Direct Printing of\nan Electrochemical Device and Its\nInterface with Paper for Uric Acid Detection in Human Sweat

Using a laser-scribed (direct printing) technique, we\nhave fabricated\nan enzymeless, mediatorless, and paper-interfaced electrochemical\ndevice (P-LSG) for uric acid detection on a flexible polyimide sheet.\n Various paper substrates were investigated, and it was found that\nWhatman filter paper-1 is promising to obtain the best electrochemical\nsignals at the small volume of electrolyte, i.e., 20 μL. Furthermore,\nthe Whatman filter paper-1 was modified with gold nanoparticles (AuNPs)\nto improve the electrocatalytic activity of the P-LSG device. The\nfabricated AuNP-modified P-LSG biosensor exhibited excellent electrocatalytic\nactivity for the detection of uric acid over a wide range of 10 to\n750 μM, with sensitivity of ∼0.214 μA μM<sup>–1</sup> cm<sup>–2</sup>, and a limit of detection\nof ∼1.4 μM. The sensor was further validated by using\nthe UHPLC-ESI-MS/MS technique, and the observed percentage recovery\nwas less than 10%. This work opens the window to modified paper substrates\nwith various nanomaterials to improve the sensing parameters. The\nelectrolyte storage capacity and rich chemistry of paper additionally\nprovide an efficient immobilization platform for biorecognition elements\nto diagnose other metabolites. Furthermore, it has the potential to\nanalyze the volume of small samples (like sweat, tears, urine, etc.)\nusing paper to develop noninvasive wearable biosensors.