Beam pen lithography as a new tool for spatially controlled photochemistry, and its utilization in the synthesis of multivalent glycan arrays†
Herein, we describe how cantilever-free scanning probes can be used to deposit precursor material and subsequently irradiate the precursor to initiate polymerization, resulting in a 3D lithographic method wherein the position, height and diameter of each feature can be tuned independently. Specifically, acrylate and methacrylate monomers were patterned onto thiol terminated glass and subsequently exposed to UV light produced brush polymers by a photoinduced radical acrylate polymerization reaction. Here, we report the first examples of glycan arrays, comprised of methacrylate brush polymers that are side-chain functionalized with α-glucose, by this new lithographic approach. Their binding with fluorophore labeled concanavalin A (ConA) was assayed by fluorescence microscopy. The fluorescence of these brush polymers was compared to glycan arrays composed of monolayers of α-mannosides and α-glucosides prepared by combining polymer pen lithography (PPL) with the thiol–ene photochemical reaction or the copper-catalyzed azide–alkyne cycloaddition. At high ConA concentration, the fluorescence signal of the brush polymer was nearly 20 times greater than that of the glycan monolayers, and the brush polymer arrays had a detection limit nearly two orders of magnitude better than their monolayer counterparts. Because of the ability of this method to control precisely the polymer length, the relationship between limit of detection and multivalency could be explored, and it was found that the longer polymers (136 nm) are an order of magnitude more sensitive towards ConA binding than the shorter polymers (8 nm) and that binding affinity decreased systematically with length. These glycan arrays are a new tool to study the role of multivalency on carbohydrate recognition, and the photopolymerization route towards forming multivalent glycan scaffolds described herein, is a promising route to create multiplexed glycan arrays with nanoscale feature dimensions.