Toward Development of Fluorescence-Quenching-Based Biosensors for Drought Stress in Plants.

Abscisic acid (ABA) is a drought stress signaling molecule, and simple methods for detecting its levels could benefit agriculture. Here, we present proof-of-concept detection for ABA in aqueous solutions by the use of a mixture of Cyanine 5.5 (Cy5.5) fluorophore- and BHQ3 quencher-conjugated endogenous ABA receptor pyrabactin resistance 1 like proteins (PYL3). These dye-conjugated PYL3 protein form dimers in solutions without ABA and monomerize upon ABA binding. When they are in dimers, fluorescence of Cy5.5 is either nearly completely quenched by the BHQ3 or 20% quenched by another Cy5.5. Consequently, mixtures of equal amounts of the two protein conjugates were used to detect ABA in aqueous solution. As the ABA concentration increased from <1 µM to 1 mM, the intensity of fluorescence detected at around 680 nm from the mixture was more than doubled as a result of ABA-induced monomerization, which leads to halt of quenching and recovery of fluorescence of Cy5.5 in monomers. Kinetic modeling was used to simulate the fluorescence response from the mixture and the results generally agree with the experimentally observed trend. This work demonstrates that fluorescence measurements of a single dissociation reaction in one spectral region are adequate to assess the ABA concentration of a solution.

Sealable Spherical Mesoporous Silica Shell Nanoreactors as Fiducial Nanoscale Probes for X-rays.

Molecular reactions in aqueous solutions are often used as dosimetric probes. A major problem with this approach is that other species such as nanoparticles or radical scavenging chemicals can often interfere with these reactions. The results measured in the presence of nanomaterials and scavengers therefore cannot correctly indicate the true dose based on the calibrated results obtained in solutions free of the interfering species. Storing these molecular probes in nanoreactors can overcome this problem. Here we demonstrate for the first time that it is possible to place common probe molecules inside spherical mesoporous silica shells and seal the pores after impregnation for the purpose of using the so-formed nanoreactors as X-ray dose probes. The reactions are isolated from the external environment, while the sealed shells still allow X-rays to freely penetrate through the walls of the nanoreactors. These nanoreactor probes can therefore fiducially report the dose of X-rays, whether the nanoreactors are in solutions, in dry form, or in the presence of scavengers and catalysts in solution.

Electron Paramagnetic Resonance Spectroscopy Investigation of Radical Production by Gold Nanoparticles in Aqueous Solutions Under X-ray Irradiation.

Nanomaterials can enhance the effect of X-rays, but the mechanisms of enhancement can be complicated. Electron paramagnetic resonance (EPR) was used here to shed light on enhancement mechanisms by detecting the originally proposed physical enhancement of the effect of X-rays by as-made large gold nanoparticles. Specifically spin trap reagent 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) was used to trap radicals produced in aqueous solutions under X-ray irradiation. Even though only BMPO hydroxyl adducts were detected at the time of EPR measurement, both hydroxyl and superoxide radicals were found to contribute to the enhancement. The measured total enhancement was 0.7-fold per weight percent (wp) of Au in water using unfiltered X-rays. The theoretically predicted physical enhancement is 0.49 fold per wp of gold in water. This information, together with scavenging experimental results and the fact that the G-values are close for both radicals, suggest that hydroxyl and superoxide radicals contributing almost equally to the total measured enhancement. Further, the enhancement was found to be linearly dependent on the amount of large gold nanoparticles in water and no additional radical was produced beyond the amount predicted by type 1 physical enhancement, indicating that hydroxyl or superoxide radicals were not produced via catalytic pathways.

Chemical enhancement by nanomaterials under X-ray irradiation.

We report here a new phenomenon of dynamic enhancement of chemical reactions by nanomaterials under hard X-ray irradiation. The nanomaterials were gold and platinum nanoparticles, and the chemical reaction employed was the hydroxylation of coumarin carboxylic acid. The reaction yield was enhanced 2000 times over that predicted on the basis of the absorption of X-rays only by the nanoparticles, and the enhancement was found for the first time to depend on the X-ray dose rate. The maximum turnover frequency was measured at 1 × 10(-4) s(-1) Gy(-1). We call this process chemical enhancement, which is defined as the increased yield of a chemical reaction due to the chemical properties of the added materials. The chemical enhancement described here is believed to be ubiquitous and may significantly alter the outcome of chemical reactions under X-ray irradiation with the assistance of nanomaterials.

Persistence of silver nanoparticles in the rat lung: Influence of dose, size, and chemical composition.

Increasing silver nanoparticle (AgNP) use in sprays, consumer products, and medical devices has raised concerns about potential health effects. While previous studies have investigated AgNPs, most were limited to a single particle size or surface coating. In this study, we investigated the effect of size, surface coating, and dose on the persistence of silver in the lung following exposure to AgNP. Adult male rats were intratracheally instilled with four different AgNPs: 20 or 110 nm in size and coated with either citrate or polyvinylpyrrolidone (PVP) at 0.5 or 1.0 mg/kg doses. Silver retention was assessed in the lung at 1, 7, and 21 d post exposure. ICP-MS quantification demonstrated that citrate-coated AgNPs persisted in the lung to 21 d with retention greater than 90%, while PVP-coated AgNP had less than 30% retention. Localization of silver in lung tissue at 1 d post exposure demonstrated decreased silver in proximal airways exposed to 110 nm particles compared with 20 nm AgNPs. In terminal bronchioles 1 d post exposure, silver was localized to surface epithelium but was more prominent in the basement membrane at 7 d. Silver positive macrophages in bronchoalveolar lavage fluid decreased more quickly after exposure to particles coated with PVP. We conclude that PVP-coated AgNPs had less retention in the lung tissue over time and larger particles were more rapidly cleared from large airways than smaller particles. The 20 nm citrate particles showed the greatest effect, increasing lung macrophages even 21 d after exposure, and resulted in the greatest silver retention in lung tissue.

Influence of particle size on persistence and clearance of aerosolized silver nanoparticles in the rat lung.

The growing use of silver nanoparticles (AgNPs) in consumer products raises concerns about potential health effects. This study investigated the persistence and clearance of 2 different size AgNPs (20 and 110 nm) delivered to rats by single nose-only aerosol exposures (6 h) of 7.2 and 5.4 mg/m(3), respectively. Rat lung tissue was assessed for silver accumulations using inductively-coupled plasma mass spectrometry (ICP-MS), autometallography, and enhanced dark field microscopy. Involvement of tissue macrophages was assessed by scoring of silver staining in bronchoalveolar lavage fluid (BALF). Silver was abundant in most macrophages at 1 day post-exposure. The group exposed to 20 nm AgNP had the greatest number of silver positive BALF macrophages at 56 days post-exposure. While there was a significant decrease in the amount of silver in lung tissue at 56 days post-exposure compared with 1 day following exposure, at least 33% of the initial delivered dose was still present for both AgNPs. Regardless of particle size, silver was predominantly localized within the terminal bronchial/alveolar duct junction region of the lung associated with extracellular matrix and within epithelial cells. Inhalation of both 20 and 110 nm AgNPs resulted in a persistence of silver in the lung at 56 days post-exposure and local deposition as well as accumulation of silver at the terminal bronchiole alveolar duct junction. Further the smaller particles, 20 nm AgNP, produced a greater silver burden in BALF macrophages as well as greater persistence of silver positive macrophages at later timepoints (21 and 56 days).