Research On The Design Of Paper-Based Sensors Based On Nanocellulose Hydrogel

Foodborne illnesses can place an additional burden on our existing health systems.Most traditional methods are used for foodborne pathogenic bacteria contamination monitoring,but these methods are relatively cumbersome,requiring trained operators and complex instrumentation,and cannot meet the demand for simple and convenient real-time detection.Therefore,it is urgent and necessary to develop a rapid,portable,low-cost,and highly sensitive method for the detection of foodborne pathogenic bacteria.Currently,nanotechnology has become an excellent tool for the detection of food-borne pathogenic bacteria.The unique optical and plasmonic properties of metal nanoparticles make them uniquely novel for integration into biosensors for bacterial detection.In particular,gold nanoparticles(AuNPs)have outstanding advantages in the sensing field due to their unique localized surface plasmon resonance optical properties,exhibiting different colors with shape and size,interparticle distance,and refractive index of the surrounding medium.Secondly,hydrogel is a porous material with three-dimensional nanostructure composed of nanoparticles or polymer molecular chains,which has low density,high porosity,high pore volume and high specific surface area.More importantly,colorimetric sensors have recently attracted attention in many sensing applications due to their high sensitivity,portability,and even the ability to be observed by the naked eye.In this paper,a simple and rapid colorimetric detection material for foodborne pathogenic bacteria was established by exploiting the unique localized surface plasmon resonance optical properties of AuNPs and the three-dimensional porous structure of hydrogels.Specifically,this study modified filter paper substrate based on all-polysaccharide TOCN/CGG hydrogel and made a novel test strip substrate by freeze-drying.TEMPO oxidized cellulose nanofibers(TOCN)and cationic guar gum(CGG)were loaded on filter paper layer by layer to obtain hydrogel-modified filter paper substrate,and further freeze-drying treatment to obtain freeze-dried hydrogel-modified test strips(FD-HMP).The preparation process is simple,no cross-linking agent is required,and the cross-linked network can be constructed in a few minutes,which has the advantages of simple and easy preparation method.More importantly,the hydrogel-modified filter paper has excellent adsorption properties and is lightweight and portable.The results confirmed that the solid content of TOCN and CGG affects the porosity of the final paper base material and thus the adsorption performance of the hydrogel-modified test strips,and the performance of the test strips can be optimized by adjusting the solid content and loading amount.It was further found that the use of freeze-drying could enable the hydrogel to maintain its original pore structure and reduce the destruction of the adsorption performance,which is suitable for the loading of foodborne pathogenic bacteria sensing detection substances.The results showed that the prepared lyophilized hydrogel-modified test strips had excellent adsorption properties when WTOCN:WCGG=1:1,the solid content of TOCN solution and CGG solution was 0.5%,the number of loading layers was 2,and the total loading volume was 1 mL.Secondly,gold nanoparticles(AuNPs@DADA)functionalized with D-alanyl-D-alanine(DADA)were synthesized with a concentration of 0.05μM and a particle size of 6.0 nm with more sensitive bacterial colorimetric sensing effect.The prepared AuNPs@DADA system was loaded onto FDHMP,and a simple and convenient visual colorimetric detection of foodborne pathogenic bacteria was achieved using this paper-based sensor.The paper-based sensor can effectively detect Gram-negative(e.g E.coli)and Gram-positive(e.g S.aureus)bacteria as foodborne pathogens.The bacteria can be judged within 15 min by naked eye observation,and the bacterial detection limit is as low as 10 CFU/mL.Finally,gold nanoparticles(AuNPs@TOCN)synthesized with TOCN(carboxyl content of 2.4 mmol/g and solid content of 0.55%)as stabilizer and ascorbic acid as reducing agent were used as the sensing system with a concentration of 0.01 μM and a particle size of 5.14 nm,another biosensing test strip device for rapid detection of foodborne bacteria was developed.Similarly,the prepared AuNPs@TOCN system was loaded onto FD-HMP,and this hydrogel test strip was used to achieve a portable visual colorimetric detection of foodborne pathogenic bacteria.The hydrogel-modified strips were also effective in detecting E.coli and S.aureus food-borne pathogenic bacteria.The bacteria could be quickly and accurately determined within 5 min by naked eye observation,and the detection limit of bacteria was as low as 10 CFU/mL.In summary,this study successfully designed and prepared a portable,rapid,simple paper-based sensor for bacterial detection,which has a broad application prospect.This work provides a new idea for the design of paper-based sensors and an effective way for the application development of biomass materials including nanocellulose.