3-Hydroxy-N-(5-mercapto-1,3,4-thiadiazol-2-yl) benzamide (HMTB) was synthesized and self-assembled on the surface of gold electrode. The self-assembled monolayer of HMTB (Au-HMTB SAM) so formed was electrochemically characterized by using cyclic voltanunetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of K-3[Fe(CN)(6)]/K-4[Fe(CN)(6)] as a redox couple and found to be well-assembled free from defects and pinholes. Atomic force microscopy (AFM) was used to examine the morphology of Au-HMTB-SAM and confirmed that the molecules of HMTB form dense and well-packed SAM on gold electrode. The Au-HMTB SAM was applied as a platform for impedimetric sensing of various metal ions by measuring R-ct values from the fit of Randles circuit. EIS results indicated that Au-HMTB SAM electrode exhibited a selective impedimetric response towards Co2+ over a wide linear concentration range of 1.0 x 10(-10) M to 1.0 x 10(-4) M (r(2) = 0.991 +/- 0.054) at pH = 6 with a detection limit of 2.5 x 10(-11) M. The impedimetric sensor selectively respond to Co2+ in the presence of diverse interfering ions such as Na+, K+, Mg2+, Ca2+, Ni2+, Cd2+, Cu2+, Hg2+, Zn2+, Pb2+, Ag+, Fe3+ and Cr3+. The sensor has been successfully applied for estimation of cobalt content in different environmental samples such as water, soil and food crops (wheat and rice). The impedimetric cobalt sensor based on Au-HMTB SAM could serve as a simple, reliable and sensitive method for the electrochemical detection of cobalt(II) in other environmental and biological samples.