Dielectrophoretically Modulated Optical Spectroscopy of Colloidal Nanoparticle Solutions in Microfluidic Channels

Abstract

Optical spectroscopic techniques (e.g., extinction, scattering, and fluorescence spectroscopies) are important for the analysis of colloidal solutions of nanoparticles (NPs). They are routinely applied to plasmonic and quantum-dot NP samples assuming that these contain a single population of particles with modest size and shape dispersity. However, these spectroscopic techniques become less effective when the sample is a mixture of particles with different sizes, shapes, or composition. Here, an original microfluidic method is proposed for the optical spectroscopic analysis of colloidal NP solutions that combines periodic trapping of NPs by dielectrophoresis (DEP) with in situ optical extinction spectroscopy. The periodic trapping leads to modulation of the continuously monitored optical spectrum depending on the DEP properties of the NPs. DEP-modulated spectroscopy is demonstrated using colloidal gold NPs as small as 40 nm diameter. It is found that the DEP modulation is significantly enhanced when employing suitable microfluidic flow over a multielectrode array. Finally, it is shown that the method can identify and characterize the NP species simultaneously present in a mixture of 40 and 80 nm gold NPs, opening the way toward optical spectroscopic analysis of higher complexity NP mixtures through the combination of the DEP-modulated spectroscopy with chemometric methods.

On-chip light sheet illumination for nanoparticle tracking in microfluidic channels

“…49 It can be combined with in-channel microelectrodes for dielectrophoretically assisted spectroscopic multicomponent analysis. 35 In its simplest form, integrated light sheet illumination of a microfluidic channel provides a flow cell for imaging cytometry 50 and for in situ optical microscopy and spectroscopy at the single-particle level with suppression of the out-of-focus background.…”

“…The solutions were prepared according to a previously described procedure, starting from commercially available citrate-stabilized GNPs (BBI Solutions or Sigma-Aldrich), replacing the unspecied citrate medium with a solution of sodium lipoate and NaOH, through several centrifugation-concentration-resuspension cycles. 35 The centrifugation steps were 30 min each, at 800×g and 400×g centrifugal acceleration (RCF), for 50 nm and 80 nm gold NPs, respectively. 36 Polystyrene latex beads of 500 nm and 220 nm diameters were used as light scatterers (Fluoresbrite® 24 054, Polyscience).…”

Integration of 2D Nanoporous Membranes in Microfluidic Devices

“…Automation is inherent in microfluidic systems, overcoming the limitations posed by manual handling in microscopic setups . The majority of microfluidic systems are amenable to high-quality optical and electrical investigation in situ, offering real-time and simultaneous measurement, which is impractical in diffusion cells. − The integration can extend to biochemical assays, facilitating a cohesive platform for applications too.…”