Comparison of signal to background (S/B) ratios of different systems.

<p>HEK293 cells expressing either SNAP_f-ADRβ2 or IFP1.4 were used. Both SNAP_f-ADRβ2 and IFP1.4 are under the control of the CMV promoter. SNAP_f-ADRβ2 expressing cells (293-SNAP_f) were stained with BG-800 (SNAP_f/BG-800) or BG-782 (SNAP_f-BG-782), respectively. IFP1.4 expressing cells were incubated with biliverdin (IFP/BV). The excess substrate and biliverdin were washed away after reaction. The fluorescence signals of the cells were scanned on the culture plate without trypsinization and concentration. Signals were detected at their respective optimal wavelength (Ex/Em: 785/820 nm for BG-800 and BG-782; 685/720 nm for IFP1.4). The signals of HEK293 parental cells stained with the respective substrates or biliverdin were defined as background.