Measurement of enzyme activity using a plug-based electrochemical microdevice

Determination of the activity of an enzyme in a solution of nL order was conducted using an electrochemical device with a plug-based microfluidic processing function. β-galactosidase (β-Gal) and adenosine triphosphatase (ATPase) were used as analyte enzymes. β-Gal is often used to be conjugated with antibodies, whereas the latter plays critical roles in cell functions. The activity of the enzymes was determined by measuring the concentration of one of the final products, p-aminophenol (PAP) or hydrogen peroxide (H₂O₂) by coulometry. Preparation of plugs of solutions of predetermined volumes and mixing of solutions was carried out using a T-junction on the device. A partially shallow flow channel structure was designed in the sensing area to improve collection efficiency. The observed output charge was correlated well with the amount of PAP or H₂O₂, which served as an indicator of the enzyme activity.