  The analysis of nano-and microparticle suspensions with micro systems affords
improved space-time yields, selectivity, reaction residence times and
conversions capabilities. These capabilities are of primary importance in
various fields of research and industry. The few microfluidic lab-on-a-chip
approaches that have been developed are essentially designed to analyse fluid
phases or involve the use of benchtop particle sizing instruments. We report a
novel microscale approach to characterize the particle size distribution and
absolute concentration of colloidal suspensions. The method is based on a
photonic lab-on-a-chip with three scale-specific detection channels to record
simultaneous light extinction spectra. Experiments carried out on particle
standards with sizes ranging from 30 nm to 0.5 $\mu$m and volume concentrations
of 1 to 1000ppm, clearly demonstrate the value and potential of the proposed
method.
