An efficient and rapid synthesis route to highly fluorescent copper microspheres for the selective and sensitive excitation wavelength-dependent dual-mode sensing of NADH

Abstract Fluorescent copper microspheres (CMS) with high quantum yield (72.9 %) were synthesized by an efficient, one-pot, and rapid aggression-induced mechanism. The CMS was bright brick-red luminescent under UV light and have shown an excitation independent emission at 670 nm. The emission intensity of CMS was significantly quenched by the addition of nicotinamide adenine dinucleotide (NADH) when excited at 275 nm, providing a linear range with the logarithmic concentration of NADH, suitable for the detection of low concentrations of NADH. Similarly, the emission intensity at 670 nm was enhanced when excited at 340 nm, providing a linear range for NADH determination in the higher concentration. Thus, a dual-mode sensing platform for the determination of NADH was established by utilizing the fluorescent quenching and enhancement properties of NADH over CMS. Addition of other common interfering molecules and ions induced only a meager change in the fluorescent intensity of CMS, suggesting the high selectivity of the sensor. The linear range observed for NADH by exploring the fluorescent quenching properties was from 24.8−575.2 µM (R2 = 0.99) with a L.O.D of 2.4 µM. Meanwhile, the linear range observed for NADH by utilizing the fluorescent enhancing properties was from 625 µM-2.30 mM (R2 = 0.98) with a L.O.D of 322.5 µM.