Subcellular Fate of a Fluorescent Cholesterol-Poly(ethylene glycol) Conjugate: An Excellent Plasma Membrane Imaging Reagent

Cholesterol-containing molecules or nanoparticles play a significant role in achieving favorable plasma membrane imaging and efficient cellular uptake of drugs by the excellent membrane anchoring capability of the cholesterol moiety. By linking cholesterol to a water-soluble component (such as poly­(ethylene glycol), PEG), the resulting cholesterol-PEG conjugate can form micelles in aqueous solution through self-assembly, and such a micellar structure represents an important drug delivery vehicle in which hydrophobic drugs can be encapsulated. However, the understanding of the subcellular fate and cytotoxicity of cholesterol-PEG conjugates themselves remains elusive. Herein, by using cholesterol-PEG2000-fluorescein isothiocyanate (Chol-PEG-FITC) as a model system, we found that the Chol-PEG-FITC molecules could attach to the plasma membranes of mammalian cells within 10 min and such a firm membrane attachment could last at least 1 h, displaying excellent plasma membrane staining performance that surpassed that of commonly used commercial membrane dyes such as DiD and CellMask. Besides, we systematically studied the endocytosis pathway and intracellular distribution of Chol-PEG-FITC and found that the cell surface adsorption and endocytosis processes of Chol-PEG-FITC molecules were lipid-raft-dependent. After internalization, the Chol-PEG-FITC molecules gradually reached many organelles with membrane structures. At 5 h, they were mainly distributed in lysosomes and the Golgi apparatus, with some in the endoplasmic reticulum (ER) and very few in the mitochondrion. At 12 h, the Chol-PEG-FITC molecules mostly aggregated in the Golgi apparatus and ER close to the nucleus. Finally, we demonstrated that Chol-PEG-FITC was toxic to mammalian cells only at concentrations above 50 μM. In summary, Chol-PEG-FITC can be a promising plasma membrane imaging reagent to avoid the fast cellular internalization and quick membrane detachment problems faced by commercial membrane dyes. We believe that the investigation of the dynamic subcellular fate of Chol-PEG-FITC can provide important knowledge to facilitate the use of cholesterol–PEG conjugates in fields such as cell surface engineering and drug delivery

Highly Sensitive and Selective Detection of Dopamine Using One-Pot Synthesized Highly Photoluminescent Silicon Nanoparticles

A simple and highly efficient method for dopamine (DA) detection using water-soluble silicon nanoparticles (SiNPs) was reported. The SiNPs with a high quantum yield of 23.6% were synthesized by using a one-pot microwave-assisted method. The fluorescence quenching capability of a variety of molecules on the synthesized SiNPs has been tested; only DA molecules were found to be able to quench the fluorescence of these SiNPs effectively. Therefore, such a quenching effect can be used to selectively detect DA. All other molecules tested have little interference with the dopamine detection, including ascorbic acid, which commonly exists in cells and can possibly affect the dopamine detection. The ratio of the fluorescence intensity difference between the quenched and unquenched cases versus the fluorescence intensity without quenching (Δ<i>I</i>/<i>I</i>) was observed to be linearly proportional to the DA analyte concentration in the range from 0.005 to 10.0 μM, with a detection limit of 0.3 nM (<i>S</i>/<i>N</i> = 3). To the best of our knowledge, this is the lowest limit for DA detection reported so far. The mechanism of fluorescence quenching is attributed to the energy transfer from the SiNPs to the oxidized dopamine molecules through Förster resonance energy transfer. The reported method of SiNP synthesis is very simple and cheap, making the above sensitive and selective DA detection approach using SiNPs practical for many applications

Carbon Dot-Based Platform for Simultaneous Bacterial Distinguishment and Antibacterial Applications

In this work, we prepared quaternized carbon dots (CDs) with simultaneous antibacterial and bacterial differentiation capabilities using a simple carboxyl–amine reaction between lauryl betaine and amine-functionalized CDs. The obtained quaternized CDs have several fascinating properties/abilities: (1) A long fluorescence emission wavelength ensures the exceptional bacterial imaging capability, including the super-resolution imaging ability; (2) the polarity-sensitive fluorescence emission property leads to significantly enhanced fluorescence when the quaternized CDs interact with bacteria; (3) the presence of both hydrophobic hydrocarbon chains and positively charged quaternary ammonium groups makes the CDs selectively attach to Gram-positive bacteria, realizing the bacterial differentiation; (4) excellent antimicrobial activity is seen against Gram-positive bacteria with a minimum inhibitory concentration of 8 μg/mL for <i>Staphylococcus aureus</i>. Besides, the quaternized CDs are highly stable in various aqueous solutions and exhibit negligible cytotoxicity, suggesting that they hold great promise for clinical applications. Compared to the traditional Gram staining method, the selective Gram-positive bacterial imaging achieved by the quaternized CDs provides a much simpler and faster method for bacterial differentiation. In summary, by combining selective Gram-positive bacterial recognition, super-resolution imaging, and exceptional antibacterial activity into a single system, the quaternized CDs represent a novel kind of metal-free nanoparticle-based antibiotics for antibacterial application and a new type of reagent for efficient bacterial differentiation

Glutathione-Depleting Gold Nanoclusters for Enhanced Cancer Radiotherapy through Synergistic External and Internal Regulations

The therapeutic performance of cancer radiotherapy is often limited by the overexpression of glutathione (GSH) in tumors and low radiation sensitivity of cancerous cells. To address these issues, the facilely prepared histidine-capped gold nanoclusters (Au NCs@His) were adopted as a radiosensitizer with a high sensitization enhancement ratio of ∼1.54. On one hand, Au NCs@His can inherit the local radiation enhancement property of gold-based materials (external regulation); on the other hand, Au NCs@His can decrease the intracellular GSH level, thus preventing the generated reactive oxygen species (ROS) from being consumed by GSH, and arrest the cells at the radiosensitive G2/M phase (internal regulation)