Study On Preparation Of Fluorescent Carbon Dots And Their Interaction With Human Serum Albumin/as Fluorescence Probe For Determination Of Ciprofloxacin

Fluorescent carbon dots?CDs?as a new class of carbon nanomaterialshave developed rapidly in recent years.In addition to their excellent optical properties,CDs possess photobleaching resistance,low toxicity,and good biocompatibility,and are widely applied as environmentally-friendly fluorescent nanomaterials in the fields of biomedicine,detection and so on.In this paper,two types of water-soluble fluorescent CDs were prepared by melting method.And then the CDs binding to human serum albumin and CDs as fluorescent probe for the detection of ciprofloxacin were studiedThe results are as follows:1.One novel type of fluorescent CDs was successfully fabricated by a simple and facile one–pot solid phase pyrolysis process using citric acid and glycine as raw materials.The obtained CDs under the optimal synthetic conditions have a fluorescence quantum yield up to 35.6%and show a spherical shape with an average diameter of about 3.0 nm.Moreover,CDs can emit strong blue fluorescence when excited at 345 nm and the surfaces of CDs were decorated with lots of carboxyl,hydroxyl and amine groups.In order to elucidate the interaction mechanism between the as-prepared CDs and human serum albumin at the molecular level.In this paper,steady-state fluorescence,time-resolved fluorescence,UV-vis absorption spectrum,circular dichroism spectrum?CD?,and Raman spectroscopic techniques as well as cyclic voltammetry?CV?were employed to explore the interaction of CDs with HSA in the simulated physiological environment.The experimental data reveal that the quenching mechanism of HSA by CDs is static quenching,which was verified by the stern-volmer curves,and absorptuion spectra and fluorescence lifetime.CDs could quench the intrinsic fluorescence of HSA via the formation of a ground-state complex with the association constants of the order of 10⁴ L/mol.The values of thermodynamic parameters obtained at three different temperatures suggest that the binding reaction of CDs with HSA mainly driven by hydrophobic forces and hydrogen bonds was spontaneous.Furthermore,the displacement experiments confirmed that the binding of CDs primarily took place in site I of HSA.The average distance between CDs and tryptophan?Trp?residue of HSA was estimated to be 2.3nm according to the theory of F?rster non-radiation energy transfer.Finally,the analysis of synchronous fluorescence,three-dimensional fluorescence?3D?,Raman,and CD spectra manifests that HSA underwent some conformational changes by unfolding the polypeptides of protein and increasing the polarity of the micro-environment surrounding both Trp and tyrosine?Tyr?residues in the presence of CDs.The results provide some experimental data and theoretical reference for the practical application of fluorescent carbon dots.2.Using malic acid as a carbon source and ammonium phosphate as a passivation agent,one-step synthesis of fluorescent CDs was performed by a fusion method.CDs was obtained under the optimum synthesis conditions.It was found that the CDs with a fluorescence quantum yield of 20.7%was spherical and dispersed uniformly with an average diameter of about 3.3 nm.The results of FT-IR and XPS indicated that the surfaces of the as-prepared CDs contained functional groups such as-COOH,-OH and-NH₂.The prepared CDs as a fluorescent probe were used to determine the concentration of ciprofloxacin?CIP?based on the enhancement of CDs fluorescence upon adding CIP.It was found that the optimum concentration of carbon dots was7.50×10^-6mol/L,the optimum pH was 5.91,and the optimal incubation time was 3min for the detection of CIP.under the optimal conditions,the enhancement of CDs fluorescence has a good linear relationship with the concentration of CIP ranged from0.39×10^-6mol/L to 4.00×10^-5mol/L,the correlation coefficient is R²=0.994.The linear regression equation is:?F=1.61×10⁷[CIP]-3.28.The detection limit and the precision are 0.12×10^-66 mol/L and 4.2%,respectively.The interference experiments indicated that except copper ions,other ions have no significant effects on the detection of CIP,and the interference of copper ions can be masked with 4%ammonium oxalate solution.Finally,the concentration of CIP in the actual sample was determined and the recovery was from 90%to 110%.The proposed method with good selectivity and wide linear range is simple,fast,reliable and has been used to determine CIP with a satisfactory result.