Determination of dopamine at the nanogram level based on the formation of Prussian blue nanoparticles by resonance Rayleigh scattering technique

In pH 2.6 HCl solution, dopamine (DA) could reduce Fe(III) to Fe(II), which further reacted with [Fe(CN) 6 ] 3− to form a Fe 3 [Fe(CN) 6 ] 2 complex. By virtue of hydrophobic force and Van der Waals force, the complex aggregated to form Fe 3 [Fe(CN) 6 ] 2 nanoparticles with the average diameter of about 20   nm. This resulted in a significant enhancement of resonance Rayleigh scattering (RRS). The maximum wavelength of the ion-association complex was located at about 350   nm. The increment of scattering intensity (Δ I RRS ) was directly proportional to the concentration of DA in the range of 0.06–1.0   μg/mL. This method has high sensitivity and the detection limit (3 σ ) for DA was 3.43   ng/mL. In this work, the characteristics of absorption and RRS spectra of this reaction have been studied. The optimum reaction condition and influencing factors have been investigated. The method was applied to the determination of DA in pharmaceutical samples with satisfactory results. Furthermore, the reaction mechanism and the reasons of RRS enhancement have been explored.