Two-Photon Fluorescent Probes for Detecting Enzyme Activities in Live Tissues

Abstract

Enzyme regulation is crucial in living organisms to catalyze various biosyntheses to maintain several physiological functions. On the contrary, abnormal enzyme activities can affect bioactivities leading to various serious disorders including cancer, Alzheimer’s disease, Parkinson’s disease, heart disease, and so on. This biological significance led to the development of various techniques to map specific enzyme activities in living systems to understand their role and distribution. Two-photon microscopy (TPM) in particular has emerged as a promising system for in situ real-time bioimaging owing to its robustness, high sensitivity, and noninvasiveness. It was achieved through the use of a two-photon (TP) light source of an optical window (700–1450 nm) beneficial in deeper light penetration and extraordinary spatial selectivity. Therefore, developing enzyme sensors utilized in TPM has significance in obtaining in vivo enzyme activities with minimal perturbation. The development of an efficient detection tool for enzymes has been continuously reported in the previous literature; here, we meticulously review the TP design strategies that have been attempted by researchers to develop enzyme TP fluorescent sensors that are proving very useful in providing insights for enzyme investigation in the biological system. In this review, the representative TP enzymatic probes that have been made in the past 5 years and their applications in tissue imaging are discussed in brief. In addition, the prospects and challenges of TP enzymatic probe development are also discussed.

Structural, Photophysical, and Water Sensing Properties of Pyrazolo[1,5‐a]pyrimidine‐Triphenylamine Hybrid Systems

“…Fluorescent organic compounds with exceptional photophysical properties have gained much attention for their applications in sensing, [1][2][3][4] bioimaging, [5][6][7] light-emitting devices (OLED), [8,9] etc. Probes exhibiting solvatofluorochromism could be used in organic electronics and optical switching, where charges are actively involved.…”

New ICT-based Ratiometric Two-Photon Near Infrared Probe for Imaging Tyrosinase in Living Cells, Tissues and Whole Organisms

“…autofluorescence, and light scattering. To avoid these drawbacks, a technique can be used that consists in the excitation of the fluorophore by means of two simultaneous photons of a wavelength that doubles or exceeds that needed to excite the same fluorophore with a single photon [4][5][6]. Two-photon microscopy (TPM) was predicted by Nobel laureate Maria Goeppert Mayer in 1931 [7] and was applied by Webb in a cellular environment in 1990 [8].…”

Photostable Organic Two‐photon Dyes with Ultrahigh Brightness for Long‐term Fluorescence Imaging

“…All these issues prevent the achievement of high‐quality and reproducible imaging results. In principle, dye with high brightness decreases laser intensity and thus eliminate the laser‐induced damage but couldn't address photobleaching and photocytotoxicity issues [8] . To fundamentally eliminate photobleaching and photocytotoxicity, inhibiting the ISC dynamics of two‐photon dye is a straightforward strategy.…”

“…In principle, dye with high brightness decreases laser intensity and thus eliminate the laser-induced damage but couldn't address photobleaching and photocytotoxicity issues. [8] To fundamentally eliminate photobleaching and photocytotoxicity, inhibiting the ISC dynamics of twophoton dye is a straightforward strategy. However, developing photostable two-photon dye to withstand prolonged exposure to femtosecond laser without occurring ISC remains a great challenge.…”