THE EFFECT OF PURIFICATION PROCESS ON COLOIDAL GOLD AND SILVER CAPPED BY ORGANIC MATERIALS AND ITS APPLICATION AS PLASMONIC BIOSENSOR Azza Azahra Ronald(a), Dinta(a), Setiya Rahayu(a), Herman (a), and Priastuti Wulandari(a*)
a) Physics of Magnetism and Photonics Research Division, Bandung Institute of Technology, Bandung, Indonesia
*pwulandari[at]itb.ac.id
Abstract
Nanotechnology is rapidly advancing, particularly in the use of gold (AuNPs) and silver nanoparticles (AgNPs) for biosensor applications. These metal nanoparticles exhibit localized surface plasmon resonance (LSPR), enabling strong light absorption and scattering at specific wavelengths based on size, shape, and environment, making them highly sensitive probes for biosensing applications. Capping agents such as citrate are commonly used to prevent nanoparticle aggregation and to facilitate further functionalization. In our study, we attempt to develop stable colorimetric biosensor probes based on AuNPs and AgNPs capped by citrate. Nanoparticles were synthesized via a chemical reduction method and purified through high-speed centrifugation to remove excess ions and unreacted substances. Characterization was conducted by used of Ultraviolet-Visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, and Transmission Electron Microscopy (TEM). The results show the appearance of plasmonic peaks at 522 nm for citrate capped Au (AuCA) with a red-wine color, while citrate capped Ag (AgCA) exhibits peak at 426 nm with a brownish-yellow color. FTIR analysis reveals distinct chemical interactions between capping agent and metal surfaces. In our experiment, the optimum speed and time of centrifugation process for purification of our synthesized nanoparticles are 8000 rpm and 20 min of time duration for AuCA, while 8000 rpm and 10 min of time duration for AgCA. TEM images confirm homogeneous and stable distribution of both nanoparticles after purification with average nanoparticle diameters are 15.1 nm for AuCA and 38.4 for AgCA. Colorimetric assays indicate aggregation through spectral shifts of plasmonic peaks in both AuCA and AgCA upon avidin-biotin interaction. However, in our experiment the visual detection of color changes in the colloidal solutions are not clearly visible.
