Study On Synthesis And Anti-Inflammatory Effect Of Salicylic Acid And Thiourea-based Carbon Nanodots

Objectives:Inflammatory responses play an important role in the occurrence and development of different diseases,and it is of great significance to inhibit excessive inflammation and prevent the progression of inflammation.The drugs widely used to treat many inflammatory diseases include steroid hormones,non-steroidal anti-inflammatory drugs and some biological anti-inflammatory agents,which have good anti-inflammatory effects,but still show some application defects such as adverse drug reactions,side effects,and short half-life and high production cost.Due to the unique nanometer size,the properties that could be modified with multifunctions and good biological safety,nanomaterials show a good application prospect in biological anti-inflammatory effects.In this study,we hope to synthesize a pharmaceutical carbon nanodots with clarified chemical characterizations and good biological safety,and explore the bioimaging and anti-inflammatory effects of drug carbon nanodots.Methods:1.The salicylic acid/thiourea based carbon nanodots(CDots)were synthesized by a one-step microwave heating treatment.To reveal the elemental composition,morphology and structure of the CDots,transmission electron microscopy(TEM)and X-ray powder diffraction(XRD)were carried out.In order to reveal the chemical structure and the formation mechanism of CDots,energy-dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared(FTIR)characterizations were performed.And to detecte the photoluminescence(PL)properties of the CDots,fluorescence photos was taken and PL emission spectrum was measured.Finally,the mechanism of special optical properties of CDots was analysed by a designed control test,and was verified through theoretical calculations.2.The stability of the CDots was evaluated by observing the PL intensity of the CDots in organic solution and under fluorescence microscope,respectively.The biological safety of the CDots was evaluated by MTT assay,fluorescence-activated cell sorting and in vivo injection performed in nude mice.The in vitro and in vivo bioimaging of the CDots was observed under confocal laser scanning microscopy(CLSM)and in nude mice,respectively.At last,a lipopolysaccharide-induced cellular inflammation model was established,and the anti-inflammatory effect of CDots in the model was tested by RT-q PCR、Western blot and ELISA assays.Results:1.The well-resolved lattice spacing of CDots can be observed by TEM and XRD,with uniform particle size distribution of 2.5-6 nm.EDS showed that all of the elements of CDots derived from the reaction of raw materials,salicylic acid and thiourea,and are free of other doping elements.The XPS and FTIR spectra analyzed the functional groups of the CDots,and the results show that the formation of CDots based on the dehydration condensation and further carbonization between carboxyl/hydroxyl groups of salicylic acid and the amine groups of thiourea,and the synthesized CDots formed the amide bond with anti-inflammatory function.Both PL emission spectrum and fluorescence photos show that the CDots have yellow-green fluorescence,with the PL emission peak at 560 nm,and there was no obvious aggregation-induced fluorescence quenching in the aggregated state.The result of control testing and the density functional theory calculations shown that S element doped into CDots is critical in governing the PL emission color.2.The CDots exhibit remarkable resistance to common organic solvents,and its PL intensity could preserved more than 90% even after 65 min of irradiation.MTT assay,fluorescence-activated cell sorting and hematoxylin and eosin(H&E)staining of important organs of mice in the CDots group showed that the CDots have good biological safety.Under the excitation of 405 nm,the CDots can be seen co-localized with cells under CLSM,and the image of the CDots-treated mice presented strong PL emission,revealing that the CDots have effective bioimaging effects.RT-q PCR and Western blot assays detected that CDots could inhibit TNF-α and IL-1β significantly in the LPS-induced inflammation model.Conclusions:1.CDots with nanometer size,amide bond,and greenish-yellow fluorescence without aggregation-induced fluorescence quenching were prepared.2.The prepared salicylic acid and thiourea-based CDots have good stability,biological safety,effective in vivo and in vitro imaging and stronger anti-inflammatory effects than salicylic acid.