Metallic copper nanoparticles (CuNP) are formed from the reduction of hierarchical copper-based micro/nanostructures previously electrodeposited on polypyrrole-polystyrene sulfonate (PPy-PSS) thin films. The application of a high reduction potential causes the erosion of the micro/nanostructures nanosheets and the formation of CuNP. The CuNP are used in a series of preliminary tests in order to assess their performance in the sensing of nitrate. The sensing performance is improved with the introduction of polyethyleneimine-functionalized multiwall carbon nanotubes (MWNT-PEI) to the PPy-PSS films. Electrochemical impedance spectroscopy studies show that the nanotubes increased the electronic conductivity of the reduced films. The limit of detection of the PPy-PSS-MWNT-PEI-CuNP nanocomposite is 30 mM nitrate. The materials need further development and optimization work in order to be applied as sensors.