A smartphone-integrated colorimetric aptasensor enabled by green-synthesized aptamer-gold nanoparticles derived from longan peel extract for on-site streptomycin detection in waters

In this study, a green synthesis strategy was developed to fabricate highly stable gold nanoparticles (AuNPs) using the extract from discarded longan peel, designated GN-LP. The synthesized GN-LP has an average particle size of 11.94 ± 4.83 nm, a zeta potential of – 28.4 mV, a typical face-centered cubic (fcc) crystal structure and enriched with oxygen-containing functional groups, acted as the primary reducing agents. The optimal conditions for streptomycin (STR) detection were as follows: 0.6 M potassium chloride (KCl), an aptamer concentration of 75 nM, and a reaction time of 45 min. Under these optimized conditions, a smartphone-based colorimetric aptasensor was established, exhibiting a linear absorbance–concentration relationship within the range of 400.0 ng·mL-1–2400.0 ng·mL-1. The limit of detection (LOD) and limit of quantification (LOQ) were calculated as 126.74 and 425.48 ng·mL-1, respectively. The method was successfully applied to detect STR in environmental waters, yielding recovery rates between 96.8% and 109.4%, with values of relative standard deviation (RSD) below 9.6%. The results offer operational simplicity, high sensitivity, minimal solvent consumption, and environmental sustainability, making it well-suited for on-site STR monitoring in real water.