Pesticide Nanoformulations Based on Sunlight-Activated Controlled Release of Abamectin.

A controlled release system that enables the sunlight-triggered release of a model agrochemical, abamectin (abm), is presented. The release system consists of polydopamine functionalized halloysite nanotubes (HNT-PDA) utilized as photothermal nanocarriers to encapsulate 25 wt % abm and 37 wt % lauric acid (LA), a phase change material, that acts as a heat-activable gatekeeper stopping or facilitating the abm release. When exposed to sunlight for 20 min at 1 and 3 sun light density, the temperature of the photothermal nanocarriers reaches 51 and 122 °C, respectively, which triggers the melting of LA and the consequent release of abm from the nanocarriers. Abm was shown to be released gradually over a period of 10 days when nanohybrids were exposed to sunlight for 6 h per day and to remain stable and kill Myzus persicae (Sulzer) (Hemiptera: Aphididae), green peach aphids, at a mortality rate of over 70% for at least 10 days. Aqueous dispersions of the LA/abm@HNT-PDA nanohybrids were studied in terms of their potential as aqueous sprayable pesticide nanoformulations and presented over 30% suspensibility, 36 mg/cm2 foliar retention, strong rainwater resistance, and a 50% mortality rate for M. persicae at a concentration of 9 mg/mL. The proposed sunlight-activated controlled release system based on photothermal, LA-functionalized HNT-PDA nanocarriers holds great potential as controlled release pesticide nanoformulations.

Indocyanine Green-Loaded Halloysite Nanotubes as Photothermal Agents.

Photothermal nanoparticles with light-to-heat conversion properties have gained interest in recent years and have been used in a variety of applications. Herein, indocyanine green (ICG), which is commonly employed as a photothermal agent suffering from low photostability, was loaded into halloysite nanotubes (HNTs) resulting in photothermal HNT-ICG nanohybrids. The photothermal heating patterns of the prepared photothermal nanohybrids as a result of near-infrared (NIR) irradiation were carefully examined. The nanohybrids reached a temperature of 216 °C in 2 min under NIR light, and in contrast to free NIR, the ICG loaded into HNTs remained stable over 10 heating and cooling cycles. Moreover, HNT-ICG nanohybrids incorporated into polyacrylonitrile (PAN) were electrospun into nanofibers for use as photothermal nanofibers, and composite nanofibers, which heat up to 79.3 °C under 2 min of NIR irradiation, were obtained. To demonstrate the potential of the PAN/HNT-ICG nanofibers as light-activated antibacterial nanofibers, their NIR light-activated killing activity on Staphylococcus aureus (S. aureus) cells has been explored. The composite nanofibers reduced the number of bacteria on their surface by 7log upon 10 min of NIR irradiation. Encapsulation of ICG in HNTs as a carrier has been demonstrated as an effective way to stabilize ICG and incorporate it into materials and coatings without compromising its functionality.

Carbon nanotube/waterborne polyurethane nanocomposites with light-to-heat conversion properties.

Photothermal materials and coatings which can create temperature elevations under light irradiation can be utilized in various applications requiring remote heating. Here, multiwalled carbon nanotubes (MWNT) were incorporated into waterborne polyurethane (PU) to obtain photothermal coatings with light-to-heat conversion properties. Resulting PU-MWNT coatings were demonstrated to heat up to 80 °C under sunlight irradiation at 2 sunlight density for 18 min. Pseudomonas aeruginosa (P. aeruginosa) cells attached to surfaces coated with PU-MWNT nanocomposites were killed upon near infrared (NIR) light irradiation at 808 nm for 15 min, whereas the same cells attached to control neat PU-coated surfaces remained alive under the same irradiation conditions. Furthermore, a scratch of 1 cm width on the PU-MWNT coating was shown to be healed under 12 min of sunlight irradiation. The PU-MWNT nanocomposites have strong potential as photothermal coatings, which can be remotely heated with NIR light activation.

High-yield production of active recombinant S. simulans lysostaphin expressed in E. coli in a laboratory bioreactor.

Staphylococcus aureus (S. aureus), which has developed multidrug resistance, leads to many healthcare-associated infections resulting in significant medical and economic losses. Therefore, the development of new efficient strategies to deal with these bacteria has been gaining importance. Lysostaphin is a peptidoglycan hydrolase that has considerable potential as a bacteriocin. However, there have been few reported optimization and scale-up studies of the lysostaphin bioproduction process. Our preliminary results have revealed that the composition of auto-induction media at 30 °C increases the produced lysostaphin around 10-fold in shake flasks. In this study, achieving higher yields for recombinant lysostaphin in E. coli at a laboratory scale has been the aim, through the use of auto-induction media. Optimized medium composition and fermentation parameters were transferred to a laboratory-scale bioreactor. The tested conditions improved protein yields up to 184 mg/L in a 3 L stirred bioreactor and the productivity was improved 2-fold in comparison to previously published reports. Furthermore, this study also showed that lysostaphin is an effective bacteriocin on both commercially available and isolated S. aureus strains. These results will contribute to future larger-scale production of lysostaphin via the proposed fermentation conditions.

Purification and Sorting of Halloysite Nanotubes into Homogeneous, Agglomeration-Free Fractions by Polydopamine Functionalization.

Halloysite nanotubes (HNTs) have attracted great attention in the field of nanotechnology as natural, high value-added nanomaterials. Despite their significant potential as carriers of active agents and fillers in nanocomposite structures, inhomogeneity of HNTs in terms of length and diameter along with their agglomeration tendency poses important obstacles for the utilization of them in a wider range of applications. Here, a facile, three-step separation protocol that allows the sorting of HNTs into agglomeration-free, uniform size fractions is reported. The protocol consists of coating of HNTs with polydopamine to impart hydrophilicity and aqueous dispersibility, followed by their ultrasonication and centrifugation at varying velocities for size-based separation. Particle size distribution analysis by scanning electron microscopy and dynamic light scattering has demonstrated that the separation protocol resulted in uniform HNT fractions of varying agglomeration states and particle sizes. The highest quality fraction obtained with 18% yield was free of agglomerations and consisted of HNTs of uniform lengths and diameters. The polydopamine coating on HNTs which facilitated the separation was demonstrated to be removed by a simple heat treatment that preserved the crystal structure of HNTs. The impact of the separation protocol on the loading and functionalization capacity of halloysites was investigated. Highest quality HNTs presented 4.1-fold increase in lumen loading and 1.9-fold increase in covalent surface coupling ratios compared to the loading and functionalization ratios obtained with raw HNTs. Similarly, sorted, high-quality HNTs were demonstrated to be better dispersed in a polymeric matrix, resulting in polymeric nanocomposites with significantly enhanced mechanical properties compared to nanocomposites prepared with raw HNTs. The three-step separation protocol presented here provides a toolbox that allows sorting of raw HNTs into uniform fractions of different size ranges, from which HNTs of desired qualities required by different applications can be selected.

Enhanced production of recombinant Staphylococcus simulans lysostaphin using medium engineering.

Staphylococcus aureus, among other staphylococcal species, developed multidrug resistance and causes serious health risks that require complex treatments. Therefore, the development of novel and effective strategies to combat these bacteria has been gaining importance. Since Staphylococcus simulans lysostaphin is a peptidoglycan hydrolase effective against staphylococcal species, the enzyme has a significant potential for biotechnological applications. Despite promising results of lysostaphin as a bacteriocin capable of killing staphylococcal pathogens, it is still not widely used in healthcare settings due to its high production cost. In this study, medium engineering techniques were applied to improve the expression yield of recombinant lysostaphin in E. coli. A new effective inducible araBAD promoter system and different mediums were used to enhance lysostaphin production. Our results showed that the composition of autoinduction media enhanced the amount of lysostaphin production 5-fold with the highest level of active lysostaphin at 30 °C. The production cost of 1000 U of lysostaphin was determined as 4-fold lower than the previously proposed technologies. Therefore, the currently developed bench scale study has a great potential as a large-scale fermentation procedure to produce lysostaphin efficiently.

DNA Directed Self-Assembly of Single Walled Carbon Nanotubes into Three-Way Junction Nanostructures.

Utilization of a self-assembled two-dimensional DNA nanostructure to arrange single-walled carbon nanotubes (SWNTs) into predetermined structures at controllable angles is presented. A specially designed DNA three-way junction (3WJ) composed of three double-stranded DNA arms containing single-stranded overhang sequences was prepared by annealing of partially complementary ssDNA sequences and ultrasonicated with SWNTs, resulting in DNA-3WJ/SWNT hybrid nanostructures. Utilization of DNA-3WJ not only allowed the precise dispersion of SWNTs but also acted as a rigid template for the self-assembly of SWNTs into three-armed junctions at an angle of approximately 120° to each other as visualized by scanning electron microscopy and atomic force microscopy. Prepared DNA-3WJ/SWNT nanostructures were also demonstrated to have the appropriate binding sites for fluorophores, providing a simple method for the fluorescent labeling of SWNTs. When ssDNA sequences forming the DNA-3WJ are ultrasonicated with SWNTs, followed by annealing of resulting ssDNA wrapped SWNTs, instead of hybrid junctions composed of three SWNT molecules, a web-like structure composed of interconnected SWNT junctions was obtained. The design approaches demonstrated here provide simple methods for the arrangement of SWNTs into desired nanostructures utilizing pre-assembled DNA nanostructures as linkers in aqueous solution through noncovalent interactions which can greatly contribute to efforts along the controlled assembly of SWNTs.

Carbon nanotube decorated magnetic microspheres as an affinity matrix for biomolecules.

Carbon nanotube (CNT) decorated magnetic microspheres were fabricated to develop a multimodal platform that utilizes non-covalent molecular interactions of CNTs to magnetically separate biomolecules. Hybrid CNT-microspheres prepared by a feasible method reported herein had a well-defined structure as characterized by Raman spectroscopy and scanning electron microscopy. Binding interactions of resulting magnetic CNT-microspheres with DNA oligonucleotides were studied to demonstrate that single stranded DNA (ssDNA) in a solution can be effectively recovered by magnetic CNT-microspheres through strong physical wrapping of DNA around CNTs' walls. The magnetic character of these CNT-microspheres combined with their capability to bind other molecules including DNA allows their use as an affinity matrix that can be utilized in affinity separation of biomolecules, and also as a platform to monitor non-covalent binding interactions of CNTs with other biomolecules. As a proof of concept, we report on the use of these CNT-microspheres in in vitro selection of ssDNA aptamers against carcinoembryonic antigen (CEA), a cancer biomarker, by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). ssDNA aptamer candidates that have strong affinity towards CEA were successfully separated magnetically from a pool of ssDNA (∼1014 molecules). Our results demonstrate that CNT-microspheres can serve as strong tools for affinity separation methodologies and can be utilized for various affinity pairs in solution.

Fluorescent DNA nanotags based on a self-assembled DNA tetrahedron.

Progress in fluorescence detection and imaging technologies depends on the availability of fluorescent labels with strong light absorption/emission characteristics. We have synthesized intercalator dye arrays on a compact 3-dimensional DNA-tetrahedron nanostructure. The template tolerates the structural distortions introduced by intercalation and allows concentration of multiple fluorophores within a small volume, resulting in brightly fluorescent nanotags with effective extinction coefficients in the order of 10(6) M(-1) cm(-1). Efficient energy transfer from intercalated donor dyes to covalently attached acceptor dyes in the nanotags allows the emission wavelength to be shifted to the red relative to the excitation light, providing wavelength tunability. The compact nature of the supramolecular DNA tetrahedron also provides a protective medium for the fluorophores, leading to improved photostability and enhanced resistance to nuclease digestion, relative to one- or two-dimensional nanotags described previously.

A rainbow of fluoromodules: a promiscuous scFv protein binds to and activates a diverse set of fluorogenic cyanine dyes.

Combined magnetic and fluorescence cell sorting were used to select Fluorogen Activating Proteins (FAPs) from a yeast surface-displayed library for binding to the fluorogenic cyanine dye Dimethyl Indole Red (DIR). Several FAPs were selected that bind to the dye with low nanomolar Kd values and enhance fluorescence more than 100-fold. One of these FAPs also exhibits considerable promiscuity, binding with high affinity to several other fluorogenic cyanine dyes with emission wavelengths covering most of the visible and near-IR regions of the spectrum. This significantly expands the number and wavelength range of scFv-based fluoromodules.