Electrophoretic Migration and Axial Diffusion of Individual Nanoparticles in Cylindrical Nanopores

Membranes with straight, vertical nanopores have found widespread applications in chemical and biological sciences, including separation, detection, catalysis, and drug delivery. They can also serve as a model system to understand molecular behavior and fundamental mechanisms of separation, bridging the gap between conventional model systems such as flat surfaces and real chromatographic stationary phases such as micrometer-sized porous particles. We recently found that the axial motion of individual biomolecules inside nanopores can be significantly slower than in bulk solution. This suggests that either chromatographic adsorption was present and/or the viscosity inside the nanopores was unusually high. In this study, we measured the electrophoretic motion as well as the axial diffusion of individual nanoparticles in cylindrical alumina nanopores. We found that the electrophoretic mobilities and the diffusion coefficients of polystyrene nanoparticles were both substantially smaller compared to bulk solution independent of particle size or pore diameter. The results imply that the apparent solution viscosity in nanodomains is anomalous

Solid-Phase Synthesis of Highly Fluorescent Nitrogen-Doped Carbon Dots for Sensitive and Selective Probing Ferric Ions in Living Cells

Carbon quantum dots (C-Dots) have drawn extensive attention in recent years due to their stable physicochemical and photochemical properties. However, the development of nitrogen-doped carbon quantum dots (N-doped C-Dots) is still on its early stage. In this paper, a facile and high-output solid-phase synthesis approach was proposed for the fabrication of N-doped, highly fluorescent carbon quantum dots. The obtained N-doped C-Dots exhibited a strong blue emission with an absolute quantum yield (QY) of up to 31%, owing to fluorescence enhancement effect of introduced N atoms into carbon dots. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe³⁺ caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe³⁺. The probe exhibited a wide linear response concentration range (0.01–500 μM) to Fe³⁺ with a detection limit of 2.5 nM. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility, and high photostability. All these features are favorable for label-free monitoring of Fe³⁺ in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Fe³⁺. As an efficient chemosensor, the N-doped C-Dots hold great promise to broaden applications in biological systems

In Situ Synthesis of MIL-100(Fe) in the Capillary Column for Capillary Electrochromatographic Separation of Small Organic Molecules

Because of the unusual properties of the structure, the metal organic frameworks (MOFs) have received great interest in separation science. However, the most existing methods for the applications of MOFs in separation science require an off-line procedure to prepare the materials. Here, we report an in situ, layer-by-layer self-assembly approach to fabricate MIL-100­(Fe) coated open tubular (OT) capillary columns for capillary electrochromatography. By a controllable manner, the OT capillary columns with a tailored MIL-100­(Fe) coating have been successfully synthesized. The results of SEM, XRD, FT-IR, and ICP-AES indicated that MIL-100­(Fe) was successfully grafted on the inner wall of the capillary. Some neutral, acidic and basic analytes were used to evaluate the performance of the MIL-100­(Fe) coating OT capillary column. Because of the size selectivity of lattice aperture and hydrophobicity of the organic ligands, three types of analytes were well separated with this novel MIL-100­(Fe) coating OT capillary column. For three consecutive runs, the intraday relative standard deviations (RSDs) of migration time and peak areas were 0.4–4.6% and 1.2–6.6%, respectively. The interday RSDs of migration time and peak areas were 0.6–8.0% and 2.2–9.5%, respectively. The column-to-column reproducibility of retention time was in range of 0.6–9.2%. Additionally, the 10 cycles OT capillary column (10-LC) could be used for more than 150 runs with no observable changes on the separation efficiency

Ratiometric Detection of Intracellular Lysine and pH with One-Pot Synthesized Dual Emissive Carbon Dots

Recently, the development of new fluorescent probes for the ratiometric detection of target objects inside living cells has received great attention. Normally, the preparation, modification as well as conjugation procedures of these probes are complicated. On this basis, great efforts have been paid to establish convenient method for the preparation of dual emissive nanosensor. In this work, a functional dual emissive carbon dots (dCDs) was prepared by a one-pot hydrothermal carbonization method. The dCDs exhibits two distinctive fluorescence emission peaks at 440 and 624 nm with the excitation at 380 nm. Different from the commonly reported dCDs, this probe exhibited an interesting wavelength dependent dual responsive functionality toward lysine (440 nm) and pH (624 nm), enabling the ratiometric detection of these two targets. The quantitative analysis displayed that a linear range of 0.5–260 μM with a detection limit of 94 nM toward lysine and the differentiation of pH variation from 1.5 to 5.0 could be readily realized in a ratiometric strategy, which was not reported before with other carbon dots (CDs) as the probe. Furthermore, because of the low cytotoxicity, good optical and colloidal stability, and excellent wavelength dependent sensitivity and selectivity toward lysine and pH, this probe was successfully applied to monitor the dynamic variation of lysine and pH in cellular systems, demonstrating the promising applicability for biosensing in the future