Trithiocyanato(4,4',4 ''-tricarboxy-2,2':6',2 ''-terpyridine)ruthenium(II), "black dye", was adsorbed on a rutile TiO2(110) surface and imaged by an ultrahigh vacuum scanning tunneling microscope. The TiO2 (110)-(1 x 1) surface was prepared in a vacuum, covered with pivalate monolayer, and immersed in acetonitrile containing black dye. Black dyes exchanging preadsorbed pivalates were observed on the surface as protrusions with lateral dimensions from 2 to 10 nm. Protrusions with a minimum lateral dimension of 2 nm were assigned to single, isolated black dyes, and larger protrusions were attributed to aggregated dyes. When deoxycholic acid was added to the dye solution, the number ratio of the single dyes to the aggregated dyes increased, while adsorbed deoxycholic acid was not observed.