Sea-urchin-like cobalt-MOF on electrospun carbon nanofiber mat as a self- supporting electrode for sensing of xanthine and uric acid Md. Wasi Ahmad a,⇑ , Baban Dey b , Gautam Sarkhel b , Duck-Joo Yang c , Arup Choudhury b,⇑ a Department of Chemical Engineering, Birla Institute of Technology, Ranchi 835215, India b Department of Chemical Engineering, College of Engineering, Dhofar University, Salalah, P.O. Box 2509, 211, Oman c Department of Chemistry and the Alan G. MacDiarmid NanoTech Institute, The University of Texas at Dallas, 800 W. Campbell Road, Richardson, TX 75080, United States ARTICLE INFO Keywords: Cobalt-MOF Carbon nanofiber mat Electrochemical sensor Xanthine Uric acid ABSTRACT The early detection of abnormal levels of purine derivatives such as xanthine (XA) and uric acid (UA) in the body fluid could be helpful to prevent various diseases. A novel free-standing biosensor electrode was fabri- cated by solvothermal deposition of sea-urchin-like cobalt(benzene 1,3,5-tricarboxylic acid)MOF (Co(TMA) MOF) on the surface of electrospun porous carbon nanofibers (CNFs) and explored for the electrochemical detection of XA and UA in the alkaline medium (pH ∼13). The morphological and textural features of the as-fabricated Co(TMA)MOF@CNF hybrid mat were evaluated. The electrochemical investigation of the Co (TMA)MOF@CNF electrode demonstrated an excellent electrocatalytic response toward the selective detection of XA and UA. The diffusion-controlled electrooxidation reactions of XA and UA were identified. The calibra- tion plots of amperometric current response vs analyte concentration were found linear over a broad concen- tration range 25–700 μM, along with low detection limits (LOD, S/N = 3) of 96.2 nM and 103.5 nM for the XA and UA, respectively. The sensor sensitivity is calculated to be 14.28 μA μM -1 cm -2 for XA and 5.78 μA μM -1 cm -2 for UA. The present hybrid sensor was investigated to monitor XA and UA in blood serum and urine of gout patients, and the results were satisfactory with recovery values around 99 %. 1. Introduction In recent years, it has become increasingly important to detect and quantify the xanthine (XA) and uric acid (UA) in our extracellular flu- ids and urine, because the presence of these bio-compounds in the physiological fluids at an abnormal level could lead to various diseases like xanthinuria, Alzheimer's, gout, toxemia, epilepsy, and renal fail- ure, etc [1,2]. An average concentration of xanthine in human plasma is between 0.5 and 2.5 μM (40–160 μM in urine) [3]. An irregular metabolism of purine leads to generate xanthine as a significant inter- mediate, followed by the production of uric acid as an end product [4,5]. In addition, in the food industry, the XA is used as an indicator of the freshness of fish/meat products due to its accumulation in the tissues after a fish/animal has died [6,7]. Indeed, the inosine monophosphate in the fresh fish/meat could undergo microbial degra- dation to inosine and subsequently to XA. The consumption of spoilage fish and meat products could increase the XA level in our blood and consequently lead to several diseases. Therefore, it is imperative to develop therapeutic and diagnostic methodologies that detect these biomarkers (XA and UA) at an early stage. Not only for clinical pur- poses, the sensitive and selective detection of XA is also highly essen- tial to food quality control. For simultaneous analysis the Xn and UA, various analytical procedures have been developed including enzy- matic assay techniques, spectroscopic methods, chemiluminescence, high-performance liquid chromatography, electroosmotic technique, and electrochemical measurements [8]. Among them, the cost-effec- tive electrochemical methods offer several advantages like ease of operation, fast response, high sensitivity, and selective [9,10]. How- ever, the electrochemical detection of these biomarkers still remains challenging because of the high polarization potentials of XA and UA, as well as electrode fouling effects. Hence, the development of stable catalytic electrode materials for the fabrication of highly sensi- tive and selective sensors for simultaneous measurements of XA and UA is greatly demanded. In recent years, there are various nanocomposite-based electrode materials such as metal and metal oxide nanoparticles-decorated gra- phene [11,12] or carbon nanotubes (CNTs) [13,14], carbon quantum dots (CQDs)/metal oxide composites [15,16], conducting polymers/- https://doi.org/10.1016/j.jelechem.2022.116646 Received 20 December 2021; Received in revised form 12 June 2022; Accepted 19 July 2022 Available online 22 July 2022 1572-6657/© 2022 Published by Elsevier B.V. ⇑ Corresponding authors. E-mail addresses: mwahmad@du.edu.om (M.W. Ahmad), arup@bitmesra.ac.in (A. Choudhury). Journal of Electroanalytical Chemistry 920 (2022) 116646 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem