Construction Of The Methods For Detecting Cobalt,copper And Lead With Gold And Silver Nanomaterials And Their Application In Forest Foods

In recent years,with the enhancement of people's health concept,the consumption of forest foods has increased year by year,but the safety problems of forest foods caused by heavy metal pollution have often occured.The salts of cobalt(Co),copper(Cu2+),and lead(Pb2+)are widely used in industrial and agricultural productions.The forest foods may be polluted by Co,Cu and Pb at any time,which poses a serious threat to people's health.In this paper,based on the local surface plasmonic resonance characteristics of gold and silver nanomaterials,the highly sensitive colorimetric sensors of Co2+,Cu2+ and Pb2+ were constructed to solve the problems of the imperfect detection technology of heavy metals in forest foods and the incomplete monitoring projects in our national standards of heavy metals in forest foods.The visualization detections of Co2+,Cu2+ and Pb2+ were simple,sensitive and selective,which provided new methods for the detections of Co,Cu and Pb in forest foods.The details are as follows:1.Construction and application of highly sensitive colorimetric detection of cobalt ions based on Fenton-like reaction etching of gold nanostarsStable gold nanostars were synthesized by using 4-hydroxyethyl piperazine ethanesulfonic acid(HEPES)as reducing agent and capping agent and HAuCl4 as gold source.In the presence of CTAB,KSCN and NaHCO3,cobalt ions initiate the Fenton-like reaction and produce a large number of superoxide radicals,which oxidize Au0 on the gold nanostar surface to Au+,resulting in the peak blue shift of local surface plasmonic resonance(LSPR),and the color of the solution gradually changes from blue-green to purple and finally red.When the cobalt ion concentration reaches as low as 500 pmol/L,the naked eye can distinguish the color change.There was a good linear relationship between the concentration of cobalt ions and the wavelength variation of LSPR in the range of 100 pmol/L to 20 ?mol/L(R2=0.996),and the detection limit was 33 pmol/L.The method was simple,easy to operate,and has high sensitivity and anti-interference ability.It showed good reproducibility(RSD<5%)for the determination of cobalt content in forest food samples,as well as high accuracy(close to the determination results of graphite furnace atomic absorption spectrometry).2.Construction and application of highly sensitive colorimetric detection of copper ions based on the etching reaction of silver-coated gold nanostarsIn the presence of Na2S2O3,dissolved oxygen oxidizes elemental silver to form Ag(S2O3)23-,and copper ion can be used as a catalyst to accelerate this reactiol.The presence of copper ions will decrease the thickness of silver layer in GNSs@Ag,redice the intensity of the maximum UV-Vis absorption peak,and change solution color.When the concentration of copper ion is higher than 200 pmol/L,the naked eye can distinguish the color change.The linear relationship between Cu2+concentration and the absorbance at the maximum UV-Vis absorption wavelength was established in the range of 50 pmol/L to 50 ?mol/L(R2=0.994),with the detection limit of 15 pmol/L.The method had the advantages of simple operation,high sensitivity and good selectivity,and achieved good results in the determination of copper content in forest food samples.3.Construction and application of different sensitive colorimetric detection of lead ions based on three kinds of gold nanoparticles with different morphologies(spherical gold nanoparticles,gold nanorods and gold nanocrystals)(1)Lead ions in solution were detected by inducing the aggregation of glutathione functionalized gold nanoparticles(GSH-GNPs).The reason is that GSH and lead ions have strong chelating ability,and the aggregation of nanoparticles leads to the change of LSPR spectrum and the corresponding color of the solution.Lead ion concentration has a good linear relationship versus absorbance ratio(A680/A518)in the range of 0.02?mol/L to 20 ?mol/L(R2=0.993),and the detection limit is 6 nmol/L.The naked eye can distinguish the color changes caused by lead ions as low as 50 nmol/L.This method was simple,easy to operate,and has good selectivity.It achieved good results in detecting lead content in forest food samples.(2)The special catalysis of lead ions for etching gold nanorod was utilized to detect lead ions in solution.In the presence of dissolved oxygen,Na2S2O3 was added to the gold nanorod solution,and an Au(S2O3)23-coat was formed on the surface of the gold nanorod by means of the covalent bonding force of Au-S.After adding lead ions and 2-mercaptoethanol,lead ions were reduced to Pb0 and deposited on the surface of nanoparticles,which accelerated the leaching of gold by 2-mercaptoethanol,resulting in the morphology change of the nanorods and the change of the wavelength position of the maximum absorption peak.There was a good linear relationship between lead ion concentration and the maximum absorption peak wavelength in the range of 500 pmol/L to 50 ?mol/L(R2=0.995),and the detection limit was 150 pmol/L.The naked eye can distinguish the color changes caused by lead ions as low as 2 nmol/L.This method was simple,easy to operate,and has good selectivity.It achieved good results in detecting lead content in forest food samples.(3)The special catalysis of lead in gold nanostar etching system was used to detect lead ions in solution.In the presence of dissolved oxygen,Na2S2O3 was added to the gold nano-star solution to form a layer of Au(S2O3)23-membrane on the surface of the gold nanostars through the complexation of Au-S bond.After the addition of lead ions and 2-mercaptoethanol,lead ions were reduced to Pb0 and deposited on the surface of particles to catalyze the dissolution of Au by 2-mercaptoethanol,resulting in the etching of gold nanoparticles.When the concentration of lead ions increased over the range of 0?mol/L to 10?mol/L,the color of the solution changed from blue-green to blue-purple,red and finally colorless.When the concentration of lead ions reaches 200 pmol/L,the naked eye can distinguish the color change.With the concentration of lead ions was in the range of 2 pmol/L to 1 ?mol/L,there was a good linear relationship(R2=0.998),and the detection limit was 0.6 pmol/L.The method was simple,easy to operate,high sensitivity and strong anti-interference ability,and had a good detection effect on lead content in forest foods.The morphology and structure of gold and silver nanoparticles plays an important role in the sensitivity of the sensor to detect heavy metals.The structure of GNPs is highly symmetrical,and the local surface plasmon resonance(LSPR)depends on the size of GNPs particle size.The vertical structure of GNRs is different from the horizontal structure,and the LSPR depends on the aspect ratio of GNRs.GNSs has a special star structure,and the gold atoms at its edge and tip have high chemical activity.LSPR mainly depends on the number and length of the branches of GNRS.Therefore,compared with GNPs and GNRs sensors,GNSs sensors have a wider detection range and higher detection sensitivity.