Abstract
We present a plasmonic-enhanced dielectrophoretic (DEP) phenomenon to improve optical DEP performance of a floating electrode optoelectronic tweezers (FEOET) device, where aqueous droplets can be effectively manipulated on a light-patterned photoconductive surface immersed in an oil medium. To offer device simplicity and cost-effectiveness, recent studies have utilized a polymer-based photoconductive material such as titanium oxide phthalocyanine (TiOPc). However, the TiOPc has much poorer photoconductivity than that of semiconductors like amorphous silicon (a-Si), significantly limiting optical DEP applications. The study herein focuses on the FEOET device for which optical DEP performance can be greatly enhanced by utilizing plasmonic nanoparticles as light scattering elements to improve light absorption of the low-quality TiOPc. Numerical simulation studies of both plasmonic light scattering and electric field enhancement were conducted to verify wide-angle scattering light rays and an approximately twofold increase in electric field gradient with the presence of nanoparticles. Similarly, a spectrophotometric study conducted on the absorption spectrum of the TiOPc has shown light absorption improvement (nearly twofold) of the TiOPc layer. Additionally, droplet dynamics study experimentally demonstrated a light-actuated droplet speed of 1.90 mm/s, a more than 11-fold improvement due to plasmonic light scattering. This plasmonic-enhanced FEOET technology can considerably improve optical DEP capability even with poor-quality photoconductive materials, thus providing low-cost, easy-fabrication solutions for various droplet-based microfluidic applications.
Highlights
Microfluidic systems have drawn great interest in numerous chemical and biological applications due to their capability to precisely manipulate micro/nanoscopic particles, including cells, droplets, and colloids [1,2,3]
We present a plasmonic field enhancement to greatly improve light absorption performance of the low-quality titanium oxide phthalocyanine (TiOPc) material and result in an enhanced dielectrophoretic force for effective manipulation of an oil-immersed aqueous droplet on a floating electrode optoelectronic tweezers (FEOET) device
Even with a poor photoconductive material such as TiOPc, plasmonic light scattering induced by the nanoparticles has enabled a more than 11-fold increase in instantaneous actuation speed of a droplet than the one without any nanoparticles
Summary
Microfluidic systems have drawn great interest in numerous chemical and biological applications due to their capability to precisely manipulate micro/nanoscopic particles, including cells, droplets, and colloids [1,2,3]. A non-uniformity of the electric field was created for DEP operation due to the locally modified electric impedance They have experimentally demonstrated the generation of optical traps for large-scale parallel manipulation of 15,000 particles on a 1.3 × 1.0 mm area without any complex wiring and interconnection issues. We present a plasmonic field enhancement to greatly improve light absorption performance of the low-quality TiOPc material and result in an enhanced dielectrophoretic force for effective manipulation of an oil-immersed aqueous droplet on a FEOET device. Using plasmonic nanoparticles as light scattering elements can considerably enlarge optical DEP performance even with low-quality photoconductive materials, offering low-cost and simple FEOET devices for a broad range of droplet-based microfluidic applications
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