NHS-PEG-Maleimide Coupling to Amine Particles

If a NHS-PEGn-maleimide compound is used for this type of activation and coupling, the intermediate maleimide-activated particle should be quickly washed free of excess crosslinker and used to couple ligand immediately. This is due to the fact that the maleimide hydrolyzes in aqueous solution at a higher rate than that of a maleimide on an SMCC-type crosslinker, because of the extreme hydrophilicity of the PEG spacer arm compared to the cyclohexane spacer of SMCC. 

Wash 10 mg of amine particles into 10 mM sodium phosphate, pH 7.2 (coupling buffer) using centrifugation. Resuspend the particles in 1 ml of the same buffer. 

Dissolve NHS-PEGg-maleimide (MW 601.6) into dimethyl sulfoxide (DMSO) at a concentration of 20 mM. PEG-type crosslinkers often exist as a thick oily mass, and preparing the solution may involve dissolving an entire vial of the compound into DMSO to determine accurately the required concentration. 

Add 50 pi of the NHS-PEGg-maleimide solution to the 1 ml particle suspension and mix thoroughly to dissolve. 

React for 1 hour at room temperature with mixing. 

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