Research On The Performance Of Carbon Nitride Heterojunction Based Photoelectrochemical Aptasensor For Antibiotics Detection

The design and development of a fast,low-cost,and efficient analytical technology for the trace detection of antibiotics is of great significance to the safety of water environment and human health.Photoelectrochemical（PEC）aptasensors possess the advantages of fast response,high sensitivity,high selectivity,simple equipment,and easy miniaturization,which plays an indispensable role in the fields of food safety,environment monitoring and life analysis.Photoactive materials with high photoelectric conversion efficiency are the key to determine the sensitivity of PEC aptasensors.In this paper,the application of bulk graphitic carbon nitride（g-C₃N₄）in the field of PEC aptasensors is limited due to its low visible light utilization and high photogenerated carrier’s recombination rate.The introduction of metal oxides or hydroxides can enhance the visible light absorption and the separation/migration ability of photogenerated charges of g-C₃N₄,and amplify the photocurrent signal,thereby constructing PEC aptasensors for highly selective and sensitive detection of trace antibiotics.The influence mechanism of heterojunctions effect on the enhancement of the signal amplification of PEC aptasensors has been systematically clarified,and the mechanism of PEC aptasensors for antibiotics detection has further been studied.The specific research content of this paper is as follows:（1）Considering the problem that low light visible utilization rate of g-C₃N₄restricts the practical application of g-C₃N₄-based PEC aptasensors,Co₃O₄/g-C₃N₄heterojunction was synthesized by using metal oxide of Co₃O₄ with strong visible light absorption and matched band structure with g-C₃N₄,and an oxytetracycline（OTC）PEC aptasensor was constructed.Under the bias voltage of–0.2 V,the photocurrent of Co₃O₄/g-C₃N₄/indium tin oxide（ITO）electrode was about 1.5 times compared with that of g-C₃N₄/ITO.Using theπ-πconjugated interaction between g-C₃N₄ and OTC aptamer,a PEC aptasensor was constructed for specifical recognition of OTC.Based on the mechanism of steric hindrance effect inhibiting the electrons transfer,Co₃O₄/g-C₃N₄/ITO-based PEC aptasensor exhibited a wide linear range(1×10^–2-5×10² nmol L^–1),a detection limit(3.5 pmol L^–1)and high selectivity for OTC detection.This design clarifies that metal oxides can enhance the visible light utilization of g-C₃N₄ to realize the amplification of photocurrent signal and broadens the application of g-C₃N₄-based photoactive materials in the field of environmental analysis.（2）Considering the problems that g-C₃N₄ possesses high recombination rate of photogenerated carriers and Co₃O₄/g-C₃N₄ composites exhibited better PEC performance under the bias voltage in the first work,layered double hydroxide（LDH）materials were utilized owing to the visible light response and easy preparation.NiFe LDH/g-C₃N₄ composites was successfully synthesized,and an ofloxacin（OFL）PEC aptasensor was constructed.Flower-like NiFe LDH composed of nanosheets can form a close contact interface with sheet-like g-C₃N₄,promoting the effective separation and migration of photogenerated charges.Under no bias voltage,the photocurrent of NiFe LDH/g-C₃N₄/ITO was significantly higher than that of g-C₃N₄/ITO.Depending on theπ-πconjugation of OFL aptamer-g-C₃N₄ can effectively anchor OFL aptamer.Based on the mechanism that the OFL-aptamer complex dropped off the electrode surface,NiFe LDH/g-C₃N₄/ITO-based PEC aptasensor for OFL detection exhibited a wide linear range(1×10^–4-1 nmol L^–1)and a low detection limit(35 fmol L^–1),and is expected to realize high selectivity and high reproducibility analysis of actual water and milk samples.（3）In order to further optimize the detection performance of OFL PEC aptasensor in the previous work,two-dimensional/two-dimensional（2D/2D）heterojunction was utilized owing to the characteristics of sufficient interface contact and the formation of high-speed charges transfer channel in this work.2D/2D CoAl LDH/g-C₃N₄ heterojunction was successfully synthesized,and an OFL PEC aptasensor was further fabricated.2D/2D heterojunction is beneficial to shortening the transfer path of photogenerated carriers,and prolonging the lifetime of charges,leading to the significant amplification of photocurrent signal.OFL-aptamer complex was stabilized on the electrode surface owing to the synergistic interaction between OFL aptamer-g-C₃N₄ and OFL aptamer-metal ions,and large amounts of holes were involved in the oxidation of OFL molecules.CoAl LDH/g-C₃N₄/ITO-based PEC aptasensor exhibited a wider linear range(1×10^–5-1×10² nmol L^–1)and a lower detection limit(3.4 fmol L^–1)than that of NiFe LDH/g-C₃N₄/ITO.Based on the previous works,the design can clarify that metal hydroxides can boost the charges separation and migration ability to amplify the photocurrent signal of g-C₃N₄,which broadens research ideas for the field of PEC analysis and environmental detection.