Drop on demand in a microfluidic chip

TL;DR

This paper presents a novel in-chip drop on demand technique in microfluidic chips, enabling precise, high-frequency dispensing of microdrops and gas bubbles, with potential applications in lab-on-a-chip systems.

Contribution

The work introduces a new method for controlled drop and bubble generation in microfluidics using piezoelectric actuators, compatible with inexpensive electronics.

Findings

Dispenses drops at frequencies up to 2.5 kHz with precise volume control.

Demonstrates merging and moving drops within the chip.

Shows compatibility with low-cost audio electronics.

Abstract

In this work, we introduce the novel technique of in-chip drop on demand, which consists in dispensing picoliter to nanoliter drops on demand directly in the liquid-filled channels of a polymer microfluidic chip, at frequencies up to 2.5 kHz and with precise volume control. The technique involves a PDMS chip with one or several microliter-size chambers driven by piezoelectric actuators. Individual aqueous microdrops are dispensed from the chamber to a main transport channel filled with an immiscible fluid, in a process analogous to atmospheric drop on demand dispensing. In this article, the drop formation process is characterized with respect to critical dispense parameters such as the shape and duration of the driving pulse, and the size of both the fluid chamber and the nozzle. Several features of the in-chip drop on demand technique with direct relevance to lab on a chip applications are presented and discussed, such as the precise control of the dispensed volume, the ability to merge drops of different reagents and the ability to move a drop from the shooting area of one nozzle to another for multi-step reactions. The possibility to drive the microfluidic chip with inexpensive audio electronics instead of research-grade equipment is also examined and verified. Finally, we show that the same piezoelectric technique can be used to generate a single gas bubble on demand in a microfluidic chip.