Characterization of size-resolved effective density of atmospheric particles in an urban atmosphere in Southern China.

Effective density (ρeff) is one of the most important physical properties of atmospheric particles, providing important references in exploring the emissions and aging processes of fresh particles. In this study, a combined system of differential mobility analyzer, centrifugal particle mass analyzer, and condensation particle counter was used to periodically measure the ρeff of atmospheric particles in Shenzhen from Oct. 2021 to Jan. 2022. Results showed that the ρeff of particles with various size presented a bimodal distribution, which could be divided into main density (ρm, main peak, corresponding to relatively dense particles after aging) and sub density (ρs, sub peak, corresponding to fresh particles). The occurrence frequencies of ρs of particles with diameters of 50 and 80 nm were less than 20%, but were as high as about 40% of that with diameters from 120 to 350 nm. The ρm showed increasing trend with the size of particles, while ρs decreased as the increasing of the size of particles. The ρeff on pollution day varied significantly with chemical compositions. The increasing of the proportion of sulfate could promote the increasing of ρeff, while black carbon and organic matter caused opposite effects, which may be related to various factors, including the difference of the material density and morphology of various chemical components. The ρeff of 50, 80 and 120 nm particles decreased considerably during the new particle formation event, indicating that organic condensation was an important contributor to new particle growth.

The nuclear localization signal sequence of porcine circovirus type 2 ORF2 enhances intracellular delivery of plasmid DNA.

The phospholipid bilayer of the cell membrane is a natural barrier that prevents large molecules from entering the cell. Cationic liposomes are commonly used for transfection of plasmid DNA but they have high cost and toxicity. Many reports have shown that cell-penetrating peptides (CPP) are able to translocate across the cell membrane efficiently. The VP22 peptide of herpes simplex virus (HSV) was synthesized as a CPP. Two fusion protein candidates, containing binding/condensing protein (VP22-TmHU) and porcine circovirus type 2 nuclear localization signal (VP22-TmHU-PCV2.NLS), were constructed and expressed in E. coli in an attempt to improve delivery of plasmid DNA (pDNA). Firstly, as shown by the electrophoretic mobility shift assay (EMSA), VP22-TmHU (VT) and VP22-TmHU-PCV2.NLS (VTN) were able to bind to pDNA (pEGFP-N1) effectively. Secondly, intracellular transport of pEGFP-N1 was observed by fluorescence microscopy and quantified by flow cytometry after transfection. VTN was successful in delivering pEGFP-N1 intracellularly but VT was not. Thirdly, two protein candidates were combined with Lipofectamine, and both VT and VTN enhanced the transfection rate to 65%, compared to 25% with Lipofectamine alone. Lastly, mice were injected intramuscularly with PBS, pcDNA3-ORF2, pcDNA3-ORF2 plus Lipofectamine, pcDNA3-ORF2 plus VT, pcDNA3-ORF2 plus VT plus Lipofectamine, pcDNA3-ORF2 plus VTN, and pcDNA3-ORF2 plus VTN plus Lipofectamine. The highest level of antibodies raised against PCV2 ORF2 Cap protein was detected with pcDNA3-ORF2 plus VTN. Contrary to the in vitro results, VTN delivered pDNA effectively in vivo without Lipofectamine. In summary, the nuclear localization signal sequence of porcine circovirus type 2 ORF2 can enhance intracellular delivery of pDNA.