Proteins to QDs Using EDC

The following protocol describes the coupling of amine-containing proteins to carboxylated QDs using a single-step EDC reaction, as recommended by several manufacturers. 

Prepare a carboxylated QD solution in lOmM sodium borate, pH 7.4 (reaction buffer), at a concentration of 1 pM. The supplier of QDs usually will provide the reagent concentration as a molar quantity, which treats each particle as though it was a single molecule. A typical QD solution as obtained from a manufacturer may be about 8 pM starting concentration. 

Dissolve the protein to be conjugated to the QD in reaction buffer at a concentration of l-10mg/ml. 

Add a quantity of the protein solution to the QD solution with mixing to obtain the desired molar excess of protein over the concentration of nanoparticles. Using a 1- to 20-fold molar excess typically works well, but optimization should be done to determine the best ratio for a particular application. 

Prepare a solution of EDC in water at a concentration of lOmg/ml. Immediately add 57pl of this solution to the protein/QD solution. Mix well. 

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