Effect of the A‑Site Cation on the Biexciton Dynamics in Lead Bromide Perovskite Nanocrystals

A systematic and comprehensive understanding of different aspects of the carrier dynamics of lead halide perovskite nanocrystals (LHP NCs) is the key to improving the performance of this highly anticipated material. Recent research suggests that the A-site cation of LHP materials has a significant effect on their photophysical processes, but there is still a lack of a systematic study on how the A-site cation affects their biexciton dynamics. Herein, we fabricated CsPbBr3, MAPbBr3, and FAPbBr3 NCs with similar sizes and morphologies and conducted femtosecond transient absorption (FTA) experiments on them. By a global analysis, we found that all the FTA spectra of CsPbBr3, MAPbBr3, and FAPbBr3 NCs include three decay-associated spectra (DAS) components under high pump fluence, which, respectively, are attributed to hot carrier cooling, biexciton Auger recombination (AR), and exciton recombination. By analyzing the DAS component of biexciton of CsPbBr3, MAPbBr3, and FAPbBr3 NCs, we extract their biexciton AR lifetime and biexciton binding energy. It is found that the biexciton AR lifetime of APbBr3 NCs becomes shorter as the A-site cation changes from Cs+ to MA+ and to FA+ (∼77 ps for CsPbBr3, ∼56 ps for MAPbBr3, and ∼42 ps for FAPbBr3), while the biexciton binding energy of APbBr3 NCs becomes greater as the A-site cation changes from Cs+ to MA+ and to FA+ (∼32 meV for CsPbBr3, ∼39 meV for MAPbBr3, and ∼45 meV for FAPbBr3). We also investigated how the A-site cation of APbBr3 NCs affects their hot carriers cooling time and found a consistent result as the literature’s report (J. Am. Chem. Soc. 2019, 141, 3532–3540)

Structural Heterogeneity in the Collision Complex between Organic Dyes and Tryptophan in Aqueous Solution

The heterogeneity on photoinduced electron transfer (PET) kinetics between a labeled fluorophore and an amino acid residue has been extensively studied in biopolymers. However in aqueous solutions, the heterogeneity on PET kinetics between a fluorophore and a quencher has rarely been reported. Herein, we selected four commonly used fluorophores, such as tetramethylrhodamine (TMR), Rhodamine B (RhB), Alexa fluor 546 (Alexa546), and Atto655, and studied their respective PET kinetics in 50 mM tryptophan solutions with femtosecond transient absorption spectroscopy to explore the structural heterogeneity in their corresponding collision complexes. We measured the decay of the first excited electronic state of respective fluorophore with and without 50 mM tryptophan in aqueous solutions, and derived the charge separation rate in their corresponding collision complexes. We found that the PET process of all selected fluorophores in 50 mM tryptophan solutions has two charge separation rates, which indicates that the relevant states in the collision complex between respective fluorophore and tryptophan have strong structural heterogeneity. These femtosecond PET measurements are in agreement with Vaiana’s molecular dynamics simulation (<i>J. Am. Chem. Soc.</i> <b>2003</b>, <i>125</i>, 14564). In addition, with the obtained PET kinetic parameters, we derived the relative brightness of the collision complex between respective fluorophore and tryptophan, which are important parameters for the PET based fluorescence correlation spectroscopy study involving these fluorophores in biopolymers

Time-Resolved Study on Xanthene Dye-Sensitized Carbon Nitride Photocatalytic Systems

Dye sensitization is a promising strategy to extend the visible light absorption of carbon nitride (C₃N₄) and increase the photocatalytic hydrogen evolution efficiency of C₃N₄ under visible light irradiation. However, the interaction dynamics between C₃N₄ and a sensitized dye has not been reported in the literature. Herein, we selected four commonly used xanthene dyes such as fluorescein, dibromofluorescein, eosin Y, and erythrosine B and prepared their corresponding dye-sensitized-C₃N₄ composites. For the first time, we derived the electron transfer rate from the LUMO of each photoexcited xanthene dye to the conduction band of C₃N₄ using picoesecond time-resolved fluorescence measurements. We also obtained the reduction potentials of all selected xanthene dyes and C₃N₄ with cyclic voltammetry measurements. The cyclic voltammetry measurements gave a consistent result with the picosecond time-resolved fluorescence measurements. Besides, the possibility of the selected xanthene dye as an acceptor for the hole of the photoexcited C₃N₄ was also discussed. We believe this study is significant for the researcher to understanding the fundamental aspects in the xanthene dye-sensitized-C₃N₄ photocatalytic systems

TIMP-1 Promotes Accumulation of Cancer Associated Fibroblasts and Cancer Progression

<div><p>Treatment options for late stage prostate and colon cancer are limited and there is an urgent need to develop more effective and targeted novel therapies, which starts with identification and validation of novel therapeutic targets. Recent clinical studies have demonstrated that tissue inhibitor matrix metalloproteinase-1 (TIMP-1) levels are elevated in cancer patient plasma and elevated TIMP-1 levels are associated with worse clinical outcomes. However, it is unknown whether TIMP-1 serves merely as a biomarker of cancer progression or has a functional role in promoting cancer progression and can serve as a cancer therapeutic target, which is the main objective of this study. Here, we show that stroma of human prostate and colon cancer express higher levels of TIMP-1 compared to their normal counterparts and increased expression of TIMP-1 promotes <i>in vivo</i> growth of both cancer types. We demonstrate for the first time that increased TIMP-1 expression stimulates accumulation of cancer associated fibroblasts (CAFs) within prostate and colon cancer tissues and that TIMP-1 enhances prostate CAF proliferation and migration <i>in vitro</i> and promotes ERK1/2 kinase activation in these CAF cells. Our results establish the novel promotive effects of TIMP-1 on cancer progression and on accumulation of CAFs that in turn provides a pro-tumor microenvironment. Together, these results establish the potential of TIMP-1 as a novel target for cancer therapy and the mechanism underlying the pro-tumor activity of TIMP-1.</p> </div

Presence of Salmonella AvrA in colorectal tumor and its precursor lesions in mouse intestine and human specimens

Evidence directly supporting an association between Salmonella infection and colorectal cancer in human subjects is sparse. It has been well recognized that Salmonella infection increases the risk of gallbladder cancer. AvrA, a bacterial protein from Salmonella enterica, plays a crucial role in establishing chronic infection. To our knowledge, the presence of the bacterial AvrA has never been studied in human samples. Here, we demonstrated the presence and cellular localization of AvrA in inflamed, colorectal tumor and its precursor lesions, using both animal experimental infection models and human clinical specimens. We performed a newly developed AvrA serological assay and to determine the presence of anti-Salmonella AvrA antibody in chronic infected mouse serum samples. Further, we tested the presence of AvrA gene in healthy human fecal samples, in order to advance etiological studies of Salmonella AvrA in human population. Our study suggests a potential role of this bacterial protein in human colorectal cancer. Moreover, our new serological assay may serve a useful tool to identify individuals at increased risk for colorectal cancer

Pulmonary Permeability Assessed by Fluorescent-Labeled Dextran Instilled Intranasally into Mice with LPS-Induced Acute Lung Injury

<div><p>Background</p><p>Several different methods have been used to assess pulmonary permeability in response to acute lung injury (ALI). However, these methods often involve complicated procedures and algorithms that are difficult to precisely control. The purpose of the current study is to establish a feasible method to evaluate alterations in lung permeability by instilling fluorescently labeled dextran (FITC-Dextran) intranasally.</p><p>Methods/Principal Findings</p><p>For the mouse model of direct ALI, lipopolysaccharide (LPS) was administered intranasally. FITC-Dextran was instilled intranasally one hour before the mice were euthanized. Plasma fluorescence intensities from the LPS group were significantly higher than in the control group. To determine the reliability and reproducibility of the procedure, we also measured the lung wet-to-dry weight ratio, the protein concentration of the bronchoalveolar lavage fluid, tight and adherens junction markers and pathological changes. Consistent results were observed when the LPS group was compared with the control group. Simultaneously, we found that the concentration of plasma FITC-Dextran was LPS dose-dependent. The concentration of plasma FITC-Dextran also increased with initial intranasal FITC-Dextran doses. Furthermore, increased fluorescence intensity of plasma FITC-Dextran was found in the intraperitoneally LPS-induced ALI model.</p><p>Conclusion/Significance</p><p>In conclusion, the measurement of FITC-Dextran in plasma after intranasal instillation is a simple, reliable, and reproducible method to evaluate lung permeability alterations <i>in vivo</i>. The concentration of FITC-Dextran in the plasma may be useful as a potential peripheral biomarker of ALI in experimental clinical studies.</p></div

TIMP-1 enhances expression of Snail, MMP-2, and MMP-9 in prostate cancers.

<p>Expression levels of several EMT markers, such as Snail (A, E, I, M), Slug (B, F, J, N), MMP-2 (C, G, K, O), and MMP-9 (D, H, L, P) were assessed on the tumor sections derived from PC3/LAPC-4 control cells (A-D and I-L, respectively) and PC3/LAPC-4-TIMP-1 cells (E-H and M-P, respectively). The results show that TIMP-1 enhances expression of Snail, MMP-2, and MMP-9 but not Slug in the prostate cancer tissues. Bar, 50 µm in A, B, E, F, I, J, M, N and 100 µm in C, D, G, H, K, L, O, P. </p

H&E staining shows pathological alterations that are characteristic of acute lung injury at 6 h after LPS instillation.

<p><i>A</i>: The gross appearance showed yellow FITC-Dextran on the pulmonary surface after i.n. instillation with 10 mg of FITC-Dextran/kg body weight (b.w.) for 1 hour. The lungs of the LPS model group showed red dots and swelling. <i>B</i>: Representative normal lung histology. <i>C</i>: Lung edema (arrow) and alveolar wall thickening (arrow head) in the ALI mice. <i>D</i>: Infiltration of many inflammatory cells (arrow shows neutrophils) in the ALI mice induced with i.n. instillation with 0.5 mg of LPS/kg b.w. for 6 h (n = 4). B, C, D the magnification is 400X.</p

Numbers of <i>Salmonella</i> in different organs at 27 weeks postinfection <i>in vivo</i>.

<p>(A) Feces. (B) Spleen. (C) Gallbladder. (D) Liver. N = 5 mice in each group.</p

Percentage of mice with liver abscess.

<p>Percentage of mice with liver abscess.</p