| Microfluidic chip is becoming more and more important for detection of cell and molecular biology, high precision chemical reaction and drug synthesis and screening. One of the most pivotal technologies is that accurate detect to the parameters of microfluid in the microfluidic chip. The microfluidic chip channel size is often the micro/nano scale, which will restrict the size of the detection equipment in a certain extent. Although the flow rate can be precisely controlled by sampling pump, there is a certain delay when the microfluid flow into the microfluidic chip from the sampling pump, and which will result in a deviation from the flow rate measurement. Therefore, the accurate and sensitive detection of flow rate in microfluidic chip is an urgent problem to be solved.This paper introduces the optical manipulation technology, using optical fiber to manipulate polystyrene (PS) microsphere. We use the manipulation distance between microsphere and optical fiber probe to reaction the flow rate of microfluid. Main process is that the 980nm wavelength output laser have certain optical force to PS microsphere, and microfluidic also produced flow force to it, while two kinds of force in the opposite direction. We can establish the mathematical model of flow rate of the microfluid and the manipulation distance through establish, destroy and restructure the force balance of the microsphere, thus achieve the flow sensing of microfluid.We design the experiment that Optofluidic tunable manipulation of microparticles by integrating graded-index fiber taper with a microcavity. We introduced the manufacture process of fiber taper and other devices. Through software simulation the variation process of microcavity length, we demonstrate the conclusion that the focus of the beam will be changed with the variation of microcavity length when the beam via the graded-index fiber taper and was focused. The conclusion that microcavity control the force balance of microsphere also be demonstrated in the experiments. We often adjust the optical power and flow rate to achieve establishment, destruction and reconstruction of the force balance of the microsphere in the experiment. Experimental results show that the microsphere can be steady manipulated at any position when the tunable range of the manipulation distance is between 20μm to 45 μm, and the distance between the fiber tip and the focus point of the light beam is 18.9±1.0 μm when the length of the microcavity is set to 57 μm.The aim that understand the mechanism of light manipulate the microsphere is that use optical manipulation technology to achieve flow rate sensor. In order to simplify the structure of the device and reduce the loss of light, we use the cleaved single-mode fiber to manipulate microsphere. Established the relationship between the manipulation length and flow rate by using ray optics model, and the reliability of the model was verified through numerical simulation of force balance. We testing the characteristic parameters of the sensing, such as flow rate measuring range, linearity, repeatability, time domain stability and accuracy. We obtain the maximum manipulation length of 715 μm; The measurement range of about three orders of magnitude is achieved, from 20 nL/min to 14000 nL/min, corresponds to laser power of 41 mW. The stability of microparticle is very good in our experiment, it can last for several hours. The measurement accuracy of the flow rate can achieve 10 nL/min when v< 100 nL/min. We also compared the performance parameters with different flow rate sensors, and these parameters proved that the optical manipulation is especially good at highly-sensitive detection at low flow rate. The sensor has the potential to provide lower detection limit. It is worth noting that these parameters are obtained in a small range of laser power, so that the performance parameters of the sensor have a certain mining space. |
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