Visualisation of suspended nanoparticles by light scattering in a microfluidic chip and manual 2-D tracking for size determination

We present the visualisation of very small particles down to a diameter of 87 nm in a microfluidic chip. By laser light scattering and subsequent tracking of the Brownian motion without flow, the particle size is determined. Rapid prototyping methods with dry film resist were applied to produce disposable, inexpensive microfluidic chips. The device design and laser illumination arrangement were optimised in order to reduce stray light and improve visibility of particles for tracking purposes. The proposed method has the potential for flow visualisation and size analysis of small sample amounts containing nanoparticles of unknown size.