Sensitivity Enhanced Surface Plasmon Resonance Sensor By Tin Dioxide For Heavy Metal Ions Detection

Heavy metal pollutions have been reorganized as one of the main threats to global public health and safety,which seriously destroy the ecological environment and human health.As the most dangerous heavy metal pollutant,mercury ions(Hg²⁺),can stably exist in the natural environment and be enriched in the human body through the food chain,causing irreversible and permanent damage to the human liver,kidneys and nervous system.Therefore,the development of high-sensitivity mercury ion sensors is of great significance to environmental monitoring,ecosystem protection,and human health early warning.Surface plasmon resonance sensors have unique advantages such as label-free,non-destructive in-situ detection,and rapid response.They have been widely studied and applied to the detection of heavy metal ions,providing a new way to solve the increasingly serious health crisis and environmental problems.Aiming at the problems of low sensitivity and poor selectivity of the current surface plasmon resonance heavy metal ion sensors,a new type of surface plasmon resonance based on chitosan/polyvinyl alcohol/tin dioxide composite film modification is proposed.The sensor realizes high-sensitivity detection of low-concentration Hg²⁺solutions.The main research contents are as follows:（1）Based on the finite element analysis method,the physical model of the prism-coupled SPR sensor is established,and the sensing mechanism and sensitivity enhancement method of the SPR sensor are systematically studied.Firstly,the effect of the metal plasma material and thickness on the spectral characteristics and sensitivity of the sensor was analyzed by simulation,and the optimal metal plasma material（Au）and the optimal thickness（50nm）were obtained.Secondly,the SPR sensor modified by SnO₂ sensitive layer was studied.The electromagnetic field enhancement characteristics show that the SnO₂ sensitive layer can effectively enhance the evanescent field intensity on the sensor surface（from 62314.07 V/m to 75529.63 V/m）,thereby improving the sensor sensitivity.Compared with the pure gold film SPR sensor,the sensitivity of the sensor is improved by 42%after the SnO₂ sensitive layer is modified.（2）A strategy of using the CS/PVA composite film to improve the selective adsorption capacity of the sensor for Hg²⁺has been proposed,the CS/PVA-SPR sensor was designed and prepared,and the Hg²⁺detection experimental research was carried out.First,based on the built-up SPR sensor system,the spectral response of the sensor to different heavy metal ions was compared and tested.The results showed that the sensor had the highest sensitivity when detecting Hg²⁺（6.024 nm/μg/L）,successfully realized the selective detection of Hg²⁺,and solved the problem of pure Hg²⁺.The gold film SPR sensor cannot selectively detect the problem of Hg²⁺.Secondly,using FTIR spectroscopy analysis technology to study the sensor’s specific adsorption mechanism for Hg²⁺,it is found that the-NHCOCH₃ group and-NH₂ group in the composite film provide specific binding sites for Hg²⁺.（3）A strategy of using SnO₂ to enhance the surface electric field intensity of the sensor to improve the detection sensitivity of the sensor has been proposed,and the CS/PVA/SnO₂-SPR sensor is designed and prepared.Firstly,the sensitization characteristics of SnO₂ were experimentally studied,and the feasibility of SnO₂improving the sensitivity of SPR sensors was verified.Secondly,by optimizing the CS/PVA/SnO₂ composite material,the component ratio has obtained the best detection sensitivity of the sensor（25.429 nm/μg/L）,which is 4 times higher than the sensitivity of the CS/PVA-SPR sensor.The selectivity and repeatability of the sensor are further studied.Finally,based on the Langmuir isotherm adsorption equation,the sensor’s adsorption model for Hg²⁺is established,and the detection limit of the sensor is calculated to be 6.51ng/L（0.032n M）,which is significantly lower than the mercury ion content of drinking water set by the U.S.Environmental Protection Agency.Standard（10n M）.