Cadmium-free CuInS2-doped ZnS quantum dots (QDs) are synthesized through a two-step non-injection synthetic method. The resulting QDs are small (∼8 nm or less) and relatively isotropic with photoluminescence quantum yields (PL QY) up to almost 70% and emission peaks in the 560–600 nm window, depending on the amount of the Zn precursor added. The results indicate that small CuInS2 clusters within a zinc blende ZnS lattice are the radiative recombination centers in the nanoparticle. Interestingly, higher ensemble photoluminescence quantum yields (PL QY) result when cation exchange is less extensive (∼80% ZnS composition), while a reduction in blinking is observed when ZnS composition exceeds 99%. A wide heterogeneity in blinking behavior from QD to QD is evident, and a subpopulation statistical analysis shows that the on state dwell times change from multiexponential (or inverse power law) behavior toward monoexponential behavior for particles that spend more of their time in the on state. These results indicate that as the number of CuInS2 emitting centers is reduced, the number of pathways leading to the off state decreases, and a model is proposed to relate this behavior to the QD structure. These results provide a novel route toward CuInS2-doped visible-light-emitting ZnS QDs with high quantum yield and reduced blinking and provide insights into how the composition of the dopant and host matrix affects the radiative recombination mechanisms in single particles.

Quantum dots (QDs) can be used as fluorescent probes in single molecule localization microscopy to achieve subdiffraction limit resolution (super-resolution fluorescence imaging). However, the toxicity of Cd in the prototypical CdSe-based QDs can limit their use in biological applications. Furthermore, commercial CdSe QDs are usually modified with relatively thick shells of both inorganic and organic materials to render them in the 10–20 nm size range, which is relatively large for biological labels. In this report, we present compact (4–6 nm) CuInS2/ZnS (CIS/ZnS) and compare them to commercially sourced CdSe/ZnS QDs for their blinking behavior, localization precision and super-resolution imaging. Although commercial CdSe/ZnS QDs are brighter than the more compact Cd-free CIS/ZnS QD, both give comparable results of 4.5–5.0-fold improvement in imaging resolution over conventional TIRF imaging of actin filaments. This likely results from the fact that CIS/ZnS QDs show very short on-times and long off times which leads to less overlap in the point spread functions of emitting CIS/ZnS QD labels on the actin filaments at the same labeling density. These results demonstrate that CIS/ZnS QDs are an excellent candidate to complement and perhaps even replace the larger and more toxic CdSe-based QDs for robust single- molecule super-resolution imaging.

No abstract

The c terminus of the Albino3 (Alb3) translocase in chloroplasts is a region fundamental to the integration of LHCPs into the thylakoid membrane in cooperation with the cpSRP. Alb3 is an integral membrane protein containing five transmembrane helices in an N‐in, C‐out orientation in the thylakoid membrane. The c terminus of Alb3 is responsible for recruiting the cpSRP43 subunit of cpSRP to the thylakoid membrane for successful integration of LHCPs. This region of Alb3 has previously been described as intrinsically disordered. In more recent developments, intrinsically disordered proteins have been shown to carry out vital functions within cells. While our findings show that cAlb is predominately disordered, we have discovered a region in this protein which has a high propensity towards an ordered structure. This region was first isolated by secondary structural sequence analysis using multiple prediction software. Single point mutations which would contribute to the displacement of structure were made within this region, followed by structural characteristic analysis. Results derived from Far‐UV‐Circular Dichroism, intrinsic fluorescence, and trypsin digestion reveal that the mutations show a decrease in overall structure. Inter‐residue distance and energetics were acquired from smFRET analysis of this region, in its native state and upon denaturation. Differences in smFRET histograms show the region is able to be unfolded with increasing denaturant. Additionally, computational methods show a structural propensity in this region and agree with the smFRET results. These combined biophysical and computational results reveal a region of structure in the N‐terminal of cAlb. The local structure found in this study may prove to be important to the binding event with the cpSRP43 subunit of cpSRP Support or Funding Information Department of Energy (DOE)

Epithelial-mesenchymal transition (EMT) is the fundamental transdifferentiation process of an epithelial cell to a mesenchymal cell, which includes losing epithelial-type cell-cell adhesion and gaining the mesenchymal-type enhanced cell motility. EMT has been observed to be a multistep process with partial EMT states, for which the cell expresses both epithelial and mesenchymal markers simultaneously. These partial EMT states play a central role in pathological conditions such as cancer metastasis. Experimentally, computational models have served as a valuable tool to predict mechanisms governing EMT phenotype transitions. However, long-term model predictions for an individual experiment often fail due to parameter uncertainty, since the parameters are determined using averages or extrapolations from multiple experimental conditions. Thus, model simulations generally represent typical responses of the system to perturbations, not necessarily the specific experiment responses of an individual system. Here, we propose a data-assimilation approach that improves long-term predictions by combining limited noisy observations with predictions from a computational model of TGF-b-induced EMT. We tested our approach in a series of ''synthetic'' in silico experiments, in which a forecasting system was tasked with reconstructing EMT dynamics of a phenotypically different ''true'' system and predicting the response to a series of perturbations, specifically time-varying inputs of exogenous TGF-b doses. We found that the forecasting system -with optimal data-assimilation algorithmic parameterssuccessfully predicted the response of the true system and accurately reconstructed its final phenotypical cell state (either epithelial, mesenchymal, or partial EMT). Future work will include testing and optimizing our approach over a wider range of physiological perturbations that will promote or suppress EMT and ultimately testing against in vitro experimental data.