Hydrophilic Assemblies Of Cu_2-xSe/rGO And Their Applications In Dark-Field Light Scattering Imaging Analysis

Localized surface plasmon resonance (LSPR) in doped semiconductor nanocrystals (NCs) have received considerable attention recently, especially the near-infrared (NIR) LSPR in Copper chalcogenides. In contrast to the LSPR in metals (i.e., Au and Ag), which is attributed to the collective oscillations of free electrons, the NIR LSPR in these heavily-doped copper chalcogenides arises from free carriers (holes) in the valence band, which are provided by cationic vacancies or extrinsic dopants. Cu2-xSe exhibits good biocompatibility as well as strong NIR LSPR for broad applications. Until now, small Cu2-xSe NCs has been usually synthesized through an oil-phase, high-temperature and complicated procedure. These hydrophobic products, without favorable surface modification, may greatly restrict their potential applications in vitro or in vivo. Herein, a facile and green aqueous chemical approach is developed for one-pot synthesis of hydrophilic Cu2-xSe/rGO nanocomposites at room temperature, which exhibit intense LSPR absorption in the NIR region and favorable properties in cellular dark-field microscopic imaging (iDFM). Furthermore, homogeneous hollow Cu2-xSeyS1-y/rGO nanocomposites also have been synthesized by this facile one-pot aqueous chemical approach via H2S gas bubbles generated in situ. The research contains following contents:(1) The hydrophilic and monodispersed Cu2-xSe/rGO nanocomposites are obtained by a facile and green aqueous chemical approach at room temperature, without the use of any surfactants, wherein the reduction of GO and the in situ growth of Cu2-xSe NPs on the rGO sheets occur simultaneously. With the introduction of ascorbic acid (AA), a green natural product, which serves not only as a mild reducing agent, but also as a capping reagent, individual Cu2-xSe NPs are uniformly decorated on the rGO sheets without apparent aggregation. Cu2-xSe/rGO nanocomposites are then characterized by TEM, SEM, EDX, AFM, XRD, XPS, FT-IR, Raman and DLS, which suggest the as-obtained cubic Cu2-xSe/rGO nanocomposites exhibit uniform size (-40 nm), high purity and good solubility. Excellent optical properties and the intense absorption in the NIR region are found in Cu2-xSe/rGO nanocomposites. The NIR absorption band red-shifts with increasing solvent refractive index, as expected for an LSPR feature. Owing to the nonstoichiometric composition of cubic Cu2-xSe decorated on the rGO sheets, the NIR LSPR in Cu2-xSe/rGO nanocomposites could be well-tuned from 1360 to 1050 nm by adjusting the density of free carriers (holes) through the reaction time, with the preservation of the crystal phase and morphology of Cu2-xSe NCs. Furthermore, the as-prepared Cu2-xSe/rGO nanocomposites exhibit good biocompatibility as well as unique dark-field light scattering properties, strong blue scattering signals, and are well applied as efficient probes for cellular dark-field microscopic imaging (iDFM) in vitro.(2) Hollow nanostructures have been diversely applied in many fields and researchers make great efforts to develop their various synthesis methodologies. Herein, we report a facile one-pot aqueous chemical approach for the controllable synthesis of homogeneous hollow Cu2-xSeyS1-y/reduced graphene oxide (rGO) nanocomposites via H2S gas bubbles at room temperature. Morphology evolution and composition variation of Cu2-xSeyS1-y/rGO nanocomposites are obtained by adjusting the S/Se molar ratio in the precursors. The TEM images clearly confirm the hollow nanostructure of Cu2-xSeyS1-y, and The N2 adsorption-desorption isotherms of Cu2-xSeyS1-y/rGO nanocomposites belong to the typical type Ⅳ isotherm, revealing a disordered mesoporous structure, respectively 2D hexagonal Cu2-xSeyS1-y nanosheets self-assemble into the large hollow nanospheres on the rGO sheets via H2S gas bubbles generated in situ, and rGO plays a critical role in maintaining the structural integrity of single-crystal hollow Cu2-xSeyS1-y nanospheres. A "gas-liquid interface aggregation mechanism" is proposed to explain the morphology and crystal phase formation in the synthesis, with the assistant of SEM and XRD characterization. Cu2-xSeyS1-y/rGO nanocomposites exhibit a strong NIR LSPR, arising from the high density of free carriers (holes) in Cu2-xSeyS1-y NCs. Owing to the higher holes effective mass and assembly degree in Cu2-xSeyS1-y, a continuous red shift of LSPR is revealed with increasing S content in Cu2-xSeySi-y/rG0 nanocomposites. Furthermore, Cu2-xSeyS1-y/rGO nanocomposites exhibit good dark-field light scattering properties, and are applied in dark-field microscopic imaging (iDFM).In summary, we develop a facile and green aqueous chemical approach for the one-pot synthesis of Cu2-xSe/rGO nanocomposites at room temperature, which echibit good solubility without the favourable surface modification and are suitable for further appilication in analysis and cell bioimaging. The LSPR frequency in Cu2-xSe/rGO nanocomposites could be well-tuned by changing the reaction oxidation time or adjusting the elements contents through extrinsic dopants. The unique dark-field light scattering properties of Cu2-xSe/rGO nanocomposites are uncovered, for the fisrt time, and are well applied as efficient probes for cellular dark-field microscopic imaging (iDFM) in vitro.