Facile Synthesis of Prussian Blue-Filled Multiwalled Carbon Nanotubes Nanocomposites: Exploring Filling/Electrochemistry/Mass-Transfer in Nanochannels and Cooperative Biosensing Mode

We report on mild and selective filling of multiwalled carbon nanotubes (MWCNTs) with Prussian blue (PB) to explore the filling/electrochemistry/mass-transfer in nanochannels and the biosensing mode of nanochannel interior-exterior cooperation. PB-filled MWCNTs (MWCNTs-PBin) are prepared by filling MWCNTs with the gradually growing PB and then selectively removing the outer-surface PB by careful chemical washing. The prepared MWCNTs-PBin composites possess high filling yield (mass ratio of PB to MWCNTs, (30 +/- 3)%) and electroactivity percentage (mass ratio of electroactive PB to total PB, (45 +/- 3)%). The MWCNTs-PBin composites on Au electrode exhibit strong and stable electrocatalytic activity of filled PB for H2O2 reduction and electroanalysis. The filling of the MWCNTs with electroactive PB also provides a new experimental platform to deal with the widely concerned issue of mass transfer inside nanochannels. The normalized cyclic voltammetric responses of filled PB on MWCNTs-PBin electrode at relatively low scan rates (below 125 and 75 mV s(-1) for mass transfer of K+ and K+ + H2O2, respectively) were found to be equivalent to those of conventionally electrodeposited PB on MWCNTs/Au and Au electrodes, demonstrating that the mass transfer of K+ and H2O2 inside our MWCNTs is comparable to those outside our MWCNTs at the low scan rates. Furthermore, the unoccupied outer surfaces of MWCNTs-PBin are conveniently exploited to bind 4-(1-pyrenyl) butyric acid through pi-pi stacking interaction and then to anchor glucose oxidase or lactate oxidase through the EDC/NHS chemistry. Thus, we have developed a novel cooperative biosensing mode by combining outer-surface biocatalyzed oxidation of substrate with interior PB-catalyzed reduction of enzymatically generated H2O2, which endows our biosensors with low detection potential (-0.1 V) and satisfactory sensitivity/selectivity.