Ultrasensitive Determination of Piroxicam at Diflunisal-Derived Gold Nanoparticle-Modified Glassy Carbon Electrode TAYYABA SHAIKH , 1,5 SIRAJ UDDIN, 1 FARAH N. TALPUR, 1 ABDUL R. KHASKELI, 2 MUHAMMAD H. AGHEEM, 3 MUHAMMAD R. SHAH, 4 TUFAIL H. SHERAZI, 1 and SAMIA SIDDIQUI 1 1.—National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan. 2.—Department of Pharmacy, Shaheed Mohtarma Benazir Bhutto Medical University, Larkana, Pakistan. 3.—Center for Pure and Applied Geology, University of Sindh, Jamshoro 76080, Pakistan. 4.—International Center for Chemical and Biological Sciences, HEJ Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan. 5.—e-mail: tayyabashaikh30@yahoo.com We present a simple and green approach for synthesis of gold nanoparticles (AuNps) using analgesic drug diflunisal (DF) as capping and stabilizing agent in aqueous solution. Characterization of the synthesized diflunisal-derived gold nanoparticles (DF-AuNps) was performed by ultraviolet–visible (UV–Vis) spectroscopy, revealing the surface plasmon absorption band at 520 nm under optimized experimental conditions. Fourier-transform infrared (FTIR) spec- troscopy established the effective interaction of the capping agent with the AuNps. Topographical features of the synthesized DF-AuNps were assessed by atomic force microscopy (AFM), revealing average particle height of 29 nm to 32 nm. X-ray diffractometry was used to study the crystalline nature, revealing that the synthesized DF-AuNps possessed excellent crystalline properties. The synthesized DF-AuNps were employed to modify the surface of glassy carbon electrode (GCE) for selective determination of piroxicam (PX) using differential pulse voltammetry technique. The fabricated Nafion/DF- AuNps/GCE sensor exhibited high sensitivity compared with bare GCE. The current response of the fabricated sensor was found to be linear in the PX concentration range of 0.5 lM to 50 lM, with limit of detection (LOD) and limit of quantification (LOQ) of 50 nM and 150 nM, respectively. The proposed sensor was successfully utilized for sensitive and rapid determination of PX in human serum, urine, and pharmaceutical samples. Key words: Gold nanoparticles, diflunisal, differential pulse voltammetry, piroxicam INTRODUCTION Piroxicam (PX) is an analgesic drug frequently administered to relieve pain related to rheumatoid arthritis and postoperative dental problems. 1,2 As with other analgesics, long-term use of this drug increases the risk of gastrointestinal side-effects, 3,4 therefore determination of the drug in human biological fluids is of significant interest. Moreover, quality control and assurance of pharmaceutical formulations relies on quantitative determination of active ingredients, so rapid and accurate methods for quantitation of PX in pharmaceutical formula- tions are highly needed. Official analytical methods for determination of PX in pharmaceuticals are high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) methods based on the United States pharmacopoeia (USP) and British pharmacopoeia (BP) monographs, respectively. 5 Besides these, spectrophotometry is commonly employed for determination of PX in (Received March 20, 2017; accepted May 6, 2017) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-017-5573-y Ó 2017 The Minerals, Metals & Materials Society