Low cost and eco-friendly nanoparticles from cockle shells as a potential matrix for the immobilisation of urease enzyme

Abstract

Cockle shells (a marine mollusc) are by-products or waste from the seafood industry, primarily made up of calcium carbonate (CaCO3) and are beneficial for the immobilisation of urease (Urs). In this study, a composition of 99.5% CaCO3 nanoparticles (NPs) from cockle shells was synthesised using a simple and environmentally friendly method involving the grinding and milling of cockle shells. Findings showed that the production of the pure NPs resulted in CaCO3 aragonite polymorphs approximately 78 nm in size and primarily functionalised with acrylic acid N-hydroxysuccinimide ester, which had a succinimide group that bound to the amine group of Urs. Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed peaks at 1120 cm−1 and 1016.63 cm−1, which were due to the presence of aliphatic amine C-N and amide bonds, revealing the immobilisation of Urs on functionalised NPs. Moreover, X-ray photoelectron spectroscopy (XPS) analysis showed changes in binding energy (eV) before and after immobilisation with Urs, with peaks at 131 eV and 170 eV representing phosphate and sulphur, respectively, from the Urs enzyme. Approximately 85.8% of Urs were successfully immobilised covalently on the larges surface areas of the NPs, enabling greater enzyme loading for the potential development of urea biosensors.