Browsing by Author "Zhou, Shaochen"

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  • Bright and Photostable Fluorescent Metal Nanocluster Supraparticles from Invert Emulsions
    (2022-10-04) Zhou, Shaochen; Peng, Bo; Duan, Yanyan; Liu, Kai; Ikkala, Olli; Ras, Robin H.A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fluorescent supraparticles of gold, silver and copper nanoclusters are synthesized by simply drying of invert emulsions, resulting in a dozen-fold increase in photoluminescence quantum yield (up to ≈80 %) and a significant improvement in photostability. The inhibition of the ligand twisting during the intramolecular charge transfer is found to be responsible for the enhancement, especially for the gold nanocluster supraparticles. This research provides a general, flexible, and easy method for producing highly luminescent and photostable metal nanocluster-based materials that promise practical applications in white-light-emitting diodes.
  • Bright and stable gold nanocluster assemblies by silica/zirconia double-shell encapsulation
    (2022-07-14) Zhou, Shaochen; Duan, Yanyan; Liu, Kai; Ras, Robin H.A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Ultrasmall gold nanoclusters are fascinating fluorescent materials with many unique properties, yet, to render them highly luminescent and stable remains challenging. In this work, solvent-induced aggregates of gold nanoclusters are encapsulated in silica/zirconia nanostructures, realizing a significantly enhanced photoluminescence efficiency and stability. These silica and zirconia coated gold nanocluster aggregates achieved a photoluminescence quantum yield of ∼55%, with high resistance to photobleaching and water, due to the stabilization by the dual-oxide matrix. Furthermore, we demonstrate their suitability for visualizing latent fingerprints.
  • Design of Fluoro-Free Surfaces Super-Repellent to Low-Surface-Tension Liquids
    (2023-07-20) Wong, William S.Y.; Kiseleva, Mariia S.; Zhou, Shaochen; Junaid, Muhammad; Pitkänen, Leena; Ras, Robin H.A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Super-liquid-repellent surfaces feature high liquid contact angles and low sliding angles find key applications in anti-fouling and self-cleaning. While repellency for water is easily achieved with hydrocarbon functionalities, repellency for many low-surface-tension liquids (down to 30 mN m−1) still requires perfluoroalkyls (a persistent environmental pollutant and bioaccumulation hazard). Here, the scalable room-temperature synthesis of stochastic nanoparticle surfaces with fluoro-free moieties is investigated. Silicone (dimethyl and monomethyl) and hydrocarbon surface chemistries are benchmarked against perfluoroalkyls, assessed using model low-surface-tension liquids (ethanol–water mixtures). It is discovered that both hydrocarbon- and dimethyl-silicone-based functionalization can achieve super-liquid-repellency down to 40–41 mN m−1 and 32–33 mN m−1, respectively (vs 27–32 mN m−1 for perfluoroalkyls). The dimethyl silicone variant demonstrates superior fluoro-free liquid repellency likely due to its denser dimethyl molecular configuration. It is shown that perfluoroalkyls are not necessary for many real-world scenarios requiring super-liquid-repellency. Effective super-repellency of different surface chemistries against different liquids can be adequately predicted using empirically verified phase diagrams. These findings encourage a liquid-centric design, i.e., tailoring surfaces for target liquid properties. Herein, key guidelines are provided for achieving functional yet sustainably designed super-liquid-repellency.
  • Highly Luminescent Gold Nanocluster Frameworks
    (2019) Chandra, Sourov; Nonappa, Nonappa; Beaune, Grégory; Som, Anirban; Zhou, Shaochen; Lahtinen, Jouko; Jiang, Hua; Timonen, Jaakko; Ikkala, Olli; Ras, Robin
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Metal nanoclusters (NCs) are being intensely pursued as prospective luminophores because of their tunable electronic and optical properties. Among the various fluorescent NCs, gold nanoclusters (GNCs) are attractive due to their biocompatibility and excellent photostability, even if so far, they have had limited application potential due to poor quantum yield (QY). In this context, a facile route is demonstrated to tune up the photophysical and photochemical activities of water‐borne luminescent GNCs through the formation of self‐assembled nanocluster superstructures. The approach involves the controlled introduction of Sn2+ ions, directing GNCs from individual particles into 3D spherical gold nanocluster colloidal frameworks (GNCFs). In these, the reduction in the nonemissive relaxation pathways leads to significant enhancement of luminescence signals (QY from ≈3.5% to ≈25%), likely owing to restricted movements of ligands. This approach paves ways for GNCFs as a potent agent for biomedical imaging and therapies, while their high photocatalytic activity is an added advantage
  • Light-patterned fluorescent gold nanoclusters in polycarbonate films
    (2021-12-01) Bitarafan, Mohammad H.; Zhou, Shaochen; Hänninen, Jussi; Duan, Yanyan; Leino, Martti; Ras, Robin H.A.; Toivonen, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fluorescent metal nanoclusters embedded in rigid matrices are attractive for many applications, such as for use as light-emitting diodes and for optical data storage. Given the advantages of polycarbonate films, like high transparency and excellent toughness, the development of metal nanoclusters in these films could further enhance various applications. Herein, we fabricated fluorescent gold nanoclusters in a polycarbonate film using a photochemical process. The polymer film is doped with gold chloride and a photoinitiator and then irradiated by a light-emitting diode (365 nm), leading to the photoreduction of gold ions and the formation of bright fluorescent nanoclusters with a quantum yield of 15%. The as-formed nanoclusters display good photostability and retain their emission spectral shape over an extended period of time. These highly fluorescent structures have potential applications in the fabrication of authenticity markings and optoelectronic devices.
  • pH-Responsive Near-Infrared Emitting Gold Nanoclusters
    (2023-12-04) Zhou, Shaochen; Gustavsson, Lotta; Beaune, Grégory; Chandra, Sourov; Niskanen, Jukka; Ruokolainen, Janne; Timonen, Jaakko V. I.; Ikkala, Olli; Peng, Bo; Ras, Robin H. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Near-infrared (NIR) fluorophores with pH-responsive properties suggest merits in biological analyses. This work establishes a general and effective method to obtain pH-responsive NIR emissive gold nanoclusters by introducing aliphatic tertiary amine (TA) groups into the ligands. Computational study suggests that the pH-responsive NIR emission is associated with electronic structure change upon protonation and deprotonation of TA groups. Photo-induced electron transfer between deprotonated TA groups and the surface Au-S motifs of gold nanoclusters can disrupt the radiative transitions and thereby decrease the photoluminescence intensity in basic environments (pH=7–11). By contrast, protonated TA groups curb the electron transfer and restore the photoluminescence intensity in acidic environments (pH=4–7). The pH-responsive NIR-emitting gold nanoclusters serve as a specific and sensitive probe for the lysosomes in the cells, offering non-invasive emissions without interferences from intracellular autofluorescence.
  • Photoluminescent Gold Nanoclusters in Soft Matrices
    (2023) Zhou, Shaochen
     School of Science | Doctoral dissertation (article-based)
    Photoluminescent gold nanoclusters (AuNCs), composed of several to tens of gold atoms, are versatile ultrasmall nanomaterials that show promise in applications like imaging, sensing, lighting, and catalysis. However, the inferior photoluminescence performance and lack of functional properties, have hindered AuNCs from extensive application. This thesis discusses AuNCs confined in three types of soft matrices, namely assemblies, double-layered structures, and polymers. Confinement of AuNCs in the soft matrices can result in great performance improvement and interesting functional properties. The mechanisms behind the performance enhancement and functional properties are studied and discussed. The AuNCs in the soft matrices show potential for various applications. Publication 1 establishes supraparticles as a promising soft matrix for AuNCs, achieving a significant improvement in photoluminescence emission brightness and resistance to photobleaching. Publication 2 reports a dual-layered oxide shell as an effective matrix for AuNCs, achieving comprehensive enhancement in stability. Publication 3 introduces a simple, direct strategy for both generation and encapsulation of AuNCs in the polymer film, exhibiting moderate photoluminescence efficiency and excellent shelf and photo-stability. Publication 4 outlines that confinement of AuNCs in the aliphatic tertiary amine group-rich polymer scaffold leads to pH-responsive near-infrared emission, promising great bio-application potential. Overall, these works demonstrate various strategies for obtaining gold nanoclusters with improved photoluminescence performance and functional properties.