Synthesis And Performance Studies Of Fluorescent Probes For Mental Ions Based On 1,8-Naphthalimide And Rhodamine B

Metal ions exist widely in the biological systems and environment, many metal ions play a very important role in biological activity. Fluorescence spectrometry has become a popular research method for the detection of metal ions because of good selectivity, high sensitivity and non-destructive.Rhodamine B and 1,8-Naphthalimide are ideal fluorescent carriers, which have good light stability and high quantum yield. In the present paper, three fluorescent probes were reported according to sensing mechanism.First, a ratiometric fluorescent probe RN was developed based on rhodamine B and 1,8-naphthalimide. In CH3OH/ CH3CN/ HEPES buffer solution, The presence of Hg²⁺ can induce an intensive absorption at 556 nm. The change of absorption spectrum results in a color change from light green to orange in response to Hg²⁺.Significantly, the probe RN gives rise to a ratiometric fluorescent response to Hg²⁺.Upon addition of Hg²⁺, a significant fluorescence enhancement at 580 nm and meanwhile the gradual disappearance of the emission at 540 nm were observed,which were ascribed to the fluorescence resonance energy transfer?FRET? from1,8-naphthalimide moiety to the ring-opened rhodamine B moiety. The ratiometric fluorescence signal for Hg²⁺ was not affected by other coexisting mental ions.Second, A fluorescent probe NT was developed based on 1,8-naphthalimide,which was synthesized for specific detection of Cu²⁺. In CH3CN/ HEPES buffer solution,the presence of Cu²⁺ induces a large blue shift in emission, meanwhile the yellow to blue color change of the luminescence occurs. Other metal ions have no effect on the response of NT to Cu²⁺, and the response is applicable over a wide pH range. In addition, the probe has been used for imaging of Cu²⁺ in living Hela cells.Third, a new fluorescent probe for the detection of Hg²⁺ was designed and synthesized by attaching N-methylisatin to rhodamine B hydrazide via an imine linkage. In ethanol/Tris buffer medium, the addition of Hg²⁺ caused a visual color change from colorless to pink and a fluorescence change from colorless to red. Other coexisting metal ions did not interfere with the detection of Hg²⁺. Based on ESI-MSanalysis, a sensing mechanism that Hg²⁺ induces a ring-opening reaction of spirolactam and then a hydrolysis reaction of imine linkage was proposed.