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An aqueous dispersion was prepared by attaching positively charged gold nanoparticles to the surface of poly-sodium-p-styrenesulfonate-modified Fe3O4 nanoparticles. The Fe3O4@positively charged gold nanoparticles offer high monodispersion, stability against aggregation, and high magnetization with uniform size. The Fe3O4@positively charged gold nanoparticles were efficient and recyclable catalysts due to the formation of a positively charged gold layer on the surface of Fe3O4 nanoparticles and were stable in aqueous solution for over forty-eight hours and hence may have a broad range of applications.

A functional composite of Fe3O4@SiO2-Au was prepared and used for latent fingerprint detection. Material characterization results confirmed the successful fabrication of the Fe3O4@SiO2-Au composite. In latent fingerprint detection, the Fe3O4@SiO2-Au composite provides a better performance than commercial copper powder and also gold nanoparticles. More importantly, the Fe3O4@SiO2-Au composite can be used in both powder and suspension forms, and also for common surfaces including glass, polyethylene bags, and paper. The favorable pH range (2.0–5.0) for the compositein finger marks detection is much wider than that of the traditional multi-metal deposition method (pH ranging from 2.0 to 3.0). The mechanism for the Fe3O4@SiO2-Au composite in fingerprint detection was explored and discussed. This study provides a favorable choice for a one-step deposition method for latent fingerprint detection.