Probe sonicator

PTX-loaded PLGA NPs (PTX@NP) were prepared with three different PLGA polymers by the single-emulsion method. Briefly, 50 mg of PLGA (4, 30 or 150 kDa) was dissolved in 4 mL of CH₂Cl₂ and mixed with 50 μL of 5 wt% PTX (i.e., 2.5 mg) in CHCl₃. The PTX/PLGA mixture was added to 10 mL of 4 wt% polyvinyl alcohol (PVA) in water, and emulsified by a probe sonicator (Sonics Vibracell, Newtown, CT, USA) for 2 min in ice, pulsing at a power level of 7W and a 2:1 duty cycle every 6 sec. The emulsion was added to 20 mL of deionized (DI) water and stirred for 1 h, and the organic solvent was removed by rotary evaporation for 1 h. The resulting PTX@NP was collected by centrifugation at 16,000 rcf for 20 min at 4 °C and washed twice with DI water. For preparation of DiR-loaded PLGA NPs (DiR@NP), DiR were dissolved in the organic phase with PLGA at a target DiR content of 0.25 wt%.
An aqueous suspension of 0.1 wt% PTX@NP (1 mL) was mixed with an equal volume of 0.1 wt% dopamine HCl in Tris buffer (10 mM, pH 8.5). The mixture was incubated on an orbital shaker for 3 h at room temperature to coat the NP surface with a layer of polydopamine (pD). The pD-coated NP (NP-pD) was collected by centrifugation at 16,000 rcf for 20 min at 4 °C and re-dispersed as a 2 wt% suspension.