Highly fluorescent copper nanoclusters as a probe for the determination of pH

A simple, one-pot synthetic route was developed for the preparation of green-emitting and pH-responsive Cu nanoclusters (NCs). The Cu NCs were obtained using cysteine (Cys) as both the reducing agent and the capping agent under alkaline conditions at room temperature. The Cu NCs were characterized using spectroscopic and microscopic techniques and exhibited excellent water solubility, ultrasmall size, good dispersion, bright fluorescence and good photostability. Moreover, the Cu NCs were stable even in a high ionic strength medium such as 1M NaCl. Interestingly, the Cys-Cu NCs showed an intrinsically reversible response toward pH change in the range 4-10, and thus can be utilized as an effective and reversible pH indicator.