Infrared absorption enhancement is observed as occurring at silver colloidal particles spread on an infrared transparent substrate. Its applicability to qualitative analysis was tested by comparing the transmission spectra of 9,10-anthraquinone (AQ) on a KRS-5 plate with and without silver colloidal particles. The largest enhancement factor observed was about 100, and the detection limit for AQ appeared to be less than 10 ng/cm2. The scanning electron micrograph indicated that the colloidal silver film consisted of irregularly shaped islands. AQ does not possess a functional group reactive to silver, so that the infrared absorption enhancement could be assumed to occur through the long-range electromagnetic enhancement mechanism.
So Young Kang, Cheol Jeon, and Kwan Kim, "Infrared Absorption Enhancement at Silver Colloidal Particles," Appl. Spectrosc. 52, 278-283 (1998)