Enzymatic pathways comprising multi-step biochemical reactions in biological cells constitute a key part of life. Biomimetic reconstruction of these metabolic pathways holds tremendous promise for developing sustainably powered devices. In biological cells, enzymatic components are kept in strict compartments or in serial networks. To mimic this complex hierarchical assembly of enzymes found in nature, a common approach is immobilizing these enzymes on the surface of porous substrates i.e., anodic aluminum oxide (AAO) membrane. However, one common limitation has been immobilization of multiple enzymes with a single type surface chemistry. As a result, these approaches have failed to provide enough capability to control spatial localizations of enzymes on AAO surfaces. Solid-binding peptides (SBPs) offer a novel solution to circumvent these problems with their exquisite recognition and long range solid-coverage properties. The ease of genetic conjugation of these short peptides with large proteins makes them an ideal candidate in utilization as molecular linkers in designing new multi-enzymatic devices. In this study, the utilization of a gold binding peptide (AuBP) as a molecular linker in combination with histidine-tag to immobilize Lactate Dehydrogenase (LDH) and Formate Dehydrogenase (FDH) enzymes on AAO based flow bioreactor was demonstrated. The efficacy of the described approach was tested by monitoring the sequential lactate and formate break down by LDH and FDH enzymes spectrophotometrically. The overall sequential catalytic conversion with greater than 90% yield was observed. Furthermore, the surface selectivity of the SBP conjugated enzymes were tested by visualizing their localization on Ni-NTA patterned gold surface using fluorescence microscopy. Cumulatively, this study highlights the utility of solid binding peptides as a molecular linker for addressable immobilization of multiple enzymes in the AAO based devices.

Breast cancer is the most common cancer in women. Even with advancing treatment techniques, breast cancer is still the cause of tens of thousands of death in the U.S. alone. Combined treatments including surgery, radio and chemotherapy are commonly implemented for breast cancer. However, the survival rate of metastatic breast cancer remains low, so new targeted therapy strategies are needed. In recent years, nanotechnology has opened a new route for targeted therapy of breast cancer. Nonetheless, some challenges still remain for nanoparticles (NPs) used in breast cancer treatments. After loaded with anticancer drugs, fluorophores and targeting ligands, NP drug delivery systems suffer from issues of size limit, stability, target cell internalization and biodegradability. Anti-human epidermal growth factor receptor 2 (HER2/neu) monoclonal antibody is a good targeting ligand for some breast cancer cells for two main reasons. Firstly, about 1/4 of breast cancer patients overexpress HER2/neu. Secondly, monoclonal antibodies have a better targeting effect than small molecule, protein and aptamer-based targeting ligands. However, the bulky size of the antibodies can change the desired physiochemical properties of NPs. Therefore, an anti-HER2/neu peptide, which is a small exocyclic peptide derived from the antibody, is utilized for targeting purposes. Moreover, paclitaxel (PTX) is a strong anticancer drug that can restrain mitotic spindle assembly and chromosome segregation, and in turn prevent breast cancer growth. Here we report anti-HER2/neu peptide-conjugated and PTX loaded iron oxide NPs (IONP-PTX-AHNP) that are small size, highly stable and biocompatible in biological medium for breast cancer treatment. Significantly, the IONP-PTX-AHNP showed targeted cell uptake into HER2/neu overexpressed breast cancer cells and PTX-mediated cancer cell death.

 Glioblastoma multiform (GBM) is the most common and aggressive malignant primary brain tumor and accounts for about 70% of new cases of primary brain tumors in the US annually.  Current treatments are very aggressive and have a high risk of systemic toxicity due to non-specificity of current cancer therapeutic agents. Iron oxide nanoparticles (IONPs) have shown great promise as versatile targeted drug delivery vehicles for effective cancer treatment.  In this research presentation, the development of two multifunctional IONPs for targeted GBM therapy will be discussed.  The first is an IONP covalently conjugated with anti-cancer drug, gemcitabine (GEM), using hyaluronic acid as a bridging molecule.  The second is an IONP conjugated with carboxylated ß-cyclodextrin and loaded with paclitaxel (PTX) via hydrophobic interactions.  Both IONPs were conjugated with chlorotoxin (CTX), a GBM targeting agent that can cross the blood-brain barrier (BBB), and fluorescent dyes.  Through characterization by TEM, DLS, and HPLC, the IONPs showed small size, high stability, and proper drug loading.  More importantly, the GEM-conjugated IONPs showed prolonged blood circulation time and BBB permeability in vivo.  The PTX-conjugated IONPs showed enhanced cell killing of the GBM cells and drug-resistant GBM cells compared to the free drug.  The two multifunctional IONPs have shown great promise for effective treatment of GBM.

Stille coupling, Suzuki coupling, and Kumada coupling are some of the most commonly used reactions in the synthesis of polymers for organic solar cells and organic electrical devices. They are highly effective in creating new carbon-carbon (C-C) bonds. However, when synthesizing a conjugated polymer for organic solar cell applications through these conventional reactions, the process can be challenging and lead to many synthetic steps. In addition, some of the materials used are expensive and extremely toxic to both human health and the environment. In this project, I work individually to synthesize a new benzobisoxazole-based compound which can potentially serves as the monomer for conjugated polymer of organic polymer. The goal of the project is to create a compound in which the inert carbon-hydrogen (C-H) bonds are strongly weakened and easily broken. Potentially, organic solar cells production via this new compound can be more efficient, and as a result, reduces the cost and makes it more environmentally friendly. Recently, the lab’s collaborators at Emory University synthesized a benzobisthiazole-based monomer with two solubilizing alkyl thiophene groups. However, the monomer has limited solubility in organic solvents as well as C-H activation ability. To improve the monomer, I attached a further 2-ethyl hexyl chain to the 2-position on each thiophene solubilizing group and also replaced thiazole with the more electron deficient oxazole unit. Right now, I have successfully synthesized the desired compound and been in the process of activating it using a Gold-based catalyst. If C-H activation is possible for this compound, oligomers of at least three monomers are expected to form.

Due to dwindling non-renewable energy sources, people have started to harvest clean and sustainable energy. Utilized to capture solar energy, organic photovoltaics (OPVs) are developed due to their ability to be printed on a flexible substrate, ease of production, and lightweight. Current researches are focused on improving the device efficiency and durability. Therefore, OPVs may compete with their inorganic counterparts, which are currently more popular although limited by the expensive material and manufacturing process. Phenyl-C61-butyric acid methyl ester (PC61BM) and poly(3-hexylthiophene-2,5-diyl) (P3HT) nanowires are widely-used acceptor and donor polymers, respectively, in an OPV’s active layer. A desirable morphology of the active layer is a bulk heterojunction structure. One of the factors that affect the morphology is the processing of these polymers. The purpose of this project is to investigate how the PC61BM addition affects the P3HT nanowire formation. The experiment involves nanowire development in three cases: (1) pure P3HT, (2) P3HT with PC61BM added after the formation, and (3) P3HT with PC61BM added before the formation. Samples from the three cases were characterized using UV-Visible spectroscopy and X-ray Diffractometer to determine the crystallinity and morphology of the polymer chains. The morphology of polymers is discussed as a function absorbance ratio, which indicates chain planarity, and crystallite size. The results were then compared with those from previously published papers. Due to considerable differences observed, the regioregularity of the P3HT precursor was tested using Nuclear Magnetic Resonance spectroscopy. The result was a lower regioregularity than that of P3HT which is typically used for photovoltaic applications. Therefore, a different batch of P3HT was used to investigate the morphological differences between the three cases. Assessment of the polymers’ morphology were correlated with OPV device performances in published literatures. A determination of the PC61BM-addition effect may assist future fabrication of OPV with superior performance.

Current commercial Li-ion batteries use carbon-based anode materials, most commonly graphite. The low theoretical capacity (372 mAh/g) [1, 2] and slow Li-ion diffusion (10^-8cm²s^-1) [2] through graphite limits the batteries energy density and power capability. Molybdenum disulfide (MoS₂) is a promising graphite replacement. The layered structure of the 2H trigonal prismatic phase is very similar to graphite where van der Waals (vdW) interaction between layers of S-Mo-S slabs accommodates Li-ion intercalation [3, 1]. MoS₂ has high initial capacity (669 mAh/g), low discharge voltage (0.6V), and low diffusion barrier, but has poor cycling stability resulting in short cycle-life [2]. Herein it is proposed that the degradation in capacity over cycling could be mitigated by engineering a restacked MoS₂-polymer composite material using a one-pot wet chemical synthesis method. The MoS₂ slabs are first exfoliated and then restacked in the presence of a polymer, inserting organic layers in the vdW gap. This work probes the effectiveness of this synthesis technique by comparing materials prepared with PEO and PEDOT. Characterizations will be conducted with X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC) to confirm the synthesis of restacked MoS₂-polymer composites. XRD will be used to determine the d-spacing that correlates to an expansion in the c-direction, specifically looking for peak shifts of (002) or (004), and with no shifting of the (hk0) directions. FTIR will be used to verify the presence of PEO and PEDOT in the composite. TGA and DSC will be used to check the stoichiometry of the polymer in the prepared composites. Pristine MoS₂ and synthesized composite materials will be compared in Lithium half cells to determine effect of restacking on cycling stability. Restacked MoS₂ would be an ideal anode material for Li-ion batteries if it brings enhanced energy density and greater cycle-life.

Due to society’s increasing energy demand and the push for technological innovation within key industries (e.g. consumer electronics and electric vehicles), major advancements in energy storage technology, specifically battery technology, are needed. While Li-ion batteries are currently regarded as one of the premier options for reusable energy storage, they are not as safe, environmentally-friendly, or cost-effective as currently researched alternatives. One promising alternative is the rechargeable Zn/MnO₂ battery which offers many benefits such as high energy density, low cost, and the ability to use non-corrosive electrolytes. In addition, the cathode material, MnO₂, can exist in a variety of crystal structures which will offer distinct pathways or mechanisms for Zn-ion transport. This project explores how the crystal structure of MnO₂ influences the electrochemical reaction mechanisms and subsequent performance of the Zn/MnO₂ battery. Three different phases of MnO₂ (α, β, and δ) were synthesized hydrothermally for use as cathode materials. Coin cells consisting of a Zn metal anode, MnO₂ cathode, and an aqueous ZnSO₄ electrolyte were then assembled and cycled to determine the charge/discharge behaviors of the batteries. Finally, the results of this project will help identify optimal cathode materials for improving the electrochemical performance of Zn/MnO₂ batteries. 

As the worldwide population grows and society’s thirst for goods continues to thrive, mankind’s negative impacts on Earth are quickly becoming visible. Environmental concerns have led scientists and engineers to take a critical look at packaging, one of the foremost contributors to landfill waste. Manufacturers have in response begun substituting compostable and biodegradable polymers in place of non-degradable petroleum based plastics. The purpose of this project has been to analyze, within the realm of packaging, the current and potential uses of one such polymer, polylactic acid (PLA), as well as the consideration of barriers to its widespread use and solutions to these obstacles. While PLA has comparatively good mechanical properties, the downsides to the plastic have been its brittleness and low melting temperature. Packaging applications often require a material that is tough and, in the case of food packaging, one that can withstand temperature variations. Several different approaches have been taken to improve the properties of PLA, and while many of these approaches have been successful, the continued biodegradability and food safety of the polymer becomes a concern. Another issue is the amount of water used to manufacture the polymer; most PLA is derived from corn, giving it a high rate of water used per kilogram produced compared to other plastics. These barriers present considerable challenges, yet PLA remains at the forefront of innovative packaging materials, offering a potentially sustainable pathway to a packaging industry free of petroleum-based plastics.

High aspect ratio nanostructures have been targeted for use in nanoscale electronics and photonics integration, as well as energy storage and conversion due to quantum confinement effects and high curvature. For instance, 3rd generation solar cells based on Si semiconductor nanowires exhibit improved absorption and current generation due to high aspect ratio and quantum confinement, yet widespread adoption of these technologies is limited due to lack of scalable synthesis methods. Solution-liquid-solid growth of semiconductor nanowires is a cheap, potentially scalable, environmentally-benign process that uses bismuth nanocrystallites as a growth site. Synthesis of Bi nanoparticles, however, is currently achieved by using costly and lethal reagents, in a technically difficult process that is sensitive to O2 and H2O. Furthermore, storage of these reagents is a large concern due to their volatility and the particles themselves tend to oxidize extremely quickly.  In this work, we evaluate a one-pot reaction for the production of bismuth nanoparticles using benign Bi2O3 as a precursor. We observe that the size of these particles depends directly on reaction time, and we hypothesize particle synthesis occurs through nucleation-and-growth process. In addition, these Bi nanoparticles show a remarkable resistance to oxidation after storage for weeks in an atmospheric environment. We speculate surface is passivated with a fluoride shell as a synthesis byproduct, which inhibits oxidation. We have studied these particles in different ways including SEM and XPS to determine the size and composition respectively. Our synthesis uses safe precursors and produces particles which are much more stable over the long term; this has the potential to make the use of bismuth nanoparticles a much more viable process and increase our understanding of bismuth on the nanoscale.

When two-dimensional materials, such as graphene, boron nitride, or transition metal dichalcogenides (TMDs) are stacked on one another, van der Waals forces bind the layers together to form vertical heterostructures. These have recently sparked interest in the device physics community. Heterostructures fabricated with two differing layers of transition metal dichalcogenides with type-II band alignment are of particular interest as they allow for the hole and electron to separate and be localized into the different monolayers of the heterostructure. Further, the separated charge carriers may bind together to form spatially indirect excitons at the interface. This species of exciton has been shown to exhibit a number of interesting properties including long-range drift-diffusion in the 2D plane, long-lived valley polarization, and an increase in the interlayer exciton lifetime by many orders of magnitude in WSe2–MoSe2heterostructures. A long exciton lifetime is particularly important for investigations of excitonic superfluidity and condensation, which are exciting phenomena in fundamental scientific research. Here, we use a hexagonal boron nitride (h-BN) monolayer to further separate the layers of the WSe2-MoSe2heterostructure and measure the change in the interlayer exciton lifetime. If the lifetime is long enough and exciton density high enough, these bound states can cool and condense into a degenerate Bose gas that exhibits superfluidity. We investigate the interlayer exciton lifetime in the MoSe2–h-BN–WSe2heterostructure by time-resolved photoluminescence. Further, the power dependence of the spatial distribution of the interlayer exciton photoluminescence will elucidate how these excitons migrate throughout the sample, which demonstrates the exciton superfluid phase transition. This research provokes further exploration into interlayer exciton condensation and other quantum-correlated effects in 2D heterostructures.

Tooth discoloration is a common aesthetic concern for many individuals, and in response the dental profession and public expend considerable amounts of time and money to improve the appearance of stained teeth. Although many treatments are available to attempt whitening discolored teeth, these methods are typically expensive or cause more harm to the oral health of the individual due to the use of harsh chemicals, e.g. hydrogen peroxide, which often results in tooth hypersensitivity. The peptide-enabled aqueous whitening approach restores the color of teeth by forming a mineral layer on the tooth enamel and consequently masking the underlying discoloration, offering a suitable alternative to conventional bleaching methods. In this approach, peptides direct Ca²⁺ and PO₄^3- ions to form a new mineralized layer on the tooth surface. The aim of this study is to develop a suitable vehicle to deliver remineralization components to an oral environment, promoting enamel remineralization and built-in tooth whitening. With this aim, lozenges composed of varying concentrations of peptide, Ca2⁺, PO₄^3- and other inactive ingredients were manufactured using a hydraulic compression machine, and a suitable formulation was selected based on disintegration times optimized in artificial saliva. The whitening lozenge was then applied to human teeth samples under conditions mimicking the oral environment. Structural and optical properties of the resulting mineral layer were characterized using scanning electron microscopy and a chromameter, respectively. Our results demonstrate that surface discoloration has been successfully masked using whitening lozenges in vitro and, therefore, the color of the teeth was aesthetically improved. The technology developed in this study offers a simple oral hygiene product that acts biogenically in water and results in an additive treatment. The whitening lozenge is expected to considerably impact the dental and cosmetic industry as an over-the-counter product.

Dental hypersensitivity (DS) is one of the most common diseases in the United States, affecting the majority of the adult population. DS is commonly accompanied by gingival recession and occurs at the cervical third of the crown. DS is usually triggered externally, e.g. by cold, hot, acid, or basic conditions in the saliva, and produces a sharp pain at the root of the tooth. Our objective is to develop a biomimetic treatment protocol comprising a peptide gel formulation to treat DS. Current approaches include desensitizing nerve ends by blocking the axonic action via potassium salts, limiting the permeability of dentinal tubules using synthetic adhesive sealers, e.g. NaF, bioactive glasses, oxalic acid and glass ionomer cements, or forming coagulates inside the tubules using protein cross-linker agents. Although these agents may be effective, clinical validation is still lacking and their short durability against daily tooth brushing, various foods, or drinking of acidic beverages makes their occlusion effects incomplete. We propose to form a mechanically and thermally stable mineral layer and thereby occlude exposed dentinal tubules using a peptide-remineralization approach. Working closely with the Dental School, our approach involves exposing underlying dentin by removing cement tissue at the coronal root surface by scraping away dentin on extracted human tooth to mimic hypersensitivity conditions. The samples are next treated with peptide-enabled remineralization resulting in tens of micrometer-thick new layer over the damaged dentin. The stability of the newly formed layer is then mechanically and thermally evaluated using nanomechanical testing and thermal-cycling, respectively. Our results demonstrate that exposed dentinal tubules are successfully occluded by mechanically and thermally stable mineral layer. Through a molecular biomimetic approach, the method described herein offers a unique solution to dentinal hypersensitivity, which can be used as a platform technology to develop effective in-clinic and over-the-counter hypersensitivity treatments.

3D printing of materials has been expanding from a process used solely for manufacturing of parts and prototypes in industry to the medical fields during the last decades. The 3D printing process with hydrogels has been used for biomedical applications and the process is also gaining popularity in dental industry, though mainly for model and mold creation, although it has yet to be used for dental composites. The most common dental fillers are either metals, alloys, or resin-based composites. The traditional dental composites, such as ionomers and synthetic resins in addition to metal amalgam are non-adherent to tooth and have different thermal expansion coefficients, which can lead to cracking of the fillers and additional damage to patient’s tooth. Common fillers also have non-natural colors and can leach into the blood stream or oral cavity, causing allergic and harmful reactions. In this research, our aim is to develop a biogenic dental filler using micro-extrusion 3D printing process combined with biomineralizing hydrogel technology. For 3D printable tooth filler, alginate gel was used as the main molecular scaffold along with biomineralizing peptides. After optimizing the rheological characteristics of alginate gel by tuning its concentration, crosslinking properties as well as biomineralization, the efficacy has been characterized in vitro in the presence of Ca⁺² and PO₄^-3 precursor ions. Furthermore, nano- and microstructures of biomineralized dental filler have been tested using scanning electron microscopy and X-ray diffraction techniques. Our results so far indicate that 3D printable, biomineralizing tooth filler can successfully be developed and, when fully optimized, the technique will allow filler material to be custom-made for patient’s caries. In summary, while the novel tooth filler produces internal structures mimicking the natural tooth and well interfaced with the existing tissue, the filler material is also 3D easily fabricated for clinical implementations.