Design And Synthesis Of Novel SO₂ Fluorescent Probe And Its Application In Food And Biological Systems

Sulfur dioxide(SO₂)and its derivatives are used as food additives in the process of food production,storage and transportation,which play anti-corrosion,color protection,anti-oxidation and preservation functions.Illegal discharge or addition in the environment or food will lead to excessive SO₂ content in products.Fluorescent probes have many advantages such as excellent optical performance,targeted tracking ability,high selectivity and sensitivity,and the ability to intuitively obtain the distribution of analytes in the sample and in-situ real-time imaging,so 1hey are considered to be the most effective molecular detection tools.In this article,we designed and synthesized two different fluorescent probes,studied their optical properties and applicable conditions,and realized the efficient,accurate and rapid detection and imaging of SO₂ in food environment and biological systems.The research content is as follows:1.A new type of ratio-based fluorescent probe(KQ-SO₂)based on reaction response was obtained by the carbazole formaldehyde derivative and the positively charged indolium salt derivative through the aldol condensation reaction,with a maximum emission of 600 nm and orange fluorescence signal.First,the spectral study of the ratio response of KQ-SO₂ to SO₂ was carried out.KQ_SO₂ emits a blue fluorescence(475 nm)signal after responding to SO₂.As the concentration of SO₂ increases,the fluorescence intensity of the long wavelength emission peak at 600 nm gradually decreases,and the fluorescence intensity of the short wavelength emission peak at 475 nm gradually increases.The distance between the two emission peaks is 125 nm,so KQ-SO₂ has good emission spectrum resolution and ratio detection capabilities.In addition,KQ-SO₂ has the advantages of short response time(1 min),high selectivity,high sensitivity and low cytotoxicity,and it exhibits a good linear relationship within the SO₂ concentration range of(0-1.0)?M,with low detection limits to 10.28 nM.Tissue and in vivo imaging studies have shown that KQ-SO₂ emits two non-interfering imaging signals in the blue and red channels,respectively,realizing the imaging analysis of SO₂ in biological samples.In addition,KQ-SO₂ has been successfully applied to the detection of SO₂ in water samples,food samples,onion tissues and zebrafish.2.A two-photon ratiometric reversible fluorescent probe(NPXH)based on two-photon fluorescence resonance energy transfer(TP-FRET)was constructed by connecting the donor two-photon naphthalimide fluorophore 4 and the acceptor xanthone fluorophore 7 with a non-conjugated linking group.The probe solution emits bright deep red fluorescence(630 nn)and has an oxonium structure that can be used as a response site for the reversible detection of SO₂ and formaldehyde(FA).The spectroscopic study of its reversible response to SO₂/FA was first carried out.After responding to SO₂,NPXH emits a bright green fluorescent signal,and the red:fluorescent signal disappears.As the SO₂ concentration gradually increases,the fluorescence intensity of the long wavelength emission peak at 630 nm gradually decreases,and the fluorescence intensity of the short wavelength emission peak at 535 nm gradually increases.Besides,the adduct of NPXH and SO₂ can be reduced to NPXH by FA within 1 min.NPXH has an ultra-short response time(<8 s),a significant ratio increase(about 6 times),a good linear relationship(within the SO₂ concentration range of 0-1.0 ?M,and the detection limit is as low as 7.48 nM.At the same time,the selective experiment shows that the selective response of NPXH to SO₂ has strong specificity.Tissue and in vivo imaging studies have shown that NPXH has fluorescence imaging signals in the red and green channels respectively,and there is no crosstalk of optical signals between the two channels.In addition,NPXH has been successfully applied to the detection of SO₂ in food samples and water samples,and has shown superior detection performance.