title: Synthesis of fluorescent carbohydrate-protected Au nanodots for detection of Concanavalin A and Escherichia coli.
abstract: 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).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 8.6%, 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 = 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) = 0.96), with the LOD of E. coli being 7.20 x 10(5) cells/mL.
authors.affiliation: Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan.
authors.forename: Chih-Ching
authors.initials: CC
authors.lastname: Huang
authors.forename: Chao-Tsen
authors.initials: CT
authors.lastname: Chen
authors.forename: Yen-Chun
authors.initials: YC
authors.lastname: Shiang
authors.forename: Zong-Hong
authors.initials: ZH
authors.lastname: Lin
authors.forename: Huan-Tsung
authors.initials: HT
authors.lastname: Chang
mesh_terms: D015374:Biosensing Techniques; D003208:Concanavalin A / Q000032:analysis*; D004926:Escherichia coli / Q000302:isolation & purification*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008358:Mannose / Q000138:chemical synthesis / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D003208:Concanavalin A; D006046:Gold; D008358:Mannose