Cu-based metal-organic frameworks-derived copper nanoclusters with tunable emission for ratiometric pH sensing

Copper nanoclusters (Cu NCs) have emerged as promising platform for biosensing, but it remains a challenge to fabricate highly stable Cu NCs with controllable photoluminescence. Herein, we propose a new and elaborate strategy to prepare photoluminescent Cu NCs by using Cu-based metal-organic frameworks (Cu-MOFs) as the precursor. The generated Cu NCs display ordered nanowire structure and superior stability due to the crystal structure of Cu-MOFs. Moreover, the Cu NCs possess unique pH-dependent photoluminescence property. With pH increasing, the yellow-green emission of Cu NCs at 520 nm decreases, and new cyan emission at 455 nm appears and increases gradually. This process might be related to the structure change of the Cu NCs from aggregated nanowire into dispersed spherical particle. On the basis, a facile ratiometric fluorescent sensing platform for pH is fabricated. This ratiometric sensor has great anti-interference capacity and excellent reversibility. In addition, it was successfully applied to monitor the pH of microorganisms, demonstrating the great potential in bioassays. This new synthetic strategy for preparing Cu NCs with tunable emission property may propose new opportunities for their applications.