Nitrogen-Doping Enhanced Fluorescent Carbon Dots: Green Synthesis and Their Applications for Bioimaging and Label-Free Detection of Au³⁺ Ions

Fluorescent carbon dots (CDs) hold great promise for a myriad applications due to their fascinating attributes. However, the development of CDs with high fluorescence quantum yield (QY) and unique surface property is still in its infancy. Herein, we report a simple and green strategy to produce water-soluble nitrogen-doped CDs (N-CDs) via the one-pot hydrothermal carbonization of the mixture of natural peach gum polysaccharide (PGP) and ethylenediamine. The resulting N-CDs exhibit a remarkably enhanced QY (28.46%) as compared with that of undoped CDs (5.31%). In addition, the N-CDs show stable fluorescence against ionic strength variation and pH change. Preliminary biological studies reveal that N-CDs possess low cytotoxicity and high fluorescent contrast in cells. Moreover, we present here for the first time that the obtained N-CDs can exhibit a fast and highly sensitive and selective fluorescence quenching effect toward Au³⁺ ions. The detection limit can reach 6.4 × 10^–8 M, which compares favorably to other reported fluorescent probes. We have also demonstrated that the N-CDs can be employed to sense Au³⁺ ions in real river water. Considering the easy synthetic process and excellent performance of the N-CDs, this investigation opens up new opportunities for preparing high-quality fluorescent CDs to meet the requirement of many applications

Multihydroxy Dendritic Upconversion Nanoparticles with Enhanced Water Dispersibility and Surface Functionality for Bioimaging

Upconversion nanoparticle (UCNP) as a new class of imaging agent is gaining prominence because of its unique optical properties. An ideal UCNP for bioimaging should simultaneously possess fine water dispersibility and favorable functional groups. In this paper, we present a simple but effective method to the synthesis of a UCNP-based nanohybrid bearing a multihydroxy hyperbranched polyglycerol (HPG) shell by the combination of a “grafting from” strategy with a ring-opening polymerization technique. The structure and morphology of the resulting UCNP-<i>g</i>-HPG nanohybrid were characterized in detail by Fourier transform infrared, ¹H NMR, thermogravimetric analysis, and transmission electron microscopy measurements. The results reveal that the amount of grafted HPG associated with the thickness of the HPG shell can be well tuned. UCNP-<i>g</i>-HPG shows high water dispersibility and strong and stable upconversion luminescence. On the basis of its numerous surface hydroxyl groups, UCNP-<i>g</i>-HPG can be tailored by a representative fluorescent dye rhodamine B to afford a UCNP-<i>g</i>-HPG-RB nanohybrid that simultaneously presents upconversion and downconversion luminescence. Preliminary biological studies demonstrate that UCNP-<i>g</i>-HPG shows low cytotoxicity, high luminescent contrast, and deep light penetration depth, posing promising potential for bioimaging applications

Modulating the Depolymerization of Self-Immolative Brush Polymers with Poly(benzyl ether) Backbones

We have synthesized a series of stimuli-responsive brush polymers by grafting azide-terminated side chains onto a self-immolative, alkyne-bearing poly­(benzyl ether) backbone, which is prepared by anionic polymerization of quinone methide-based monomers. Upon exposure to a decapping reagent (Pd(0) or F^–), these brush polymers undergo an irreversible degradation cascade from head to tail to yield individual side chains. It is observed that several factors affect the depolymerization kinetics, including solvent polarity, type of counterion, the rate of the decapping chemistry, and interestingly, the rigidity of the side chains

One-Step Fabrication of Graphene Oxide Enhanced Magnetic Composite Gel for Highly Efficient Dye Adsorption and Catalysis

Graphene oxide (GO) is emerging as a potential adsorbent for environmental cleanup due to its attractive attributes associated with high removal efficiency toward water pollutants. However, it is difficult to separate GO from water after adsorption. Until now, the development of an effective approach that can simultaneously take advantage of the adsorption feature of GO and overcome the separation problem is still a challenge. Herein, we demonstrate a simple one-step approach to fabricate magnetic GO/poly­(vinyl alcohol) (PVA) composite gels (mGO/PVA CGs), which not only exhibit convenient magnetic separation capability but also show remarkably enhanced adsorption capacity for cationic methylene blue (MB) and methyl violet (MV) dyes as compared with the one without GO (e.g., the adsorption capacities of mGO/PVA-50% and mGO/PVA-0% for MB are 231.12 and 85.64 mg/g, respectively). Detailed adsorption studies reveal that the adsorption kinetics and isotherms can be well-described by pseudo-second-order model and Langmuir isotherm model, respectively. Moreover, the adsorbent could be well regenerated in an acid solution without obvious compromise of removal efficiency. Considering the facile fabrication process and robust adsorption performance of the mGO/PVA CG, this work opens up enormous opportunities to bring GO from experimental research to practical water treatment applications. In addition, the mGO/PVA CG can act as a magnetic support for in situ growth of noble metal nanocatalyst with excellent catalytic performance, as exemplified by the synthesis of mGO/PVA-Pt catalyst in this paper

Accelerated Preparation of Polypeptides and Related Hybrid Materials from a Disintegrable Initiator Array with Masked Carbenium Precursors

We report a disintegrable initiator array for the synthesis of well-defined polypeptides using raw N-carboxyanhydride monomers that are purified in situ. Free polypeptides can be obtained through the superfast disintegration of the initiation system after polymerization, simultaneously revealing unmasked, highly active benzhydrylium (BHD) ends for efficient conjugation. The polypeptide synthesis and conjugation combined can be accomplished in 3.5 h starting from amino acids. The high activity of BHD on the polypeptides can be utilized to construct complex hybrid materials with ease, shown in two proof-of-concept examples. The BHD-capped polypeptide presents the first reported case of the polymer being used as a dopant, which grafts onto and dopes poly(3-hexylthiophene) directly to give biocompatible, conductive polypeptide brushes. In addition, such polypeptides can directly decorate two-dimensional MoS2 nanosheets for significantly improved dispersibility and activity as a heterogeneous catalyst

Accelerated Preparation of Polypeptides and Related Hybrid Materials from a Disintegrable Initiator Array with Masked Carbenium Precursors

We report a disintegrable initiator array for the synthesis of well-defined polypeptides using raw N-carboxyanhydride monomers that are purified in situ. Free polypeptides can be obtained through the superfast disintegration of the initiation system after polymerization, simultaneously revealing unmasked, highly active benzhydrylium (BHD) ends for efficient conjugation. The polypeptide synthesis and conjugation combined can be accomplished in 3.5 h starting from amino acids. The high activity of BHD on the polypeptides can be utilized to construct complex hybrid materials with ease, shown in two proof-of-concept examples. The BHD-capped polypeptide presents the first reported case of the polymer being used as a dopant, which grafts onto and dopes poly(3-hexylthiophene) directly to give biocompatible, conductive polypeptide brushes. In addition, such polypeptides can directly decorate two-dimensional MoS2 nanosheets for significantly improved dispersibility and activity as a heterogeneous catalyst