Nanogold-plasmon-resonance-based glucose sensing

Abstract

Noble metal nanoparticles are well known for their strong interactions with light through the resonant excitations of the collective oscillations of the conduction electrons on the particles, the so-called surface plasmon resonances. The close proximity of two nanoparticles is known to result in a red-shifted resonance wavelength peak, due to near-field coupling. We have subsequently employed this phenomenon and developed a new approach to glucose sensing, which is based on the aggregation and disassociation of 20-nm gold particles and the changes in plasmon absorption induced by the presence of glucose. High-molecular-weight dextran-coated nanoparticles are aggregated with concanavalin A (Con A), which results in a significant shift and broadening of the gold plasmon absorption. The addition of glucose competitively binds to Con A, reducing gold nanoparticle aggregation and therefore the plasmon absorption when monitored at a near-red arbitrary wavelength. We have optimized our plasmonic-type glucose nanosensors with regard to particle stability, pH effects, the dynamic range for glucose sensing, and the observation wavelength to be compatible with clinical glucose requirements and measurements. In addition, by modifying the amount of dextran or Con A used in nanoparticle fabrication, we can to some extent tune the glucose response range, which means that a single sensing platform could potentially be used to monitor microM --> mM glucose levels in many physiological fluids, such as tears, blood, and urine, where the glucose concentrations are significantly different.

Fig. 1.

Glucose sensing mechanism: the dissociation of Con A-aggregated dextran-coated gold nanoparticles.

Fig. 2.

Synthetic scheme for the preparation of the dextran-coated gold nanoparticles.

Fig. 3.

Normalized absorbance spectra of dextran-coated gold nanoparticles 500 k (A), 170 k (B), and 64 k (C) in different buffers with the pH varying between 3 and 11.

Fig. 4.

Flocculation parameter versus the pH of the medium.

Fig. 5.

Normalized absorption spectra of 500 k dextran-coated 20-nm nanogold, cross-linked with different concentrations of Con A.

Fig. 6.

Time-dependent change in absorbance at 650 nm for 500 k dextran coated gold nanoparticles (A), 170 k dextran-coated gold nanoparticles (B), and 64 k dextran-coated gold nanoparticles (C) with different initial amounts of Con A.

Fig. 7.

Change in absorbance at 650 nm for 500 k dextran-coated gold nanoparticles: experimental data and the model fit.

Fig. 8.

Maximum change in absorbance at 650 nm for dextran-coated gold nanoparticles versus the concentration of Con A used.

Fig. 9.

TEM images of 170 k dextran-coated 20-nm gold nanoparticles before (A) and after (B) the addition of 110 mM Con A.

Fig. 10.

Time-dependent cumulative change in absorbance at 650 nm for 500 k dextran-coated gold nanoparticles after the addition of glucose (A), Cumulative change in absorbance at 650 nm for 500 k dextran-coated gold nanoparticles versus the concentration of glucose (B).

Fig. 11.

Time-dependent cumulative change in absorbance at 650 nm for 170 k dextran-coated gold nanoparticles after the addition of glucose (A), Cumulative change in absorbance 650 nm for 170 k dextran-coated gold nanoparticles versus the concentration of glucose (B).

Fig. 12.

Time-dependent cumulative change in absorbance at 650 nm for 64 k dextran-coated gold nanoparticles after the addition of glucose (A), Cumulative change in absorbance 650 nm for 64 k dextran-coated gold nanoparticles versus the concentration of glucose (B).

Fig. 13.

Time-dependent change in absorbance at 650 nm for 500 k dextran-coated 10-nm gold nanoparticles and the subsequent reduction in ΔA₆₅₀ by the addition of glucose, i.e., −ΔA₆₅₀.