pH-controlled delivery of luminescent europium coated nanoparticles into platelets

Abstract

Water soluble, luminescent gold nanoparticles are delivered into human platelets via a rapid, pH-controlled mechanism using a pH low insertion peptide, pHLIP. The approach introduces cocoating of gold nanoparticles with a europium luminescent complex, EuL and the pHLIP peptide to give pHLIP•EuL•Au. The 13-nm diameter gold nanoparticles act as a scaffold for the attachment of both the luminescent probe and the peptide to target delivery. Their size allows delivery of approximately 640 lanthanide probes per nanoparticle to be internalized in human platelets, which are not susceptible to transfection or microinjection. The internalization of pHLIP•EuL•Au in platelets, which takes just minutes, was studied with a variety of imaging modalities including luminescence, confocal reflection, and transmission electron microscopy. The results show that pHLIP•EuL•Au only enters the platelets in low pH conditions, pH 6.5, mediated by the pHLIP translocation across the membrane, and not at pH 7.4. Luminescence microscopy images of the treated platelets show clearly the red luminescence signal from the europium probe and confocal reflection microscopy confirms the presence of the gold particles. Furthermore, transmission electron microscopy gives a detailed insight of the internalization and spatial localization of the gold nanoparticles in the platelets. Thus, we demonstrate the potential of the design to translocate multimodal nanoparticle probes into cells in a pH dependent manner.imaging | lanthanides | multimodal probes | pH low insertion peptide

pHLIP peptide targets nanogold particles to tumors

“…Davies et al recently reported the pHLIP-mediated, pH-controlled delivery of 13 nm water-soluble gold nanoparticles coated with luminescent europium into human platelets in vitro (18). In related work presented here, we show that pHLIP not only induces the binding of 1.4 nm gold nanoparticles to cancer cells at acidic pH in vitro but also that it stabilizes binding in tumors established in mice.…”

Targeting acidity in diseased tissues: Mechanism and applications of the membrane-inserting peptide, pHLIP

“…pHLIPs have been successfully used to anchor relatively large cargoes to the cell surface, such as nanogold particles (16, 90) and proteins. Cell-surface decoration of tumor cells with pHLIP anchored antigens has been used to recruit an acquired immune response in several model systems (Unpublished data) and several approaches are being evaluated for the use of pHLIPs to deliver antigens to tumors in vivo .…”

Evaluation of quinoline as a remote sensitiser for red and near-infrared emissive lanthanide(iii) ions in solution and the solid state

“…We have previously demonstrated that quinoline sensitisers are useful for epi-fluorescence imaging of the luminescence from nanoparticle-bound lanthanide complexes in human platelets using standard glass optics and an excitation wavelength of 365 nm. 17 The overall luminescence quantum yields (Φ) for EuL and SmL were found to be 4% and 0.1%, respectively. These values take into account the overall excitation-energy transfer and emission process from the quinoline sensitiser to the metal ion, as well as the efficiency of the radiative decay process at the trivalent metal ion itself.…”