Synthesis,Characterization Of Fluorescent Carbon Dots And Their Applications In Pharmaceutical Analysis

As an excellent optical probe,carbon dots?CDs?have shown their advantages in stability and biocompatibility,which has aroused great interest of researchers.Compared with conventional nano-materials,CDs possess higher specific surface area,smaller size and better optical properties.Over the years,the research about CDs in chemistry,physics,materials,biology and other cross-science has been carried out comprehensively.Through the unremitting efforts and exploration of scientists,CDs have been successfully applied to bioimaging,environmental detection,analytical sensing,energy conversion,information encryption,photocatalysis,drug delivery and other fields.Therefore,it is of great significance to explore a green,simple and effective synthetic method to prepare CDs with excellent properties and to broaden their application in the field of analysis and detection.In this paper,we have prepared different fluorescent CDs by hydrothermal method.And then we have explored the composition and stability of obtained CDs in detail.Meanwhile,we have built fluorescence analysis methods for detecting multiple drugs based on their fluorescence signals and explored their mechanism of action.The detail research contains the following two parts:?1?Carbon dots derived from tobacco for visually distinguishing and detecting three kinds of tetracyclinesAlthough a number of methods to perform assays of tetracyclines using fluorescent probes have been reported,approaches for discriminating and detecting tetracyclines?TCs?are few.Herein,bright-blue fluorescent T-CDs with a quantum yield?QY?up to27.9%were hydrothermally synthesized using tobacco as the carbon source,which not only had uniform particles but also excellent optical properties.The T-CDs mainly contain three elements:C,N and O.And the maximum excitation and emission spectra of T-CDs were obtained at 320 nm and 420 nm,respectively.The abundant functional groups of the T-CDs lead to the surface defects formed.To be specific,the different TCs possess diverse reaction sites with the T-CDs and the bonding amounts between the T-CDs and TCs are various,thus the fluorescence of T-CDs varied after the reaction.Importantly,the as-prepared CDs were employed as a fluorescent probe,enabling selective differentiation of three tetracyclines using a test strip and the related quantitative detection.Towards the mechanism,three kinds of tetracyclines showed different interactions with the CDs,leading to variations in their fluorescence emissions.To be specific,the fluorescence of CDs was quenched by tetracycline?TC?without a fluorescence shift?Em=440 nm?,which was caused by an inner filter effect rather than a change in the energy band gap.The decrease of fluorescence intensity?F₀/F-1?was linearly related to the concentration of the added TC solution in the range of 15.5nmol/L-6?mol/L,and the detection limit was 5.18 nmol/L.Moreover,the introduction of chlorotetracycline?CTC?resulted in a blue shift?Em=415 nm?of the fluorescence of the CD;this phenomenon was induced by the enlarged energy band gap.At the same time,the electron cloud density of conjugated rings in chlorotetracycline Mecule is lower than that of tetracycline and oxytetracycline?OTC?due to the existence of electron-withdrawing radicals?-Cl?.It is easier to bind with negatively charged T-CDs and forms a more stable system,which results in the enhancement of fluorescence signal.The enhancement of fluorescence intensity?F/F₀-1?has a good linear relationship with the concentration of CTC solution in the range of 20 nmol/L-0.2?mol/L.The detection limit is 14 nmol/L.Again,the CDs also responded to OTC,and their corresponding fluorescence experienced a red shift?Em=500 nm?due to the narrowed band gap.Consequently,a detection strategy for OTC has been proposed based on the quantitative evaluation of its concentrations in broad range from 20nmol/L-2?mol/L.The detection limit is 6.06 nmol/L.More importantly,the work demonstrates an additional,effective approach to assaying TCs.It has the potential to enable the visually identification between TC,OTC and CTC based on variations in the CDs'fluorescence emitting from the test strips.?2?Carbon dots derived from carboxymethylcellulose for sensing isoniazid and H₂O₂Isoniazid has been widely used in the treatment of human anti-tuberculosis in the recent years.It is a first-line clinical therapy,however high doses of isoniazid in vivo can cause side effects such as hepatotoxicity and so on.So,the accurate detection of isoniazid has important practical significance.Towards developing a facile way to synthesize CDs,herein,blue-fluorescence CDs derived from carboxymethylcellulose have been innovatively synthesized with well-distributed sizes.The optimum excitation and emission wavelengths of the CDs are 320 and 420 nm,respectively.And the obtained CDs with a quantum yield of 13.49%are resistant to photobleaching.The results of XPS and FITR indicated that C and O are the main components of CMC-CDs,and their surfaces are rich in oxygen-containing functional groups.Subsequently,a sensitive assay of isoniazid and H₂O₂ has been further proposed based on the hydrogen bond formation between CDs and isoniazid and the further oxidation of isoniazid by H₂O₂.To be specific,the richness of carboxyl groups and hydroxyl groups on the CDs enables isoniazid to be adsorbed on the surface of CDs,resulting in effective fluorescence quenching through aggregation.Moreover,we have taken the advantage of the oxidation reaction between isoniazid and H₂O₂ to achieve the immediate recovery of the fluorescence of CDs.Thereby,an analytical strategy for detecting both isoniazid and H₂O₂ has been established.Consequently,the fluorescent intensity decrease?F₀/F-1?versus the logarithmic plot of isoniazid concentration displayed a linear range of 20nmol/L-6?mol/L.The corresponding detection limit was 5.1 nmol/L at a signal-to-ratio of 3.Similarly,the fluorescence of CDs recovered?F/F₀-1?as well as the logarithmic of H₂O₂ concentrations?4-800 nmol/L?with a detection limit of 1.6 nmol/L at a signal-to-noise ratio of 3 were obtained.And its practicability is subsequently validated by detecting actual samples,suggesting that the current"on-off-on"strategy may broaden the avenues for sensing both isoniazid and H₂O₂.In summary,all of the above experimental results were the exploration about the preparation and characterization of CDs and its application on drug identification and sensing.These researches will help us to better understand the characterization and function of CDs better.Interestingly,the proposed CDs may possibly broaden the approaches for fluorescence sensing and drug identification etc.