A wax-assisted stamp-transfer approach towards tetracycline monitoring by silver nanoprism using smartphone-based digital image analysis.

Tetracycline is a broad-spectrum antibiotic used in livestock farming and food production. The persistence of tetracycline in the environment and food products can lead to environmental and human health problems. Therefore, monitoring this compound is essential in the field of pharmacological and environmental analysis. In this study, we attempted to prepare and evaluate a novel flexible and portable polymeric substrate for monitoring the concentration level of tetracycline in real samples. An optical sensor based on silver nanoparticles was utilized for identifying tetracycline, using only a single drop of the optical probe and a single drop of the analyte. For this purpose, a 32-zone pattern was initially designed using AUTOCAD software, and then a metal mold was fabricated via computer numerical control (CNC) machining. Subsequently, the transfer of the pattern onto a flexible Parafilm substrate was carried out as a creative idea by transferring molten wax. The zones formed on the substrate (micro-scale polymeric colorimetric device (µPCD)) were then modified with silver nanoparticles, which possessed a triangular morphology and unique plasmonic properties. The analyte-probe interaction was then assessed using a smartphone and based on RGB analysis via the standard color-picker app, and the results were evaluated. According to the results, the optical sensor was capable of identifying micro molar concentrations of tetracycline (low limit of quantification = 0.025 µM), demonstrating the application of this novel tool in pharmaceutical analysis in human plasma samples. To confirm the interaction between the nanoparticle and the analyte, zeta potential and conductivity data were evaluated to investigate the electrostatic interaction between the silver nanoprism and tetracycline. The zeta potential and conductivity for the silver nanoprism were obtained as -25.7 mV and 0.687 mS cm, respectively, which changed to +21.91 mV and 7.62 mS cm upon interaction with the analyte. Validation studies indicated the proper functioning of the engineered optical sensor for tetracycline analysis. Therefore, in this research, a new method for identifying tetracycline in human plasma samples without using routine laboratory devices was introduced.