Rewritable magnetic fluorescence-encoded microspheres: preparation, characterization, and recycling

Rewritable magnetic fluorescence-encoded microspheres were prepared by coating magnetic microspheres with a fluorescence-encoded melamine-formaldehyde (MF) shell. Fluorescence encoding was realized by varying the dye types and concentrations incorporated into the MF shell. Ten sets of magnetic fluorescence-encoded microspheres including four sets doped with single dye and six sets doped with two dyes were obtained and successfully identified through flow cytometric analysis. High encoding capacity could be achieved by increasing the dye number and intensity levels. More importantly, the original fluorescence-encoded MF shell could be removed via calcination. The inner magnetic microspheres remained unaffected and could be re-coated with a new fluorescence-encoded MF shell easily. The fluorescent MF coating (encoding writing) and calcination (encoding erasing) composed a cycle. Results demonstrated that the magnetic microspheres retained their original characteristics after writing-erasing cycles and the writing-erasing cycle could be repeated numerous times. These kinds of rewritable magnetic fluorescence-encoded microspheres enabled recycling and regeneration. Combining magnetic separation and re-encoding, which can significantly simplify the analysis processes and decrease the analysis cost, these microspheres are expected to be widely used in suspension arrays for high-throughput analyses.