Post-Stress Thickening of Dextran/Concanavalin A Solutions Used as Sensitive Fluids in a Viscosimetric Affinity Assay for Glucose

Abstract

Glucose-dependent low-stress and high-stress rheology of a sensitive fluid (SF) containing high-molecular-weight dextran (30 g/L) and Concanavalin A (ConA, 10 g/L) was studied to define conditions for reproducible glucose determination by a viscosimetric sensor. The viscosity of the investigated SF was reproducibly glucose-dependent only at sufficient shear stresses (>0.5 Pa). Rheometric parameters measured at low stresses (<0.1 Pa) were strongly dependent on the shear history. Low-stress viscosity measured after laminar flow with a high rate (90 s, 100 s -1 , 4.5 Pa) increased by more than 2 orders of magnitude with slow kinetics. Solutions thickened after laminar flow acquired gel-like properties (storage modulus nearly equal to loss modulus in a broad range of frequencies). The highly viscous and gel-like state developed after flow was stable up to a yield stress of ca. 0.05 Pa. The ConA-mediated contribution to high-stress viscosity was almost completely suppressed by the presence of glucose (100 mM), whereas thickening after flow was rather insensitive to the competing sugar. Interaction of diffusion-controlled ligand exchange at the ConA binding sites with convective displacement of dextran molecules has been considered a main reason for the observed thickening effect. It is proposed that the shear field has an orientating effect on lectin distribution in the dextran matrix, whereby far-reaching lamellar affinity clusters are developed. In the subsequently unloaded fluid, residues of these structures can reorientate and be cross-linked to a weak metastable gel by redistributing ConA.

A Capacitive MEMS Viscometric Sensor for Affinity Detection of Glucose

“…In particular, methods that use equilibrium affinity binding of glucose have shown great promise [5]–[8]. These methods, in which glucose is not consumed, do not carry the risk of interfering with the local glucose concentration in the tissue or generating erosive reaction products.…”

Compensation of Temperature and Concanavalin A Concentratration Effects for Glucose Determination by the Viscometric Affinity Assay

“…The contribution of the affinity bonds to the viscosity of the SL is resistant to a shear stress larger than 1500 Pa (Figure 5), which could not be tested with the precision rheometer used in our earlier study (8). The high glucose sensitivity of F r at strongly increased shear stress demonstrates that the tendency stated previously (8) is continued in the range of high shear forces. The dextran/ConA solution shows less shear‐thinning in the absence of the sugar than in its presence, since the sugar destabilizes the cross‐links between dextran molecules of neighboring shear planes.…”

“…As a result of the strong modulation of the viscosity by ConA and glucose, a simple test based on the use of glass capillaries was sufficient to demonstrate the potency of the viscometric affinity assay and to describe the principle course of the characteristic curves of the lectin and the sugar (7). A rheologic study (8) showed that the sugar effect on the shear viscosity of the SL is reproducible at sufficient shear stress (1−100 Pa), whereas viscosity measured at very low shear stress (<0.2 Pa) is strongly dependent on prior shear treatments.…”

UV Cross-Linked Dextran Methacrylate—Concanavalin A Methacrylamide Gel Materials for Self-Regulated Insulin Delivery

“…Addition of free glucose displaces the polysaccharide reversibly from the con A receptor sites, dismantling the connections, and producing a sol. The rheology of the material is dependent on the glucose content and has been described previously (Beyer, Ehwald, & Fleischer, 1997). Variations are documented in which the polysaccharide has been replaced by semisynthetics such as polysucrose and glucosesubstituted acrylics (Valuev, Chupov, Stayton, & Plate, 1997).…”