Induced pH-dependent shift by local surface plasmon resonance in functionalized gold nanorods

Localized surface plasmon resonance (LSPR) spectroscopy of metallic nanoparticles is a powerful tool for chemical and biological sensing experiments. In this study, we observed LSPR shifts of 11-mercaptoundecanoic acid modified gold nanorods (GNR-MUA) for the pH range of 6.41 to 8.88. We proposed a mechanism involving changes of the dipole moment after protonation/deprotonation carboxylic groups of 11-mercaptoundecanoic acid (MUA) which plays an important role by modulating LSPR around the functionalized GNR. Such a stable and easily prepared GNR-MUA has potential to become one of the most efficient and promising pH nanosensors to study intra- or extra-cellular pH in a wide range of chemical or biological systems.