The Dynamic Single-Cell Intracellular pH Sensing by a SERS-Active Nanopipette
Glass nanopipette has shown promise in applications for single-cell manipulation, analysis, and imaging. In recent years, plasmonic nanopipette has been developed for single-cell analysis to take the advantage of surface-enhanced Raman spectroscopy (SERS) measurement. In this work, we developed a SERS-active nanopipette that can perform long-term and reliable intracellular analysis of single living cell with minimal damage, which is achieved by optimizing the nanopipette geometry and the surface density of gold nanoparticle (AuNP) layer at the nanopipette tip. To demonstrate its capability in single-cell analysis, we have applied the nanopipette for intracellular pH sensing. Intracellular pH (pHi) is vital to cells as it influences cell functions, behaviors and pathological conditions. The pH-sensitivity was realized by simply modifying the AuNP layer with pH reporter molecule 4-Mercaptobenzoic acid. With a response time of less than 5 seconds, the pH sensing range is from 6.0 to 8.0 and the maximum sensitivity is 0.2 pH units. We have monitored the pHi change of individual HeLa and Fibroblast cells, triggered by the extracellular pH (pHe) change. The HeLa cancer cell can better resist pHe change and adapt to the weak acidic environment. The plasmonic nanopipette can be further developed to monitor other intracellular biomarkers.