Research On Read Out Technology Of Microcantilevers Biosensor

The microcantilevers biosensor based on Microelectromechanical Systems has theadvantages of easy to use, high sensitivity, label-free, real-time detection and analysis,which has great prospect in applications, such as identification of biomolecular, detection ofantibody, measurement the concentration of blood glucose, diagnosis of cancer, monitoringenvironment and acquisition the information of battlefield. Because the variation is smallfor the measured object, the effective reading method is the key problem for improvementthe sensitivity, resolution, autonomous recognition and anti-jamming of the sensor.The read out technologies for microcantilevers biosensor have been widely investigatedat home and abroad firstly. After that, we determined the topics and contents of our researchwork based on it. In our work, the specific sensitive layer was firstly modified on thesurface of microcantilevers, and the surface stress will cause the microcantilever slightlydeflection due to the interaction between biochemical analyze and the sensitive layer. Thesmall variation of micro-cantilever can be detected by the methods of optical and electrical,and we can realize the real-time detection and analysis for the biochemical reactions. Then,we briefly introduced the structural and characteristics of the micro-cantilever. At the sametime, the readout method of the optimized Wheatstone bridge which based on thepiezoresistive principle has been emphasizes. In order to improve the signal noise ratio, themodulation and demodulation signal has been conducted using mathematical theory, andthe time domain and frequency domain were also simulated. The readout methods havebeen elaborated for the intensity of plane mirror reflector structure and equilibrium positionof reflective diffraction grating, and the theoretical analysis and experimental verificationhave also been conducted in our work. The details information as follows:(1) According to the proposed readout method, we have designed the piezoresistivecantilever sensor array, whose four microcantilevers were integrated with fourforce-sensitive resistors. At the same time, the reflecting grating and reflecting plane mirrorwas integrated on the microcantilevers, and the characteristic of the optical readoutmicrocantilever sensor has also been discussed in our work.(2) The optimized Wheatstone bridge has been developed based on the piezoresistivemicrocantilever structure. The high precision automatic closed loop zero-setting approachhas been proposed to solve the problem of the difference for four piezoresistors, which can’t allow the post-amplifier very large. The automatic gain control technology was alsoimplied to amplify the weak signal, which can reduce the quantization error. The electronicswitch modulation method was also utilized to achieve the carrier modulation of analogweak signal, and the lock amplification filter technology based on relevant principles wasintroduced to improve the signal noise ratio of the system. The measured results show thatthe fabricated sensor can real-time detects the concentration of biochemical analyte, and themeasured data can also be transmitted to the computer by USB for storage and playback.(3)The light intensity measurement system based on the fiber optic reflectiveself-focusing has been designed for the reflecting plane mirror structure of microcantileverbiosensor. In this system, the non-coherent light source was focused on the microcantileverby fiber, and the reflected light from the microcantilever was also detected by highsensitivity PIN-FET detector. The sensitivity and linearity for this system was alsoinvestigated, and the measured results prove that this method has the advantages of simple,high resolution and sensitivity.(4) The diffraction feedback balanced measurement system was also developed for themicrocantilever biosensor, which based on reflection grating structure. We have proposedthe balanced control system which is based on grating diffraction feedback. In this system,the650nm laser was used as light source to reflect on the grating structure, and the gratingdiffraction pattern was received using CCD. In order to remain the spectra at initialequilibrium position, the precision micro-displacement rotary stage was controlled tocompensate for deflection of the cantilever according to the spectra processing results, andthen the microcantilever deflection angle was measured. This measured system has thecharacteristics of high precision and large test range.We have discussed the readout technology of biochemical microcantilever biosensorin perspective of the electrical and optical, which based on microelectromechanical systems.The fabricated biosensor was used for glucose concentration detection and toxinidentification, and the detection limitation can reach to microgram level. Both thetheoretical analysis and experimental results are show that the fabricated biosensor has theadvantages of high sensitivity and resolution, strong anti-interference ability, which hasgreat prospect in biochemical detection.