Construction Of Portable Biosensor Assisted By Stimulus-responsive Hydrogel And Its Applications

Stimulus-responsive hydrogel is an intelligent material capable of responding to external stimuli.Several detection methods have been developed based on changes in the gel-sol phase transition,but these methods often require complex operational steps,large instruments and specialist technicians.The portable sensor is a simple-to-operate and low-cost quantitative device that greatly meets the demand for Point-of-care testing(POCT).Hence,we aim to construct portable biosensors with the assistance of stimulus-responsive hydrogels and propose a multiple-signal output approach to improve the accuracy of detection results,and provide new strategies and ideas to develop portable biosensors for POCT.There are four main parts in the thesis as follows:Chapter 1 firstly introduces the definition and classification of hydrogels,with a view to highlight the category and applications of stimulus-responsive hydrogels,and then summarizes the research progress of the portable sensors at home and abroad,mainly including their signal output methods and application fields.On this basis,the topic idea for this thesis is presented.In Chapter 2,a copper alginate(Cu-Alg)hydrogel-mediated paper-based distance sensor was constructed to detect alkaline phosphatase(ALP)and alpha-fetoprotein(AFP),based on the difference in flow distance on pH test paper due to the viscosity change during the gel-sol phase transition.The detection of ALP was achieved using the response of Cu-Alg hydrogels to pyrophosphate(PPi)and the hydrolysis of PPi by ALP,with a limit detection(LOD)of 1.7 mU/mL.Based on this,a paper-based immunosensor with distance as the readout signal was built for the detection of AFP with a LOD of 0.8 ng/mL using ALP as the marker enzyme.The sensor was also successfully utilized to monitor ALP and AFP in real samples(human serum),which demonstrates its promising applications in early clinical diagnosis and pathological studies of related diseases.In Chapter 3,with the assistance of the gelatin hydrogel embedded with enzymes and 3,3’,5,5’-tetramethylbenzidine(TMB),a multimodal(three signal output modes,namely color,temperature and distance)portable sensor was fabricated for the rapid and sensitive detection of glucose.Horseradish peroxidase(HRP),glucose oxidase(GOx)and TMB were embedded in the gelatin hydrogel.In the presence of glucose,the product oxTMB had a blue signal and photothermal effect,while the concentration of glucose corresponded to the color and temperature signal of the reaction system,which enabled the detection of glucose with LODs of 1.3 μM and 1.5 μM,respectively.In addition,based on the temperature response and gel-sol phase transition properties of gelatin,the interrelationship was established between the temperature signal of the reaction system and its flow distance on the pH test paper and detection of glucose could be realized with LOD of 1.6 μM,which is close to the LODs obtained from the color and temperature signals.This multimodal biosensor with the advantage of high specificity and diverse output modes has great potential for early diagnosis and home care of diabetes.In Chapter 4,based on MnO2 nanoflowers(NFs)and gelatin hydrogel,a multimodal(three signal output modes,namely color,temperature and distance)portable immunosensor was developed for the detection of carcinoembryonic antigen(CEA).The capture antibody was immobilized on the paper substrate,and sequentially bound to the CEA and detection antibodies labelled by MnO2 NFs to form a sandwich complex.MnO2 NFs can catalyze TMB to produce oxTMB that not only produces color signal but also possess photothermal effect,resulting in the detection of CEA based on color and temperature signals.In addition,this system is combined with the temperature-responsive gelatin hydrogel to produce a flow distance on the pH test paper based on the gel-sol phase transition,which allows for the detection of CEA.The LODs based on these three signals are 1.4 ng/mL,1.5 ng/mL and 2.5 ng/mL,respectively,relatively close to each other.The biosensor constructed by this strategy has some advantages such as simple preparation steps,low cost and three signals complement each other,and it is possible to modify different detection antibodies by MnO2 NFs to provide a universal method for the detection of targets.