Abstract We investigate the effect of bis(imino)pyridine (BIP) ligands in guiding self-assembly of semiconducting CdSe/ZnS quantum dots (QDs) into three-dimensional multi-layered shells with diameters spanning the entire mesoscopic range, from 200 nm to 2 μm. The assembly process is directed by guest–host interactions between the BIP ligands and a thermotropic liquid crystal (LC), with the latter’s phase transition driving the process. Characterization of the shell structures, through scanning electron microscopy and dynamic light scattering, demonstrates that the average shell diameter depends on the BIP structure, and that changing one functional group in the chemical scaffold allows systematic tuning of shell sizes across the entire range. Differential scanning calorimetry confirms a relationship between shell sizes and the thermodynamic perturbation of the BIP molecules to the LC phase transition temperature, allowing analytical modeling of shell assembly energetics. This novel mechanism to controllably tune shell sizes over the entire mesoscale via one standard protocol is a significant development for research on in situ cargo/drug delivery platforms using nano-assembled structures.
We investigate the effect of surface modification of CdSe/ZnS quantum dots (QDs) with bis(imino)pyridine (BIP) ligands. BIPs are a class of redox noninnocent ligands known to facilitate charge transfer in base metals on the molecular scale, but their behavior in nano- to mesoscale systems has been largely unexplored. Using electron microscopy, crystallography, and ultrafast spectroscopy, we reveal that structure-specific π–π stacking of the BIP molecules alters interdot separation in QD films, thereby leading to changes in optical and electronic properties. The three variations used are unsubstituted (BIP-H), dimethyl (BIP-Me), and diisopropyl (BIP-Ipr) BIP, and when compared with the native octadecylamine ligand, we find that both energy and charge transfer efficiencies between QDs are increased postligand exchange, the highest achieved through BIP-Ipr despite its larger unit cell volume. We further investigate charge transfer from QD films to conducting (indium tin oxide, ITO) and semiconducting (zinc oxide, ZnO) substrates using time-resolved spectroscopy and determine that the influence of the ligands is QD band gap-dependent. In QDs with a large band gap (2.3 eV), the BIP ligands facilitate charge transfer to both ITO and ZnO substrates, but in dots with a small band gap (1.9 eV), they pose a hindrance when ZnO is used, resulting in reduced recombination rates. These results highlight the importance of investigating multiple avenues in order to optimize surface modification of QDs based on the end goal. Finally, we verify that BIP ligands hasten the rate of QD photobrightening under continuous illumination, allowing the ensemble to achieve stable emission faster than in their native configuration. Our study sets the stage for novel charge transfer systems in the meso- and nanoscale, yielding a diverse selection of new surface ligands for applications such as conductive materials and energy production/storage devices employing QDs.
Hybrid chestnut (Castanea dentata × C. mollissima) has the potential to provide a valuable agroforestry crop on formerly coal mined landscapes. However, the soil interactions of mycorrhizal fungi and buried metals associated with mining are not known. This study examined soil, plant tissue, and ectomycorrhizal (ECM) root colonization on eight-year-old hybrid (BC 1 F 3 and BC 2 F 3 ) and American chestnuts on a reclaimed coal mine in Ohio, USA. Chestnut trees were measured and ECM colonization on roots was quantified. Leaves, flowers, and soil were analyzed for heavy metals. Differences were not detected among tree types regarding metal accumulation in plant tissue or ECM colonization. BC 2 F 3 hybrids had greater survival and less cankers than American chestnuts (P= 0.006 and <0.0001). Taller trees were associated with greater ECM root colonization and correlated with an increase in Al uptake (P= 0.02 and 0.01). When comparing tissue, manganese and aluminum were in higher concentrations in leaves than flowers, where copper and selenium were significantly higher in floral tissue (P< 0.05). All trees were flowering at this time meriting further examination in nut tissue. Block effects for selenium and zinc indicate the variability in reclaimed soils requiring further monitoring for possible elemental transfer to nut and wood tissue.
Titanium dioxide (TiO2) is commonly used for photocatalytic decomposition of organic contaminants for the purpose of water purification. One promising method to enhance TiO2 photocatalysis is the incorporation of surface plasmon resonance on its surface where photocatalytic reactions take place. Herein, a novel methodology using plasmonically tuned aluminum nanostructures to enhance the rate of photodecomposition of aqueous methyl orange is demonstrated. These nanostructures are tuned to the TiO2 band gap in the UV regime and patterned on TiO2-coated substrates using nanosphere lithography. Compared to a blank TiO2 film, the plasmonics is found to enhance the initial TiO2 photocatalytic rate by up to 10 times, and further enhancement is possible upon refinement of the plasmonic technology.
The Appalachian Regional Reforestation Initiative outlines planting methods that include preparation of a deep-rooting zone for healthy tree establishment (> 1.3 m deep).Continued monitoring may show that soil-ripping has pronounced effects in later years.However, little is known about the interactions of reclamation methods, buried metals, and micronutrients in soils on reclaimed coal mined sites.This study examined soil samples and plant tissue in eight-year-old pure American (Castanea dentata) and hybrid chestnuts BC1F3, and BC2F3 (C.dentata × C. mollissima) on a reclaimed coal mine site located in Dresden, Ohio under various treatments: 1) untreated control plots, 2) plots plowed and disked to 30 cm depth, 3) plots deep-ripped to 1 m depth, and 4) a combination of ripped and plowed/disked.Soil samples were collected in triplicate from all four treatments (n=3).Leaves were collected from a randomly selected subset of 108 trees (n=9).Flowers were collected from this subset (22 individuals), representing all treatments.Soil, leaves, and floral tissue were analyzed for silver (Ag), aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) using inductively coupled plasma-mass spectrometry.No differences were detected when metal concentrations in soil, foliage, and floral tissue were compared among soil preparation treatments and chestnut tree types.Soil concentrations of Cu, Mn, and Se were detected at higher levels than county averages.Differences were noted when metal concentrations in soil were compared to chestnut leaves and chestnut floral tissue (P < 0.05).Elements including As and Cd were detected in soils but not found in tree tissue, indicating no potential transfer into the food chain.However, Se and Cu concentrations in chestnut floral tissue were significantly higher when compared to foliage (P = 0.004 and < 0.0001), which merits monitoring focused on metal concentrations in developing chestnut seeds.
New tools are needed to enable rapid detection, identification, and reporting of infectious viral and microbial pathogens in a wide variety of point-of-care applications that impact human and animal health. We report the design, construction, and characterization of a platform for multiplexed analysis of disease-specific DNA sequences that utilizes a smartphone camera as the sensor in conjunction with a hand-held "cradle" that interfaces the phone with a silicon-based microfluidic chip embedded within a credit-card-sized cartridge. Utilizing specific nucleic acid sequences for four equine respiratory pathogens as representative examples, we demonstrated the ability of the system to utilize a single 15 μL droplet of test sample to perform selective positive/negative determination of target sequences, including integrated experimental controls, in approximately 30 min. Our approach utilizes loop-mediated isothermal amplification (LAMP) reagents predeposited into distinct lanes of the microfluidic chip, which when exposed to target nucleic acid sequences from the test sample, generates fluorescent products that when excited by appropriately selected light emitting diodes (LEDs), are visualized and automatically analyzed by a software application running on the smartphone microprocessor. The system achieves detection limits comparable to those obtained by laboratory-based methods and instruments. Assay information is combined with the information from the cartridge and the patient to populate a cloud-based database for epidemiological reporting of test results.
New tools are needed to enable rapid detection, identification, and reporting of infectious viral and microbial pathogens in a wide variety of point-of-care applications that impact human and animal health. We report the design, construction, and characterization of a platform for multiplexed analysis of disease-specific DNA sequences that utilizes a smartphone camera as the sensor in conjunction with a handheld instrument that interfaces the phone with a silicon-based microfluidic chip. Utilizing specific nucleic acid sequences for four equine respiratory pathogens as representative examples, we demonstrated the ability of the system to use a single 15-μL droplet of test sample to perform selective positive/negative determination of target sequences, including integrated experimental controls, in approximately 30 minutes. The system achieves detection limits comparable to those obtained by laboratory-based methods and instruments.
