Fast and Simultaneous Determination of the Number and Mass Concentrations of Gold Nanorod Colloid Using an Improved Optical Extinction-Scattering Spectroscopic Method

Accurate determination of the concentrations, including the mass concentration (MC) and number concentration (NC), of metal nanoparticle (NP) colloid is highly demanded in the synthesis, metrology, and application of NPs. The commonly used inductively coupled plasma mass spectrometry (ICP-MS) can only measure the MC of NPs, which is destructive to the NPs and requires advanced operation skills. Here, we present a simple approach based on an improved optical extinction-scattering spectroscopic (OESS) method to fast determining the MC and NC of metal nanorod colloids simultaneously. Unlike most existing spectroscopic methods that can only deal with low-concentration NP colloids, the improved OESS method can accurately solve the inverse scattering problem of NP colloids with higher concentrations, so that a two-dimensional joint probability density function of both the width and aspect ratio of nanorods can be retrieved, which makes the basis for the accurate determination of the MC and NC of the colloids in a large range of concentration. The reliability and accuracy of the method are validated by measuring several typical nanorod colloids with different concentrations and comparing the results with those obtained by the standard ICP-MS method. It is shown that the improved OESS method can cover a broad MC measurement range of at least 10–50 µg/mL and a NC measurement range of 10 9 –10 11 /mL. The uncertainty and sources of error in the measurement are also analyzed. Since the improved OESS method is fast, cost-effective, non-destructive, and easy to implement, it provides a simple way to determine the concentrations of metal NPs and has the potential to be extended to other metal NPs.