Coupling of dark-field microscopy with redox-magnetohydrodynamics microfluidics to characterize individual nanoparticles in mixed suspensions.

by Sikes, Jazlynn C.; Wonner, Kevin; Nicholson, Aaron G.; Cignoni, Paolo; Fritsch, Ingrid; Tschulik, Kristina

A method has been developed that offers high-throughput single particle differentiation and tracking by combining dark field microscopy (DFM) and redox-MHDs (RMHD) microfluidics. The resulting RMHD-DFM was used to identify, quantify, and size a flowing suspension mixt. of two types of particles, 82 ± 9 nm silver and 140 ± 10 nm silica-core gold-shell (Ag and Au@Si). DFM can monitor and differentiate individual nanoparticles in situ and operando in a relatively inexpensive way by using the localized surface plasmon resonance (LSPR), which depends on particle size and elemental compn. RMHD microfluidics is driven by a body force, FB that results from the cross product of ionic c.d. (j, A/cm2) and magnetic flux d. (B, Tesla), FB = j × B. Thus, the fluid velocity is tunable through variation of the orientation and magnitude of j and B. Several hundred individual nanoparticles were differentiated from each other by localized surface plasmon resonance and further sized by their Brownian motion, yielding diffusion coeffs. from their 1-dimensional mean square displacements. The bidirectional pumping capability provides the advantage of multiple observations of the same part of the sample. More precise information about the size distribution can be obtained compared to a unidirectional pumping system. Addnl., the ability to reverse pumping increases the probability of observing particles previously outside of the plane of view, permitting the anal. of relatively low concns. of nanoparticles. The presentation will describe the most recent results on the RMHD-DFM method and draw comparisons to other methods used for nanoparticle characterization: nanoparticle tracking anal. (NTA), transmission electron microscopy (TEM), and dynamic light scattering (DLS). We envision that RMHD-DFM can be applied to investigations of a broad range of nanoparticle suspensions, both aq. and nonaq., for studies of dynamic interactions, catalysis, and synthesis.