Incubation of MDA-MB-231 cells with NalGYOrn(PEG4SH)R-TxR at 1 nM, 10 nM, 100 nM, 1000 nM and 10000 nM at 37°C for 60 min, followed by analysis of fluorescence intensity using a plate reader (A), Incubation of MDA-MB-231 cells with 1000 nM of NalGYOrn(PEG4SH)R-TxR at 37°C, followed by analysis of fluorescence intensity at 5 min, 30 min and 60 min (B).