Antigen specific memory B cells are considered as a homogeneous population. Here, we wanted to isolate antigen-specific memory cells from mice in order to both characterize the response to the immunization regimine and identify high-affinity candidate BCRs for expression. For this, we used single cell RNA sequencing (scRNA-seq) to describe the diversity of anti-fentanyl B cells elicited by a fentanyl-immunization platform and identify the different markers for each subbpopulation. We use this appoach to select the switched memory B cell, study their BCR repertoir and identify the BCR sequences from the most potent memory B cells. Overall design: Fentanyl specific B cells from mice spleens were isolated by Fluorescence-activated cell sorting (FACS) according to several markers and their specificity for fentanyl and analyzed using scRNAseq. **Please note that raw data is not provided due to proprietary concerns regarding the raw sequences**