Electrokinetically Driven Mixing in a Microchamber for Lab-on-a-Chip Applications Narayan Sundaram Abstract Micro-Total-Analysis-Systems (μTAS) have been the focus of recent world wide research due to their varied applications. Much of the motivation for the development of μTAS stems from applications in biotechnology and biomedicine. A typical μTAS device includes a number of functional units ranging from sample injection or ingestion, pre-concentration, mixing with reagents, chemical reactions, separation, detection, and possibly a chemical response. Mixing of constituents is one of the key functions desired of these systems for conducting analyses in a short span of time. The flow regime in these small devices (typical sizes 100μm) being predominantly laminar (Reynolds number, Re < 1), it becomes difficult to rapidly mix the constituent species. Hence for effective mixing, it is necessary to increase the Reynolds number and/or induce bulk motion such that the material interface between the components to be mixed is continously augmented. The method developed to induce such motion is by the application of an AC fluctuating potential field across a microchamber in which mixing is to be performed. The externally applied electric field applies a force on free ions in the charged Debye layer very close to the surface (1-10 nanometers) and induces a flow velocity which is proportional to the electric field. This applied fluctuating electric field gives rise to hydrodynamic instabilities which are responsible for increasing the material contact surface and hence augmenting the rate of mixing by an order of magnitude or more over pure diffusion. To further enhance mixing, microbaffles are strategically placed inside the microchamber and the mixing time was further decreased by a factor of two. Mixing was also studied in a neutral (no charge on the walls) microchamber. It was found that the mixing achieved in the absence of surface charge was comparable to the mixing achieved in the case with microbaffles. This work establishes that CFD is a useful tool that is capable of providing insight into the flow physics in devices with very small length scales. / Master of Science

This thesis, written by Ingrid Öberg Månsson at KTH Royal Institute of Technology and entitled “Electroanalytical devices with fluidic control using textile materials and methods”, presents experimental studies on the development of textile based electronic devices and biosensors. One of the reasons why this is of interest is the growing demand for integrated smart products for wearable health monitoring or energy harvesting. To enable such products, new interdisciplinary fields arise combining traditional textile technology and electronics. Textile based devices have garnered much interest in recent years due to their innate ability to incorporate function directly into, for example, clothing or bandages by textile processes such as weaving, knitting or stitching. However, many modifications of yarns required for such applications are not available on an industrial scale. The major objective of this work has been to study how to achieve the performance necessary to create electronic textile devices by either coating yarns with conductive material or using commercially available conductive yarns that are functionalized to create sensing elements. Further, liquid transport within textile materials has been studied to be able to control the contact area between electrolyte and electrodes in electrochemical devices such as sensors and transistors. Yarns with specially designed cross-sections, traditionally used in sportswear to wick sweat away from the body and enhance evaporation, was used to transport electrolyte liquids to come in contact with yarn electrodes. The defined area of the junction where the fluidic yarn meets the conductive yarn was shown to increase stability of the measurements and the reproducibility between devices. The results presented in the two publications of this thesis as well as additional results presented in the thesis itself show the promising potential of using textile materials to integrate electronic and electrochemical functionality in our everyday life. This is shown by using basic textile materials and processing techniques to fabricate complex devices for various application areas such as sensors and diagnostics as well as electrical and energy harvesting components. / Denna avhandling, skriven av Ingrid Öberg Månsson vid Kungliga Tekniska Högskolan och titulerad ”Elektroanalytiska sensorer med vätskekontroll integrerad genom användande av textila material och metoder”, presenterar experimentella studier inom utvecklingen av textilbaserade elektroniska komponenter och biosensorer. Detta är av intresse på grund av den ökade efterfrågan på integrerade smarta produkter som till exempel bärbara sensorer för hälsoövervakning eller för att samla upp och konvertera energi till elektricitet. För att möjliggöra denna typ av produkter föds nya interdisciplinära fält där traditionell textilteknologi och elektronik möts. Textilbaserade enheter har väckt stort intresse under de senaste åren på grund av den naturliga förmågan att integrera funktion i till exempel kläder eller förband genom textila tillverkningsprocesser som väveri, stickning eller sömnad. Många modifikationer hos garner som krävs för att möjliggöra sådana tillämpningar är dock inte tillgängliga i större skala. Därför har det huvudsakliga syftet med denna studie varit att undersöka hur man kan uppnå den prestanda som krävs för att tillverka elektroniska textila komponenter, antingen genom att belägga garner med elektroniskt ledande material eller genom att använda kommersiellt tillgängliga ledande garner som sedan modifieras kemiskt för att skapa sensorer. Utöver detta har vätsketransport inom textila material studerats för att kunna styra och kontrollera kontaktytan mellan elektrolyt och elektroder i elektrokemiska enheter så som sensorer och transistorer. Garner med speciella tvärsnitt, som traditionellt använts i sportkläder för att transportera svett bort från kroppen och underlätta avdunstning, har använts för att transportera elektrolytvätska till elektroder av garn. Den definierade kontaktytan där det vätsketransporterade garnet korsar elektrodgarnet har visats öka stabiliteten av mätningen och reproducerbarheten mellan mätenheter. Resultaten som presenteras i de två artiklar som denna avhandling bygger på samt i avhandlingen själv visar på lovande potential för användandet av textila material för att integrera elektronisk och elektrokemisk funktionalitet i våra vardagsliv. Detta har uppnåtts genom att använda grundläggande textila material och tillverkningsprocesser för att tillverka komplexa enheter för olika tillämpningsområden så som sensorer för diagnostik samt elektroniska komponenter. / <p>QC 2020-08-21</p>