Noninvasive methods to monitor dynamic single-cell events

Adaptations to changing environments manifest in various cellular activities across multiple timescales, where single-cell responses can occur asynchronously between individual cells. Hence, accurate delineation of transient or rare activities often requires real-time monitoring of single cells over hours or days. While great strides have been made in the throughput of molecular analysis methodologies, most biochemical methods are cell destructive and, therefore, can only provide snapshots of dynamic processes. Noninvasive observations of natural cell behaviors offer unique insights into key dynamic events. In this feature review article, we discuss current toolkits for monitoring real-time dynamics of diverse cellular activities in living cells, as well as their advantages and challenges. We also speculate on new avenues for noninvasive single-cell monitoring that will be feasible in the foreseeable future.