ASMI is a ratiometric, two-photon excited fluorescent probe, composed of a highly two-photon active and biocompatible merocyanine fluorophore and an acrylate moiety as a thiol reactive site. ASMI is able to selectively detect and monitor mitochondrial Cys with rapid responsiveness, imaging living cells and intact tissues with high contrast and brightness at a depth of 150 μm. The two-photon action cross section (Φσmax) of ASMI is 65.2 GM, corresponding to an excitation wavelength (λex) of 740 nm.
ASMI is a cell-permeable, non-toxic, biocompatible, photostable, positively charged, mitochondria targeting styryl-methylpyridinium based compound that acts as a rapid, cysteine selective, sensitive, and ratiometric (F 518 /F 452 nm) fluorescent turn-on probe (0.5 - 40 μM of [Cys]). Under physiological conditions, cysteine thiol reacts with the ASMI acrylate moiety in a time-dependent manner, and induces a facile intramolecular cyclization to release fluorogenic oxystyryl methylpyridinium. ASMI displays high selectivity over other biothiols (Kobs= 0.75, 0.038, 0.011 & 0.012 min -1 for Cys, Hcy, GSH & Na 2 S, respectively) and with no interference from other biologically relevant amino acids, essential metal ions, and anions, including Na2S. Shown to monitor mitochondrial Cys levels in HeLa cells and in deep tissues (150 μm of penetration depth) by two-photon excited fluorescence microscopy.
