A novel self-immobilizing and near-infrared fluorogenic probe has been reported to visualize extracellular enzyme activity in living mouse.

γ-Glutamyl transpeptidase (GGT), a type of cell membrane-bound enzyme, is closely involved in a wide range of physiological and pathological processes, and a large number of fluorogenic probes have been developed to detect the activity of GGT. However, the use of these imaging reagents to visualize GGT activity in vivo is largely limited because of rapid diffusion and clearance of activated fluorophores. Herein, by merging quinone methide and a fluorogenic enzyme substrate, we report an activatable self-immobilizing near-infrared probe for the in vitro and in vivo imaging of GGT activity. This probe is initially fluorescently silent, but the selective activation by GGT is able to significantly increase its fluorescence intensity at 714 nm and covalently anchor activated fluorophores at the site of interest. We have shown that this probe induced a much stronger fluorescence on live GGT-overexpressing cells compared to regular fluorogenic probes and allowed wash-free and real-time imaging of enzyme activity. More importantly, the use of this probe in the imaging of GGT activity in U87MG tumor-bearing mice by i.v. administration indicates that this self-immobilizing reagent is capable of efficiently enhancing its retention at the detection target and thus leads to much improved detection sensitivity compared to regular fluorogenic probes. This study demonstrates the advantage of fluorogenic probes with activatable anchors in the noninvasive imaging of enzyme activity in highly dynamic in vivo systems.

Quinone methide (QM) as a latent trapping unit has been widely explored in activity‐based self‐immobilizing reagents. However, further application of this strategy has been largely hampered by the limited labeling efficiency to proteins. In this study, a thorough investigation on the labeling efficiency and the structure of QM‐based trapping unit is presented, from which a QM with multiple leaving groups was identified as an optimal trapping unit. An alkaline phosphatase (ALP) immobilizing reagent featured with this multiple‐labeling trapping unit exhibited lower nonspecific binding and, remarkably, a significantly higher labeling efficiency over other immobilizing reagents upon enzymatic activation. The utility of this imaging reagent was further demonstrated with the in vitro and in vivo visualization of the ALP activities. Furthermore, the multiple functional trapping unit may find greater value in the other activity‐based immobilizing probes.

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Infrared radiometer measuring experiment, infrared radiometer calibration is extremely important part, which determines the correctness and accuracy of infrared radiation characteristics of the background and objectives of the radiometer measurements. Article first introduces the necessity of an infrared radiometer and infrared radiometer calibration, focusing on the MR170 type IR radiometer calibration method for analysis. Experiments using cavity blackbody radiation as a standard, and then analyzed using MATLAB to fit the measured data to obtain the desired curve fitting and fitting function. Finally, the article summarizes the experimental and analytical precision experiments.