  Biolasers show considerable potential in the biomedical field. Fluorescent
protein (FP) is a type of biomaterial with good luminescence efficiency that
can be used as the luminescent gain medium in biolasers. Due to the higher
cell/tissue permeability, lower cell phototoxicity, and relatively less
background fluorescence than other fluorescent proteins, the red fluorescent
protein is more suitable in biological applications. MCherry is the most
extensively used high-quality red fluorescent protein because of its short
maturation time and stable luminescence properties. In this study, using
mCherry and microbubble cavity, we realize a highly stable mCherry fluorescent
protein laser. The laser resonator achieves a quality factor of 10^8, which is
the highest Q factor among the currently available FP lasers. Moreover, this
laser exhibits low threshold of 286 fJ, which can effectively protect the
luminescent material from being damaged by pump light. Such a threshold is the
lowest in the FP lasers as per our knowledge. The prepared laser shows
excellent stability in a wide pH range with good photobleaching resistance and
can be stored at 4 degree for nearly a month. Also, the laser can serve as a
high-sensitivity molecular concentration detector with mCherry as biomarker,
owing to its lasing threshold behavior.
