Development of a SERS-active pH nanosensor
The merging of the molecular specificity of Raman spectroscopy with the extraordinary optical properties of metallic nanoparticles settled the basis of the so-called Surface Enhanced Raman Spectroscopy (SERS), which in the last few decades proved its worth as powerful analytical tool with detection limits improved to the single molecule recognition.
The study here proposed is aimed to the development of a SERS-based pH nanosensor made up of gold nanoparticles (AuNPs) conjugated with the pH-sensitive molecular probe 4-mercaptobenzoic acid (4MBA), a benzene derived consisting of a thiol group, which covalently binds to the AuNPs surface, and a carboxylic acid. The SERS band of such probe show a strong sensitivity to the pH of the environment, depending on the protonation degree of the carboxyl.
Primarily, the functionalization procedure will be optimized in order to obtain a stable sensor with a high coverage of 4MBA on the AuNPs. The dynamic range of sensitivity of the nanosensor will be identified by SERS measurements in liquids for different pH and a calibration curve will be provided in terms of the relative intensity of selected pH-dependent SERS bands. The possibility to tune the working point of the nanosensor will be further explored by employing nanoparticles of different sizes and material.
Our approach will enable to obtain a versatile tool for the evaluation of the pH on the nanoscale, showing a great potential for biological measurements at the single cell level.