VOLUME 6 NUMBER 1 (January to June 2013)

by Alan Rodelle M. Salcedo* and Fortunato B. Sevilla III

Research Center for the Natural and Applied Sciences
University of Santo Tomas, España, Manila, Philippines

Citrate-capped gold nanoparticles were prepared bychemical reduction of HAuCl₄ using citrate as thereducing agent and stabilizer. The synthesizednanoparticles showed an intense localized surfaceplasmon resonance absorption band at 520nm.Uniformly distributed spherical gold nanoparticles with averageparticle diameter size of 12.2±1.65nm were verified throughTransmission Electron Microscopy (TEM) analysis. The stabilityof the gold nanoparticles was affected by pH and Cu²⁺.Aggregates are formed at pH < 3 due to surface chargeneutralization of the citrate-capped gold nanoparticles. WithCu²⁺, aggregation is being initiated at a certain concentration.Visual observations, UV-Vis spectroscopy and TEM analysiswere used to characterize the aggregated system. At optimumparameters (i.e., wavelength, reaction time, and pH), acalibration curve for Cu²⁺ determination was constructed. Thecalibration curve has good linearity (r²=0.9822) and sensitivityof 0.0036 A.U./mM for the linear range from 2.5mM to 100mM.Reproducible absorbance readings (r.s.d.= 1.56-6.15%, n=6) forthe linear concentration range of 2.5mM to 100mM wereobtained. The detection limit for Cu²⁺ determination method is5.0 mM.