Laser-induced graphene from paper for non-enzymatic uric acid electrochemical sensing in urine

Laser-induced graphene from paper (paper-LIG) was applied in non-enzymatic electrochemical sensing of uric acid (UA) in human urine. Paper-LIG was formed by CO2 laser modification of paper into a 3D graphene arrangement. Kinetic analysis of paper-LIG electrodes returned effective heterogeneous electron transfer standard rate constants of 1.4 x 10(-3) cm s(-1) and 7.8 x 10(-4) cm s(-1) for [Ru(NH3)(6)](2+/3+) and [Fe(CN)(6)](4)(-)(/3)(-) redox probes, respectively. These electrodes were able to detect and quantify uric acid in PBS within the 10-300 mu M range at pH between 5.6 and 7.4. At pH 7.4, a linear response (R-2 = 0.999) from 10 to 250 mu M was achieved, with a limit of detection of 3.97 mu M and a sensitivity of 0.363 mu A cm(-2) mu M-1. Paper-LIG electrodes denoted adequate selectivity in synthetic urine as well as in ascorbic acid (AA) and dopamine (DA)-containing electrolytes. Determination of urinary UA content in human samples returned a concentration of c.a. 1.8-1.9 mM, within the range for healthy individuals. Recoveries of samples spiked with 50 and 100 mu M UA were 100.6% and 95.4%, respectively, with satisfactory reproducibility and stability. These cheap, lightweight, flexible, and eco-friendly paper-LIG biosensors for non-enzymatic quantification of UA in human urine pave the way to widespread application in the detection of other important biomarkers.