Power-free, digital and programmable dispensing of picoliter droplets using a Digit Chip

Pushbutton-activated microfluidic cartridge as a user-friendly sample preparation tool for diagnostics

Microfluidic technologies have several advantages in sample preparation for diagnostics but suffer from the need for an external operation system that hampers user-friendliness. To overcome this limitation in microfluidic technologies, a number of user-friendly methods utilizing capillary force, degassed poly(dimethylsiloxane), pushbutton-driven pressure, a syringe, or a pipette have been reported. Among these methods, the pushbutton-driven, pressure-based method has a great potential to be widely used as a user-friendly sample preparation tool for point-of-care testing or portable diagnostics. In this Perspective, we focus on the pushbutton-activated microfluidic technologies toward a user-friendly sample preparation tool. The working principle and recent advances in pushbutton-activated microfluidic technologies are briefly reviewed, and future perspectives for wide application are discussed in terms of integration with the signal analysis system, user-dependent variation, and universal and facile use.

Towards practical sample preparation in point-of-care testing: user-friendly microfluidic devices

Microfluidic technologies offer a number of advantages for sample preparation in point-of-care testing (POCT), but the requirement for complicated external pumping systems limits their wide use. To facilitate sample preparation in POCT, various methods have been developed to operate microfluidic devices without complicated external pumping systems. In this review, we introduce an overview of user-friendly microfluidic devices for practical sample preparation in POCT, including self- and hand-operated microfluidic devices. Self-operated microfluidic devices exploit capillary force, vacuum-driven pressure, or gas-generating chemical reactions to apply pressure into microchannels, and hand-operated microfluidic devices utilize human power sources using simple equipment, including a syringe, pipette, or simply by using finger actuation. Furthermore, this review provides future perspectives to realize user-friendly integrated microfluidic circuits for wider applications with the integration of simple microfluidic valves.

Pressure-controlled microfluidic sub-picoliter ultramicro-volume syringes based on integrated micro-nanostructure arrays

Ultramicro-volume syringes were fabricated by integrating micro-nanostructure arrays in microchannels for quantitatively dispensing sub-picoliter volumes of liquids. Using this system, liquids were dispensed in volume increments as low as 0.5 pL with 96% accuracy. Specifically, the controllable synthesis of nanocrystals was achieved using a lab-on-chip platform that was integrated with the syringes.

Finger-actuated microfluidic device for the blood cross-matching test

A blood cross-matching test should be carried out to prevent a hemolytic transfusion reaction as the final verification step. To simplify complicated procedures of a conventional blood cross-matching test requiring bulky systems and skilled people, we present a finger-actuated microfluidic device for the blood cross-matching test. Although finger actuation is a simple action that anyone can easily accomplish, there would be a variation in the individual finger actuation that may induce the user-dependent errors of the device. Therefore, the working principle of the finger-actuated microfluidic device is newly designed to reduce the user-dependent errors by indirectly controlling the pressure of fluidic channels. The constant volume was repeatedly dispensed by pushing and releasing a pressure chamber regardless of the different pushed depths of the pressure chamber, the pushing time interval, and the end-users. The dispensed volume was linearly increased according to the number of pushing times applied to the pressure chamber and determined by adjusting the diameter of an actuation chamber. In addition, multiple fluids can be dispensed with a desirable ratio by pushing and releasing the pressure chamber. Finally, a finger-actuated microfluidic device for the blood cross-matching test was developed, which can simultaneously actuate four fluidic channels. After loading 50 μL of whole blood samples from a donor and a recipient into two inlets of the device, the blood plasma from each individual was separated through the two plasma separation membranes. The blood cross-matching test results can be achieved by cross-reacting the donor's blood plasma with the recipient's whole blood as well as the donor's whole blood with the recipient's blood plasma by pushing and releasing only a single pressure chamber within 10 min.