| Iron plays a key role in biological metabolism,and oral iron supplements can effectively prevent diseases caused by iron deficiency.Iron supplements release Fe（II）or Fe（III）in the body,and these two valence states of iron ions have different biological activities and different biological effects.Qualitative and quantitative simultaneous detection of Fe（II）and Fe（III）is important for accurate assessment of the biological effectiveness and physiology and pathology of iron.In this paper,nano-functional materials were prepared using nitrogen-doped carbon quantum dots（N-CQDs）as carriers and applied to construct electrochemical sensors for the stable and efficient simultaneous detection of Fe（II）and Fe（III）,and the main research is as follows:（1）N-CQDs were prepared by a one-step hydrothermal method using sunflower pectin as the carbon source and ammonia as the nitrogen source.The optimal preparation process conditions（reaction temperature of 180 °C,reaction time of 8 h,nitrogen source of 0.3 m L,and yield of 26.93%）were optimized by single-factor experiments.The structural characterization was carried out by Fourier infrared transform spectroscopy（FT-IR）,ultraviolet-visible absorption spectroscopy（UV-vis）,fluorescence spectroscopy（FS）,zeta potential and X-ray diffraction（XRD）,and the morphology was characterized by transmission electron microscopy（TEM）.Finally,N-CQDs with good electrochemical activity and abundant functional groups on the surface were obtained.（2）The electrochemical characterization of bare glassy carbon electrode（GCE）,carbon quantum dots modified electrode（CQDs/GCE）and nitrogen-doped carbon quantum dot modified electrode（N-CQDs/GCE）was investigated by electrochemical AC impedance spectroscopy（EIS）and cyclic voltammetry（CV）,and N-CQDs/GCE showed the strongest electrochemical response to Fe（II）.N-CQDs were selected as the working electrode modification material to construct an electrochemical sensor for Fe（II）.The sensor had good reproducibility and selectivity with a limit of detection（LOD）of 0.098 m M,a detection range of 0.18～1.79 m M,and a degree of linearity of 0.988.（3）Nitrogen-doped carbon quantum dots/silver nanoparticles（N-CQDs/Ag NPs）composites were prepared using N-CQDs and silver nitrate as precursors.The structures of the composites were investigated by FT-IR,UV-vis and X-ray photoelectron spectroscopy（XPS）.The morphologies were characterized by scanning electron microscopy（SEM）.The electrochemical behavior of N-CQDs/Ag NPs composite modified electrodes（NCQDs/Ag NPs/GCE）was investigated by EIS and CV.Based on this,an electrochemical sensor was constructed for Fe（III）with a detection limit of 0.31 m M,a detection range of 1～10 m M,and a degree of linearity of 0.995.（4）Nitrogen-doped carbon quantum dots/silver nitrate nanoparticles/β-cyclodextrin（NCQDs/Ag NPs/β-CD）composites were prepared by a one-pot method using nitrogen-doped carbon quantum dots,silver nitrate and β-cyclodextrin（β-CD）as raw materials.The structural properties were investigated by structural characterization,morphological characterization,and electrochemical characterization.The electrochemical sensor constructed based on this composite for the simultaneous detection of Fe（II）and Fe（III）had a detection limit of 0.20 m M for Fe（II）and a detection range of 0.6～10 m M,and a detection limit of 0.033 m M for Fe（III）and a detection range of 0.2～10 m M.The sensor had good selectivity,stability,reproducibility,which had been successfully applied to the simultaneous detection of Fe（II）and Fe（III）released from iron supplements in simulated gastric fluid（SGF）. |
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