Sponge-Based Flow Control in Laminate Capillary-Driven Electrochemical Microfluidic Devices for Viscous Sample Analysis

Microfluidic systems are an attractive strategy for developing environmentally safer analytical methods and collecting real-time information to perform ″in loco″ analyses. Laminate capillary-driven microfluidic devices are a promising approach that can achieve fast results using low-cost devices. Despite significant advancements in capillary-driven microfluidic devices, analyzing viscous samples, particularly biological fluids, remains a challenge because the flow is highly dependent on the viscosity of the solution. Additionally, there has been a limited ability to control the flow rate. Herein, we proposed a laminate capillary-driven microfluidic device to overcome the flow issues where commercial sponges are used as passive pumps. A capillary-driven microfluidic device was coupled to electrochemical detection to provide quantitative results. After optimization, sponges provide sufficient control flow independent of the material type used to make the device. Additionally, the proposed microfluidic design enables analysis using higher viscosity solutions without compromising the electrochemical signal. The device was used to quantify paracetamol in undiluted human saliva using a generator-collector mode, with a recovery rate of nearly 100%. An important finding in this work was the possibility of analyzing viscous saliva without requiring any dilution. Additionally, the new design, which utilizes the sponge as a passive pump, opens the possibility of performing reactions (sample preparation steps) within the microfluidic channel, as the flow can be controlled by simply replacing the sponge. These results pave the way for the development of capillary-driven microfluidic devices with electrochemical detection for saliva analysis outside laboratory settings.