基于稀土上转换纳米粒子传感器的构建及其在食品添加剂检测中的应用

Construction of a Rare Earth Up-Conversion Nanoparticle Sensor and Its Application in the Detection of Food Additives

稀土上转换纳米粒子(UCNPs)因其具有毒性小、化学稳定性好和背景荧光低等优点被用于构建荧光纳米传感器。通过溶剂热法制备核壳UCNPs,采用柠檬酸钠对其进行表面配体交换得到水溶性核壳UCNPs(Cit-CS-UCNPs),以Cit-CS-UCNPs作为荧光传感器的能量供体,二氧化锰(MnO_(2))纳米片作为荧光传感器的能量受体,采用荧光共振能量转移(FRET)机理,构建了一种用于食品添加剂二氧化氢(H_(2)O_(2))和叔丁基对苯二酚(TBHQ)检测的荧光纳米传感器(Cit-CS-UCNPs-MnO_(2))。通过扫描电镜(SEM)、荧光光谱和紫外可见吸收光谱(UV-Vis)等分析测试手段对制备的纳米材料的形貌结构和性能进行表征。考察了猝灭剂浓度、孵育温度及孵育时间等实验条件对荧光传感体系检测性能的影响。荧光光谱和UV-Vis实验结果表明,Cit-CS-UCNPs最大发射峰位于654nm,Cit-CS-UCNPs与MnO_(2)结合后,核壳UCNPs发生荧光猝灭,当存在H_(2)O_(2)时,Cit-CS-UCNPs的荧光恢复,说明在此波段H_(2)O_(2)与MnO_(2)纳米片发生氧化还原反应,MnO_(2)纳米片被还原成Mn^(2+),逐渐从Cit-CS-UCNPs的表面解离下来;存在TBHQ时,Cit-CS-UCNPs-MnO_(2)与TBHQ体系峰位与TBHQ偏移到253nm,为TBHQ与MnO_(2)纳米片发生氧化还原反应,使得Cit-CS-UCNPs-MnO_(2)体系中FRET效应减弱,荧光强度回升。SEM结果表明,MnO_(2)纳米片均匀包覆在Cit-CS-UCNPs的周围,在水中仍可保持良好的分散性,表明MnO_(2)纳米片修饰到Cit-CS-UCNPs表面。对猝灭剂高锰酸钾(KMnO4)的浓度进行了优化。结果表明,当KMnO4浓度为10mol·L^(-1)时,猝灭效率可达90%。对检测条件进行优化,结果表明H_(2)O_(2)的检测孵育时间为25min时,MnO_(2)和H_(2)O_(2)之间氧化还原反应基本完全,Cit-CS-UCNPs-MnO_(2)荧光恢复值最大;TBHQ的检测孵育时间为30min。在最佳实验条件下,Cit-CS-UCNPs-MnO_(2)的荧光强度变化比率与H_(2)O_(2)浓度(0~1000μmol·L^(-1))及TBHQ浓度(0~0.6 mmol·L^(-1))分别具有良好的线性关系。保持最佳实验条件,选取食品中存在的代表性金属离子(如K+、Na+、Ca^(2+)和Mg^(2+))和常见的食品添加剂苯甲酸(BA)、D-葡萄糖(Glu)、山梨酸钾(PS)、蔗糖(Suc)、纳他霉素(Nat)和肌醇(Ino)作为研究对象进行选择性测试,发现与H_(2)O_(2)相比,Cit-CS-UCNPs-MnO_(2)对其他添加物质没有强烈的反应,传感器整体荧光信号波动不大,因此Cit-CS-UCNPs-MnO_(2)对H_(2)O_(2)和TBHQ可进行特异性检测。

Rare earth up-conversion nanoparticles(UCNPs)have been used to construct fluorescent nanosensors because of their low toxicity,good chemical stability,and low background fluorescence.Core-shell UCNPs were prepared using the solvothermal method,and water-soluble core-shell UCNPs(Cit-CS-UCNPs)were obtained by surface ligand exchange with sodium citrate.The Cit-CS-UCNPs were used as the energy donor of the fluorescence sensor,and manganese dioxide(MnO_(2))nanosheets were used as the energy receptor of the fluorescence sensor.Based on the fluorescence resonance energy transfer(FRET)mechanism,a fluorescence nanosensor(Cit-CS-UCNPs-MnO_(2))was constructed for the detection of hydrogen dioxide(H_(2)O_(2))and tertbutylhydroquinone(TBHQ)as food additives.The prepared nanomaterials'morphology,structure,and properties were characterized by scanning electron microscopy(SEM),fluorescence spectrum,and ultraviolet spectrum(UV-vis).The effects of quenching agent concentration,incubation temperature,and incubation time on the detection performance of the fluorescence sensing system were investigated.According to the fluorescence spectra and UV-Vis experimental results,the maximum emission peak of Cit-CS-UCNPs is 654nm.After the combination of Cit-CS-UCNPs and MnO_(2),core-shell UCNPs undergo fluorescence quenching.When H_(2)O_(2)is present,the fluorescence of Cit-CS-UCNPs recovers.The results indicate that H_(2)O_(2)and MnO_(2)nanosheets undergo redox reaction at this band,and MnO_(2)nanosheets are reduced to Mn^(2+),which gradually dissociates from the surface of Cit-CS-UCNPs.In the presence of TBHQ,the peak of the Cit-CS-UCNPs-MnO_(2)and TBHQ system was shifted to 253nm,indicating that the redox reaction occurred between TBHQ and MnO_(2)nanosheets,and the FRET effect was reduced in the Cit-CS-UCNPs-MnO_(2)system,and the fluorescence intensity increased.It can be seen from the SEM results that MnO_(2)nanosheets are uniformly coated around Cit-CS-UCNPs,and maintain good dispersion in water,indicating that MnO_(2)nanosheets are modified on the surface of Cit-CS-UCNPs.The concentration of the quencher potassium permanganate(KMnO4)was optimized,and the results showed that when the concentration of KMnO4is 10mol·L^(-1),the quenching efficiency can reach 90%.The detection conditions were optimized,and the results showed that when the incubation time of H_(2)O_(2)was 25min,the redox reaction between MnO_(2)and H_(2)O_(2)was complete.The fluorescence recovery value of Cit-CS-UCNPs-MnO_(2)was the maximum.The incubation time of TBHQ was 30min.Under the optimal experimental conditions,the fluorescence intensity of Cit-CS-UCNPs-MnO_(2)has a good linear relationship with the concentration of H_(2)O_(2)(0~1000μmol·L^(-1))and TBHQ(0~0.6 mmol·L^(-1)).The optimal experimental conditions were maintained,and representative metal ions(such as K+,Na+,Ca^(2+)and Mg^(2+))and common food additives(BA,Glu,PS,Suc,Nat and Ino)in food were selected as research objects.The results showed that compared with H_(2)O_(2),Cit-CS-UCNPs-MnO_(2)did not react strongly to other added substances,and the overall fluorescence signal of the sensor did not fluctuate much.Therefore,it can be seen that Cit-CS-UCNPs-MnO_(2)can detect the specificity of H_(2)O_(2)and TBHQ.