Light Fluid Technology-based Biomedical Microfluidic Chips

Biomedical microfluidic devices are the integrated micro/nano devices that are used for the biological detection with advantages in integration, minimization, high speed, and low assumption for detection. In most of the biomedical researches, it is achieved by the optical methods to detect biomolecules and cells.Optofluidic technique as a state-of-an-art research direction is proposed to focus on how to integrate microfluidic devices and optical devices. Different from traditional solid optical devices, optofluidic devices have better performance in optics and tunabilities. Most importantly, because most of the optical materials of the optofluidic devices are fluids, this makes it easy to achieve the optical components by fluids in microfluidic devices for optical detection, and this also makes it natural to integrate with other components of the microfluidic devices.Based on the advantages of optofluidics, the content of this thesis is focused on how to use microfluidic structures to control light, and how to achieve the optical detection for fluorescent molecules, particles in micro scale with the integration of optofluidic devices with other microfluidic components. The main content and novel work of this thesis are focused on the following aspects:(1) The two dimensional tunable liquid lens based on liquid gradient refractive indices with variable light focusing has been proposed and achieved by using a novel microfluidic structure. The two dimensional profile of gradient refractive index is achieved by diffusion between high and low refractive index liquids in microfluidic chamber. The refractive index profile and focal point can be adjusted by flow rates. The fluorescent enhancement is achieved by focusing light using liquid lens.(2) The fluorescent molecules and silver nanoparticles are added into the core of liquid waveguides, and the fluorescent enhancement has been detected. Single and multiple-mode liquid waveguides have been built using liquid core. The collection and enhancement of fluorescent light in a certain angle have been achieved using total internal reflection and surface plasmon resonance inside the liquid waveguides. The fluorescent excitation and enhancement have also been achieved by the coupling between liquid waveguides.(3) According to the optical properties on the interfaces of high and low refractive index liquids, the evanescent waves are achieved on the liquid-liquid interfaces using liquid waveguides and microfluidic total internal reflection devices, and the single fluorescent particle inside the fluid has been successfully detected using evanescent waves and hydrodynamic focusing. This is a new method to use the evanescent waves on liquid interfaces for optofluidic detection.(4) According to the property of diffusion between liquids in microfliudic channels, we have achieved the tunability of optical focusing by liquid gradient refractive index lens using surface acoustic waves to change the diffusion of high refractive index liquid.(5) The surface acoustic waves and microfluidic devices are combined for particle separation. By the different forces on particles with different diameters caused by surface acoustic waves in micro channels, the particles can be moved in micrometer scale, and the particle separation is achieved by using acoustic waves inside microfluidic channels.(6) Because of the focusing effect of gradient forces of surface acoustic waves in microfluidic channels, by integration between surface acoustic waves for particle focusing and optofluidic total internal reflection on liquid interface for light exciting in microfluidic devices, it is achieved to focus and detect single fluorescent particle. This method is firstly proposed to combine acoustic and optical methods for high-speed detection of fluorescent particles.(7) It the first time to achieve the light scattering detection on the cell membranes caused by surface acoustic waves in microfluidic devices. By using the mechanical vibration on single cell from surface acoustic waves, the scattered light from single cell membrane is detected to analyze the cell mechanics of a single cell.In conclusion, this thesis has successfully achieved several novel optical methods for biomedical detection based on microfluidic devices by taking the advantages of optofluidics. These optofluidic methods are successful in fousing light, constructing evanescent waves on the Liquid-Liquid interface for fluorescent detection, and integrating optical structures and surface acoustic waves for fluorescent detection and light scattering detection of cells. All these new methods proposed in this thesis have potentially important applications for integrating optical detection devices to the Lab-On-A-Chip devices for biomedical research.