Electrochemical And Electrochemiluminescence Biosensor For Determination Of Organophosphorus Based On Graphitic Carbon Nitride

Organophosphorus pesticides（OPs）are widely used in pesticides because of their highly toxic properties.OPs residual can be found in the soil,food,environment,and threat human health.World Health Organization exhibited that OPs residus of agricultural products could cause Parkinson’s disease,Alzheimer’s disease,cardiovascular and cerebrovascular disease,diabetes,leukemia and other serious diseases.Therefore,OPs detection becomes an urgent problem to be solved.Electrochemistry is widely used for OPs detection due to its simple operation,high accuracy and low cost.Electrochemiluminescence（ECL）as a new analytical technology has the advantages of low background signal,high sensitivity and fast detection for OPs.We synthesised new graphite carbon nitride（g-C₃N₄）nanocomposites and designed novel electrochemical and ECL biosenor for detection of OPs based on the combination nanocomposites and enzyme inhibition.In this work,we used ethyl paraoxon as model OPs.The detailed researches are listed as follows.1.Electrochemical biosensor for detection of organophos phate pesticides and huperzine-A based on Pd wormlike nanochains/graphitic carbon nitride nanocompositesg-C₃N₄ has been widely used in the chemiluminescence and electrochemiluminescence because of its good thermal and chemical stability.However,reports of g-C₃N₄ in electrochemistry were few.In the work,g-C₃N₄ could combine with Pd wormlike nanochains（Pd WLNCs）to produce the nanocomposites（Pd WLNCs/g-C₃N₄）.A new electrochemical biosensor was developed for OPs and huperzine-A（hupA）detection based on Pd WLNCs/g-C₃N₄ nanocomposites and AChE,which broadened the application of g-C₃N₄ in electrochemistry..The morphologies and components of the nanocomposites were analyzed by transmission electron microscopy（TEM）and X-ray photoelectron spectroscopy（XPS）.The Pd wormlike nanochains/graphitic carbon nitrid（Pd WLNCs/g-C₃N₄）nanocomposites could effectively immobilize enzymes and promote the signal amplification.Under the optimum condition,the proposed biosensor displayed well performance.The linear response ranges for the determination of OPs and hupA were 1.00 nmol·L^-1 to 14.96 μmol·L^-1 and 3.89 nmol·L^-1 to 20.80 μmol·L^-1,respectively.The corresponding detection limits were 0.33 nmol·L^-1 and 1.30 nmol·L^-1（S/N=3）.Meanwhile,the biosensor owned good reproducibility and stability,and could also be applied to analyze practical samples,which would be a new hopeful method for pesticide analysis.2.A highly sensitive electroche miluminescence biosensor for detection of organophosphate pesticides based on cyclodextrin functionalized graphitic carbon nitrideOPs can inhibit the activity of ACh E,leading to the decreased yield of thiocholine and Acetic acid（HAc）produced by the hydrolysis of acetylthiocholine（ATCl）using AChE.In previous reports,most of OPs detection methods were based on the amount change of thiocholine.However,few research studies have been reported about using HAc as a quantitative entry point for OPs detection.In this work,we developed a new method for OPs detection based on acid-base reaction.A novel nanocomposite of b-cyclodextrin（b-CD）functionalized g-C₃N₄ was synthesized,which improved dispersity,stability and luminous efficiency compared with single g-C₃N4.Meanwhile,the obtained g-C₃N₄–CD also exhibited excellent supramolecular recognition property to ferrocenecarboxylic acid（Fc-COOH）,based on which a host-guest inclusion complex（g-C₃N₄–CD–Fc-COOH）was prepared.In addition,ACh E could be effectively immobilized on g-C₃N₄–CD–Fc-COOH to form a new biocomposite of g-C₃N₄–CD–Fc-COOH/ACh E via amidation reaction.Then,a signal on ECL biosensor based on the obtained biocomposite of g-C₃N₄–CD–Fc-COOH/AChE was constructed for OPs detection through enzyme inhibition mechanism.HAc in situ generated by enzymatic reaction could consume coreactant triethylamine（Et3N）around the electrode surface,leading to an obviously decreased ECL signal.Upon the addition of OPs,the consumption of Et3 N decreased because of inhibition on ACh E activity,leading to an enhanced ECL signal.Under the optimum conditions,t he new biosensor for OPs detection exhibited a wide linear range from 1.0 pmol·L^-1 to 0.5 μmol·L^-1 with a low detection limit of 0.3 pmol·L^-1.The novel strategy proposed in this work has the advantages of a low background signal,fast response time,good stability and reproducibility,which might hold a new promise for OPs detection applied in real-life samples.3.Ultrasensitive electroche miluminescence biosensor for organophosphate pesticides detection based on carboxylated graphitic carbon nitride-poly（ethylenimine）As we know,the critical factor in the construction of ECL biosensor is the amplif ication of signal.Most of reports indicated that metallic materials could achieve the amplif ication of signal for g-C₃N₄.Few polymers are used to amplify the ECL signal of C-g-C₃N₄.Poly（ethylenimine）（PEI）as one of a number of polycations were successfully bonded with carboxylated g-C₃N₄（C-g-C₃N₄）to improve the luminous efficiency.A signal on ECL biosensor was designed for sensitive OPs detection based on a novel composite of C-g-C₃N₄-PEI and AChE.The C-g-C₃N₄-PEI nanocomposite which was prepared through covalent bonding between the –COOH of C-g-C₃N₄ and the –NH2 of PEI exhibited significantly enhanced ECL efficiency and stability.K₂S₂O₈ as the coreactant of C-g-C₃N₄-PEI could be consumed by thiocholine,produced by the hydrolysis of ATCl in the presence of AChE.Since OPs are one of AChE inhibiter,the consumption of coreactant K₂S₂O₈ decreased with the increasing concentration of OPs,thus enhancing ECL signal.Under the optimum conditions,the proposed biosensor for OPs detection exhibited a wide linear ranging from 1.0 pmol·L^-1 to 5.0 μmol·L^-1 with a low detection limit of 0.3 pmol·L^-1.The novel strategy has the advantages of fine practicality,good stability and reproducibility,which might provide a new promise for OPs detection in real-life samples.Herein,electrochemical and electrochemiluminescence biosensors were constructed to achieve the detection of OPs based on Pd WLNCs/g-C₃N₄ nanocomposites,g-C₃N₄-CD nanocomposites,C-g-C₃N₄-PEI nanocomposites and AChE.The introduction of other materials improved the dispersion,conductivity,luminous efficiency of g-C₃N₄,which broadened the application of g-C₃N₄ and improved the biosensor sensitivity.In our work,the amount of HAc and thiocholine produced by the enzyme catalysis were used as an index for quantitative detection of OPs.The experimental results showed that the biosensors could detect sensitively OPs with a wide detection range and a low detection limit,which peovided the opportunity for the fast and immediate detection of OPs.