The Synthesis And Properties Study Of Fluorescent Probe For Biothiols Based On Heptamethine Indocyanine

Biothiols such as cysteine(Cys),homocysteine(Hcy)and glutathione(GSH)play significant roles in maintaining the redox balance during many physiological and pathological processes.In fact,a number of works have shown that abnormal level of thiols can result in some diseases.Therefore,developing an analytical method that can effectively detect biothiols is meaningful.Compared with other methods,fluorescence detection has been widely concerned by virtue of sensor simplicity,high sensitivity,good selectivity,noninvasiveness and convenient operation etc..Near-infrared fluorescent probes can reduce background fluorescence,penetrate much deep and cause less damage to biological samples.Therefore,two fluorescent probes that can specifically identify biothiols were designed and synthesized based on heptamethine indocyanine dye.And then the properties of the two probes were studied.In this paper,a biothiols' fluorescent probe 9 was synthesized firstly based on asymmetric heptamethine indocyanine and its absorption and fluorescence spectra were investigated.It was found that both the absorption spectra and solution color of probe 9 had obvious response to different pH,which let the probe could be used as a ‘naked eye' pH indicator.In addition,after treatment with biothiols,the fluorescence intensity of probe 9 at 560 nm increased remarkably,and the probe showed good selectivity toward biothiols.In addition,a fluorescent probe 10 was designed and synthesized based on symmetrical heptamethine indocyanine dye,which can be used to detect biothiols with good selectivity and better sensitivity.With the addition of biothiols,the probe displayed ~30-fold fluorescence enhancement at 625 nm.Meanwhile,the solution color changed remarkably from green to red,which provides a method to recognize biothiols by the ‘naked eye'.The detection limit of GSH,Cys and Hcy are 1.99 nM,2.24 nM and 4.46 nM,respectively.The response mechanism of probe 10 toward biothiols was speculated and confirmed by experiments,that the sulfhydryl group in biothiol caused the fracture of the sulfonate bond of probe 10 by nucleophilic attack,which results in the structure change of probe 10.Thus the absorption spectra,fluorescence emission spectra as well as the solution color of probe 10 were changed.