In this paper, we have synthesized codoped alpha-MnO2-Co3O4 nanoparticles (NPs) by a facile solvothermal technique using active reducing agents in alkaline reaction systems. The doped NPs are investigated using UV/vis, FT-IR spectroscopy, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscopy (XEDS), and field-emission scanning electron microscopy (FESEM). alpha-MnO2-Co3O4 NPs are fabricated onto a flat-glassy carbon electrode (GCE, surface area, 0.0316 cm(2)) to give a chemo-sensor with a fast response toward chloride ions (similar to 10 s) in liquid phase. The chemo-sensor also shows good sensitivity, long-term stability, reproducibility, and enhanced electrochemical responses. The calibration plot is linear (r(2) = 0.9794) over the large chloride ions concentration (1.0-0.1 mu M) ranges. The sensitivity and detection limit is calculated as similar to 1.062 mu A cm(-2) mM(-1) and similar to 0.35 +/- 0.05 mu M (signal-to-noise ratio, at a SNR of 3) respectively. We also discuss the possible future prospective uses of the transition-metal doped semiconductor nanomaterials in terms of chemical sensing. (C) 2013 Elsevier Ltd. All rights reserved.