Thioglucose-stabilized gold nanoparticles as a novel platform for colorimetric bioassay based on nanoparticle aggregation

• Published in: Colloids and surfaces, B, Biointerfaces Vol. 81; no. 2; pp. 570 - 577
• Main Authors: Watanabe, Shigeru, Yoshida, Kazuma, Shinkawa, Keitarou, Kumagawa, Daisuke, Seguchi, Hideki
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-12-2010
• Subjects: Agglomeration; Binding; Bioassay; Biological Assay - methods; Carbohydrate; Carbohydrates; Colorimetric bioassay; Colorimetry; Colorimetry - methods; Concanavalin A - analysis; Enzyme-Linked Immunosorbent Assay; Glucose - analogs & derivatives; Glucose - chemistry; Gold; Gold - chemistry; Gold nanoparticle; Lectin; Metal Nanoparticles - chemistry; Nanoparticles; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Particle Size; Surface chemistry; Surface Plasmon Resonance; Surface Properties; Thioglucose; Lectin; Carbohydrate; Surface plasmon resonance; Colorimetric bioassay; Thioglucose; Gold nanoparticle
• ISSN: 0927-7765; 1873-4367
• DOI: 10.1016/j.colsurfb.2010.07.061

Gold nanoparticles stabilized with thioglucose (TGlu-AuNPs), which have carboxyl groups on the particle surface as anchoring sites for covalent immobilization of biomolecules, were prepared by the chemical reduction of HAuCl
4 using 1-thio-β-
d-glucose as a reducing and stabilizing agent, and their application to colorimetric bioassay was demonstrated using the carbohydrate–lectin system. p-Aminophenyl α-
d-mannose (Man-NH
2) was covalently attached by a conventional method to the activated carboxyl groups on the TGlu-AuNPs. On addition of Con A to the Man-AuNPs, multiple binding events occurred between Con A and the mannoses immobilized on the particle surface. This Con A-induced aggregation resulted in a significant red shift in local surface plasmon resonance. The binding isotherm showed a sigmoidal curve, indicating cooperativity in the binding of Con A and the Man-AuNPs. In addition, Hill plots showed two nonequivalent binding modes, with the
K
d values for high- and low-affinity binding of 11.3 and 66.5
pM, respectively, which was significantly lower than that for methyl-α-
d-mannose binding to Con A. The enhanced binding affinity between Man-AuNPs and Con A involves the cluster effect of the carbohydrate groups on the AuNPs. A linear correlation curve was obtained in the range 10–100
nM (
R
2
=
0.983). The limit of detection (LOD) for Con A was 9.0
nM in aqueous buffer, which is comparable to that of other conventional methods such as ELISA.