Synthesis Of Photoelectrochemical Nanocomposits And Their Applications In Photoelectrochemical Biosensing

Photoelectrochemical(PEC)biosensor is a newly emerged but vibrantly developing technique,which possesses some inherent merits,such as simple instruments,low cost and easy miniaturization.More importantly,benefited from the complete separation of excitation source and electrochemical detection signals,it possesses the advantages of high sensitivity and low background.To date,it has achieved tremendous progress in bioanalysis fields.This doctoral dissertation focused on the synthesis of PEC active nanocomposite materials and their applications for design of highly sensitive PEC biosensors.The main contents are described as below:A highly sensitive signal-on PEC immunosensor was fabricated by using Mn2+ doped CdS quantum dots(QDs)modified TiO2 electrode(CdS:Mn/TiO2)as PEC sensing platform,and silver nanoclusters and graphene nanocomposites(AgNCs-GR)as signal amplification tags.When AgNCs-GR was assembled on the CdS:Mn/TiO2 matrix by sandwich immunoreaction,it improved the conductivity of the sensing interface,facilitated the charge separation,and reduced the recombination of electron-hole pairs,which improved the photo-to-current conversion efficiency and turned the detection mode from signal-off to signal-on type.Based on the photocurrent enhancement,the signal-on immunosensor showed excellent analytical performance to carcinoembryonic antigen(CEA),a model analyte related to many malignant diseases.Under optimal conditions,a wide linear range from 1.0 pg/mL to 100 ng/mL and a low limit of detection of 1.0 pg/mL was obtained.Graphene nanodisks(GRD)with good conductivity and plenty of edge sites were synthesized to load glucose oxidase(GOD)and coupled with CdS:Mn/TiO2 for highly sensitive PEC immunosensing of CEA.A dramatically enhanced signal amplification was achieved based on the synergistic effect of GRD and GOD.GOD could catalyze glucose to produce large amount of H2O2,which acted as electron donors to scavenge photogenerated holes of the CdS:Mn,thus facilitating the separation of the electron-hole pairs and improving the PEC efficiency.The conductive GRD acted as a scaffold to load a large amount of GOD molecules,and also offered a continuous pathway for electrons transfer,which improved the conductivity of the insulated protein layers and further improved the PEC response.Based on the dual signal amplification strategy,CEA as a model analyte was detected by a competitive method.Under optimal conditions,a wide linear range from 10 fg/mL to 1.0 ng/mL and a low limit of detection of 5.65 fg/mL was obtained.A cathodic PEC immunosensor was developed by using p-type cuprous oxide(Cu2O)as electrode matrix and SiO2 nanoparticles as signal amplification labels.The Cu2O/FTO based sensing matrix showed high cathodic photocurrent under the irradiation of visible light.After the sandwich immunoreaction,the assembly of CEA and SiO2-Ab2 nanocomposites on the sensing matrix significantly reduced the photocurrent,which was caused by the severe steric hindrance effect of the non-conductive protein and nanoparticles.Combining the excellent PEC property of Cu2O and the great signal amplification of the SiO2 nanolabels,the fabricated immunosensor exhibited a low detection limit of 61 fg/mL for CEA detection,which was better than most of the previously reported cathodic PEC immunoassays.A highly sensitive PEC detection platform for organophosphorus compounds(OPs)was developed by integrating the highly photocatalytic activity of a triphenylamine-based organic dye and TiO2 nanocomposites(TCA-TiO2)with enzymatic reactions of acetylcholinesterase(AChE).The TCA with a nonplanar structure and a high molar extinction coefficient at visible light region could stably anchor to TiO2 nanoparticles via its carboxyl group.Since the nonplanar structure of triphenylamine could prevent TCA from aggregation and retard the recombination of charge carriers,the TCA-TiO2 exhibited considerably high catalytic activity.Regarding that thiolcholine is an important product of AChE catalyzed hydrolysis reaction and the activity of AChE can be inhibited by OPs,the TCA-TiO2 nanocomposites were applied for the PEC detection of OPs,based on the photocurrent change before and after the OPs inhibition.