Research On Photoelectrochemical Biosensor Based On Novel Nanomaterial And Nucleic Acid Signal Amplification

Photoelectrochemical（PEC）biosensor served as an emerging detection equipment displays the merits of low background noise and high sensitivity due to completely different and separated energy forms of the"photo excitation-electrical detection"mode,which has attracted much attention in trace analysis of target.Researches suggest that photoactive material as light-to-electricity converter can quickly switch biological or chemical substance into electrical signal under light excitation,playing a core role in PEC assay system.Accordingly,the selection and reasonable design of photoactive material are key to improve the analytical performance of PEC sensor.Herein,new nanomaterial formed by combining two or more materials together provides ideas for exploring material with high photoelectric conversion efficiency and multiple characteristics,as it can not only shorten the electron transfer distance by reducing macroscopic phase separation,but also effectively integrate the excellent properties of various materials.At the same time,in order to convert trace analyte into plentiful nucleic acid molecular outputs that can cause changes in photocurrent,some nucleic acid amplification strategies are usually required,such as cycle amplification with enzyme digestion,strand displacement reaction,rolling circle amplification and so on.In view of this,proceeding from the explore of novel nanomaterial,coupled with efficient DNA cyclic amplification technologies,and this paper designed near-zero background and integrating dual-wavelength and polarity-switchable PEC biosensors for sensitive and accurate detection of target.The specific research content is as follows:1.AuNPs/CdS QDs/CeO₂ ternary nanocomposite combined with 3D DNA walker mediated cycling amplification for the construction of sensitive PEC biosensorIn view of the low photoelectric conversion efficiency and limited application in the PEC biosensing field of cerium oxide（CeO₂）,CeO₂ was modified with CdS quantum dots（CdS QDs）and gold nanoparticles（AuNPs）to synthesize a novel ternary nanocomposite（AuNPs/CdS QDs/CeO₂）with excellent photoelectric conversion efficiency.The nanocomposite was used as photoactive signal probe and combined with scrollable three-dimensional（3D）DNA walker mediated shearing cycle amplification to construct a near-zero background PEC biosensor for sensitive mi RNA-182-5p detection.Impressively,the formation and rolling of scrollable 3D DNA walker triggered by target could realize dynamic,rapid and specific digestion of hairpin DNA on electrode with the aid of ExonucleaseⅢ（ExoⅢ）,which thus exposed abundant binding sites for assembling DNA labeled AuNPs/CdS QDs/CeO₂ nanoprobes.Thanks to the formation of type-II heterojunction（between CeO₂ and CdS QDs）and Schottky junction（generated by CeO₂ and AuNPs）,an ideal photoelectric conversion efficiency accompanied with stunningly improved photocurrent was thus acquired for significantly improving the detection sensitivity.It turned out that the detection limit（LOD）of biosensor was ultralow(31 amol·L^-1).Significantly,the proposed PEC biosensor would exhibit great potential for the nanocomposite as a splendid indicator and provide an effective avenue for constructing the sensing platform with excellent sensitivity and ultralow background.2.An accurate and sensitive PEC sensing platform based on a novel covalent organic polymer mediated dual wavelength and polarity switchConsidering the problems of single wavelength PEC biosensor developed by single performance photoactive material,such as single sensing mode,susceptible to the fluctuation of instrument or environmental and poor anti-interference ability in real samples,a dual-wavelength and polarity-switchable PEC biosensor based on the multiple PEC characteristics of porphyrinic covalent organic polymer（TPAPP-PTCA PCOP）was constructed.It is worth noting that this PCOP was synthesized for the first time and possessed the characteristics of both n-type and p-type semiconductor,enabling the switch of photocurrent from cathode to anode by changing the excitation wavelength.And it could be regulated by ferrocene（Fc）and electron donor hydrogen peroxide（H₂O₂）.Based on this,combining T7 exonuclease（T7 Exo）mediated rapid ligand-oligonucleotide transduction and rolling circle amplification（RCA）,and utilizing gold nanoparticles（GNPs）with glucose-oxidase like（Gox-like）activity,a PEC biosensor that integrated dual wavelength and polarity switch was construct for accurate and sensitive detection of food pollutant aflatoxin M1（AFM1）.The results indicated that this PEC biosensor possessed the wide linear range of 0.75 pg·m L^-1-500 ng·m L^-1 and a LOD as low as 0.089 pg·m L^-1 towards AFM1 assay.Impressively,target exhibited a completely opposite photocurrent difference to the interfering substances,and the linear correlation coefficient of assay was improved compared to single wavelength detection.The construction of this PEC sensing platform not only provided a basis for exploring multi-characteristics photoactive material,but also innovatively developed the detection mode of PEC biosensor.