We present the study of dye-sensitized nanoparticles and their agglomerates with stochastic electrochemistry. We use a fluorine doped tin oxide (FTO) ultramicroelectrode (UME) with diameter in the range of 40 to 80 micrometers. To prepare the UME a sheet of perfluoroalkoxy alkane (PFA) is perforated to produce a recessed micro disk of the transparent conductive oxide. We demonstrate that the detection of the colloidal nanoparticles (NPs) sensitized with N719 is achieved via the interactions between agglomerates of the NPs that collide with the FTO. The NPs photooxidize MeOH and we detect the charge transfer from the NPs to the FTO ultramicroelectrode. The interactions between the dye sensitized NPs and the FTO yields oscillations that increase with exposure time. This increment in oscillation amplitude is assigned to changes in the aggregation of the NPs during the illumination even in the presence of 0.1 M supporting electrolyte. The formation of agglomerates is verified by dynamic light scattering and indicates that the agglomerates are able to separate photo-generated electrons and inject the carriers to the UME. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.