Browsing by Subject "Biosensor"

Now showing 1 - 4 of 4
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    Development of advanced analytical chemistry approaches for small and large molecule detection
    (2022-10) He, Jiayi
    In this dissertation, the first chapter is about the Chapter One summarize the basis of building biosensors including the introduction of biorecognition elements and binding affinity characterization techniques; the working principle of electrochemical and electronic detection techniques including cyclic voltammetry (CV), amperometry, and field-effect transistor. Then the recent five years sensor design improvement development for the neurotransmitter detections. In Chapter Two, a polymer-modified electrolyte-gated transistor (EGT) is used for the detection of soybean agglutinin (SBA), a common food allergen protein. The polymer affinity agent, poly(N-acetyl galactosamine ethyl methacrylamide) or P(MAGalNAc), was chemically synthesized, and the affinity between SBA and the P(MAGalNAc) polymer of varied molecular weight was determined through isothermal titration calorimetry (ITC) to identify the optimal affinity agent. This platform has been used to detect different concentrations of aqueous soybean agglutinin with a simple electronic readout and achieved a limit of detection of 5.7 nM. Furthermore, excellent selectivity was maintained even in the presence of common interfering proteins. In Chapter Three, reusable electrolyte-gated transistors (EGT) was fabricated with a structure shifting aptamer as a binding affinity agent to achieve sensitive and selective detection of serotonin. The device was designed such that the sensing happens away from the transistor portion of the device, which facilitates stable and convenient affinity agent modification and detection. The aptamer functionalization was characterized with a range of techniques. The binding between the aptamer and serotonin was characterized for the first time using surface plasmon resonance (SPR). Finally, the reusability of the device following treatment with base suggests that the regeneration mechanism is related to pH-driven changes to the negatively charged aptamer structure. In Chapter Four, we explored the impacts of two antimalaria drugs, chloroquine and quinine, on the chemical messenger secretion by blood platelets. The secreted neurotransmitters were explored at bulk cell and single cell level respectively through high performance liquid chromatography (HPLC) and carbon-fiber microelectrode amperometry. The results showed that the two drugs reduce the number of platelet exocytosis events and delay fusion pore opening and closing. This work promotes understanding of how the two antimalaria drugs quantitatively and qualitatively influence exocytosis, which informs future therapeutic malarial treatment development. The second part of my thesis will be about the co-op project I performed in Merck. Chapter Five and Chapter Six evaluated the influence of polysorbate 80 hydrolysis byproducts (oleic acid) on mAb stability through the mixing study of oleic acid and mAbs solutions. Polysorbate(PS) has been widely used in pharmaceutical formulations as the surfactant to stabilize the monoclonal antibody (mAb). The correlation between polysorbate degradation and the increased subvisible particles in the protein drug products is not well understood. In these two studies, we revealed that the oleic acid is related to the proteinaceous particle formation and proposed the mechanism of the mAb aggregation through the electrostatic interactions by tuning the ionic strength, pH, and isoelectric points. The formation of the particles are also reversible upon the addition of additional salt or human serums protein. All these findings help with the understanding of the root cause of particle formation in the pharmaceutical industry.
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    Large-scale engineered metallic nanstructures for high-throughput surface plasmon resonance biosensing and surface-enhanced Raman spectroscopy
    (2012-07) Lee, Si Hoon
    Precise measurements of binding kinetics and affinity of receptor-ligand interactions play an important role in pharmaceutical development as well as basic biology. Since a new drug discovery requires tremendous amount of time and cost, the demand for a high-throughput screening as well as precise kinetics measurement has increased dramatically. Although the commercially available BIAcoreTM system has been the gold standard for label-free and real-time biosensing, it is not capable of high-throughput kinetic measurements that are required for large-scale proteomics studies. To address the critical challenges, high-throughput SPR imaging instruments based on plasmonic nanohole arrays is demonstrated in this dissertation. The key advantage of nanohole-based SPR setup is that plasmons can be excited at normal incidence, which enables simple optical alignment and high-resolution imaging. Using template stripping technology, massively parallel and highly homogenous nanohole arrays, which is the prerequisite to perform high-throughput SPR imaging, are obtained over a large area (~cm2). Linewidths of extraordinary transmission (EOT) peaks are optimized by reducing the damping losses of surface plasmon polaritons (SPPs), leading to the improved detection limits of the sensor. By combining the highly parallel microfluidics with periodic nanohole arrays, our SPR imaging spectrometer system enables high-throughput, label-free, real-time SPR biosensing, and its full-spectral imaging capability increases the dynamic range of detection. Additionally, molecular identification via surface-enhanced Raman spectroscopy (SERS) is also presented in the second portion of the dissertation. Two approaches include planar-type nanohole structures aimed for highly reproducible SERS substrates with low-cost and dynamic nanogaps pearlchains via dielectrophoresis (DEP) for the rapid and ultrasensitive molecular detection and identification.
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    Optimization of Fabrication Conditions and Calibration of Polyvinylidene Fluoride for use as a Biosensor
    (2022-08) Danley, Matthew
    The Transcatheter Aortic Valve Replacement (TAVR) is a minimally invasive procedure that utilizes a catheter to deploy a replacement valve in patients with valve stenosis. Although TAVR has lowered the risk of some complications, such as in-hospital mortality rates, there are documented increases in complications compared to open heart surgery, such as increasing numbers of pacemaker implantation after the procedure. The underlying mechanisms of these complications have not been identified. It is thought that 3D printing a replica of a patient’s aorta would allow for flow shear stress analysis, pressure compressive tests, and investigation of cyclic distension of the aortic walls. Polyvinylidene fluoride is a piezoelectric polymer that is a promising material to be used as a sensor to detect the shear stress, compressive forces, and distension inside the aorta model. Porous PVDF membranes have been shown to have higher piezoelectric properties compared to nonporous PVDF. It is thought the increase in porosity leads to a greater deformation, and in turn, a larger piezoelectric response to mechanical stresses. The goals of this study are to optimize the fabrication process of porous PVDF membranes using ZnO nanoparticles to induce pores and to design and build a flow chamber to then calibrate the PVDF membranes to physiological conditions. One issue identified in the fabrication process has been the removal of ZnO nanoparticles. The ZnO nanoparticles were added to a solution of PVDF and 2-butanone, cast and dried on a petri dish. 1cm by 1cm squares were cut from the PVDF membranes, weighed, and then placed in a hydrochloric acid bath. The HCl dissolved ZnO, which then diffused out of the membrane as ZnCl2. The mass of the membrane was measured at various time points while in the acid bath. These measurements were used to model the diffusion of ZnCl2 out of the membrane. The removal of ZnO was predicted to follow a shrinking core assumption, or a unimolecular diffusion of ZnCl2. The effective diffusivity of ZnCl2 was calculated for PVDF/ZnO membranes at 10%, 20%, 30%, and 40% wt ZnO as well as for 35-45nm, 80-200nm, and 500nm particle sizes. The effective diffusivities increased from 20% wt ZnO and peaked at 40% wt ZnO and decreased as the particle sizes increased from 35-45nm to 500nm. Further studying the porosity and tortuosity of PVDF membranes would allow for calculation of the diffusion coefficient of ZnCl2 out of the PVDF matrix. A flow chamber was built to calibrate PVDF membranes at physiological conditions in the aorta. 1” diameter tubing was used as the aorta segment and a submersible pump generate pressure and flow in the flow chamber. The voltages from the PVDF sensors were collected under varying flow rates (150mL/s – 400mL/s) and varying pressures (5mmHg to 30mmHg). The flow chamber mimicked the physiological flow rates of the aorta but did not mimic physiological pressure. The PVDF sensors generated decreasing signal as pressure and flow rates increased, which was not expected. Going forward, increasing the pressure in the flow chamber should allow for calibration of PVDF membranes under forces similar to those seen in the aorta.
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    Self-assembled nanotube/nanoparticle biosensors.
    (2010-05) Lee, Dongjin
    The self-assembled carbon nanotube (CNT) and indium oxide nanoparticle (INP) multilayers are presented for the applications to electrochemical pH and biological sensing. The excellent electrochemical properties of the nanomaterial thin film made of layer-by-layer self assembly is exploited to design and fabricate sensors targeted for a facile and low-cost application. The pH-sensitive conductance of the self-assembled CNT/INP chemoresistor and ion-sensitive field-effect transistor (ISFET) is studied, and its shift mechanisms are elucidated. There are two primary factors influencing the conductance of the semiconducting nanomaterial thin film: the direct protonation/deprotonation and the proximal ion effect. The CNT chemoresistor experiences the conductance change due to the molecular protonation/deprotonation of carboxylic groups. The effect of proximal ions demonstrates conventional semiconductor theory, where the pH increase corresponds to negative shift in gate voltage resulting in a higher conductance in p-type CNTs. The additional silica nanoparticle (SNP) layer adjusts the pH-sensitive conductance behavior, particularly from nonlinear to linear response, which is beneficial to the implementation of pH sensors. Indeed, the electrochemical properties of nanomaterial thin film are tunable by exploiting a different type of the nanomaterial, surface chemistry, and structure. Glucose biosensors and immunosensors are designed and implemented based on the conductance shift mechanisms explored. The sensitivity of CNT chemoresistor and ISFET glucose sensors is 10.8 and 18-45 μA/mM, respectively, on a linear range of 0-10 mM with a response time of a few minutes. An INP chemoresistor sensor array is designed to address variant electrical properties of the nanomaterial films, allowing the statistical analysis of data with one-shot of sample delivery. The INP immunoglobulin G (IgG) ISFET sensor exhibits a resolution of 40 pg/ml, and the CNT conductometric H1N1 swine influenza virus (SIV) sensor demonstrates a detection limit of 180 viruses TCID50/ml with a specificity to non-SIVs. The nanomaterial thin film electrochemical transducers are proven to be a potent candidate for the next-generation of the chemical and biological sensors possessing a high sensitivity and resolution. Due to a facile implementation and operation, nanomaterial biosensors could be used for domestic and clinical diagnosis, point-of-care detection, and a sensing component in lab-on-a-chip systems.