Preparation Of Red Carbon Dots And Applications In Organelles Imaging And Acid-Base Titration

Organelles are the basic unit of cells and play vital roles in maintaining the basic functions.Fluctuations in the content of substances in organelles may cause various diseases.Therefore,it is helpful for the diagnosis and treatment of diseases to target specific organelles to detect the content of certain substances.Some organic fluorescent probes have been widely used in organelle imaging,but the photo-stability and biocompatibility need to be further improved.The exploration on endoplasmic reticulum probe is still in the early phase.As a classical analytical method,acid-base titration has been widely applied to determine acids,alkalis,and carbonates in chemical products,foods,and other daily necessities.There are need for sensitive indicator to indicate the endpoint in acid-base titration analysis.Methyl orange and methyl red are the generally used indicators for the acid endpoint for alkali analysis,which turn orange from yellow at the endpoint.However,it is so hard to distinguish the color change by naked eyes that experienced operators always miss the endpoint.To sharpen the color change at the endpoint,mixed indicators concluding bromocresol green and methyl red are employed.It is important to develop new indicators for acid endpoint indication that composed by single composition and offer obvious color changes.Carbon dots(CDs)are novel materials featured with excellent chemical and optical stability,biocompatibility and tunable fluorescence,which enable their wide applications in sensing,subcellular imaging and photoelectric devices.Their extremely small size,stable photo property and high sensitivity,enable CDs versatile tools for labeling of various organelles and detecting chemical substances.The tunable structures of CDs provide new method for exploring indicator.In this paper,a kind of red carbon dots was prepared,the optical properties were investigated systematically,and the applications in organelle imaging and acid-base titration were studied.(1)Preparation of red CDs and the optical properties: red color CDs are prepared via hydrothermal treatment of o-phenylenediamine and urea.The red CDs show dualemission at 600 nm and 650 nm when excited 540 nm and 580 nm,with the absolute quantum yield of 20.1%.The red carbon dots show absorption band at 280,537,570 nm,which are attributed to n-?* transition of C-N/C=N and C-O/O=C-O bonds,indicating conjugated ? electron system.(2)The as-prepared carbon dots show low cytotoxicity and high photostability.When incubated with cells,the CDs enter cell via caveolin/lipid-raft-mediated internalization pathways,and then located in the endoplasmic reticulum.This demonstrate the great potential of the CDs as targeting probe of endoplasmic reticulum.(3)The acidichromism feature and mechanism: the as-prepared red CDs exhibit acidichromism feature,showing color change from red to purple at p H 4.4,as well as color change from purple to blue at p H 3.3.According to the analysis of X-ray photoelectron spectrum,the decrease of double bond and increase of single bond generate acidichromism phenomenon in acidic condition.The CDs are used for acidbase titration analysis of mixed alkali and industrial alkali,and the results show no significant differences in contrast with those of tested by the national standard method.