Zhijun Chen

Natural‐Product‐Derived Carbon Dots: From Natural Products to Functional Materials

Nature provides an almost limitless supply of sources that inspire scientists to develop new materials with novel applications and less of an environmental impact. Recently, much attention has been focused on preparing natural-product-derived carbon dots (NCDs), because natural products have several advantages. First, natural products are renewable and have good biocompatibility. Second, natural products contain heteroatoms, which facilitate the fabrication of heteroatom-doped NCDs without the addition of an external heteroatom source. Finally, some natural products can be used to prepare NCDs in ways that are very green and simple relative to traditional methods for the preparation of carbon dots from man-made carbon sources. NCDs have shown tremendous potential in many fields, including biosensing, bioimaging, optoelectronics, and photocatalysis. This Review addresses recent progress in the synthesis, properties, and applications of NCDs. The challenges and future direction of research on NCD-based materials in this booming field are also discussed.

Multifunctional chiral nematic cellulose nanocrystals/glycerol structural colored nanocomposites for intelligent responsive films, photonic inks and iridescent coatings

Structural colored nanocomposites with photonic liquid crystal structures are desirable owing to their excellent optical performances, unique structural features and intelligent responsive behaviors. Herein, a series of cellulose nanocrystal (CNC)-based nanocomposite materials that mimic the cholesteric structural colored creatures in nature were prepared and their functional applications investigated. Multicolored, flexible and intelligent responsive iridescent films were constructed by mixing cellulose nanocrystals (CNCs) and glycerol (Gly) in different ratios. Consequently, redshifted structural colors were obtained from the increase in the helical pitch of the chiral nematic structures according to the microstructure analysis. In addition to improving the mechanical properties of the composite films, glycerol also promoted the crystallinity of the films to different degrees. The CNC/Gly20 films exhibited reversible reflection colors at different relative humidity because of the strong water absorption capability of glycerol. Furthermore, CNC/Gly composite suspensions were used as photonic inks to obtain photonic writing with unique fingerprint textures. Moreover, the CNC/Gly nanocomposites were also used to make iridescent coatings on different substrates. The incorporation of glycerol improved the compatibility between the interfaces. Thus, photonic nanocomposites from cellulose nanocrystals can potentially be developed as optical sensors, security markings and functional coatings.

A new drug carrier with oxygen generation function for modulating tumor hypoxia microenvironment in cancer chemotherapy

Hypoxia is the main characteristic of tumor microenvironment, and the one of the key factors that cause the drug resistance of cancer cells for chemotherapy. Anticancer drug such as DOX cannot react with sufficient oxygen to produce reactive oxygen species (ROS) in hypoxic environment, which affects the therapeutic efficiency of the drug. In this work, we constructed a multi-functional nano-carrier (named as FeSiAuO) containing Fe3O4, mesoporous SiO2 and Au2O3 with magnetic, large surface ratio and light induced oxygen production properties. The Au2O3 may decompose into oxygen (O2) and Au under the light irradiation to improve the oxygen concentration of the microenvironment of cancer cells, which increases the sensitivity of cancer cells to drug (DOX), reduces the drug resistance, and effectively exerts the anticancer effect of DOX. Meanwhile, the release of the as-loaded DOX molecule from the porous of SiO2 will be also promoted under light irradiation in diverse pH conditions. With the helping of the magnet effect of the Fe3O4, the DOX can be also targeted delivered to the tumor site under the magnetic field. All of above results were thoroughly examined by the cell and small animal assays, which demonstrate that the FeSiAuO can be served as the multifunctional drug nano-carrier to achieve the targeted high-efficient cancer therapy.

A nanocomposite probe consisting of carbon quantum dots and phosphotungstic acid for fluorometric determination of chromate(VI) with improved selectivity

AbstractA fluorometric quenching assay is described for the determination of chromate(VI) by using a nanocomposite probe consisting of carbon quantum dots (CQDs) and phosphotungstic acid (HPW). The stable nanoprobe was synthesized via hydrothermal carbonization of glucose in the presence of HPW. HPW promotes the dehydration and carbonization and acts as an “electronic receptor”. It blocks the radiative electron/hole recombination in the CQDs and leads to a product whose fluorescence (with excitation/emission peaks at 360/463xa0nm) is quenched. The CQD/HPW was characterized by transmission electron microscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, UV-vis absorption and fluorescence spectroscopy to characterize their surface morphology, functional groups and elemental composition, crystal structure and optical properties. The nanocomposite is nearly mono-disperse with an average particle diameter of 1.7xa0nm, and displays excitation wavelength-dependent and pH-dependent photoluminescence. Fluorescence drops on addition of chromate(VI) due to an inner filter effect. The ability of receiving electron for HPW can hinder the electron transfer from CQD/HPW to other metal ions, so the nanocomposite showed excellent selectivity towards chromate(VI). Fluorescence drops linearly with the concentration of chromate(VI) in the range from 2 to 80xa0μM, with a limit of detection of 0.16xa0μM.n Graphical abstractHydrothermal carbonization preparation of carbon quantum dots and phosphotungstic acid nanocomposite probe for fluorometric determination of chromate(VI) based on inner filter effect.

Seeking value from biomass materials: preparation of coffee bean shell-derived fluorescent carbon dots via molecular aggregation for antioxidation and bioimaging applications

Bifunctional carbon dots have shown a large amount of potential in bioimaging and antioxidation applications. However, the hydrothermal method for the preparation of bifunctional carbon dots requires a high energy input and an expensive setup. Moreover, this method breaks down sensitive compounds in the raw materials and could decrease the antioxidation ability of the resulting carbon dots. Here, phenolic extracts of coffee bean shells were used to prepare carbon dots via a cheap, energy-saving, mild molecular aggregation method. The as-prepared carbon dots were characterized by TEM, HPLC, XPS and Raman spectroscopy. The carbon dots had a diameter ranging from 1 to 5 nm and mainly contained three kinds of phenolic compounds including 3,4,5-trihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid. The carbon dots demonstrated a strong antioxidation capacity, which was comparable to the commercially available butylated hydroxytoluene. The EC50 of the carbon dots was 110 μg mL−1. The carbon dots had a pH-/excitation-dependent fluorescence. The as-prepared carbon dots also showed anti-bleaching fluorescence, which was better than that of the commercially available 4′,6-diamidino-2-phenylindole. Based on this finding, the excellent biocompatibility of carbon dots enabled them to be successfully used for banana storage and imaging both cancer cell nuclei and tumors in vivo.

Preparation of a Smart and Portable Film for in Situ Sensing of Iron Microcorrosion

Corrosion of iron-containing materials, which presents serious economic and safety problems, normally begins with microcorrosion, which refers to the early stages of corrosion before visible changes appear on the surface. If microcorrosion could be detected and repaired immediately, corrosion damage could be greatly reduced. Current technology and materials, however, are not able to detect microcorrosion of iron in a cheap and convenient manner. Here, we have used a natural product, ellagic acid (EA), to fabricate an EA-functionalized poly(vinyl alcohol) (PVA) film (EAF) for in situ sensing of the initial stage of microcorrosion. EAF was able to effectively sense iron microcorrosion via an obvious color change. The film also had good long-term stability and mechanical strength. Since EAF can be easily prepared from inexpensive and green raw materials, the film opens up a new opportunity for the detection of iron microcorrosion.