Harald Fitzek (left) Christian Hill and Christian Neuper (right) at the sensor platform, which uses laser light to detect nanoplastic particles in liquids. [Image: Lunghammer—TU Graz]
Microplastics—as well as the smaller nanoplastics—are everywhere, including in our food, drinking water and even our bodies. These tiny pieces of plastic are not biodegradable, so they accumulate and persist in the environment. Many microplastics originate from the breakdown of larger plastics, such as plastic bags and bottles and clothing made with synthetic textiles.
Now, a team of researchers from Austria, Australia and the United Kingdom has developed a new optical technique for the continuous, real-time detection of microplastics in liquids (Anal. Chem., doi: 10.1021/acs.analchem.3c04657). The method, which combines optofluidic force induction with Raman spectroscopy, will aid the team’s investigation on whether intraocular lenses release nanoplastics.
Microplastics in the eye
Microplastics, defined as plastic particles ranging in size from 1 μm to 5 mm, have been identified in human feces, blood and tissues. These can break down further into nanoplastics, which are sized between 1 nm and 100 nm. The health effects of microplastics are not yet fully understood, but in vitro and in vivo studies have shown that they can cause physical stress and damage, cell death, inflammation, oxidative stress and immune responses.
Two years ago, the laboratory of Harald Fitzek, Graz Center for Electron Microscopy and Nanoanalysis, Austria, began a collaboration with startup company BRAVE Analytics, Austria, to study the impact of microplastics in the field of ophthalmology. To achieve this goal, the research team needed a particle detection method with the critical components of minimal sample preparation, high sample throughput and single particle–based identification.
“Our aim was to develop a technique that can detect micro- and nanoparticles in liquids in a practical and application-focused setting,” said Fitzek. “We saw a chance to achieve this by combining Raman spectroscopy as an analytical technique with the OptoFluidic Force Induction (OF2i) platform developed by BRAVE Analytics, as a single particle–based, high-throughput method.”
Combining two techniques
To achieve this goal, the research team needed a particle detection method with the critical components of minimal sample preparation, high sample throughput and single particle–based identification.
Fitzek and his colleagues leveraged the commercial OF2i system as a starting point. OF2i is a tool for nanoparticle characterization based on the optical counting and manipulation of individually trapped particles.
“The particle detection is done using a weakly focused, doughnut-shaped laser that simultaneously illuminates the particles and by optical forces focuses them into the measurement spot, as well as accelerates them through the focus spot,” said Fitzek. “This particle flow is observed with an ultramicroscope, which makes it possible to determine the size and concentration of the particles by observing their acceleration and counting them, respectively.”
The researchers added a Raman spectrometer to the OF2i platform to measure the inelastic scattering of each individual particle, allowing for a unique identification of the particle composition on a particle-by-particle basis. The technique is also suitable for continuous, real-time measurements, which broadens the set of possible applications.
So far, the technique has successfully detected microplastics in water, and the team says it can be applied to clear bodily fluids, such as urine, tear fluid or blood plasma. The researchers are currently exploring the extent to which intraocular lenses spontaneously yield nanoplastics after mechanical stress or when exposed to laser energy—a topic of interest for ophthalmic surgeons and lens manufacturers alike.