Concanavalin A-functionalized nanogold – a glycan tag for surface enhanced Raman spectroscopy

Bacterial infections constitute one of the major health issues for the next decades, and their detection through affordable methods is currently an urgency. Cell surface glycans constitute interesting biomarkers, since they are specific, abundant, and diverse. However, their identification has been commonly based on sophisticated, high-cost techniques, such as mass spectrometry or immunolabeling. We herein propose a surface-enhanced Raman spectroscopy (SERS) approach based on optically active gold nanoparticles targeted to D-mannoside and D-glucoside, two common terminal sugars of bacterial glycans. To do so, nanoparticles were decorated with Concanavalin A through a simple physisorption step before using them to generate Raman signals. The use of the construct with beta-methyl-D-mannoside, a well-known Concanavalin A ligand, was found to generate SERS signals of dose-dependent intensities. Moreover, the application of the functional system with three different bacterial species induced differential SERS profiles that included Raman bands specific to cell surface glycolipids. Transmission electron microscopy analyses of bacterial-nanogold preparations revealed that both cell surface and secreted glycans can be tagged by using the gold-lectin construct. Further research is therefore encouraged to better assess this functional nanotag in microbial detection.