A novel formaldehyde (HCHO) sensor fabricated by electrodeposition of AgPd alloy nanoparticles (NPs) on chitosan (Ch)-ionic liquid (IL, i.e., 1-octyl-3-methylimidazolium hexafluorophosphate, OMIM-PF6) films is developed. A scanning electron micrograph of the AgPd/Ch-IL composite film shows a uniform distribution of spherical AgPd NPs with particle sizes of 30-60 nm. Energy-dispersive X-ray measurements indicate that the mass ratio of Pd and Ag in the alloy is 21:5. Cyclic voltammetric studies show that an electrode coated with the AgPd/Ch-IL composite film exhibits high electrocatalytic activity and stability towards electrooxidation of HCHO. The HCHO sensor exhibits linear behavior in the concentration range from 0.060 mM to 20 mM, allowing quantitative analysis of HCHO with a detection limit of 0.022 mM (S/N = 3). (C) 2012 Elsevier B.V. All rights reserved.