Surfactant-assisted electroless deposition of silver nanoparticles on Ge crystal for ultra-sensitive detection by surface-enhanced infrared absorption spectroscopy

Abstract

Silver nanoparticles (AgNPs) were electrolessly grown on Ge crystal to form substrate for ultra-sensitive detection by surface-enhanced infrared absorption (SEIRA) measurements. To effectively control the morphology of AgNPs, a surfactant-assisted electroless deposition method was proposed in this work. By addition of surfactant into the reaction solution, both reaction rate and behavior in agglomeration of AgNPs were significantly altered. To explore the role of surfactants, three types of surfactants were studied; cationic, anionic and Zwitterionic surfactants. Among them, cationic surfactant of cetyl trimethyl ammonium bromide (CTAB) showed best SEIRA effect as a labile interaction exists between the amine group in CTAB and the formed AgNPs. Also, the hydrophobic long tail of CTAB effectively protects the AgNPs from serious agglomeration. For Zwitterionic surfactants of amino acids, the polar groups on both ends caused severe percolation of AgNPs. With a strong interaction to AgNPs, anionic surfactant of sodium dodecyl benzene sulfonate (SDBS) regulated the AgNPs into a square shaped crystal, which resulted a distortion of infrared absorption band. Based on the obtained results, the substrates prepared with the optimal condition found in this work were at least 5 times higher than that of conventional electroless deposition method. The overall increase of the infrared absorption falls in a range between 300 to 400 times.