Characterization of Nanoparticles in Diverse Mixtures Using Localized Surface Plasmon Resonance and Nanoparticle Tracking by Dark-Field Microscopy with Redox Magnetohydrodynamics Microfluidics

Abstract

Redox magnetohydrodynamics (RMHD) microfluidics is coupled with dark-field microscopy (DFM) to offer high-throughput single-nanoparticle (NP) differentiation in situ and operando in a flowing mixture by localized surface plasmon resonance (LSPR) and tracking of NPs. The color of the scattered light allows visualization of the NPs below the diffraction limit. Their Brownian motion in 1-D superimposed on and perpendicular to the RMHD trajectory yields their diffusion coefficients. LSPR and diffusion coefficients provide two orthogonal modalities for characterization where each depends on a particle's material composition, shape, size, and interactions with the surrounding medium. RMHD coupled with DFM was demonstrated on a mixture of 82 ± 9 nm silver and 140 ± 10 nm gold-coated silica nanospheres. The two populations of NPs in the mixture were identified by blue/green and orange/red LSPR and their scattering intensity, respectively, and their sizes were further evaluated based on their diffusion coefficients. RMHD microfluidics facilitates high-throughput analysis by moving the sample solution across the wide field of view absent of physical vibrations within the experimental cell. The well-controlled pumping allows for a continuous, reversible, and uniform flow for precise and simultaneous NP tracking of the Brownian motion. Additionally, the amounts of nanomaterials required for the analysis are minimized due to the elimination of an inlet and outlet. Several hundred individual NPs were differentiated from each other in the mixture flowing in forward and reverse directions. The ability to immediately reverse the flow direction also facilitates re-analysis of the NPs, enabling more precise sizing.

Applications of magnetic and electromagnetic forces in micro-analytical systems

“…The well-controlled RMHD pumping enabled a continuous, reversible, and uniform flow for precise and simultaneous NP tracking of the Brownian motion. 270 4.2.4 Effects of MHD and spin-selectivity on water splitting. Water splitting or water electrolysis is a wellknown electrochemical reaction to produce molecular hydrogen and molecular oxygen from water.…”

“…The well-controlled RMHD pumping enabled a continuous, reversible, and uniform flow for precise and simultaneous NP tracking of the Brownian motion. 270…”

Magnetic field-enhanced redox chemistry on-the-fly for enantioselective synthesis

“…in electrocatalysis and electrodeposition of metals and polymers.29-31 Furthermore, due to the possibility to control the fluid flow around the electrode surface, this concept has been also extended to redox magnetohydrodynamic microfluidics and self-propulsion of active matter. [31][32][33][34] Recently, the synergy between the spontaneous ion flux produced by self-electrophoretic swimmers and an external magnetic field was proposed as an interesting alternative to boost their propulsion speed by up to 2 orders of magnitude.35 These Lorentz force-driven Janus swimmers exhibit a predictable clockwise or anticlockwise rotational motion as a function of the magnetic field orientation. The concept is complementary to already well-studied magnetic field-driven swimmers, where motion is triggered either by a pulling mechanism or rotating/undulating magnetic fields.…”

Size characterization of plasmonic nanoparticles with dark-field single particle spectrophotometry

“…Given the difficulties found during the manufacturing processes, the need for accurate methods to measure their size is peremtory. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) definitely represent the gold standard techniques to measure the size of nanoparticles 19 – 21 ; the high spatial resolution achieved with these techniques (< 5 nm) allows visualizing any morphological nanoparticle features with excellent quality 22 , 23 .…”