Blue‐green emission of pepsin‐stabilized copper nanoclusters ultrafast detection of hemoglobin in human urine

Abstract This work proposed a straightforward synthesis of copper nanoclusters (CuNCs) with an emission wavelength of 496 nm and a quantum yield of 2.2% by directly using pepsin as a template with low toxicity NaBH4 and ascorbic acid as reducing agents. The chemical composition and optical properties of the pepsin‐stabilized CuNCs (pepsin‐CuNCs) were well‐characterized by spectroscopy‐related techniques. The pepsin‐CuNCs retained the fluorescence intensity at neutral pH, at 37°C, and in high salinity, proving their suitability in biological systems. Although the pepsin‐CuNCs remained only half of the initial fluorescence intensity after 24 days due to air oxidation, their storage stability was comparable to that of CuNCs reported in the literature. Given that the absorption peaks of hemoglobin overlap the excitation and emission wavelengths of pepsin‐CuNCs, this feature allowed pepsin‐CuNCs to serve as a luminescence turn‐off sensor for sensing hemoglobin through the inner‐filter effect process. The pepsin‐CuNC probe provided a fast (within 1 min) platform for hemoglobin detection with a dynamic quantitative range of 0.1–10 μM and a detection limit of 70 nM. Importantly, the proposed probe was well‐suited to detect hemoglobin in nearly undiluted human urine, demonstrating its great potential for the clinical diagnosis of trace hemoglobin in urine.