Together these data demonstrate that Probe-TAMRA is a highly potent and selective tool for covalently labelling FPR1 in living cells. Tracer-FITC alone (6, dark blue), Probe-TAMRA alone (2, red), in combination (3, cyan), or in sequence with photoirradiation (4, 5). For the latter, cells were first incubated with Probe-TAMRA for 30 min, irradiated with 365 nm light for 30 sec, washed, incubated with Tracer-FITC for 30 min and analysed (5, dark red), or with the inclusion of an addition incubation and irradiation step (4, grey). Probes were used at a concentration of 10 nM. Samples were washed twice before analysis and 10,000 cells were measured per sample.