Capacitive Sensing for Monitoring of Microfluidic Protocols Using Nanoliter Dispensing and Acoustic Mixing

Abstract

The development of protocols for bio/chemical reaction requires alternate dispensing and mixing steps. Whilst most microfluidic systems use the opening of additional parts of the channel to allow the ingress of fixed volumes of fluid, this requires knowledge of the protocol before the design of the chip. Our approach of using a microfluidic valve to regulate the flow into an initially empty cavity allows for on-chip protocol development and refinement. Mixing is provided by way of surface acoustic wave excitation; this high-frequency vibration causes steady-state streaming flows. We show that capacitive sensing can be used to measure fluid levels, even if multiple fluid types are used, such that nanolitre dispensing accuracy is achieved. Also, the capacitive readout can be used to establish mixing quality and to monitor temperature fluctuations. These capabilities allow for protocols to be conducted without optical assessment, and so will allow for multiplexing, such that reactions could be conducted, simultaneously, in multiple chambers across a chip.

Acoustofluidic cell micro-dispenser for single cell trajectory control

“…70 In future works, rather than fixing the actuation time, the desired number of cells to be trapped can be predetermined, and utilizing a feedback system, the release could be automated once that number has been reached. 71 The capability of adjusting the FIDT actuation time in conjunction with the ability to extract undesired cells ondemand allows this device to overcome the Poisson statistics, rendering it a highly accurate and reproducible tool for single cell trapping and dispensing. Moreover, the design of the device along with the trapping mechanism utilized would provide users with the flexibility of using different cell types of various diameters.…”

“…70 In future works, rather than fixing the actuation time, the desired number of cells to be trapped can be predetermined, and utilizing a feedback system, the release could be automated once that number has been reached. 71…”

Making immotile sperm motile using high-frequency ultrasound

“…In SAW systems, the acoustic waves propagate from a piezoelectric substrate into a fluid volume, generating nonlinear acoustic radiation forces that cause the displacement of the particles or cells allowing patterning and sorting ( 35 ). A second nonllinear effect is acoustic streaming, which causes a steady bulk flow of fluid ( 36 ), causing microfluidic mixing ( 37 ). Aside from these physical effects, SAWs have also been used to alter the behavior of adherent cells to inhibit surface attachment and decrease cell spreading while increasing the rate of metabolic activity ( 38 ).…”

Capacitive Sensor and Alternating Drive Mixing for Microfluidic Applications Using Micro Diaphragm Pumps

“…For example, the sensor system described in [ 19 ] uses the capacitance change induced by air bubbles injected into a fluid stream for continuous flow measurement. Another example for non-continuous flow is the dosing system developed by Zhang et al [ 20 ], which uses a capacitive sensor electrode to measure the fluid amount dosed into a channel cavity.…”