Optical urea biosensor based on polyelectrolyte complex (PEC) pectin-chitosan membrane and anthocyanin from Catharanthus roseus L for a salivary simple urea detection

This work aimed to fabricate an optical urea biosensor using anthocyanins extracted from the Catharanthus roseus L as pH-sensitive substances and immobilised on a polyelectrolyte complex (PEC) pectin-chitosan membrane. The PEC pectin-chitosan/anthocyanin system's first layer is an optical pH sensor optimised in previous research. Then, the optimised pH sensor was further modified as an optical urea biosensor by immobilising the urease as the second layer. The biosensor relied on pH changes resulting from the reaction between urease and urea. The best sensitivity was observed at 0.09 mg urease, the optimum response was obtained at 0.03 M phosphate buffer solution of pH 7, and the stability was achieved after 5 min of measurement. The sensitivity reached at the widest dynamic range of urea concentration (1 x 10-10 to 1 x 10-1 M) was 0.0218 with a detection limit of 5.2 x 10-12 M. The optimised urea biosensor has repeatability with a percentage relative standard deviation of 10.2 %. The lifetime was evaluated for 30 days of measurements, where fluctuation in sensor sensitivity was observed.