Zhai J Xie X Bakker E 2015 Traditionally, optical titrations of inorganic ions are based on a rapid and visible color change at the end point with water-soluble organic dyes as indicators. Adequate selectivity is required for both the indicator and the complexing agent, which is often limited. We present here alternative, heterogeneous ionophore-based ion-selective nanospheres as indicators and chelators for optical titrations. The indicating nanospheres rely on a weaker extraction of the analyte of interest by ion-exchange, owing to the additional incorporation of a lipophilic pH indicator in the nanosphere core. Ca(2+) titration was demonstrated as a proof-of-concept. Both the chelating and the indicating nanospheres showed good selectivity and a wide working pH range. https://sonar.ch/global/documents/269267 eng info:eu-repo/semantics/altIdentifier/doi/10.1021/ac504213q info:eu-repo/semantics/altIdentifier/pmid/25622089 Analytical chemistry. - 2015 Ion-selective optode nanospheres as heterogeneous indicator reagents in complexometric titrations. http://purl.org/coar/resource_type/c_6501