Bovine serum albumin protected Cd8 nanoclusters as efficient two-photon absorbers for near-infrared excited fluorescence imaging of intracellular pH

• Published in: Sensors and actuators. B, Chemical Vol. 394; p. 134427
• Main Authors: Cheng, Yuchi, Zhao, Yu, Yuan, Hao, Zhou, Huangmei, Xu, Jinming, Chen, Xihang, Zhang, Kun, Antoine, Rodolphe, Zhang, Sanjun
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2023; Elsevier
• Subjects: Cadmium nanoclusters; Chemical Sciences; Excited state dynamics; Nonlinear optics; pH sensor; Two-photon excited imaging; Cadmium nanoclusters; Excited state dynamics; Nonlinear optics; pH sensor; Two-photon excited imaging
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2023.134427

Metal nanocluster-based fluorescent sensors have made great progress in the field of analytical chemistry, but their practical applications in biological sensing were limited by poor stability, short wavelength excitation and low quantum yield. It is of great significance to develop NIR-excited metal nanocluster-based fluorescence sensors with high quantum yield. In contrast to noble metal nanoclusters (e.g., Au, Ag, and Pt), stable and affordable fluorescent metal nanoclusters have received relatively less research attention, with the exception for Cu nanoclusters. Herein, we developed a rapid one-pot route to synthesize cadmium nanoclusters employing bovine serum albumin (BSA) as both reducing and templating agent. The obtained Cd8NCs exhibited bright fluorescence emission with quantum yield of 13.8%. Of particular interest, the Cd8NCs showed remarkable capability as two-photon absorbers, with a two-photon absorption (TPA) cross section up to 1588 GM (excited at 730 nm). The TPA cross section was higher than that of BSA-protected AuNCs, and even exceeded that of conventional dyes by two orders of magnitude. In addition, the Cd8NCs exhibited pH-sensitive photoluminescence, and the pH-responsive mechanism was revealed by time-resolved fluorescence spectroscopy, transient absorption spectroscopy, etc. Benefiting from protein coating, Cd8NCs showed excellent biocompatibility and were successfully utilized as two-photon excited fluorescence sensors for intracellular pH. •A novel bright BSA-protected cadmium nanocluster was synthesized.•The two-photon absorption cross section of Cd8NCs was up to 1588 GM.•The pH-dependent excited states dynamics of Cd8NCs was elucidated.•Cd8NCs were used as two-photon excited fluorescent sensors for intracellular pH.