Label-Free Biosensors for Studying Carbohydrate-Protein Interaction

Carbohydrate-protein interactions are omnipresent in nature controlling critical functions of cell proliferation, cell adhesion, and cell migration in the human body. However, the detailed mechanisms of these interactions are still poorly understood. Glycan microarrays where glycans are immobilized on glass slides, or membranes, or in multi-well plate formats have been developed and used as a major tool to analyze the specificity of glycan-binding proteins. These arrays require fluorescent labeling of glycan-binding proteins (or a second antibody that specifically recognizes them) for readout, which can change their biointeraction properties. Moreover, labeling a cell may significantly interfere with its cellular activities, resulting in unwanted cell responses. To understand the interaction mechanisms, or even to identify the specific surface biomarkers for diagnosis and treatment, real-Time, noninvasive, and label-free techniques are more valuable as they allow the measurement of the thermodynamics and kinetics of carbohydrateprotein interactions without interference from the applied methods. In this chapter, we summarize different strategies to study the carbohydrate-protein interactions for both molecular and cellular analyses in biology. These include electrochemical, piezoelectric, optical, and micromechanical sensors and arrays that all rely upon the glycan immobilization methods, which are based on surface coupling chemistry and the innovations in the readout protocols. Illustrative examples of these strategies have been discussed with emphasis on the immobilization and interaction chemistry while also focusing on future trends. However, it is also noted that challenges still exist in transforming carbohydrateprotein interactions with high throughput and high information content as an alternate for nucleic acid or antibody-based interactions. An option for integrating the transduction mechanisms in the formation of electrochemical quartz crystal microbalance sensors and the use of multifunctional glycosylated conductive polymer biointerfaces are presented. The examples of such integrations have distinct advantages over the existing label-free biosensors based on a single transduction mechanism for studying carbohydrate-protein interactions. They provide more detailed and accurate information for revealing the mechanism of complicated carbohydrate-protein interactions. In reviewing all these topics, it is envisaged that this chapter will reinstigate studies into label-free biosensors based on carbohydrate-protein interactions with a focus on real-Time, non-invasive, label-free measurements with high information content alongside providing a general understanding of the topic for a range of applications including viral infections, inflammatory disorders, cancers, and development of vaccines.