Research On Optical Properties And Detection Technology Of Porous Silicon Biosensor Based On Microcavity Structure

In recent years,optical biosensors have been widely used in the food industry,environmental monitoring,fermentation industry,medicine and so on.Free-lable,high sensitivity,fast response,good real-time,remote control,portable,no electromagnetic interference and high security are now the characteristics of optical biosensors,which is also the goal of the laboratory research and commercial applications.Porous silicon,due to its huge specific surface area,good biocompatibility,fluorescence characteristics and the refractive index of the superiority of the medium,coupled with its easy preparation,low cost advantages,is the best of all kinds of materials for the preparation of biosensors.Therefore,optical biosensors based on porous silicon substrates are being extensively studied.In this thesis,nano-porous silicon is used as the base material,and the special optical microcavity structure is used to prepare biosensors with high sensitivity and free-lable.The new methods are used to detect small biomolecules and large molecular weight molecules for effective and reliable detection.The image method was proposed,improve detection sensitivity of spectral device through the characteristics of quantum dots,prepared and theoretically analyzed of splice microcavities.1.Reflection angle spectrum detection method was proposed,which has the virtues of label-free and spectrometer-free.It can be used for biological detection with high detecting resolution.Taking advantage of the optical properties of porous silicon microcavity,the refractive index changes caused by biological reaction can be detected by measuring the incident angle of the minimum reflected light intensity.Based on the above method,label-free eight-base pair DNA detection can be realized with a corresponding detection limit is as low as 87 nM.2.Transmission angle spectrum detection method was proposed,with the advantages of label-and spectrophotometer-free.In this approach,the refractive index change induced by the biological reactions of a sample in a porous silicon microcavity is detected by measuring the change in the incidence angle corresponding to the maximum transmitted intensity of a near infrared semiconductor laser.It reports that the proposed method can achieve the label-free detection of 43 kDa molecular weight hydatid disease antigens with high sensitivity.The prepared biosensor has a sensitivity of 1.292°/mg/ml and a detection limit of 0.16 ng/ml.3.Image detection method was proposed,and used to optical biological detection based on porous silicon microcavity microarray.The porous silicon microcavity array obtains the reflected light image of the device array unit through the digital imaging device under laser irradiation,and the change of the refractive index detected by the device can be achieved by calculating the gray value of the image.This method can detect the magnitude of the refractive index change of 10^-4.4.Reflection spectrum detection method was optimized by introduction of quantum dots.The spectral reflectance of porous silicon microcavity was measured by spectroscopic equipment,and the change of refractive index was determined by the movement of reflection spectrum due to the reaction of DNA biomolecules in porous silicon microcavity device.DNA-coupled CdSe/ZnS water-soluble quantum dots enhanced the optical response signal of the target DNA,resulting in a greater position shift of the porous silicon microcavity reflection spectrum,thereby improving the detection sensitivity of the optical biosensor.5.A new preparation method of splice microcavity was proposed.The unique part of this approach lies in the innovation of structural preparation.The main idea is that the Bragg reflector composed of alternating high and low refractive indices,the first layer is a low refractive index dielectric layer with a high porosity,twice the physical thickness of the other low refractive index layers,a multiple cycle of Bragg mirrors below the microcavity layer.And then split the two Bragg mirrors together to form a Bragg mirror with multiple cycles,the porous silicon microcavity consisting of two chambers and an air layer.The target molecules can directly dip into the first layer of the microcavity structure with high porosity and low refractive index.Since the first layer thickness of the microcavity structure is much smaller than the thickness of the overall structure of the porous silicon,it is possible to ensure that the reagents and biomolecules can smoothly enter the dielectric layer,making the molecular detection more reliable.6.Theoretical study on porous silicon microcavity was carried out.Porous silicon microcavity is a special one-dimensional photonic crystal structure,the Bragg mirror cycle number,cavity thickness,cavity on both sides of the Bragg reflector whether the symmetry has affected the characteristics of microcavity.After the biomolecules enter the different dielectric layers of the porous silicon microcavity,the change of the wavelength shift of the resonant peak of the porous silicon microcavity is affected.The dielectric layer refractive index changes are slightly different when biomolecules dip into the porous microporous cavity of different porosity of the dielectric layer.