Optical Nanoimpacts of Dielectric and Metallic Nanoparticles on Gold Surface by Reflectance Microscopy: Adsorption or Bouncing?

Abstract

Optical modeling coupled to experiments show that a microscope operating in reflection mode allows imaging, through solutions or even a microfluidic cover, various kinds of nanoparticles, NPs, over a (reflecting) sensing surface, here a gold (Au) surface. Optical modeling suggests that this configuration enables the interferometric imaging of single NPs which can be characterized individually from local change in the surface reflectivity. The interferometric detection improves the optical limit of detection compared to classical configurations exploiting only the light scattered by the NPs. The method is then tested experimentally, to monitor in situ and in real time, the collision of single Brownian NPs, or optical nanoimpacts, with an Au-sensing surface. First, mimicking a microfluidic biosensor platform, the capture of 300 nm FeOx maghemite NPs from a convective flow by a surface-functionalized Au surface is dynamically monitored. Then, the adsorption or bouncing of individual dielectric (100 nm polystyrene) or metallic (40 and 60 nm silver) NPs is observed directly through the solution. The influence of the electrolyte on the ability of NPs to repetitively bounce or irreversibly adsorb onto the Au surface is evidenced. Exploiting such visualization mode of single-NP optical nanoimpacts is insightful for comprehending single-NP electrochemical studies relying on NP collision on an electrode (electrochemical nanoimpacts).

In Situ Optical Monitoring of the Electrochemical Conversion of Dielectric Nanoparticles: From Multistep Charge Injection to Nanoparticle Motion

“…Apart from AFM imaging, or in situ TEM, which are often restrictive owing to the slowness of the scanning imaging process or to e-beam dose perturbations, high resolution optical microscopies offer high throughput, quantitative, and dynamic analysis of single NPs electrochemistry . They afford complementary in situ mechanistic insights into various phenomena ranging from chemical transformations (double layer charging, – NP conversion, ,,− nanobubbles electrogeneration) to motion, , or local polarization due to structural changes ,,, associated with the electrochemical actuation of NPs. Although powerful, these strategies have been mostly applied to plasmonic nanomaterials and more rarely employed to depict the electrochemistry of dielectric NPs …”

Optical monitoring of the electrochemical nucleation and growth of silver nanoparticles on electrode: From single to ensemble nanoparticles inspection

“…Another pathway is to separate NPs in space by combining electrochemistry to high resolution visualization techniques, ideally operando, [27][28][29][30][31][32][33][34][35][36][37][38][39][40] or ex situ for the ultimate tracking at the atomic scale. 41 The local images of the resolved NPs can be further analyzed and provide insights into nanoscale electrochemistry.…”

Electrochemistry and Optical Microscopy

“…It is illusory to seek for absolute optical measurement. One would rather evaluate relative variations of a quantity (mass, volume, etc…) from optical intensity variations and resort to calibration procedures to verify the predicted trends, using different molecular probes or NP gauges, and cross-correlating the optical images with multiple microscopic observations [75][76][77][78]. Resolution is the ability of an imaging tool to distinguish (resolve) in an image two objects.…”

“…If the validity of the Gaussian shape may be argued for fitting the PSF of asymetric entities (nanorods or strongly polar fluorophores, [79,80]), the Gaussian PSF provides accurate localization of the object centroid with 5-20nm resolution. This strategy is used to track with unprecedented resolution the motion (translational or rotational) of individual objects at surfaces during the course of a (electro)chemical process, such as micro or nano particles near or at electrodes by scattering- [78,[81][82][83] or fluorescence [84,85] -based microscopies, or molecules confined in Raman hot spots [66], during their (electro)chemical conversion, or nanobubbles produced by gas evolving reactions [86,87]. More subtly, the superlocalization of the Airy disk highlights the centroid of the electric dipole of a nanoobject upon its electrochemical charging [83,88].…”