Study On The Detection Of Salicylic Acid Based On Fluorescent Molecular Probes

Salicylic acid?SA?is a necessary signal molecule to stimulate the systemic acquired resistance?SAR?of plant and plays an important role in the signal transduction of SAR.In recent years,the role of SA has been of great concern in stimulating system acquired resistance of plant,so it is very urgent to find a way to detect endogenous SA in plants.Fluorescent molecular probe has the advantages of high selectivity,low detection limit and real-time detection.It has great potential for real-time detection of endogenous small molecules,and it is an ideal method for detecting endogenous SA.Since SA has a good affinity for Cu²⁺,and SA can be combined with Cu²⁺ by combining with the protein.Therefore,we envisioned the selective detection of SA by designing a Cu²⁺-containing complex probe.Firstly,a probe with good affinity with Cu²⁺ was designed and synthesized.Then,the selective detection of SA was realized by using the formed copper ion complex probe.Based on the above ideas,we designed and synthesized three kinds of fluorescent molecules such as rhodamine,coumarin and curcumin,and studied their properties.The curcumin?3?in the DMF/H2O?7:3,v/v?solution was used to detect the multi-function of Cu²⁺ and SA by complexation.When 1.0 equivalent Cu²⁺ is added to the probe 3,the fluorescence intensity is quenched about 63.7 times,and in the presence of other metal ions,the probe 3 also has a good selectivity for Cu²⁺.When the probe 3 and Cu²⁺ were reacted at a 1 : 1 ratio to form complex probe 3-Cu²⁺,the fluorescence intensity was increased about 34.8 times when 20 equivalent SA was added to the system,complex probe 3-Cu²⁺ can still exhibit better selectivity for SA in the presence of the other salicylic acid analogs.The mechanism of Cu²⁺ and SA was identified by probe 3 and complex probe 3-Cu²⁺ respectively by 1H NMR titration and high resolution mass spectrometry.The probe 3 and complex probe 3-Cu²⁺ were able to rapidly identify Cu²⁺ and SA within 10 s,respectively,and their detection limits for Cu²⁺ and SA were 15 nM and 3 ?M,respectively.In addition,we also achieved the detection of Cu²⁺ and SA in mouse kidney cells using probe 3 and complex probe 3-Cu²⁺,respectively.The structure of the probe 3 was modified,the response of the probes 3a and 3b to Cu²⁺ and SA was low with the reduction of hydroxyl groups on the benzene ring in probe 3 in DMF/H2O?7:3,v/v?.While the comparative electron-withdrawing substituents,the curcumin derivatives containing electron-donating substituents were beneficial for the compounds to recognize SA.