| The target binding affinity of functional nucleic acids can rival to or even better than that of antibodies,of which,aptamers are regarded as "chemical antibodies".Therefore,aptamer biosensors have recently caused extensive concern in the analysis of antigens/antibodies,DNA,microRNA,cell,the evaluation of enzymes or drugs,small organic moleculars,and metal ions,et al.Heavy metal contaminations have posed significant health concerns to the general public,and one way to minimize the chance of metal poisoning is to develop analytical tools for metal detection.Analytical techniques,such as atomic absorption spectrometry,inductively coupled plasma mass spectrometry,anodic stripping voltammetry,capillary electrophoresis,and X-ray fluorescence spectrometry,have been routinely used for metal ion analysis with high sensitivity(often<ppb level).Many of them can quantify multiple metal ions simultaneously.However,it is generally believed that most of the above techniques require sophisticated equipments,sample pretreatment,or skilled operators,making it difficult for on-site,real-time monitoring of metal ions.Therefore,the development of facile,fast,effective,and economic sensors to recognize important analytes has long been a focus of research for many areas,including environmental monitoring,industrial quality control,and medical diagnostics.Photoelectrochemical(PEC)detection has the advantages of high sensitivity,simple device,and easy miniaturization,which has made it one of the most attractive detection methods.Herein,coupling the high specificity of functional nucleic acids and the high sensitivity of PEC sensors,the PEC metal-ion sensors will be developed with excellent analytical performance.Specific works are as follows:1.A novel in situ-generated nano-gold plasmon-enhanced PEC aptasensor for Hg2+ ions was fabricated using a perylene-3,4,9,10-tetracarboxylic acid/graphene(PTCA/GR)heterojunction.The fabricated PEC aptasensor was based on thymine-Hg2+-thymine coordination chemistry and the plasmonic near-field absorption enhancement effect of the subsequent specific catalytic formation of nano-gold.The energetic electrons from the surface plasmons of the nano-gold were injected into the LUMO orbit of the organic PTCA semiconductor and then rapidly transferred to the electrode through GR due to the possible Hg2+-DNA molecular wires following irradiation with the visible light(?>450 nm)and at the bias voltage of 0.2 V.The fabricated aptasensor was linear in its response to the concentration of Hg2+ ions in the range of 5-500 pmol L-1 with a detection limit of 2 pmol L-1.The presence of up to 200-fold greater concentrations of other common metal ions did not interfere with the detection of Hg2+ ions in an aqueous system,and the results corresponded well with those obtained by ICP-MS.This novel plasmon-enhanced PEC aptasensor exhibited good performance with its high sensitivity,good selectivity,low cost,and portable features.The strategy of the localized surface plasmon resonance through the in situ generation of noble metal nanoparticles paves a new way for performance improvements of PEC aptasensors.2.One-dimensional(1D)semiconductor architectures are important in photovoltaic applications due to the large surface area,morphological control,efficient light trapping and superior charge transport.Herein,a robust aptasensor for silver ions(Ag+)was first proposed based on the enhanced ZnO nanorod-based photoelectrochemistry by the in situ generated AgBr via layer-by-layer assembly.The coupling of the visible-light-response AgBr and the facile electrodeposition of ZnO nanorod array resulted in an enhanced photoelectric conversion efficiency by means of the extended visible light response,the fast separation of charge carriers and the light scattering in the nanorod array.Owing to the highly specific interaction of C-Ag+-C coordination chemistry and the specific ionic interaction between Ag+ and Br-,it also has an unusual high selectivity.Under the optimized conditions,the fabricated aptasensor had a detection limit of 150 pmol L-1,which was 1-3 orders lower than most of the previous methods.This work opens up ID ZnO nanorod array applied in PEC sensing.And more than that,the strategy of in situ generated a narrow-bandgap semiconductor paves a new way for PEC sensing.3.A label-free PEC aptasensor for K+ was first constructed using Mn-doped ZnO nanorods prepared by one-step electrodeposition.The fabricated PEC aptasensor was based on the highly specific interaction of K+ and its aptamer of the G-quadruplex,which can efficiently prevent the electron donor of quercetins reaching the electrode surface and then proportionately affects the enhanced photocurrent response.The ultrasensitivity of the PEC aptasensor was mainly due to the rapid separation of the more long-lived photon-generated carriers and the extended visible light absorption caused by Mn doping.Under the optimized experimental conditions,the fabricated biosensor was linear in its response to the concentration of K+ in the range of 12 pmol L-1 to 12.0 nmol L-1 with a detection limit of 4.0 pmol L-1 at a signal-to-noise ratio of 3.The common coexist ions did not interfere with the detection of K+ in urine sample,and the results corresponded well with those obtained by ICP-MS.This novel fabricated PEC aptasensor for K+ exhibited good performance with ultrasensitivity,good selectivity,simplicity,and economy.In the way of electrode modification,this work provided a convenient direct assembly strategy with no trouble utilizing ionic polymer such as PDDA as the electron transfer relay.And this paves a new way for the immobilization of molecular probe of label-free photoelectrochemical aptasensor.4.A new fabrication strategy of Au nanoparticles(NPs)embedded between ZnO nanowire array and a conducting substrate was experimentally demonstrated using a template-free electrodeposition method.This facile method could be applied to investigate novel disordered photonics coupled with plasmonics for efficiently enhanced photocurrent.Under the optimized plasmonic substrate,the photocurrent of disorder-enhanced Au-ZnO nanowire array is about 20-fold that of ZnO nanowire array at 0.2 V vs SCE(sat.KCI)following a tungsten light irradiation.Both the plasmonic effect of Au NPs such as the stationary localized surface plasmons(LSPs),the propagating surface plasmon polarizations(SPPs)and the disorder-enhanced photonics in the hybrid structure are available to improve the photoelectric conversion efficiency by enhancing the trapping of the simulated sunlight and the collection of charge carriers.Herein,disordered photonics was first coupled with plasmonics to explain for the enhanced PEC performance.This work also provided a new fabricating avenue for plasmonic noble metals embedded in semiconductor devices. |
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