Dynamic manipulation of modes in an optical waveguide using dielectrophoresis.

The emergence of optofluidics has brought a high degree of tuneability and reconfigurability to optical devices. These possibilities are provided by characteristics of fluids including mobility, wide range of index modulation, and abrupt interfaces that can be easily reshaped. In this work, we created a new class of optofluidic waveguides, in which suspended mesoparticles were employed to greatly enhance the flexibility of the system. We demonstrated tuneable quasi single mode waveguides using spatially controllable mesoparticles in optofluidics. The coupling of waveguiding modes into the assembly of mesoparticles produces strong interactions and resonant conditions, which promote the transitions of the waveguiding modes. The modal response of the system depends on the distribution of packed particles above the polymeric rib waveguide which can be readily controlled under the appropriate combination of dielectrophoresis and hydrodynamic forces.

Thermal analysis of nanofluids in microfluidics using an infrared camera.

We present the thermal analysis of liquid containing Al(2)O(3) nanoparticles in a microfluidic platform using an infrared camera. The small dimensions of the microchannel along with the low flow rates (less than 120 µl min(-1)) provide very low Reynolds numbers of less than 17.5, reflecting practical parameters for a microfluidic cooling platform. The heat analysis of nanofluids has never been investigated in such a regime, due to the deficiencies of conventional thermal measurement systems. The infrared camera allows non-contact, three dimensional and high resolution capability for temperature profiling. The system was studied at different w/w concentrations of thermally conductive Al(2)O(3) nanoparticles and the experiments were in excellent agreement with the computational fluid dynamics (CFD) simulations.

Active control of silver nanoparticles spacing using dielectrophoresis for surface-enhanced Raman scattering.

We demonstrate an active microfluidic platform that integrates dielectrophoresis for the control of silver nanoparticles spacing, as they flow in a liquid channel. By careful control of the nanoparticles spacing, we can effectively increase the surface-enhanced Raman scattering (SERS) signal intensity based on augmenting the number of SERS-active hot-spots, while avoiding irreversible aggregation of the particles. The system is benchmarked using dipicolinate (2,6-pyridinedicarboxylic acid) (DPA), which is a biomarker of Bacillus anthracis. The validity of the results is discussed using several complementing characterization scenarios.

Optofluidics incorporating actively controlled micro- and nano-particles.

The advent of optofluidic systems incorporating suspended particles has resulted in the emergence of novel applications. Such systems operate based on the fact that suspended particles can be manipulated using well-appointed active forces, and their motions, locations and local concentrations can be controlled. These forces can be exerted on both individual and clusters of particles. Having the capability to manipulate suspended particles gives users the ability for tuning the physical and, to some extent, the chemical properties of the suspension media, which addresses the needs of various advanced optofluidic systems. Additionally, the incorporation of particles results in the realization of novel optofluidic solutions used for creating optical components and sensing platforms. In this review, we present different types of active forces that are used for particle manipulations and the resulting optofluidic systems incorporating them. These systems include optical components, optofluidic detection and analysis platforms, plasmonics and Raman systems, thermal and energy related systems, and platforms specifically incorporating biological particles. We conclude the review with a discussion of future perspectives, which are expected to further advance this rapidly growing field.

Dielectrophoresis-Raman spectroscopy system for analysing suspended nanoparticles.

A microfluidic dielectrophoresis platform consisting of curved microelectrodes was developed and integrated with a Raman spectroscopy system. The electrodes were patterned on a quartz substrate, which has insignificant Raman response, and integrated with a microfluidic channel that was imprinted in poly-dimethylsiloxane (PDMS). We will show that this novel integrated system can be efficiently used for the determination of suspended particle types and the direct mapping of their spatial concentrations. We will also illustrate the system's unique advantages over conventional optical systems. Nanoparticles of tungsten trioxide (WO(3)) and polystyrene were used in the investigations, as they are Raman active and can be homogeneously suspended in water.

Novel tuneable optical elements based on nanoparticle suspensions in microfluidics.

This work demonstrates the application of dielectrophoretic (DEP) control of silica nanoparticles to form tuneable optical elements within a microfluidic system. The implementation consisted of a microfluidic channel with an array of curved microelectrodes along its base. Various DEP conditions were investigated at alternating current voltage amplitudes, flow rates and frequencies from 5 to 15 V, 2 to 10 microL/min and 0 to 20 MHz, respectively. The fluid channel was filled with deionized water suspending silica particles with diameters of 230 and 450 nm. Experiments were conducted to demonstrate DEP concentration and deflection of the particles and the impact of these particles distributions on the optical transmission through the fluid channel. Both confinement and scattering of the light were observed depending on the particle dimensions and the parameters of the DEP excitation. The results of this investigation illustrate the feasibility of DEP control in an optofluidic system and represent a significant step toward the dynamic formation of electrically controlled liquid optical waveguides.