Browsing by Subject "Nanomaterials"

As the cost of medical care increases, people are relying increasingly on internet diagnosis and community care rather than the expertise of medical professionals. Technological and medical advances have facilitated a partial answer through the increase in handheld sensing apparatuses. Yet even with these developments, significant further advancements are required to further drive down fabrication requirements (both in terms of cost and environmental impact) and facilitate fully-integrated and easy to use sensors. Printing electronics could be a powerful tool to accomplish this as printing allows for low-cost fabrication of high-area electronics. The vast majority of printed electronics reports focus on utilization of already developed commercial inks to create devices with new functionalities. This significantly limits development because current inks both necessitate damaging post processing—which precludes the use of delicate substrates, making skin-integration impossible—and many inks require bespoke printing processes, which increases fabrication complexity and thus cost. Further, with the proliferation of single-use medical testing, consideration must be made towards environmental compatibility. Therefore, innovations in electronic ink formulation and printing geared towards addressing the post-processing and environmental impact concerns are needed to enable continued progress towards printed POC sensors. The work contained in this dissertation centers around the development of inks intended to advance electronic biosensing applications. Focus is on using aerosol jet printing to enable the printing of nanomaterials and utilizes the unique properties of these nanomaterials—such as functionality immediately after printing, recyclability, and compatibility with deposition directly on biological surfaces (i.e., human skin)—to develop technologies intended to democratize healthcare. Notably, low temperature printable silver nanowire (AgNW) inks for the creation of biologically integrated electronics are demonstrated. Electrically conductive inks are created that are capable of achieving high conductivities when directly deposited onto living tissue at temperatures compatible with life (20 °C). The conductive lines yielded high resistance to degradation from bending strain, with a mere 8% decrease in conductivity when the plastic film on which they were printed was folded in half. As a demonstration, the AgNW ink was printed onto a human finger and used to illuminate a small light that remained illuminated even when the finger was bent. These results pave the way towards patient-specific medical diagnostics that are comfortable to wear, easy to use, and designed towards the needs of each individual patient. Next, a printing method to deposit biological sensing proteins for biomedical assays is investigated. Traditional techniques require extended time and the use of large quantities of immensely expensive proteins to make biosensors. Herein, a decade-old belief that aerosol jet printing is incompatible with the deposition of proteins is overturned, and, in doing so, highly sensitive biosensors for carcinoembryonic antigen (CEA) that compare favorably the mainstay fabrication technique that is known to impart no damage to the printed biological inks is demonstrated. Finally, the co-printing of a bio-recognition element with the previously mentioned electrically conductive AgNW ink demonstrate the potential for the future investigation of a fully aerosol-jet printed electronic biosensor. To address the environmental waste accumulation concern that plagues the advancement of ubiquitous patient-guided sensing, inks that facilitate the creation of fully-printed, all-carbon recyclable electronics (ACRE) are investigated. The combination of nanocrystalline cellulose, graphene and semiconducting carbon nanotubes enable the first fully recyclable transistor device. The ACRE transistors maintain high stability for over 10 months, display among the best performance of any printed transistor (Ion/Ioff: 104 and Ion 65 µA µm-1) and can be entirely deconstructed for recapture and reuse of the constituent CNT and graphene inks with near 100% nanomaterial retention and the biodegradation of the cellulose-based components. ACRE-based lactate sensors are used as an illustration of utility to show the versatility of the platform. Finally, as a culminating demonstration, a fully-printed chip for the handheld measurement of blood clot time (prothrombin time) was developed. Printing the entirety of the device allows for the creation of a low-cost chip for the simple, fast, and robust measurement of human blood clot times. In addition, a custom-designed, handheld control system with a 3D-printed case was developed to create a fully integrated point-of-care measurement platform towards simplifying medicine dosing strategies. The work described herein marks a significant leap in the development of printed inks to enable custom biological sensing applications. Once fully realized, these applications will mark a watershed, ushering in an era of individualized medicine with ubiquitous sensing to actively track disease progression in real-time. We are at the dawn of a new era in medicine that focuses more on prevention and control as opposed to reaction. One future direction for this work is promoting directly printed and reusable on-skin theragnostics for bespoke patient care such as the delivery and monitoring of pain medication that allows for better oversite over use and misuse.

Lanthanide-doped materials have been studied for decades for their unique photophysical properties derived from their f-block orbitals. More recently, the prominence of techniques allowing for the study and characterization of nanoscale materials has led to a renewed interest in these materials on the nanoscale. This work has led to a wealth of studies on the synthesis and characterization of a number of lanthanide doped nanomaterials as well as numerous proposals and preliminary demonstrations of their applications. This dissertation focuses on three key aspects of this field: (1) a synthetic means to controlling the relative intensities of the emissive bands in upconversion nanoparticles (UCNPs) (2) the development of a 3D imaging modalities that leverage the unique photophysical properties of upconverting nanomaterials and (3) the application of scintillating nanoscale radiation detection materials as an alternative to the single-crystal bulk lanthanide doped materials and plastic scintillators currently employed.

In many proposed applications of upconverting nanomaterials, the relative intensities of emission bands are a key component. For instance, security inks rely on measuring the ratio of the green and red emission peaks to distinguish between authentic and counterfeit materials. While multiple upconversion compositions have been identified with varying relative emission intensities, there has been little study into effective means of synthetically manipulating the intensities of these emission bands within a single composition. Research presented here focuses on understanding the fundamental influences on the coprecipitation reaction method and ultimately manipulating the synthetic techniques to achieve meaningful changes in the emission properties without changing the overall composition of the nanoparticle. An injection reaction method is developed that allows for manipulating the interionic distance between sensitizer and activator pairs resulting in a significant decrease in the red emission. It is further shown that this change in interionic distance is a likely overlooked contributing factor in the emission properties of other compositions that have been studied. This work represents the first steps towards designing application specific emission properties via synthetic control rather than developing applications specific nanomaterial compositions.

Owing to their NIR excitation, lack of tissue autofluorescence, and photostability UCNPs are a promising target for bio-imaging applications. Past studies have demonstrated the potential for UCNPs for cellular, tissue and whole body imaging. However, an imaging system that fully incorporates these materials and leverages their properties to improve upon existing imaging capabilities has yet to be shown. An optical emission computed tomography imaging (OECT) system is modified to enable NIR excitation and imaging of the upconversion signal. Using this system, the first 3D modeled upconversion imaging is demonstrated. By coupling the transmission and upconversion signals in this imaging modality, precise structural imaging is possible and background free images of both the bronchial pathways in the lungs as well as white pulp structures in the spleen are shown using upconversion enhanced OECT.

In addition to upconversion processes, the f-block orbitals can also be utilized in scintillation processed to convert ionizing radiation into visible light. Typically, lanthanide based single crystals are used in the bulk for developing large radiation detectors. However, recent advances in the Therien lab have seen the development of nanoscale [Y2O3] nanomaterials and their incorporation into a fiber optic detector (nanoFOD). This detector is shown here to function as a quality assurance tool in monitoring brachytherapy radiation treatments. Further, using the 3D printing method of fused deposition modeling, this scintillating nanomaterial is incorporated into a first of its kind low-cost radiation-imaging screen. In both applications, the nanomaterial is demonstrated to be highly effective at detecting and monitoring radiation. The low cost, and ease of manufacture for these devices as well as their instantaneous detection of radiation dose rates are a significant improvement over the current detector technologies employed.

Synthetic control of metal nanocrystal shape is a common strategy to control their properties. Shape control is often achieved by controlling the crystal structure of the seed crystals, as well as through the use of additives which are thought to block atomic addition to certain facets. However, the effect of crystal structure or additives on the rate of atomic addition to a specific facet is not usually quantified, making it difficult to design nanocrystal syntheses. This work combines seed-mediated growth, single-crystal electrochemistry measurements and Raman spectroscopy to understand the roles of capping agents and planar defects in the anisotropic growth of silver nanocrystals. The roles of citrate, polyvinylpyrrolidone (PVP), and halides have been investigated. Synthetic results show citrate is a {111} capping agent, PVP is a weak {111} capping agent, chloride and bromide are weak {100} capping agents. However, when chloride or bromide is added with PVP, they become strong {100} capping agents. Electrochemical measurements show the anisotropic growth is caused by capping agents selectively suppressing the oxidation of ascorbic acid (a reducing agent) on a specific crystal facet. The effect of capping agents on silver ion reduction is not facet-selective. Further comparison between the growth of single-crystal seeds and seeds with planar defects indicates defects can catalyze silver atom deposition by up to 100 times and cause greater anisotropic growth than can be explained by facet-selective passivation. Overall this work advances our understanding of nanocrystal chemistry, and informs the design of nanocrystal synthesis to obtain a desired nanocrystal morphology with a desired set of properties.

Nano-structures were investigated for the advancement of energy conversion technology because of their enhanced catalytic, thermal, and physiochemical interfacial properties and increased solar absorption. Hydrogen is a widely investigated and proven fuel and energy carrier for promising "green" technologies such as fuel cells. Difficulties involving storage, transport, and availability remain challenges that inhibit the widespread use of hydrogen fuel. For these reasons, in-situ hydrogen production has been at the forefront of research in the renewable and sustainable energy field. A common approach for hydrogen generation is the reforming of alcoholic and hydrocarbon fuels from fossil and renewable sources to a hydrogen-rich gas mixture.

Unfortunately, an intrinsic byproduct of any fuel reforming reaction is toxic and highly reactive CO, which has to be removed before the hydrogen gas can be used in fuel cells or delicate chemical processes. In this work, Au/alpha-Fe2O3 catalyst was synthesized using a modified co-precipitation method to generate an inverse catalyst model. The effects of introducing CO2 and H2O during preferential oxidation (PROX) of CO were investigated. For realistic conditions of (bio-)fuel reforming, 24% CO2 and 10% water the highest document conversion, 99.85% was achieved. The mechanism for PROX is not known definitively, however, current literature believes the gold particle size is the key. In contrast, we emphasize the tremendous role of the support particle size. A particle size study was performed to have in depth analysis of the catalysts morphology during synthesis. With this study we were also able to modify how the catalyst was made to further reduce the particle size of the support material leading to ~99.9% conversion. We also showed that the resulting PROX output gas could power a PEM fuel cell with only a 4% drop in power without poisoning the membrane electrode assembly.

The second major aim of this study is to develop an energy-efficient technology that fuses photothermal catalysis and plasmonic phenomena. Although current literature has claimed that the coupling of these technologies is impossible, here we demonstrate the fabrication of reaction cells for plasmon-induced photo-catalytic hydrogen production. The localized nature of the plasmon resonance allows the entire system to remain at ambient temperatures while a high-temperature methanol reformation reaction occurs at the plasmonic sites. Employing a nanostructured plasmonic substrate, we have successfully achieved sufficient thermal excitement (via localized surface plasmon resonance (LSPR)) to facilitate a heterogeneous chemical reaction. The experimental tests demonstrate that hydrogen gas can indeed be generated in a cold reactor, which has never been done before. Additionally, the proposed method has the highest solar absorption out of several variations and significantly reduces the cost, while increasing the efficiency of solar fuels.