Highly sensitive photothermal paper-based analytical devices for monitoring of melamine levels in milk samples

This study presents the first demonstration of a photothermal-based paper analytical device (PT-PAD) for melamine monitoring in milk samples. The sensor utilizes plasmonic gold nanoparticles (AuNPs) as effective photothermal materials to enable melamine detection. In our technique, melamine induces the aggregation of AuNPs on the paper substrate, resulting in a temperature change proportional to melamine levels. This temperature variation can be measured using a portable and inexpensive thermometer, enhancing affordability. The sensor provides a linear range between 125.0 and 1500.0 ng mL⁻¹ with a R² value of 0.9965 and a detection limit of 27.0 pg mL⁻¹. It demonstrates excellent selectivity with no observed interference, and achieves high accuracy and precision in real milk samples, with recoveries between 97.3 and 108.5% and a maximum RSD of 7.5%. The results are statistically comparable to HPLC, confirming the method’s reliability. Furthermore, while the assay requires only low-cost commercial tools such as a laser pointer and a thermometer, its detection efficiency is significantly higher than other previous PAD methods for melamine detection. Overall, our developed PT-PAD sensor is well-suited for monitoring melamine levels in milk samples, offering advantages such as affordability, sensitivity, and ease of use. The approach also presents a promising platform for future expansion into other analytes by integrating plasmonic nanomaterials with microfluidic technologies, broadening its application across food safety and environmental monitoring.

Graphic Abstract