Controlled Photo Electro Thermal Generation of Micro Bubble for Manipulation of Cells

Abstract

Controlled micro-bubble formation has been an area of growing interest for many researchers due to ubiquitous presence of micro-bubbles in multitude of biological, chemical and physical systems. The important biophysical applications of micro-bubbles include sonoluminescence, flow control in microfluidic channels, contrast enhancement in ultrasound imaging and targeted efficient drug delivery. The earlier techniques for the formation micro bubbles include resistive heating or heat generation using focused laser beam. While resistive heating requires microelectronic pre-fabrication, micro bubble formation by focused laser beam necessitates either selective placement of optically absorbing particles near the pre-decided site(s) or a very high power ultrafast laser beam. Here, we present a novel method of generating micro-bubbles at desired microscopic location by photo-electro-thermal (PET) method, where very low power light is made to shine on a photoconductive coating, made on the ITO-glass substrate, thus forming virtual electrodes. Optimization of the ac frequency and voltage applied between the two ITO-glass substrates led to efficient generation of bubble(s) at the location(s) of shining light beam(s). The power of light beam required to generate micro-bubbles was found to be several orders of magnitude lower than existing laser techniques to form bubbles. The micro-bubbles are found to be very stable up to few hours. Kinetics of bubble formation and performance characteristics of the PET method will be presented. Applications of these micro-bubbles in cellular manipulation including cellular disruption, microinjection and microfluidic actuation will also be covered.