Among the various transition metals ions, zinc is the most abundant ion in the human body1. It is widely found in proteins where it plays important role in various biological processes. The biological imbalance in its concentration has been linked to many neurological disorders such as Alzheimer’s and Parkinson’s diseases2. Recently, the zinc ions have been regarded as quantitative imaging biomarker for the early detection of prostate cancer3. Out of the total Zn2+ ion (approximately 0.2 mM) content in mammalian cells, fee Zn2+ concentration is as low as picomolar to nanomolar levels. A number of one photon fluorescent probes for the detection of zinc ions have been developed and investigated4. However these probes have certain limitations as they requires a rather short excitation wavelength that limits their use in tissue imaging up to deep penetration depth (<100 μm), photo-bleaching and cellular auto-fluorescence.
Realizing the importance of zinc in biological cell and limitation of using one photon microscopy, we have design and synthesized two-photon fluorescent probes SZn1 and SZn1-Acid, which consist of two naphthalene-derived fluorophore unit and a methoxy derivative of N,N-di-(2-picolyl)ethylenediamine as the Zn2+ chelator. Both derivatives show the dramatic increase in their fluorescence intensities upon the addition of Zn2+ ions. Further the good water solubility, high selectivity, Kd values in nanomolar range and insensitivity to biological relevant pH range make them suitable candidate for monitoring the zinc ions in live cells and tissues. In the oral presentation, the synthesis, photo-physical behaviour and bio-imaging applications of these probes will be discussed.
1. Frederickson, C. J.; Koh, J. Y.; Bush, A. I. Nat. Rev. Neurosci. 2005, 6, 449.
2. (a) Bush, A. I. Curr. Opin. Chem. Biol. 2000, 4, 184. (b) Bush, A. I. Trends Neurosci. 2003, 26, 207.
3. Ghosh, S. K.; Kim, P.; Zhang, X. A.; Yun, S. H.; Moore, A.; Lippard, S. J.; Medarova, Z. Cancer Res. 2010, 70, 6119.
4. (a) Sensi, S. L.; Ton-That, D.; Weiss, J. H.; Rothe, A.; Gee, K. R. Cell Calcium 2003, 34, 281. (b) A Guide to Fluorescent Probes and Labeling Technologies, 10th ed.; Haugland, R. P., Ed.; Molecular Probes: Eugene, OR, 2005.