To demonstrate biorthogonal reactivity and luminogenic behaviour of complex 4 we employed metabolic labelling using BCN-modified (Ac4ManNBCN). This modified monosaccharide has been reported as efficiently metabolized via the sialic acid biosynthesis pathway, thus leading to high level of reporter group expression on the surface of cell organelles. Once expressed into the cell, the BCN group can then react via IEDDA with the triazine metal complex 4. This biorthogonal ligation will be accompanied by appearance of luminescence. Complex 4 was selected for this experiment as this click product is excitable using a 488 nm laser, due to similarities between its absorption spectrum and that of the model compound 8. Therefore, to investigate luminescent behaviour of the triazine iridium complex 4 following click reaction, A-375 cells were incubated with 50 μM of BCN-sugar for 48 h prior to treatment with 10 μM of complex 4 for 30 min at 37°C, and subsequently imaged by fluorescence confocal microscopy. Cells without treatment or treated only with Ac4ManNBCN or complex 4 were implemented as negative controls. Strong luminescence was detected for cells treated successively with Ac4ManNBCN and 4 (Figure ), while much weaker fluorescence was measured for cells not pre-incubated with the BCN-sugar (Figure ). Analysis by fluorescence-activated cell sorting (FACS) of cells treated with increasing concentrations of 4 (0.5 to 50 M) showed an increase of luminescence signal for cells pre-labelled with Ac4ManNBCN (Figure ). The control cells without pre-labelling with Ac4ManNBCN did not show luminescence. These results demonstrate successful Ac4ManNBCN glycometabolism by A-375 cells, as well as bioorthogonal luminogenic reaction to visualised metabolically glycosylates cells using complex 4.