Design and Fabrication of a Fully-Integrated, Miniaturised Fluidic System for the Analysis of Enzyme Kinetics

Abstract

The lab-on-a-chip concept, enabled by microfluidic technology, promises the integration of multiple discrete laboratory techniques into a miniaturised system. Research into microfluidics has generally focused on the development of individual elements of the total system (often with relatively limited functionality), without full consideration for integration into a complete fully optimised and miniaturised system. Typically, the operation of many of the reported lab-on-a-chip devices is dependent on the support of a laboratory framework. In this paper, a demonstrator platform for routine laboratory analysis is designed and built, which fully integrates a number of technologies into a single device with multiple domains such as fluidics, electronics, pneumatics, hydraulics, and photonics. This facilitates the delivery of breakthroughs in research, by incorporating all physical requirements into a single device. To highlight this proposed approach, this demonstrator microsystem acts as a fully integrated biochemical assay reaction system. The resulting design determines enzyme kinetics in an automated process and combines reservoirs, three-dimensional fluidic channels, optical sensing, and electronics in a low-cost, low-power and portable package.

Keywords: fluidics; integrated devices; integration; lab-on-a-chip; miniaturised total analysis system; optofluidics; sensors.

Figure 1

(a) Schematic representation of the passive and active components, detectors and connections between the components used in the design of the fluidic device. (b) Schematic of the proposed device architecture comprising a fluidic and a control layer.

Figure 2

(a) Layout of the CAD for the sacrificial fluidic network; (b) 3D CAD of the proportional pneumatic valves (c) 3D CAD of the chaotic mixer; (d) 3D printed sacrificial mould, post acetone surface treatment with the LED and phototransistor attached; (c) PDMS fabricated fluidic device, with added fluidic interconnects to the control layer and waste reservoir; (d) the final device, integrating fluidics with the PCB and casing containing the battery, pumps, and valve system; (e) plan view of the fluidic device showing the pneumatic valve control tubes (left) and the liquid waste output tube (right), (f) photograph of the full system, filled with blue liquid to help visualise the liquid flow-path.

Figure 3

(a) Calibration curve of the photometric sensor showing a linear increase in output voltage with increased product concentration. (b) Calibration curve of the two pneumatic valves. The voltage readings were taken for different pressures applied in each active valve after the mixture of the two reservoirs was pumped in the analysis chamber.

Figure 4

(a) Continuous measurement showing the output voltage of the photometric sensor over a period of 300 s. The graph displays the reaction rate for the six different concentrations of substrate used to perform the enzyme kinetics analysis. (b) Enzyme kinetics analysis using the Michaelis–Menten model, with K_m = 58 µM ± 4 µM.