Study On Novel Photoelectrochemical Biosensors Based On Different Sensing Strategy

Photoelectrochemical（PEC）biosensor is a new analysis method based on PEC process and specific bio-recognition process.In PEC detection,the incident light source excites photoactive materials to generate the photocurrent as a detection signal,and the specific biomolecule is usually used as a bio-recognition probe for capturing analyte.PEC biosensor exhibits fast response,simple operation and easy miniaturization,which is attributed to optical analysis and electrical a nalysis.Due to the specific interaction between the biological probe and the analyte,PEC analysis also has high selectivity and high sensitivity.In addition,the complete separation of incident light source and detection signal can effectively reduce th e background signal.These remarkable characteristics of PEC biosensor make it a valuable and sensitive biological detection tool,which has aroused the interest of a large number of researchers.Although there have been various PEC biosensors with excelle nt performance,there is still a lot of room for innovation in the photoelectric properties of photoelectric materials and design strategies of sensor.Moreover,coexisting oxidized or reduced species in complex real samples or the detection matrix may produce false positive or false negative signals,thereby affecting the accuracy of detection.Therefore,improving photoelectric performance and developing sensing strategy are research hotspots in the field of PEC bioanalysis.This paper mainly develops the following new PEC biosensors to realize the highly sensitive and selective detection of M.Sss I MTase activity,DNA,mi RNAs and Pb²⁺:（1）Based on the excellent PEC properties of Cd Se quantum dots（Cd Se QDs）and the high efficiency of the‘‘Z-scheme’’heterojunction to enhance the photocurrent,a novel“Z-scheme”heterojunction（Cd Se QDs/amino group functionalized GQDs（af GQDs））was prepared for the construction of PEC sensor.First,the indium tin oxide（ITO）electrode was modified with the poly（diallyldim ethylammonium chloride）（PDDA）-reduced graphene oxide（P-r GO）.Then,Cd Se QDs were assembled on ITO/P-r GO electrode by electrostatic interaction between positive-charged P-r GO and negative-charged carboxy-groups-functionalized Cd Se QDs.To assemble the GQD s on Cd Se QDs,GQDs were functionalized with amino groups and then covalently connected to carboxy-groups-functionalized Cd Se QDs.Switching of the photocurrent direction from the anodic photocurrent of ITO/P-r GO/Cd Se QDs to an enhanced cathodic photocurrent of ITO/P-r GO/Cd Se QDs/af GQDs occured due to the formation of a new“Z-scheme”heterojunction（Cd Se QDs/af GQDs）.Based on the“Z-scheme”Cd Se QDs/af GQDs heterojunction and the multiple signal amplification strategies（precipitation effect of benzo-4-chlorohexadienone（4-CD）,the energy transfer（ET）effect between af GQDs and gold nanoparticles（Au NPs）,and the steric hindrance effect of Au-polyamidoamine（PAMAM）-Mn O₂）,a sensitive PEC biosensor had been developed for M.Sss I MTase activity assay and a goo d analytical performance could be obtained with a wide linear response ranging from 0.1 to 60 U m L^-1 and a low detection limit of 0.046 U m L^-1.The developed PEC biosensor may have potential application in MTase inhibitor screening,cancer early diagnostic s and anti-cancer drugs discovery.（2）Based on the DNA-linked Cd Se QDs/af GQDs“Z-scheme”system,an ultrasensitive and highly selective PEC sensing platform has been constructed for DNA assay.Firstly,the ITO electrode was modified with the P-r GO to fix and disperse Cd Se QDs.The obtained ITO/P-r GO/Cd Se QDs electrode generated an anode photocurrent.After catalytic hairpin assembly（CHA）and hybridization chain reaction（HCR）processes triggered by target DNA（T-DNA）,abundant and long double-strand DNA（ds DNA）were introduced to the sensing platform.And then,numerous af GQDs were intercalated into the ds DNA strands,resulting in the formation of DNA-linked Cd Se QDs/af GQDs“Z-scheme”system and the change of the response signal from anodic to cathode photocurrents.Due to the target-induced photocurrent-polarity switching,the constructed PEC sensing platform features with negative background signal and excellent selectivity,and T-DNA was sensitively detected（linear range,1a M-100 p M;detectable limit,0.1 a M）.Therefore,the sensor platform has promising application in bioanalysis and disease diagnosis.（3）A photocurrent-polarity switching“Z-scheme”system Cd Se QDs/ds DNA/porous Ag-Au nanosphere（PAu-Ag Ns）/af GQDs was prepared to establish an ultrasensitive PEC biosensor for micro RNA（mi RNA）-141 assay on the basis of negative background signal and dual signal amplification strategy.To fix and disperse Cd Se QDs,the P-r GO with a positive charge was first coated on the ITO electrode.Then,hairpin DNA probe 1（HP1）was immobilized on the ITO electrode via Cd-S bond.After duplex-specific nuclease（DSN）-assisted target recycling amplification and strand displacement amplification（SDA）reaction,abundant HP1-HP3 duplex were formed on the electrode surface.The streptavidin（SA）-labeled PAu-Ag Ns/af GQDs were introduced on the electrode surface via the special reaction between SA and biotin,forming the photocurrent-polarity switching“Z-scheme”system Cd Se QDs/ds DNA/PAu-Ag Ns/af GQDs.In the“Z-scheme”system,ds DNA and PAu-Ag Ns was acted as the electron mediators to facilitate the photogenerated electrons transfer from Cd Se QDs to af GQDs.Under optimum conditions,the switching photocurrent signals were correlated to the mi RNA-141 concentrations.The linear range was from 1 a M to 1 n M,and the detection limit can be calculated to be0.20 a M.Because of the negative background signal and DNA-based amplification strategy,the designed PEC sensing platform can avoid the effects of the initial signal and background noise,and has the improved sensitivity and anti-interference ability.Therefore,this PEC biosensor may have potential application in the early diagnosis of cancer and tumor.（4）Based on the matched energy level between Cd Se QDs and nitrogen-doped porous carbon-Zn O（NPC-Zn O）polyhedra obtained via the carbonization treatment of zeolitic imidazolate framework（ZIF）-8,a novel photocurrent-direction switching system（Cd Se QDs//NPC-Zn O polyhedra）had been developed.Furthermore,by coupling Cd Se QDs//NPC-Zn O polyhedra photocurrent-direction switching system with target-triggered SDA strategy,a new PEC sensing platform had been constructed to sensitively detect mi RNA-155.First,the ITO slice was modified with the P-r GO and Cd Se QDs,and utilized as the photoelectrode.HP1 was then immobilized on the electrode and opened in the presence of mi RNA-155.After SDA process between mi RNA-155 and biotinylated HP2,the SA-labeled Au NPs/NPC-Zn O polyhedra were attached to the electrode surface by the special reaction between SA and biotin.As a result,the photocurrent direction of the electrode was switched from a anodic photocurrent to a cathodic photocurrent,and the movement of photogenerated electrons of the cathode photocurrent follow ed the“Z-scheme”path.Based on this photocurrent-direction switching system,mi RNA-155 was detected sensitively（linear range,0.1 f M-10 n M;detection limit,49 a M）.Importantly,the developed PEC sensing platform had negative background signal due to the different photocurrent directions resulted from the target and interferents.Additionally,the sensor exhibited good stability,acceptable reproducibility and excellent selectivity,making this platform have broad application prospects in early tumor diagnosis by utilizing mi RNAs as the biomarkers.（5）A facile and sensitive PEC biosensor based on DNAzyme-induced disassembly of“Z-scheme”system Ti O₂/Au/Cd S QDs was established for lead ion(Pb²⁺)assay.Ti O₂/Au modified ITO electrode was utilized to immobilize substrate strand DNA1 via Au-S bond.Subsequently,the Cd S QDs labeled catalytic strand DNA2 was introduced to the electrode surface via hybridization,forming the“Z-scheme”system Ti O₂/Au/Cd S QDs and generating an enhanced PEC signal.Once the target Pb²⁺existed,the Pb²⁺-specific DNAzyme was activated and then catalyzed the cleavage of DNA1,which induced the dissociation of DNA1-DNA2 double helix and the disassembly of“Z-scheme”system Ti O₂/Au/Cd S QDs.As a result,the PEC signal decreased.The developed PEC biosensor exh ibited excellent performance for Pb²⁺assay with a wide linear response range of 0.5 p M-10 n M and a low detection limit of 0.13 p M,and good applicability in water and human serum samples,demonstrating great potential for practical applications in environment monitoring and clinical analysis.（6）Taking ZIF-8 polyhedra as the carriers of GQDs,GQDs-embedded ZIF-8polyhedra（denoted as GQDs@ZIF-8 polyhedra）were successfully prepared and used as the multi-functional signal quenchers to construct a new signal-off PEC biosensor for M.Sss I MTase activity assay.Firstly,the ITO slice was modified with Ti O ₂,PDDA and Cd Te QDs.The obtained electrode was used as the photoelectrode and labeled as ITO/Ti O₂/Cd Te QDs.Then,single-stranded DNA（S1）was anchored on the photoelectrode surface via Cd-S bond.After hybridization between S1 and biotinylated single-stranded DNA（S2）,the SA-labeled GQDs@ZIF-8 polyhedra were introduced to the modified electrode via the specific reaction between biotin and SA.As the signal quenchers,GQDs@ZIF-8 polyhedra could not only inhibit the photocurrent signal of the ITO/Ti O₂/Cd Te QDs electrode due to the steric hindrance effect,but also acted as peroxidase mimetics to catalyze precipitation reaction of4-chloro-1-naphthol（4-CN）,resulting in the evident depression of the photocurrent signal.For the specially designed ds DNA（S1/S2）,the decreased photocurrent was quantitatively correlated with the M.Sss I MTase activity(linear response range,0.005-150 U m L^-1;detection limit,0.004 U m L^-1).The developed GQDs@ZIF-8 polyhedra and related PEC biosensor may have potential applications in clinical research and disease diagnosis.