The S28H mutation on mNeptune generates a brighter near-infrared monomeric fluorescent protein with improved quantum yield and pH-stability.

Li ZY, Wang DB, Zhang ZP, Bi LJ, Cui ZQ, Deng JY, Zhang XE. 

Acta Biochim Biophys Sin (Shanghai). 2014 Jul 25. pii: gmu063.

Abstract 

　　For living deep-tissue imaging, the optical window favorable for light penetration is in near-infrared wavelengths, which requires fluorescent proteins with emission spectra in the near-infrared region. Here, we report that a single mutant Ser28His of mNeptune with a near-infrared (≥650 nm) emission maxima of 652 nm is found to improve the brightness, photostability, and pH stability when compared with its parental protein mNeptune, while it remains as a monomer, demonstrating that there is still plenty of room to improve the performance of the existing near infrared fluorescence proteins by directed evolution. 

http://abbs.oxfordjournals.org/content/early/2014/07/25/abbs.gmu063.short