A PDMS viscometer for assaying endoglucanase activity

A poly(dimethylsiloxane) (PDMS) viscometer was developed to analyze the activity of endo-β-1,4-glucanases (EC3.2.1.4) on hydrolyzing sodium carboxymethylcellulose (NaCMC). In the viscometer, a PDMS pump was used as the vacuum source to drive the fluid flow in the PDMS microchannel. The numerical simulation by COMSOL suggested that the vacuum level of the PDMS pump increased during the viscosity measurement. The increasing vacuum level of the PDMS pump allowed more stable fluid flow than the constant vacuum of the conventional vacuum pump. By monitoring the fluids traveling in the microchannel, the viscosity of the endoglucanase-NaCMC solution was derived at different reaction times. The non-Newtonian behavior of the NaCMC solution was studied to ensure that the viscosity measurement was performed in the Newtonian range. A protocol was established to convert the viscometric activity to the activity of standard international units with Almin's method. The PDMS viscometer required only 20 μL sample for the endoglucanase assay and the results were in good agreement with the results from Ubbelohde viscometers.