Localized Surface Plasmon Resonance Effect of Gold Nanoparticles Using 3-Mercaptopropionic Acid as Capping Material for Sensing Probe

Gold nanoparticles (AuNP) has been used in a wide range of applications especially in medicine and optoelectronic applications due to its localized surface plasmon resonance (LSPR) effect. LSPR observation of AuNP solution shows that the plasmonic peak in the absorbance spectra lies in the range of visible light around 520 nm with deep red-wine color. The optical characteristic is controlled by the size and shape of the nanoparticles including its surface functionalization. Our research is focused on the adsorption study of 3-mercaptopropionate (3-MP) on AuNP (AuMP) surface synthesized by ligand exchange method and also by direct reduction method. The characterizations are conducted by use of UV-vis and FTIR spectroscopies in order to investigate the effect of LSPR. The absorbance spectra show that both experimental methods of AuMP give a similar profile of red-shifted in the plasmonic peaks in comparison to that of citrate-capped AuNP as a reference from 519 nm to 520 nm. The ligand exchange method of AuMP synthesis results in an unstable colloidal solution after being stored for a week at room temperature while the reduction method results in a stable colloidal solution of AuMP even though it has been stored for 2 months. The FTIR spectra show the difference in vibrational peak intensities between the 3-MP on AuNP and the 3-MPA as reference. The peak of carboxylate (COO-) asymmetric stretching is shifted to low frequency from 1708 cm -1 to 1632 cm -1 indicate the effect of LSPR while the shift to high frequencies for some vibrational peak intensities relates to the strong effect of chemical coordination between gold and capping material. The simulation of the vibration energy by use of the Density Functional Theory (DFT) method shows a similar tendency to that of the peak intensities along the infrared spectrum from experimental results.