title: Color-switchable, emission-enhanced fluorescence realized by engineering C-dot@C-dot nanoparticles.
abstract: This paper reports the preparation and properties of color-switchable fluorescent carbon nanodots (C-dots). C-dots that emit dark turquoise and green-yellow fluorescence under 365 nm UV illumination were obtained from the hydrothermal decomposition of citric acid. Dark green fluorescent C-dots were obtained by conjugating prepared C-dots to form C-dot@C-dot nanoparticles. After successful conjugation of the C-dots, the fluorescence emission undergoes a blue-shift of nearly 20 nm (∼0.15 eV) under UV excitation at 370 nm. The C-dots emit goldenrod, green-yellow, and gold light under excitation at 455 nm, which shows that the prepared C-dots are color-switchable. Furthermore, conjugation of the C-dots results in enhanced, red-shifted absorption of the π-π* transition of the aromatic sp(2) domains due to the conjugated π-electron system. N incorporation in the carbon structure leads to a degree of dipoles for all the aromatic sp(2) bonds. The enhanced absorption in a wide range from 226 to 601 nm indicates extended conjugation in the C-dot@C-dot structure. The time-resolved average lifetimes for the three different types of C-dots prepared in this study are 7.10, 7.65, and 4.07 ns. The radiative rate (reduced decay lifetime) increases when the C-dots are conjugated in the C-dot@C-dot nanoparticles, leading to the enhanced fluorescence emission. The fluorescence emission of the C-dot@C-dot nanoparticles can be used in applications such as flow cytometry and cell imaging.
authors.affiliation: CAS Key Lab of Bio-Medical Diagnostics, Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences , No. 88, Keling Road, Suzhou New District 215163, People's Republic of China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Guo
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Lianqun
authors.initials: L
authors.lastname: Zhou
authors.forename: Haiwen
authors.initials: H
authors.lastname: Li
authors.forename: Hongmei
authors.initials: H
authors.lastname: Wang
authors.forename: Caroline
authors.initials: C
authors.lastname: Andreazza-Vignolle
authors.forename: Pascal
authors.initials: P
authors.lastname: Andreazza
authors.forename: Dongxu
authors.initials: D
authors.lastname: Zhao
authors.forename: Yihui
authors.initials: Y
authors.lastname: Wu
authors.forename: Quanlong
authors.initials: Q
authors.lastname: Wang
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
authors.forename: Keming
authors.initials: K
authors.lastname: Jiang
mesh_terms: D002244:Carbon / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry; D003116:Color; D005434:Flow Cytometry; D005453:Fluorescence; D008027:Light; D053758:Nanoparticles / Q000737:chemistry*
chemical_list: D019343:Citric Acid; D002244:Carbon
keywords: color switching; conjugating nanoparticles; emission enhancement; fluorescent carbon nanodots