Fluorescence imaging for in situ detection of cell surface sialic acid by competitive binding of 3-(dansylamino)phenylboronic acid.

Sialic acid (SA) usually locates at the terminal position of the sugar chains on cell membranes, and its expression level is closely associated with cancer. Here polysialic acid (PSA) embedded gold nanoparticles (AuNPs) were prepared and functionalized with fluorescent 3-(dansylamino)phenylboronic acid (DAPB) for in situ imaging and detection of cell surface SA. The fluorescence resonance energy transfer (FRET) from DAPB to AuNPs quenched the fluorescence of DAPB. In the presence of additional SA or SA-abundant cells, the competitive binding of DAPB with SA and PSA led to the release of the assembled DAPB from the surface of PSA-embedded AuNPs, resulting in fluorescence of DAPB on SA-abundant cell surface. The proposed methods realized the in situ imaging and monitoring of cell surface SA, and could also be applied to the quantification of cell number and the amounts of cell surface SA. This work not only proposed a convenient visualization method for the analysis of SA on cell membranes, but also provided a potential tool for accelerating the elucidation of the basic role of SA in various biological processes and development of anti-cancer therapies.