Highly efficient multiple‐labeling probes for the visualization of enzyme activities

: 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.