Cell surface carbohydrates (glycans) play many important roles in health and disease, 1 and significant advances have been made in deciphering the so-called 'glyco-code' through studies of the recognition of glycan sequences by glycan-binding proteins. As the same glycan motifs are sometimes recognised by multiple biologically distinct protein partners (Figure ), Nature deploys local glycan concentrations to generate selectivity, not only by varying 3D presentation and density, but also spatial-segregation: e.g. the human bronchial and alveolar epithelia interact with and are colonised by different influenza viruses. Biosensing or diagnostics using glycan sequences as targets is limited by glycan cross-reactivities, for example using sialic acids or heparan sulfates as attachment sites for COVID, which have lower selectivity than antibody-based systems. This raises the challenge as to how one can develop small molecule probes for diagnostics or therapeutics that can distinguish between the interactions of different proteins with the same glycan.