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Herein, we report a phenylboronic acid functionalized gold nanoparticle (GNP)-based colorimetric assay for rapid detection of Staphylococcus aureus (S. aureus) with high sensitivity. In this approach, GNPs can bind to S. aureus by the reaction of phenylboronic acid with the cis-diol configuration in glycans on the bacterial surface, providing a colorimetric readout of the binding event. Using this strategy, we have been able to quantify S. aureus at a concentration of 50 cells per mL (three times the standard deviation divided by the slope of the working curve) in aqueous solution.

In order to develop a novel high-throughput tool for monitoring carbohydrate-protein interactions, we prepared carbohydrate or glycoprotein microarrays by immobilizing amino modified carbohydrates on aldehyde-derivatized glass slides or glycoprotein on epoxide-derivatized glass slides and carried out lectin binding experiments by using these microarrays, respectively. The interaction events are marked by attachment of gold nanoparticles followed by silver deposition for signal enhancement. The attachment of the gold nanoparticles is achieved by standard avidin-biotin chemistry. The detection principle is resonance light scattering (RLS). The well-defined recognition systems, namely, three monosaccharides (Man-alpha, Glc-beta and Gal-beta) or three glycoproteins (Asf, RNase A and RNase B) with two lectins (ConA and RCA120), were chosen here to establish the RLS assay, respectively. Highly selective recognition of carbohydrate-protein down to 25.6 pg/mL for RCA120 in solution and 8 microM for Gal-beta and 32 ng/mL for Asf on the microarray spots is demonstrated.

To develop a novel high-throughput tool for monitoring specific affinity of microbes with lectins, a kind of lectin microarray has been fabricated by immobilizing lectins on epoxide-derivatized glass slides and used to capture microbes. The capturing events are marked by attachment of lectin-conjugated gold nanoparticles followed by silver deposition to enhance the resonance fight scattering (RLS) of the particles. The interactions of 16 lectins with four bacteria and one fungus were profiled by this approach. We demonstrated that the gold-nanoparticle-labeled array was suitable for identifying the binding affinity of lectin with bacterium, as well as determining the bacterium with high sensitivity. More importantly, we found that the growth of microbial strains in different culture media resulted in significant changes in their binding affinities with lectins, which might be important to the pathogenesis of the organisms.

In this paper, we propose an effective protocol for bacterial detection using antibody microarray-based strategies with gold nanoparticle probes. In this approach, bacteria are captured by immobilized IgGs on the microarray spots. The capturing events are marked by attachment of lectin (e.g. Ricinus Communis Agglutini (RCA) and Concanavalin A (ConA)) conjugated gold nanoparticles followed by silver deposition for signal enhancement. The detection principle is resonance light scattering (RLS). Using this technique, highly selective discrimination of bacterial strain types (i.e., gram-negative, gram-positive and fungus) down to 10(3) cells per assay with a dynamic range of nearly three orders of magnitude are demonstrated. In addition, the capturing process can be inhibited by lipopolysaccharides (LPS), which gives further evidence of the binding mechanism. Furthermore, antibacterial assay with antibacterial drugs (amoxicillin and vancomycin) demonstrates that the approach enables to detect antibacterial efficiency as well as derive MIC (minimum inhibitory concentration) plots.

To develop a novel high-throughput tool for monitoring carbohydrate-protein interactions, carbohydrate or glycoprotein microarrays have been prepared for binding with lectins. The interaction events are marked by attachment of fluorescent dyes and gold nanoparticles. The attachment of the fluorescent dyes and gold nanoparticles is achieved by standard avidin-biotin chemistry. The detection principle is fluorescence or resonance light scattering (RLS). The electroless deposition of silver onto the gold particles has been employed for RLS signal enhancement. Well-defined recognition systems, three monosaccharides (Man-alpha, Glc-beta, and Gal-beta) or three glycoproteins (Asf, RNase A, and RNase B) with two lectins (ConA and RCA120), are chosen here to establish the microarray-based assay, respectively. Highly selective recognition of carbohydrate-protein down to 25.6 pg/mL for RCA120 in solution and 8 microM for Gal-beta and 32 ng/mL for Asf on the microarray spots is demonstrated.

Here, a three-dimensional (3D) carbohydrate microarray-based plasmon resonance light scattering (RLS) assay has been established for studying carbohydrate-lectin binding with high selectivity. The 3D carbohydrate microarray is fabricated by immobilizing amino-modified carbohydrates on the home-made fourth-generation (G4) NH(2)-terminated poly(amidoamine) dendrimers (PAMAM)-modified substrate. After marking the carbohydrate-lectin binding events by 13 nm peptide-stabilized gold nanoparticles through the biotin-avidin reaction, the 3D microarray can be directly detected by the RLS scanner without the conventional silver enhancement step. The well defined recognition systems: three monosaccharides (Man-α, Glc-α and Gal-β) with two lectins (Con A and RCA 120), have been chosen here to establish the RLS assay, respectively. Quantitative determination of the surface dissociation constants (K(D,surf)) for surface carbohydrates and lectins has been achieved. In addition, inhibition values (i.e. the inhibition constants (K(i)) and the concentrations of inhibitors required to produce 50% inhibition (IC(50))) for inhibitors in solution are also demonstrated by the saccharide competing assays.