Manipulation of liquid marbles by electric field and its applications

Abstract

To manipulate liquid marbles by electric field, the fundamental understanding on how liquid marbles response to the electric field is of crucial importance. In this thesis, we mainly focus on the responses of liquid marbles to an externally applied electric field, the realization of manipulating liquid marbles, and the physical mechanism behind the manipulation of liquid marbles. To explore the capacity of our technology, we have also tested some proof-of-concept applications by using liquid marbles as miniature micro-bioreactors. Chapter 2 focuses on the development of a robust method to manipulate liquid marbles by electric field in a controlled manner. Motivated by the great potential of nonwetting droplets as microreactors for chemical and biological applications, a general and robust method is developed for controlled manipulation of nonwetting droplets. The motion and coalescence of the resulting droplets (termed “liquid marbles”) are actuated at a sufficiently large applied voltage on inkjet-printed devices covered by a dielectric layer. This critical actuation voltage, which determines the driving force and the displacement of actuation, is highly dependent on the initial position of the liquid marble. This finding is ascribed to the fraction of the interfacial area that is electrostatically polarized; as a result, the amount of electrostatic energy released to accelerate the marble to reach peak velocity is position-dependent, as confirmed experimentally. By fine-tuning the driving voltage, individual liquid marbles are actuated and coalesced on demand. Moreover, in our system, cross-contamination between droplets during manipulation is avoided due to the nanoparticle shell, as confirmed by the absence of any trace DNA after amplification using a loop mediated isothermal amplification reaction. In Chapter 3, by using liquid marbles as miniature micro-bioreactors, we demonstrate some proof-of-concept applications by combining the manipulation of liquid marbles with conventional detecting technology. Enzymatic colorimetric method is used to quantitatively measure the concentration of glucose in samples, and the results of using microwells as containers are compared with those from using liquid marbles as miniature micro-bioreactors. We find that the linear correlation between absorbance and concentration, which is used to quantify the concentration of glucose, still holds true for liquid marbles. Moreover, liquid marbles encapsulating cells are manipulated by electric field. The experimental results confirm that the cells stay viable after being encapsulated and cultured in liquid marbles for hours. Finally, we demonstrate that, by using our system to manipulate liquid marbles to move, coalesce and mix, we can trigger chemiluminescence reaction in liquid marbles.