Rapid and Efficient Prediction of Optical Extinction Coefficients for Gold Nanospheres and Gold Nanorods

Optical determination of the exact concentration of any given colloidal suspension of nanoparticles (NP) is complicated by the relative scarcity of NP-specific extinction coefficients and the rigor and expense of determining these constants experimentally. The discrete dipole approximation (DDA) theoretical technique allows for facile determination of NP energetic properties, therefore relating the extinction intensity provided by DDA to the extinction coefficient needed to determine the concentration of NP solutions would be extremely beneficial. We experimentally determine the extinction coefficients for a range of gold nanosphere and gold nanorod sizes, supplement these values with available literature values, and then use the Discrete Dipole Approximation theoretical technique to model the optical properties of each of these nanoparticles. We then develop a relationship between the theoretical extinction intensity provided by DDA and the extinction coefficients obtained experimentally. These relationships will allow future users to accurately predict extinction coefficients that are specific to the exact dimensions of the gold nanosphere or gold nanorod in question. Use of these relationships will greatly reduce both the time-scale and the cost of determining nanoparticle extinction coefficients by circumventing the need for costly, time-consuming analytical experiments.