Preparation Of Novel Photocathodic Composite Materials And Their Photoelectrochemical Sensing Applications

Potoelectrochemical(PEC)analysis has become a flourishingly developed sensing technology.It possesses many attractive merits of rapid response,high sensitivity,reduced background signal,reasonable costs,miniaturized instrument,and has been successfully applied in the fields of biological analysis,environmental pollution detection,clinical application and so on.In recent years,cathodic PEC assay served as an effective complement to anodic sensing strategy has also attracted research interest.The photocathode is readily interacted with analytes that prone to accept photogenerated electrons rather than be oxided by holes,which thus avoid the intrinsic oxidation reaction of absorbed reductive species at the photoanode/electrolyte interface and result an improved selectivity(especially for biosensor).In this thesis,new types of cathodic PEC materials with favourable photoactivity were designed to prepare functional electrodes,and the modified photocathodes were further combined with different specific recognition methods to realize the selective detection of certain target analytes.The research contents of this dissertation were indicated below.(I).Cu O-Cu₂O heterojunction was synthesized via a one-step flame spray pyrolysis(FSP)process and employed as photoactive material in construction of a PEC sensing device.The surface analysis showed that Cu O-Cu₂O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface.Under visible light irradiation,the Cu O-Cu₂O-coated electrode exhibited admirable cathodic photocurrent response,owing to the favorable property of the Cu O-Cu₂O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron-hole pairs.On the basis of the interaction of L-cysteine(L-Cys)with Cu-containing compounds via the formation of Cu-S bond,the Cu O-Cu₂O was proposed as a PEC sensor for L-Cys detection.While L-Cys was present in the solution,a decrease of photocurrent response was observed,owing to the the binding interaction of L-Cys molecules and Cu O-Cu₂O nanoparticles resulted in an increased steric hindrance on the electrode surface.Influence factors including Cu O-Cu₂O concentration,coating amount of Cu O-Cu₂O and applied bias potential on the PEC response toward L-Cys were optimized.Under optimum conditions,the photocurrent of the proposed sensor was linearly declined with increasing the concentration of L-Cys from 0.2?M to 10?M,with a detection limit(3S/N)of 0.05?M.Moreover,this cathodic PEC sensor displayed high selectivity,reproducibility and stability.The potential applicability of the proposed PEC sensor was assessed in human urine samples.(II).A novel p-type semiconductor-based cathodic“signal-on”photoelectrochemical aptasensor was proposed for highly sensitive and selective detection of chloramphenicol(CAP).The photocathode was fabricated with hierarchical porous flower-like Bi-Bi OI@C composite synthesized via a one-pot solvothermal method using glucose as both green reductant and carbon precursor.Due to the surface plasmon resonance(SPR)effect of Bi and high-conductivity of carbon,the composite exhibited an enhanced cathodic photocurrent as compared with pure Bi OI or Bi-Bi OI.When CAP-binding aptamer was immobilized as recognition element on Bi-Bi OI@C modified electrode,the CAP molecules could be specifically captured by aptamer and then effectively accepted photogenerated electrons on Bi-Bi OI@C to increase the cathodic photocurrent.Thus,a cathodic PEC aptasensor showing specific“signal-on”response to CAP was constructed.Some influencing factors such as coating amount of Bi-Bi OI@C suspension,applied bias potential,and aptamer concentration were studied.Under the optimum conditions,the cathodic photocurrent of the constructed PEC aptasensor increased linearly with CAP concentration from 2 n M to 250 n M,with a detection limit(3S/N)of 0.79 n?.The proposed cathodic PEC aptasensor was successfully applied to the determination of CAP in pharmaceutical tablet,eye drop and lake water samples.(III).The progesterone(P4)level in body fluids can act as an indicator for early pregnancy diagnosis and offers insight into mammalian somatic function.In this work,we designed an antibody-aptamer based sandwich assay as a cathodic photoelectrochemical biosensor for P4 detection.The composites of carbon dots and graphene oxide(CDs-GO)with favorable cathodic photocurrent response were used as photoactive materials on which the antibody(Ab)of P4 was immobilized.Meanwhile,high affinity truncated P4 aptamer was immobilized on Au-Cu O-Cu₂O nanocomposites to act as a bioconjugate.When P4 was present,the aptamer-Au-Cu O-Cu₂O bioconjugate could amplify the cathodic photocurrent of CDs-GO modified electrode through Ab-P4-aptamer interactions.Under optimum conditions,the cathodic photocurrent of the constructed PEC biosensor was found to linearly increase with P4 in a wide concentration range from 0.5 n M to 180 n M,with a low detection limit(3S/N)of 0.17 n?.The proposed cathodic PEC sensing platform demonstrated high selectivity,satisfying reproducibility and good stability.Moreover,the sensor was successfully applied in the determination of P4 in human serum samples.