Optofluidic control is emerging as a promising tool in wide applications like pharmaceutics, chemistry, energy, and biology, due to the development of micro-fluidic chip. However, complex optical set-ups or special materials for working fluid or micro-channel are usually required. Fluidic control includes flow initiation, selection of fluidic flow direction, flow sequence of a few reagents, close/open microchannels and so on. Microvalves are one of the key control components in the micro-fluidic chip. On this basis, the concept of plasmon-assisted optofluidics was proposed by Donner and coworkers, which utilizes the thermal response of plasmonic nanostructures to induce fluid convection at the nanoscale, and therefore to get rid of the huge and complex external devices.
This project focuses on the micro-flow control problem, which plays a crucial role in the lab-on-a-chip and micro-robot applications. The outcomes of the project can be directly applied to improve the traditional microfluidic technique, which, to be more specific, can be used to help us to get rid of the complicated external control devices, simplify the operation procedure, lower the cost, and improve the portability of the whole microfluidic control system. Meanwhile, the proposed technique does not require adding any additives to the working fluid, which avoids the contamination of the test samples for its biological applications. Additionally, this project may bring a new concept for micropump or micromotor, which is powered by micro-flow induced by thermoplasmonic effect of nanoparticle arrays without any chemical fuel. This outcome can be applied as the remote controllable power source for nanorobots, which is of significant importance for the application of clinical medicine and the environment, such as precise delivery and release of drugs, monitoring, and collection of pollutants.
The main objectives of this project include:
(1) To build a numerical model that can be used to describe the nanoscale photothermal transportation and fluid flow process coupled with the thermoplasmonic effect of nanoparticle arrays. The proposed model can provide both qualitative and quantitative descriptions of the influence factor for the light-controlled micro-flow problem.
(2) To provide a novel effective micro-flow control method. This project aims to design a light-controlled microvalve that can be used to regulate fluid flow in distributary micro-channels. The microvalve consists of a nanoparticle array that is placed in the bifurcations and an external monochromatic light source. No complex external devices are required. By adjusting the characteristic parameters (wavelength, intensity, and polarization state), the monochromatic light source can be used to control the temperature of the nanoparticle array.
The main conclusion of this project is summarized as follows:
we have systematically investigated the fundamental issues involved in the manipulation of microfluid and particles, from the optical properties of plasmonic nanoparticles to their photothermal and photoacoustic effects. A light-controlled microvalve that can be used to regulate fluid flow in distributary micro-channels is designed. The microvalve consists of a nanobrick array that is placed in the bifurcations and an external monochromatic light source. No complex external device is required. The basic principle is to take advantage of the natural convection of the fluid in micro-channels caused by temperature-induced buoyancy force. For the Y-shaped distributary micro-channels, we found that the mass flow rate in the downstream threads can be regulated by tuning the polarization state and the intensity of the incident light.
