Raman spectroscopic imaging of pH values in cancerous tissue by using polyaniline@gold nanoparticles

A core-shell nanocomposite consisting of polyaniline and gold nanoparticles (PANI@AuNPs) is shown to enable intracellular monitoring of pH values by surface-enhanced Raman scattering (SERS) spectroscopy. The method exploits the pH-responsive property of PANI and the SERS-enhancing effect of AuNPs. The intensity of the PANI Raman peak at 1164 cm^-1 decreases on increasing the pH value from 4.6 to 7.4. This is the pH range encountered in normal cells and in cancer cells. The PANI@AuNPs were incorporated into HeLa cancer cells and 5 other kinds of cells for Raman based imaging of pH values. The results show that this pH nanoprobe can be applied for imaging of both normal cells and cancer cells. The core-shell composite was also applied to tissue imaging. In our perception, this core-shell nanoprobe is a valuable tool for imaging pH values of cancerous tissue. Graphical abstract Schematic presentation of a core-shell nanocomposite, polyaniline@gold nanoparticle, which was synthesized via a rapid method. With the pH of solution changing from alkaline to acidic, the polyaniline can change from emeraldine base (EB, blue shell) transition to emeraldine salt (ES, green shell) transition. Due to the pH-responsive property of polyaniline combined with the surface-enhanced Raman scattering spectroscopy effect of AuNPs. The polyaniline@gold nanoparticles were successfully applied as an intracellular pH probe.