Dual-emission carbonized polymer dots for ratiometric sensing and imaging of l-lysine and pH in live cell and zebrafish

It is highly desired to accurately and selectively detect and image intracellular l-lysine and pH in biological systems because they could act as the biomarkers in certain abnormal conditions and may give us a warning of the occurrence of diseases. It has been attracted more focuses to design new ratiometric fluorescent probe for monitoring l-lysine and pH to improve detection accuracy. Carbonized polymer dots (CPDs), which possess carbon/polymer hybrid structure rather than pure carbon structure and constitute of a carbon core and large amounts of functional groups/polymer chains on the surface, rise up as a new type of fluorescent nanomaterials and especially display many advantages for bioanalysis. In this study, o-phenylenediamine (o-PD) and poly(styrene-co-maleic anhydride) (PSMA) are used as the precursors to synthesize the desired CPDs through one-step hydrothermal amide method. The prepared CPDs display two well-resolved fluorescence emission bands, i.e., a very weak emission centered at 470 nm in blue region and a strong emission centered at 558 nm in yellow region. It is found that the two emissions are both responsive to l-lysine based on the surface passivation mechanism, whereas, only the yellow emission is responsive to pH due to the protonation/deprotonation process of the amino groups. Based on the different responsive behaviors, ratiometric detection and imaging of l-lysine and pH are achieved. The prepared ratiometric CPDs probe is successfully applied for l-lysine and pH sensing and imaging at two emission channels in live cell and zebrafish with satisfactory results.