Accurate measurements of intracellular pH are of crucial importance in understanding the cellular activities and in the development of intracellular drug delivery systems. Here we report a highly sensitive pH probe based on a fluorescein-conjugated Au22 nanocluster. Steady-state photoluminescence (PL) measurements have shown that, when conjugated to Au22, fluorescein exhibits more than 160-fold pH-contrasting PL in the pH range of 4.3-7.8. Transient absorption measurements show that there are two competing ultrafast processes in the fluorescein-conjugated Au22 nanocluster: the intracore-state relaxation and the energy transfer from the nonthermalized states of Au22 to fluorescein. The latter becomes predominant at a higher pH, leading to dramatic PL enhancement of fluorescein. In addition to the intrinsically low toxicity, fluorescein-conjugated Au22 nanoclusters exhibit high pH sensitivity, wide dynamic range, and excellent photostability, providing a powerful tool for the study of intracellular processes.
Bibliographical noteFunding Information:
D.L. acknowledges support by the Korea CCS R&D Center (KCRC) Grant (NRF-2014M1A8A1074219) and NRF Grants NRF-2017R1A2B3006651 and NRF-2009-0093823. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of science, office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry