Study On Highly Sensitive Electrochemical Biosensor Based On The Metal Nanomaterials

Recently, the electrochemical biosensors developed by integrating biosensors with the electrochemical analytical method show board application prospects due to their advantages of high sensitivity, good selectivity, fast response, easy operation and low cost, etc. Metal nanomaterials possess the characteristic of large surface area, excellent electric conductivity, strong absorption ability, good biocompatibility and efficient electrocatalytic activity, etc. Thus, when used in electrochemical biosensors, the metal nanomaterials could amplify the electrochemical signal and enhance the sensitivity by their electrocatalytic effect on the substrate or increasing the immobilization of biomolecules and electroactive substances. Considering that, the research focuses on the utilization of metal nanomaterials as redox probes, electrocatalyst and nanocarriers for the fabrication of a series of electrochemical biosensors with high sensitivity.Part1Label-free electrochemical immunosensor based on silver-graphene oxide nanocomposites as redox probesIn this work, a highly sensitive electrochemical immunosensor for a-1-fetoprotein (AFP) was fabricated by using silver-graphene oxide (Ag-GO) as redox probe. Initially, Ag-GO nanocomposites were prepared by in situ reducing silver nanoparticles (AgNPs) onto graphene oxide (GO) substrate, which were redispersed in Nafion to obtain Ag-GO-Nf nanocomposite. Then, the nanocomposite was coated onto the gold electrode, following by the electrodeposition of gold nanoparticles (AuNPs) for anti-AFP immobilization onto the electrode. Finally, bovine serum albumin (BSA) was used to block possible remaining activie sites and eliminate nonspecific adsorption. Ag-GO with good biocompatibility and chemical stability, gave a pair of well-defined redox peaks. Owing to its large surface area, GO could increase the immobilization amount of redox-active AgNPs, thus improving the electrochemical signals and sensitivity. In addition, AuNPs could amplify the electrochemical signal and enhance the sensitivity due to their high conductivity and large surface area. Under the optimal condition, the designed immunosensor for AFP showed a wide range from0.01to100ng·mL-1and a lower detection of3pg·mL-1. Thus, it displayed the advantages of simple preparation, high sensitivityand satisfactory stability.Part2Highly sensitive electrochemical aptasensor based on highly loaded hemoglobin spheres-encapsulated platinum nanoparticles composites as signal labels and electrocatalystsFor the first time, a sandwich-type electrochemical aptasensor was fabricated for sensitive detection of thrombin (TB) based on direct electrochemistry and electrocatalytic activity of highly loaded hemoglobin spheres-encapsulated platinum nanoparticles (PtNPs@Hb). PtNPs@Hb as tag was used to label the thrombin binding aptamer (TBA) and BSA was employed to block the unoccupied sites, forming PtNPs@Hb-TBA-BSA bioconjugate probe as the secondary aptamer. Through the specific recognition between TB and TBA, as well as the TBA immobilized on the electrode, PtNPs@Hb-TBA-BSA was captured on the electrode to form sandwich-type sensing system. The Hb produced the detectable electrochemical signal due to its direct electron transfer at the electrode, avoiding the use of extraneous redox mediators and simplifying the preparation of aptasensor. Moreover, the high loading of Hb spheres could enhance the electrochemical signal and sensitivity. Besides, the synergetic electrocatalytic behavior of Hb and PtNPs toward H2O2greatly amplified the electrochemical signal, resulting in the high sensitivity. Consequently, under optimal conditions, the designed aptasensor exhibited a lower detection limit of0.05pmol·L-1and wide linear range from0.15pmol·L-1to40nmol·L-1for TB detection. Additionally, the proposed electron mediator-free and highly sensitive electrochemical aptasensor showed great potential in portable and cost-effective TB sensing devices.Part3Enzyme signal amplified electrochemical aptasensor based on porous platinum nanotubes modified with dendrimers as nanocarriers and electrocatalystsHerein, an electrochemical thrombin apatsensor with high sensitivity was developed by using porous platinum nanotubes modified with dendrimers porous (PtNTs-PAMAM) as nanocarriers and electrocatalysts in combination with 3-(mercaptopropyl)trimethoxysilane-horseradish peroxidase biocomposites (MPTS sol-HRP). Porous PtNTs possessed large surface area and peroxidase-like activity. Coupling with PAMAM with rich amino groups, PtNTs-PAMAM as excellent nanocarrier was used to carry the toluidine blue (Tb) and TBA, thus achieving PtNTs-PAMAM-Tb-TBA-BSA bioconjugate probe as the secondary aptamer. The sensitive interface of aptasensor was obtained by stepwise assembly of AuNPs, MPTS sol-HRP biocomposite and AuNPs for TBA immobilization onto bare glassy carbon electrode. The secondary aptamer was assembled onto the electrode by the formation of sandwich structure complex (TBA/TB/PtNTs-PAMAM-Tb-TBA-BSA), which made the electrode exhibit the characteristic electrochemical signal of Tb. PtNTs-PAMAM provided numerous surface active sites and increased the immobilization amount of Tb and TBA, which effectively enhanced the current signal and sensitivity. Secondly, porous PtNTs and HRP could greatly amplify the electrochemical signal by their corporate electrocatalysis toward H2O2reduction, resulting in the further enhanced sensitivity. Thus, the electrochemical thrombin aptasensor achieved a detection limit as low as0.03pmol·L-1.