Synthesis And Biological Application Of Fast Response Formaldehyde Fluorescent Probe

In recent years,the"role"played by formaldehyde in life activities has received more and more attention.Formaldehyde is not only found in the environment or in food,but also in the human body.The endogenous formaldehyde produced by human body can accelerate the cell reproduction and regulate the formation of memory within a certain concentration range.But if the exogenous formaldehyde enters the human body through some ways to make the formaldehyde content exceeding the normal range,it will impair the body function or induce some diseases.Many molecular probes have been reported to detect formaldehyde content in cells by using fluorescence probe technology,most of which are based on PET mechanism and emit strong fluorescence after reaction with formaldehyde.Because of the different structures of these probes and the different types of reactions with formaldehyde,the response time will also be different,with some taking 30min or even longer,requiring 120min.By comparison,it was found that many probes have longer response time,but polymerization reactions are prone to occur between formaldehyde molecules.Fluorescent probes do not respond to paraformaldehyde,so the longer the response time,the greater the error.In this paper,a fluorescent probe based on PET mechanism for rapid and sensitive detection of formaldehyde was designed and synthesized by optimizing the structure of the probe.In the second chapter,four coumarin-based fluorescent probes were designed and synthesized,namely Coun-1,Coun-2,Coun-3 and Coun-4.The fluorescence properties of the molecule are changed by linking different substituents at the same site of the coumarin fluorophore and linking the same substituents at different active sites.The substituents are methyl（-CH₃）,trifluoromethyl（-CF₃）and benzothiazole,respectively,and the substitution sites are 3 and 4,respectively.The four probes all used hydrazine as the recognition group,based on the PET mechanism realizing the change of fluorescence intensity.The fluorescence intensity of the probe before the reaction is relatively weak or almost none,and the reaction with formaldehyde inhibits the PET process and emits strong fluorescence.Firstly,the UV-visible absorption spectrum,fluorescence emission spectrum and response time to formaldehyde of the four probes were tested,and the probes which were the most responsive to formaldehyde and most suitable for testing in the biological field were selected.The test result is that the probe Coun-4 with formaldehyde have the fastest response speed,and the maximum fluorescence intensity can be reached after 4 minutes of reaction,and then remains basically unchanged;The probe Coun-4 has a maximum absorption wavelength of 432 nm and is the longest of the four probes.The cell is minimally damaged as an excitation wavelength when imaging.Therefore,the probe Coun-4 was selected as the optimal probe for detecting intracellular formaldehyde.In the third chapter,the formaldehyde fluorescence probe Coun-4 was further tested.We explored the optimal pH conditions,linear concentration range,selectivity,and cell imaging experiments.Finally,we got the following results:the optimal pH value was 7⁸;the linear range was 5¹00μM,the fluorescence intensity and formaldehyde concentration showed a good linear in this range,the equation is y=2.041 x+293,R²=0.9966;the probe can detect formaldehyde in HepG₂ cell.