Dimensional characterization of gold nanorods by combining millisecond and microsecond temporal resolution single particle ICP-MS measurements

A systematic investigation of single particle inductively coupled plasma mass spectrometry (spICP-MS) signal profiles recorded with normal (ms-range) and high (mu s-range) temporal resolution for spherical and rod-shaped gold nanoparticles was performed. The experiments with nanorods were carried out on hemispherically capped cylindrical particles synthesized in the aspect ratio range from 1.5 to 4.5. A comparison of NP signals and time profiles for spherical and rod-shaped NPs revealed that (i) the volume of the particles can be assessed by conventional spICP-MS measurements using a joint, linear calibration plot; and (ii) the shape of signal time profiles and transit times for equal-volume spherical and rod-shaped NPs are different, based on which the aspect ratio can be calculated. By using the statistical evaluation of the high resolution signal time profiles, an analytical method was developed for the discrimination and dimensional analysis of nanorod-shaped NPs. The method is based on observing the shortest and longest transit times for nanoparticles. In the case of spherical NPs, these transit times are very similar, whereas in the case of nanorods, the shortest and longest transit times correlate with the characteristic width and length of the particles, respectively. This method is the first nanorod dimensional characterization method in the literature, which is based solely on ICP-MS measurements. It was shown that the accuracy of the method is very good -the characteristic length and width of the particles could be determined with less than 6% error.