Highly Sensitive Porous Silicon Optical Biosensor Enhanced By Quantum Dots

In recent years,as the substrate of optical biosensors,porous silicon has been used in biomolecular analysis,food detection,environmental monitoring and clinical medicine.The porous silicon Bragg mirror biosensor is used to detect DNA molecules.Based on the digital image of porous silicon Bragg mirror,we use carboxylated water-soluble CdSe/ZnS quantum dots to label DNA molecules,which can not only achieve refractive index amplification,but also generate fluorescence after the quantum dots in the reactant are excited by a certain wavelength of light,the average gray value change of digital image before and after biological reaction was calculated to calculate the concentration of DNA molecules.The detection process has the advantages of low cost,high speed and high sensitivity.The main contents of this paper are as follows:1.Because the reflection spectrum of the actual prepared porous silicon microcavity is quite different from that of the theoretical design,the porous silicon Bragg mirror is selected as the biosensor substrate,and the wavelength at the edge of the photonic band gap is 633 nm.The porous silicon Bragg mirror was prepared by electrochemical etching method,and was functionalized.The probe DNA was fixed on the inner wall of the hole of Bragg mirror,and hybridized with CdSe/ZnS quantum dots with different concentrations of target DNA.The wavelength of the probe light was the same as that of the lowest reflectivity at the edge of the band gap of the Bragg mirror.The detector received the reflected light on the surface of Bragg mirror,and the digital imaging equipment obtained the reflected light before and after the biological reaction.The detection limit of DNA was 20.74 pM.2.Porous silicon devices with 633 nm photonic band gap edge of Bragg mirror were fabricated and functionalized.Firstly,different concentrations of target DNA were fixed on the inner wall of the hole of Bragg mirror,then CdSe/ZnS quantum dots were used to couple with probe DNA,and finally hybridized with target DNA in the hole of porous silicon.The new dual signal light detection technology was used.The first signal light in this method was the detection light from the laser,and then the porous silicon entering the Bragg structure was then removed from the table surface reflection.The second signal light was the fluorescence of quantum dots in the reactant in the porous silicon hole excited by a certain wavelength of light.The fluorescence signal is further enhanced by porous silicon Bragg structure.The digital images of two kinds of light superimposed on the surface of porous silicon Bragg mirror before and after the reaction were obtained by the digital microscope,and the relationship between the average gray value change and the target DNA concentration was obtained.The detection limit of DNA was 0.42 pM by this method.