A high luminescence efficiency is an important property of colloidal quantum dots (QDs), and quantum yields higher than 90% have been reported for coreÀshell QDs. 1 High efficiencies are especially important for application of QDs as luminescent biolabels, 2 in QD lasers, 3 in spectral converters for warm white LEDs, 4,5 electroluminescent devices, 6 and solar concentrators. 7 Luminescence efficiencies are strongly temperature-dependent. 8 Extensive temperature-dependent luminescence studies for colloidal QDs have been conducted at cryogenic temperatures (0.3À300 K). 9À15 In this temperature region, interesting effects were observed, including a prolonged lifetime below 20 K related to brightÀdark state splitting, 11,16 thermally activated quenching due to surface defect states, 9,10,17 and temperature antiquenching assigned to a phase transition in the capping layer. 14,15 However, the luminescence properties of QDs above room temperature (RT) are hardly investigated, and yet, for most applications in luminescent devices, the working temperature is higher than 300 K. An interesting example is the recent application of QDs as color converters in warm-white LEDs, 18 in which QDs serve as narrow band red emitters under excitation with blue light from a (In,Ga)N LED. The narrow emission bandwidth renders QDs superior to classical phosphors based on broad band emission from luminescent ions. 19 In high-power LEDs for general lighting applications, the heat generated in the pÀn junction and phosphor converter layer leads to temperatures as high as 150À200°C in the layer applied on top of the blue diode. 20 To avoid these high temperatures, the QD phosphor layer can be placed in a more remote configuration. Still, temperatures in such a configuration are expected to be well above 50°C due to heat dissipation of the QDs themselves (excess energy from converting the blue into red light). Clearly, the quenching of QD luminescence at elevated temperatures is relevant for application of QDs in luminescent devices, and a better insight in the quenching behavior is needed.Despite its importance, research on luminescence temperature quenching above RT is very limited for QDs. It is theoretically expected for a QD to have a very high luminescence quenching temperature (T q ). Three generally accepted mechanisms for thermal quenching involve thermally activated crossover from the excited state to the ground state, multiphonon relaxation, and thermally activated photoionization. The first mechanism is generally depicted in a simple configurational coordinate diagram. 8,21 The energy difference between the minimum * Address correspondence to a.meijerink@uu.nl.Received for review July 18, 2012 and accepted September 14, 2012. Published online 10.1021/nn303217qABSTRACT Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300À500 K) luminescence studies are reported for highly ef...
Hyaluronan is a biologically active polymer, which can be formulated into nanoparticles. In our study, we aimed to probe atherosclerosis-associated inflammation by using hyaluronan nanoparticles and to determine whether they can ameliorate atherosclerosis. Hyaluronan nanoparticles (HA-NPs) were prepared by reacting amine-functionalized oligomeric hyaluronan (HA) with cholanic ester and labeled with a fluorescent or radioactive label. HA-NPs were characterized in vitro by several advanced microscopy methods. The targeting properties and biodistribution of HA-NPs were studied in apoe–/– mice, which received either fluorescent or radiolabeled HA-NPs and were examined ex vivo by flow cytometry or nuclear techniques. Furthermore, three atherosclerotic rabbits received 89Zr-HA-NPs and were imaged by PET/MRI. The therapeutic effects of HA-NPs were studied in apoe–/– mice, which received weekly doses of 50 mg/kg HA-NPs during a 12-week high-fat diet feeding period. Hydrated HA-NPs were ca. 90 nm in diameter and displayed very stable morphology under hydrolysis conditions. Flow cytometry revealed a 6- to 40-fold higher uptake of Cy7-HA-NPs by aortic macrophages compared to normal tissue macrophages. Interestingly, both local and systemic HA-NP–immune cell interactions significantly decreased over the disease progression. 89Zr-HA-NPs-induced radioactivity in atherosclerotic aortas was 30% higher than in wild-type controls. PET imaging of rabbits revealed 6-fold higher standardized uptake values compared to the muscle. The plaques of HA-NP-treated mice contained 30% fewer macrophages compared to control and free HA-treated group. In conclusion, we show favorable targeting properties of HA-NPs, which can be exploited for PET imaging of atherosclerosis-associated inflammation. Furthermore, we demonstrate the anti-inflammatory effects of HA-NPs in atherosclerosis.
Immunological complexity in atherosclerosis warrants targeted treatment of specific inflammatory cells that aggravate the disease. With the initiation of large phase III trials investigating immunomodulatory drugs for atherosclerosis, cardiovascular disease treatment enters a new era. We here propose a radically different approach: implementing and evaluating in vivo a combinatorial library of nanoparticles with distinct physiochemical properties and differential immune cell specificities. The library's nanoparticles are based on endogenous high-density lipoprotein, which can preferentially deliver therapeutic compounds to pathological macrophages in atherosclerosis. Using the apolipoprotein E-deficient (Apoe −/− ) mouse model of atherosclerosis, we quantitatively evaluated the library's immune cell specificity by combining immunological techniques and in vivo positron emission tomography imaging. Based on this screen, we formulated a liver X receptor agonist (GW3965) and abolished its liver toxicity while still preserving its therapeutic function. Screening the immune cell specificity of nanoparticles can be used to develop tailored therapies for atherosclerosis and other inflammatory diseases.nanomedicine | drug delivery | immunotherapy | molecular imaging | atherosclerosis
To explore the thermal response of the densely packed inner regime of poly(N-isopropylacrylamide) (PNIPAM) brushes grafted to gold nanoparticles (AuNPs), we systematically studied the thermoresponsive properties of NIPAM oligomeric brushes affected both by oligomer molar mass and Au core size. A series of NIPAM oligomers with various molar masses ranging from ca. 600 to 3400 g/mol were obtained by RAFT polymerization and fractionated with HPLC. The AuNPs stabilized with various NIPAM oligomers were prepared by a one-pot reaction and further fractionated to achieve three pairs of AuNP fractions with narrow size distributions. When decreasing the molar mass of brush chains from ca. 3300 to 700 g/mol, a significant molar mass effect on the thermal transition was found, i.e., the phase transition temperature (defined as the endothermic peak temperature T p by DSC) shifted from ca. 31 to 15 °C and the endothermic peak became broadened. As a comparison, we also studied the aqueous solutions of free NIPAM oligomers (molar mass from ca. 3400 to 600 g/mol) by turbidity measurements. They showed a completely opposite trend of the thermally induced phase transitions; i.e., the transition shifted to higher temperature with decreasing molar mass. The Au core size also affected the thermal response of NIPAM oligomer brushes, especially in the case of the shortest oligomers. Large Au cores caused the thermal transition of NIPAM oligomer brush to occur at lower temperatures compared to the small Au cores. This was attributed to the hydrophobic nature of Au nanocrystal surfaces. Enthalpy changes (∆H) associated with the thermal transitions of the oligomer brushes are indicative of strong interchain interactions in the brushes, especially on large Au cores.
The application of nanoparticle drug formulations, such as nanoliposomal doxorubicin (Doxil), is increasingly integrated in clinical cancer care. Despite nanomedicine's remarkable potential and growth over the last three decades, its clinical benefits for cancer patients vary. Here we report a non-invasive quantitative positron emission tomography (PET) nanoreporter technology that is predictive of therapeutic outcome in individual subjects. In a breast cancer mouse model, we demonstrate that co-injecting Doxil and a Zirconium-89 nanoreporter (89Zr-NRep) allows precise doxorubicin (DOX) quantification. Importantly, 89Zr-NRep uptake also correlates with other types of nanoparticles' tumour accumulation. 89Zr-NRep PET imaging reveals remarkable accumulation heterogeneity independent of tumour size. We subsequently demonstrate that mice with >25 mg kg−1 DOX accumulation in tumours had significantly better growth inhibition and enhanced survival. This non-invasive imaging tool may be developed into a robust inclusion criterion for patients amenable to nanotherapy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.