Fabrication And Application Of Paper-Based Hg²⁺ Sensors Based On Silver Nanozymes

As a potential rapid detection product,paper-based sensors possess more advantages such as simple preparation and rapid analysis.Therefore,they have been widely used in analytical monitoring,disease diagnosis,food safety and other fields.Hg²⁺as a highly toxic heavy metal pollutant that can induce a variety of diseases by enriching in the human body through the food chain.It therefore is of great significance to develop rapid and sensitive Hg²⁺detection method in the field of environmental protection and human health.Nanozymes is a kind of nanomaterials with enzyme-like catalytic properties,which has been widely used in the field of analytical sensing because of their good catalytic stability and adjustable structures.In recent years,application and development of portable and highly sensitive nanozymes paper-based sensors have become a research hotspot in this field.In view of this,heparin silver nanoparticles（Hep-Ag NPs）nanozymes with adjustable catalytic activity was prepared.It then was used to develop liquid phase and paper-based sensing strategies with color and temperature readout signals,effectively solving the problem of low signal resolution and accuracy of traditional sensing method with single analytical signal,and realizing high sensitivity and high specificity detection of trace Hg²⁺in environmental water samples.The main contents of this paper are as follows.Chapter 1.Heparin silver nanoparticles（Hep-Ag NPs）with stable ellipsoidal-like structure and excellent catalytic performance were prepared by hydrothermal method.It was found that Hg²⁺are more likely located close to the negatively charged groups of Hep owing to the electrostatic interactions.The negatively charged groups of Hep can reduce the spatial distance and accelerate interactions among 3,3′,5,5′-tetramethylbenzidine（TMB）,Hg²⁺,and Hep-Ag NPs through nonspecific/electrostatic force,which could be the main reason for“turn-on”the catalytic activity of the nanozyme.Kinetic tests showed that Hep-Ag NPs have a prominent affinity toward substrate TMB,and exhibiting excellent advantages such as fast result presentation,high specificity and good sensitivity for Hg²⁺detection.Chapter 2.Due to the modulation of Hg²⁺on Hep-Ag NPs oxidase-like activity,as well as the resultant regulation of the blue colored oxidation product of oxTMB with a good photothermal conversion efficiency that catalytically oxidized from TMB,a dual-mode analytical sensing strategy with color and temperature signal readout was developed to overcome the defects of low resolution and sensitivity of single colorimetric sensing method.Under the optimized experimental conditions,the linear range of liquid-phase colorimetric sensing Hg²⁺was 2.5-30μM with a detection limit of 69.8 nM,and the linear range of photothermal sensing Hg²⁺was 2.5-20μM with a detection limit of46.6 nM.Chapter 3.Based on above investigation,we developed a method for preparing a portable colorimetric/photothermal paper-based sensor.Hep-Ag NPs nanozymes and the substrate TMB were uniformly fixed on the chromatography paper surface through a simple soaking process,finally constructing a simple,fast and convenient Hg²⁺testing paper.By combining RGB color pick-up software of smartphone and infrared thermal imager,a rapid quantitative detection of Hg²⁺can be achieved easily.Under the optimized experimental conditions,the linear range of colorimetric sensing Hg²⁺was 0.025-1 m M,with a detection limit of 9.73μM,and the linear range of photothermal sensing Hg²⁺was10-500μM with a detection limit of 4.75μM.