Effect of amines on formation of gold nanoparticles (AuNPs)/polymer nanocomposites has been observed and studied. Nanocomposites based on polyurethane foam and AuNPs were synthesized by interaction between the polymer modified with sodium borohydride and aqueous solution of tetrachloroauric acid. It has been shown that some amines cause a remarkable decrease of the surface plasmon resonance band of AuNPs in the nanocomposite material. Both aliphatic and aromatic amines as well as amines containing several amino groups were studied. A possible mechanism of the effect is discussed. It is probably based on stabilization of AuNPs with an amine that entails a decrease in the degree of their adsorption on PUF and appearance of the stabilized AuNPs in solution. The decrease of the nanocomposite surface plasmon resonance band is proportional to the concentration of amine in the solution. Based on this effect, a method for the determination of cetylamine, β-naphthylamine and neomycin in water and medical formulations using a monitor calibrator as a portable household tool is proposed. Under the selected conditions, the detection limits for amines were in the range of 0.7–1.5 μM, the determination ranges were approximately an order of magnitude. The observed color change of the nanocomposite samples also provides a good basis for semiquantitative determinations. Display omitted •Au/polyurethane nanocomposites were prepared using the polymer modified with borohydride.•Amines cause a decrease of a surface plasmon resonance band of an Au nanocomposite.•Both aliphatic and aromatic amines/polyamines prevent formation of gold nanoparticles.•A method for the determination of amines using a household monitor calibrator was proposed.•The observed nanocomposite color change also suggests naked-eye detection.