Water-dispersible near-infrared luminescent silicon nanocrystals -immobilization on substrate
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esearch Letter
Water-dispersible near-infrared luminescent silicon nanocrystals –immobilization on substrate Takashi Kanno, Shinya Kano, Hiroshi Sugimoto, Yasuhiro Tada, and Minoru Fujii, Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan Address all correspondence to S. Kano at [email protected] and M. Fujii at [email protected] (Received 27 July 2016; accepted 13 October 2016)
Abstract We demonstrate formation of allylamine (AAm) and acrylic acid (AAc)-functionalized colloidal silicon nanocrystals (Si NCs) exhibiting nearinfrared (NIR) luminescence and immobilization of the NCs on substrates via covalent bond. The surface functionalization is confirmed by IR absorption spectroscopy and specific binding property of functionalized NCs. Atomic force microscope observations reveal that AAm- and AAc-functionalized Si NCs are chemically immobilized on self-assembled monolayers via covalent bonds. The functionalized Si NCs exhibit photoluminescence in a NIR region (1.5–1.6 eV), which is not significantly affected by the functionalization.
Introduction Colloidal semiconductor nanocrystals (NCs) are a powerful tool for bioimaging and biosensing as fluorescent markers.[1] Specific properties required for a fluorescent NC in the biomedical application are: (i) water dispersibility, (ii) pH stability, (iii) photostability, and (iv) low interactions between NCs and biomolecules for long term. These properties of colloidal semiconductor NCs have been studied in detail on cadmium or leadchalcogenide NCs.[2] However, high toxicity of these material is always a concern for the in vitro and in vivo applications.[3] Silicon (Si) NCs have been attracting significant attention in biomedical fields due to the low toxicity.[4] Water-dispersible Si NCs are obtained by surface functionalization with hydrophilic molecules such as amine groups,[5,6] carboxylic acid groups,[7,8] and poly(ethylene glycol) chains,[9] and micelleencapsulated structures.[10,11] These organic functionalized Si NCs usually exhibit luminescence in the ultraviolet–visible (UV–VIS) ranges, and those having luminescence in the nearinfrared (NIR) biological window region (1.2–1.8 eV) are very limited. Recently, we have developed a new type of all-inorganic colloidal Si NCs. The Si NCs have high boron (B) and phosphorus (P) concentration shells (B and P co-doped Si NCs)[12–15] and are dispersed in water and alcohol without organic ligands. The all-inorganic Si NCs exhibit bright and stable luminescence in the biological window.[14] It is beneficial to develop the process to functionalize the surface with organic molecules without scarifying the solution dispersibility and the NIR luminescence efficiency for further applications. With the molecules, NCs can be chemically immobilized onto the specific surface of biosensing devices and biomaterials such as protein and antibody by
conjugation via peptide bond,[16] thiol bond,[17] and azide alkyne cycloaddition.[18] In this work, w
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