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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-PB in ) are prepared by filling MWCNTs with the gradually growing PB and then selectively removing the outersurface PB by careful chemical washing. The prepared MWCNTs-PB in 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-PB in composites on Au electrode exhibit strong and stable electrocatalytic activity of filled PB for H 2 O 2 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-PB in electrode at relatively low scan rates (below 125 and 75 mV s −1 for mass transfer of K + and K + + H 2 O 2 , 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 H 2 O 2 inside our MWCNTs is comparable to those outside our MWCNTs at the low scan rates. Furthermore, the unoccupied outer surfaces of MWCNTs-PB in are conveniently exploited to bind 4-(1-pyrenyl) butyric acid through π−π 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 H 2 O 2 , which endows our biosensors with low detection potential (−0.1 V) and satisfactory sensitivity/selectivity.

The heavy metal (HM) ion-enzyme interaction is an important research topic in many areas. Using glucose oxidase (GOx) as an example, a comprehensive experimental platform based on quartz crystal microbalance and electroanalysis techniques is developed here to quantitatively study the HM ion-enzyme interactions and amperometric inhibitive assays of HM ions. The effects of some common HM ions on the bioactivities of solution-state GOx (GOx(s)), electrode surface-adsorbed GOx (GOx(ads)), and polymer-entrapped GOx (GOx(e)) are comparatively examined on the basis of anodic amperometric detection of enzymatically generated H(2)O(2). Ag(+) shows the strongest inhibition effect among the HM ions examined, and the inhibitive assays of Ag(+) based on GOx(s), GOx(ads), and GOx(e) entrapped in poly(l-noradrenalin) (PNA) give limits of detection (LOD) of 2.0, 8.0, and 5.0 nM (S/N = 3), respectively. Inhibition effects of Hg(2+), Cu(2+), and Co(2+) are detectable only at 15 μM or higher concentrations, and the other HM ions show undetectable inhibition even at 1.0 mM. The developed experimental platform allows one to quantify the number of the bound HM ions per GOx(ads) molecule at various inhibition percentages. In addition, the electrosynthesized PNA matrix to entrap GOx for an inhibitive assay of Ag(+) shows the lowest competitive affinity to HM ions and gives the highest sensitivity, as compared with several other polymer matrixes commonly used for the inhibitive assay. The suggested experimental platform is recommended for wide applications in enzymatic inhibitive assays and quantitative studies of the inhibition effects of HM ions on many other redox-event-relevant enzymes.

Two-dimensional (2D) porous bimetallic oxide nanosheets are attractive for high-performance gas sensing because of their porous structures, high surface areas, and cooperative effects. Nevertheless, it is still a huge challenge to synthesize these nanomaterials. Herein, we report a general strategy to fabricate porous cobalt-based bimetallic oxide nanosheets (Co–M–O NSs, M = Cu, Mn, Ni, and Zn) with an adjustable Co/M ratio and the homogeneous composition using metal–organic framework (MOF) nanosheets as precursors. The obtained Co–M–O NS possesses the porous nanosheet structure and ultrahigh specific surface areas (146.4–220.7 m2 g–1), which enhance the adsorption of CO molecules, support the transport of electrons, and expose abundant active sites for CO-sensing reaction. As a result, the Co–M–O NS exhibited excellent sensing performances including high response, low working temperature, fast response–recovery, good selectivity and stability, and ppb-level detection limitation toward CO. In particular, the Co–Mn–O NS showed the highest response of 264% to 100 ppm CO at low temperature (175 °C). We propose that the excellent sensing performance is ascribed to the specific porous nanosheet structure, the relatively highly active Co3+ ratio resulting from cation substitution, and large amounts of chemisorbed oxygen species on the surface. Such a general strategy can also be introduced to design noble-metal-free bimetallic metal oxide nanosheets for gas sensing, catalysis, and other energy-related fields.