Abstract An environment-friendly method is used to prepare lysozyme coated fluorescent copper nanoclusters (CuNCs) of size 2.87 ± 0.09 nm as obtained from the transmission electron microscopy. The CuNCs show UV–vis absorption at around 365 nm and the corresponding fluorescence emission is obtained at around 449 nm. X-ray photoelectron spectroscopy study confirms that the valency of the prepared CuNCs lies between 0 and + 1. The pH dependent fluorescence emission behaviour of as-synthesized ultra-small CuNCs is studied in buffer solution within the pH range, approximately from 2.5 to 7.5. The CuNCs show excellent stability in the whole pH range and show highly reversible emission behaviour with pH variation. For having such superior property, the lysozyme coated CuNCs can be used as a potential candidate for pH sensing. Fourier transformed infrared spectroscopy study confirms that the structural modification of lysozyme protein is responsible for showing such reversible optical behaviour. The mechanism of such reversible emission behaviour with pH variation is also proposed.

中文翻译：

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溶菌酶包覆的荧光铜纳米团簇的 pH 依赖性可逆发射行为

摘要 采用一种环境友好的方法制备了溶菌酶包被的荧光铜纳米团簇（CuNCs），其尺寸为 2.87 ± 0.09 nm，由透射电子显微镜获得。CuNCs 在约 365 nm 处显示出紫外-可见吸收，并在约 449 nm 处获得相应的荧光发射。X 射线光电子能谱研究证实，所制备的 CuNCs 的化合价介于 0 和 + 1 之间。在 pH 值范围内（大约从 2.5 到 7.5）的缓冲溶液中研究了合成的超小 CuNCs 的 pH 依赖性荧光发射行为. CuNCs 在整个 pH 范围内表现出优异的稳定性，并且随着 pH 的变化表现出高度可逆的发射行为。由于具有如此优越的性能，溶菌酶包被的 CuNCs 可用作 pH 传感的潜在候选者。傅里叶变换红外光谱研究证实，溶菌酶蛋白的结构修饰是显示这种可逆光学行为的原因。还提出了这种随 pH 变化的可逆发射行为的机制。