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Protein–protein interactions are fundamental biological processes. While strong protein interactions are amenable to many characterization techniques including crystallography, weak protein interactions are challenging to study due to their dynamic nature. Single-molecule FRET can monitor dynamic protein interactions in real time, but are generally limited to strong interacting pairs because of the low concentrations needed for single-molecule detection. Here we describe a nanovesicle trapping approach to enable single-molecule FRET study of weak protein interactions at high effective concentrations. We describe the experimental procedures, summarize the application in studying the weak interactions between intracellular copper transporters, and detail the single-molecule kinetic analysis of bimolecular interactions involving three states. Both the experimental approach and the theoretical analysis are generally applicable for studying many other biological processes at the single-molecule level.

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Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1–P3, based on head-to-head-linked 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur–oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are ∼1.0 eV lower than that of regioregular poly­(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents (I offs) of 10–10–10–11 A and large current on/off ratios (I on/I offs) at the level of 106. Among them, polymer P2 with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μe) of 0.31 cm2 V–1 s–1 in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly­(naphthalene diimide-alt-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (P2) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of n-hexadecyl (P1) and 2-butyloctyl (P3) side chains leads to reduced film ordering and results in 1–2 orders of magnitude lower μes, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.

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Fluorescent polymer quantum dots derived from poly(3,4-ethylenedioxythiophene) are synthesized and utilized for optical imaging and Hg2+ sensing applications.

The composition of mammalian intestinal microflora is related to many environmental and geographical factors, and it plays an important role in many aspects such as growth and development. Sequencing data of the bacterial 16S rRNA gene from sable (Martes zibellina) samples using next-generation sequencing technology are limited. In our research, 84,116 reads obtained by high-throughput sequencing were analyzed to characterize and compare the intestinal microflora of wild sables and housed sables. Firmicutes (31.1 %), Bacteroidetes (26.0 %) and Proteobacteria (21.5 %) were the three most abundant phyla present in wild sables, whereas Firmicutes (55.6 %), Proteobacteria (29.1 %) and Actinobacteria (6.0 %) were the three predominant phyla present in housed sables. At the phylum level, wild sables exhibited a significant difference in the relative abundances of Bacteroidetes and Actinobacteria, whereas housed sables only exhibited significant changes in TM7 at the phylum level, and Clostridia, at the class level. The predominance of Bacteroidetes in wild sables warrants further research. These results indicate that a sudden change in diet may be a key factor that influences fecal bacterial diversity in mammals.