Optics and photonics enable important technological solutions for critical areas such as health, communications, energy, and manufacturing. Novel nanofabrication techniques, on the other hand, have enabled the realization of ever shirking devices. On-chip photonic micro-resonators, the fabrication of which was made possible in the recent decade thanks to the progress in nanofabrication, provide a sensitive and scalable transduction mechanism that can be used for biochemical sensing applications. The recognition and quantification of biological molecules is of great interest for a wide range of applications from environmental monitoring and hazard detection to early diagnosis of diseases such as cancer and heart failure. A sensitive and scalable biosensor platform based on an optimized array of silicon nitride microring resonators is proposed for multiplexed, rapid, and label-free detection of biomolecules. The miniature dimension of the proposed sensor allows for the realization of handheld detection devices for limited-resource and point-of-care applications. To realize these sensors, the design, fabrication, stabilization, and integration challenges are addressed. Especially, the focus is placed on solving a major problem in using resonancebased integrated photonic sensors (i.e., the insufficiency of wavelength scan accuracy in typical tunable lasers available) by using an interferometric referencing technique for accurate resonance tracking. This technique can improve the limit of detection of the proposed sensor by more than one order of magnitude. The method does not require any temperature control or cooling, and the biosensor platform does not require narrow linewidths necessary for the biosensors based on ultrahigh quality factor resonators, thus enabling low-cost and reliable integration on the biosensor platform.

In this dissertation, three types of paper-based analytical devices for point-of-care biosensing, a potentiometric method for analyzing percent hemoglobin A1c (%HbA1c) and a PDMS-glass microelectrochemical device for highly reproducible amperometric measurement in microdroplet, are described. The first paper-based sensing device is fabricated using the principles of origami (paper folding). The three-dimensional origami paper analytical device (oPAD) is fabricated on a single sheet of flat paper in a single photolithographic step and assembled by simply folding the paper by hand. Following analysis, the device can be unfolded to reveal each layer for optical and fluorescent read-out. The second type of paper-based device has an integral aluminum/air battery as the power source and reports its output using Prussian blue as an electrochromic indicator. The integrated aluminum/air battery powers both the electrochemical sensor and the electrochromic read-out. The applicability of the device to point-of-care sensing is demonstrated by qualitative detection of glucose and H2O2 in artificial urine. The third type of paper-based device (oPAD 2) uses an aptamer to recognize the analyte, adenosine, a glucose oxidase tag to modify the relative concentrations of an electroactive redox couple, and a digital multimeter to transduce the result of the assay. Adenosine is quantitatively determined using this device with a detection limit of 11.8 uM. The method for measuring HbA1c concentration, hemoglobin concentration, and thus %HbA1c in human blood is based on potentiometry. We use Alizarin red s (ARS) as a redox indicator. The potential shift of ARS owing to diol-boronic acid complexation is used to determine the HbA1c, which is a competitor of ARS for the complexation reaction. The concentration of Hb is determined by reacting it with Fe(CN)₆³⁻ and measuring the potential shift arising from the reduction of Fe(CN)₆³⁻ by Hb. The results obtained for %HBA1c in human blood are in good agreement with those determined using a reference method. The method for highly reproducible chronoamperometric analysis of the contents of microdroplets is developed. Aqueous microdroplets (~ 1 nL) and separated by a fluorocarbon solvent are generated within a microfluidic device using a T-shaped junction. Highly reproducible quasi-steady-state currents (relative standard deviations = ~ 2%) are observed when the microdroplets are stretched by a factor of 10 in a narrowed segment of a microchannel, which leads to desirable intradroplet mass transfer characteristics. Importantly, the design of the microelectrochemical device ensures direct contact between intradroplet redox molecules and the electrode surface to study inner-sphere electrocatalytic processes such as the oxygen reduction reaction. Finite-element simulations are presented that are in accord with the experimental findings. / text

Compared with traditional radioimmunoassay and fluoroimmunoassay for early diseases detection, the magnetic immunoassay utilizing magnetic nanoparticles as bio-labels and magnetic signal sensors as detectors has remarkable advantages because most biological samples exhibit no magnetic background and highly sensitive measurements can be performed. This thesis presents the development of biodetection platform taking advantage of the physical-and chemical-stability, low-toxicity, and environmentally-safety of magnetic iron oxide nanoparticles (IONPs) and the high-sensitivity, low-cost, and portable capabilities of magnetoresistive (MR) sensors. The first part explained why a magnetic biodetection platform is desirable, and what advantages it possesses. Then the magnetism of IONPs utilized in this detection system was introduced, followed by the introduction of main synthesis methods to obtain the desirable IONPs. The working principle of MR sensor was explained, and the recent advances about the biodetection platforms with various magnetoresistive sensors and magnetic IONPs labeling was reviewed. A brief summary of new contributions reported in this thesis was summarized. Then the establishment of home-made measurement setups for the characterization of MR sensor was described. The MR loops of MR sensors can be obtained with the instrument using two-point probe measurement, four-point probe measurement, or Wheatstone bridge measurement. The single MTJ sensor, MTJs array sensor, and the GMR spin valve sensor in Wheatstone bridge were characterized here. The magnetic IONPs were prepared through co-precipitation method and thermal decomposition method, and then surface-functionalized using citric acid and fatty acids to acquire carboxyl groups for the binding ability with biomolecules. The physical and chemical properties, sterilizing-treatment tolerability and biocompatibility of nanoparticles were studied. Furthermore, two new synthesis methods were developed to obtain novel magnetic gold/iron oxide nanocomposites for their potential use as magnetic bio-labels. A magnetic detection platform was built, and the detection of 10-nm superparamagnetic IONPs with MR sensor was first realized here. The output signal of the giant magnetoresistive (GMR) sensor in Wheatstone bridge exhibited log-linear function of the concentration of IONPs, making our sensing system suitable for use when ultra-small bio-labels are needed. The biodetection platform with MR sensor and IONPs was successfully developed and applied for the detection of antigen biomolecules. The feasibility of magnetic biodetection system, based on magnetic tunneling junction (MTJ) sensors and carboxyl-group functionalized IONPs, to detect AFP antigens (liver cancer biomarker) and p24 antigens (HIV biomarker) was demonstrated here for the first time. By taking advantages of its high sensitivity, low power consumption, low cost, and feasibility to be miniaturized, the development of magnetoresistive biodetection platform will bring revolutionary impact on the biodetection techniques for clinical early diseases diagnosis. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Η παρακολούθηση σε πραγματικό χρόνο των βιομοριακών αλληλεπιδράσεων παρουσιάζει ιδιαίτερο ενδιαφέρον διότι παρέχει άμεσα πληροφορία σχετικά με την κινητική πρόσδεσης και τις σταθερές ισορροπίας. Σε αυτή την αναφορά, παρουσιάζεται μια μεθοδολογία η οποία βασίζεται στη Φασματοσκοπία Ανάκλασης Λευκού Φωτός και ενδείκνυται για την παρακολούθηση σε πραγματικό χρόνο των βιομοριακών αντιδράσεων που λαμβάνουν χώρα σε στερεά υποστρώματα. Η οπτική διάταξη αποτελείται από μια VIS–NIR οπτική πηγή η οποία επικοινωνεί μέσω οπτικής ίνας με φασματοφωτόμετρο συνδεδεμένο σε Η/Υ. Το εξωτερικό τμήμα της οπτικής ίνας κατευθύνει το φως κάθετα πάνω στην επιφάνεια όπου συμβαίνουν οι αλληλεπιδράσεις μεταξύ των βιιομορίων. Το ανακλώμενο φως συγκεντρώνεται από το εσωτερικό τμήμα της οπτικής ίνας και κατευθύνεται στο φασματοφωτόμετρο. Οι αντιδράσεις λαμβάνουν χώρα σε επιφάνεια διοξειδίου του πυριτίου επικαλυμμένη με πολυμερικό υμένιο. Μια αντλία χρησιμοποιείται για την παροχή των αντιδραστηρίων με ελεγχόμενο ρυθμό σε ένα μικρορρευστομηχανικό κανάλι. Το φάσμα της ανάκλασης καταγράφεται σε πραγματικό χρόνο. Οι αντιδράσεις μεταξύ των πρωτεϊνικών μορίων γίνονται αντιληπτές σαν μετατοπίσεις του μήκους κύματος εκεί που παρατηρείται το φαινόμενο της ενισχυτικής συμβολής. Οι μετατοπίσεις αυτές στο μήκος κύματος συμβαίνουν λόγω του σχηματισμού πρωτεϊνικού στρώματος είτε κατά τη διάρκεια της προσρόφησης των αντισωμάτων στο στερεό υπόστρωμα ή λόγω αλλαγής στο πάχος του πρωτεϊνικού στρώματος όταν τα συμπληρωματικά αντιγόνα δεσμεύονται από τα ήδη ακινητοποιημένα αντισώματα. Η προτεινόμενη μεθοδολογία εφαρμόστηκε για την παρακολούθηση σε πραγματικό χρόνο, χωρίς τη χρήση ιχνηθέτη της αντίδρασης μεταξύ των συμπληρωματικών μορίων βιοτίνης-στρεπταβιδίνης όπως επίσης και για την ανίχνευση της πρόσδεσης των αντιγόνων mouse IgG από ήδη ακινητοποιημένα αντισώματα anti-mouse IgG. Mouse IgG σε συγκεντρώσεις μικρότερες των 150 pM ανιχνεύτηκαν σε πολύ μικρούς χρόνους αντίδρασης (10 min). Ο οπτικός αισθητήρας είναι μια απλή, γρήγορη, χαμηλού κόστους διάταξη για την παρακολούθηση σε πραγματικό χρόνο των βιομοριακών αλληλεπιδράσεων που τον καθιστά κατάλληλο για διάφορες αναλυτικές εφαρμογές. / Label-free monitoring of biomolecular reactions in real-time is of great interest since it can provide direct results concerning binding kinetics and equilibrium constants. In this report, a method based on White Light Reflectance Spectroscopy (WLRS) is presented that is capable for real-time monitoring of biomolecular reactions taking place on a solid surface. The optical setup consists of a VIS–NIR light source connected through a bifurcated optical fiber to a PC-driven spectrophotometer. The outer part of the optical fibre guides the light vertically onto the surface where the biomolecular reactions occur. The reflected light is collected from the central part of the optical fibre and is directed to the spectrophotometer. The reactions take place on the top of a polymer covered silicon dioxide surface. A microfluidic module in combination with a micropump is used to supply the reagents in an adjustable rate. The reflectance signal is recorded in real-time. The biomolecular interactions are monitored as shifts of the wavelength where constructive interference is observed. These wavelength shifts correspond to biomolecular film thickness changes during either the adsorption of biomolecules onto the substrate or during biomolecule’s reaction with the immobilized counterpart molecules. The proposed methodology has been applied for real-time and label-free monitoring of streptavidin binding to surface-immobilised biotinylated protein as well as of mouse IgG onto immobilized anti-mouse IgG antibody. Mouse IgG at concentrations less than 150 pM were detected in short reaction times (10 min). The proposed reflectance spectroscopy sensor provides a simple, fast, low cost approach for label-free monitoring of biomolecular interactions thus making the developed sensor suitable for various analytical applications.

No description available.

No description available.

It has recently been shown that elevated C-reactive protein (CRP) levels are associated with a blunted systemic endothelial vasodilator function, indicative of a systemic inflammatory response. It has also been recognized that inflammation may contribute to all stages of the atherosclerotic process. Several prospective studies have shown that the level of CRP is a strong predictor of future myocardial dysfunction, stroke, peripheral arterial disease, and vascular death among individuals without known cardiovascular disease. CRP is also found in association with the senile plaques and neurofibrillary tangles of Alzheimer disease. Hence, determination of the blood serum levels of CRP is of a great clinical importance. / This thesis discusses the results on the development of two electrochemical immunosensors: (i) the avidin (model) immunosensor, and (ii) the CRP immunosensor. The suitability of using a range of electrochemical techniques in probing antibody-antigen interactions was also investigated. / It was shown that a gold working electrode surface could be successfully modified by covalent binding of NHS-biotin to a self-assembled-monolayer of cystamine dihydrochloride, resulting in the construction of the avidin immunosensor. Avidin could then bind to this immunosensor (biotinated electrode) and detected using the electrochemical techniques of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and chronoamperometry (CA). It was also shown that polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) can be used to qualitatively and quantitatively characterize avidin bound to the immunosensor. The results demonstrated that all experimental techniques used were suitable in characterizing with high sensitivity the avidin-biotin interaction, and the amount of avidin in solution. The avidin calibration curves showed high linearity in concentrations ranging from 10-10 to 5 x 10-7 M. AFM imaging confirmed that avidin forms clusters upon binding to the immunosensor, with the cluster size ranging between 28 and 33 nm. The avidin-biotin binding constant was determined to be 3.09 x 1012 M-1 . It was also determined that the avidin-biotin equilibrium is reached in ca. 20 minutes. / The CRP immunosensor was then designed on the basis of the avidin immunosensor architecture. Using a range of electrochemical techniques and PM-IRRAS, it was demonstrated that a gold electrode surface could be functionalized by CRP antibodies, covalently attached to the surface through a duplex cystamine/glutaraldehyde layer. This architecture represents the CRP immunosensor. It was then shown that CRP antigen specifically binds to the CRP immunosensor (i.e. the immobilized CRP antibody). This interaction could be characterized with high sensitivity using the electrochemical techniques of CV, EIS, DPV and CA. The CRP concentration range investigated was 10-14 to 10-8 M. A linear calibration plot was obtained. The CRP antibody-antigen binding constant was determined to be 3+/-1 x 108 M-1. The corresponding binding equilibrium is reached in ca. 10 minutes. The results show that the developed CRP immunosensor is a good candidate for further research towards developing a commercial CRP immunosensor.

<p>Selective serotonin re-uptake inhibitors (SSRIs) are a new class of antidepressants used mainly for the treatment of depression and other forms of related disorders. There are a number of side effects associated with these drugs which include loss of weight, sexual dysfunction, nervousness and nausea. A fast and reliable detection method such as biosensing for the determination of the SSRIs metabolic profile is therefore essential for the appropriate dosing of these drugs. Biosensors for the determination of the SSRIs biotransformation were prepared with cytochrome P450 (2D6) isoenzyme and poly (anilinonapthalene sulfonic acid) film electrochemically deposited on gold.</p>

The concentration of diacetyl in the fermenting process of beer is important to control as it is both a measure of the quality of the beer and yeast viability. Presently there is no on line method for monitoring diacetyl levels during beer production, which can result in submitting the beer to a longer high temperature diacetyl degradation period than necessary. This is detrimental to the yeast and increases the time of the overall process. The ability to continuously monitor diacetyl levels on line would provide a decided advantage in control of the fermentation and maturation of the beer, two important factors impacting production quality and cost. The purpose of this project is to design a biosensor that will measure diacetyl levels on line, thereby providing a profile of diacetyl concentrations during beer production. This will lead to increasing not only the production rate, but the quality and consistency of the final product and can serve as a foundation for future improvements in yeast management in general. / The initial goal of the project is to evaluate existing biosensor technology in relation to its application in the beer fermentation process. The second is to design a biosensor which will measure diacetyl levels and surmount existing biosensor disadvantages based on the information collected in the observation process. The last objective is to construct a prototype in order to test this design. The combined results of this study will be of value to the brewing industry specifically and help expand the role biosensors play in introducing new more effective methods into the food processing industry.

Defective alkanethiol monolayers were studied as a model system to understand the stress changes observed in microcantilever-based DNA hybridization experiments. An exponential relationship between defect density and surface stress was found by performing simultaneous electrochemical/stress-sensing experiments. Microcantilevers with a range of defective alkylthiol self assembled monolayers were prepared and stress change/electrochemical data were collected in perchlorate, chloride, and bromide-containing electrolytes. Defects were probed using a ferrocene-thiol labeling technique which provides quantitative measurement of defect area. Using defects and solutions containing charge transferring adsorbates is suggested as a method for enhancing the surface stress signals in cantilever sensor systems. The best response from this study was obtained in bromide, as its exponential function had the sharpest increase with defect density.