Electrochimica Acta 55 (2010) 2186–2190 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Redox polymer covalently modified multiwalled carbon nanotube based sensors for sensitive acetaminophen and ascorbic acid detection Nathaniel Havens a , Phong Trihn a , Daniel Kim b , Manelich Luna b , Adam K. Wanekaya b , Amos Mugweru a,∗ a Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA b Chemistry Department, Missouri State University, Springfield, MO 65897, USA article info Article history: Received 25 August 2009 Received in revised form 13 November 2009 Accepted 16 November 2009 Available online 24 November 2009 Keywords: Redox polymer PEG-DA gel Electrochemical catalysis Photopolymerization abstract A sensitive electrochemical detection method was developed involving multiwalled carbon nanotubes (MWCNTs) covalently modified with osmium-based redox polymer. The polycationic redox polymer, poly[4-vinylpyridine Os(bipyridine) 2 Cl]-co-ethylamine (POs-EA), was first synthesized and covalently attached to MWCNTs. The redox polymer modified MWCNTs were then trapped in a hydrogel formed from polyethyleneglycol diacrylate (PEG-DA) using 1-phenyl-2-hydroxy-2-methyl-1-propanone as a photoini- tiator. Upon exposure to aqueous media, the gel swelled to allow movement of analytes in and out of the gel without having any effect on the redox polymer modified nanotube signal. Cyclic voltamme- try showed reversible pairs of oxidation–reduction peaks at 0.35 V (vs Ag/AgCl) corresponding to the Os II /Os III . This assembly was able to catalytically oxidize both acetaminophen and ascorbic acid (AA). Amperometric data showed a linearity between 0 and 100 M(R 2 of 0.999, n = 10) 0.5 mV vs Ag/AgCl (sensitivity 0.003 A/M) for ascorbic acid, while for acetaminophen the linearity was between 0 and 1.5 M(R 2 of 0.9999, n = 8) with a sensitivity of 65 A/M. This sensing system was found to exhibit remarkable stability over several weeks with excellent reproducibility. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) are promising inorganic platforms with high surface area, ideal for immobilization of different elec- tron transfer mediators. They are also used as electrode materials in electrochemical reactions to promote electron transfer reactions, a new and unique application [1]. The applications of carbon nan- otubes for fabrication of electrochemical sensors are increasingly being explored for detection of various analytes [2–10]. Some of the advantages of using CNTs include rigid structures, insolubility in organic solvents, and large surface area. For sensor fabrication, the sidewalls of CNTs can be functionalized through covalent bond- ing or noncovalent modification methods without changing the mechanical and electronic properties of the inner nanotube [11]. Hybrid materials consisting of conductive polymers and carbon nanotubes have been observed to induce a synergic effect of the resulting hybrid material, attributed to the fact that the conduct- ing polymer can immobilize and connect CNTs, while the CNTs can interact with the polymer to form aggregates that are able to reduce the ion intercalation distance [12,13]. This facilitates charge trans- ∗ Corresponding author at: Department of Chemistry and Biochemistry, Rowan University, 201 Mullica Hill Rd, Glassboro, NJ 08028, USA. Fax: +1 856 256 4478. E-mail address: mugweru@rowan.edu (A. Mugweru). fer and increases the conductivity of the composite polymeric film. To immobilize CNTs, they are first oxidized to introduce carboxylic groups that can be used to covalently bond other molecules [14]. The CNTs can also be functionalized with amino groups to allow further covalent bonding to different molecules [15]. Acetaminophen is widely used as an analgesic antipyretic drug with action similar to aspirin. It is a suitable alternative for patients who are sensitive to aspirin and is safe up to therapeutic doses. The large scale therapeutic use of that drug has gener- ated the need for the development of rapid and reliable methods for the determination of acetaminophen. Electrochemical methods involving composite electrodes have been used for biosensors for acetaminophen detection [16–18]. Most electrochemical studies of acetaminophen and ascorbic acid have been developed with conventional glassy carbon or carbon paste electrodes that suffer from fouling and hence require periodic polishing or activation processes. Other work in the litera- ture has involved noncovalent bonding of nanotubes with polymers including poly(aminoquinone) [19], poly(vinylimidazole) com- plexed with Os(4,4 ′ -dimethylbpy) 2 Cl [20], polypyrrole [21,22], and poly(ethylene glycol) [23] to make the nanotubes bio- compatible. Recently, we used biocompatible PEG-DA hydrogel networks to physically trap both the redox polymer and glucose oxidase on polyimide sheets for glucose sensor applications [24,25]. The osmium-based redox polymer replaced oxygen as 0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.11.054