We report herein polyethylenimine mediated synthesis of copper-iron hexacyanoferrates (Cu Fe HCFs) and nickel-iron hexacyanoferrates (Ni Fe HCFs) nanoparticles from single precursor potassium ferricyanide [K-3[Fe(CN)(6)]]. It has been found that Cu2+ or Ni2+ are converted in respective mixed metal hexacyanoferrate (Cu Fe HCF or Ni Fe HCF) nanoparticles having average size of 5 nm to 30 nm in the presence of K-3[Fe(CN)(6)], polyethylenimine (PEI), and HCl at 60 degrees C in 3 h with following major findings: (i) the process allow to control the desired molar ratio of Cu:Fe or Ni:Fe in the respective mixed metal hexacyanoferrate nano particles justifying controlled transition of Prussian blue character to respective metal hexacyanoferrate (CuHCF/NiHCF) as evidenced from cyclic voltammetric measurements, (ii) the process also allow the conversion of similar nanoparticles when K-3[Fe(CN)(6)] is replaced by K-4[Fe(CN)(6)] with poor electrochemical behaviour, (iii) the process also allow the synthesis of Cu Fe HCFs/Ni Fe HCFs at 25 degrees C in 4 days and within 2 hat 90 degrees C with significant variation in electrochemical behaviour of respective nanomaterial, (iv) Cu Fe HCFs show better electrocatalytic activity for dopamine and H2O2 sensing while the same for Ni Fe HCFs is better for hydrazine sensing, and (v) both Cu Fe HCF and Ni Fe HCF nanoparticles display good homogeneous catalytic activity as peroxidase mimetic with Michaelis-Menten constant (K-m) to the order of 1.5 mM and 4.2 mM respectively. The as made nanomaterials have been characterized by UV-vis spectroscopy, Fourier Transformation Infrared Spectroscopy (FT-IR), X-ray diffraction analysis (XRD), Energy. ispersive Spectroscopy analysis (EDS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and cyclic voltammetry. (C) 2016 Elsevier B.V. All rights reserved.