Nanoscale biological particles, such as lipoproteins (10–80 nm) or extracellular vesicles (30–200 nm), play pivotal roles in health and disease, including conditions like cardiovascular disorders and cancer. Their effective analysis is crucial for applications in diagnostics, quality control, and nanomedicine development. While elasto-inertial focusing offers a powerful method to manipulate particles without external fields, achieving consistent focusing of nanoparticles (<500 nm) has remained a challenge. In this study, elasto-inertial focusing of nanoparticles as small as 25 nm is experimentally demonstrated using straight high-aspect-ratio microchannels in a sheathless flow. Systematic investigations reveal the influence of channel width, particle size, viscoelastic concentration, and flow rate on focusing behavior. Additionally, through numerical simulations and experimental validation, insights are provided into particle migration dynamics and viscoelastic forces governing nanoparticle focusing. Finally, biological particles, including liposomes (90–140 nm), extracellular vesicles (100 nm), and lipoproteins (10–25 nm) is successfully focused, under optimized conditions, showcasing potential applications in medical diagnostics and targeted drug delivery. These findings mark a significant advancement toward size-based high-resolution particle separation, with implications for biomedicine and environmental sciences.

Plastics and their derivatives have forever changed the nature of human activity. Their various material advantages, such as versatility, low cost, and ease of fabrication, have made them essential for virtually all industries. While their resistance to degradation is often considered one of their greatest traits, it has also been found to be a significant danger. As proper disposal methods fail, large plastics slowly degrade into micro and nanoplastics. These contaminants are extremely small, hard to detect, and challenging to remove from both the environment and consumer goods. This leads to their accumulation in all ecosystems and in the human body, raising questions for policymakers and society at large about how dangerous these contaminants actually are. For this reason, novel monitoring solutions must be developed to enable micro and nanoplastic sample preparation and identification, so that the lifecycle of plastics can be studied and their impact on human life can be better understood.

To address the challenge of managing contaminants at these size ranges, acoustofluidics – a fusion of acoustic actuation and microfluidics – is a promising candidate due to its ability to manipulate particles even during flow. The work presented in this thesis focuses on developing an acoustofluidic platform, termed the EchoGrid, capable of trapping micro and nanoplastics at throughputs traditionally considered unattainable for both microfluidics and acoustofluidics, in a way that is compatible with endpoint analysis.

In Paper I, we presented the EchoGrid as a novel device capable of enriching microplastics at high flow rates. Additionally, we developed the silica-enhanced seed particle method to address samples with low concentrations of microplastics, while further increasing the flow rate. We also evaluated the complex manner in which microplastics of different sizes organize themselves around a silica cluster.

Status: Accepted. 

Reference: Costa, M., Hammarström, B., Van Der Geer, L., Tanriverdi, S., Joensson, H. N., Wiklund, M., & Russom, A. (2024). Echogrid: High-throughput acoustic trapping for enrichment of environmental microplastics. Analytical Chemistry, 96(23), 9493–9502.

In Paper II, we reported on the EchoTilt, a microfluidic method using the EchoGrid to maximize nanoplastic capture by manipulating the way the acoustic field interacts with the sample flow lines. This was achieved by altering the angle at which the transducer was integrated with the microchannel, an angle determined through the use of simulation and algorithms. Here, we also demonstrated that the silica-enhanced seed particle method can capture very small nanoplastics, as small as 25 nm, at high throughput.

Status: Submitted to Micromachines.

In Paper III, we presented a study using fluorescence imaging and Raman spectroscopy to examine the geometry and internal structure of the acoustic clusters levitated by the EchoGrid, investigating how microparticles of different sizes organize themselves around and within the silica clusters. We also successfully detected different types of plastic in the same acoustic cluster, paving the way for handling complex, real-life samples.

Status: Manuscript

In Paper IV, we employed an elasto-inertial microchannel for size-based separation using a non-Newtonian fluid, achieving highly selective microparticle focusing relevant to environmental and biomedical applications. This comprehensive study evaluated the impact of particle size, flow rate, viscoelasticity, and channel dimensions on the ultimate focusing positions of the particles.

Status: Accepted. 

Reference: Tanriverdi, S., Cruz, J., Habibi, S., Amini, K., Costa, M., Lundell, F., Mårtensson, G., Brandt, L., Tammisola, O., & Russom, A. (2024). Elasto-inertial focusing and particle migration in high aspect ratio microchannels for high-throughput separation. Microsystems & Nanoengineering, 10(1), 87.

In Paper V, we extended elasto-inertial separation to nanoparticles, highlighting how size affects focusing quality when combined with different concentrations of viscoelastic fluid. Additionally, we successfully achieved focusing of biomedical nanoparticles essential for medical diagnostics at size ranges not seen before in microfluidics.

Status: Manuscript

Plaster och deras derivat har för alltid förändrat karaktären av mänsklig aktivitet. Deras olika materialfördelar, såsom mångsidighet, låg kostnad och enkel tillverkning, har gjort dem oumbärliga för i princip alla industrier. Plasternas motståndskraft mot nedbrytning har hyllats som en av deras främsta egenskaper, men har även visat sig vara en betydande fara. När korrekt avfallshantering misslyckas, bryts större delar av plast långsamt ner till mikro- och nanoplaster. Dessa föroreningar är extremt små, svåra att upptäcka och utmanande att ta bort från både miljön och konsumentprodukter. Detta leder till deras ackumulering i alla ekosystem och i människokroppen, vilket i sin tur väcker frågor hos beslutsfattare och samhället i stort om hur farliga dessa föroreningar egentligen är. Av denna anledning bör nya övervakningslösningar utvecklas för att möjliggöra provberedning och identifiering av mikro- och nanoplaster så att plasternas livscykel kan studeras och deras påverkan på människor bättre kan förstås. 

För att hantera utmaningen att kontrollera föroreningar i dessa storlekar är akustofluidik – en sammanslagning av akustisk manipulering och mikrofluidik – en lovande kandidat. Detta beror på dess förmåga att manipulera partiklar även under flöde. Arbetet som presenteras i denna avhandling fokuserar på att utveckla en akustofluidisk plattform, kallad EchoGrid, som kan fånga mikro- och nanoplaster även vid genomflöden som traditionellt anses oåtkomliga för både mikro- och akustofluidik på ett sätt som är kompatibelt med slutpunktsanalys. 

I Artikel I presenterar vi EchoGrid, ett nytt instrument som är kapabel att koncentrera mikroplaster vid höga flödeshastigheter. Dessutom utvecklar vi en kiselberikad fröpartikel-metod för att hantera prover med låg koncentration av mikroplaster, där flödeshastigheten ökas ytterligare. Vi utvärderar också det komplexa sättet som mikroplaster i olika storlekar organiserar sig runt ett kluster av kiseldioxid.

I Artikel II rapporterar vi om EchoTilt, en mikrofluidisk metod som använder EchoGrid för att maximera nanoplast-uppfångning genom att manipulera hur det akustiska fältet interagerar med provets flödeslinjer. Detta görs genom att ändra vinkeln vid vilken transducern är integrerad med mikrokanalen, en vinkel som bestämdes med hjälp av simulering och algoritmer. Här bevisar vi även att den kiselberikade fröpartikel-metoden kan användas för att fånga även mycket små nanoplaster ner till 25 nm vid hög genomströmning. 

I Artikel III visar vi en studie baserad på fluorescens och Ramanspektroskopi av den geometri och interna struktur hos de akustiska kluster som leviteras av EchoGrid, och studerar hur mikropartiklar i olika storlekar organiserar sig runt och inom kiseldioxid-klustren. Vi lyckas även detektera olika typer av plast i samma akustiska kluster, vilket banar väg för komplexa, verkliga provtagningar i fält. 

I Artikel IV använder vi en elastoinertiell mikrokanal för att göra storleksbaserad separation med en icke-Newtonsk vätska, och uppnår en hög selektiv fokusering av mikropartiklar som är relevant för miljö- och biomedicinska tillämpningar. Denna studie utvärderar den påverkan partikelstorlek, flödeshastighet, viskoelasticitet och kanalens dimensioner har på partiklarnas slutgiltiga fokuseringspositioner. 

I Artikel V använder vi elastoinertiell separation för nanopartiklar och visar hur storlek påverkar fokuseringskvaliteten när den kombineras med olika koncentrationer av viskoelastisk vätska. Dessutom lyckas vi fokusera biomedicinska nanopartiklar, som är viktiga för medicinsk diagnostik, med samma metod och vid storleksintervall som inte tidigare setts.

The health hazards of micro- and nanoplastic contaminants in drinking water has recently emerged as an area of concern to policy makers and industry. Plastic contaminants range in size from micro- (5 mm to 1 μm) to nanoplastics (<1 μm). Microfluidics provides many tools for particle manipulation at the microscale, particularly in diagnostics and biomedicine, but has in general a limited capacity to process large volumes. Drinking water and environmental samples with low-level contamination of microplastics require processing of deciliter to liter sample volumes to achieve statistically relevant particle counts. Here, we introduce the EchoGrid, an acoustofluidics device for high throughput continuous flow particle enrichment into a robust array of particle clusters. The EchoGrid takes advantage of highly efficient particle capture through the integration of a micropatterned transducer for surface displacement-based acoustic trapping in a glass and polymer microchannel. Silica seed particles were used as anchor particles to improve capture performance at low particle concentrations and high flow rates. The device was able to maintain the silica grids at a flow rate of 50 mL/min. In terms of enrichment, the device is able to double the final pellet’s microplastic concentration every 78 s for 23 μm particles and every 51 s for 10 μm particles at a flow rate of 5 mL/min. In conclusion, we demonstrate the usefulness of the EchoGrid by capturing microplastics in challenging conditions, such as large sample volumes with low microparticle concentrations, without sacrificing the potential of integration with downstream analysis for environmental monitoring.

Micro- and nanoplastics have become increasingly relevant as contaminants to be monitored due to their potential health effects and environmental impact. Nanoplastics, in particular, have been shown to be difficult to detect in drinking water, requiring new capture technologies. In this work, we applied the acoustofluidic seed particle method to capture nanoplastics in an optimized, tilted grid of silica clusters even at the high flow rate of 5 mL/min. Moreover, we achieved, using this technique, the enrichment of nanoparticles ranging from 500 nm to 25 nm as a first in the field. We employed fluorescence to observe the enrichment profiles according to size, using a washing buffer flow at 0.5 mL/min, highlighting the size-dependent nature of the silica seed particle release of various sizes of nanoparticles. These results highlight the versatility of acoustic trapping for a wide range of nanoplastic particles and allow further study into the complex dynamics of the seed particle method at these size ranges. Moreover, with reproducible size-dependent washing curves, we provide a new window into the rate of nanoplastic escape in high-capacity acoustic traps, relevant to both environmental and biomedical applications.

The combination of flow elasticity and inertia has emerged as a viable tool for focusing and manipulating particles using microfluidics. Although there is considerable interest in the field of elasto-inertial microfluidics owing to its potential applications, research on particle focusing has been mostly limited to low Reynolds numbers (Re<1), and particle migration toward equilibrium positions has not been extensively examined. In this work, we thoroughly studied particle focusing on the dynamic range of flow rates and particle migration using straight microchannels with a single inlet high aspect ratio. We initially explored several parameters that had an impact on particle focusing, such as the particle size, channel dimensions, concentration of viscoelastic fluid, and flow rate. Our experimental work covered a wide range of dimensionless numbers (0.05 < Reynolds number < 85, 1.5 < Weissenberg number < 3800, 5 < Elasticity number < 470) using 3, 5, 7, and 10 µm particles. Our results showed that the particle size played a dominant role, and by tuning the parameters, particle focusing could be achieved at Reynolds numbers ranging from 0.2 (1 µL/min) to 85 (250 µL/min). Furthermore, we numerically and experimentally studied particle migration and reported differential particle migration for high-resolution separations of 5 µm, 7 µm and 10 µm particles in a sheathless flow at a throughput of 150 µL/min. Our work elucidates the complex particle transport in elasto-inertial flows and has great potential for the development of high-throughput and high-resolution particle separation for biomedical and environmental applications. (Figure presented.)