Fabrication Of Paper-based SERS Sensor And Its Application In Rapid Analysis Of Characteristic Aroma Components In Wine

There are many kinds of aroma substances in wine,some of which are too small to detect and recognize,make it presents a variety of flavors and textures.For example,the volatile small molecules such as sulfur dioxide and aldehydes in wines.Traditional detection methods are often expensive,time-consuming,labor-intensive and require complex sample pretreatment.Surface-enhanced Raman scattering（SERS）is emerging as a powerful technique for on-site monitoring of additives and pollutants directly,and provides“fingerprint”spectral signatures of analytes.Most aroma molecules possess low SERS cross-section and weak affinity toward SERS substrate,limiting the application in rapid analysis of aroma components in wine.Paper-based SERS substrates has the characteristics of simple preparation,large specific surface area and easy to carry.However,how to develop paper-based SERS materials with high specificity and high sensitivity and establish a method for rapid detection of aroma components of wine based on SERS technology still face huge challenges.Therefore,the fabrication of reactive paper-based SERS devices has important theoretical value and practical significance for fast screening and instant detection of aroma components in wine.The first chapter,the introduction part introduce the Raman spectrum and SERS discovery and principle,the preparation of SERS substrates and its carriers,and also introduce the application of paper-based SERS substrates.Finally,introduce the significance and content of the topic.The second chapter,this study design a SERS substrate material for colorimetric/SERS dual-mode sensing method for on-site and rapid analysis SO₂ by combining headspace sampling（HS）with paper-based analytical device（PAD）.First,the smart and multifunctional PAD is fabricated with a vacuum filtration method in which 4-mercaptopyridine（Mpy）-modified gold nanorods（GNRs）-reduced graphene oxide（rGO）hybrids（rGO/MPy-GNRs）,anhydrous methanol and starch-iodine complex are immobilized into cellulose-based filter papers.However,the addition of SO₂ induces the Karl-Fischer reaction,resulting in the decrease of color and increase of SERS signals.A distinguishable change in the color was observed at a SO₂ concentration of 5μM by naked eye.The UV-vis spectroscopy and SERS method’s detection limit for SO₂ is found to be 1.45μM and 1μM,respectively.The HS-PAD based colorimetric/SERS method is applied for the determination of SO₂ in wine,and the detection results match well with those obtained from the traditional Monier-Williams method.This study not only offers a new method for on-site monitoring of SO₂ but also provides a new strategy for designing of paper-based sensor platform for wide range of field-test applications.The third chapter,the method is developed a flexible SERS substrate fast discrimination of formaldehyde（FA）and acetaldehyde（AA）in aqueous sample solutions.First,paper-based SERS sensor with 4-aminothiophenol（Atp）-modified reduced graphene oxide（rGO）/[Ag（NH₃）₂]⁺（rGO/[Ag（NH₃）₂]⁺/Atp）was prepared.The addition of FA or AA induces the conversion of[Ag（NH₃）₂]⁺complex to silver nanoparticles（AgNPs）because of aldehyde-induced silver reduction reaction.The AgNPs possess strong SERS activity.It is also found that the changes in the spectral shapes and the relative intensity ratio of the bands at 1143 and 1072 cm^-1 result from the difference in the pH value of the surrounding solution.The paper sensor can be used as a SERS dipstick and swab for on-site determination of FA or AA in wine via the differences in the intensity of the SERS peaks.The assay’s detection limits are 0.15 and 1.3 ng/L for FA and AA.The method enables selective discrimination of FA and AA from complex matrix samples with a high sensitivity,thus permitting rapid point-of-care assessments of components in wine.