Study on the kinetics of homogeneous enzyme reactions in a micro/nanofluidics device

In this paper, a micro/nanofluidic preconcentration device integrated with an electrochemical detector has been used to study the enrichment of enzymes and homogeneous enzyme reaction kinetics. The enzymes are first concentrated in front of a nanochannel via an exclusion-enrichment effect (EEE) mechanism of the nanochannel integrated in a microfluidics device. If a substrate is electrokinetically transported to the concentrated enzymes, homogeneous enzymatic reaction occurs. The enzymatic reaction product can penetrate through the nanochannel to be detected electrochemically. In this device, the enriched enzymes can be well retained and repeatedly used, thus, the enzymatic reaction occurs in a continuous-flow mode. For demonstration, Glucose oxidase (GOx) was chosen as the model enzyme to study the influence of enzyme concentration on its reaction kinetics. The different concentration of GOx in front of the nanochannel was simply achieved by using different enrichment time. When substrate glucose was introduced electrokinetically, a rapid electrochemical steady-state response could be obtained. It was found that the electrochemical response to a constant glucose concentration increased with the increase of enzyme enrichment time, which is expected for homogeneous enzymatic reactions. Under proper conditions, the electrochemical responds linearly to the glucose concentration ranging from 0 to 15 mM, and the Michaelis constants (Km) are relatively low, which indicates a more efficient complex formation between enzyme and substrate. These results suggest that the present micro/nanofluidics device is promising for the study of enzymatic reaction kinetics and other bioassays such as cell assays, drug discovery, and clinical diagnosis.