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 photoinitiator. 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 voltammetry showed reversible pairs of oxidation-reduction peaks at 0.35V (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 mu M (R-2 of 0999, n=10) 0.5 mV vs Ag/AgCl (sensitivity 0.003 mu A/mu M) for ascorbic acid, while for acetaminophen the linearity was between 0 and 1 5 mu M (R-2 of 0.9999, n=8) with a sensitivity of 65 mu A/mu M. This sensing system was found to exhibit remarkable stability over several weeks with excellent reproducibility (C) 2009 Elsevier Ltd. All rights reserved.