Hongchen Sun

Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging

Fluorescent carbon-based materials have drawn increasing attention in recent years owing to exceptional advantages such as high optical absorptivity, chemical stability, biocompatibility, and low toxicity. These materials primarily include carbon dots (CDs), nanodiamonds, carbon nanotubes, fullerene, and fluorescent graphene. The superior properties of fluorescent carbon-based materials distinguish them from traditional fluorescent materials, and make them promising candidates for numerous exciting applications, such as bioimaging, medical diagnosis, catalysis, and photovoltaic devices. Among all of these materials, CDs have drawn the most extensive notice, owing to their early discovery and adjustable parameters. However, many scientific issues with CDs still await further investigation. Currently, a broad series of methods for obtaining CD-based materials have been developed, but efficient one-step strategies for the fabrication of CDs on a large scale are still a challenge in this field. Current synthetic methods are mainly deficient in accurate control of lateral dimensions and the resulting surface chemistry, as well as in obtaining fluorescent materials with high quantum yields (QY). Moreover, it is important to expand these kinds of materials to novel applications. Herein, a facile and highoutput strategy for the fabrication of CDs, which is suitable for industrial-scale production (yield is ca. 58%), is discussed. The QY was as high as ca. 80%, which is the highest value recorded for fluorescent carbon-based materials, and is almost equal to fluorescent dyes. The polymer-like CDs were converted into carbogenic CDs by a change from low to high synthesis temperature. The photoluminescence (PL) mechanism (high QY/PL quenching) was investigated in detail by ultrafast spectroscopy. The CDs were applied as printing ink on the macro/micro scale and nanocomposites were also prepared by polymerizing CDs with certain polymers. Additionally, the CDs could be utilized as a biosensor reagent for the detection of Fe in biosystems. The CDs were prepared by a hydrothermal method, which is described in the Supporting Information (Figure 1a; see also the Supporting Information, Figure S1). The reaction was conducted by first condensing citric acid and ethylenediamine, whereupon they formed polymer-like CDs, which were then carbonized to form the CDs. The morphology and structure of CDs were confirmed by analysis. Figure 1b shows transmission electron microscopy (TEM) images of the CDs, which can be seen to have a uniform dispersion without apparent aggregation and particle diameters of 2–6 nm. The sizes of CDs were also measured by atomic force microscopy (AFM; Figure S2), and the average height was 2.81 nm. From the high-resolution TEM, most particles are observed to be amorphous carbon particles without any lattices; rare particles possess well-resolved lattice fringes. With such a low carbon-lattice-structure content, no obvious D or G bands were detected in the Raman spectra of the CDs (Figure S3). The XRD patterns of the CDs (Figure 1c) also displayed a broad peak centered at 258 (0.34 nm), which is also attributed to highly disordered carbon atoms. Moreover, NMR spectroscopy (H and C) was employed to distinguish sp-hybridized carbon atoms from sp-hybridized carbon atoms (Figure S4). In the H NMR spectrum, sp carbons were detected. In the C NMR spectrum, signals in the range of 30–45 ppm, which correspond to aliphatic (sp) carbon atoms, and signals from 100–185 ppm, which are indicative of sp carbon atoms, were observed. Signals in the range of 170– 185 ppm, which correspond to carboxyl/amide groups, were also present. In the FTIR analysis of CDs, the following were observed: stretching vibrations of C OH at 3430 cm 1 and C H at 2923 cm 1 and 2850 cm , asymmetric stretching vibrations of C-NH-C at 1126 cm , bending vibrations of N H at 1570 cm , and the vibrational absorption band of C=O at 1635 cm 1 (Figure S5). Moreover, the surface groups were also investigated by XPS analysis (Figure 1d). C1s analysis revealed three different types of carbon atoms: graphitic or aliphatic (C=C and C C), oxygenated, and nitrous (Table S1). In the UV/Vis spectra, the peak was focused on 344 nm in an aqueous solution of CDs. In the fluorescence spectra, CDs have optimal excitation and emission wavelengths at 360 nm and 443 nm, and show a blue color under a hand-held UV lamp (Figure 2a). Excitation-dependent PL behavior was [*] S. Zhu, Q. Meng, Prof. J. Zhang, Y. Song, Prof. K. Zhang, Prof. B. Yang State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University Changchun, 130012 (P. R. China) E-mail: byangchem@jlu.edu.cn

Strongly green-photoluminescent graphene quantum dots for bioimaging applications

Strongly fluorescent graphene quantum dots (GQDs) have been prepared by one-step solvothermal method with PL quantum yield as high as 11.4%. The GQDs have high stability and can be dissolved in most polar solvents. Because of fine biocompatibility and low toxicity, GQDs are demonstrated to be excellent bioimaging agents.

Facile Aqueous-Phase Synthesis of Biocompatible and Fluorescent Ag2S Nanoclusters for Bioimaging: Tunable Photoluminescence from Red to Near Infrared

Low toxicity and fluorescent nanomaterials have many advantages in biological imaging. Herein, a novel and facile aqueous-phase approach to prepare biocompatible and fluorescent Ag(2)S nanoclusters (NCs) is designed and investigated. The resultant Ag(2)S NCs show tunable luminescence from the visible red (624 nm) to the near infrared (NIR; 724 nm) corresponding to the increasing size of the NCs. The key for preparing tunable fluorescent Ag(2)S NCs is the proper choice of capping reagent, glutathione (GSH), and the novel sulfur-hydrazine hydrate complex as the S(2-) source. As a naturally occurring and readily available tripeptide, GSH functions as an important scaffold to prevent NCs from growing large nanoparticles. Additionally, GSH is a small biomolecule with several functional groups, including carboxyl and amino groups, which suggests the resultant Ag(2)S NCs are well-dispersed in aqueous solution. These advantages make the as-prepared Ag(2)S NCs potentially applicable to biological labeling as well. For example, the resultant Ag(2)S NCs are used as a probe for MC3T3-EI cellular imaging.

A Galvanic Replacement Route to Prepare Strongly Fluorescent and Highly Stable Gold Nanodots for Cellular Imaging

Fluorescent gold nanodots (GNDs) are an important kind of nanoprobes. Herein, the application of galvanic replacement for the preparation of fluorescent GNDs is reported. Using presynthesized and size-controlled Ag nanodots (Ag NDs) as templates, the as-prepared GNDs have strong fluorescence (quantum yields ~10%) with high stability and surface bioactivity. The resultant GNDs show excellent photoluminescence properties with high photo-, time-, metal-, and pH-stability, which are attributed to the protective surface layer of glutathione (GSH) and the presence of Au(I)-S complexes on the surface of the gold core. GSH, a naturally occurring and readily available tripeptide with carboxyl and amino functional groups, allows good dispersion of the as-prepared GNDs in aqueous solution and favorable biocompatibility. These advantages, combined with their small size, mean that the as-prepared GNDs have potential application in biological labeling, especially as a DNA probe for the specific detection of nucleic acids. In this study, the CAL-27 cells are used as a model to evaluate the fluorescence imaging of GNDs.

Composite Photothermal Platform of Polypyrrole-Enveloped Fe3O4 Nanoparticle Self-Assembled Superstructures

Photothermal nanoplatforms with small size, low cost, multifunctionality, good biocompatibility and in particular biodegradability are greatly desired in the exploration of novel diagnostic and therapeutic methodologies. Despite Fe3O4 nanoparticles (NPs) have been approved as safe clinical agents, the low molar extinction coefficient and subsequent poor photothermal performance shed the doubt as effective photothermal materials. In this paper, we demonstrate the fabrication of polypyrrole (PPy)-enveloped Fe3O4 NP superstructures with a spherical morphology, which leads to a 300-fold increase in the molar extinction coefficient. The basic idea is the optimization of Fe3O4 electronic structures. By controlling the self-assembly of Fe3O4 NPs, the diameters of the superstructures are tuned from 32 to 64 nm. This significantly enhances the indirect transition and magnetic coupling of Fe ions, thus increasing the molar extinction coefficient of Fe3O4 NPs from 3.65 × 10(6) to 1.31 × 10(8) M(-1) cm(-1) at 808 nm. The envelopment of Fe3O4 superstructures with conductive PPy shell introduces additional electrons in the Fe3O4 oscillation system, and therewith further enhances the molar extinction coefficient to 1.12 × 10(9) M(-1) cm(-1). As a result, the photothermal performance is greatly improved. Primary cell experiments indicate that PPy-enveloped Fe3O4 NP superstructures are low toxic, and capable to kill Hela cells under near-infrared laser irradiation. Owing to the low cost, good biocompatibility and biodegradability, the PPy-enveloped Fe3O4 NP superstructures are promising photothermal platform for establishing novel diagnostic and therapeutic methods.

Coating urchinlike gold nanoparticles with polypyrrole thin shells to produce photothermal agents with high stability and photothermal transduction efficiency.

Photothermal therapy using inorganic nanoparticles (NPs) is a promising technique for the selective treatment of tumor cells because of their capability to convert the absorbed radiation into heat energy. Although anisotropic gold (Au) NPs present an excellent photothermal effect, the poor structural stability during storage and/or upon laser irradiation still limits their practical application as efficient photothermal agents. With the aim of improving the stability, in this work we adopted biocompatible polypyrrole (PPy) as the shell material for coating urchinlike Au NPs. The experimental results indicate that a several nanometer PPy shell is enough to maintain the structural stability of NPs. In comparison to the bare NPs, PPy-coated NPs exhibit improved structural stability toward storage, heat, pH, and laser irradiation. In addition, the thin shell of PPy also enhances the photothermal transduction efficiency (η) of PPy-coated Au NPs, resulting from the absorption of PPy in the red and near-infrared (NIR) regions. For example, the PPy-coated Au NPs with an Au core diameter of 120 nm and a PPy shell of 6.0 nm exhibit an η of 24.0% at 808 nm, which is much higher than that of bare Au NPs (η = 11.0%). As a primary attempt at photothermal therapy, the PPy-coated Au NPs with a 6.0 nm PPy shell exhibit an 80% death rate of Hela cells under 808 nm NIR laser irradiation.

pH- and Temperature-Sensitive Hydrogel Nanoparticles with Dual Photoluminescence for Bioprobes.

This study demonstrates high contrast and sensitivity by designing a dual-emissive hydrogel particle system, whose two emissions respond to pH and temperature strongly and independently. It describes the photoluminescence (PL) response of poly(N-isopropylacrylamide) (PNIPAM)-based core/shell hydrogel nanoparticles with dual emission, which is obtained by emulsion polymerization with potassium persulfate, consisting of the thermo- and pH-responsive copolymers of PNIPAM and poly(acrylic acid) (PAA). A red-emission rare-earth complex and a blue-emission quaternary ammonium tetraphenylethylene derivative (d-TPE) with similar excitation wavelengths are inserted into the core and shell of the hydrogel nanoparticles, respectively. The PL intensities of the nanoparticles exhibit a linear temperature response in the range from 10 to 80 °C with a change as large as a factor of 5. In addition, the blue emission from the shell exhibits a linear pH response between pH 6.5 and 7.6 with a resolution of 0.1 unit, while the red emission from the core is pH-independent. These stimuli-responsive PL nanoparticles have potential applications in biology and chemistry, including bio- and chemosensors, biological imaging, cancer diagnosis, and externally activated release of anticancer drugs.

Near infrared Ag/Au alloy nanoclusters: Tunable photoluminescence and cellular imaging

The fluorescent nanomaterials play an important role in cellular imaging. Although the synthesis of fluorescent metal nanoclusters (NCs) have been developing rapidly, there are many technical issues in preparing metal alloy NCs. Herein, we used a facile galvanic replacement reaction to prepare Ag/Au alloy NCs. The characterizations of UV, PL, HRTEM, EDX and XPS confirm one fact the Ag/Au alloy NCs are carried out. As-prepared Ag/Au alloy NCs display near-infrared (NIR) fluorescence centered at 716 nm and show tunable luminescence from visible red (614 nm) to NIR (716 nm) by controlling the experimental Ag/Au ratios. Moreover, as-prepared Ag/Au alloy NCs are protected by glutathione (GSH) whose some functional groups including thiol, carboxyl and amino groups make the as-prepared alloy NCs exhibit good dispersion in aqueous solution, high physiological stability and favorable biocompatibility. Together with NIR fluorescence, these advantages make alloy NCs be promising candidate in biological labeling.

Enhanced Biocompatibility of PLGA Nanofibers with Gelatin/Nano-Hydroxyapatite Bone Biomimetics Incorporation

The biocompatibility of biomaterials is essentially for its application. The aim of current study was to evaluate the biocompatibility of poly(lactic-co-glycolic acid) (PLGA)/gelatin/nanohydroxyapatite (n-HA) (PGH) nanofibers systemically to provide further rationales for the application of the composite electrospun fibers as a favorable platform for bone tissue engineering. The PGH composite scaffold with diameter ranging from nano- to micrometers was fabricated by using electrospinning technique. Subsequently, we utilized confocal laser scanning microscopy (CLSM) and MTT assay to evaluate its cyto-compatibility in vitro. Besides, real-time quantitative polymerase chain reaction (qPCR) analysis and alizarin red staining (ARS) were performed to assess the osteoinductive activity. To further test in vivo, we implanted either PLGA or PGH composite scaffold in a rat subcutaneous model. The results demonstrated that PGH scaffold could better support osteoblasts adhesion, spreading, and proliferation and show better cyto-compatibility than pure PLGA scaffold. Besides, qPCR analysis and ARS showed that PGH composite scaffold exhibited higher osteoinductive activity owing to higher phenotypic expression of typical osteogenic genes and calcium deposition. The histology evaluation indicated that the incorporation of Gelatin/nanohydroxyapatite (GH) biomimetics could significantly reduce local inflammation. Our data indicated that PGH composite electrospun nanofibers possessed excellent cyto-compatibility, good osteogenic activity, as well as good performance of host tissue response, which could be versatile biocompatible scaffolds for bone tissue engineering.

A pluronic F127 coating strategy to produce stable up-conversion NaYF4:Yb,Er(Tm) nanoparticles in culture media for bioimaging†

Up-conversion nanoparticles (UCNPs) have exhibited great potential in biological imaging and labeling. The further development of the correlated techniques strongly depends on the stability of UCNPs in buffers and biological growth media. In this paper, Pluronic F127, a nonionic triblock copolymer of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO), is applied to coat the originally hydrophobic NaYF4:Yb,Er(Tm) UCNPs, leading to an oil-to-water phase transfer. After the phase transfer, F127-coated UCNPs are well dispersed in water with more than 43% UC luminescence preserved. Because of the nonionic nature of F127, the F127-coated UCNPs are quite stable in culture media, and exhibit excellent biocompatibility and low toxicity. The biocompatible decoration using F127 is facile and repeatable, thus facilitating the biological applications of UCNPs. As an example, the bioimaging of caenorhabditis elegans is demonstrated.