Real time monitoring of fluorescence change (F/F0) in the microgel sensors in a collagenase solution. (a) Typical image of microgel sensors in a 1 μg/ml collagenase solution right after exposure (left), after 30 minutes (middle) and after an hour (right). Scale bars, 50 μm. (b) Fluorescence change (F/F0) monitored for 1 hour in various concentrations of collagenase solution. (c) Fluorescence changes (F/F0) in the microgel sensors in 0 ng/ml, 200 ng/ml, 1 μg/ml and 5 μg/ml collagenase concentrations after 5 min, 30 min and after an hour.