Microbe removal using a micrometre-sized optical fiber

Multi-Stage Particle Separation based on Microstructure Filtration and Dielectrophoresis

Particle separation is important in chemical and biomedical analysis. Among all particle separation approaches, microstructure filtration which based particles size difference has turned into one of the most commonly methods. By controlling the movement of particles, dielectrophoresis has also been widely adopted in particle separation. This work presents a microfluidic device which combines the advantages of microfilters and dielectrophoresis to separate micro-particles and cells. A three-dimensional (3D) model was developed to calculate the distributions of the electric field gradient at the two filter stages. Polystyrene particles with three different sizes were separated by micropillar array structure by applying a 35-Vpp AC voltage at 10 KHz. The blocked particles were pushed off the filters under the negative dielectrophoretic force and drag force. A mixture of Haematococcus pluvialis cells and Bracteacoccus engadinensis cells with different sizes were also successfully separated by this device, which proved that the device can separate both biological samples and polystyrene particles.

Optofluidic organization and transport of cell chain

Controllable organization and transport of cell chain in a fluid, which is of great importance in biological and medical fields, have attracted increasing attentions in recent years. Here we demonstrate an optofluidic strategy, by implanting the microfluidic technique with a large-tapered-angle fiber probe (LTAP), to organize and transport a cell chain in a noncontact and noninvasive manner. After a laser beam at 980-nm wavelength launched into LTAP, the E. coli cells were continuously trapped and then arranged into a cell chain one after another. The chain can be transported by adjusting the magnitudes of optical force and flow drag force. The proposed technique can also be applied for the eukaryotic cells (e. g., yeast cell) and human red blood cells (RBCs). Experiment results were interpreted by the numerical simulation, and the stiffness of cell chain was also discussed.

Recent advances in optical fiber devices for microfluidics integration

This paper examines the recent emergence of miniaturized optical fiber based sensing and actuating devices that have been successfully integrated into fluidic microchannels that are part of microfluidic and lab-on-chip systems. Fluidic microsystems possess the advantages of reduced sample volumes, faster and more sensitive biological assays, multi-sample and parallel analysis, and are seen as the de facto bioanalytical platform of the future. This paper considers the cases where the optical fiber is not merely used as a simple light guide delivering light across a microchannel, but where the fiber itself is engineered to create a new sensor or tool for use within the environment of the fluidic microchannel.

Optical regulation of cell chain

Formation of cell chains is a straightforward and efficient method to study the cell interaction. By regulating the contact sequence and interaction distance, the influence of different extracellular cues on the cell interaction can be investigated. However, it faces great challenges in stable retaining and precise regulation of cell chain, especially in cell culture with relatively low cell concentration. Here we demonstrated an optical method to realize the precise regulation of cell chain, including removing or adding a single cell, adjusting interaction distance, and changing cell contact sequence. After injecting a 980-nm wavelength laser beam into a tapered optical fiber probe (FP), a cell chain of Escherichia colis (E. colis) is formed under the optical gradient force. By manipulating another FP close to the cell chain, a targeted E. coli cell can be trapped by the FP and removed from the chain. Further, the targeted cell can be added back to the chain at different positions to change the cell contact sequence. The experiments were interpreted by numerical simulations and the impact of cell sizes and shapes on this method was analyzed.

Electrokinetic preconcentration of particles and cells in microfluidic reservoirs

We present an electrokinetic (EK) technique for in-reservoir particle and cell preconcentration via induced-charge electroosmosis (ICEO) and dielectrophoresis (DEP).

Continuous separation principles using external microaction forces

During the past decade, methods for the continuous separation of microparticles with microaction forces have rapidly advanced. Various action forces have been used in designs of both microchannel and capillary continuous separation systems, which depend on properties such as conductivity, permittivity, absorptivity, refractive index, magnetic susceptibility, and compressibility. Particle migration velocity has been used to characterize the particles. Biological cells have been the most interesting targets of these continuous separation methods.