DNA-directed immobilisation of glycomimetics for glycoarrays application: Comparison with covalent immobilisation, and development of an on-chip IC50 measurement assay

Glycoarrays are powerful tools for the understanding of protein/carbohydrate interactions and should find applications in the diagnosis of diseases involving these interactions. Immobilisation of the carbohydrate probe is a key issue in the elaboration of high performance devices. In the present study, we have compared the fluorescent signal intensity and determined the lower detection limit of glycoconjugates immobilised at two concentrations (0.5 and 25 μM) by DNA-directed immobilisation (DDI), to glycoconjugates covalently immobilised on the solid support (borosilicate glass slide). At 0.5 μM, DDI led to a stronger fluorescence signal (by a factor of 4.5) and to a lower detection limit (20 nM) than covalent immobilisation (higher than 200 nM). We also report the development of an IC50 measurement assay of DDI immobilised glycoconjugates. We found that the relative affinity per galactose residue of RCA 120 for glycoconjugates bearing one or three galactose residues was different by a factor of 23 when measured under IC50 conditions or by direct fluorescence reading.