Printed, Flexible Lactate Sensors: Design Considerations Before Performing On-Body Measurements.

This work reports the process of sensor development, optimization, and characterization before the transition to on-body measurements can be made. Sensors using lactate oxidase as a sensing mechanism and tetrathiafulvalene as a mediator were optimized for sporting applications. Optimized sensors show linear range up to 24 mM lactate and sensitivity of 4.8 μA/mM which normalizes to 68 μA*cm-2/mM when accounting for surface area of the sensor. The optimized sensors were characterized 3 different ways: using commercially available reference and counter electrodes, using printed reference and counter electrodes, and using a printed reference electrode with no counter electrode. Sensors intended for measuring sweat must be selective in the presence of sweat constituents. Thus, in addition to traditional characterization in pH 7.0 buffer, we characterized sensor performance in solutions intended to approximate sweat. Sensor performance in pH 7.0 buffer solution was not reflective of sensor performance in artificial sweat, indicating that further characterization is necessary between sensor measurement in pH 7.0 buffer and on-body measurements. Furthermore, we performed enzyme activity measurements and sensor measurements concurrently in five different salts individually, finding that while NH4Cl and MgCl2 do not affect enzyme activity or sensor performance in physiologically relevant ranges of salt concentration, NaCl concentration or KCl concentration decreases enzyme activity and sensor current. On the other hand, CaCl2 induced a nonlinear change in sensor performance and enzyme activity with increasing salt concentration

Low-temperature characterization of Nb-Cu-Nb weak links with Ar ion-cleaned interfaces

We characterize niobium-based lateral Superconductor (S) - Normal metal (N) - Superconductor weak links through low-temperature switching current measurements and tunnel spectroscopy. We fabricate the SNS devices in two separate lithography and deposition steps, combined with strong argon ion cleaning before the normal metal deposition in the last step. Our SNS weak link consists of high-quality sputtered Nb electrodes that are contacted with evaporated Cu. The two-step fabrication flow enables great flexibility in the choice of materials and pattern design. A comparison of the temperature-dependent equilibrium critical supercurrent with theoretical predictions indicates that the quality of the Nb-Cu interface is similar to that of evaporated Al-Cu weak links. Aiming at increased sensitivity, range of operation temperatures, and thermal isolation, we investigate how these SNS structures can be combined with shadow-evaporated aluminum tunnel junctions for sensor applications that utilize the superconducting proximity effect. To this end, we demonstrate a hybrid magnetic flux sensor based on a Nb-Cu-Nb SNS junction, where the phase-dependent normal metal density of states is probed with an Al tunnel junction.Comment: 5 pages, 3 figure

Development of an Amperometric Biosensor for Lactate.

A gold enzyme electrode for lactate, fabricated on silicon has been developed. Standard silicon processing and micromachining techniques have been applied to the fabrication of three sensor types. Two planar types and a containment sensor are presented. The enzyme lactate oxidase (LOX) was immobilised in a suitable matrix and placed on a planar gold electrode or in a gold coated, KOH etched silicon cavity. Activity and stability of the enzyme LOX was assessed in a modified BSA gel and two sol gel matrices. The enzyme has shown above average stability of three months, stored dry, when immobilised in a sol gel matrix. The modified BSA gel also showed potential for use with a gold enzyme electrode. A three electrode configuration in the amperometric mode was used to detect lactate. A linear range of up to 1OmM lactate has been observed using a sol gel as an immobilisation matrix, and a response time as low as 40 seconds. A modified BSA gel has shown a linear range of up to 12mM lactate. Lactate has also been successfully detected using the containment sensor

Bench-Scale Production of Heterologous Proteins from Extremophiles- Escherichia coli and Pichia pastoris based expression systems

Over the past few years considerable research attention has been assigned to extremophiles as sources of extremozymes due to their applicability in industrial processes, and the development of eco-friendly technologies. The establishment of efficient production strategies for heterologous proteins is an empirical process requiring broad background knowledge on available expression systems together with their major advantages and shortcomings. The studies conducted during the course of this thesis has included four enzymes originating from thermophiles namely, thermostable glycoside hydrolases, xylanase and cellulase from Rhodothermus marinus, cyclomaltodextrinase from Anoxybacillus flavithermus and a phospholipase from alkaliphilic Bacillus halodurans. Batch cultivation of R. marinus in the presence of xylan allowed low production of the native xylanase in sufficient amounts to probe cell-attachment studies by enzymatic and immunological techniques. Higher levels of the target proteins were achieved by intracellular and extracellular heterologous production using an Escherichia coli and Pichia pastoris based expression system respectively. The production of a functional enzyme is intimately related to the host's cellular machinery furthermore, as a prerequisite, the establishment of efficient bioprocess strategies is crucial for attaining optimum enzyme production yields. The results presented include bench-scale production strategies employing high cell density fed-batch cultivations with E. coli as a host. Also efficient extracellular production of thermostable xylanase and alkaliphilic phospholipase production using the methylotrophic yeast P. pastoris as a host is reported

Next Generation of Applications of Metal-Organic Frameworks for Energy and Environmental Sustainability

My PhD work aimed at using Metal-organic frameworks (MOFs) for mitigating the environmental issues and energy crisis associated with anthropogenic activities. Specifically, we developed robust platforms and/ or systems using MOF as “scaffolds” to allow for model pollutant detection and CO2 sequestration and benign transformation respectively. First, I detailed how photocatalytic properties of 2,5-furandicarbocylic acid (FDCA) in its alone and its MOF- integrated form (MIL-160) were used for the first time for the reduction of Ag+ at room conditions. Such photocatalytic activities could then be used in user-designed hybrids (i.e., Ag/MIL-160) to form sensorial platforms for prevalent phenol (p-NP) contaminant detection. This new detection method is envisioned to allow effective control and regulation of p-NP, all under low-cost and environmentally friendly conditions. Next, I studied how a green strategy based on carbonic anhydrase (CA) could be used for CO2 transformation. Specifically, we demonstrated the feasibility of MOFs for CAs’ immobilization on both hydrophilic-MIL-160 and hydrophobic-ZIF-8 frameworks, and enzyme functionality was dependent on the support’s characteristics, with MIL-160 revealing promising advantages for CA enhanced activity and stability. Further, we extended such analysis to possible industrial implementation of the CA-MOF approach; briefly, by developing a membrane system, we showed the feasibility of a CA-MOF based novel membrane for CO2 adsorption with possible implementation in enzyme-based green technologies to mitigate global warming. The development and integration of MOFs for energy or environmental sustainability is meritorious and transformative and allows for creating new pathways for industrial extensions and integration of laboratories demonstration