A silver colloid produced by reduction with hydrazine as support for highly sensitive surface-enhanced Raman spectroscopy

Reduction of aqueous silver nitrate by hydrazine dihydrochloride in weakly alkaline solution results in a polydisperse colloid that is stable for many months without addition of any stabilizing compounds. The average size of the predominantly spherical particles depends on the initial concentration of silver ions, ranging between 40 and 70 nm in diameter. The colloidal sol utions exhibit a characteristic absorption in the blue region of the visibl e spectrum and are not turbid below a formal silver concentration of 4.5 x 10(-4) M. With colloids prepared from 1.5 x 10(-4) M silver(I), the SERS sp ectra of dyes such as nile blue A could be recorded from a solution with co ncentrations as low as 10(-10) M, whereas no SERS signal was observed for d ye concentrations higher than 10(-4) M. The maximum signal intensity was ob tained at a concentration of about 10(-7) M. With colloids prepared from gr eater than or equal to3 x 10(-4) M silver(I), no SERS signal was obtained f rom highly diluted solutions, but the concentration limit for the maximum s ignal intensity of around 10(-7) M became even sharper. The thus prepared s ilver colloids can therefore be recommended for qualitative detection of ce rtain organic compounds-in the parts per billion range as well as for a sem iquantitative determination in the parts per million range.