Green Synthesis,characterization Of Radix Hedysari-mediated AgNPs And Their Application In Colorimetric Detection

Silver nanoparticles（AgNPs）are silver nanomaterials with at least one dimension in the range of 1 nm～100 nm in three-dimensional microstructure.AgNPs have been widely used in the fields of electrochemistry,optics science,material science,medical and biomedical science due to its special performances such as surface plasmon resonance property,Surface-Enhanced Raman Scattering effect,fluorescence property,adsorption property and catalytic property.AgNPs can be synthesized by a variety of ways such as chemical synthesis method,laser ablation method,microemulsion method and two-phase synthesis.The surface plasmon resonance effect enables AgNPs to absorb light of a certain wavelength,which endow the solution of AgNPs a specific color.AgNPs have been widely used as colorimetric sensors for the colorimetric detection of various targets.Metal ions,small chemical molecules,drug molecules,and biological macromolecules are common detection objects of AgNPs colorimetric sensors.AgNPs are universally synthesized by chemical synthesis methods which are simple and time saving.However,because most of chemical synthesis methods involve the use of toxic chemicals,which may cause environmental pollution,it’s nanoparticle products also have poor safety and biocompatibility.With the improvement of environmental protection awareness,the method of green synthesis of AgNPs by using natural plant extracts has attracted significant attention of the researchers.In this study,based on the principle of green chemistry,AgNPs were prepared by using the extract or components of traditional Chinese medicine Radix Hedysari as reducing agent,stabilizer and modifier.The obtained AgNPs was then applied in the detection of certain targets.The main research contents and conclusions are as follows:（1）A safe,rapid,and environment-friendly green synthesis for AgNPs using the alcohol extract of Radix Hedysari（RH-AgNPs）was developed,the alcohol extract of Radix Hedysari（RH）was acted as the reducing agent,stabilizer,and modifier.The main components of RH were determined by using High Performance Liquid Chromatography（HPLC）.The particle size and morphology of RH-AgNPs were optimized and characterized by a series of techniques.The size distribution,zeta potential,element distribution,and crystalline nature of RH-AgNPs were all determined.It was indicated that RH-AgNPs showed great sensitivity for lead ion(Pb²⁺)detection with the LOD of 1.5μM and a wide range of 10～500μM.The selectivity was also explored for common metal ions.RH-AgNPs was then well applied to the detection of Pb²⁺spiked in Yellow River samples,and the possible mechanism was based on the crosslink reaction between hydroxide radical,carboxylate radical and Pb²⁺.（2）HPLC was used to confirm the components of ethyl acetate extract of Radix Hedysari（ER）,in which it was surprisingly found that formononetin accounted for more than 85%in total contents.Thus,formononetin standard was tried to green synthesis AgNPs,FMT-AgNPs was successfully systhesized through one-pot reaction method.After optimization,FMT-AgNPs were characterized and confirmed by a series of techniques.A simple,fast and sensitive colorimetric method for common pesticide of formothion was realized.A wide linear range from 0.1μM to 10μM was established with a low detection limit of 14.6 nM.As formononetin acted multiple roles in reaction,it was reasonably confirmed that detection mechanism depended on the aldol condensation,intermolecular hydrogen bonds and electrostatic attraction between formononetin and formothion.Finally,the green synthesized FMT-AgNPs was further applied in various samples including fruit,vegetable,urine and serum samples,indicating the huge market potential.（3）AgNPs（HPS-AgNPs）were successfully synthesized by using astragalus polysaccharide（HPS）as reduce agent,stabilize agent and modifier.Basis on obtained HPS-AgNPs,a filter paper detection device for the detection of methimazole with HPS-AgNPs act as the detection substrate was established.The detection mechanism of this device is the specific aggregation effect of HPS-AgNPs and methimazole and the retention effect of small aperture filter paper on large nanoparticle.The detection limit is nM with a wide range of 0.1～10μM.Finally,this paper-based device was applied in the detection of urine and serum samples.As a paper-based assay,this detection device are proven to be stable,sensitive,specific and fast.