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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 CO 2 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 × 10−3 cm s−1 and 7.8 × 10−4 cm s−1 for [Ru(NH 3) 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 μM range at pH between 5.6 and 7.4. At pH 7.4, a linear response (R2 = 0.999) from 10 to 250 μM was achieved, with a limit of detection of 3.97 μM and a sensitivity of 0.363 μA cm−2 μM−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 μM 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. [Display omitted] • "Green" graphene electrodes by CO 2 laser irradiation of paper ("paper-LIG"). • Uric acid (UA) quantification at clinically relevant concentrations and pH (5.6–7.4). • Limit of detection of 3.97 μM and a sensitivity of 0.363 μA cm−2 μM−1 (pH = 7.4). • Adequate selectivity in synthetic urine, as well as in ascorbic acid and dopamine-containing electrolytes. • Recoveries of 100.6% and 95.4% for human urine samples spiked with 50 and 100 μM UA. [ABSTRACT FROM AUTHOR]

Direct laser scribing (DLS) technology is applied to commercial polyimide (PI) coated optical fibers producing laser-induced graphene (LIG) coated optical fibers. The PI-coated optical fiber is first inscribed with off-center Bragg gratings via point-by-point method using a femtosecond laser system. Then, the off-center Bragg grating is irradiated with a CO 2 laser and the PI coating is photothermally converted into LIG without affecting the grating. Scanning electron microscopy (SEM) and Raman spectroscopy prove the presence of the laser-induced graphene layer on the optical fiber, and Fourier transform infrared (FTIR) spectroscopy confirms that all the PI coating was converted into LIG. The resulting LIG-coated off-center Bragg grating (FBG) sensors respond to variations of the surrounding refractive index (RI) with a sensitivity of 38.08 ± 1.57 nm per RI units (RIU). In addition, after removal of the PI coating, obtaining a bare-FBG, the sensitivity decreases to 25.63 ± 0.66 nm R I U − 1 . Therefore, this strategy, here reported for the first time, paves the way to produce promising novel optical transducers aiming to develop bio- and chem-sensing devices. • Direct laser scribing technology applied to commercial polyimide optical fibers. • Laser-induced graphene produced directly on optical fiber for sensing. • The resulting LIG-coated off-center FBG sensors respond to variations of the surrounding RI. • High sensitivity compared with after removal of the PI coating. [ABSTRACT FROM AUTHOR]