Highly Specific\nNon-Enzymatic Electrochemical Sensor\nfor the Detection of Uric Acid Using Carboxylated Multiwalled Carbon\nNanotubes Intertwined with GdS-Gd<sub>2</sub>O<sub>3</sub> Nanoplates\nin Human Urine and Serum

Herein, the electrochemical sensing efficacy of carboxylic\nacid\nfunctionalized multiwalled carbon nanotubes (C-MWCNT) intertwined\nwith coexisting phases of gadolinium monosulfide (GdS) and gadolinium\noxide (Gd<sub>2</sub>O<sub>3</sub>) nanosheets is explored for the\nfirst time. The nanocomposite demonstrated splendid specificity for\nnonenzymatic electrochemical detection of uric acid (UA) in biological\nsamples. It was synthesized using the coprecipitation method and thoroughly\ncharacterized. The presence of functional groups and disorder in the\nas-synthesized nanocomposite are confirmed using Fourier transform\ninfrared spectroscopy and Raman spectroscopy. Furthermore, field emission\nscanning electron microscopy, high-resolution transmission electron\nmicroscope, X-ray powder diffraction, and X-ray photoelectron spectroscopy\nprovides a clear understanding of the morphology, coexisting phases,\nand elemental composition of the as-synthesized nanocomposites. The\ndifferential pulse voltammetry technique was utilized to elaborate\nthe electrochemical sensing of UA using a GdS-Gd<sub>2</sub>O<sub>3</sub>/C-MWCNT modified glassy carbon electrode (GCE), The sensor\nshowed an enhanced current response by more than 2-fold compared to\nbare GCE. Also, the sensor’s performance was further improved\nby dispersing the nanocomposite in an ionic liquid with the exceptional\nreproducibility (SD = 0.0025, <i>n</i> = 3). The fabricated\nUA sensor GdS-Gd<sub>2</sub>O<sub>3</sub>/C-MWCNT/IL/GCE demonstrated\na wide linear detection range from 0.5–30 μM and 30–2000\nμM, effectively covering the entire physiological range of UA\nin biological fluids with a limit of detection (LOD) of 0.380 μM\n(+3SD of blank) and a sensitivity of 356.125 μA mM<sup>–1</sup> cm<sup>–2</sup>. Moreover, the electrodes exhibited storage\nstability for 2 weeks with decrease in zero-day current by only 4.5%.\nThe sensor was validated by quantifying UA in 12 unprocessed clinical\nhuman urine and serum samples, and its comparison with the gold standard\ntest yielded remarkable results (<i>p</i> < 0.05). Hence,\nthe proposed nonenzymatic electrochemical UA sensor is selective,\nsensitive, reproducible, and stable, making it reliable for point-of-care\ndiagnostics.