In the present investigation, we applied the application potential of nanomaterials and smartphone analysis to develop a specific, sensitive and portable method. In this study, we report a silver nanoparticles-based colorimetric nanosensor for the determination of lidocaine hydrochloride (LHC) up to 0.05 ng mL⁻¹ with good linear correlation in the range from 0.1 to 4.5 ng mL⁻¹ with a correlation coefficient of 0.9914. Coexisting substances, including acetaminophen, diazepam, nitrazepam, lorazepam, zolpidem, atropine, bupivacaine, clonazepam and morphine did not interfere in the determination of LHC. The developed sensor proved to be a smart alternative lab-on-phone device, which would help in the on-the-spot determination of LHC in forensic toxicological drug screening. Herein, we utilized easily accessible vitreous humor, which is often unnoticed for toxicological drug screening along with blood for real sample analysis.