| Developing biosensors that integrate microfluidic chips and sensor electronics has important application significance in the biomedical field.Currently,most biomedical workers in China use optical detection equipment to complete the separation and parameter detection of biomarkers.However,due to the limitations of light sources,laser pulses,and optical pathways,measurement costs are high and equipment is redundant.It is difficult to achieve low-cost and miniaturized device detection or finer size sensor chips.Using microwave electromagnetic resonance characteristics to detect biomarkers is a new technology,which has unique advantages in low cost,low power consumption,non-fluorescent labeling,miniaturization,real-time monitoring,and other aspects.In this paper,RF biosensors based on microfluidic chips are discussed in detail.The response characteristics of various types of sensors were studied using microfluidic chips with different structures.Research work was carried out on the separation of cells using microfluidic chips and the quantitative measurement of glucose concentration using radio frequency biosensors.The working mechanism of microfluidic chips and the sensing mechanism of radio frequency sensors were explained.The main research contents of this paper are as follows:(1)A microfluidic quantitative cavity structure was designed to assist the sensor in quantitative measurement,reducing the uncertainty of sensor measurement.As sensors work based on sensitive areas,an important method to improve sensor sensitivity is to increase the sensitive area or limit environmental changes to the sensitive area.Increasing the sensitive area is relatively difficult and requires a high cost.That is,achieving a large area of sensitive areas through micro/nano processes causes a waste of resources to a certain extent,so a second method is needed to improve the sensitivity of the sensor.Materials that limit environmental changes require strong plasticity,can be made into arbitrary shapes,can effectively grow on the substrate,and have minimal impact on sensor performance.PDMS has high light transmittance,good flexibility,strong electrostatic adsorption ability,and is easy to adhere to other materials.It can also process microfluids with different softness according to the amount of solidified material added.Therefore,PDMS is selected as the processing material for the microfluidic quantitative cavity in this paper.(2)Based on the fast response advantage of interdigital capacitor structure,a mutual winding capacitor based on a glass substrate was designed,and the parameters such as line width,gap,and number of turns of the microstrip line electrodes were determined.According to the sensing mechanism of the capacitor sensor,the concentration of glucose solution was measured,and the linear relationship between the capacitor value and the concentration of glucose solution was obtained.At the same time,to avoid the impact of ambient temperature on the measurement of glucose solution concentration,a resistor sensor is designed in front of the capacitor structure to measure the temperature of glucose solution.Finally,different capacitor values of the same concentration of glucose solution at different temperatures are measured,which serves to calibrate the ambient temperature.(3)After verifying the processing feasibility of the PDMS microfluidic quantitative chamber and the glass substrate,an optimized design of the microfluidic quantitative chamber was carried out,and a microfluidic chip structure capable of cell separation by cell size was designed and fabricated.When cells flow in the microfluidic channel,they undergo deterministic lateral displacement based on the effect of inertial lift forces,so the separation of cells can be completed without relying on external actions.The two-stage separation channel designed in this paper can isolate over 80% of large diameter cells.Based on this principle,the selectivity of microwave biosensors can be improved,which has certain guiding significance for the practical application of microwave biosensors.(4)A dual pass band microwave biosensor with integrated microfluidic chips was proposed.The PDMS microfluidic chips and microwave biosensors based on glass substrates were fixed together through a bonding process,enabling selective application of biosensor measurements.In actual measurement,the mixed cells were passed into a microfluidic chip,and after separation,they were transported to different microwave sensor working passbands through different paths for sensing response detection.The test results show that the microwave biosensor has a good linearity and a small error in repeated measurements,which can play a role in quantitative detection,shape detection,and positioning detection,greatly increasing the stability of the microwave biosensor. |
