Construction And Application Of Photoelectrochemical Sensor Based On Reactive Organic Photosensitive Molecules

As a newly emerging analytical technology,photoelectrochemical（PEC）sensor based on the photoelectric effect has attracted extensive attention in recent years.PEC analysis uses external illumination as the excitation source and photocurrent as the output signal.Since two completely different input and output physical quantities are used,PEC analysis can avoid the interference from the excitation light source.Therefore,PEC analysis has higher signal-to-noise ratio and sensitivity in theory.In addition,the combination of spectroscopic and electrochemical analysis methods can also develop PEC sensors with diverse structures and applications,and make them simple,fast,low-cost,and easy to miniaturize.Compared with commonly used inorganic photoactive materials,organic photosensitive molecules have many unique properties,including precise composition,adjustable photophysical properties,diversified structures,and ease of functionalization,which endow them with great potential in PEC sensing.The expansion of various organic photosensitive molecules and synthesis methodologies also provides an opportunity for the construction of photoelectrochemical sensors with ideal structures and excellent performance.In this study,we propose three reactive PEC sensing strategies based on target analytes-induced in situ reactions to form organic photosensitive molecules.The specific research contents are as follows:（1）Using thiophenol（Ph SH）as the target analyte,a signal-enhanced PEC sensor was constructed by utilizing the spontaneous cyclization of 3-（2-hydroxyphenyl）acrylonitrile derivative to form a coumarin dye.First,a 2,4-dinitrobenzene（DNP）recognition group was assembled on a pyridine-containing 3-（2-hydroxyphenyl）acrylonitrile compound to obtain a coumarin dye precursor molecule（Dye-Ph SH）.Second,titanium dioxide（Ti O₂）nanorod array substrate electrodes were prepared on the surface of conductive glass（FTO,fluoride-doped tin oxide）by a hydrothermal method.Then,the Dye-Ph SH was covalently coupled to the Titanium dioxide（FTO/Ti O₂）substrate via a bromosilane reagent（Br PTMS）to obtain the PEC photoanode.Dye-Ph SH has only a weak photocurrent response due to the photoinduced electron transfer（PET）effect caused by the strong electron-withdrawing properties of DNP.Ph SH can trigger the departure of the DNP group in the dye molecule,and then the released phenolic hydroxyl group can nucleophilically attack its adjacent cyano group for intramolecular cyclization to form a coumarin photosensitizer（Dye’-Ph SH）.As a result,the photocurrent response was significantly enhanced.It was found that there was a good linear relatingship between the photocurrent signal and the logarithm concentration of Ph SH（0.2-30.0μM）,the correlation coefficient R²=0.9944 and the detection limit was 1.1 n M.The PEC sensor has many advantages,such as good selectivity,high sensitivity and excellent stability.（2）Another coumarin precursor molecule（Dye1-Ph SH）with a similar structure to（1）containing a DNP recognition group was designed and synthesized for fluorescence（FL）and PEC dual detection of thiophenol.In solution,Dye1-Ph SH can realize the fluorescence quantitative analysis of Ph SH.Covalently coupled to the Ti O₂ nanoarray substrate,Dye1-Ph SH can realize the photoelectrochemical detection of Ph SH.Both signals are generated due to the tandem reaction of Dye1-Ph SH in responding to Ph SH,which involves the removal of DNP group and then the intramolecular cyclization,thus leading to the formation of a coumarin dye（Dye1’-Ph SH）with obvious fluorescence and photoelectric signals and achieving a highly selective dual detection of Ph SH.The experimental results showed that the linear range of fluorescence detection of Ph SH was 1.0-12.0μM,and the detection limit was 0.23μM;the linear range of photoelectrochemical detection of Ph SH was 0.05-50.00μM,and the detection limit was 1.90 n M.The proposed Dye1-Ph SH can realize the FL-PEC dual detection of the target by a single probe molecule,which provides a new idea for the development of dual sensing platforms for other analytes for environmental and biological applications.（3）A 4-nitrobenzyl-containing coumarin precursor（Dye-NTR）was designed and synthesized for PEC detection of nitroreductase（NTR）.The photoanode FTO/Ti O₂/Br PTMS/Dye-NTR was obtained through covalently coupling Dye-NTR to FTO/Ti O₂ nanoarray substrate birdging by Br PTMS.After reacting with NTR,the 4-nitrobenzyl group is removed and the photosensitive molecule is intramolecularly cyclized to form a coumarin dye with obvious photoelectric effect,thus realizing highly selective detection of NTR.It was found that there was a good linear relatingship between the photocurrent response signal and the concentration of NTR（0.2-1.0μg/m L）and the detection limit was 91.0ng/m L.It is expected that the proposed FTO/Ti O₂/Br PTMS/Dye-NTR photoanode has great potential in the monitoring of biological enzyme.