Efficient Dye-Loaded Polymeric Beads for Raman Imaging

Rdots were prepared based on previously published procedures (23 (link), 24 (link), 25 (link)). Here, IR780 (425,311, Sigma Aldrich) was used instead of IR783 (Fig. 1a) because IR780 is incorporated into beads more efficiently than IR783, while their Raman spectra are the same. A mixture of 150-µL, 2.5%, 40-nm PS beads (Invitrogen, C37232), 150-µL, 2%, F-127 (Invitrogen, P6867), and 300-µL Milli-Q were put in a 1.5-mL plastic tube. The mixture of 30-µL, 30-mM cyanine dye solution in DMSO and 270-µL tetrahydrofuran was added to the tube dropwise. The mixture was then vortexed for 10 min, followed by gentle agitation for another 10 min. Then, 14-mL Milli-Q water was added to the mixture to quench the dye loading. The mixture was then centrifuged (4000 rpm, 10 min) using 100 K MWCO filters (Millipore, UFC910024) to remove the solvents. The stained beads were washed with 15-mL Milli-Q water five times.