Myriad kinds of plastics have found their way into our environment, including many that either do not degrade or do so on the time scale of a thousand years. As plastics in the environment are subject to weather conditions, they break down into smaller particles, eventually reaching micron and even nanoparticle sizes. The presence of these size range plastic particles in our drinking water supplies is of concern, but readily available home water kits do not test for microplastics. One historical way of determining if a suspected sample is plastic is the “hot-needle” method, which encompasses sticking a particle with a heated needle to observe if the particle chars or melts. While simple, this process is time-consuming as it requires serial evaluation of individual particles and also becomes increasingly difficult to use as the particulate scale becomes smaller (1-100 microns). Any scaled‐up operation to provide a home water testing kit for microplastics would necessitate the development of rapid screening techniques.
In order to evaluate many particulates at once, we created a way to simultaneously heat and observe particles caught on silicon nanomembrane filters, which are inert over the common temperature ranges used to liquefy plastic polymers. Through heating the membrane all at once under the microscope, researchers can determine at what temperature each plastic is melting, essentially performing a more efficient hot needle test with an entire sample of microparticulates. This technique allows for efficient characterization of plastics within environmental samples, and additional particle analysis—such as the measurement of thermo‐birefringence or nonradiative activation energies—can also be implemented for yet more insight into the nature of the different microplastic particles.
This is a very useful tool for those studying microplastics as it allows for a quick assessment of plastic content and composition without the use of expensive and time-consuming technology such as FT-IR or Raman microspectroscopy. The ability to perform heating operations directly on the filter also allows for less transfer of material and contamination. The invention could be expanded to include precise weighing of the sample as it is heated (thermogravimetric analysis), which would also give additional mass and composition information.