Preparation and characterisation of a stable silver colloid for SER(R)S spectroscopy

Abstract

A method for the reproducible preparation of a silver colloid with strong surface-enhanced Raman scattering (SERS) properties, good stability with a zeta potential of À55 mV and a shelf life exceeding 1 year is reported. The mean particle size is 20 nm with a narrow size distribution of 10-30 nm. The colloid is produced by the reduction of silver nitrate with hydroxylamine phosphate to give a negatively charged phosphate surface on the silver particles. This is an ultrafast room temperature reaction and with controlled rapid addition and dispersion of reagents, very reproducible batches of colloid can be prepared making it suitable for commercial applications of Surface enhanced resonance Raman scattering(SER(R)S) spectroscopy. The stability of the colloid is attributed to the extremely low solubility product (K sp ) of silver phosphate. Characterisation and stability study data for this colloid have been obtained by ultraviolet-visible spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, particle size analysis and SERS analyses using a 514 nm laser on a Raman spectrometer. A SERS method to detect and to identify riboflavin in a vitamin B complex tablet is reported to illustrate a SERS application based upon the use of this silver colloid.

Effect of phosphate buffer on aggregation kinetics of citrate-coated silver nanoparticles induced by monovalent and divalent electrolytes

“…In other words, NaNO 3 is more efficient in aggregating cit-AgNPs at higher buffer concentration than at lower buffer concentration. The increased cit-AgNPs aggregation with the increased phosphate buffer concentration is presumably due to the sorption of phosphate anions on the surface of AgNPs 52 , resulting in increased reduction of AgNP surface charge at higher buffer concentrations (see discussion below).…”

“…Cit-AgNPs are negatively charged without any buffer (zeta potential of -41.7±2.0 mV). The addition of phosphate anions results in a decrease in the zeta potential of cit-AgNPs, which can be attributed to the sorption/complexation of the phosphate anions on AgNP surfaces, 52,53 due to the high affinity of phosphate anions to silver (K sp = 8.89 x 10 -17 M). 54 The zeta potential of cit-AgNPs decreases rapidly at low buffer concentrations (ca.…”

“…Phosphate anions can replace the citrate coating and bind to the NP surface through its oxygen atoms, resulting in phosphate coated AgNPs. 52 Aggregation of phosphate coated AgNPs takes place through physical surface charge screening by counter ions (Na + and Ca 2+ ) according to DLVO theory. 7…”

Rapid detection of 2,2′,4,4′‐tetrabromodiphenyl ether (BDE‐47) using a portable Au‐colloid SERS sensor

“…Surface‐enhanced Raman scattering (SERS) provides a rapid and efficient platform for chemical analysis due to the explosive development in nanofabrication . Compared with the traditional chromatographic methods, SERS can selectively identify single component in complex matrices due to the specific close contact between the analyte and noble metal nanoparticles (NPs).…”

“…Surface-enhanced Raman scattering (SERS) provides a rapid and efficient platform for chemical analysis due to the explosive development in nanofabrication. [2,3] Compared with the traditional chromatographic methods, SERS can selectively identify single component in complex matrices due to the specific close contact between the analyte and noble metal nanoparticles (NPs). Unfortunately, the hydrophobic nature of polycyclic aromatic hydrocarbons, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers prevents their approach to the metallic nanostructure.…”