Towards Microfluidic Color Detection Using Micropumps

Abstract

Microfluidic systems are effective tools for carrying out a wide range of chemical and biological analyses. Utilizing colorimetry in conjunction with microfluidic devices has proven to be a highly effective method for conducting various analyses that require rapid results. Such systems have significant applications in lab-on-a-chip systems and other medical devices that necessitate a colorimetric measurement to obtain quantitative results about the chemical composition of a given sample. Currently, most state-of-the-art techniques for performing microfluidic color detection use expensive cameras to study the captured image or are paper-based analytical devices that use capillary action to analyze color information. However, paper-based microfluidic devices are limited by the evaporation of test samples during experiments and therefore require high volumes of samples. Additionally, the surface tension of the liquid sample plays a crucial role in this process, and if not properly managed, the device may not provide accurate results. To overcome these limitations, a low-cost automated color detection system that could be used in conjunction with planar microfluidic pumps is presented in this work. The color detection system uses a light-emitting diode (LED) and a light-dependent resistor (LDR) to obtain color information. The LED is used to sequentially shine the primary color component wavelengths - red, green, blue - on the sample, and the color information is obtained from the light intensity incident onto the LDR after reflecting from the sample. The results showed that the system is accurate up to 92% and could be readily readily used to conduct different types of chemical analyses using colorimetry and can be employed in various industries to automate chemical and other biomedical processes completely. The flexible, planar micropumps discussed in this work are based on a nozzle-diffuser design that employs a central chamber connected to two trapezoidal flow diodes. The pump was fabricated using polydimethylsiloxane (PDMS) as a two-layer structure: a bottom layer with molded channels and the chamber, encapsulated by a planar top layer. The transparency of the pump and biocompatibility of PDMS make it an excellent material for biomedical and colorimetric applications. The pump design was characterized for its performance, both when placed on a flat surface and surfaces of different bending radii, by counting the number of compression cycles required for a known volume of fluid, here water, to flow from the inlet to the outlet. The pump produced a flow rate per compression cycle of 5.53 µl on a flat surface and that of 4µl, 3.6 µl when placed on surfaces of bending radii of 71cm and 45 cm, respectively. Finally, the pumping mechanism was completely automated by replacing the diaphragm with a dielectric elastomer actuator (DEA) and using a tesla valve for fluidic channels. The pressure difference imparted by the deformation of the actuator when a sinusoidal voltage is applied is converted to fluid flow (velocity). We also propose a microfluidic system that employs three microfluidic pumps and a central color detection module to perform effective microfluidic color detection. The proposed system provides a cost-effective solution for conducting chemical analyses using colorimetric assays.