Highly Selective Colorimetric and Smartphone-Based Paper Assay Using Malic Acid-Functionalized Silver Nanoparticles for Thiram Detection.

A facile sensing assay was demonstrated for the selective and sensitive detection of thiram, using malic acid-functionalized silver nanoparticles (MA-AgNPs) as colorimetric probes. The factors affecting the synthesis of the MA-AgNPs were optimized and characterized by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The MA-AgNPs were spherical, with an average diameter of 7.8 nm and a maximum absorbance at 390 nm. Further, the stability of the storage time, buffer pH, and salinity of the MA-AgNPs was investigated. The MA-AgNPs were employed to detect thiram in environmental samples. Good linearity of the calibration curve was achieved (0.1-1.0 ppm), with of 0.998 and a limit of detection (LOD) of 0.009 ppm. Additionally, the assay displayed good anti-interference toward thiram over other coexisting pesticides. More importantly, a smartphone-assisted colorimetric assay integrated with test paper was established for thiram detection, with an LOD of 0.71 ppm. This work shows the potential feasibility of the rational design for thiram detection in actual samples.