Gold nanoparticles prepared from reduction of gold chloride by sodium borohydride at room temperature without adding stabilizing agents were applied directly for the development of latent fingerprints on various substrates. The negatively charged gold nanoparticles can be adsorbed on the protonated residual of the ridges through electrostatic force. Consequently, the fingerprints can be visualized. In addition, influences of pH value of the solutions were investigated. Latent fingerprints could be visualized in a wide range of pH value (2.0～4.9) on non-porous and semi-porous substrates, especially, superior results were shown at pH＝3.0.

Key words: latent fingerprints, gold nanoparticles, sodium borohydride