等离子体光纤光栅超痕量汞离子传感器

Plasmonic Fiber Grating Sensors for Ultra-Trace Mercury Ion Detection

为实现特异性、超痕量、原位的重金属汞离子检测,提出一种基于适配体和磁性纳米粒子增强倾斜光纤布拉格光栅-表面等离激元共振(TFBG-SPR)汞离子传感器。首先,在倾斜光纤布拉格光栅包层区域溅射厚度合适的金膜以激发表面等离激元共振,在探针末端镀金从而形成反射式传感结构。然后,采用具有胸腺嘧啶(T)碱基失配的适配体修饰TFBG-SPR栅区,进行特异性汞离子识别。最后,选择链霉亲和素包被的磁性纳米粒子作为信号放大标签,以提高离子检测性能。汞离子与T碱基作用激活适配体序列,连接磁性纳米粒子,传感器表面折射率发生变化,TFBG-SPR包层模式的振幅产生响应。结果表明:采用差分幅度解调,传感器对汞离子的检测极限为0.5 pmol/L,检测范围为1 pmol/L~10μmol/L,所提传感器具备良好的特异性以及再生性,同时通过测量临床样品的回收率,可以证实其在即时、快速检测领域中的应用前景。

Objective Mercury(Hg)is a volatile and highly toxic heavy metal element.Under the action of atmospheric deposition and ocean circulation,mercury ions(Hg2+)easily enter fresh water or the ocean,causing harm to the ecological environment and human body.It is of great significance to develop a high-sensitivity mercury ion detection system for environmental protection and human health.In recent years,various methods for the detection of mercury ions have been developed,including atomic absorption spectrometry,fluorescent probe method,solid-phase extraction,and inductively coupled plasma optical emission spectrometry techniques.However,these methods often require sophisticated instruments,specialized operators,and time-consuming procedures.In addition,some of these methods are prone to interference from other metal ions,which can lead to false positive results.DNA biosensor research has taken center stage in the past decade,marking a significant advancement in heavy metal ion detection.Mercury ions selectively bind to two thymidines(T).During the hybridization of DNA molecules,mercury ions can change the structure of some double helix bases of DNA and form a T—Hg2+—T mismatch structure,which is more stable than the base pair.The specific detection of mercury ions as a heavy metal can be realized by using the T—T mismatch mechanism of DNA molecules.However,it still faces the problems of low sensitivity,long response time,and low accuracy.Therefore,the demand for rapid and precise mercury ion detection in clinical settings and environmental pollutant monitoring necessitates innovative approaches.Methods In order to achieve specific,ultra-trace,and in situ mercury ion detection,a tilted fiber Bragg grating-surface plasmon resonance(TFBG-SPR)biosensor based on aptamer and magnetic nanoparticles(MNPs)enhancement is designed.TFBG-SPR has a rich mode field distribution and narrow linewidth,which enables the high-performance detection of physical changes and chemical reactions without being affected by the external environment.To accurately detect mercury ions,a streptavidin(SA)aptamer with T bases is specially designed to form T—Hg2+—T pairing with mercury ions,and SA-coated MNPs are used as signal amplification labels to improve ion detection performance.In the experiment,a 50 nm gold film is sputtered on the TFBG cladding region to excite SPR,and the end face of the probe is plated with a gold film to form a reflective sensing structure.Then,an aptamer with mismatched T bases is used to modify the TFBG-SPR grating surface for specific mercury ion recognition.Finally,the mercury ions interacted with T bases to activate the aptamer sequence and connect the MNPs.The refractive index of the sensor surface would change,and the amplitude of the TFBG-SPR cladding mode responded to the perturbation of the refractive index.Results and Discussions In this paper,a TFBG-SPR-aptamer-MNPs biosensor is proposed and used for mercury ion detection.As mercury ions interact with T—T bases in the aptamer,and magnetic nanoparticles bond,the sensor surface refractive index increases,and the SPR envelope redshifts.The plasma fiber envelope amplitude changes.According to the unique characteristics of the TFBG-SPR cladding modes(opposite amplitude changes occur on both sides of the SPR cladding mode),the final amplitude variation can be measured by differential amplitude demodulation,realizing highsensitivity,high-resolution,and high-Q refractive index change measurements.In the experiments,the amplitude variation is found to be 3.633 dB for a Hg2+concentration of 10μmol/L(Fig.3),and the detection range is 1 pmol/L‒10μmol/L.In Fig.4,a linear relationship between the amplitude response and logarithmic value of the Hg2+concentration is obtained.Thus,the limit of detection(LOD)of mercury ion is estimated to be 0.5 pmol/L based on the mean of the blank background signal plus three times the standard deviation of the noise.In addition,the sensor exhibits good specificity(Fig.5)and reproducibility(Fig.6),and the application potential of environmental pollutant monitoring and point-of-care testing technology is confirmed by sample recovery measurements(Table 1).We obtain a recovery of 92.48%‒105.38%with a relative standard deviation of 2.56%‒10.20%for the actual samples.Conclusions In summary,we demonstrate a unique biosensor using aptamer-SA-MNPs structure based on TFBG-SPR for ultra-trace mercury ion detection.Aptamer-based sensors with high affinity and strong specificity solve the key problems of stability and selectivity of biosensors in mercury ion detection.TFBG-SPR sensors operate in the common communication wavelength band and exhibit minimal temperature cross-sensitivity and a high refractive index sensitivity.By combining the high amplitude sensitivity of TFBG-SPR,the specific recognition of aptamer-mercury ion,and the effective signal amplification of MNPs,our sensor has achieved an LOD down to 0.5 pmol/L and a detection range of 10−12‒10−5 mol/L.This sensor also exhibits good selectivity for Hg2+over other divalent metal ions.Furthermore,this biosensor presents good recovery and is suitable for mercury ion detection in tap water and rabbit serum.The proposed sensor can be applied in environmental monitoring and clinical diagnosis,including tumor microenvironment and point-ofcare testing technology.