Nanoscale Hydroxyapatite for Electrochemical Sensing of Uric Acid: Roles of Mesopore Volume and Surface Acidity

A consolidated mechanistic perspective of uric acid (UA) sensing by hydroxyapatite (HA) correlating the surface properties with its sensing efficacy is lacking in the literature for prospective tuning of synthetic protocols of the material. Keeping this in mind, in the current investigation, the influence of mesopore volume and surface acidity of nanoscale HA particles on the electrochemical sensing of UA is investigated. In the present study, nanoscale HA particles have been synthesized via the chemical precipitation route in the presence and absence of Triton X-100 (TX-100) employing three post-treatment techniques such as hydrothermal, reflux, and ultrasonication. The structural and chemical features of HA, namely, structural integrity, surface acidity, surface Ca/P ratio, and surface C-carbonate/P ratio, have been studied employing various analytical tools such as X-ray diffraction, Fourier transform infrared spectroscopy, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy. Furthermore, morphological and pore characteristics of HA particles were investigated using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption analysis. Electrochemical sensing was influenced mainly by the surface acidity of discrete HA particles, whereas in the case of agglomerated HA powder, the sensing was influenced by mesopore volume. A plausible mechanism showing the interaction of urate ion with Lewis acid sites of discrete HA particles has been proposed for the electrochemical sensing of UA. The most proficient electrode was found to exhibit a wide linear current response in the concentration range of 0.068-50.0 mu M, with 0.05 mu M as a limit of detection.