Yegermal Tesfaw Atalay

Design and optimization of a double-enzyme glucose assay in microfluidic lab-on-a-chip.

An electrokinetic driven microfluidic lab-on-a-chip was developed for glucose quantification using double-enzyme assay. The enzymatic glucose assay involves the two-step oxidation of glucose, which was catalyzed by hexokinase and glucose-6-phosphate dehydrogenase, with the concomitant reduction of NADP(+) to NADPH. A fluorescence microscopy setup was used to monitor the different processes (fluid flow and enzymatic reaction) in the microfluidic chip. A two-dimensional finite element model was applied to understand the different aspects of design and to improve the performance of the device without extensive prototyping. To our knowledge this is the first work to exploit numerical simulation for understanding a multisubstrate double-enzyme on-chip assay. The assay is very complex to implement in electrokinetically driven continuous system due to the involvement of many species, which has different transport velocity. With the help of numerical simulation, the design parameters, flow rate, enzyme concentration, and reactor length, were optimized. The results from the simulation were in close agreement with the experimental results. A linear relation exists for glucose concentrations from 0.01 to 0.10 g l(-1). The reaction time and the amount of enzymes required were drastically reduced compared to off-chip microplate analysis.

Computational fluid dynamics model for optimal flow injection analysis biosensor design

This paper presents the optimization of a flow injection analysis (FIA) biosensor with respect to its design and operational parameters such as flow cell geometry, microfluidic channel dimensions, and flow rate. Since it is time consuming and costly to investigate the effect of each factor on the biosensor performance by building it, computational fluid dynamics (CFD) theory is presented as a great tool for finding optimal parameter values. This modeling approach has a high potential in the design of high accuracy FIA-biosensors, regardless of the chosen enzyme substrate system. As an example the optimal design for a glucose/glucose oxidase FIA biosensor is calculated with the CFD theory

Model-based design and optimization of a multiplexed microfluidic biochip for multi-analyte detection

Multiple enzyme assays were systematically performed for simultaneous quantification of sucrose, D-glucose and D-fructose in a single microchannel reactor. The assay was based on optical detection of the reaction product, NADH, formed through a cascade of enzymatic reactions. For design optimization of the system, a model was developed for the microfluidic flow, enzyme kinetics and mass transfer of the different species involved in the analysis. The performance of the device was then optimized using the reduced form of these models in terms of process conditions (reagents volume and flow rate) thereby facilitating biosensor development. The proposed multiplexed device increases throughput and improves user-friendliness compared to equivalent microtiter plate assays. All sugars were quantified within 2.5 min in the optimized microchip based continuous system whereas it took at least two hours in standard microtiter plate analysis. Parallelization can further improve the throughput. In addition, the amount of reagents consumed reduced drastically. For example, the amount of Hexokinase used to detect glucose in 96 well microtiter plates with a total volume of 200 muL was 21.7 ng whereas in the designed microfluidic chip it only required 4.1 ng.