Fumed silica nanoparticles–chitosan nanobiocomposite for ochratoxin-A detection Ajeet Kaushik a,b , Pratima R. Solanki a , K.N. Sood a , Sharif Ahmad b , Bansi D. Malhotra a, * a Department of Science and Technology Centre on Biomolecular Electronics, Dr. K.S. Krishnan Marg, National Physical Laboratory, New Delhi 110012, India b Materials Research Laboratory, Department of Chemistry, Jammia Millia Islamia, New Delhi 110025, India article info Article history: Received 11 June 2009 Received in revised form 29 July 2009 Accepted 11 August 2009 Available online 14 August 2009 Keywords: Fumed silica Chitosan Nanobiocomposite Immunosensor Ochratoxin-A abstract Fumed silica nanoparticles (NanoSiO 2 ) and chitosan (CH) based nanobiocomposite film have been used to co-immobilize rabbit-immunoglobulin antibodies (r-IgGs) and bovine serum albumin (BSA) for ochratoxin- A (OTA) detection. The observed three-dimensional (3D) arrangement of NanoSiO 2 in CH matrix via hydro- gen bonding, available NH 2 /OH groups and excellent film-forming ability of CH results in increased effective surface area of CH–NanoSiO 2 nanobiocomposite for r-IgGs immobilization. Electrochemical studies suggest that presence of NanoSiO 2 leads to enhanced electrochemical behaviour of CH resulting in increased elec- tron transport between the medium and the electrode. BSA/r-IgGs/CH–NanoSiO 2 /ITO immunoelectrode exhibits improved sensing characteristics such as linearity (0.5–6 ng/dL), detection limit (0.3 ng/dL), response time (25 s) and sensitivity (18 lA ng/dL cm 2 ) with correlation coefficient as 0.98. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Ochratoxin-A (OTA) detection has recently become important since it is the most abundant mycotoxin in food commodities and found in tissues and organs of animals causing nephrotoxicity, teratogenicity, carcinogenicity and immunotoxicity. The interna- tional agency for research on cancer (IARC) has classified OTA as a possible human carcinogen (group 2B, possibly by induction of oxidative DNA damage) based on evidence for carcinogenicity in animal studies (IARC 1993) [1–6]. Chromatographic techniques presently being used for OTA detection are time-consuming, expensive, necessitate multiple steps and require expertise. In this context, electrochemical immu- nosensors have been considered important due to rapid, selective detection with improved stability and orientation of electrode- bound antibodies. To obtain sensitive, compact and stable immu- nosensing platform, desired antibodies should be immobilized in suitable orientation onto an appropriate matrix [1]. Chitosan (CH) due to its excellent film-forming ability, mechan- ical strength, biocompatibility, non-toxicity, high permeability towards water, susceptibility to chemical modification, cost-effec- tiveness, etc. have been used for immobilization of desired IgGs. The available amino groups of CH provide a hydrophilic environ- ment compatible with IgGs. It is known that performance of CH based biosensor can be improved by enhancing electrochemical properties and surface modification of CH via incorporation of bio- compatible electro-active nanomaterials [2,9]. Among the various biocompatible electro-active nanomateri- als, fumed silica nanoparticles (NanoSiO 2 ) with controlled particle size, morphology, porosity and surface area, along with its chem- ical, thermal and easy functionalization properties, make Nano- SiO 2 suitable for technological applications such as adsorption, catalysis, chemical separation, nano-devices, biosensors, etc. [8– 10]. Besides this, biocompatibility, non-toxicity, high ionic con- ductivity and high surface-to-volume ratio of NanoSiO 2 are advantageous for biosensing. And surface functionalization of NanoSiO 2 may perhaps improve loading of desired biomolecules and direct electrochemistry of enzymes resulting in enhanced sensing characteristics. The surface functionalization of NanoSiO 2 with organic moieties or another nanostructure may result in controlled release and molecular recognition capabilities of Nano- SiO 2 for drug/gene delivery and biosensing applications, respec- tively [8–13]. However, there is a considerable scope to explore properties of nanobiocomposite of SiO 2 with CH for application to immunosensor. In this manuscript, we report results of studies relating to the fabrication of CH–NanoSiO 2 nanobiocomposite to co-immobilize r-IgGs and BSA for OTA detection. 2. Materials and methods All the chemicals were purchased from Sigma Aldrich (USA) and were used without any further purification. To prepare the CH– NanoSiO 2 nanobiocomposite, 4 mg NanoSiO 2 [CABOSIL, A-200, 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.08.016 * Corresponding author. Tel.: +91 11 45609152; fax: +91 11 45609310. E-mail address: bansi.malhotra@gmail.com (B.D. Malhotra). Electrochemistry Communications 11 (2009) 1919–1923 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom