| Oblique-incidence reflectivity difference(OIRD)technique is a newly-established optical detection technology,which is sensitive to the local dielectric constant of the reflective interface.It offers a powerful tool for study of various surface/interface processes by detecting the difference between the relative change of s-and p-polarized reflectivities in elliptically polarized incident light with the advantages of real-time,labelfree,high throughput,and non-destructive detection.OIRD has been successfully applied to the detection of a broad variety of solid/liquid and solid/gas interfacial processes,such as biological microarray chip detection and metal oxide film epitaxial growth process monitoring.Exploring the new application fields of the OIRD technique is of great significance to promote the scientific research that involves the surface/interface process and to further improve this technique.Polyaniline(PANI)is a widely studied conjugated conducting polymer that has the advantages of easy fabrication,and unique physiochemical properties,is widely used in the fields of energy,sensing,and surface modification and protection.The conjugated structure of PANI changes responding to the external redox and/or doping/dedoping stimulation,and results in the change of its dielectric constant,which is accessible to the OIRD.Therefore,PANI is a very suitable polymer material for mediating OIRD detection and expanding the application of OIRD.In this thesis,taking PANI film as the signal tranducer medium and using the sensitive response of the OIRD technique to its conjugate structure,we explore the new applications of OIRD in three aspects: the detection of label-free biochemical sensing chip,the in-situ detection and imaging of electron transfer process at microorganism/electrode interface and the detection of local p H in an electrolyzer.The main contents of this thesis are as follows:(1)The content of biological small molecules in the human body is of great significance for health evaluation and disease diagnosis.In the first work,an OIRD sensing chip(bienzyme-PANI/FTO)based on PANI film-fixed oxidase/horseradish peroxidase was constructed to quantitatively detect hydrogen peroxide,glucose,lactic acid,and cholesterol.These small molecules are oxidized by dissolved oxygen and produce hydrogen peroxide with the biocatalysis of corresponding oxidase,and the strong oxidizing free radicals produced by hydrogen peroxide catalyzed by peroxidase induce the oxidation of PANI film.In this process,the benzene unit in the molecular structure of PANI is transformed into quinone unit,resulting in the change of dielectric constant,thus enabling OIRD detection.The results show that this sensing chip can detect a variety of target molecules with high sensitivity,and the limit of detection(LOD)for hydrogen peroxide,glucose,and lactic acid is 1 μM,the LOD for cholesterol is 1.25 μM.Meanwhile,the high specificity of biological enzymes makes the chip realize multiplexed detections of different components in complex samples,and realize the regeneration and recycling of this chip by using electrochemical reduction.(2)Extracellular electron transfer(EET)is a key process in the operation of microbial fuel cells(MFCs)and affects the output power of MFCs.Due to the heterogeneity of the bacterial anode,the detection of the EET process with spatiotemporal resolution is of great significance to understanding the fundamental mechanism of the EET process and optimizing the performance of MFCs.In the second work of this thesis,the EET process between the S.putrefaciens CN32 and PANI film was detected by the OIRD technique.Under anaerobic conditions,the electroactive bacteria can use redoxactive PANI film as electron receptors to realize the normal metabolism through the EET process.During this period,the quinone unit in the molecular structure of PANI will be reduced/transformed into benzene unit,resulting in the change of its dielectric constant,which is monitored by OIRD.The results show that the method used in this work with a high spatiotemporal resolution.The measured OIRD real-time signal and OIRD twodimensional image show that the electron transfer process is uneven in this case.(3)The energy conversion realized by electrolyzing water is considered to be one of the important means to deal with the excess electricity on the grid.The local p H change of the anode and cathode during the electrolyzing is often directly related to the performance of the catalyst.Therefore,it is of great significance to detect the local p H change in the electrolyzer for geometric optimization of the cell,and high-throughput screening of catalysts.In the third work of this thesis,PANI is used as a p H-sensitive element,and the OIRD technique is used to detect and image the local p H value change near the two electrodes when electrolyzing water with FTO conductive glass as the overall hydrolysis catalyst under neutral conditions.The change of the environmental p H of the both electrodes will lead to the de-doping or doping behavior of PANI.resulting in the change of the conjugated structure,and dielectric constant and in turn OIRD response.The results show that the de-doping of PANI in an alkaline environment will cause an increase in the OIRD signal,while the doping of polyaniline in an acidic environment will cause a decrease of the OIRD signal,and the OIRD signal changes more violently under the condition of strong acid or strong base.Similarly,during total hydrolysis,the increase of p H near the cathode will lead an increase in the OIRD signal,while a decrease in p H near the anode will lead to a decrease in the OIRD signal.This provides a new method for evaluating the apparent activity of catalysts and optimizing the structure of electrolyzers.In summary,this thesis focuses on the redox or doping/dedoping-triggered PANI film changes and its OIRD responses,and explore three new applications of OIRD technique,which enriches our understanding on this new optical detection technique,also offers an important tool for various research. |
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