Biological pH sensing based on the environmentally friendly Raman technique through a polyaniline probe.

The biological pH plays an important role in various cellular processes. In this work, a novel strategy is reported for biological pH sensing by using Raman spectroscopy and polyaniline nanoparticles (PANI NPs) as the pH-sensitive Raman probe. It is found that the Raman spectrum of PANI NPs is strongly dependent on the pH value. The intensities of Raman spectral bands at 1225 and 1454 cm-1 increase obviously with pH value varying from 5.5 to 8.0, which covers the range of regular biological pH variation. The pH-dependent Raman performance of PANI NPs, as well as their robust Raman signals and sensitivities to pH, was well retained after the nanoparticles incorporated into living 4T1 breast adenocarcinoma cells. The data indicate that such PANI NPs can be used as an effective biological pH sensor. Most interestingly, the PANI spherical nanostructures can be acquired by a low-cost, metal-free, and one-pot oxidative polymerization, which gives them excellent biocompatibility for further biological applications.