Synthesis and Characterization of PEGylated Near-IR-Emitting Ag2S Quantum Dots for Tumor Imaging and Therapy

Near-infrared (NIR) emitting semiconductor quantum dots (QDs) have emerged as a new class of fluorescent probes in recent years due to better penetration depth into thetissue and elimination or significant reduction of tissue autofluorescence.Ag2S quantum dots are the most popular NIR emitting quantum dots in recent years becausedramatically improved cytocompatibility compared to heavy metal containing, more traditional QDs such as PbS, PbSe, CdHgTe.Previously, we have developed cationic polyethyleneimine (PEI)-25 kDa and 2MPA coated Ag2S QDs with high quantum yields.However, cationic QDs show some toxicity. Inorder to reduce such toxicity and prevent adsorption of blood components, we pegylated the cationic Ag2S QDs. PEGylation also enabled Doxorubicin® (Dox) loading tothese NIR QDs. Hence, PEG-PEI/2MPA coated aqueous Ag2S NIRQDs showed enhanced cytocompatability, theranostic and diagnostic potential.MaterialsBranched polyethyleneimine (PEI) (Mw 25 kDa) and N,N’-carbonyldiimidazole (CDI) were obtained from Aldrich. Methoxy polyethylene glycol (mPEG-OH, 2 kD) and chloroformwere purchased from Rapp Polymere and Merck Millipore, respectively.MethodsPEI and 2-MPA coated Ag2S QDs have been synthesized according to our previos report [5]. PEGylation was performed using CDI chemistry by activation of hydroxyl terminalgroups of the mPEG with CDI and conjugation of activated mPEG to QDs. Finally, washed samples were loaded with Dox. All cytotoxicity and optical imaging studies wereperformed with HeLa cells.ResultsPEI/2MPA Ag2S QDs have been conjugated with mPEG using CDI chemistry. NMR proved the conjugation. Particles were stable and highly luminescent even after PEGylation(Figure 1 a). Doxorubicin was loaded in PEGylated particles in high efficiency (Figure 1b). PEGylation improved the viability of HeLa cells especially at high doses (Figure 1c).Yet, Dox reduced viability.DiscussionIn this study, PEI and 2MPA coated and PEGylated Ag2S QDs have been developed as new theranostic nanoparticles which allows optical imaging at the NIR window andeffective delivery of a cancer drug into cells. Particles were stable in aqueous medium and luminesce strongly around 820 nm. Dox which is mostly used cancer drug wasloaded to the PEGylated particles to evaluate the QDs as a cancer drug delivery agent. In addition to increased viability of cells after PEGylation, Dox loading increased thetoxicty, provin g effcient delivery of Dox into the cells which was confirmed by confocal microscopy (Figure 1d). The drug release and apoptosis/necrosis studies will beperformed as next steps.ConclusionAs a conclusion, we have developed PEGylated cationic Ag2S QDs with high stability and strong luminesence in the NIR region. Such particles have high cytocompatability tobe used as safe optical imaging and drug delivery agents. This was demonstrated with Dox loading and delivery into HeLa cells.Figure 1. Photoluminescence and absorbance spectra of PEI/2MPA and PEG-PEI/2MPA Ag2S QDs (a), fluorescence intensity of Dox loaded PEG-QDs (b), cytotoxicityevaluation (c) and cell internalization of the nanoparticles (Arrows and red color show PEG-QDs in the HeLa cells) (d)