Synthesis of Fluorescent Carbohydrate-Protected Au Nanodots for Detection of Concanavalin A and Escherichia coli

摘要

This study describes a novel, simple, and convenient method for the preparation of water-soluble biofunctional Au nanodots (Au NDs) for the detection of Concanavalin A (Con A) and Escherichia coli (E. coli). First, 2.9 nm Au nanoparticles (Au NPs) were prepared through reduction of HAuCl_(4)(centre dot)3H_(2)O with tetrakis(hydroxymethyl)phosphonium chloride (THPC), which acts as both a reducing and capping agent. Addition of 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-SH) onto the surfaces of the as-prepared Au NPs yielded the fluorescent mannose-protected Au nanodots (Man-Au NDs) with the size and quantum yield (QY) of 1.8 (+-0.3) nm and 8.6percent, respectively. This QY is higher than those of the best currently available water-soluble, alkanethiol-protected Au nanoclusters. Our fluorescent Man-Au NDs are easily purified and by multivalent interactions are capable of sensing, under optimal conditions, Con A with high sensitivity (LOD velence 75 pM) and remarkable selectivity over other proteins and lectins. To the best of our knowledge, this approach provided the lowest LOD value for Con A when compared to the other nanomaterials-based detecting method. Furthermore, we have also developed a new method for fluorescence detection of E. coli using these water-soluble Man-Au NDs. Incubation with E. coli revealed that the Man-Au NDs bind to the bacteria, yielding brightly fluorescent cell clusters. The relationship between the fluorescence signal and the E. coli concentration was linear from 1.00 X 10~(6) to 5.00 X 10~(7) cells/mL (R~(2) velence 0.96), with the LOD of E. coli being 7.20 X 10~(5) cells/mL.