Echobeam: Acoustofluidic Cluster Analysis for Micro and Nanoplastic Identification Using Fluorescence and Raman Spectroscopy

This abstract reports on the analysis of acoustically levitated clusters containing micro and nanoplastics enriched at high-throughput from complex aqueous samples containing different types and sizes of these contaminants.Specifically, we used our previously reported acoustofluidic device, the EchoGrid 1 , to capture microplastics, increasing throughput from 200 L/min to 5 mL/min (25x increase) while working at the drinking water-relevant concentration of 10 4 particles/min (100x lower).We have also captured nanoplastics of sizes down to 50 nm (from 200 nm) using the silica enhanced seed particle (SE-SP) method for the first time, even at 4 mL/min.Furthermore, we have evaluated the 3-D shape of the clusters and how different particles behave in these systems using fluorescence, as well as successfully detected a complex mixture of three distinct plastic types (PMMA, PE and PS) simultaneously using Raman spectroscopy in our levitated clusters during the EchoGrid's operation.Finally, we even detected 500 and 200 nm nanoplastics within the silica clusters using this method.Plastic production has skyrocketed for the last 70 years and is projected to almost quadruple by 2050 2 to support countless industries that range from medicine to consumer goods 3 .However, plastic overuse has led to a growing ecological and public health concern as micro and nanoplastics are found in remote ecosystems 4 and also in the human body 5 .These are generated by the degradation of mismanaged larger plastic bodies that now freely degrade in the natural world into many shapes, types, and sizes.The morphological complexity of these samples at the micro and nanoscale has highlighted the need for new systems capable of standardized and reliable monitoring 6 to better address this issue of public health.Towards this, we optimized the EchoGrid (Figure 1) to increase its throughput and have integrated it with Raman spectroscopy.This technique been used in the past for the evaluation of microplastics 7 while being compatible with fluidic applications unlike other approaches such as FTIR (Fourier-transform infrared spectroscopy) or GC-MS (gas chromatography/mass spectroscopy).Our system is now capable of retaining the silica clusters against a 50 mL/min flow, capturing microplastics (10, 23 m) at 5 mL/min and 10 4 particles/mL concentration (Figure 2A)a first-time environmentally relevant concentration 8 .We also push the boundary of nanoparticle capture, capturing nanoplastics down to 50 nm at 4 mL/min, which, to our knowledge, in terms of size and throughput, is unreported 9 (Figure 2B).We employ fluorescence tools to investigate the 3-D structure of the SE-SP clusters (Figure 3), usually visualized in 2-D 10 , allowing for a new window into the complex forces at work in high capacity acoustofluidic systems.Using Raman spectroscopy, we have successfully detected both micro (10-23 m -PMMA, PE, PS simultaneously) and nanoplastics (500 nm, 200 nm) in real time (Figure 4).In conclusion, we present a novel study on the fluorescence and spectroscopic analysis of complex acoustically-levitated micro and nanoplastic clusters.We leverage our previously reported, yet improved, EchoGrid device and SE-SP method and effectively integrate it with Raman spectroscopy as a first in highthroughput micro and nanoplastic environmental monitoring.