Localized surface plasmon resonance effect of 3-mercaptopropionic acid capped on silver nanoparticles for sensing probe application

Abstract

Metal nanoparticles such as gold and silver are often used in various nanotechnology applications due to the localized plasmon resonance effect that occurs when incident photons interact with metal nanoparticles. 3-mercaptopropionic acid (3-MPA) is one of the capping molecules that can be provided for surface functionalization on gold or silver core because it has thiol and carboxylic group as a linking biomolecule, and this allows the use of nanoparticles for biosensor applications. In this study, we successfully synthesized silver nanoparticles capped by 3-mercaptopropionic acid (AgMPA) by use of two kinds of methods i.e ligand exchange and direct reduction, which reveal the unique characteristic plasmonic peaks of AgNP around 430 nm and 436 nm, respectively with spherical shape of AgNP and diameter size about 6-20 nm. The transmittance spectra from Fourier Transform Infrared (FTIR) measurement shows that S-H coordination from 3-MPA is invisible after 3-MPA attach on Ag core due to the strong coordination between Ag and the sulfur (S) ion, while the broaden peaks at 1589 and 1385 cm-1 for AgMPA are assigned to asymmetric and symmetric vibrations of carboxylate groups which overlap between carboxylate from citrate and 3-MPA. Finally, the colorimetric detection using AgCA and AgMPA as sensing probe was carried out by use of Biocytin-Avidin system molecule as analyte, which resulted in the colour changed rapidly from yellow to transparent-yellow and the red-shifted of absorbance spectra indicating the attachment of analyte to functionalized molecule of our synthesized AgCA and AgMPA.