Manipulation schemes and applications of liquid marbles for micro total analysis systems

Micro total analysis systems (microTAS) provide the opportunity to create complete analytical microsystems by integrating various functional modules, such as sample preparation, separation and detection, into a single chip sized microfabricated device. Microfluidics is the enabling technology for implementing the concept of microTAS. Liquid marble (LM), as a promising separate digital microfluidic platform, has the great potential to enhance the broad applications of microTAS. LMs are small liquid droplets encapsulated by multilayered hydrophobic particles and have attracted a great interest from the microfluidics research community due to their non-wetting property. A LM maintains its integrity and exhibits low friction on various carrier surfaces, enabling the LM to be actuated by external electric, magnetic, gravitational and acoustic fields or other manipulation schemes. LMs can thus serve effectively for the storage and transportation of small liquid volumes. In addition, they have been widely used for the quick detection of water pollution or gas emission and, most importantly, micromixing and microreactions for chemical and biomedical purposes. This paper reviews the recent developments in the manipulation techniques and emerging applications of LMs. The review aims to facilitate better understanding of their use as a unique digital microfluidic platform to promote further advancement of microTAS. The paper begins with different manipulation schemes of LMs according to the nature of actuation energy. Next, it summarizes the diverse applications of LMs for various chemical and biological assays. Finally, this paper concludes with future perspectives regarding the research on LMs in microTAS technologies.