My research broadly covers various important aspects of microfluidic devices and biosensors. Specifically, this dissertation reports: (1) a new and effective room temperature method of bonding polydimethylsiloxane (PDMS) microfluidics to substrates such as silicon and glass, (2) a new microfluidic pump concept and implementation specifically designed to repeatedly drive a small sample volume (<1 µL) very rapidly (~500 µL/min) through a sensor-containing flow channel to significantly decrease sensor response time through advection-driven rather than diffusion-driven mass transport, (3) use of a new microfluidic material based on polyethylene glycol diacrylate (PEGDA) to implement impedance-based dynamic nanochannel sensors for protein sensing, and (4) an investigation of galvanoluminescence and how to avoid it for conditions important to fluorescence-based dielectrophoresis (DEP) microfluidic biosensors. Over the last decade, the Nordin research group has developed a lab-on-a-chip (LOC) biosensor based on silicon photonic microcantilever arrays integrated with polydimethylsiloxane (PDMS) microfluidics for protein biomarker detection. Integration requires reliable bonding at room temperature with adequate bond strength between the PDMS element and microcantilever sensor substrate. The requirement for a room temperature process is particularly critical because microcantilevers must be individually functionalized with antibody-based receptor molecules prior to bonding and cannot withstand significant heating after functionalization. I developed a new room temperature bonding method using PDMS curing agent as an intermediate adhesive layer. Two curing agents (Sylgard 184 and 182) were compared, as well as an alternate UV curable adhesive (NOA 75). The bond strength of Sylgard 184 was found to be stronger than Sylgard 182 under the same curing conditions. Overnight room temperature curing with Sylgard 184 yields an average burst pressure of 433 kPa, which is more than adequate for many PDMS sensor devices. In contrast, UV curable epoxy required a 12 hour bake at 50 °C to achieve maximum bond strength, which resulted in a burst pressure of only 124 kPa. In many biosensing scenarios it is desirable to use a small sample volume (<1 µL) to detect small analyte concentrations in as short a time as possible. I report a new microfluidic pump to address this need, which we call a reflow pump. It is designed to rapidly pump a small sample volume back and forth in a flow channel. Ultimately, the flow channel would contain functionalized sensor surfaces. The rapid flow permits use of advection-driven mass transport to the sensor surfaces to dramatically reduce sensor response times compared to diffusion-based mass transport. Normally such rapid flow would have the effect of decreasing the fraction of analyte molecules in the volume that would see the sensor surfaces. By configuring the pump to reflow fluid back and forth in the flow channel, the analyte molecules in the small sample volume are used efficiently in that they have many opportunities to make it to the sensor surfaces. I describe a 3-layer PDMS reflow pump that pumps 300 nL of fluid at 500 µL/min for 15 psi actuation pressure, and demonstrate a new two-layer configuration that significantly simplifies pump fabrication. Impedance-based nanochannel sensors operate on the basis of capturing target molecules in nanochannels such that impedance through the nanochannels is increased. While simple in concept, the response time can be quite long (8~12 hours) because the achievable flow rate through a nanochannel is very limited. An approach to dramatically increase the flow rate is to form nanochannels only during impedance measurements, and otherwise have an array of nanotrenches on the surface of a conventional microfluidic flow channel where they are exposed to normal microfluidic flow rates. I have implemented such a dynamic nanochannel approach with a recently-developed microfluidic material based polyethylene glycol diacrylate (PEGDA). I present the design, fabrication, and testing of PEGDA dynamic nanochannel array sensors, and demonstrate an 11.2 % increase in nanochannel impedance when exposed to 7.2 µM bovine serum albumin (BSA) in phosphate buffered saline (PBS). Recently, LOC biosensors for cancer cell detection have been demonstrated based on a combination of dielectrophoresis (DEP) and fluorescence detection. For fluorescence detection it is critical to minimize other sources of light in the system. However, reported devices use a non-noble metal electrode, indium tin oxide (ITO), to take advantage of its optical transparency. Unfortunately, use of non-noble metal electrodes can result in galvanoluminescence (GL) in which the AC voltage applied to the electrodes to achieve DEP causes light emission, which can potentially confound the fluorescence measurement. I designed and fabricated two types of devices to examine and identify conditions that lead to GL. Based on my observations, I have developed a method to avoid GL that involves measuring the impedance spectrum of a DEP device and choosing an operating frequency in the resistive portion of the spectrum. I also measure the emission spectrum of twelve salt solutions, all of which exhibited broadband GL. Finally, I show that in addition to Au, Cr and Ni do not exhibit GL, are therefore potentially attractive as low cost DEP electrode materials.

<p>En studie i hur känsligheten avtar från ytan hos biosensorer med höga frekvenser presenteras. Med ny teknologi som avancerade elektroakustiska tunnfilms komponenter, så kallade FBARs, blir tidigare outforskade områden som decay längden möjliga att studera.</p><p>För att undersöka hur frekvenssvaret och känsligheten påverkas av interaktioner långt ut från en sensoryta används proteinkemi. Ett protokoll har optimerats innehållande aktivering med EDC/NHS och fibrinogen för att säkerställa en jämn tjocklek och fördelning av ett adsorberat proteinlager över en yta.</p><p>Dessa ytor kontrollerades först med hjälp av ellipsometri och sedan i ett QCM instrument. Alla experiment med de högfrekventa FBAR sensorerna utfördes vid Ångströmslaboratoriet i Uppsala där pågående forskning inom området finns.</p><p>Resultaten bekräftar teorin om en avtagande känslighet i och med ett ökat avstånd från ytan. En experimentell genomförd och beräknad tjocklek för decay längden uppskattades som inte helt stämde överens med den teoretiskt beräknade.</p><p>En ny term föreslås då frekvenssvaret hos en biosensor planar ut. Detta är en effekt som sker vid dubbla tjockleken av den teoretisk beräknade tjockleken av decay längden och har fått namnet; detection length. Efter denna längd eller gräns observeras en inverterad signal som det än så länge inte finns någon förklaring till.</p> / <p>A study of the sensitivity decrease of biosensors working at high frequencies is presented. With new technology such as film bulk acoustic resonators (FBAR), issues like the decay length is no longer irrelevant theory but may cause limitation in the system as well as it offers new detection possibilities.</p><p>To investigate the frequency response and sensitivity, layer-on-layer construction chemistry was used. A protocol involving activation with EDC/NHS and coupling chemistry with fibrinogen was optimized to ensure accurate thickness and uniformly distribution of each layer over the surface.</p><p>Surfaces were characterized using null ellipsometry and the protocol was tested in a traditional quartz crystal microbalance (QCM). Experiments with the FBAR were preformed at the Ångström laboratory in Uppsala were there is ongoing research and development in FBAR technology.</p><p>The results confirmed the theory of decreasing frequency and sensitivity further out from the surface. An experimental and estimated thickness was calculated which to some extent correlates to the theoretically calculated decay length.</p><p>A new terminology is suggested when the frequency levels off. It occurs approximately at twice the distance and thickness of the theoretically calculated decay length and is given the name; detection length. Beyond the detection length an inverted signal is observed which cannot yet be explained for.</p>

Detection of both biological and chemical environmental toxicants is essential in the assessment of risk to human health. Cell-based biosensors are capable of activity- based detection of toxicity. Chromatophore cells, responsible for the pigmentation of poikilothermic animal, have shown immense potential as cell-based biosensors in the detection of a broad range of environmental toxicants. Chromatophore cells possess the motile pigment granules that intracellularly aggregate or disperse in response to external stimuli. Previous studies have assessed chromatophore cells isolated from red Betta splendens and grey Oncorhynchus tschawytscha fish for use as a biosensor. The objective of this study was to describe blue B. splendens chromatophore cells in tissue culture. Blue B. splendens chromatophore cells were assessed for their longevity in tissue culture and their responses to previously established control agents. Blue B. splendens chromatophore cells were exposed to select chemicals and pathogenic bacteria to assess their ability to respond to environmental toxicants. Three concentrations of mercuric chloride, methyl mercuric chloride, paraquat, sodium arsenite, sodium cyanide chemicals were tested. Bacillus cereus, Bacillus subtilis, Salmonella enterica serovar Enteritidis, and Salmonella enterica serovar Typhimurium were tested. Red B. splendens chromatophore cells were subjected to the select chemical and bacterial toxicants, and observed for their responses. The data collected in this and previous studies were compiled to compare chromatophore cell responses to a broad range of environmental toxicants. Chromatophore cells isolated from both blue and red B. splendens were responsive to methyl mercuric chloride and sodium arsenite. Grey O. tschawytscha chromatophore cells have shown responsiveness to mercuric chloride and sodium arsenite. Blue and red B. splendens chromatophore cells were both responsive to B. cereus and both Salmonella serovars. Grey O. tschawytscha have previously been shown to respond to B. cereus as well. In conclusion, this study reports the chromatophore cells isolated from blue B. splendens in tissue culture and showed similar responsiveness to the selected chemical and bacterial environmental toxicants as chromatophore cells isolated from red and grey colored fish. This study provides compelling evidence that the chromatophore response is not dependent on fish color and that chromatophore cells used for a cell-based detection system may be isolated from different colored fish. / Graduation date: 2012

Nature has always served as a model for mimicking and inspiration to humans in their efforts to improve their life. Researchers have been inspired by nature to produce biomimetic materials with molecular recognition properties by design rather than evolution. Molecular imprinting is one way to prepare such materials. Such smart materials with new functionalities are at the forefront of the development of a relevant number of ongoing and perspective applications ranging from consumer to space industry. Molecularly imprinted polymers were developed by mimicking the natural enzymes or antibodies that serve as host for binding target molecules. These imprints were used as a recognition element to substitute natural biomolecules in biosensors. The concept behind molecular imprinting is to mold a material (with the desired chemical properties) around individual molecules. Upon removal of the molecular templates, one is left with regions in the molded material that fit the shape of the template molecules. Thus, molecular imprinting results in materials that can selectively bind to molecules of interest. Imprinted materials resulted in applications ranging from chemical separation to bioanalytics. In this work attempts were made particularly in the development of molecularly imprinted polymer based thermometric sensors. The main effort was focused towards the development of an covalently imprinted polymer that would be able to selectively bind fructosyl valine (Fru-Val), the N-terminal constituent of hemoglobin A1c ß-chains. Taking into account the known advantages of imprinted polymers, e.g. robustness, thermal and chemical stability, imprinted materials were successfully used as a recognition element in the sensor. One of the serious problems associated with the development of MIP sensors and which lies in the absence of a generic procedure for the transformation of the polymer-template binding event into a detectable signal has been addressed by developing the "thermometric" approach. In general the developed approach gives a new insight on MIP/Analyte interactions. / In dem Bestreben, ihr eigenes Leben zu verbessern, haben die Menschen stets die Natur nachgeahmt und sich von ihr inspirieren lassen. Die Natur hat Forscher zur Erzeugung smarter biomimetischer Stoffe mit molekularen Erkennungseigenschaften nach dem Vorbild der Evolution inspiriert. Eine der Methoden zur Herstellung solcher Substanzen ist das molekulare Prägen. Smarte Materialien mit neuen Eigenschaften stehen an der Spitze der Entwicklung potentieller Anwendungen vom Verbraucher bis hin zur Raumfahrtindustrie. Durch Nachahmung von natürlichen Enzymen oder Antikörpern wurden molekular geprägte Polymere (MIPs) entwickelt, die der Bindung von Zielmolekülen dienen. Diese geprägten Polymere (imprints) wurden anstelle von Biomolekülen als Erkennungselemente in Biosensoren eingesetzt. Das Konzept, das dem molekularen Prägen zugrunde liegt, besteht in der Formung eines Polymers (mit den entsprechenden chemischen Eigenschaften) um einzelne Zielmoleküle herum. Nach Entfernen dieser molekularen Template bleiben Abdrücke im Polymer übrig, die der Form der Templatmoleküle entsprechen. Mit Hilfe des molekularen Prägens kann man also Stoffe herstellen, die sich selektiv an bestimmte Moleküle binden können. Geprägte Polymere finden breite Anwendung, etwa in chemischen Aufreinigungsprozessen und der Bioanalytik. Hauptanliegen der vorliegenden Arbeit war es, thermometrische Sensoren auf der Basis molekular geprägter Polymere zu entwickeln. Die Anstrengungen richteten sich vor allem auf die Entwicklung eines kovalent geprägten Polymers, das in der Lage ist, selektiv Fruktosyl-Valin (Fru-Val), den N-terminalen Bereich von Hämoglobin A1c, zu binden. Aufgrund der bekannten Vorzüge geprägter Polymere – z. B. Robustheit und thermische und chemische Stabilität – wurden geprägte Polymere erfolgreich als Erkennungselement im Sensor angewendet. Eine der größten Herausforderungen bei der Entwicklung von MIP-Sensoren, das Fehlen eines generischen Verfahrens zur Umwandlung der Bindungsreaktion in ein nachweisbares Signal, wurde mit der Entwicklung der thermometrischen Methode in Angriff genommen. Diese Methode führt allgemein zu neuen Einsichten in die Interaktionen zwischen MIP und Analyt.

This thesis describes a new approach to biomolecular analysis, called the volume-amplified magnetic nanobead detection assay (VAM-DNA). It is a sensitive, specific magnetic bioassay that offers a potential platform for the development of low-cost, easy-to-use diagnostic devices. The VAM-NDA consists of three basic steps: biomolecular target recognition, enzymatic amplification of the probe-target complex using the rolling circle amplification (RCA) technique, and addition of target complementary probe-tagged magnetic nanobeads which exhibit Brownian relaxation behavior. Target detection is demonstrated by measuring the frequency-dependent complex magnetization of the magnetic beads. The binding of the RCA products (target DNA-sequence coils) to the bead surface causes a dramatic increase in the bead size, corresponding essentially to the size of the DNA coil (typically around one micrometer). This causes a decrease in the Brownian relaxation frequency, since it is inversely proportional to the hydrodynamic size of the beads. The concentration of the DNA coils is monitored by measuring the decrease in amplitude of the Brownian relaxation peaks of free beads. The parameters oligonucleotide surface coverage, bead concentration, bead size and RCA times were investigated in this thesis to characterize features of the assay. It was found that all of these parameters affect the outcome and efficiency of the assay. The possibility of implementing the assay on a portable, highly sensitive AC susceptometer platform was also investigated. The performance of the assay under these circumstances was compared with that using a superconducting quantum interference device (SQUID); the sensitivity of the assay was similar for both platforms. It is concluded that, the VAM-NDA opens up the possibility to perform biomolecular detection in point-of-care and outpatient settings on portable platforms similar to the one tested in this thesis. Finally, the VAM-NDA was used to detect Escherichia coli bacteria and the spores of Bacillus globigii, the non-pathogenic simulant of Bacillus anthracis. A limit of detection of at least 50 bacteria or spores was achieved. This shows that the assay has great potential for sensitive detection of biomolecules in both environmental and biomedical applications.

Livet tas för givet av de flesta. Det finns däremot många som ägnar stora delar av sitt liv för att försöka lösa dess mysterier. En del av lösningen ligger i att förstå hur alla molekyler är sammanlänkade i det gigantiska nätverk som definierar den levande organismen. Under det senaste seklet har en hel del forskning utförts för att kartlägga dessa nätverk. Resultatet av dessa mödor kan vi se i de läkemedel som vi har idag och som har utvecklats för att bota eller åtminstone lindra olika sjukdomar och tillstånd. Dessvärre finns det fortfarande många sjukdomar som är obotliga (t.ex. cancer) och mycket arbete krävs för att förstå dem till fullo och kunna designa framgångsrika behandlingar. Arbetet i denna avhandling beskriver en analytisk plattform som kan användas för att effektivisera kartläggningsprocessen; protein-mikroarrayer. Mikroarrayer är ytor som har mikrometerstora (tusendels millimeter) strukturer i ett regelbundet mönster med möjligheten att studera många interaktioner mellan biologiska molekyler samtidigt. Detta medför snabbare och fler analyser - till en lägre kostnad. Protein-mikroarrayer har funnits i ungefär ett decennium och har följt i fotspåren av de framgångsrika DNA-mikroarrayerna. Man bedömer att protein-mikroarrayerna har en minst lika stor potential som DNA mikroarrayerna då det egentligen är mer relevant att studera proteiner, som är de funktionsreglerande molekylerna i en organism. Vi har i detta arbete tillverkat modellytor för stabil inbindning av proteiner, som lämnar dem intakta, funktionella och korrekt orienterade i ett mikroarray format. Därmed har vi adresserat ett stort problem med protein mikroarrays, nämligen att proteiner är känsliga molekyler och har i många fall svårt att överleva tillverkningsprocessen av mikroarrayerna. Vi har även studerat en metod att tillverka mikroarrayer av proteiner bundna till strukturer, som modellerats att efterlikna cellytor. Detta är särkilt viktigt eftersom många (hälften) av dagens (och säkerligen framtidens) läkemedel är riktade mot att påverka denna typ av proteiner och att studera dessa i sin naturliga miljö är därför väldigt relevant. I ett annat projekt har vi använt protein mikroarrayer för att detektera fyra vanliga droger (heroin, amfetamin, ecstasy och kokain). Detektionen baseras på användandet av antikroppar som lossnar från platser på ytan när de kommer i kontakt med ett narkotikum. Detta koncept kan enkelt utvecklas till att detektera mer än bara fyra droger. Vi har även lyckats att parallellt mäta förekomsten av en annan typ av förening på mikroarray ytan, nämligen det explosiva ämnet trinitrotoluen (TNT). Detta visar på en mångsidig plattform för detektionen av i princip vilken typ av farlig eller olaglig substans som helst - och på en yta! Vi föreställer oss därför att möjliga tillämpningsområden finns inom brottsbekämpning, i kampen mot terrorism och mot narkotikamissbruk etc. Mikroarrayerna har i denna avhandling utforskats med optiska metoder som tillåter studie av omärkta proteiner, vilket resulterar i så naturliga molekyler som möjligt. / Life is a thing taken for granted by most. However, it is the life-long quest of many to unravel the mysteries of it. Understanding and characterizing the incomprehensively complex molecular interaction networks within a biological organism, which defines that organism, is a vital prerequisite to understand life itself. Already, there has been a lot of research conducted and a large knowledge has been obtained about these pathways over, especially, the last century. We have seen the fruits of these labors in e.g. the development of medicines which have been able to cure or at least arrest many diseases and conditions. However, many diseases are still incurable (e.g. cancer) and a lot more work is still needed for understanding them fully and designing successful treatments. This work describes a generic analytical tool platform for aiding in more efficient (bio)molecular interaction mapping analyses; protein microarray chips. Microarray chips are surfaces with micrometer sized features with the possibility of studying the interactions of many (thousands to tens of thousands) (bio)molecules in parallel. This allows for a higher throughput of analyses to be performed at a reduced time and cost. Protein microarrays have been around for approximately a decade, following in the footsteps of the, so far, more successfully used DNA microarrays (developed in the 1990s). Microarrays of proteins are more difficult to produce because of the more complex nature of proteins as compared to DNA. In our work we have constructed model surfaces which allow for the stable, highly oriented, and functional immobilization of proteins in an array format. Our capture molecules are based on multivalent units of the chelator nitrilotriacetic acid (NTA), which is able to bind histidine-tagged proteins. Furthermore, we have explored an approach for studying lipid membrane bound systems, e.g. receptor-ligand interactions, in a parallelized, microarray format. The approach relies on the addressable, DNA-mediated adsorption of tagged lipid vesicles. In an analogous work we have used the protein microarray concept for the detection of four common narcotics (heroin, amphetamine, ecstasy, and cocaine). The detection is based on the displacement of loosely bound antibodies from surface array positions upon injection of a specific target analyte, i.e. a narcotic substance. The proof-of-concept chip can easily be expanded to monitor many more narcotic substances. In addition, we have also been able to simultaneously detect the explosive trinitrotoluene (TNT) along with the narcotics, showing that the chip is a versatile platform for the detection of virtually any type of harmful or illegal compound. This type of biosensor system is potentially envisaged to be used in the fight against crime, terrorism, drug abuse etc. Infrared reflection absorption spectroscopy together with ellipsometry has been used to characterize molecular layers used in the fabrication processes of the microarray features. Imaging surface plasmon resonance operating in the ellipsometric mode is subsequently used for functional evaluation of the microarrays using a well-defined receptor-ligand model system. This approach allows simultaneous and continuous monitoring of binding events taking place in multiple regions of interest on the microarray chip. A common characteristic of all the instrumentation used is that there is no requirement for labeling of the biomolecules to be detected, e.g. with fluorescent or radioactive probes. This feature allows for a flexible assay design and the use of more native proteins, without any time-consuming pretreatments.

This thesis demonstrates the application of biosensor technology for molecular biology investigations, utilizing a surface plasmon resonance based optical device for mass sensitive detection of biomolecular interactions at a chipsurface. Oligonucleotide model systems were designed for analysis of the action of DNA manipulating enzymes. DNA ligation, DNA cleavage and DNA synthesis could be quantitatively monitored in real-time. A protocol for DNA minisequencing was also established based on prevention of chain elongation by incorporation of chain-terminators. Determinations of affinities for short oligonucleotides hybridizing to an immobilized target were performed with various sequence content, length, temperature and degree of complementarity. The decrease in affinity for hybridizations involving mismatch situations was found to be strongly dependent on the relative position of the mismatch. Interestingly, also end-mismatches were clearly detectable. The stabilization effect achieved upon co-hybridization of two adjacently annealing short oligonucleotide modules (modular primer effect) was also investigated for different module combinations and hybridization situations. The modular concept of hybridizations was subsequently demonstrated to result in enhanced Capture of single stranded PCR products. The sequence based DNA analysis, first introduced with oligonucleotide modelsystems, was extended to the scanning and screening formutations in PCR amplified DNA from clinically relevant samples. Several different formats were investigated, eitherwith the PCR products immobilized on the chip and oligonucleotides injected or vice versa. Again, mismatch discrimination could be observed for wild type and mutant specific oligonucleotides hybridizing to the targets. The experimental set-up for mutation detection was further developed by the introduction of a subtractive mismatch sensitive hybridization outside the instrument and a subsequent determination of the relative amounts of remain ingoligonucleotides with analytical biosensor monitoring of hybridizations between fully complementary oligonucleotides. In conclusion, the applied technology was found to be a suitable tool for a wide range of molecular biology applications, with emphasis on hybridization analysis and mutation detection. / QC 20100611

L'obiettivo di questa tesi di dottorato era lo studio della influenza di diversi amendanti organici sulla rizosfera e la costruzione di un modello matematico per descrivere il flusso di carbonio nella rizosfera. Per questo motivo, plantule di mais sono state seminate e cresciute all'interno di sistemi rhizobox. La frazione disponibile del carbonio in ogni strato è stata valutata con il biosensore luminescente P. Fluorescence 10586 PUCD607. Inoltre sono stati determinati il carbonio organico totale (TOC), la distribuzione degli acidi organici nella rizosfera e la carica microbica totale. Un modello matematico viene presentato che descrive il flusso del carbonio nella rizosfera. Il modello risolve un'equazione di diffusione-degradazione con lo schema di discretizzazione di Crank-Nikolson ed è accoppiato all'inverse modelling software pest. Infine viene proposto un modello concettuale per la descrizione della biodisponibilità delle sostanze nel suolo. / The main aim of this work was to study the effect of different organic amendments in the rhizosphere soil with innovative techniques, and the building of a modelling tool to describe the carbon flow in the rhizosphere soil. For this reason maize plants were grown in rhizobox systems amended with different organic materials. The available fraction of organic C in each layer was assessed with the lux-marked p. fluorescens 10586 pucd607. Total organic carbon (TOC), organic acid distribution in the rhizosphere and total number of culturable cells as colony forming units (CFU) were also determined. A modelling tool is presented that describes the carbon flow in the rhizosphere. The model solves with the Crank-Nicolson discretisation scheme a diffusion-degradation equation and is coupled to the inverse modelling software pest. Finally a five-compartment conceptual model is proposed for describing organic compounds bioavailabililty in soil.

In this study, an improved potentiometric intracellular glucose biosensor was fabricated with immobilization of glucose oxidase on a ZnO nanoporous material. The ZnO nanoporous material with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose sensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a linear glucosedependent electrochemical response over a wide range of glucose concentration (500 nM-10 mM). The measurements of intracellular glucose concentrations with our biosensor were consistent with the values of intracellular glucose concentrations reported in the literature. The sensor also demonstrated its capability by detecting an increase in the intracellular glucose concentration induced by insulin. We found that the ZnO nanoporous material provides sensitivity as high as 1.8 times higher than that obtained using ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the excellent performance of the developed nanosensor in sensitivity, stability, selectivity, reproducibility and anti-interference was achieved. All these advantageous features of this intracellular glucose biosensor based on functionalised ZnO nanoporous material compared to ZnO nanorods demonstrate a promising way of enhancing glucose biosensor performance to measure reliable intracellular glucose concentrations within single living cells. / <p>Original Publication:Alimujiang Fulati, Syed M. Usman Ali, Muhammad H. Asif, Naveed Ul Hassan Alvi, Magnus Willander, Cecilia Brännmark, Peter Strålfors, Sara I. Börjesson and Fredrik Elinder, An intracellular glucose biosensor based on nanoflake ZnO, 2010, Sensors and actuators. B, Chemical, (150), 2, 673-680.http://dx.doi.org/10.1016/j.snb.2010.08.021Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/</p>

Research toward a multiplexed nucleic acid biosensor that uses quantum dots (QDs) as donors in a fluorescence resonance energy transfer (FRET) assay is described. Optical fibers were modified with mixed films composed of different colours of QDs and different oligonucleotide probes that served as scaffolds for the hybridization of the corresponding target nucleic acid sequences. Fluorescent dyes that were suitable as acceptors for each QD donor were associated with hybridization and provided an analytical signal through FRET-sensitized emission. Different detection channels were achieved through the combination of different donors and acceptors: green emitting QDs with Cyanine 3 or Rhodamine Red-X; and red emitting QDs with Alexa Fluor 647. A detection channel that used the direct excitation of Pacific Blue complemented the FRET pairs. One-plex, two-plex, three-plex and four-plex hybridization assays were demonstrated. A sandwich assay format was adopted to avoid target labeling. Detection limits were 1-10 nM (1-12 pmol) and analysis times were 1-4 h. Single nucleotide polymorphisms were discriminated in multiplexed assays, and the potential for reusability was also demonstrated. Non-selective interactions between QDs and oligonucleotides were characterized, and routes toward the optimization of the QD-FRET hybridization assays were identified. A basic model for multiple FRET pathways in a mixed film was also developed. In addition to the advantages of solid-phase assays, the combination of QDs and FRET was advantageous because it permitted multiplexed detection using a single excitation source and a single substrate, in the ensemble, and via ratiometric signals. Spatial registration or sorting methods, imaging or spatial scanning, and single molecule spectroscopy were not required. The research in this thesis is expected to enable new chip-based biosensors in the future, and is an original contribution to both bioanalytical spectroscopy and the bioanalytical applications of nanomaterials.