Luminescent ruthenium(II) tris-bipyridyl complex caged in nanoscale silica for particle velocimetry studies in microchannels

Luminescence and imaging studies of 500 nm diameter colloidal silica stained with the transition metal complex [Ru(bpy)3Cl2], [Ru(bpy)3⊂SiNP], have been detailed and suggest that such particles are ideal for particle tracking velocimetry (PTV) or particle imaging velocimetry (PIV) for analysis of fluid flow in microchannels. Silica particles were synthesized using a modification to the Stöber synthesis to cage the transition metal complex within the core of the nanoscale particles. The particles [Ru(bpy)3⊂SiNP] exhibit luminescence at 620 nm, characteristic of the caged [Ru(bpy)3]2+ species with a lifetime of 790 ns upon excitation at 450 nm. A collection of the luminescence spectra from the images of the particles in a microchannel have the same profile as the spectra collected from solutions of [Ru(bpy)3⊂SiNP], confirming that the luminescence images are attributed to [Ru(bpy)3]2+ luminescence. PIV and PTV measurements from image sequences give flow velocities that match well with the theoretical velocity profile for a rectangular-sided microchannel of 100 µm depth.