Zebra and Quagga mussels are aquatic and highly invasive freshwater bivalve molluscs native to Eurasia. They have spread at an exponential rate into bodies of water throughout the country by means of our interconnected waterway. Prior analysis of their distribution has determined a consistent global pattern in which a population of zebra mussels initially invades a body of water and subsequently, a population of quagga mussels is established in the same region. Despite differential habitat preferences, both species have been found to live and reproduce in the same location. Since both species exhibit broadcast spawning as a reproductive mechanism, the potential for hybridization exists; this potential was analyzed via evaluating the initial fertilization and early embryonic cleavage stages required for production of viable hybrid offspring. A series of hybridization crosses were performed and compared against a control. Fertilization events observed and analyzed included motility and chemotaxis, the acrosome reaction, sperm binding and entry into the egg cytoplasm, and finally cleavage and early development. Inability to produce viable offspring suggests a hybridization-block has been established between the two species at the level of fertilization or early development.

Some classes of endocrine disrupting compounds in the environment have the ability to alter thyroid function. Such thyroid disrupting compounds are known to influence growth and development, but recent studies suggest that thyroid disruption can also have adverse effects on reproduction. A recent study in the Jeffries lab demonstrated that early-life stage thyroid disruption caused decreased reproductive output in fathead minnows (Pimephales promelas), even after a prolonged period of depuration. However, the mechanisms connecting early life stage thyroid disruption to altered reproduction during adulthood remain elusive. This study sought to determine whether alterations in reproductive success following thyroid disruption were a result of male or female reproductive performance in an effort to narrow potential mechanisms by which thyroid disrupting compounds alter reproduction. The results of this study bring insight to the underlying cause of decreased reproductive output following thyroid inhibition.

Carnivorous plants occupy nutrient-poor soils and have evolved traits that allow them to obtain nutrients by capturing and digesting insects. The pale pitcher plant, Sarracenia alata, uses passive pitfall traps to capture their insect prey. Although studies have examined prey composition for S. alata, it is unknown whether this species is selective in prey capture or whether it captures insects in proportion to their abundance in the environment. The purpose of this study was to compare prey capture of S. alata pitchers with the available insects to determine whether this species is selective in prey capture. The available insects were sampled using artificial sticky traps in the vicinity of the pitchers. The insects in the study were identified first to the taxonomic level of order and then further identified to "morphospecies" as a means of examining preference on a finer scale. The relative proportions of insects in specific orders differed between artificial traps and plants. Although dipterans were a major component of capture in both artificial traps and plants, the relative proportions of morphospecies differed between the two. These results support the hypothesis that S. alata is selective in its prey capture, but further studies are needed that use different methods of measuring the available insects in order to avoid potential bias.

Our team will answer the question how Penicillium mold grows in a microgravity environment versus Earth’s gravity. This question answers or sparks several other questions such as is it a viable solution for some antibiotics in space or how do antibiotics like penicillin work in the body in space. Will it grow more or will it be the same or maybe grow less? The purpose of our experiment is to provide a viable solution to some bacterial infections in space. Bacteria in space tends to act more violently so maybe good bacteria or mold will act more furiously to kill those bacteria. Our hypothesis is that it will grow better. This is based off of the fact that in an earlier SSEP experiment the polymers absorbed more water. Which might be the same for organisms like mold so it would make it easier to absorb water. Plus with lower gravity organisms tend to grow larger at least that is many scientist hypotheses. So since there is practically no major gravity or forces in space may be the mold will grow larger than usual. Our group believes this based on the fact that we have researched.

Our experiment is about diabetes and Humalog synthetic insulin crystallization in a microgravity environment. We feel like this is a good experiment to design because we could find out if there is a way to prevent crystallization of insulin, especially if we understand how it happens in microgravity. When insulin crystallizes, the bacteria that usually makes it viable stops working. This would cause it to be ineffective for patients in dire need of this medication. To complete this experiment we are going to keep the insulin in a type 1 FME at the International space station (ISS) at above 65℉ to see if it crystallizes within a certain amount time. We will keep the experiment refrigerated at or below 40℉ during transportation to the ISS and again on arrival back to Earth’s gravity. Refrigeration slows the crystallization growth and this is how it is stored on Earth. Keeping our experiment refrigerated during transportation is an important step because the insulin crystallization growth should only be measured while in microgravity. We will be conducting the same experiment, using the same time frame and refrigeration needs before and after, for our earth bound experiment.

Our experiment is how well will a hornwort plant purify polluted water in microgravity. We will see how it will purify at the same rate as it does in full gravity. We chose this plant because they can purify water and they grow at a fast rate. This will help astronauts because if they run out of water they can grow hornwort even if the only water they have is polluted. Also, it will help them to have purified water if their water system breaks down. The hornwort plant will be growing on the way from Earth to the ISS. The experiment will be purifying the polluted water in microgravity for 5-6 days. Then the formalin will be added to the plant to stop its growth and preserve the sample. We are polluting the water with Cyanobacteria, which is more commonly known as blue green algae. We will know it has worked if the polluted water has become purified after it has been tested.

Previous studies, including those in the Jeffries lab, have shown that female animals are able to fight and survive infection better than males. However, the underlying cause of this difference remains unclear. Because many differences between males and females are due to differences in sex steroid hormone (e.g., estrogen, testosterone, etc.) concentrations, it is possible that differences in immune function are also due to such differences in hormone levels. The objective of this study is to uncover the role of sex steroid hormones in the immune response of fathead minnows (Pimephales promelas). Because females exhibit better pathogen resistance than males, it is hypothesized that estrogen (a “female” hormone) enhances immune system function. The results of this study provides insight into the potential crosstalk between the reproductive and immune systems, as well as a better understanding of the role of sex hormones in the organism.

The fathead minnow (Pimephales promelas), a small fish model often used to screen for reproductive endocrine disrupting compounds, has recently been used by some investigators to screen for chemicals with thyroid disrupting capabilities. However, it is uncertain how known thyroid disruptors affect various markers of thyroid disruption in this species. This study aimed to fill this gap in knowledge by assessing the sensitivity of endpoints known to be responsive to thyroid disruption in other closely-related species in larval fathead minnows. In addition, we sought to uncover how the timing and length of exposure influenced the response of these endpoints. To accomplish these objectives, larval fathead minnows were exposed to various doses of propylthiouracil (PTU; a known thyroid disruptor) and thyroxine (T4; a known thyroid stimulant) for 35 days. Several metrics indicative of alterations in thyroid hormone status (e.g., thyroid related gene expression, growth, thyroid cell follicular height, etc.) were measured on day 7, 21, and 35. The results of this study provide valuable information that can be utilized in developing fathead minnow thyroid disrupting chemical screening assays.

Habitat maps derived from remotely sensed data are strong predictors of wildlife distributions, outperforming traditional on the ground vegetation structure surveys. Texas Parks and Wildlife created a statewide habitat map in 2014 featuring 398 vegetation classes to 10-meter resolution. The Great Trinity Forest is the largest urban forest in the United States, with 3,000 continuous hectares within the city of Dallas. As part of our wider study of the forest’s wildlife, we edited Texas Parks and Wildlife’s habitat to more accurately and meaningfully reflect habitat distinctions in the Great Trinity Forest. First we adjusted the locations and boundaries of waterways to reflect changes in their location over the past four years. Then we reclassified the bottomland hardwood forest habitat type (BHF) to reflect different succession stages of forest growth. Using LIDAR and aerial images we calculated canopy heights and reclassified BHF using those heights as primary BHF, secondary BHF, or early successional bottomlands.

Methylmercury (MeHg) is an environmental contaminant that can have adverse effects on wildlife. Because inorganic Hg is converted to MeHg primarily in aquatic ecosystems, studies of MeHg contamination of food webs have historically focused on aquatic organisms. However, recent studies have found that emergent aquatic insects (e.g. mayflies and dragonflies) can transport MeHg to terrestrial predators like songbirds, and this could have implications for species in decline such as Red-winged blackbirds (Agelaius phoeniceus). Red-winged blackbirds are odonate (dragonflies and damselflies) predators, and odonates can make up 50 – 90% of a Red-winged blackbird’s diet during the breeding season. Red-winged blackbirds have declined throughout their range by 30% over the last 50 years. Their decline is due in part to loss of wetland habitat, but the consumption of MeHg contaminated prey items could also be having an effect. Several studies have reported MeHg contamination of Red-winged blackbirds, and yet, the potential effect of diet on MeHg contamination in Red-winged blackbirds has not been studied. I collected data on blood MeHg level of Red-winged blackbird nestlings and the emergence rate of odonates during the summer of 2017 at the Eagle Mountain Hatchery Experimental Pond Facility in Tarrant County, Texas. I used the ArcGIS Space Time Cube to identify spatiotemporal hot spots of nestling MeHg level and odonate emergence, and I used linear regression models to see how well proximity to odonate emergence hotspots predicted nestling MeHg hotspots.

Cancer is the second leading cause of death and will directly affect approximately 40% of the people in the United States over the course of their life. Chemotherapy has been shown to be an effective therapeutic strategy, but it lacks specificity, resulting in a multitude of negative side effects. Targeted therapies such as Herceptin, Iressa, and Nivolumab have shown increased effectiveness against cancer by attacking specific molecules in the target cell. For example, Herceptin inhibits the HER2 protein, which is overproduced in some breast cancer cells, and stops cell division. Biotin is an innate coenzyme for carbohydrate, lipid and protein metabolism. Certain cancer types overexpress biotin transporters on the surface of each cancer cell in order to increase biotin absorption necessary for metabolic processes. Furthermore, the intracellular environment in cancer cells is more reducing compared to non-cancer cells due to increased metabolism. Ferrocene is an iron-based organometallic molecule that has been shown to generate reactive oxygen species (ROS) in the reducing environment of cancer cells. Given that certain cancer cells absorb biotin with a higher efficiency, we hypothesize that linking biotin to ferrocene will increase the efficiency of ferrocene entering the cell and result in selective cancer cell death. Therefore, we have produced a library of biotin-ferrocene conjugates to selectively target cancer cell lines that over express biotin receptor sites. Experiments were conducted utilizing ferrocene and a variety of ferrocene-biotin conjugates (C1, C2, 2) in both cancer (MCF-7) and noncancer (HEK 293) cell lines in order to compare the relative toxicity between compounds.

Many rainbow trout (Oncorhynchus mykiss) populations exhibit partial migration, where resident and migrant individuals coexist in a single population. Due to anthropogenic, environmental, and population-specific factors, migratory individuals have been decreasing in frequency across the continental United States. Biologically, whether an individual will migrate is determined by both genetic and environmental factors. Although migration in many salmonids is known to be highly heritable, the environment plays an overriding role. Previous studies investigating the genetic basis of migration have failed to control for environmental variance and, consequently, the genes and regions of the genome underlying the development of the migratory phenotype remain unknown. We used data from a common garden experiment to identify single nucleotide polymorphisms (SNPs) significantly associated with migration in the F1 generation of a resident-by-resident and a migrant-by-migrant cross. We genotyped 192 F1 individuals on an Affymetrix SNP chip at 57,501 known polymorphic locations throughout the genome. We identified 5002 significant SNPs in the migrant-by-migrant family and 429 significant SNPs in the resident-by-resident family, using an FDR-corrected p-value of 0.01. For the migrant cross, we located significant markers associated with 28 genes whose functions are connected to pathways previously hypothesized to be important in migration. Five genes on three chromosomes were associated with migration in both familial crosses, suggesting that these regions are important in determining life history regardless of familial origin in this population. These data will be further used to develop a model to predict life history in individuals that are yet to make that determination. Understanding the genetic factors involved in the decision to migrate, through the identification of polymorphisms associated with migration, will assist fisheries managers in restoring and maintaining migratory rainbow trout populations.

The Texas horned lizard (Phrynosoma cornutum) has always been believed to be an ant specialist, especially on harvester ants. However, a population of horned lizards in south Texas seem to have a more diverse diet consisting of other insects and arachnids. The goal of this project is to build a DNA library of order Coleoptera (beetles) that are preyed upon by these horned lizards. This DNA library will be compared to DNA extracted from horned lizard scat so that we can identify which species of beetles these lizards are eating. For this process, I isolated DNA from 244 beetles collected in pit fall traps from Kenedy and Karnes City, amplified the cytochrome oxidase I (COI) gene, and sequenced it. I compared the processed sequences to those available on GenBank and BOLD (Barcode of Life Database) to identify the species of beetle.

Oxidative stress in the brain is a known contributor to the development of neurodegenerative diseases, including Alzheimer’s. The focus of this project is to target the amyloid-β plaque formations and reactive oxygen species (ROS) derived from mis-regulated metal-ions that lead to disease-causing oxidative stress. The present investigation measures both the antioxidant reactivity and metal chelating ability of 1,4,11,13-tetra-aza-bis(2,6-pyridinophane)-8,17-ol (L4).  L4 contains two radical scavenging pyridol groups along with a metal-binding nitrogen rich ligand system.  It was hypothesized that increasing the number of pyridol groups on the ligands in our small molecule library would increase the radical scavenging activity, which in turn may provide cells protection from oxidative stress.  The radical scavenging ability of L4 was quantified using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. This was compared to other radical scavenging small molecules to evaluate the effect of the additional radical scavenging group on the antioxidant activity.  The interaction of L4 with redox active metal-ions such as copper(II) was also evaluated using the coumarin-3-carboxylic acid (CCA) assay to show the molecule’s ability to target mis-regulated metal-ions in diseased tissues. With the end goal being to develop a potential biological therapeutic agent, metabolic stability studies were also performed.

The combination of inorganic porous silicon (pSi) and flexible biocompatible polymers has been shown to yield more beneficial hybrid scaffolds for tissue engineering (i.e. use of synthetic materials to facilitate healing). PSi has a variety of tunable properties, including pore size, pore volume and non-toxic degradation. The addition of a biocompatible polymer such as polycaprolactone (PCL) can provide control over shape and serve as an additional drug delivery component.
In this work, composite materials consisting of oxidized porous silicon (ox-pSi) with a particle size of ~ 30 μm and pore size of 40-100 nm and PCL porous fibers. Porous fibers were fabricated using an electrospinning method into sheets of desired thickness (0.1-0.4 mm), fiber diameter 3-4 μm, and fiber pore size 300-500 nm. Ox-pSi particles previously loaded with the anticancer drug-camptothecin (CPT) were placed between two sheets (6 mm in diameter each) and sealed at the edges, resulting in ~65% loading of ox-pSi. Drug release from the ox-pSi particles alone and ox-pSi/porous PCL fiber composites was monitored fluorometrically in phosphate buffered saline (PBS), showing a distinct release profile for each material.
Ox-pSi/p-PCL fiber composites release a CPT payload in accordance with the Higuchi release model and showed a significant decrease in burst effect compared to ox-pSi particles only. In addition, composite evolution after 5 weeks in PBS at 37 oC was examined using gravimetry, differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FESEM). Overall weight loss of the composites was about 50%, mainly attributed to pSi particles dissolution and some polymer hydrolysis. Preliminary DSC results show that high surface area porous PCL fibers are less crystalline compared to solid PCL fibers, suggesting a faster hydrolysis route.

Europium contrast agents have been extensively investigated as an alternative to typical Gd3+ species for imaging. This is due to the dual imaging modalities which can accessed dependent on the oxidation state of the europium metal center (T1 or PARACEST). To achieve these functionalities, the europium containing complex must be stable enough to support both oxidation states (+3 and +2). In collaboration with UTSW, an electrochemical investigation was completed to understand the effects of the ligand environment on the metal center as a direct result of glycine modification to the ligand scaffold, DOTA. Increasing amide functionalities in close proximity to the europium core result in a positive shift in the potential in comparison to the acetate arms associated with DOTA. Furthermore, the addition of the glycine moiety to the pendant arms results in redox activity of the ligand itself, making the ligand non-innocent in nature. Additionally, a crystal structure of Eu4 (the tetraglycinate DOTA derivative) was obtained and compared to known lanthanide complexes.

Non-conventional solvents, such as room-temperature ionic liquids and deep-eutectic solvents, have attracted a lot of attention in recent years due their diverse applications in various areas of sciences, medicine and engineering. The ability to control physical properties of these solvents by simply adjusting their structure and/or the ratio of the components favorably distinguishes ionic and eutectic solvents from traditionally used molecular solvents as it allows to custom design specific types of media for given applications.

This presentation will highlight our efforts on various aspects of the synthesis of ionic liquids and deep-eutectic solvents as well as it will describe our investigations on the physical properties and nanostructural organization of these liquids using environmental probes, such as those that feature BODIPY and aza-BODIPY motifs. In addition, our initial studies on the design of multiphase systems that utilize ionic, eutectic and molecular solvents will be presented.

Cerium (IV) oxide, or CeO2, nanomaterials have displayed antioxidant and enzyme mimetic activities due to a Ce3+/Ce4+ redox capability enhanced through oxygen vacancies and mobility. Tri-valent, fluorescent ions such as Eu3+ increase the Ce3+/Ce4+ ratio and oxygen vacancy concentration, while contributing fluorescent properties to the nanomaterial. The combination of these attributes make europium doped cerium oxide (EuCeO¬2) nanomaterials appealing candidates for various biological applications.
To complement our earlier efforts on the synthesis and properties of EuCeO2 nanowires, nanorods, and nanocubes, this presentation addresses a new, complementary structure, EuCeO2 nanotubes. The nanotubes are prepared via deposition and subsequent oxidation of Eu-doped Ce(OH)3 to form a EuCeO2 shell on sacrificial ZnO nanowires.
Previous synthetic routes to CeO2 nanotubes have been reported featuring carbon nanotubes as sacrificial templates, the etching of cerium-based nanorods, and other less-common methods . These routes have struggled with clear evidence for distinct nanotube formation, as well as control over nanotube dimensions. Our use of a ZnO core allows for facile manipulation of inner diameter and length of the nanotube following etching of the core.
The synthesized nanotubes were characterized using scanning and transmission microscopy (SEM and TEM) for morphology, energy dispersive x-ray (EDX) for elemental composition, and photoluminescence to track europium fluorescence. Synthesized nanotubes had inner diameters from 40 nm to 200 nm, based on the ZnO core. Following synthesis and characterization, the nanotubes will be tested for use as a drug delivery vector, using ibuprofen as a model.

This project is aimed to modify a leucyl-tRNA synthetase (LeuRS) to incorporate fluorescent amino acids into proteins to produce fluorescent proteins in living cells. Fluorescent proteins are useful because they are easily analyzed and tracked in living organisms. In a small scale, we successfully prepared the library of LeuRS variants in which five amino acids are randomized in the leucine-binding site of a functional LeuRS without its editing domain. Currently, we are working on a large scale production of viable bacterial cells that cover the whole diversity of library (at least 34 million different LeuRS molecules). Initially, we attempted two-step process in which an N-terminal library fragment (for two randomized amino acids) is generated first and a C-terminal fragment (for three randomized amino acids) is added later. However, this two-step cloning process did not produce enough viable cells to cover all the possible variants. In a new approach, a complete library of LeuRS will be produced by overlapping extension PCR and introduced to E. coli in a single step to ensure highest possible transformation efficiency. Consequently, the library of LeuRS variants will be subject to a genetic selection experiment to obtain LeuRS variants that incorporate only fluorescent amino acids into proteins.

Diffusiophoresis is the migration of a relatively large particle (e.g., protein, polymer, nanoparticle) induced by a gradient of salt concentration. The salt-induced diffusiophoresis of lysozyme, a model protein, at pH 4.5 and 25 °C was examined as a function of salt concentration for three chloride salts: NaCl, KCl and MgCl2. Diffusiophoresis coefficients were theoretically extracted from experimental multicomponent diffusion data by applying irreversible thermodynamics. A selected mass-transfer process was theoretically examined to show that concentration gradients of MgCl2 produce significant lysozyme diffusiophoresis. The dependence of lysozyme diffusiophoresis on salt nature was theoretically examined and linked to protein charge. The effect of salt type on hydrogen-ion titration curves was experimentally characterized to understand the role of salt nature on protein charge. Our findings indicate that diffusiophoresis may be exploited for diffusion-based separation of proteins in the presence of salt concentration gradients and for the enhancement of protein adsorption onto solid surfaces relevant to biosensing applications.

The randomization of 11 bases in the theophylline-binding domain generated a library containing millions of different theophylline riboswitch variants. The dual genetic selection of this molecular library successfully led to the identification of a caffeine-specific synthetic riboswitch. When a chloramphenicol-resistance gene was expressed under control of this caffeine riboswitch, E. coli cells showed chloramphenicol resistance only in the presence of caffeine. For a colorimetric or fluorescence assay, the caffeine riboswitch gene was inserted upstream of the B-galactosidase (LacZ) or green fluorescence protein (GFP) gene, respectively. When tested with various concentrations of caffeine, the enzymatic activity of LacZ or the fluorescence intensity of GFP was proportional to the amount of caffeine, clearly indicating the caffeine-dependent gene regulation by the caffeine riboswitch. The caffeine synthetic riboswitch can be further developed as a biosensor to detect caffeine in complex biological samples such as urine and blood.

Abacavir or Ziagen, is an antiretroviral medicine that is used in conjunction with other
medicines to treat HIV. Although it is not a cure, it has been clinically proven to be
effective in diminishing the rate of HIV replication. The synthetic process of creating
Abacavir is both timely and costly, so therefore a new synthetic process has been
created to generate a chemical analog (specifically a triazine derivative) that is cheaper
to produce that can be if not potentially more chemically effective than Abacavir. Once
the analog is produced, a series of analytical tests will be done on a micro organismic
level to determine if the analog is both effective and safe enough to be used in human
clinical studies further down the road.

The pyrrolophenanthridone alkaloid pratosine is a natural product related to hippadine, which is known to be a powerful but reversible inhibitor of spermatogenesis in rats. Hippadine has also shown cardiovascular as well as anticancer activity. Given the structural similarities between the two molecules, it is expected that pratosine and hippadine will demonstrate similar biological effects. Our work toward a laboratory synthesis of pratosine will facilitate large-scale production thus affording sufficient quantities of the material for a complete pharmacological study of its properties. Although we have a synthetic plan for preparing pratosine, several reactions have failed due to solubility problems. This research focuses on solving these problems by using an alternate starting material. The commercially available compound vanillin, which is extracted from vanilla beans, is a simple and inexpensive aldehyde with an appropriate structure for attaching other groups that should improve the solubility properties of several of the synthetic intermediates. Our goal is to find a specific substituent that will provide the required characteristics but which can also be removed later to generate the final product.

Porous silicon (pSi) is a unique nanostructured form of the elemental semiconductor Si. Due to its useful properties governed by its surface chemistry and porous morphology, pSi has been studied in the last few decades in diverse fields extending from electronic device technology to bio-relevant applications.1 Recently, one-dimensional porous nanotubes based on elemental Si (pSiNTs) with a tunable structure (sidewalls, inner void space and lengths) have been successfully synthesized.2 The well-defined structure of pSiNTs offers ample opportunities to study newly emerging properties of this material and innovative applications in multiple areas. For example, recent reports have revealed the use of SiNTs as an efficient template for loading superparamagnetic nanoparticles (Fe3O4), lithium storage and cycling, as well as acting as a template for formation of organometal perovskite nanostructures.3-5
Platinum (Pt) nanoparticles, both free-standing as well as anchored on various surfaces, have attracted widespread attention in nanocatalysis, electronics, and chemotherapeutics.6 In this work, it is suggested that pSiNTs after being functionalized with 3-(aminopropyl)triethoxysilane (APTES) can serve as a platform for Pt nanocrystal (Pt NC) formation. Particularly, incubation of APTES-functionalized SiNTs in potassium tetrachloroplatinate (II) (K2PtCl4) solution under ambient conditions subsequently yields Pt nanoclusters with sizes ranging from 1-3 nm on SiNTs. From high-resolution transmission electron microscopy (HRTEM), nanocrystals with characteristic lattice spacings associated with Pt (d = 0.21 nm) are observed on the nanotubes. The amount of Pt deposited on SiNTs can be sensitively tuned from 20-60 wt% (characterized by TEM Energy Dispersive X-ray Analysis, EDX) by varying concentration of K2PtCl4 and immersion time in this Pt salt precursor.
These findings suggest a new approach to prepare Pt NCs that are of potential benefit to a broad number of applications by using pSiNTs as a template. Further investigations into the properties of the newly discovered Pt NCs-SiNT composites are imperative to evaluate useful applications of this material.
REFERENCES
[1] Porous Silicon for Biomedical Applications, H. Santos, Ed. Cambridge: Woodhead Publishing, 2014.
[2] X. Huang, R. Gonzalez-Rodriguez, R. Rich, Z. Gryczynski, J.L. Coffer, Chem. Commun., 2013, 49, 5760-5762.
[3] P. Granitzer, K. Rumpf, R. Gonzalez, J. Coffer, M. Reissner, Nanoscale Res. Lett. 2014, 9, 413.
[4] R. Gonzalez-Rodriguez, N. Arad-Vosk, N. Rozenfeld, A. Sa'ar, J. L. Coffer, Small, 2016, 12, 4477-4480.
[5] A. T. Tesfaye, R. Gonzalez, J. L. Coffer, T. Djenizian, ACS Appl. Mater. Interfaces, 2015, 7, 20495-20498.
[6] A. Chen, and P. Holt-Hindle, Chem. Rev., 2010, 110, 3767-3804.

Urea is a low-cost, water-soluble fertilizer that is used as the major source of nitrogen in agricultural production. However, the problem with leaching, in which urea in soil is rapidly washed away through rain and irrigation, results in inefficiency in nutrient absorption, low crop yield, poor harvest, and economic failure for farmers (Broadbent 1958), as well as the environmental pollution of groundwater by the release of excessive amounts of nitrate, which adversely affects this non-rechargeable water source. Therefore, recent research attempts to design a suitable system to prolong the release of urea from water in soil to improve soil fertility, agricultural economy, and ground water protection. A prospective approach is to integrate urea into a stable matrix that releases the desired material with an optimal time window.

Porous Silicon (pSi) has been studied as the material of diverse interest, due to its surface chemistry and porous morphology that has promoted many nanotechnology advances, in conjunction with its biocompatibility and biodegradability (Canham 2014). Since pSi degrades slowly in aqueous media and does not react with the soil component, it is selected to be a possible matrix for sustaining urea release. pSi is believed to interact with urea via hydrogen bonds (via surface silanol species), and thus its porous structure is the key to trap urea particles for relatively long periods in water, while exposing the fertilizer to plants. This bioactive pSi material is produced from the eco-friendly Tabasheer-derived silica, during which pSi porosity is maintained (Kalluri et al. 2016). Loading of urea into pSi is carried out using ethanol as a solvent, with theoretical loadings ranging from 27-33% of the composite mass. Release kinetics of urea from water is currently being investigated using highly sensitive colorimetric assay that applies Jung’s method (Jung et al. 1975).

The urea-loaded pSi prepared in these experiments were characterized using several different techniques. X-ray diffraction (XRD) evaluates the crystallinity of pSi after fabrication, with the presence of three peaks consistent with a cubic unit cell structure [Si (111), (220), and (311)]. Thermal gravimetric analysis (TGA) gives the mass loss percentage between melting (132oC) and boiling (203oC) points of urea, which represents the practical loading of urea in a given sample. The results deviate 1-2% from the theoretical loading percentage. TGA also shows the stability of the composite over two months at room temperature, with the recent loading measurement analyses consistent with the previous ones. Differential scanning calorimetry (DSC) analysis confirms that the urea is incorporated in the pSi matrix. Loading and characterization studies were conducted in triplicate to ensure reproducibility of results.