Unique Energy Transfer in Fluorescein-Conjugated Au22 Nanoclusters Leading to 160-Fold pH-Contrasting Photoluminescence

Kyunglim Pyo, Nguyen Hoang Ly, Sang Myeong Han, Mohammad Bin Hatshan, Abubkr Abuhagr, Gary Wiederrecht, Sang Woo Joo, Guda Ramakrishna, Dongil Lee

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)5303-5310
Number of pages8
JournalJournal of Physical Chemistry Letters
Issue number18
Publication statusPublished - 2018 Sept 20

Bibliographical note

Funding 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.

Publisher Copyright:
© 2018 American Chemical Society.

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Physical and Theoretical Chemistry


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