Abstract
The characterization of nanoparticles is an important problem in many areas of applied physics, chemistry, medicine, and biology. Micromechanical resonators with embedded fluidic channels represent a powerful new technology for particle characterization through direct measurement of the buoyant mass of nanoparticles in solution with attogram resolution (1 ag = 10−18 g). We recently showed that correlation analysis greatly expands the range of applications by enabling measurements of mass even when the individual particles are far lighter than the conventional detection limit. Here, we extend the concept of mass correlation spectroscopy further to simultaneously measure the ensemble-averaged size and mass of nanoparticles by exploiting size-dependent differences in hydrodynamic dispersion. To do so, we first derive an approximate model of the dispersion of finite-size particles flowing through a microfluidic channel of rectangular cross-section, valid in a large range of dispersion regimes. By including this solution into the model describing the correlation function of the time-domain mass signal acquired with a micromechanical resonator, information on particle size can be obtained during mass characterization without requiring any modification of the devices. The validity of the analysis is corroborated both by numerical simulations and experimental measurements on nanoparticles of different materials ranging from 15 nm to 500 nm.
Highlights
Understanding the composition and the behavior of nanoparticles has required the development of a large variety of techniques1–8 to detect their chemical and physical properties, as well as their interactions with the environment
We have shown that the curve shape contains information on the particle size, the lack of a model describing the diffusion/dispersion behavior of the particles while crossing the embedded microfluidic channel prevented the extraction of such information
Nanoparticles of diameters ranging from a few to hundreds of nanometers were characterized by Mass Correlation Spectroscopy (MCS) to validate the ability of the analysis in detecting particle size using the developed dispersion model
Summary
Understanding the composition and the behavior of nanoparticles has required the development of a large variety of techniques to detect their chemical and physical properties, as well as their interactions with the environment. High precision characterization of particles in solution can be obtained by analytical centrifugation, which allows population separation and deconvolution during the analysis.. The high costs of the equipment and the relatively long analysis times hinder the routine application of this method. Another class of analysis method is represented by high-resolution microscopy techniques, such as electron microscopy or atomic force microscopy, which enable visual inspection of the sample. Information on the size and shape of the objects under examination can be obtained with nanometer resolution. These methods are characterized by low-throughput and potential image artifacts, caused by the extensive sample preparation required.
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