Studies On The Preparation Of N-Doped Carbon Quantum Dots And Their Applications In Cellular Imaging

Carbon quantum dots(Carbon dots)holds numerous superior properties,such as outstanding optical performance,ease of preparation and functionalization,favorable biocompatibility,anti-photobleaching and so on,making them promising materials in the field of bio-imaging,sensing,cancer theranostics.However,most of the currently reported carbon dots are excited by short wavelengths,and the emission wavelengths are mainly concentrated in the blue-green region,tending to cause auto-fluorescence interference.Meanwhile,carbon dots are poorly targeted and can not distinguish cancer cells from normal cells.These problems significantly inhibit the further applications of carbon dots in the field of biomedicine.In this paper,three kinds of N-doped fluorescent carbon dots with different characteristics have been obtained by simple one-step solvothermal methods using different raw materials to meet the diversified application needs.This article has been mainly studied from the following aspects:(1)N-doped fluorescent carbon dots(N-CDs)with up-conversion properties have been synthesized by simple and environmentally friendly one-step solvothermal methods employing 3,5-diaminobenzoic acid as carbon source,whose quantum yield is 10.2%.N-CDs with mean size of 2.48 nm,who are provided with a uniform size distribution,are rich in hydrophilic groups on the surface,which endows carbon dots with good hydrophilicity.N-CDs could produce bright blue-green fluorescence under the action of ultraviolet lamp and exhibit excitation independent luminescence.At the same time,N-CDs with good optical stability exhibit PH-sensitive and solvent-dependent luminescence.In addition,N-CDs with favorable biocompatibility could be directly applied in cellular imaging.More importantly,N-CDs exhibit significant up-conversion properties and could be used for up-conversion cellular imaging,showing great potential for development in the aspects of two-photon fluorescence imaging.(2)Red fluorescent carbon dots(R-CDs)have been obtained after a simple step of hydrothermal treatment using 3,4-diaminobenzoic acid and dopamine as raw materials.Studies show that R-CDs are rich in nitrogen,oxygen-containing groups and have good dispersion in ethanol.The R-CDs ethanol solution has several continuous absorption peaks between 500~630nm and could produce red fluorescence under ultraviolet lamp.The emission wavelength of R-CDs is always located near 659 nm exhibiting excitation independent luminescent properties,and the maximum fluorescence intensity is obtained at 540 nm.In addition,the prepared R-CDs show excellent optical stability and low toxicity,successfully applied in the research of cell imaging.(3)Targeted fluorescent carbon dots have been construct through simple one-step hydrothermal treatment by selecting folic acid and ammonia as raw materials.The studies have shown that the carbon dots contains numerous hydrophilic groups,holding excellent dispersibility in aqueous solution.The carbon dots could produce blue fluorescence under the irradiation of ultraviolet light and display excitation independent luminescence behavior.In addition,In addition,the carbon dots possess good ionic stability and anti-photobleaching ability.Compared with normal cells,this carbon dots with low toxicity could be efficiently taken up by cancer cells with highly expressed folate receptors on the surface and emit bright blue fluorescent signal,exhibiting specific targeting effects.