The effect of variation of reducing agent concentration on optical properties of silver nanoparticles as active materials in surface plasmon resonance (SPR) biosensor

Using chemical reduction methods, silver nanoparticles have been successfully synthesized. As a precursor, silver nitrate (AgNO3) was used and as a reducing agent was trinatrium citrate. In the process of synthesis, there was a variation of concentration of the reducing agent of trinatrium citrate. Optical properties of silver nanoparticles formation and structure in a colloidal solution were studied by using a UV-Vis spectrometer. In this synthesis process, the colloid nanoparticles produced dominated by silver nanoparticle grains since the yellowish color formed in the sample. The UV-Vis spectrometer shows that there is a shift in the spectrum of silver nanoparticles colloidal absorption in the range of 429.01 nm to 433.06 nm for the variation of trinatrium citrate reducing agent concentration to the colloid formation of the silver nanoparticles. A shift in the angle of SPR is observed when a thin silver layer as the active material of the sensor is coated silver nanoparticles. Increasing the concentration of reducing substances of a thin silver nanoparticles films will shifts the angle of SPR. This SPR angle shift sharpens the reflectivity value and changes the surface plasmon wave constants due to changes in the surface plasmon constant which is caused by changes in the dielectric constant of thin silver nanoparticles films. (paper)