A facile smartphone-based digital image colorimetric sensor for the determination of tetracyclines in water using natural phenolic compounds induced to grow gold nanoparticles

A cost-effective smartphone-based digital image colorimetric sensor was developed to determine tetracyclines by inducing <i>in situ</i> growth of gold nanoparticles using naturally occurring phenolic compounds derived from para rubber tree bark waste. The green intensity of the purple-red product was measured using smartphone-based digital image analysis. Under optimal conditions, the calibration graph exhibited linearity within the range 0.05 to 0.50 μg mL^-1, with a coefficient of determination (<i>R</i> ²) of 0.9940. The limits of detection (LOD) and limits of quantitation (LOQ) were 15 and 50 ng mL^-1, respectively, with levels of precision for intraday and interday less than 3.91% and 4.59%, respectively. The proposed method was effectively validated to determine the spiked tetracycline antibiotics in water samples, achieving a high relative recovery rate ranging from 86.4% to 114.4%. Our method is facile, convenient, dependable, and verifiable as an alternate procedure for measuring tetracycline levels in water.