Tunable plasmonic glucose sensing based on the dissociation of Con A-aggregated dextran-coated gold colloids

We describe a new approach for glucose determination with tunable glucose dynamic sensing ranges, dependent on the properties of new nanosensors, which are comprised of Con A-aggregated dextran-coated gold colloids. Dextran-coated 10 or 20 nm gold colloids can be aggregated with Con A in a controlled fashion, the change in absorbance at an arbitrary wavelength used to monitor the extent of aggregation, which can be optimized for sensing. The presence of any glucose competitively binds with Con A, dissociating the dextran-coated colloids, affording for the reverse gold plasmon change and hence the determination of glucose concentrations. For one of our sensor systems, a 500K dextran-20 nm gold sensor, crosslinked with 8.70 µM Con A, a change in absorbance at 650 nm of 0.03 was observed, in response to as little as 3 mM glucose. In contrast, a 500K dextran-10 nm gold 18.7 µM Con A aggregate sensor, produced a 0.05 and 0.1 change in absorbance, respectively, by the addition of 50 and 100 mM glucose. We have found that the glucose sensing ranges can be somewhat tuned by altering the properties, and therefore the extent of aggregation of the gold aggregate sensors. Reducing the gold colloid size and dextran molecular weight typically reduces the glucose sensing range (lower [glucose]) but also reduces the long-term stability of the gold aggregate sensor. Similarly the concentration of Con A used to aggregate the system also has an effect on long term sensor stability and glucose response. In this paper, we present our findings, which offer unique opportunities and perspectives for building tunable plasmonic type glucose sensors.