We report on the exploitation of metal-organic coordination polymers (MOCPs) as new and efficient matrixes to immobilize enzymes for amperometric biosensing of glucose or phenols. A ligand, 2,5-dimercapto-1,3,4-thiadiazole (DMcT), two metallic salts, NaAuCl(4) and Na(2)PtCl(6), and two enzymes, glucose oxidase (GOx) and tyrosinase, are used to demonstrate the novel concept. Briefly, one of the metallic salts is added into an aqueous suspension containing DMcT and one of the enzymes to trigger the metal-organic coordination reaction, and the yielded MOCPs-enzyme biocomposite (MEBC) is then cast-coated on an Au electrode for biosensing. The aqueous-phase coordination polymerization reactions of the metallic ions with DMcT are studied by visual inspection as well as some spectroscopic, microscopic, and electrochemical methods. The thus-prepared glucose and phenolic biosensors perform better in analytical performance (such as sensitivity and limit of detection) than those prepared by the conventional chemical and/or electrochemical polymerization methods and most of the reported analogous biosensors, as a result of the improved enzyme load/activity and mass-transfer efficiency after using the MOCPs materials with high adsorption/encapsulation capability and unique porous structure. For instance, the detection limit for catechol is as low as 0.2 nM here, being order(s) lower than those of most of the reported analogues. The enzyme electrode was also used to determine catachol in real samples with satisfactory results. The emerging MOCPs materials and the suggested aqueous-phase preparation strategy may find wide applications in the fields of bioanalysis, biocatalysis, and environmental monitoring.

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.

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.

We report on the chemical/biochemical preparation of novel polymeric bionanocomposites (PBNCs) material consisting of polydopamine (PDA), Pt nanoparticles (PtNPs), glucose oxidase (GOx), Au nanoparticles (AuNPs), and antibody for high-performance sandwich-type electrochemical immunoassay. The preparation includes chemical synthesis of PDA-PtNPs-GOx bionanocomposites with abundant GOx and PtNPs immobilized in/on the PDA matrix and biochemical synthesis of AuNPs/PDA-PtNPs-GOx bionanocomposites with highly dispersed AuNPs on the PDA-PtNPs-GOx for successive efficient adsorption of antibody and GOx, finally yielding GOx ads /antibody/AuNPs/PDA-PtNPs-GOx bionanocomposites (PBNCs 1). The thusprepared PBNCs 1 exhibit high load and activity of the enzyme label immobilized both in the interior and on the surface for ultrasensitive signal readout, as well as high load of antibody on the surface for significant immuno-recognition efficiency. Transmission electron microscopy, atomic force microscopy, UV-vis spectroscopy, and electrochemical quartz crystal microbalance are used to characterize the prepared bionanocomposites. We use PBNCs 1 to construct sandwich-type electrochemical immunosensors, which can detect the target antigen of human immunoglobulin G down to a concentration of 2 pg mL -1 . We believe that the chemical/biochemical preparation of new immuno-active PBNCs here may open a new avenue to develop other multifunctionalized PBNCs materials for wide applications in biosensing, bioseparation, and immuno-oriented drug delivery.