Signal Amplification of a Gravimetric Glucose Biosensor Based on the Concanavalin A–Dextran Affinity Assay

The mass and viscoelastic properties associated with the binding of the Concanavalin A (Con A) - dextran (M
_w
= 80 kDa) affinity assay as a function of glucose concentration, was investigated using a quartz crystal microbalance (QCM). The Con A was immobilized on the gold-coated QCM surface using a thiol linker molecule, resulting in a densely packed layer monitored by cyclic voltammetry. The resulting mass change (Am) from the immobilization of Con A ranged from 0.35 to 0.45 ± 0.09 μg cm
^-2
depending on the viscoelastic properties of the lectin layer. The subsequent mass change from the interaction with dextran (0.16 ± 0.04 μg cm
^-2
) suggests that the polysaccharide also stacks in a well-packed layer, which dissociatesin the presence of glucose (2 - 40 mM) due to competitive binding with the monosaccharide to Con A. A maximum frequency change of 10 ± 2 Hz observed in the presence of 40 mM glucose, suggests that the system has a resolution equivalent to the noise baseline of ± 0.4 mM. Cyclic tests demonstrated that the assay is reversible with time, exhibits a higher sensitivity at lower glucose concentrations, but with a relative signal magnitude that decreases for each cycle. The system was also sensitive for solution or temperature induced viscosity changes that requires compensation by an appropriate algorithm or an unmodified sensor acting as a reference.reference.