Developing a label-free full-range highly selective pH nanobiosensor using a novel high quantum yield pH-responsive activated-protein-protected gold nanocluster prepared by a novel ultrasonication-protein-assisted procedure.

A novel, label-free, ultra-selective, reproducible, and reversible pH nanobiosensor was developed for analyzing biofluids, food samples, and real water media utilizing a novel activated-protein-protected gold nanocluster with an ultra-narrow emission band, termed as ABSA-AuNCs. The ABSA-AuNCs were synthesized via a novel ultrasonication-protein-assisted procedure, for the first time, using activated bovine serum albumin as both capping and reducing agents. The ABSA-AuNCs revealed a highly narrow symmetric emission spectrum (λ = 330.0 nm upon excitation at 312-317 nm), and a highly narrow size distribution of 2.9-3.7 nm along with an enhanced quantum yield of 28.3 %. At present, with a full width at half maximum (FWHM) of 14.0 nm, ABSA-AuNCs have the narrowest bandwidth of fluorescent nanomaterials reported to date. The ABSA-AuNCs were characterized for their stability, size, morphology, crystallinity, structural, and optical properties. The ABSA-AuNCs were found to be appropriate for constructing a label-free ultraselective pH nanobiosensor. A linear range over 2.0-11.0, fast response time of less than 5 s, and long-term stability of 99.7 % after 500 min were achieved. The %RSD for repeatability, intra-day reproducibility, and inter-day reproducibility was found to be 1.4 %, 1.7 %, and 2.3 %, in order, to reveal high repeatable and reproducible results. The selectivity of the pH biosensor was evaluated upon the addition of different interferents, indicating an excellent pH selectivity for the ABSA-AuNCs. Real sample analysis proved the feasibility of the ABSA-AuNCs for accurate, precise, and reliable pH sensing in biofluids (undiluted blood and urine), a variety of food samples, and several real water samples.