DNA mediated assembly of quantum dot–protoporphyrin IX FRET probes and the effect of FRET efficiency on ROS generation

Abstract

Photodynamic therapy (PDT) involves generation of reactive oxygen species (ROS) by the irradiation of a photosensitizer. Controlled and targeted release of ROS by a photosensitizer is crucial in PDT. For achieving controlled generation of ROS, a ZnSe/ZnS quantum dot (QD) donor and protoporphyrin IX (Pp IX) acceptor based fluorescence resonance energy transfer (FRET) probe is reported here. The QDs and Pp IX are assembled either by direct conjugation or through DNA hybridization. Complementary DNA strands are individually conjugated to the QDs and Pp IX by amide coupling. Due to the overlap of the emission spectrum of QDs and the absorption spectrum of Pp IX, efficient transfer of energy from QDs to Pp IX was observed in both the cases. The FRET efficiency was quantitatively evaluated by steady-state and time-resolved spectroscopy and compared between the QD-Pp IX direct conjugate and QD-DNA-Pp IX assembly at various donor to acceptor ratios. Since a single QD can harbor a multiple number of Pp IX-DNA counterparts through DNA hybridization, the FRET efficiency was found to increase with the increase in the number of Pp IX acceptors. ROS generation from Pp IX was studied for the FRET pairs and was found to be affected by the irradiation time of the QD donor.

Two-Photon Induced Fluorescence Energy Transfer in Polymeric Nanocapsules Containing CdSexS1–x/ZnS Core/Shell Quantum Dots and Zinc(II) Phthalocyanine

“…The obtained results show that ABMDMA is more effectively (about 5 times) oxidized by the direct irradiation of ZnPc (maximum of absorbance at 669 nm) than by energy transfer (by FRET and/or reabsorption) to ZnPc after QDs excitation (isolated excitation spectrum interval 400–600 nm). This difference is probably due to the energy losses during the transfer between QDs and ZnPc since it was calculated from the TCSPC measurements that only about 16% of the energy absorbed by QDs is transferred to ZnPc. However, results obtained at the excitation at spectral range where ZnPc absorption is negligible show that FRET can be used as a tool for efficient generation of reactive 1 O 2 in our nano drug-delivery system.…”

Photodynamic therapy targeting VCAM-1-expressing human umbilical vein endothelial cells using a PpIX–VCAM-1 binding peptide–quantum dot conjugate

“…PpIX (containing carboxylic groups) and 3MPA-QDs (containing carboxylic groups) were simultaneously conjugated to VCAM-1 binding peptides (containing amino groups) using standard carbodiimide based chemistry. 23 In detail, PpIX and QDs were rstly activated by Sulfo-NHS (N-hydroxysulfosuccinimide) in the presence of EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) in MES (2-[morpholino]ethanesulfonic acid) buffer at pH 5.5, resulting in a semi-stable Sulfo-NHS ester; the above products were then reacted with the amines of VCAM-1 peptides at pH 7.2 to form amide crosslinks. PpIX-VCAM-1 peptide-QD (denoted as PVQ) conjugates were obtained at a concentration of 5 mM in which the ratio of PpIX : VCAM-1 binding peptide : QD was 50 : 50 : 1.…”

A quantum dot–MUC1 aptamer conjugate for targeted delivery of protoporphyrin IX and specific photokilling of cancer cells through ROS generation

“…24 Based on our previous findings, ZnSe/ZnS QD-photosensitizer PpIX FRET probes offer a significant and systematic increase in the ROS formation with an increase in the FRET efficiency between QDs and PpIX. 25 However, it is important that for PDT applications such a system must be specifically targeted for possible in vivo usage. 26 QDs offer notable conjugation strategies that could be adopted for linking them with various targeting entities including ssDNA aptamers.…”