Abstract
Microfluidic two-phase flow detection has attracted plenty of interest in various areas of biology, medicine and chemistry. This work presents a capacitive sensor using insulated interdigital electrodes (IDEs) to detect the presence of droplets in a microchannel. This droplet sensor is composed of a glass substrate, patterned gold electrodes and an insulation layer. A polydimethylsiloxane (PDMS) cover bonded to the multilayered structure forms a microchannel. Capacitance variation induced by the droplet passage was thoroughly investigated with both simulation and experimental work. Olive oil and deionized water were employed as the working fluids in the experiments to demonstrate the droplet sensor. The results show a good sensitivity of the droplet with the appropriate measurement connection. This capacitive droplet sensor is promising to be integrated into a lab-on-chip device for in situ monitoring/counting of droplets or bubbles.
Highlights
Microfluidic two-phase flow, especially droplet microfluidics, dealing with discrete droplets with a tiny volume at nanolitre and picolitre scale in lab-on-chip devices, has been widely used in the chemical, biological and medical areas, e.g., drug discovery [1], immunoassay [2], synthetic biology [3], cell analysis [4], cell culture [5], diagnostic testing [6], sample preparation [7,8], etc
Differing from droplet microfluidics in which the droplets are generally manipulated in enclosed microchannels, digital microfluidics (DMF), despite of some disagreements about nomenclature, has been an emerging liquid-handling technology that enables individual control of droplets on an array of electrodes, which contrasts with the continuous nature of other microfluidic systems [9,10]
We have demonstrated a capacitive microfluidic two-phase sensor employing interdigital electrodes (IDEs) and a thin insulated film
Summary
Microfluidic two-phase flow, especially droplet microfluidics, dealing with discrete droplets with a tiny volume at nanolitre and picolitre scale in lab-on-chip devices, has been widely used in the chemical, biological and medical areas, e.g., drug discovery [1], immunoassay [2], synthetic biology [3], cell analysis [4], cell culture [5], diagnostic testing [6], sample preparation [7,8], etc. A typical example of DMF-based lab-on-chip devices is the continuous-flow PCR system [11], in which DNA samples are encapsulated with PCR reagents into tiny droplets, and flow through different temperature zones to implement programmed PCR cycles. Both droplet microfluidics and DMF take full advantage of tiny volumes with high area/volume ratio, which means more efficiency, less cost of reagents and lower energy consumption. It brings new system integration and process compatibility challenges for fabrication
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