Additional file 3: Figure S3. of Rational design of Raman-labeled nanoparticles for a dual-modality, light scattering immunoassay on a polystyrene substrate

OPSS-PEG-SVA conjugation and hydrolysis. Activated OPSS-PEG-SVA can undergo two separate and competing reactions, hydrolysis and conjugation. To promote conjugation, the concentration of the protein solution was maintained at greater than 1mg/ml during conjugation and the NHS ester molecule was added to the protein solution immediately upon suspension. In addition, the NHS ester reagent was stored at −20 °C in a desiccator and under nitrogen to avoid possible hydrolysis due to ambient moisture. The hydrolysis reaction will release a NHS ester-leaving group with a maximum absorbance at 260nm. The quality of the stored NHS ester reagent was estimated by measuring the absorbance of a freshly prepared solution at 260nm and comparing that value to the initial absorbance from a newly opened vial of the reagent. (PDF 114 kb