Prussian blue nanoparticles doped nanocage for controllable immobilization and selective biosensing of enzyme Shuo Wu a,b , Yiying Liu a , Jie Wu a , Huangxian Ju a, * a MOE Key Laboratory of Analytical Chemistry for Life Science, Department of Chemistry, Nanjing University, Nanjing 210093, China b Department of Chemistry, Dalian University of Technology, Dalian 116024, China Received 24 November 2007; received in revised form 19 December 2007; accepted 21 December 2007 Available online 2 January 2008 Abstract A conductive nanocage composed of Prussian blue (PB) nanoparticles doped mesocellular silica–carbon foam was prepared. This nanocage possessed ink-bottlelike structure with narrow and controllable pore-size distribution, good biocompatibility and favorable conductivity. The Prussian blue nanoparticles dispersed homogeneously on the mesowalls and provided the nanocage with highly catalytic ability toward the reduction of hydrogen peroxide. The nanocage could be used for volume-selective entrapment of enzyme to prepare a biosensor. The use of the Prussian blue nanoparticles doped nanocage would open new horizons for fabrication of biosen- sors and biocatalysts. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Prussian blue nanoparticle; Carbon–silica mesocellular foam; Amperometric biosensors; Glucose 1. Introduction The immobilization of biomolecules in conductive nanometerscale structures with good stability and highly catalytic ability can significantly improve the performance of biosensors. Recently, several kinds of mesoporous mate- rials with straight channels have been prepared for protein immobilization [1–4]. However, protein leakage from the straight channels was unavoidable. Thus some effective methods including subsequent coating of nanoscale multi- layer shells on the protein loaded mesoporous silica and crosslinking the enzymes in the mesopores have been pro- posed to prevent the leakage of protein from the mesopores [4]. And 3-D interconnected mesocellular foams composed of carbon [5], magnetic carbon [6], or silica–carbon com- posite [7] with global mesocells have also been prepared to effectively prevent the entrapped glucose oxidase from leaking due to their bottle-neck structure. However, these materials have poor catalytic activity and the detection of glucose has to be operated at extremely high overpoten- tials, which results in poor sensitivity or poor selectivity due to either the high dissolved oxygen reduced back- ground current or the interferences with low oxidation potentials. Furthermore, the resulting biosensors have rel- atively narrow linear range up to 7.0 mM. To improve the sensitivity of resulting biosensor and lower the applied potential for amperometric detection, this work designed a novel conductive and highly catalytic nanocage by doping Prussian blue (PB) nanoparticles on the mesowalls of meso- cellular silica–carbon foam (MSCF) for immobilization of oxidase. Prussian blue has been denoted as an ‘‘artificial peroxi- dase” because of its rapid catalytic rate toward reduction of hydrogen peroxide at low overpotential [8]. Thus it has been widely used as an electron transfer mediator in the oxidase-based amperometric biosensors [9,10], which can exclude the interference from the coexisting substances such as ascorbic acid (AA), acetaminophen (AP), and uric 1388-2481/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2007.12.033 * Corresponding author. Tel./fax: +86 25 83593593. E-mail address: hxju@nju.edu.cn (H. Ju). www.elsevier.com/locate/elecom Available online at www.sciencedirect.com Electrochemistry Communications 10 (2008) 397–401