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In this study, we explore the electron transition mechanism and optical properties of the popular red fluorescent protein mCherry. By examining the charge transfer spectrum and combining it with the mCherry hole-electron distribution, we identify that the charge transfer between the phenolate and imidazolinone loops significantly contributes to the absorption spectrum. Quantitative analysis of charge transfer shows that, overall, the electrons are transferred to the C16 atom in the middle of phenolate and the imidazolinone loops during absorption. We speculate that C16 may also absorb protons to enable the photoconversion of mCherry in the excited state, similar to the blinking mechanism of IrisFP. In addition, we further investigated the optical properties of mcherry in the external field by polarizability (hyperpolarizability), showing the anisotropy of the polarization, the first hyperpolarization and the second hyperpolarization by unit spherical representation. Our results suggest that significant polarization and second hyperpolarizability occur when the field direction and electron transfer direction are aligned. We also analyzed the polarizability and first hyperpolarizabilities for different external fields. The polarizability mutated when the external field satisfies the S_0,min-> S_1 transition. Finally, the study of the first hyperpolarizability shows that adjusting the appropriate field can lead to a linear photoelectric effect or second harmonic generation of mCherry. These studies have certain reference values for various red fluorescent protein correlation simulations and experiments because of the similarity of the red fluorescent protein.

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., Comment: 10 pages, 6 figures

Biological lasers have attracted vast attention because of their potential medical application prospects, especially the low threshold biological laser, which can be used for ultrasensitive biological detection while ensuring that its luminous gain medium is not damaged by the high-energy pump light. By coupling the low concentration green fluorescent protein (GFP) solution with a high Q whispering gallery mode microbubble resonator, we managed to fabricate a miniature GFP laser with ultralow lasing threshold of 500 nJ/mm^2. The energy used to excite the GFP can be reduced to 380 fJ, two orders of magnitude lower than that of the lowest excitation energy GFP laser known. The Q value of the optical cavity in this biological laser is 5.3 x 10^7, the highest among GFP lasers at present. We further confirmed the long-term stability of the working characteristics of GFP laser for the first time and found that its optical characteristics can be maintained for at least 23 days. Finally, we measured the effects of different concentrations of fluorescent protein on the laser threshold. The data show that this biological laser can be used for a highly sensitive detection of GFP concentration., Comment: 10 pages, 6 figures