“Reactive” probe for hydrogen sulfite: Good ratiometric response and bioimaging application

4-(1H-Phenanthro[9,10-d]imidazol-2-yl)benzaldehyde (P-1) was prepared as a new ratiometric optical probe for hydrogen sulfite. Upon the addition of HSO3−, it displayed large emission wavelength shift (Δλ = 120 nm) and the detection limit was determined to be as low as 2 μM. In addition to its high selectivity for hydrogen sulfite rather than other common anions, P-1 was successfully applied to the detection of hydrogen sulfite in HeLa cells with ratiometric fluorescent methods.