Study On Electrochemical Biosensor Based On Multiple Nanocomposite Amplification

During the past few decades,by integrating electrochemical analytical technique and biosensors,the electrochemical biosensors possess various advantages such as simple operation,inherent miniaturization,fast response time,high sensitivity,good selectivity and low cost,which has received wide attention in various fields.Recently,with the rapid development of nanotechnology,various nanomaterials with different morphologies exhibit promising physical-chemical properties such as high chemical stability,large surface area,good biocompatibility and high catalytic activity,providing promising opportunities for developing electrochemical sensors with good analytical performance.The article employs various functionalized nanocomposites as signal enhancers to develop highly sensitive electrochemical biosensors for the detection of thrombin（TB）,carcinoembryonic antigen（CEA）and Lead ions（Pb2+）.Part 1 Dendritic Pt@Au nanowires as nanocarriers and signal enhancers for sensitive electrochemical detection of carcinoembryonic antigenHighly sensitive detection of carcinoembryonic antigen（CEA）is very important in clinical diagnosis and treatment assessment of cancers.In this work,we proposed a sensitive and selective electrochemical aptasensor for CEA detection using dendritic Pt@Au nanowires（Pt@Au NWs）as nanocarriers and electrocatalysts.With many advantages such as large specific surface area,good conductivity,excellent electrocatalytic activity and high stability,dendritic Pt@Au NWs were first employed as nanocarriers for immobilizing abundant thiol-terminated CEA aptamer 2（CEAapt2）and redox-active toluidine blue（Tb）,resulting in the formation of Au NWs-CEAapt2-Tb bioconjugate.In the presence of CEA,the proposed bioconjugate was captured onto the electrode surface through “sandwich” tactics.The electrochemical response was then triggered and further enhanced due to the favorable catalysis capacity of dendritic Pt@Au NWs with peroxidase mimics activity to the reduction of H2O₂ added into the electrolytic cell,which an improved sensitivity benefited from and was successfully achieved.Under the optimal experimental conditions,the proposed aptasensor exhibited a linear response to CEA in the range of 0.001 ng?m L-1-80 ng?m L-1 and the limit of detection is 0.31 pg?m L-1.Moreover,the aptasensor exhibited good selectivity,stability and reproducibility,which indicated its potential applications in clinical diagnostics.Part 2 A sensitive electrochemical aptasensor based on the co-catalysis of hemin/Gquadruplex,platinum nanoparticles and flower-like Mn O₂ nanospheres functionalized multi-walled carbon nanotubesIn this study,a sensitive electrochemical aptasensor for TB detection has been developed using hemin/G-quadruplex,platinum nanoparticles（Pt NPs）and flower-like Mn O₂ nanospheres（f Mn O₂ NSs）functionalized multi-walled carbon nanotubes（MWCNTs）as signal enhancers.Firstly,f Mn O₂ NSs with intrinsic peroxidase-like activity were attached onto the surface of MWCNTs to form the MWCNTs-Mn O₂ nanocomposites which are of large surface area,excellent electrocatalytic activity and high stability.Secondly,the MWCNTs-f Mn O₂ nanocomposites were further used as carriers for immobilization of numerous platinum nanoparticles（Pt NPs）,hemin/Gquadruplex and redox-active toluidine blue（Tb）,which resulted in the formation of secondary aptamer: hemin/G-quadruplex conjugated MWCNTs-f Mn O₂-Pt NPs-Tb.In the presence of TB,the secondary aptamer was captured onto the electrode surface through “sandwich” tactics and greatly enhanced sensitivity was achieved by the synergetic catalysis of flower-like Mn O₂ nanospheres,hemin/G-quadruplex and platinum nanoparticles toward H2O₂ reduction.The proposed TB aptasensor showed a wide linear calibration ranging from 0.1 pmol?L-1 to 30 nmol?L-1 with a lower detection limit of 0.040 pmol?L-1,indicating its potential applications as a valuable tool in the design of enzymefree biosensors.Part 3 Hemin on graphene nanosheets functionalized with flower-like Mn O₂ and hollow Au Pd for sensitive electrochemical sensor for lead ion detection based on the specific DNAzymeIn this study,integrated with DNAzyme highly specific to metal ions,hemin@reduced graphene oxide（hemin@r GO）functionalized with flower-like Mn O₂ and hollow Au Pd（h Au Pd-f Mn O₂-hemin@r GO）was used as electroactive probe and electrocatalyst to construct a sensitive electrochemical sensor for metal ion detection（lead ion Pb2+ as the model）.The proposed signal amplification strategy was mainly based on two aspects.Firstly,the designed probe not only showed high stability and excellent peroxidase-like activity originating from hemin,f Mn O₂ and h Au Pd,but also possessed intrinsic redox performance from hemin,which resulted in the promotion of electron transfer and the enhancement of the response signal.Secondly,due to the introduction of target Pb2+,the Pb2+-specific DNAzyme bound in the electrode surface could be specifically identified and cleaved,and the remained fragment（its supplementary sequence is a single-strand DNA S3）captured the nanocomposites of S3-h Au Pd-f Mn O₂-hemin@r GO on the electrode surface by the hybridization reaction.Therefore,significant improvement of electrochemical analytical performance has achieved owing to the cooperative catalysis of f Mn O₂,h Au Pd and hemin to H2O₂ reduction.The proposed electrochemical sensor wide dynamic response（0.1 pmol?L-1-200 nmol?L-1）,low detection limit（0.034 pmol?L-1）,high sensitivity and high specificity,making it become a useful tool for sensitive detection of other metal ions only by changing the corresponding specific DNAzyme.