A common issue, encountered in nanoparticle-biological system interaction studies is accurate nanoparticle concentration expression, given the critical importance of the dose-response relationships. We present here the application of quartz crystal microgravimetry (QCM) to accurately measure nanoparticle concentration in a colloidal suspension. Application of a small drop of the nanoparticle suspension in volatile solvent to the crystal surface leaves a dry nanoparticle residue after solvent evaporation and a shift in the crystal resonant frequency is recorded. Instrument was calibrated using a dilution series of Si and Ag nanopowder in methanol, rhodamine B in methanol and ferrocene in cyclohexane. The QCM showed a linear response for nanoparticle concentrations in the range from 5 to 1300 g/ml. Method was used to determine the molar concentrations of size selected octyl-terminated Si nanocrystal samples with diameters in the range from 1.1 to 14.8 nm and calculate size dependent nanocrystal extinction coefficients.
Citation: Journal of Physical Chemistry B
Pub Type: Journals
Nanoparticles, concentration, colloidal solution, extinction coefficient, dry mass, quartz crystal microbalance