Improving the signal-to-noise performance of molecular diagnostics with PEG-lysine copolymer dendrons

The synthesis, characterization, and use of dendron-like poly(ethylene glycol)-lysine (PEG-Lys) copolymers as an intermediate layer for biomolecular diagnostic signal enhancement is presented. Solid phase Fmoc-peptide synthesis was used to synthesize polymers with one, two, and three PEG-Lys comonomer units in both a linear and first and second-generation dendronic structure directly onto organosilica microspheres. The microsphere surface loadings (number of free amine sites) were modified and quantified through an innovative use of the protecting groups of coupled amino acids. Surfaces with 0.1-100% of the original loading corresponding to 0.3-270 nmol/m2 of free amines were achieved. The influence of polymer structure and surface loading (grafting density) on the signal-to-noise of the microsphere-based molecular diagnostic was assessed measuring the difference in the signal of a model protease digestion assay and reduction in the nonspecific adsorption of bovine serum albumin. Increasing the polymer grafting density and the addition of dendronic branching were both found to increase the assay signal and reduce the nonspecific protein adsorption.