Characteristics of a Liquid/Liquid Optical Waveguide Using Sheath Flow and Its Application to Detect Molecules at a Liquid/Liquid Interface

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

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.

Characterization of liquid-core/liquid-cladding optical waveguides of a sodium chloride solution/water system by computational fluid dynamics

A stable liquid/liquid optical waveguide (LLW) was formed using a sheath flow, where a 15% sodium chloride (NaCl) solution functioned as the core solution and water functioned as the cladding solution (15% NaCl/water LLW). The LLW was at least 200 mm in length. The concentration distributions of the liquid core and liquid cladding solutions in the LLW system were predicted by computational fluid dynamics (CFD) to validate the characteristics of the waveguide. The broadening of the region of the fluorescence of Rhodamine B excited by the guided light and the increase in the critical angle of the guided light with the increase in the contact time of the core and the cladding solutions were well explained by CFD calculations. However, no substantial leakage of the guided light was observed despite the considerably large change in the refractive index profile of the LLW; thus, a narrower and longer waveguide was realized.

A solid-cladding/liquid-core/liquid-cladding sandwich optical waveguide for the study of dynamic extraction of dye by ionic liquid BmimPF6

We present a sandwich liquid-core waveguide for the study of the dynamic extraction of dye molecules by ionic liquid (IL). The incident light was introduced into the core of the IL phase directly via a fused silica prism to form total reflection at the IL/cladding interface. The changes in light intensity and absorbance spectra over time were monitored during the extraction process by maintaining an optical focus on the IL/water interface. The dynamic extraction of the dye Eriochrome Black-T (EBT) by the IL 1-n-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) at different concentrations and various pH conditions was investigated. The results indicated that the accumulation of the dye at the IL/water interface and the dynamic extraction of the dye into the IL phase both contributed to the increase in absorbance. The increased signal along with the increase in pH suggests that electrostatic interaction might be the main driving force for the extraction of EBT by BmimPF(6), and the micro-circumstance provided by IL also has a decisive effect on the characteristics of the spectra recorded by the waveguide system.

Encapsulation of anilinonaphthalenesulfonates in carboxylate-terminated PAMAM dendrimer at the polarized water|1,2-dichloroethane interface

Molecular encapsulation of water-soluble anionic fluorescent dye molecules, 8-anilino-1-naphthalenesulfonic acid (ANS), and its bimolecular derivative (bis-ANS), in the generation 3.5 polyamidoamine (G3.5 PAMAM) dendrimer was investigated in the bulk aqueous phase and at the polarized water|1,2-dichloroethane interface. ANS(-) was electrostatically incorporated in the dendrimer, and the fluorescence enhancement with a blue shift of the emission maximum was observed at pH values <6, where the interior of the dendrimer was positively charged. The fluorescence enhancement of ANS was maximized around pH 3 and then decreased under more acidic conditions. The potential dependences of the molecular encapsulation and the interfacial mechanism were studied in detail by means of potential modulated fluorescence (PMF) spectroscopy. Under acidic conditions, the dendrimer incorporated ANS(-) at the positively polarized interface as well as in the aqueous phase. ANS(-) was released from the dendrimer at the intrinsic transfer potential and independently transferred across the interface. Bis-ANS exhibited relatively strong interaction with the dendrimer over a wide pH range (1 < pH < 8), and a negative shift of the transfer potential was observed under the corresponding pH condition. The PMF analysis clearly demonstrated that the interfacial mechanism of the dendrimer involves transfer and adsorption processes depending on the pH condition and the Galvani potential difference.

Water-ice chip with liquid-core waveguide functionality. Toward lab on ice

A liquid-core waveguide is fabricated with water-ice, which has lower refractive index than most of the solvents, as cladding, and provides a possibility as an ice chip for flow analyses.