The Construction Of Photoelectrochemical Sensors Basbed On Quanrum Dots And Applied To Photoelectrochemical Sensing

Photoelectrochemical is a newly established analytical method in recent years.The detection principle is that the mutual recognition of sensing elements and the target detection object under the light and lead to the change of electrical signal.The method has the advantages of high sensitivity,rapid detection,simple equipment and good selectivity,etc.Its unique advantages and potential in sensing have attracted more and more attention.Although the outstanding advantages of photoelectrochemical analysis method have been demonstrated in many reported works,the research on this aspect is still in the prototype stage.Compared with traditional electrochemical methods and optical analysis methods,the sensing elements and signal transduction mechanisms of photoelectrochemical need be further studied and expanded.In this work,a novel CdS QDs/TiO2/ITO photoelectric sensor was constructed based on CdS quantum dots(QDs)and applied to the photoelectrochemical detection of[Fe(CN)6]4-and ?-galactosidase.1.Specifically,we synthesized TGA-capped CdS QDs with high photoelectric conversion efficiency,and then composed QDs onto calcined TiO2 NPs film on the pretreated ITO glass electrodes.Subsequently,a layer-by-layer(LBL)self-assembly based on the electrostatic adsorption of positively charged poly(diallyldimethylammonium chloride)(PDDA)and negatively charged CdS QDs were assembled as a sensor,the CdS QDs/TiO2/ITO sensing electrode was successfully prepared.The photoelectric sensor combined the large bandgap TiO2 with the small bandgap CdS QDs as a photoelectric conversion unit,which greatly improved the performance of the sensing electrode.2.The experimental results show that our PEC strategy is simpler,less costly and more efficient in detecting[Fe(CN)6]4-.In this system,the[Fe(CN)6]4-acted as an electron donor to increase photocurrent with ascorbic acid(AA)synergistic.Under the optimal conditions,the increase of the photocurrent was proportional to the concentration of the[Fe(CN)6]4-ranging from 1.0-12.0 ?mol/L,and the linear equation was:y = 4.858 x + 31.46 with a correlation coefficient of 0.9985,and the limits of detection(LOD)was 0.26 ?mol/L at the S/?(? is standard deviation of ten times blank experiment)ratio of 3.3.In this work,CdS QDs/TiO2 composite materials were used as the photoelectric conversion unit,we designed a sensitive PEC sensor for accurate determination of ?-galactosidase activity.In this experiment,?-galactosidase catalyzed the hydrolysis of 4-nitrophenyl-?-D-galactopyranoside(PNPG)to p-nitrophenol(PNP),and the PNP have a good response to CdS QDs/TiO2/ITO sensing electrode in the detection system.Because of the high specificity between?-galactosidase(?-Gal)and substrate PNPG,we designed the sensor with high sensitivity and selectivity,and this method has the advantages of rapid reaction,simple portable instrument and low detection limit.Under the optimal conditions,the increase of photocurrent linearly increased with the concentration of ?-Gal in the range of 6.0 to 105.0 U/L.The linear equation was y = 0.026 x + 1.919,with a correlation coefficient R2 = 0.996,and the limits of detection(LOD)was 1.46 U/L at the S/?(? is standard deviation of ten times blank experiment)ratio of 3.In summary,we first synthesized CdS QDs with good photosensitivity and then fabricated CdS QDs/TiO2/ITO sensing electrodes by layer-by-layer self assembly.Under the specific wavelength of light,the electrons inside the CdS QDs transitioned from the valence band to the conduction band.Since the valence band of TiO2 was lower than CdS QDs,excited state electrons transferred to TiO2,which made the electrons and holes separated,thus greatly reducing the probability of electron-hole recombination and increasing photoelectric conversion efficiency.CdS QDs/TiO2/ITO sensing electrode was used to detect anti-caking agent in edible salt and the activity of ?-Gal,which fully proved that the method of PEC analysis possessed the advantages of high sensitivity,short time-consuming,simple equipment and good selectivity,and so on.