Recently, ratiometric pH nanosensors
have emerged as a robust tool
for the fluorescence sensing and imaging, but there is no report of
ratiometric sensors based on hyperbranched polymers for intracellular
pH sensing. Herein, we describe the first example of hyperbranched
polymer-based tunable fluorescent pH nanosensor with aggregation-induced
emission activity, which exhibits great potential for ratiometric
sensing of intracellular pH. These polymer nanoparticles can selectively
accumulate in the acidic organelles of living cells by endocytosis
process, and no obvious cytotoxicity was observed. The quantitative
analysis of the intracellular pH values in HeLa cells was successfully
conducted based on this new sensing platform. This platform provides
a new choice for future developments of ratiometric fluorescent nanosensors,
targeting not only protons but also a variety of other analytes of
biological interest, such as metal ions, anions, and other biomolecules.
High-performance, biobased materials can potentially be manufactured from polymerized α-amino acids (α-polypeptides). This paper reports on the synthesis, structure, and properties of both polyalanine enantiomers (PLAla and PDAla). The molecular structure of the polypeptide chains, their molecular weight, and polydispersity were investigated by (1)H NMR, MALDI-TOF, and size-exclusion chromatography. The secondary structure and crystalline order were probed via Fourier transform infrared spectroscopy, circular dichroism, and (synchrotron) wide-angle X-ray diffraction. The phase behavior and thermal stability were assessed by differential scanning calorimetry and thermogravimetric analysis. The kinetically trapped PAla chain conformation in the solid state, after synthesis or solvent treatments, is the α-helical shape. Upon heating, crystals from the α-helices convert into more stable crystals from β-sheets at a temperature higher than 210 °C. This temperature is close to where polymer degradation sets in. The β-sheet crystals combine melting with thermal degradation at temperatures above 330 °C. In the presence of superheated water, the conversion from α-helices to β-sheets happens at lower temperatures, allowing for a conversion without degradation.
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