Filling carbon nanotubes with Prussian blue nanoparticles of high peroxidase-like catalytic activity for colorimetric chemo- and biosensing.

Facile filling of multiwalled carbon nanotubes (MWCNTs) with Prussian blue nanoparticles (PBNPs) of high peroxidase-like catalytic activity was performed to develop novel colorimetric sensing protocols for assaying H2O2 and glucose. Fine control of PBNP growth was achieved by modulating the concentration ratio of K3 [Fe(CN)6] and FeSO4 precursors in an acidic solution containing ultrasonically dispersed MWCNTs, and thus size-matched PBNPs could be robustly immobilized in the cavities of the MWCNTs (MWCNT-PBin). Unlike other reported methods involving complicated procedures and rigorous preparation/separation conditions, this mild one-pot filling method has advantages of easy isolation of final products by centrifugation, good retention of the pristine outer surface of the MWCNT shell, and satisfactory filling yield of (24±2) %. In particular, encapsulation of PBNPs of poor dispersibility and limited functionality in dispersible and multifunctional MWCNT shells creates new and valuable opportunities for quasihomogeneous-phase applications of PB in liquid solutions. The MWCNT-PBin nanocomposites were exploited as a peroxidase mimic for the colorimetric assay of H2O2 in solution by using 3,3',5,5'-tetramethylbenzidine (TMB) as reporter, and they gave a linear absorbance response from 1 µM to 1.5 mM with a limit of detection (LOD) of 100 nM. Moreover, glucose oxidase (GOx) was anchored on the outer surface of MWCNT-PBin to form GOx/MWCNT-PBin bionanocomposites. The cooperation of outer-surface biocatalysis with peroxidase-like catalysis of interior PB resulted in a novel cooperative colorimetric biosensing mode for glucose assay. The use of GOx/MWCNT-PBin for colorimetric biosensing of glucose gave a linear absorbance response from 1 µM to 1.0 mM and an LOD of 200 nM. The presented protocols may be extended to other multifunctional nanocomposite systems for broad applications in catalysis and biotechnology.