Glutathione-mediated release of Bodipy® from PEG cofunctionalized gold nanoparticles

Gold nanoparticles synthesized via sodium citrate reduction of chloroauric acid (HAuCl4) were functionalized with either various concentrations of thiol-terminated Bodipy (R) FL L-cystine (0.5, 1.0, 1.5, and 2.0 mu g/mL) or Bodipy-poly(ethylene glycol) at concentrations of 0.5-18.75, 1.0-12.50, and 1.5-6.25 mu g/mL to form a mixed monolayer of BODIPY-PEG. Thiol-terminated Bodipy, a fluorescing molecule, was used as the model drug, while PEG is widely used in drug-delivery applications to shield nanoparticles from unwanted immune responses. Understanding the influence of PEG-capping on payload release is critical because it is the most widely used type of nanoparticle functionalization in drug delivery studies. It has been previously reported that glutathione can trigger release of thiol-bound payloads from gold nanoparticles. Bodipy release from Bodipy capped and from Bodipy-PEG functionalized gold nanoparticles was studied at typical intracellular glutathione levels. It was observed that the addition of PEG capping inhibits the initial burst release observed in gold nanoparticles functionalized only with Bodipy and inhibits nanoparticle aggregation. Efficient and controlled payload release was observed in gold nanoparticles cofunctionalized with only a limited amount of PEG, thus enabling the coattachment of large amounts of drug, targeting groups or other payloads.