Development And Application Of Hydrazine And Cysteine Near Infrared Fluorescent Probes

Hydrazine（N₂H₄）is common industrial necessity and bioactive molecule.It has been widely used as a reducing agent in the conservation water products,medicine and dyeing industries,while also existing in some pesticides and fuels.However,excessive N₂H₄would cause environmental pollution and serious damage to the nervous and respiratory systems of humans and animals.Cysteine（Cys）belongs to the important thiol biomolecules as a marker of oxidative stress and one of the biological thiols,maintaining the redox balance and physiological balance in living systems.Near-infrared（NIR）fluorescent probes are the preferred tools for environmental and biological detection with the advantages of deep tissue penetration,little photodamage,little luminescence interference,high spatiotemporal resolution and high sensitivity in imaging.In this study,a near-infrared fluorescent probe NIR-N₂H₄for detecting hydrazine and a near-infrared fluorescent probe NIR-Cys for detecting cysteine were synthesized using cyanine dye as the backbone to realize the real-time and sensitive detection of hydrazine and cysteine.The details are as follows:（1）We synthesized a cyanine based near-infrared fluorescent probe NIR-N₂H₄by using cyclopentanone and 2-methylquinoline as the starting materials and introducing acetyl group as recognition group.After its alkalization to remove the acetyl group,the fluorophore NIR-OH was obtained.Then the acrylate group was reintroduced as the cysteine recognition group to obtain the cyanine based near-infrared fluorescent probe NIR-Cys,the structure of which was confirmed by characterization.（2）The probe NIR-N₂H₄was used to specifically recognize N₂H₄,with acetyl group as the reactive site of hydrazine.The results of spectroscopic performance studies showed that the probe exhibited fluorescence enhancement for N₂H₄at 705nm in the NIR region.When 25μM N₂H₄was added,the fluorescence of probe solution was enhanced 47.8-fold.The probe has a linear response to N₂H₄in the 7-18μM range（R²=0.9986）and the calculated detection limit of probe NIR-N₂H₄is 4.33μM.The probe possessed high sensitivity and rapid response time（less than 6 min）.It did not respond to other tested interferents and exhibited specific recognition of N₂H₄.In view of the above excellent fluorescence performance,we successfully used it for the colorimetric detection of hydrazine in soil samples and fluorescence imaging detection of hydrazine in plant cells and living cell Hep G2.（3）The probe NIR-Cys achieved specific recognition detection of cysteine by introducing acrylate groups on the fluorophore NIR-OH.Upon the addition of cysteine,an obvious fluorescenct emission peak was generated at 716 nm.When 25μM Cys was added,the fluorescence of probe solution was enhanced by 57.6-fold.In the 6-16μM range,the fluorescent intensity of the probe at 716 nm showed a good linear relationship with the concentration of Cys（R²=0.9923）.We calculated that the detection limit of probe NIR-Cys was 4.17μM.The probe showed high sensitivity and fast response time（less than 8 min）to Cys.It did not react with other tested interferents and exhibited specific recognition to Cys.Moreover,the probe NIR-Cys successfully exhibited fluorescent response to Cys inside plant cells.The probe was successfully applied in living Hep G2 cells for the detection of endogenous and exogenous Cys and it has the ability to visualize Cys fluorescence imaging in living cells.