Disruption\nDynamics and Charge Transfer of a Single\nAttoliter Emulsion Droplet Revealed by Combined Fast-Scan Sinusoidal\nVoltammetry and Short Time Fourier Transform Analysis

Single-entity electrochemistry has gained significant\nattention\nfor the analysis of individual cells, nanoparticles, and droplets,\nwhich is leveraged by robust electrochemical techniques such as chronoamperometry\nand cyclic voltammetry (CV) to extract information about single entities,\nincluding size, kinetics, mass transport, etc. For an in-depth understanding\nsuch as dynamic interaction between the electrode and a single entity,\nthe unconventional fast electrochemical technique is essential for\ntime-resolved analysis. This fast experimental technique is unfortunately\nhindered by a substantial nonfaradaic response. In this work, we introduce\nfast-scan sinusoidal voltammetry (FSSV) combined with a short-time\nFourier transform (STFT) for analyzing single emulsion droplets. Utilizing\nultramicroelectrode and fast potential sweeps up to apparent 200 V/s,\nwe achieved high temporal resolution (8 ms per voltammogram) to capture\nthe current signals during droplet collisions. STFT analysis reveals\nthe amplitude and phase changes, allowing for the accurate detection\nof collision events even in the absence of redox species. By adopting\nan algorithm of drift-free baseline subtraction, a conventional CV\nshape was obtained in FSSV. The reacted charge from the single-entity\nvoltammogram at every 8 ms was also plotted. This method effectively\naddresses limitations in traditional techniques, providing insights\ninto emulsion dynamics such as droplet contact and droplet breakdown.