Significant technological advances of the last years have been possible by developments in Optofluidics, which is a field that deals with the integration of optics and microfluidics into single devices.

The work described in this thesis is based on five scientific publications related to the use of fiber optic technology to build integrated optofluidic devices. The first three publications are within the field of life-science and point towards in-vivo and point-of-care applications, whereas the last two publications cover the study and the use of plasmonic nanoparticles for electrical modulation of light.

Aiming at developing useful tools for in-vivo biological applications, the first publication consists of designing and testing a functional optical fiber for real-time monitoring and selective collection of fluorescent microparticles. This probe relies on a microstructured optical fiber with a hole along its cladding, which is used to selectively aspirate individual particles of interest once their fluorescence signal is detected. On the same line of research, the second publication contemplates the fabrication of a fiber probe that traps single microparticles and allows for remote detection of their optical properties. This probe is also based on a microstructured fiber that enables particle trapping by fluidic forces. The third publication addresses the development of an all-fiber miniaturized flow cytometer for point-of-care applications. This system can analyze, with excellent accuracy and sensitivity, up to 2500 cells per second by measuring their fluorescence and scattering signal. A novel microfluidic technique, called Elasto-inertial microfluidics, is employed for aligning the cells into a single-stream to optimize detection and throughput.

The fourth publication involves the experimental and theoretical study of the electrical-induced alignment of plasmonic gold nanorods in suspension and its applicability to control light transmission. This study is done by using an all-fiber optofluidic device, based on a liquid-core fiber, which facilitates the interaction of light, electric fields, and liquid suspensions. Results show that nanorods can be aligned in microseconds, providing a much better performance than liquid-crystal devices. Finally, the fifth publication consists of an upgrade of the previous device by integrating four electrodes in the cladding of the liquid-core fiber. This improvement enables nanosecond response time and the possibility of digitally switching nanorods between two orthogonal aligned states, overcoming the limitation of slow thermal relaxation.

The work presented here shows that optofluidics based on optical fibers is a robust and convenient platform, as well as a promising direction for the developing of novel instruments in fields such as life-science, non-linear optics, plasmonic, and sensing.

Efficient separation and detection of rare cells in a mixed population is important in many biomedical applications. For instance, isolating and detecting circulating tumor cells (CTCs) from whole blood samples could allow for early cancer diagnosis and prognosis during treatment. CTCs are rare cells circulating in blood detached from the primary tumor site, carrying important information such as the origin of cancer and metastatic information. The detection of CTC from blood samples, besides being a minimally invasive procedure, could be vital in case of difficulty to access the tumor site via traditional biopsies, such as colon and pancreatic cancer. Microfluidics is a research field with great promise towards the development of methods to isolate and separate cells for clinical applications. Microfluidic based cell separation has been demonstrated using biological approaches using cell surface markers, and biophysical approaches using cell size, shape, and deformability. This thesis will focus on developing passive strategy using inertial microfluidics (biophysical, paper 1-4) and affinity biomarker (biochemical, paper 5) based strategy to isolate and analyze CTCs. Inertial microfluidics relies on inherent hydrodynamic forces, inertial forces, in flow through the microfluidic channel. Depending on the geometry of the channel, inertial forces drive the particles and cells to a specific streamline position, allowing for focusing and separation. In contrast, affinity-based isolation relies on biomarkers expressed on the surface of the targeted cells, which is highly specific. In paper 1, using the elasto inertial microfluidic technique, high throughput particle focusing and separation was achieved in a curved rectangular channel with a separation efficiency of 89% for 10 μm and 99% for the 15 μm particles at a high volumetric flow rate (1 mL/min). In paper 2, a detailed analysis of particle focusing was studied experimentally and numerically in a circular cross-section. Using the FENE-P model simulating non-Newtonian fluid and an immersed boundary method to account for the particles, it was observed that a combination of inertia and elasticity leads to several intermediate focusing positions. In paper 3, we developed a portable microflow cytometer using fiberoptics capillaries. By combining elasto inertial microfluidics and optical fibers, we focused particles and cells and demonstrated particle counting at a throughput of 2500 particles/second. In paper 4, we built an all-fiber separation and detection component and demonstrated a separation efficiency of 100% for the 10 μm and 97% for the 1 μm particles as a proof of principle. In addition, the separated 10 μm particles could beiiiquantified in the all-fiber component. In paper 5, an affinity-based separation approach was carried out to utilize the surface markers to capture and release viable CTCs for downstream analysis. A novel layer-by-layer nanofilm coating strategy was developed using cellulose nanofibril (CNF) built into multiple layers and functionalized with antibodies to capture the cells. After capture, the CNF were enzymatically degraded to release the CTCs. HCT116 colon cancer cells were captured with an efficiency of more than 97%, and when spiked in whole blood, an approximately 200 fold average enrichment was achieved compared to white blood cells. 80% of the cancer cells spiked in whole blood were recovered with 97% viability in less than 30 minutes.

In summary, this thesis presents different microfluidics-based separation of cancer cells based on biophysical and biochemical properties. Using elasto inertial microfluidics, we developed several approaches to separate and detect cells and particles. Using layer-by-layer coating of CNF, we successfully demonstrated capture and release of cancer cells with maintained high viability. While the thesis has focused on different properties of cells for separation and analysis, combining these methods will be important for efficient isolation and characterization of CTCs for improved diagnostics.

Separationen och detektionen av specifika celler i en blandad population av celler är viktig i många biomedicinska tillämpningar. Som exempel, möjligheten att isolera och detektera cirkulerande tumörceller (CTC) från helblod skulle kunna tillåta tidig cancer diagnos och prognos under behandling. CTC är sällsynta celler som cirkulerar i blodet och bär med sig viktig information, som den specifika cancerns ursprung och metastatiska information. Att kunna detektera CTC med hjälp av blodprover, förutom att erbjuda en minimalt invasiv metod, skulle kunna vara viktig i fall där tumörområdet är svårtillgänglig för traditionell provtagning via biopsier, såsom kolon- och bukspottkörtel-cancer.

Mikrofluidik är ett forskningsfält med betydande potential att möjliggöra utvecklingen av metoder för att isolera och separera celler för kliniska tillämpningar. Separation av celler baserad på mikrofluidik har demonstrerats med olika angreppssätt så som biologiska med hjälp av affinitetsmarkörer, och biofysiska metoder där man utnyttjar storlek, form, och deformerbarhet för att separera celler. Denna avhandling fokuserar på att utveckla en passiv strategi som utnyttjar tröghets-baserade mikrofluidik som domineras av tröghetskrafter (papper 1-4) och strategier med affinitetsbiomarkörer (paper 5) med målet att isolera och analysera CTC. Tröghetsfokusering i mikroflöden baseras på hydrodynamiska krafter, tröghetskrafter, som utvecklas i vätskeflöden i mikrokanaler. Beroende på mikrokanalens geometriska utformning och vätskans flödes hastighet kommer tröghetskrafterna att driva partiklar eller celler till specifika positioner i strömningsfältet och i sin tur möjliggöra fokusering och separation. Å andra sidan, affinitetsbaserad isolering är beroende på biomarkörer som uttrycks på ytan av specifika celler och är därmed mycket specifik. I papper 1 utnyttjas mikrofluidisk metod med tröghetskrafter med elastiska bidrag för att möjliggöra partikel fokusering och separation vid höga volymsflöden. I papper 2, en detaljerad analys av partikelfokusering i en circulärt tvärsnitt genomfördes experimentellt och numeriskt. I papper 3, en portabel mikroflödescytometer utvecklades med hjälp av fiberoptiska kapillärer. Med hjälp av mikrofluidik som utnyttjar elastiska och tröghetskrafter tillsammans med optiska fibrer, fokuserades partiklar och celler och demonstrerade möjligheten att räkna partiklar och celler. I papper 4 beskrivs en fiber-baserad komponent för separation och detektion som demonstrerade en separationseffektivitet av 100% för 10 µm-partiklar och 97% för 1 µm-partiklar som ett bevis på principen. I papper 5, en affinitetsbaserad separationsmetod utvecklades för att utnyttja ytmarkörer som finns på cirkulerande tumörceller. En beläggningsstrategi med hjälp av nanocellulosa utvecklades för att först fånga in och och sedan frigöra levande CTC för vidare analys. Den nya nanocellulosa-baserade ytbeläggningen fångar och frigör celler med hjälp av en enzym för analys nedströms. Sammanfattningsvis, denna avhandling presenterar mikrofluidik-baserad separation av cancerceller som utnyttjar biofysiska och biokemiska egenskaper. Med hjälp av tröghetsfokusering i mikrofluidik utvecklades flera metoder för att separera och detektera celler och partiklar. Dessutom utvecklades en original metod som bygger på att ytbehandla chip med nanocellulosa för infångning och frigörande av CTCs. I avhandlingen har vi undersökt olika metoder för isolering and analys av cancer celler. Medan varje metod har sin fördel och svaga punkter, kommer det att vara viktigt att kombinera dessa metoder och andra för att bidra till bätter cancer diagnostik i framtiden.