Fabrication And Application Of Nanomaterials-based Electrochemical Biosensors

The biosensor is a device that is sensitive to biochemical substances,and transforms concentration or activity to detectable signals.Sensitive biomaterials?e.g.enzyme,antibody,antigen,nucleic acids,tissue,cells,microorganisms,et al?act as biological recognition elements,and the biosensors achieve detection of analyte molecules in the sample by signal amplification methods and appropriate physicochemical transducers,in which the biological signals can be inverted into detectable signals like sound,light,electric power,etc.Currently,there are some biosensing tools like electrochemical,optical,thermal and mass analysis,of which electrochemical biosensor is an ideal one.Combining solid electrode with bioactive materials,the sensitive biological molecules are immobilized on the electrode surface.By the specific recognition between the molecules,biological target molecules can sensitively and selectively be recognized.As a signal transducer,the electrode can export the recognition signal into electrochemical signals,thus achieving quantitative or qualitative analysis of the target molecule.As an important branch of the biosensor,electrochemical biosensor has some significant advantages,such as simple equipment,small size,simple operation,fast analysis,low cost,high sensitivity and high specificity.Therefore,in laboratory medicine,especially point of care testing?POCT?,electrochemical biosensor has potential applications.For electrochemical biosensor,finding suitable electrode materials to improve the sensing performance has played a crucial role.Graphene is two-dimensional material constituting a single layer sheet,having unique physical and chemical properties: larger surface ratio,high electron mobility,high thermal conductivity,high mechanical strength.Currently,graphene used mostly for electrochemical sensing is graphene oxide reduction?RGO?.After reduction,RGO not only has good electrical conductivity and large surface ratio,but also contains partial structure functional defects and functional groups,which can be used as an ideal material.In reduction methods,the electrochemical reduction,compared to the chemical reduction,is more rapid,simple,economical,and less environmental pollution.Meanwhile,considering the fact that gold nanoparticles?AuNPs?have high affinity as well as high load capacity,and aptamers have high specificity and strong affinity for their ligands,the study was designed to construct the AuNPs-ERGO nanocomposite on the electrode surface,immobilize aptamer on the AuNPs surface,and detect the biomolecules.In addition to finding the right electrode materials,some signal amplification methods,such as polymerase chain reaction,loop-mediated isothermal amplification,rolling circle amplification,hybridization chain reaction,and introduction of enzyme-labeled molecules,have been used to improve the performance of the electrochemical biosensors.Therefore,this study was designed to construct electrochemical DNA sensors based on terminal deoxynucleoside transferase?TdT?and silver nanoclusters?AgNCs?to amplify signal.In this study,based on the methods to improve the performance of the electrochemical biosensor,the electrochemical detection of dopamine?DA?and DNA were realized,respectively.Details are as follows:I Reduced graphene oxide-gold nanoparticles-based electrochemical aptasensor for dopamine detectionIn this study,by electrochemical reduction of graphene oxide and AuNPs,ERGO-AuNPs nanocomposite was step-wise modified onto the electrode surface.Then thiolated aptamer was immobilized on the AuNPs by Au-S bond.By detecting the electrochemical signal changes before and after aptamer-DA binding,DA could be detected.In the DA concentration range of 0.5-20 ?mol/l,DA peak current and ?I?the difference between peak current of DA and the blank?showed a good linear relationship,and the detection limit was 0.13 ?mol/l?3?/S?.In addition,in coexisting condition containing DA,uric acid?UA?,ascorbic acid?AA?,DA could be well distinguished with high selectivity.Finally,the sensor also achieved high reproducibility and stability,and DA detection in human serum samples,providing a very promising platform for disease diagnosis.II Terminal deoxynucleoside transferase and silver nanoclusters signal amplification-based electrochemical sensor for DNA detectionIn this study,the AuNPs were firstly electrochemically deposited on glassy carbon electrode?GCE?,and then thiolated DNA probe was immobilized on AuNPs by the Au-S bond.After adding target DNA,hybridized occurred between complementary DNA probe and target DNA.While TdT was added,it was capable of identifying the 3'-OH end of target DNA,extending target DNA with deoxyadenosine triphosphate?dATP?.Next,DNA fragments,AgNO₃ and NaBH₄ were sequentially added,forming AgNCs on unhybridized rich cytosine sequence.AgNCs could highly catalyze H₂O₂ to produce characteristic redox peaks,thus achieving the determination of DNA.Experiments showed that AuNPs could accelerate the electron transfer reactions on the electrode surface,and the experiment was feasible to some extent.Furthermore,this study was preliminary designed to construct electrochemical DNA biosensors based on TdT and AgNCs for sensitive,specific detection of DNA in clinical blood,urine,cells,etc.