Effect of Surface Modification on the Luminescence of Individual Upconversion Nanoparticles.

Lanthanide-doped upconversion nanoparticles (UCNPs) hold promise for single-molecule imaging owing to their excellent photostability and minimal autofluorescence. However, their limited water dispersibility, often from the hydrophobic oleic acid ligand during synthesis, is a challenge. To address this, various surface modification strategies' impact on single-particle upconversion luminescence are studied. UCNPs are made hydrophilic through methods like ligand exchange with dye IR806, HCl or NOBF4 treatment, silica coating (SiO2 or mesoporous mSiO2), and self-assembly with polymer of DSPE-PEG or F127. The studies revealed that UCNPs modified with NOBF4 and DSPE-PEG exhibited notably higher single-particle brightness with minimal quenching (3% and 8%, respectively), followed by SiO2, F127, IR806, mSiO2, and HCl (84% quenching). HCl disrupted UCNPs's crystal lattice, weakening luminescence, while mSiO2 absorbed solvent molecules, causing luminescence quenching. Energy transfer to IR806 also reduced the brightness. Additionally, a prevalence of upconversion red emission over green is observed, with the red-to-green ratio increasing with irradiance. UCNPs coated with DSPE-PEG exhibited the brightest single-particle luminescence in water, retaining 48% of its original emission due to a lower critical micelle concentration and superior water protection. In summary, the investigation provides valuable insights into the role of surface chemistry on UCNPs at the single-particle level.

Squaraine Dye-Sensitized Upconversion with Enhanced Stability and Minimized Aggregation-Caused Quenching.

Upconversion nanoparticles (UCNPs) doped with lanthanides have limited brightness due to their small absorption cross section to light. However, using organic sensitizers can significantly enhance their light absorption ability. Unfortunately, the practical application of organic sensitizers has been hindered by poor stability and aggregation-caused quenching (ACQ). To address these issues, we developed a novel squaraine-based dye, SQ-739, for sensitizing upconversion luminescence (UCL). This dye has a maximum absorption at 739 nm, and shows 1 order of magnitude and 2-fold improved chemical- and photostability, compared to the commonly used cyanine-based dye IR-806, respectively. When SQ-739 is used to sensitize UCNPs, the resulting SQ-739-UCNPs exhibit excellent photostability and reduced ACQ in the presence of polar solvents. Moreover, at the single particle level, the SQ-739-UCNPs exhibit a 97-fold increase in UCL emission compared to bare UCNPs. This squaraine dye-based system represents a new design strategy for developing highly stable and efficient NIR upconversion probes.

Enhancement of single upconversion nanoparticle imaging by topologically segregated core-shell structure with inward energy migration.

Manipulating topological arrangement is a powerful tool for tuning energy migration in natural photosynthetic proteins and artificial polymers. Here, we report an inorganic optical nanosystem composed of NaErF4 and NaYbF4, in which topological arrangement enhanced upconversion luminescence. Three architectures are designed for considerations pertaining to energy migration and energy transfer within nanoparticles: outside-in, inside-out, and local energy transfer. The outside-in architecture produces the maximum upconversion luminescence, around 6-times brighter than that of the inside-out at the single-particle level. Monte Carlo simulation suggests a topology-dependent energy migration favoring the upconversion luminescence of outside-in structure. The optimized outside-in structure shows more than an order of magnitude enhancement of upconversion brightness compared to the conventional core-shell structure at the single-particle level and is used for long-term single-particle tracking in living cells. Our findings enable rational nanoprobe engineering for single-molecule imaging and also reveal counter-intuitive relationships between upconversion nanoparticle structure and optical properties.

Voltage-Driven Flipping of Zwitterionic Artificial Channels in Lipid Bilayers to Rectify Ion Transport.

We developed a voltage-sensitive artificial transmembrane channel by mimicking the dipolar structure of natural alamethicin channel. The artificial channel featured a zwitterionic structure and could undergo voltage-driven flipping in the lipid bilayers. Importantly, this flipping of the channel could lead to their directional alignment in the bilayers and rectifying behavior for ion transport.

Molecular characterization and functional analysis of a glutathione peroxidase gene from Aphelenchoides besseyi (Nematoda: Aphelenchoididae).

Aphelenchoides besseyi, the nematode agent of rice tip white disease, causes huge economic losses in almost all the rice-growing regions of the world. Glutathione peroxidase (GPx), an esophageal glands secretion protein, plays important roles in the parasitism, immune evasion, reproduction and pathogenesis of many plant-parasitic nematodes (PPNs). Therefore, GPx is a promising target for control A. besseyi. Here, the full-length sequence of the GPx gene from A. besseyi (AbGPx1) was cloned using the rapid amplification of cDNA ends method. The full-length 944 bp AbGPx1 sequence, which contains a 678 bp open reading frame, encodes a 225 amino acid protein. The deduced amino acid sequence of the AbGPxl shares highly homologous with other nematode GPxs, and showed the closest evolutionary relationship with DrGPx. In situ hybridization showed that AbGPx1 was constitutively expressed in the esophageal glands of A. besseyi, suggesting its potential roles in parasitism and reproduction. RNA interference (RNAi) was used to assess the functions of the AbGPx1 gene, and quantitative real-time PCR was used to monitor the RNAi effects. After treatment with dsRNA for 12 h, AbGPx1 expression levels and reproduction in the nematodes decreased compared with the same parameters in the control group; thus, the AbGPx1 gene is likely to be associated with the development, reproduction, and infection ability of A. besseyi. These findings may open new avenues towards nematode control.

Characterization of the transcriptome of the Asian gypsy moth Lymantria dispar identifies numerous transcripts associated with insecticide resistance.

Although the Asian gypsy moth Lymantria dispar causes extensive forest damage worldwide, little is known regarding the genes involved in its development or response to insecticides. Accordingly, characterization of the transcriptome of L. dispar larvae would promote the development of toxicological methods for its control. RNA-seq analysis of L. dispar larvae messenger RNA (mRNA) generated 62,063 unigenes with N50 of 993 bp, from which 23,975 unique sequences (E-value < 10(-5)) were identified using a BLASTx search of the NCBI non-redundant (nr) database. Using functional classification in the Gene Ontology (GO) and Clusters of Orthologous Groups (COG) databases, 7,309 indentified sequences were categorized into 51 functional groups and 8,079 sequences were categorized into 25 functional groups, respectively. Moreover, we identified a large number of transcripts encoding known insecticide targets, or proteins involved in the metabolism of insecticides. Reads per kilobase of unigene length per million mapped reads (RPKM) analysis identified 39 high abundance transcripts, of which 27 exhibited significantly altered expression patterns across the egg, larvae, pupae, male and female adult stages. Our study provides the most comprehensive transcriptomic sequence resource for L. dispar, which will form the basis for future identification of candidate insecticide resistance genes in L. dispar.

Toxicity and affecting factors of Bacillus thuringiensis var. israelensis on Chironomus kiiensis larvae.

Abstract Bacillus thuringiensis var. israelensis (Bti) is a suitable agent for controlling Chironomus kiiensis, a major pest polluting water. In this study, laboratory bioassays were used to study toxicity and affecting factors of Bti on C. kiiensis larvae. Tests were conducted using three commercial Bti formulations (oil miscible suspension, 1,200 ITU/mL; wettable power, 1,200 ITU/mg; technical material, 5,000 ITU/mg) of Bti. The toxicity of Bti formulations to third and fourth instar C. kiiensis larvae was in decreasing order of technical material, oil miscible suspension, and wettable powder, based on the 12 and 24 hour LC50 values. Increasing larval densities (from 10 to 30 per bioassay cup) increased the LC50 values for fourth instar C. kiiensis larvae. The LC50 values for fourth instar larvae reared in sand substrate were higher than those from soil substrate, and autoclaved substrates significantly increased the LC50 values. The technical material of Bti at 12 and 24 hours responded similarly to changes in temperature between 30° C and 15° C, but the LC50 values at a range of tested temperatures showed distinct differences in time points.