(a-d) β-lactamase at 50 units/ml (a, c) or 1 unit/ml (b, d) in PBS were delivered into NHDFs using BLAST under the condition of fluid pumping but with (a, b) or without (c, d) laser pulsing. Scale bar, 100 µm. (e) Blue and green fluorescent intensities for all 4 groups were measured 5 h after β-lactamase delivery. A higher blue-to-green fluorescence ratio means more β-lactamase was delivered into cells and remained functional, and thus able to cleave CCF4 molecules. Error bars, s.d. (n = 976; 577; 1,005; 353 for 50 units/ml delivery; 50 units/ml control; 1 unit/ml delivery; 1 unit/ml control, *** p < 0.0001, t-test). The experiment was conducted 3 times with the same results.