Electrochemical Conversion Of Magnetic Nanoparticles And Its Biosensing Applications

Nanoparticle electrochemistry has opened a new branch of nano-research and shown significant prospects in various fields. Nanocomposite materials exhibit the merits and performance of the components as well as even synergetic effects, which make them broadly exploited for diversified ends. New preparation strategies and performance expansion are the frontiers and challenges. Magnetic nanoparticles(MNPs), based on their unique magnetism, electric, thermal and other physical/chemical properties, have been broadly exploited for separation/enrichment as well as other fields such as tumor therapy, however, exploitation based on electrochemistry is limited. Here, based on their diversified properties and performance, the combination with flexible electrochemistry technologies may direct to a new promising field for novel magnetic composite materials and applications, thus to develop biosensors with enhanced performance. In this dissertation, we reviewed the research process of electrochemical biosensor, MNPs and Prussian blue(PB), followed by the development of a new method of electrochemical conversion of MNPs to PB for biosensing of avian influenza virus, a chemical sensor based on PB-Au composite film prepared through combining the developed electrochemical conversion of MNPs and co-electrochemical deposition of gold, as well as a label-free aptasensor using the PB-Au composite film with the electrochemistry of PB as signal-readout. The main contents are as follows:1. We developed a new and efficient protocol for the electrochemical conversion of MNPs to Prussian blue(PB) and its biosensing application. In a neutral solution containing K3Fe(CN)6, high potential is applied to create strong acidic condition to release Fe3+ from the MNPs, and a low potential reduces K3Fe(CN)6 to K4Fe(CN)6, which reacts with Fe3+ to form highly electrochemically active PB. The concentration of K3Fe(CN)6, the time and potential of multi-potential steps are optimized. The existence of PB is confirmed by cyclic voltammetry(CV) by the pair of its characteristic redox peaks at about +0.2 V. Scanning electronic microscopy(SEM) showed the morphology of PB deposited on a gold electrode surface. Based on this novel conversion, a sandwich immunosensor is designed using MNPs as labels and the formed PB as signal. Avian influenza virus H5N1 was adopted as the analyte because of its serious worldwide threat to poultry and human health. The electrodes were modified with specific antibody to capture the H5N1 virus. This was followed by binding concanavalin A(ConA) and MNPs to create bionanocomposites through a ConA-glycan interaction. This sandwich complex modified electrodes were transferred to a neutral solution containing K3Fe(CN)6 for PB preparation. This strategy takes advantages of electrochemistry and magnetism of MNPs and subtly utilized electrochemical method to achieve the control of local acidity for PB preparation and endowed the biosensor with high sensitivity and a detection limit of 7.4×10-4 HAU, which was magnitudes lower than that of some analogues based on biosensing methods. The proposed method has great promise to create a new research field and find applications in developing sensitive, low-cost, and easy-to-observe biosensing devices.2. We prepared PB-Au nanocomposite materials of ultrahigh electrochemical activity based on the electrochemical conversion of MNPs and co-electrochemical deposition of gold, and constructed a high-performance amperometric sensor for H2O2. Briefly, PB-Au nanocomposites were rapid electrodeposited on the electrodes by as-developed electrochemical conversion of MNPs that were magnetically anchored on Au electrode surface in 0.1 M aqueous K2SO4 containing 2 mM HAuCl4 and 1 mM K3[Fe(CN)6], accompanying with the co-deposition of gold under the reductive potential, finally yielded uniformly distributed PB-Au composite film. The size and morphology of PB-Au nanocomposites could be readily adjusted by regulating the ratio of precursors. Electrochemical and scanning electronic microscopy technologies were used to characterize the morphology, electrochemistry, stability, and electro-catalytic property. The PB-Au composites film exhibited high electro-conductivity, stability and showed higher electro-catalytic ability to the reduction and oxidation of H2O2 than those based on normal PB, with a linear detection range for H2O2 from 0.002 to 5.7 mM, a sensitivity of 934 ?A·cm-2·mM-1, and a limit of detection of 72.49 nM.3. We proposed a label-free biosensor using the PB-Au nanocomposite film based on the signal readout of PB electrochemistry. The thus-prepared PB-Au composite film presented good biocompatibility, strong magnetism, and electrochemical catalysis ability, as well as plenty of binding sites on Au, which is absent on conventional PB film. Therefore, we readily immobilized aptamer through the Au-S chemistry for the capture of thrombin, then obtained signal based on the suppression of the PB electrochemical catalysis due to the hindrance of mass-transfer of the thrombin, thus realized the label-free detection. The aptasensor presented a linear detection range for thrombin from 0.1 nM to 100 nM, a sensitivity of 5.1 ?A·cm-2·nM-1, and a limit of detection of 13 pM.