A preprint reports that potential-modulated iSCAT can distinguish electrically connected parts of a patterned electrode from regions designed to be isolated by tracking how their optical signals change under an applied voltage.
The approach offers a label-free view of interfacial charging—the build-up of charge at an electrode-liquid boundary—across a wide field of view. The signal is relative, however: the study did not directly measure absolute ion concentration.
Following the signal
The patterned ITO served as the working electrode in a three-electrode cell containing an Ag/AgCl reference, a Pt counter and 100 mM LiClO4. The cell was 5 mm in diameter and 2 mm high.
The optical assay used a OneMP iSCAT microscope with circularly polarized 525 nm illumination, a 1.49-NA objective and 100× magnification.
The nanohole array included nominal diameters of 50, 75, 100 and 200 nm, with four nanoholes at each size.
To pull out the repeating signal, the analysis Fourier-transformed each nanohole trace and every image pixel, then used the complex coefficient at the drive frequency to define the modulation-amplitude maps.
A response that changed with the drive
At a modulation amplitude of 0.2 V and a frequency of 1 Hz, an individual nanohole’s intensity followed the applied waveform, and its spectrum showed a distinct peak at 1 Hz.
Across voltage tests, the optical response rose approximately linearly above about 100 mV. At lower voltages, it departed from that high-voltage trend and approached a plateau.
The low-voltage roll-off occurred near 24.8 mV, the room-temperature thermal-voltage scale cited by the authors. The paper does not present this as proof of a thermal-noise limit; instrumental noise, drift, camera noise, Fourier resolution and nonlinear charging could also contribute.
With the voltage held at 200 mV, the optical amplitude fell as modulation frequency increased. The paper interprets that attenuation as the electrical double layer, or EDL, being unable to follow faster modulation fully, but local ion measurements were not used to validate that explanation.
Testing electrical continuity
For the connectivity test, the study used a 3-by-4 array of ITO blocks separated by trenches milled through the film. The surrounding ITO remained connected, while the inner blocks were designed to be electrically isolated.
In the resulting dynamic maps, isolated block interiors had strongly suppressed modulation amplitudes compared with surrounding connected ITO, while some pattern edges showed enhanced responses.
A similar grid made with partial rather than through-milling remained connected and served as a structural control. Under voltage modulation, it produced a clear dynamic response, unlike the interiors of fully isolated blocks.
The pattern is informative but not definitive: the reported edge enhancement can have more than one optical or electrochemical origin.
Status and support
The authors conclude that potential-modulated iSCAT provides a label-free optical readout of local interfacial charging and electrical connectivity over a wide field of view. The optical response remains a relative measure, and the study does not establish a unique explanation for every edge signal.
The document is identified as arXiv:2608.23865v1, dated 24 Aug 2026.
The authors report funding from Dutch Research Council NWO-XS (OCENW.XS24.3.314), Utrecht University’s Pathways to Sustainability programme and research support from Refeyn Ltd.
Paper data and sources
Original title: Wide-Field Opto-Iontronic iSCAT Mapping of Interfacial Charging and Electrical Connectivity
Authors: Zhu Zhang, Sanli Faez
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-24
DOI: Not available
Original paper · Full text