Integration and detection of biochemical assays in digital microfluidic LOC devices

The ambition of lab-on-a-chip (LOC) systems to achieve chip-level integration of a complete analytical process capable of performing a complex set of biomedical protocols is hindered by the absence of standard fluidic components able to be assembled. As a result, most microfluidic platforms built to date are highly specialized and designed to fulfill the requirements of a single particular application within a limited set of operations. Electrowetting-on-dielectric (EWOD) digital microfluidic technology has been recently introduced as a new methodology in the quest for LOC systems. Herein, unit volume droplets are manipulated along electrode arrays, allowing a microfluidic function to be reduced to a set of basic operations. The highly reprogrammable architecture of these systems can satisfy the needs of a diverse set of biochemical assays and ensure reconfigurability, flexibility and portability between different categories of applications and requirements. While important progress was made over past years in the fabrication, miniaturization and function programming of the basic EWOD fluidic operations, the success of this technology will in great part depend on the ability of researchers to couple or integrate digital microfluidics to detection approaches that can make the system competitive for LOC applications. The detection techniques should be able to circumvent the limitations of hydrophobic surfaces and exploit the advantages of the array format, high droplet transport speeds and rapid mixing schemes. This review provides an in-depth look at recent developments for the coupling and integration of detection techniques with digital microfluidic platforms for bio-chemical applications.