strategy was based on the redshift of the surface plasmon resonance band of silver nanoparticles (AgNPs) induced by the action of captopril molecules. Under optimal experimental conditions, the interaction of AgNPs with captopril molecules in the presence of barium ions induces the aggregation of AgNPs. The final result of this process is an observable change in the color of the tested solution from pale yellow to light brown. The experiments showed that there is a linear relationship between the absorbance of the AgNP solution and the captopril concentration at about 720 nm. Thus, it is possible to assay the captopril amount just by measuring the absorbance of the examined solution at this wavelength. The calibration curve was linear in the range 1.0–6.0 μM captopril with a detection limit equal to 0.4 μM. The proposed strategy was successfully applied to the determination of captopril in pharmaceutical preparations.