Seminaphtharhodafluor or SNARF is a fluorescent dye that changes color with pH.
It can be used to construct optical biosensors that use enzymes that change pH.
The emission peak of carboxy-SNARF at pH 6.0 is at wavelength 585 nm, while that at pH 9.0 is at 640 nm.[1]
SNARF-1 can serve as a substrate for the MRP1 (multidrug resistance-associated protein-1) drug transporter, to measure the activity of the MRP1 transporter. For this purpose, an acetomethoxyester group is added to SNARF-1. Cellular esterases cleave off SNARF-1, and its transport out of the cells can be measured by following the loss of fluorescence from the cells.[2]