The Detection Of Formaldehyde In Food Using Quartz Crystal Microbalance Sensors Based On Poly-dopamine Functionalized Hollow Mesoporous Silica Spheres

Nowadays,people pay more attention to the food safety with the improvement of people's economic level and the gradual change on the food safety conscious.Adding toxic and harmful non-food items into food poses an important challenge to food safety.As a highly toxic substance and potential mutagencity,formaldehyde has been widely used as an additive for preventing food spoilage,brightening the color,and enhancing the flavor.However,people ingesting formaldehyde can develop irritation of the eyes and upper respiratory tract,childhood asthma,allergic skin reactions,and even nasopharyngeal cancer and potentially leukemia.In addition,it is considered carcinogenic by the International Agency for Research.These facts pose a significant burden to consumers'health and cause substantial economic losses to our society.The aim of this study is to provide a simple,affordable,efficient and rapid detection technology for food safety.Owing to its easy fabrication,low cost,portability and on-line monitoring,quartz crystal microbalance(QCM)gas sensors as a product of the development of science and technology are regarded as desirable approaches to the rapid detection of toxic and harmful gases,which plays an essential role in,such as sensing environment pollutants,disease diagnosis,pathogen detection,and food safety monitoring,ect.Therefore,in this study,polydopamine-functionalized hollow mesoporous silica spheres(PDA/HMSSs)are prepared and used as a sensing material for formaldehyde detection in food.The main research contents and results of this study are as follows:1.Preparation of PDA-functionalized HMSSsIn this section,HMSSs with high same specific surface area was synthesized by sol-gel method,where ammonia,cetyltrimethylamm-onium bromide and tetraethyl orthosilicate were used as alkali source,a template agent and silicon source,respectively.Then a straightforward and effective surface-modification technique based on the poly-dopamine(PDA)adhesive mechanism was applied for the preparation of PDA-functionalized MSSs and HMSSs.The materials are characterized by small-angle X-ray diffraction(SXRD),field emission scanning electron microscope(FE-SEM),transmission electron microscopy(TEM),Fourier transform infrared(FTIR),X-ray photoelectron spectrometry(XPS),and nitrogen adsorption-desorption.The characteristic results show that the as-prepared HMSSs has an average diameter of?200 nm and pore diameter(4.2 nm),high specific surface area(1134 m~2/g),and PDA has been successfully modified on the surface of HMSSs.2.Study on the gas sensing properties and sensing mechanism of as-fabricated QCM sensorsIn this chapter,gas sensing properties and sensing mechanism of as-fabricated QCM sensors were studied.Benefiting from typical hollow nanostructure and accessibly radial channels,the as-prepared sensors exhibit an extremely low limit of detection down to 100 ppb,a remarkably rapid response(<5 s),short recovery(<3 s),as well as excellent sensitivity and selectivity which is quite superior to that of PDA/MSSs.Meanwhile,the sensing mechanism was fully elaborated by both adsorption thermodynamics and in-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS).The in-situ DRIFTS result reveals that amino group reacting with formaldehyde molecules brought about the disappearance of N-H bond and appearance of C-N bond,the thermodynamic result further confirms that reversible chemical adsorption existed between PDA/HMSSs materials and formaldehyde molecules according to enthalpy change(?H=-51.97 KJ/mol).3.Application of sensors based on PDA/HMSSs for the rapid detection of formaldehyde in foodThe as-prepared sensors are directly applied in measuring formaldehyde levels in vegetables,aquatic products,beer and dry goods.The results show that the sensor exhibited excellent sensing performance with good repeatability and reliability.And samples can be detected in a short period of time.To evaluate the accuracy and precision of the proposed method,the recovery was carried out by spectrophotometry,indicating that the PDA/HMSSs-2 sensor could accurately and stably measure formaldehyde in complex food samples with the negligible interference.The spectrophotometry results further confirmed the reliability of our PDA/HMSSs-2 sensor.This method is fast,sensitive,and high efficiency,which has wide application prospect for the detection of formaldehyde in food.