Browsing by Subject "Nanomaterial"

Since its outbreak in the 1980s, the Human Immunodeficiency Virus (HIV) has become a major threat to global health. According to UNAIDS 2021 epidemiological estimates (2, 3), at the end of 2020 around 37.7 million people were living with HIV worldwide and 1.5 million new HIV infections occurred. Among those HIV-positive individuals, 10.5 million including 800,000 children did not have access to treatment, resulting in 680,000 AIDS-related deaths. Currently, different preventative measures are implemented including condom use, and pre- and post-exposure prophylaxis (4). However, these measures are not feasible for scaling up to population level because they require constant use of medication, and their efficacy depends on adherence to the treatment regimen. Vaccines are among the most cost-effective approaches to prevent infectious diseases (5). Yet, after 40 years of pandemic HIV, no vaccine has been able to provide enough protection against HIV acquisition, reflecting the formidable challenge of developing an efficacious HIV vaccine. These difficulties come from the two sides of the battle: the virus and the immune system. Virologically, HIV represents one of the most genetically diverse viruses in human history (6). Therefore, an effective vaccine will need to provide protection against an enormous set of viral strains. Moreover, the extensive glycosylation of the HIV Envelop glycoproteins (Env) protects the sites of vulnerability in the Env against antibody recognition (7), resulting in delayed emergence of neutralizing antibodies following infection (8, 9). Immunologically, antibodies with extensive neutralizing ability (known as broadly neutralizing antibodies, bnAbs) have features that disfavor their generation, such as high frequency of somatic hypermutation (SHM) (10), long complementarity determining region 3 (CDR3) (11), and high frequency of immunologically disfavored mutations (known as improbable mutations) (1). Because traditional vaccination strategies have failed to elicit broad protective immune responses, novel approaches are required for a universal HIV vaccine. The success of passive immunization with bnAbs in protecting non-human primates from the Chimeric Simian-human Immunodeficiency virus (SHIV) infection (12-17), has highlighted bnAbs as critical for protection; and elicitation of bnAbs is the ultimate goal for most current HIV vaccine designs. The features of bnAbs indicate that several rounds of SHM are required for B cells to produce bnAbs, and it is thought that the first event to drive B cells toward bnAb formation is when Env engages the B cell precursors that express the unmutated form of a bnAb, known as germline or unmutated common ancestor (UCA) (10). Different strategies have been used to engage the germline B cells such as using Env antigen of the transmitted/founder (T/F) virus that first establishes infection (18). Moreover, the use of native-like Env trimers instead of monomeric glycoproteins may enhance the immunogenicity of epitopes important for broad neutralization. To induce neutralizing antibodies against HIV, one of the vaccine candidates we tested (CH505T/F SOSIP) is a native-like trimer Env antigen designed based on the T/F virus isolated in a patient who developed the anti-CD4 binding site (CD4bs) bnAb CH103 (18). This antigen was chosen because it has demonstrated the ability to engage the CH103 UCA (19). While the mechanism of elicitation of bnAbs during natural infection are not completely elucidated, several recent studies have reported that HIV infected children develop neutralization breadth earlier and more frequently than adults (20, 21). Moreover, the few pediatric bnAbs described in the literature feature lower SHM frequency and fewer improbable mutations than adult bnAbs with similar neutralizing breath (1, 22, 23). Overall, these observations suggest that immunization in early life could present advantages for inducing bnAbs. Therefore, in one of the studies presented in this dissertation, we tested our immunization strategy in infant non-human primates. To date, only one HIV vaccine trial has demonstrated any evidence of efficacy. In the HIV vaccine trial RV144, the vaccine was correlated with a 31% reduction of HIV acquisition in the vaccinees (24). Importantly, only very limited neutralizing antibody response was induced in RV144 vaccinees, suggesting that non-neutralizing antibody functions can provide some degree of protection. Indeed, post-hoc analyses indicate that antibody-dependent cellular cytotoxicity (ADCC) was associated with reduced HIV acquisition in RV144 vaccinees (24, 25). Unlike neutralization, which is mainly regulated by the Fab region of an antibody, non-neutralizing antibody effector functions (such as ADCC and antibody-dependent cellular phagocytosis, ADCP) are regulated both by Fab and Fc regions (26, 27). Antibodies with a certain Fc phenotype exert non-neutralizing functions via selectively engaging different Fc receptors. (26, 27). As an ideal vaccine would probably need to induce antibodies that mediate neutralization as well as non-neutralizing Fc effector functions, it is important to further explore how vaccine strategies can modulate the Fc portion of the antibodies in order to enhance desired Fc functions. As traditional immunization strategies have failed to induce protective immunity against HIV, various classes of nanomaterials have been applied to HIV vaccine development in the past decade (28). That is because certain properties of nanomaterials can be harnessed to improve specific immune responses. Notably, self-assembling peptide nanomaterial such as the synthetic peptide Q11 which can self-assemble into fibrillar structure upon transition from pure water to aqueous solution with physiological salt concentration (29) are self-adjuvanting (30). Moreover, Q11 allows control of valency of the conjugated antigens (31). Thus far, Q11 has been used in immune therapy for different disease models such as malaria (32), influenza virus (33-35), psoriasis (36), and bacterial endotoxin-induced anaphylactic shock (37). Because of Q11’s engineerability and self-adjuvanting nature, it may present advantages for tailoring immune response against diseases with unknown immune correlates for protection such as HIV. The overarching goal of this dissertation project is to construct a next-generation HIV vaccine capable of inducing a broad protection against different HIV strains. We hypothesized that presenting HIV Env on Q11 improves the humoral response elicited by the Env vaccine. To test this hypothesis, we utilized Q11 to formulate different HIV vaccines, and we defined the humoral responses induced by Q11-based HIV vaccines in animal models including mice, rabbits, and infant rhesus macaques. We first conjugated gp120 from the T/F clade C virus 1086.C (38) to Q11 nanofiber and immunized wildtype mice with either the Q11-conjugated gp120 (gp120-Q11) or with soluble gp120. We demonstrated that gp120-Q11 induced higher magnitude of antibody response than gp120. More importantly, by testing the antibody binding to Envs from heterologous HIV strains, we demonstrated that gp120-Q11 also induced higher binding breadth. This enhancement in antibody binding magnitude and breadth was found to be associated with the gp120 valency on Q11 nanofiber, as diminished response was observed in mice immunized with lower valency gp120-Q11 vaccine. We then immunized rabbits with a gp120-Q11 and the corresponding gp120 to assess the function of the vaccine-elicited antibodies. The gp120-Q11 vaccine induced higher levels of tier 1 autologous virus (CH505 w4.3) neutralization, ADCC, and ADCP to heterologous Env antigen in rabbits than the gp120 vaccine. Since Fc-mediated functions such as ADCC and ADCP can be modulated by the glycosylation of the IgG Fc region, we analyzed the Fc glycan in gp120-specific IgG in the immunized rabbits and found that the gp120-Q11 vaccine induced an IgG response with higher levels of fucosylation, bisection, and mono-galactosylation. Similar glycosylation profile was also observed in gp120-Q11 immunized mice. These results suggest that Q11 nanofiber’s ability to modulate Fc glycosylation may be applicable across different mammalian species. Finally, we assess the immunogenicity of a Q11-conjugated trimeric Env construct (SOSIP) in infant rhesus macaques. Although slightly lower antibody magnitude was induced by the Q11-conjugated SOSIP vaccine as compared to SOSIP only, we found higher titers of neutralizing antibody against the autologous tier 1 HIV CH505 w4.3 in infant macaques immunized with the SOSIP-Q11 vaccine. Yet, SOSIP-Q11 and soluble SOSIP vaccine groups demonstrated similar frequency of neutralization of the autologous tier 2 virus (CH505T/F). These results may reflect differences in the animal models or on how neonatal and adult B cells respond to multivalent vaccines. Future studies should investigate the mechanism of this difference in order to define if construct optimization can improve the response to HIV Env-Q11 multivalent vaccines in pediatric settings. Taken together, in this dissertation we described a self-assembling nanomaterial as a versatile vaccine platform for HIV. This vaccine platform did not only improve the overall binding antibody response and breadth; antibodies induced by Q11 vaccine also demonstrated superior functional capacity (ADCC, ADCP and tier 1 virus neutralization). Moreover, Q11 appears to modulate the Fc glycosylation across species and these changes in glycosylation profile were associated with increased ADCC in rabbits. This finding implies an opportunity to further explore the possibility of using Q11 or other similar nanomaterials to tailor Fc-mediated antibody functions via modulating the glycan moiety.

As society becomes increasingly data-driven, the appetite of individuals, corporations, and algorithms for data sources swells, strengthening the demand for sensors. Chemical sensors are of particular interest as they provide highly human-relevant information, such as DNA sequences, cancer biomarker concentrations, blood glucose levels, antibody detection, and viral testing, to name a few. Among the most promising transduction elements for chemical sensors are nanomaterial field-effect transistors (FETs). The nanoscale size of these devices allows them to operate using very small sample sizes (an extremely small volume of patient blood, for instance), be strongly influenced by low concentrations of the target chemical, and be produced at low-cost, potentially using the same methods developed for consumer electronics (which have achieved a cost of less than 0.000001 cents per device). Nanomaterial FET-based chemical sensors also have the advantage of directly transducing a chemical presence or change to an electrical output signal. This avoids components such as lasers, optics, fluorophores, and more, that are frequently used as a part of the transduction chain in other types of chemical sensors, adding size, complexity, and cost. Much work has focused on demonstrating one-off nanomaterial FET-based sensors, but less work has been done to determine the underlying mechanisms that lead to sensitivity by mapping sensitivity against other variables in experimental devices. With challenges of consistency and reproducible operation stifling progress in this field, there is a significant need to improve understanding of nanomaterial-based FET sensitivity and operation mechanisms.

The work contained in this dissertation maps the sensitivity of nanomaterial FETs across a range of parameters, including space, time, device operating point, and analyte charge. This mapping is performed in an effort to yield insight into the underlying mechanisms that govern the sensitivity of these devices to nearby charges. In order to both draw comparisons between different device types and to make the results of this work broadly applicable to the field as a whole, four types of devices were studied that span a broad range of characteristics. The device types spanned from channels of one-dimensional nanotubes to three-dimensional nanostructures, and from partially printed fabrication to cleanroom-based nanofabrication. Specifically, the devices explored herein are carbon nanotube (CNT) FETs, molybdenum disulfide (MoS2) FETs, silicon nanowire FETs, and carbon nanotube thin-film transistors (CNT-TFTs). Fabrication processes were developed to build devices of each of these types that are capable of undergoing long-term electronic testing with reliable contact strategies. Passivation schemes were also developed for each device type to enable testing in solution and formation of solution-based sensors so that results could be extended to the case of biosensors. An automated experimentation platform was developed to enable tight synchronization between characterization instruments so that each variable impacting device sensitivity could be controlled and measured in tandem, in some cases for months on end.

Many of the obtained results showed similar trends in sensitivity between device types, while some findings were unique to a given channel material. All tested devices showed stability after a period of drain current settling caused by the occupation equilibration of charge trap states – an effect that was found to severely reduce sensitivity and dynamic range. For CNTs specifically, two new decay modes were discovered (intermediate between device stability and breakdown) along with respective onset voltages that can be used to avoid them. For CNT-TFTs, it was found that the relationship between signal-to-noise ratio (SNR) and device operating point remained consistent between ambient air and solution environments, indicating that this relationship is governed primarily by properties of the device. A simple chemical sensor made from the same devices showed a clear peak in the SNR near the device threshold voltage – a result that became increasingly meaningful when combined with similar observations in other device types obtained via separate experimental methods.

For both silicon nanowire and MoS2 FETs, sensitivity was mapped in space with sub-nanometer precise control over analyte position. Both device types manifested distinct sensitivity hotspots spread across the geometry of the channel. These hotspots were found to be stable in time, but their prominence depended heavily on the device operating point. When SNR was mapped across a range of operating points for these devices, a clear peak was discovered, with the hotspot intensity culminating at the peak. Ideal operating points were identified to be near the threshold voltage for both device types, with findings (and a developed numerical model) in MoS2 indicating that the operating point where SNR is maximized may depend upon the extent of the channel that is influenced by the analyte. Observations from multiple devices and approaches revealed that SNR peaks below the point of maximal transconductance, offering increased resolution to a matter that has previously been of some debate in the literature. In MoS2 FETs, a significant asymmetry was discovered in the response of devices to analytes of opposing polarity, with analytes that modulate devices toward their off-state eliciting a much larger response (and, correspondingly, SNR). This asymmetry was confirmed by a numerical model that suggested it to be a general result applicable to all FET-based charge detection sensors, leading to the recommendation that sensor designers select FETs that will be turned off by the target analyte.

Each finding contributed by this dissertation provides insight into future sensor designs and increases clarity of the underlying mechanisms leading to sensitivity in nanomaterial FET-based sensors. The discovery of decay modes, hotspots, ideal operating points, asymmetries, and other trends comprise substantial scientific advancements and propel the field closer to the goal of providing ubiquitous access to critical information, diagnoses, and measurements that promptly and correctly inform decisions.

Peptide-based vaccines have received growing interest due to their specificity and ability to limit off-target effects, and they are currently being explored toward a variety of infectious diseases and therapeutic targets. However, the efficacy and applicability of such epitope-based vaccines are currently limited by difficulties in predicting immunogenic epitopes in outbred populations and a reliance on carrier proteins and adjuvants that can cause pain and swelling. Current vaccine platforms are further limited in their ability to combine multiple different epitopes, making it difficult to adjust humoral and cellular responses systematically. A vaccine platform containing broadly reactive T-cell epitopes that boosts responses to co-delivered antigens with minimal inflammation could address these limitations. To that end, the focus of this dissertation was to create peptide epitopes that can be incorporated within a supramolecular nanomaterial platform, together acting as a nano-adjuvant, a term that we will use here to describe materials whose adjuvanting properties depend on their nanoscale structure. To achieve this, we took inspiration from a class of materials termed glatiramoids, which promote anti-inflammatory and TH2 immune responses. We created an immunomodulatory supramolecular nanomaterial system inspired by the randomized nature of glatiramoids termed KEYA-Q11. By creating a glatiramoid-like peptide library integrated within self-assembling Q11 nanofibers, numerous epitopes can be presented simultaneously along the nanofibers for maximum antigen presenting cell uptake and activation. The first half of this document (Chapters 3 and 4) describes how this nanomaterial increased immunogenicity of co-assembled epitopes while also creating a KEYA-specific non-inflammatory response to the randomized component. Additionally, capitalizing on the potential for KEYA-Q11 to amplify immune responses to co-assembled epitopes, this technology is applied in the second half of this document (Chapters 5 and 6) to an epitope-based influenza vaccine. Initially we designed and synthesized a self-assembling nanomaterial inspired by glatiramoids and evaluated its TH2 T-cell polarizing properties (Chapter 3). Glatiramoids raise strong, protective immune responses in patients and have been examined in a variety of contexts from Multiple Sclerosis to HIV. However, due to their randomized polysequence structure, it remains challenging to incorporate glatiramoids into other materials and strategies to optimize them for specific therapeutics. Therefore, we designed a polysequence peptide sequence and synthesized it onto the chemically defined, supramolecular Q11 nanofiber platform to straightforwardly titrate it into other nanomaterial formulations. This polysequence nanomaterial was termed KEYA-Q11 for the four amino acids, lysine, glutamic acid, tyrosine, and alanine, that comprise its structure. Due to the extensive number of possible KEYA sequences, multiple batches of KEYA-Q11 were first examined with an array of biophysical characterization techniques to confirm reproducible synthesis and assembly. The optimal number of polysequence amino acid additions was determined to be 20 amino acids as (KEYA)20Q11 could reliably be synthesized and raise strong Type 2/TH2/IL-4 immune responses. Moreover, by modulating the concentration of KEYA-Q11 in a Q11 immunization, the strength of KEYA-specific B-cell responses were similarly altered. KEYA modifications dramatically improved uptake of peptide nanofibers in vitro by antigen presenting cells and served as strong B-cell and T-cell epitopes in vivo, inducing a KEYA-specific Type 2/TH2/IL-4 phenotype. KEYA modifications also increased IL-4 production by T cells, extended the residence time of nanofibers, and decreased overall T cell expansion compared to unmodified nanofibers, further suggesting a TH2 T-cell response with minimal inflammation. Subsequently, we exploited the modularity of the self-assembling system to maximize application of KEYA-Q11 as a nanoscale adjuvant without inflammation (Chapter 4). Adjuvants are commonly required to raise strong immune responses to peptide therapeutics, but often induce swelling and pain at the injection site and typically drive immune phenotype. Relative to common adjuvants, KEYA-Q11 had no detectable injection site swelling and was more effective at raising humoral responses despite a genetically diverse in vivo population. Furthermore, when combined with peptide epitopes KEYA-Q11 augmented antibody production against co-assembled B-cell epitopes for cytokine TNF, D-chiral MMP cross linker, and a conserved segment of the M2 influenza protein, and increased T-cell stimulation specific to co-assembled T-cell epitopes PADRE and a conserved segment of the nucleoprotein of influenza. Likewise, when combined with the influenza surface protein hemagglutinin, KEYA modifications strengthened the resulting influenza-specific cellular immune responses. Augmented immune responses typically followed native epitope polarization, as in a co-assembly of KEYA-Q11 and the nucleoprotein epitope raised Type 2/TH2/IL4 producing KEYA-specific responses and magnified the Type 1/IFN producing nucleoprotein-specific responses that epitope would produce without an adjuvant, and thus using KEYA-Q11 as the adjuvant allowed for finer control over immune phenotype. Building on the success of KEYA-Q11 as a nano-scale adjuvant without inflammation, we utilized these properties to decrease the severity of influenza infection and provide broad protection via immunization with peptide epitopes (Chapters 5 and 6). Much of the current focus on influenza vaccines revolves around partial or whole proteins to induce broadly protective antibodies, while other have demonstrated cross-reactive T-cell responses are vital for heterologous protection. Conserved peptide epitopes have been discovered but typically are included with larger proteins and adjuvants to increase immunogenicity. Supramolecular assemblies based on the Q11 peptide system containing KEYA, a B-cell epitope from a conserved surface protein on influenza, and CD4+ and CD8+ T-cell epitopes from influenza nucleoprotein and polymerase acidic protein, respectively, raised strong immune responses against all three epitopes. Inclusion of the KEYA component in prophylactic immunizations with these materials significantly improved protection following a lethal influenza challenge. It has been established that while peptide-based immunotherapies can have finely directed specificity for chosen epitopes, they generally lack sufficient immunogenicity to provoke suitable immune responses. This new strategy for augmenting immune responses to peptide-based therapeutics, especially those employing nanomaterials, and especially for applications where non-inflammatory responses are prioritized, can be employed for a variety of potential applications in vaccine development, towards infectious diseases and towards non-infectious applications such as inflammatory autoimmune diseases, wound healing, or graft rejection. KEYA-Q11 is a unique fusion of two materials, a highly ordered system with a highly disordered system, and examination of this nanomaterial has provided valuable insight into both randomly polymerized structures and non-inflammatory nano-scale adjuvants.

Carbon nanomaterials have a wide range of promising and exciting applications. One of the most heavily investigated carbon nanomaterial in recent history has been the carbon nanotube. The intense interest in carbon nanotubes can be attributed to the many exceptional characteristics which give them great potential to revolutionize modern mechanical, optical and electronic technologies. However, controlling these characteristics in a scalable fashion has been extremely difficult. Although some progress has been made in controlling the quality, diameter distribution and other characteristics of carbon nanotube samples, several issues still remain. The two major challenges which have stood in the way of their mainstream application are controlling their orientation and their electronic characteristics. Developing and understanding a Chemical Vapor Deposition based carbon nanotube synthesis method has been the major focus of the research presented here. Although several methods were investigated, including the so-called "fast-heating, slow-cooling" and large feeding gas flowrate methods, it was ultimately found that high-quality, perfectly aligned carbon nanotubes from a variety of metal catalysts could be grown on quartz substrates. Furthermore, it was found that using MeOH could selectively etch small-diameter metallic carbon nanotubes, which ultimately led to the productions of perfectly aligned single-walled carbon nanotube samples consisting almost entirely of semiconducting carbon nanotubes. Thiophene was utilized to investigate and support the hypothesized role of MeOH in producing these selectively gown semiconducting carbon nanotube samples. Additionally, this sulfur-containing compound was used for the first time to demonstrate a two-fold density enhancement in surface grown carbon nanotube samples. This method for selectively producing perfectly aligned semiconducting carbon nanotubes represents a major step towards the integration of carbon nanotubes into mainstream applications.

Although extremely useful in a variety of technologies, carbon nanotubes have proven impractical for use in H₂ storage applications. As such, microporous carbons have been heavily investigated for such ends. Microporous carbons have distinguished themselves as excellent candidates for H₂ storage media. They are lightweight and have a net-capacity of almost 100%, meaning that nearly all of the H₂ stored in these materials is easily recoverable for use in devices. However, developing a microporous carbon with the appropriately small pore diameters (~1nm), large pore volumes (>1cm3) and large surface areas (≥3000m2/g) has proven exceedingly difficult. Furthermore, maintaining the ideal graphitic pore structure has also been an unresolved issue in many production means. Several microporous carbon synthesis methods were investigated herein, including inorganic and organically templated production schemes. Ultimately, thermally treating poly (etherether ketone) in CO₂ and steam environments was found to produce large surface area porous carbons (≥3000m2/g) with the appropriately small pore diameters (<3nm) and large pore volumes (>1cm3) necessary for optimized storage of H2. Furthermore, the surface chemistry of these pores was found to be graphitic. As a result of these ideal conditions, these porous carbons were found to store ~5.8wt.% H₂ at 77K and 40bar. This represents one of the most promising materials presently under investigation by the United States Department of Energy H₂ Sorption Center of Excellence.

The success of both of these materials demonstrates the diversity and promise of carbon nanomaterials. It is hoped that these materials will be further developed and will continue to revolutionize a variety of vital technologies.

Purpose: To demonstrate specific methods of small animal dosimetry and quality assurance through (1) machine-specific quality assurance and (2) target-specific quality assurance (QA) protocols for different types of biological irradiators: (a) a large-field orthovoltage irradiator, (b) a small-field orthovoltage irradiator, and (c) a 137Cs irradiator. Additionally, (3) a dosimetric characterization of a novel nano-scale phosphor detector for small animal dosimetry is performed.

Materials and Methods: (1) Machine-specific QA: (a) Large-field irradiator: Dose measurements were performed with an ion chamber and include: beam profile measurements at 50 cm SSD, linearity of output, in-air output for various irradiation settings, and light and radiation field coincidence measurement. A kVp meter was used to measure kVp and HVL for different irradiation settings. (b) Small-field irradiator: Dose measurements were completed using an ion chamber and MOSFET dosimeters. For the diagnostic mode measurements, the ion chamber was placed on the irradiation table and various diagnostic protocols were measured including table attenuation. MOSFETs were used to measure the backscatter factors (BSF) for various collimator sizes under therapy mode.

(2) Target-specific QA: (a) Large-field irradiator: A tissue-equivalent mouse phantom (2 cm diameter, 8 cm length) was used. MOSFET dosimeters were calibrated in air with an ion chamber and f-factor was applied to derive the dose to tissue. The MOSFET detectors were then placed in the phantom at center of the body and irradiated under the following settings: 320 kVp, 12.5 mA, for 30s for four runs. (b) Small-field irradiator: Accuracy of mouse dose between TG-61 based look-up table was verified with the MOSFET technology. The look-up table was obtained by TG-61 based commissioning data and used a tissue-equivalent block and radiochromic film. A tissue-equivalent mouse phantom was used with MOSFETs placed at the center of the body. MOSFETs were calibrated in air with an ion chamber and f-factor was applied to derive the dose to tissue. In CBCT mode, the phantom was positioned such that the system isocenter coincided with the center of the MOSFET with the active volume perpendicular to the beam. The absorbed dose was measured three times for seven different collimators, respectively. The exposure parameters were 225 kVp, 13 mA, and an exposure time of 20s. (c) 137Cs irradiator: Tissue-equivalent mouse phantoms were tested in target-specific set-ups. TLD calibration was performed on site. (3) The nano-scale phosphor detector was tested in both the small-field irradiator and the 137Cs irradiator. Calibration was performed equivalent to MOSFET/TLD calibration for the small-field irradiator and 137Cs irradiator. Other measurements included angular dependence measurements in-air and in-phantom, with and without the table.

Results: (1) Machine-specific QA: (a) Large-field irradiator: The output was shown to be linear. The kVp measurements were consistent for both data sets. The light and radiation field coincidence measurement yielded a shift in the left-right direction of 3 mm and the front-rear direction of 2 mm with respect to the radiation field. The in-air output measurements for the exposure settings of 320 kVp, 12.5 mA, and 165s for 4 filters were: 252.9 (no filter), 208.6 (F1), 76 (F2), and 176.3 (F4) cGy/min. (b) Small-field irradiator: A kVp check and HVL measurements were performed and dose or dose rate for the diagnostic protocols are as follows: 4.5 and 3.9 cGy/min AP and PA, respectively, for the 40 kVP protocol and 1.9 and 1.7 cGy/min AP and PA, respectively, for the 80 kVp protocol (fluoroscopy), 0.47 cGy (scout), and 8.6 ± 0, 4.3 ± 0.1, and 1.7 ± 0.1 cGy/min for two 40 kVp protocols (first one has half the rotations per minute) and an 80 kVp protocol (CBCT). (2) Target-specific QA: (a) Large-field irradiator: The average DR for the head and body was calculated to be 228.6 ± 3.1 cGy/min and 228.1 ± 2.4 cGy/min, respectively, for a total average DR of 228.3 ± 2.0 cGy/min. (b) Small-field irradiator: For a 10 mm, 15 mm, and 20 mm circular collimator, the dose measured by the phantom was 4.3%, 2.7%, and 6% lower than TG-61 based measurements, respectively. For a 10 x 10 mm, 20 x 20 mm, and 40 x 40 mm collimator, the dose difference was 4.7%, 7.7%, and 2.9%, respectively. (c) 137Cs irradiator: Lab 1: The average dose rates for the head DRhead 1-5 ¬ were between 138.7 ± 10.5 cGy/min for level 1 to 167.8 ± 10.5 cGy/min for level 5. The average dose rates for the body DRbody 1-5 was 156.4 ± 7.4 cGy/min for level 1 to 179.5 ± 4.6 cGy/min for level 5 . Lab 2: The average dose rate for the head DRhead was 133.8 ± 0.5 cGy/min and the average dose rate for the body DRbody was 140.4 ± 3.8 cGy/min for an averaged DRavg of 137.1 ± 1.9 cGy/min. (3) The nano-scale phosphor detector behaved strictly linear for a dose range of 2 - 350 cGy with a variation in sensitivity of about 0.3%. The limit of detection was observed to be about 0.44 cGy in air. The in-air angular response was shown to have a coefficient of variation of 4.3%, while the in-phantom measurement without the table had a coefficient of variation of only 1.2%.

Conclusion: (1) Machine-specific QA: (a) Large-field irradiator: Machine-specific quality assurance checks dosimetric and mechanical parameters of the irradiator. (b) Small-field irradiator: Baseline quality assurance data was accumulated for all diagnostic mode protocols. The BSF was determined for therapy mode and shown to agree with published data. (2) Target-specific QA: (a) Large-field irradiator: The target-specific quality assurance performed using a mouse phantom yield a dose rate 14% higher than that estimated by the investigator. (b) Small-field irradiator: The MOSFET data was systematically lower than the commissioning data. The dose difference is due to the increased scatter radiation in the solid water block versus the dimension of the mouse phantom leading to an overestimation of the actual dose in the former. The MOSFET method with the use of mouse phantom provides less labor intensive geometry-specific dosimetry and accuracy with better dose tolerances of up to ± 2.7%. (c) 137Cs irradiator: Lab 1: Dose measurements from levels 3 and 4 were compared with the estimated dose rate. The average measured dose was found to be 19.8 ± 2.6% and 13.8 ± 2.0 % lower than the estimated dose. Lab 2: No comparison could be made due to user-error during irradiation. (3) The nano-scale phosphor detector displays equivalent or superior dosimeteric characteristics in comparison to commonly used TLD and MOSFET dosimeters for small animal dosimetry.