The Application Of Dye And Bi₂S₃ Sensitized Nano-tin Dioxide Semiconductor Electrode In Photoelectrochemical Biosensing Detection

Photoelectrochemical?PEC?process refers to the electron excited to produce charge transfer,which due to the absorption of photons of the molecular,ion or semiconductor materials,so as to realize the conversion from light energy to electric energy.PEC biosensor is based on the photocurrent or photovoltage changes in the PEC reaction process and the relationship between the concentration of the subject to be measured for quantitative detection.Tin dioxide?SnO₂?is a commonly used nano-semiconductor material due to its advantages of high thermochemical stability,low preparation cost and high electron mobility.Therefore,it is often used as the basic material for PEC sensors.As a n-type wide bandgap semiconductor material,the forbidden band width is approximately 3.5 eV.And the corresponding absorption light is ultraviolet light.However,ultraviolet light only accounts for about 5%of sunlight.In addition,ultraviolet radiation has a strong lethality to living things.These parts limit its further application in the PEC sensor.Therefore,it is necessary to modify SnO₂ to expand its light absorption range and further improve the photoelectric conversion efficiency by inhibiting the combination of photogenerated electron hole pairs.Therefore,the improvement of photoelectric conversion rate and stability of electrode materials can provide an important guarantee for the high sensitivity and stability of PEC biosensor.In this paper,the dye and narrow bandgap semiconductor materials are mainly used to sensitize the wide-bandgap semiconductor material SnO₂.Based on this,the corresponding PEC biosensor is constructed for different targets to be tested,including small molecules or biomacromolecules,to achieve specific and sensitive detection of them.The specific work of this paper includes the following aspects:1.Detection of M.SssI methyltransferase activity and the effects of its inhibitors by PEC methodIn this work,Ru?bpy?₂?dppz?²⁺?Ru=Ruthenium,bpy=2,2'-bipyridine,dppz=dipyrido[3,2-a:2',3'-c]phenazine?dye was used to sensitize SnO₂,and Ru?bpy?₂?dppz?²⁺was used as DNA embedding agent to act as PEC signal molecule.Firstly,the 5'-terminated amino DNA strand?containing the methylation recognition site 5'-CCGG-3'?was covalently linked to the surface of the ITO/SnO₂ electrode adsorbed with polyacetylamine?PEI?by glutaraldehyde cross-linking.In the presence of methyltransferase and methyl donor s-adenosine methionine?SAM?,the5'-CCGG-3'sequence in the DNA strand is methylated.The methylated DNA strand is not spliced by the nucleic acid restriction enzyme HpaII.Thus,more intact DNA strands are retained on the electrode surface,providing more binding sites for the PEC signal molecule Ru?bpy?₂?dppz?²⁺,leading to a higher PEC response.The experimental results showed that the activity range of methyltransferase in M.SssI detected by this method was 5-80 U·mL^-1,and the detection limit was 0.45 U·mL^-1.The sensor did not respond to other methyltransferases,indicating good selectivity.In addition,we also used this sensor to investigate the effect of methyltransferase inhibitor 5-Aza-2'-deoxycytidine?5-Aza-dC?on the enzyme activity of M.SssI,and the measured semi-inhibitory concentration was 8.43?M,which was similar to the results measured by other methods,indicating that this PEC sensor can also be used for the rapid screening and evaluation of methyltransferase inhibitors.This sensing mode can be extended to detect the activity of other DNA methyltransferases by changing the DNA sequence.2.The construction of PEC sensor for the detection of tobramycin based on Bi₂S₃sensitized SnO₂ combined with aptamer of nucleic acidIn this work,composite semiconductor materials were prepared by combining narrow bandgap semiconductor Bi₂S₃ with wide bandgap SnO₂ through the preparation method of continuous ion layer adsorption reaction?SILAR?.Due to the energy matching between Bi₂S₃ and SnO₂,Bi₂S₃ can effectively shift the light absorption band of SnO₂ into the visible light region.In addition,the nucleic acid aptamer of tobramycin?TOB?can be conveniently fixed on the surface of the composite electrode through the bismuth sulfur bond,so as to construct a PEC sensor that can selectively and sensitively detect TOB.In the detection process,it can be seen that Bi₂S₃ on the composite nano-electrode under light is excited to generate electrons and holes,and oxalic acid in the electrolyte as an electron donor can effectively capture the photoinduced holes of Bi₂S₃,so that more photogenerated electrons flow into the external circuit and generate a strong PEC response.When the TOB molecule under test exists,it can specifically interact with the aptamer on the electrode surface to form a complex,which leads to the increase of electrode interface impedance and the decrease of photocurrent,thus establishing the correlation between the concentration of TOB and the intensity of photocurrent.Under the optimal detection condition,the sensor has a good linear response to TOB within 5-50 nM,and the detection limit is 4.28 nM.In addition,calcined under 450°C for SnO₂/Bi₂S₃electrode membrane stability is very good,can significantly improve the stability of the optical chemical sensor.Besides,this sensor also realized the quantitative determination of trace TOB in actual sample milk.3.The construction of PEC sensor for chloramphenicol detection based on ferritin-oxalic acid double signal amplification strategyIn order to further improve the sensitivity of PEC sensor,in the third work we developed a PEC sensor that can detect chloramphenicol?CAP?with super sensitivity based on the ferritin-oxalic acid double signal amplification strategy combined with nucleic acid aptamer.First,in the presence of the molecule CAP to be measured,CAP can compete with the CAP aptamer combined with S1 from the electrode surface to make it separate from the electrode surface,resulting in a smaller impedance at the electrode interface,thus increasing the photocurrent.In addition,the aptamer detached from the electrode surface also carries ferritin bound at its end,which makes the reduction of ferritin content and the reduction of oxalic acid consumption.As a result,more oxalic acid in the solution can provide electrons to the Bi₂S₃ hole,resulting in the decrease of the recombination rate of Bi₂S₃ photogenerated electron hole pairs and further increase of photocurrent.The above two steps play the role of double amplification of PEC signal.The sensor constructed in this work showed good linearity in the range of CAP concentration from 0.05 to 2 nM,and the detection limit was 0.046 nM.Depending on the aptamer,the sensor array can also be used to detect other antibiotics.