BACKGROUND The lifetime of chromatography resins typically averages between 10 and 300 cycles for the manufacture of a therapeutic protein. Developing and establishing the robustness of the method for each separation process represents a significant challenge and is subject to extensive regulatory oversight. This paper presents a novel fluorescence-based assay for residual aggregated proteins to aid the evaluation of the extent of resin regeneration. RESULTS The versatility of this method was demonstrated by using strong anion and cation exchange agarose resins Praesto Q and SP in conjunction with bovine serum albumin and monoclonal antibody feed materials. The assay entails applying a molecular rotor dye to a sample of free resin and measuring the fluorescence intensity using a plate reader or visualizing under a confocal laser scanning microscope to gain a more detailed characterization. Following five consecutive chromatography cycles, both methods revealed a 10-fold increase in fluorescence intensity along with a proportional reduction in dynamic binding capacity. Furthermore, the use of the assay suggested that fouling was dependent on spatial bead position in the column, bead channel structure and cleaning conditions. CONCLUSION This work presents a simple assay suitable for use in resin lifetime studies to enhance process understanding. (c) 2019 Society of Chemical Industry