Detection and monitoring of lactate and glucose levels in biological fluids and cell cultures are essential for understanding metabolic disorders. While electrochemical biosensors are commonly used, traditional enzymatic sensors face challenges related to stability, reproducibility, and cost. To address these limitations, we developed non-enzymatic sensors for lactate and glucose detection using nanostructured nickel oxide (NiO)–modified screen-printed carbon electrodes. The sensors were fabricated by drop-casting a NiO/Nafion/ethanol dispersion onto the working electrode, and their performance was evaluated using cyclic voltammetry and amperometry. Optimal sensitivity and linearity were achieved at a working potential of ∼0.5 V. The sensors exhibited linear responses for both lactate and glucose in the 0.1–5 mM range, with detection limits of 0.03 mM (lactate) and 0.025 mM (glucose), and sensitivities of 1.564 μA/mM (lactate) and 1.842 μA/mM (glucose) in 0.1 M NaOH–KCl electrolyte. To address glucose interference in lactate sensing, dual-sensing strategies were employed by varying Nafion concentration, applying differential potentials, or modifying the sensors with Prussian Blue to achieve selective detection. Validation against commercial lactate and glucose assay kits in cell culture medium showed good agreement, confirming the sensors’ accuracy. Finally, the sensor was integrated with a microfluidic chip, demonstrating its potential as a flow-through, enzyme-free metabolic sensor for future organ-on-a-chip applications.

Particles in the micrometer and nanometer size range are present in the environment (e.g., microplastics, nanoplastics) as well as in living organisms(e.g., cells, bacteria, tumors, and exosomes) in different forms and structures. Regardless of their compositions, there is a need to understand how these particles can be manipulated for both environmental and biomedical applications.

Nature and our daily lives are surrounded by micro- and nanoplastics. Their presence carries potential risks for the environment and the health of living beings. Although plastics were initially invented because of their advantages in industrial fields, such as low cost and versatility, their degradation results in small particles that are not easy to monitor or detect, and can penetrate into the body while staying in nature potentially for hundreds of years. Their detection, identification, and analysis are crucial to determine their danger level for all. The rise of global plastic production has led to the increasing prevalence of micro and nanoplastics in the environment. The absence of standardized handling methods complicates efforts to manage their environmental impact. The current state of this issue, along with projections for the upcoming years, appears bleak, prompting scientists and legislators to intensify efforts to develop and implement better solutions.

Biological particles, such as bacteria, platelets, circulating tumor cells, or extracellular vesicles, either through their presence or their concentration levels in bodily fluids or tissues, contain critical information about the state of a living organism. Isolation of these particles from blood or plasma is crucial to enable downstream analysis needed to assess the current status of a patient. Thus, high-throughput and high-resolution particle manipulation are needed for diagnostics and therapeutical applications.

In this thesis, we presented novel microfluidic devices with high aspect ratio geometries utilizing elasto-inertial microfluidics. These devices show a capacity to manipulate both micro- and nanoplastics, and biological particles.

In Paper I, we reported a microfluidic device comprising a single-inlet and high aspect ratio straight microchannels with two sections: focusing and migration section. Here, we aimed at focusing microparticles in the focusing section and then separating pre-focused particles based on their sizes in the migration section. Moreover, we presented an extensive study on particle focusing, investigating parameters affecting particle focusing, such as particle size, viscoelastic concentration, flow rate, and channel geometry. Finally, we showed how to increase throughput of the system by increasing the channel depth. The presented results demonstrate the potential of high aspect ratio microchannels in an elasto-inertial microfluidics setup for applications that require high throughput and high-resolution particle separation.

In Paper II, we presented a high aspect ratio microchannel with a smaller channel width than the one presented in the first paper. Here, we demonstrated, for the first time, the focusing of submicron particles down to 25 nm using elasto-inertial microfluidics. Furthermore, we confirmed these results using biological nanoparticles, namely liposomes and exosomes. Focusing of such small biological particles in a low-cost microfluidic device has great potential for developing further particle manipulation strategies in biomedical applications.

In Paper III, we presented a method that combines elasto-inertial microfluidics and optical coherence spectroscopy. A typical elasto-inertial microfluidic setup employs fluorescently labelled particles and a fluorescence microscope to track the position of the labelled particles. However, such a setup can only provide two-dimensional information. Using optical coherence microscopy, information about the third dimension in a microfluidic channel can be provided, which is critical to understand particle motion in a viscoelastic fluid.

In Paper IV, we reported a novel acoustofluidic device called the EchoGrid. This device was used for the enrichment of microplastics at high flow rate, which can be used for sample preparation in environmental applications. In addition, we developed a method using silica particles as an enrichment strategy in samples with a low concentration of microplastics.

In Paper V, we improved our findings from Paper IV and worked to capture of nanoplastics by modifying the acoustic field and the sample flow lines. The method relied on the EchoGrid device and the angle of transducer that was integrated in the device. We employed computational methods to determine the optimal angle and demonstrated the capture of nanoplastics down to size of 25nm at high throughput.

Partiklar i storleksintervallet mikro- och nanometer förekommer i miljön (mikroplaster, nanoplaster etc.) och i kroppar hos levande organismers (celler, bakterier, tumörer, exosomer etc.) i olika former och strukturer. Oavsett sammansättning behöver dessa partiklar manipuleras för både miljö- och biomedicinska tillämpningar.

I både naturen och i våra vardagliga liv omges vi av mikro- och nanoplaster, och deras närvaro medför potentiella risker för både miljö och levande organismers hälsa. Ursprungligen utvecklades plaster med sina industriella fördelar, såsom låg produktionskostnad och mångsidighet, i fokus. Emellertid har det uppdagats att nedbrytningen lett till små partiklar som är svåra att upptäcka och kontrollera. Dessa partiklar har potential att tränga in i kroppen eller stanna kvar i naturen i hundratals år. Det är därför avgörande att kunna upptäcka, identifiera och analysera dessa partiklar för att fastställa i vilken utsträckning de utgör fara. Den globala ökningen av plastproduktion har lett till en ökande förekomst av mikro- och nanoplaster i miljön. Avsaknaden av standardiserade hanteringsmetoder försvårar insatserna för att hantera deras miljöpåverkan. Den nuvarande situationen, tillsammans med prognoserna för de kommande åren, verkar dyster och får forskare och lagstiftare att intensifiera sina ansträngningar för att utveckla och implementera bättre lösningar.

Närvaro eller deras koncentrationsnivån av biologiska partiklar, såsom bakterier, blodplättar, cirkulerande tumörceller eller extracellulära vesiklar, i kroppsvätskor och vävnader, innehåller viktig information om en levande organism. Isolering av dessa partiklar från blod eller plasma är ett viktigt steg i nödvändiga analyser för att fastställa cellens eller kroppens aktuella tillstånd. Hög genomströmning och högupplöst partikelmanipulation behövs för diagnostiska och terapeutiska tillämpningar.

I denna avhandling presenterade vi nya mikrofluidiska enheter med stort höjd-/breddförhållande, baserade på elasto-inertiell mikrofluidik. Dessa enheter visar sin förmåga att manipulera både mikro- och nanoplaster samt biologiska partiklar.

I Artikel I rapporterade vi om raka mikrokanaler med stort höjd-/breddförhållande och endast ett inlopp, som innehåller två sektioner: en fokuseringssektion och en migrationssektion. Syftet var att fokusera mikropartiklar i fokuseringssektionen och sedan separera förfokuserade partiklar baserat på deras storlek i migrationssektionen. Dessutom presenterade vi en omfattande studie av partikel-fokusering och undersökte alla parametrar som påverkar denna process. Slutligen visade vi hur systemets genomströmning kan ökas genom att öka kanalens djup. De presenterade resultaten visar potentialen för mikrokanaler med stort höjd/breddförhållande i elasto-inertiella mikrofluidiska system för tillämpningar som kräver höggenomströmning och högupplöst partikelseparation.

I Artikel II presenterade vi mikrokanaler med stort höjd/breddförhållande och en smalare kanalbredd än i första studien. Här visade vi för första gången fokusering av submikronpartiklar ned till 25 nm med hjälp av elasto-inertiell mikrofluidik. Dessutom bekräftade vi resultaten med biologiska nanopartiklar, såsom liposomer och exosomer. Fokusering av så små biologiska partiklar i en kostnadseffektiv mikrofluidisk enhet har stor potential för att utveckla ytterligare partikelmanipuleringsstrategier inom biomedicinska tillämpningar.

I Artikel III presenterade vi en metod som kombinerar elasto-inertiell mikrofluidik och optisk koherensmikroskopi. En typisk elasto-inertiell mikrofluidikmetod använder fluorescensmärka partiklar och ett fluorescensmikroskop. En sådan uppsättning ger dock endast information i två dimensioner. Genom att använda optisk koherensmikroskopi får man information om den tredje dimensionen i en mikrofluidisk kanal, vilket är avgörande för att förstå partikelrörelser i viskoelastiska vätskor.

I Artikel IV rapporterade vi om en ny akustofluidisk enhet kallad EchoGrid. Denna enhet användes för att anrika mikroplaster vid höga flödeshastigheter, vilket kan användas för provberedning i miljöapplikationer. Dessutom utvecklade vi en metod som använde kiseldioxidpartiklar för prover med lågkoncentration av mikroplaster.

I Artikel V förbättrade vi resultaten från Artikel IV och riktade in oss på att fånga nanoplaster genom att påverka det akustiska fältet och flödeslinjerna i proverna. Metoden baserades på EchoGrid-enheten och vinkeln på transducern som integrerades i enheten. Vi använde beräkningsmetoder för att justera vinkeln och demonstrerade fångsten av nanoplaster ned till 25 nm med hög genomströmning.

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.

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.)