Naked-eye detection of Pd2+ ion using a highly selective fluorescent heterocyclic probe by “turn-off” response and in-vitro live cell imaging

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2020-05, Vol.394, p.112441, Article 112441
• Main Authors: Mahata, Satyajit, Bhattacharya, Araghni, Kumar, Jadi Praveen, Mandal, Biman B., Manivannan, Vadivelu
• Format: Article
• Language: English
• Subjects: Blue fluorescence; Cell imaging; DFT calculation; Heterocycle; Isoquinoline; Palladium
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2020.112441

[Display omitted] •The new diazaheterocycle, 3-(1-isoquinolinyl)imidazo[5, 1-a]isoquinoline (IQ) is selective for sensing palladium(II) ion.•Blue fluorescence exhibited by IQ upon exciting with 359 nm light gets “turn-off” upon adding Pd(II) ion.•The probe IQ shows a remarkably low limit of detection of 0.210 μM.•A 5 μM solution of IQ showed low cytotoxicity towards L929 cells thus Pd2+ ion can be detected in living cells. The heterocyclic probe 3-(1-isoquinolinyl)imidazo[5, 1-a]isoquinoline (IQ) in CH3OH/HEPES buffer system (5 mM, pH = 7.4, 6:4, v/v), exhibits blue fluorescence (λem = 454 nm) upon excitation with 359 nm light. Upon adding Pd2+ ion solution, IQ shows “turn-off” response when observed under long UV light. Using IQ bivalent palladium can be detected with a low limit of detection (0.210 μM) within the pH range of 2-8. In the presence of large varieties of metal ion, colorimetric and fluorescence responses did not exhibit any perceptible change. A small change in fluorescence life-time in TRPL study indicates the static nature of quenching. Binding of probe IQ with Pd2+ ion can be reversed using Na2EDTA. Job’s plot and ESI mass spectrometric analysis reveal a 1:1 ratio for binding of IQ with Pd(II) ion. DFT/TDDFT calculations performed on [Pd(IQ)Cl(CH3CN)]+ ion support the experimental findings. Cytotoxic studies showed that probe IQ suppressed the growth of L929 and Hela cells in a dose-dependent manner. Fluorescence imaging in the absence and presence of Pd2+ revealed that IQ can be successfully applied on living cells with outstanding sensitivity.