Reconfigurable liquid-core/liquid-cladding optical waveguides with dielectrophoresis-driven virtual microchannels on an electromicrofluidic platform

Abstract

An electrically reconfigurable liquid-core/liquid-cladding (L(2)) optical waveguide with core liquid γ-butyrolactone (GBL, ncore = 1.4341, εcore = 39) and silicone oil (ncladding = 1.401, εcladding = 2.5) as cladding liquid is accomplished using dielectrophoresis (DEP) that attracts and deforms the core liquid with the greater permittivity to occupy the region of strong electric field provided by Teflon-coated ITO electrodes between parallel glass plates. Instead of continuously flowing core and cladding liquids along a physical microchannel, the DEP-formed L(2) optical waveguide guides light in a stationary virtual microchannel that requires liquids of limited volume without constant supply and creates stable liquid/liquid interfaces for efficient light guidance in a simply fabricated microfluidic device. We designed and examined (1) stationary and (2) moving L(2) optical waveguides on the parallel-plate electromicrofluidic platform. In the stationary L-shaped waveguide, light was guided in a GBL virtual microchannel core for a total of 27.85 mm via a 90° bend (radius 5 mm) before exiting from the light outlet of cross-sectional area 100 μm × 100 μm. For the stationary spiral waveguide, light was guided in a GBL core containing Rhodamine 6G (R6G, 1 mM) and through a series of 90° bends with decreasing radii from 5 mm to 2.5 mm. With the stationary straight waveguide, the propagation loss was measured to be 2.09 dB cm(-1) in GBL with R6G (0.01 mM). The moving L-shaped waveguide was implemented on a versatile electromicrofluidic platform on which electrowetting and DEP were employed to generate a precise GBL droplet and form a waveguide core. On sequentially applying appropriate voltage to one of three parallel L-shaped driving electrodes, the GBL waveguide core was shifted; the guided light was switched at a speed of up to 0.929 mm s(-1) (switching period 70 ms, switching rate 14.3 Hz) when an adequate electric signal (173.1 VRMS, 100 kHz) was applied.

Integrating microfluidics and biosensing on a single flexible acoustic device using hybrid modes

“…1,2 In this context, digital microfluidic systems have allowed the use of mature fabrication processes through photolithography techniques 3 and the elimination of the need for external modules or complicated geometries such as pumps or valves. 4,5 Amongst several actuation mechanisms for digital microfluidics, such as electrowetting-on-dielectrics (EWOD), 6 dielectrophoresis (DEP), 7 opto-electrowetting, 8 thermocapillary, 9 magnetic actuation, 10 microfluidic devices based on surface acoustic waves (SAWs)/Lamb waves have proven advantageous as they are able to provide a host of useful effects, including acoustic streaming in droplets, efficient mixing, transportation and jetting, and acceleration of hybridization reactions of biochemical assays. 11,12 More generally, acoustic wave devices are uniquely attractive to generate fully integrated LOC systems, as they can also enable biosensing in addition to liquid actuation, wirelessly, [13][14][15] thus significantly reducing complexity of the system and operation/manufacturing costs.…”

Dielectrophoresis-actuated in-plane optofluidic lens with tunability of focal length from negative to positive

“…Real-time modulation of the focal length can be achieved by changing the applied voltage. And the DEP exerts a net force on the fluidic interface to drive the liquid of greater permittivity into the strong electric field region originally occupied by the medium of smaller permittivity [34]. Most of the previous electric liquid lenses are out-of-plane lens, like the conventional solid lens, the beams are manipulated in the direction perpendicular to the microfluidic substrate [35][36][37][38].…”

A Liquid-core Liquid-cladding Optical Waveguide Based on Thermal Gradients across the Laminar Flow of Water in Capillary Tubing

“…Recently, liquid-core/liquid-cladding optical waveguides (LLWs), whose concept was firstly introduced by us, [1][2][3][4] have widely been studied as a key element of optofluidics. [5][6][7][8][9][10][11][12] LLWs are usually built using two kinds of miscible liquids that have different refractive indices such as 50% ethanol/water, 5% NaCl aqueous solution/water and etc. Tang et al, on the other hand, proposed an LLW using thermal gradients across homogeneous liquids in microchannels where two streams of water at higher temperature (30 to 80 C) sandwich a stream of water at a lower temperature (21 C), 13 based on the phenomenon that the refractive index (RI) of water decreases along with increasing temperature.…”