<p>In this study, ionic-liquid submicron particles (ILSPs) encapsulating the luminophore tris(2′,2-bipyridyl)ruthenium (II) ([Ru(bpy)₃]²⁺) were developed as a carrier for an electrochemiluminescence immunoassay (ECLIA). The ILSPs were applied to quantitative determination of the model analyte prostate-specific antigen (PSA). The electrochemiluminescence of [Ru(bpy)₃]²⁺ was measured with 2-(dibutylamino)ethanol as a co-reactant in nine ionic liquids (ILs). The electrochemiluminescence intensity was higher in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSA]) and <i>N</i>-(2-methoxyethyl)-<i>N</i>-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide ([MEMP][TFSA]) than the other ILs. ILSPs were prepared using polyoxyethylene sorbitan monolaurate and sorbitan monooleate as surfactants and either [BMIM][TFSA] or [MEMP][TFSA]. The [BMIM][TFSA] ILSPs had a mean particle size of 244&#xa0;nm and zeta potential of − 21.0&#xa0;mV, and the [MEMP][TFSA] ILSPs had a mean particle size of 293 nm and zeta potential of − 17.9 mV. Microscope images showed that ILSPs were IL-in-water emulsions that completely encapsulated [Ru(bpy)₃]²⁺. The ILSPs with [BMIM][TFSA] were more stable than those with [MEMP][TFSA], and [BMIM][TFSA] ILSPs was selected as a carrier in ECLIA for PSA determination. The calibration curve of PSA for ECLIA using the [BMIM][TFSA] ILSPs showed a good linear relationship (<i>y</i> = 0.29<i>x</i> + 4.02, <i>r</i> = 0.95) for the PSA concentration range of 100&#xa0;pg/mL–100&#xa0;μg/mL. The limit of detection and limit of quantification were 544&#xa0;pg/mL and 35&#xa0;ng/mL, respectively. Our results demonstrate that ECLIA using ILSPs can be used to easily determine the PSA concentration even with ILSPs in the particle state.</p> Graphical abstract <p></p>