Preparation, Characterization And Chemo-/Biosensing Applications Of New Materials Of Prussian Blue-filled Multiwalled Carbon Nanotubes

Nanocomposite materials are being developed rapidly in recent years. Carbon nanotubes (CNTs) with special nanochannels have attracted considerable interest owing to their unique nanostructures, excellent mechanical, electronic, thermal and physical/chemical properties. Numerous studies revealed that filling of foreign materials into the cavity of CNTs may significantly alter their electronic, magnetic, conducting, optical and mechanical properties. However, most of the filling methods involve rigor conditions and the filled electroactive substances reported so far are rather limited. Mass transfer inside nanochannels is also an important issue for relevant nanoscience and nanotechnology, while obtaining quantitative information via electrochemistry method is still lacking to date. In addition, inner-filled CNTs with their outer-wall surfaces unoccupied allow outer-surface modification of other active materials to develop bi-/multifunctional integrated devices owing to flexibly selected functional materials and the synergetic effects of various active substances. However, very few such researches (including conceptual explotation) are reported to date. In this thesis, resent advances in electrochemical biosensors, nanomaterials, and Prussian blue (PB) are briefly reviewed. Moreover, we explore here the interior-only modification of electroactive PB in multiwalled CNTs (MWCNTs) under mild experimental conditions for exploring filling/electrochemistry/mass-transfer in nanochannels and a cooperative biosensing mode. The main contents are as follows.1.We prepared PB-filled MWCNTs nanocomposites (MWCNTs-PBin) for high-performance biosensing. At first, ultrasonic treatment of cap-opened MWCNTs in aqueous K3Fe(CN)6followed by exposure of the centrifugation-isolated MWCNTs mixture in aqueous FeSO4yields MWCNTs modified by PB at both interiors and outer surfaces (PB/MWCNTs-PBin), and removal of the outer-surface PB by careful NaOH rinse and then HCl treatments yields MWCNTs-PBin. Electrochemical, optical, and microscopic methods are used to characterize the filling selectivity, electrochemical property, and catalytic property. The MWCNTs-PBin/Au electrode exhibits high and stable electrocatalytic activity for H2O2reduction, with a linear detection range for H2O2from0.01to6.5mM, a sensitivity of116μA mM-1cm-2and a limit of detection of0.2μM. In addition, the unoccupied outer surfaces of MWCNTs-PBin are exploited to bind4-(1-pyrenyl) butyric acid through stacking interaction and then to anchor glucose oxidase through the EDC/NHS chemistry, and the cooperation of outer-surface biocatalyzed oxidation of substrate with interior PB-catalyzed reduction of enzymatically generated H2O2endows our biosensors with low detection potential (-0.1V) and good sensitivity/selectivity.2.We prepared MWCNTs-PBin based on the nanoconfined effect of CNTs, host-guest match, and adjustment of the size of PB nanoparticles through regulation of the ratio of precursors. Electrochemical, optical and microscopic methods are used to characterize the optical property, morphology property, stability, and catalytic property. The MWCNTs-PBin/Au electrode exhibits high and stable electrocatalytic activity for H2O2reduction, with a linear detection range for H2O2from0.01to8mM, a sensitivity of71.5μAmM-1cm-2, and a limit of detection of0.8μM. Again, the unoccupied outer surfaces of MWCNTs-PBin are conveniently exploited to bind4-(1-pyrenyl) butyric acid through stacking interaction and then to anchor lactate oxidase through the EDC/NHS chemistry, and the cooperation of outer-surface biocatalyzed oxidation of substrate with interior PB-catalyzed reduction of enzymatically generated H2O2endows our biosensors with low detection potential (-0.1V) and good sensitivity/selectivity. This controllable nanofilling strategy through regulating the size of active nanoparticle has a wide universality which can be expanded to other nanochannel filling for preparation and applications of new filled-nanocomposites.3.Mass transfer inside nanochannels as a very important and difficult issue is rarely investigated by electrochemistry methods owing to the lack of electroactive substance filled nanomaterials. Since PB shows electroactivity highly dependent on coexisting electrolyte K+and high electrocatalytic activity toward H2O2reduction, investigating the electrochemistry of MWCNT-PBin can provide abundant and sufficient information on the mass-transfer in nanochannels, from which a novel electrochemical platform can be built to examine the mass-transfer in the filled nanochannels. Through cyclic voltammetry experiment, we found that at relatively low scan rates (below125and75mV s-1for mass transfer of K+and K++H2O2, respectively), the MWCNTs-PBin/Au electrode virtually gives negligible differences in the normalized electroactivity and catalytic activity of PB versus MWCNTs/Au and Au electrodes modified with conventionally electrodeposited PB, while the mass-transfer at MWCNTs-PBin/Au electrode is more sluggish than that at MWCNTs/Au and Au electrodes at higher scan rates. In addition, we have exploited QCM to quantitatively evaluate filling yield (FY) and electroactivity percentage (EP) for the first time, and we have also conducted careful theoretical discussion on FY, EP, and mass-transfer.