Synthesis and Stability of Fluorescent Gold Nanoparticles by Sodium Borohydride in the Presence of Mono-6-deoxy-6-pyridinium-β-cyclodextrin Chloride

Abstract

Gold nanoparticles in the range of 5−6 nm were synthesized by the reduction of gold(III) chloride trihydrate by sodium borohydride (SBH) in the presence of newly synthesized mono-6-deoxy-6-pyridinium-β-cyclodextrin chloride (p-βCD). NMR, mass spectroscopy, and UV−vis spectroscopy illustrated that SBH would simultaneously reduce both p-βCD and gold salt even though the reduction of the latter occurs more rapidly. Resulting gold nanoparticles were capable of oxidizing the reduced p-βCD, leading to the formation of the p-βCD−gold complex via hydrogen bonding and ionic interaction. Gold nanoparticles were synthesized from a much higher concentration (1.0 mM vs 0.25 mM in the absence of p-βCD) of gold salt and were not susceptible to aggregation by NaCl, phosphate (pH 4−10), acetate, citrate, and borate. The p-βCD−gold nanoparticle assembly displayed intensified fluorescence with emission at 498 nm when excited at 470 nm, a phenomenon known as metal-enhanced fluorescence. The gold nanoparticles acted as electr...