Sensing pH of individual microdroplet by combining SERS and indicator paper

Kedong Gong, Robin Raffe Jones, Kejian Li, Guanjun Xu, Hanyun Cheng, Yiqing Feng, Ventsislav Kolev Valev, Liwu Zhang

Research output: Contribution to journalArticlepeer-review

8 Citations (SciVal)


Microdroplets present unique physiochemical properties, which can influence chemical reactions and atmospheric aerosol processes. The microdroplets’ pH is one of the most important factors that dictate chemical processes, such as heterogeneous and condensed reactions. However, currently, there is no well-established method for directly measuring the pH in microdroplets. Herein, we develop a straightforward method, for the first time, to directly measure the pH of size-resolved, micron-sized single droplets with Surface Enhanced Raman Scattering (SERS)-activated pH-indicator paper; realized by embedded Au nanoparticles (20, 40 and 60 nm). We establish the key parameters for optimizing the method, and demonstrate its accuracy by benchmarking various acids and solutions with different ionic strength. With the established method, we report the pH dependence on the size of microdroplets. Microdroplets of sizes down to 230 nm can be analyzed by our method. We also showcase our method's applicability to ambient samples, establishing its promising potential beyond the laboratory environment.

Original languageEnglish
Article number130521
JournalSensors and Actuators B: Chemical
Early online date30 Jul 2021
Publication statusPublished - 1 Nov 2021


  • pH measurement
  • Plasmonics
  • Raman spectroscopy
  • SERS
  • Single microdroplet

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry


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