Local Surface Chemistry Dynamically Monitored by Quantitative Phase Microscopy

Abstract

Surface modification by photo grafting constitutes an interesting strategy to prepare functional surfaces. Precision applications, however, demand quantitative methods able to monitor and control the amount and distribution of surface modifications, which is hard to achieve, particularly in operando conditions. In this paper, a label‐free, cost‐effective, all‐optical method based on wavefront sensing which is able to quantitatively track the evolution of grafted layers in real‐time, is presented. By positioning a simple thin diffuser in the close vicinity of a camera, the thickness of grafted patterns is directly evaluated with sub‐nanometric sensitivity and diffraction‐limited lateral resolution. By performing an in‐depth kinetic analysis of the local modification of an inert substrate (glass cover slips) through photografting of arydiazonium salts, different growth regimes are characterized and several parameters are estimated, such as the grafting efficiency, density and the apparent refractive index distribution of the resulting grafted layers. Both focused and widefield‐grafting can be quantitatively monitored in real time, providing valuable guidelines to maximize functionalization efficiency. The association of a well‐characterized versatile photografting reaction with the proposed flexible and sensitive monitoring strategy enables functional surfaces to be prepared, and puts surface micro‐ to submicro‐structuration within the reach of most laboratories.

Operandosurface optical nanometrology reveals diazonium salts’ visible photografting mechanism

“…Treatment of the raw speckle patterns deformation is carried out using the demon algorithm, as previously described, 17,34 implemented in Matlab. All subsequent data treatment was performed in Matlab 2021.…”

“…Among several available radical precursors, aryldiazonium salts are particularly popular ones, owing to their easiness of activation and of preparation from anilines. 10,11 Diazonium based strategies have been shown to enable the modification of a large variety of surfaces, including metals 12,13 , semiconductors, 10,14 carbon-based materials 15,16 and even insulating surfaces 17,18 . When no spatial resolution is required, grafting over conductive surfaces remains the most popular usage of these molecules, as cleavage of the N 2 leaving group can be conveniently activated through electrochemical reduction.…”

“…Our group has recently shown that controlled photografting of diazonium salts is possible using only visible light in aqueous media without the presence of any additives or special conditions 17 . Such simplicity, associated to the ability to manipulate optical fields, enables sub-micrometric range patterning with relatively modest instrumentation (visible laser and a microscope).…”

Wavefront Microscopy Using Quadriwave Lateral Shearing Interferometry: From Bioimaging to Nanophotonics

“…This technique recently proved effective for applications in 3D nanolocalization of nanoparticles 37 and chemistry at the microscale. 38…”

“…This modality slightly reduces the spatial resolution and/or the field of view compared with QLSI but remains much better than Shack-Hartmann and cost-effective. This technique recently proved effective for applications in 3D nanolocalization of nanoparticles and chemistry at the microscale …”