A correlated OF2i®-Raman method for micro- and nanoplastic chemical analysis in liquids

Micro- and nanoplastic particle contaminations in the environment, especially in water, are increasingly seen as a health risk in recent years. To assess this threat, a method for directly detecting and identifying microand nanoplastics in liquids is being developed in the recently launched Nano-Vision project. It is based on a correlation between an optofluidic force induction method (OF2i®) and Raman microscopy.
Optofluidic Force Induction OF2i® is a novel high throughput counting technique that uses optical and fluidic forces for single-nanoparticle characterization. The OF2i technology uses weakly focused structured laser light to trap particles in liquids on the intensity maximum of a laser beam and (de)accelerate them in a microfluidic flow channel through momentum transfer between light and matter. An ultramicroscope setup records the scattering light and the acceleration of the illuminated particles at a 90° angle. From the obtained data, a calibration-free model provides particle size, size distributions, and concentrations ranging from several tens of nanometers up to several micrometers. As the OF2i-technique examines the elastically scattered light, it can naturally be combined with a Raman microscope by introducing a second path for the inelastically scattered
light. In contrast to conventional Raman techniques, which usually operate with laser powers in the milliwatt range, a 2-watt laser is used in the recently developed OF2i-Raman approach. This should help in overcoming the small signal strength of Raman scattering.
The flow channel of the OF2i-Raman technique can be operated in both forward (dynamic) and backward directions (steady-state). First promising results show dynamic single-particle Raman signals of polystyrene in the μm-range and steady-state measurements in the submicrometer regime. A combination of the OF2i® technology with Raman microscopy could enable the chemical analysis of nanoparticles with unmatched speed and versatility.