1,721,152 research outputs found
Compact zwitterion-coated iron oxide nanoparticles for in vitro and in vivo imaging
No full textWe have recently developed compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand coated superparamagnetic iron oxide nanoparticles (SPIONs) for use in various biomedical applications. The defining characteristics of ZDS-coated SPIONs are small hydrodynamic diameters, low non-specific interactions with fetal bovine serum, the opportunity for specific labeling, and stability with respect to time, pH, and salinity. We report here on the magnetic characterization of ZDS-coated SPIONs and their in vitro and in vivo performance relative to non-specific interactions with HeLa cells and in mice, respectively. ZDS-coated SPIONs retained the superparamagnetism and saturation magnetization (M[subscript s]) of as-synthesized hydrophobic SPIONs, with M[subscript s] = 74 emu g[superscript −1] [Fe]. Moreover, ZDS-coated SPIONs showed only small non-specific uptake into HeLa cancer cells in vitro and low non-specific binding to serum proteins in vivo in mice.National Institutes of Health (U.S.) (MIT-Harvard Center for Cancer Nanotechnology Excellence Grant 1U54-CA119349)National Cancer Institute (U.S.) (Grant R01-CA126642)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-07-D-0004)National Science Foundation (U.S.) (Collaborative Research in Chemistry Program CHE-0714189
Using the shortwave infrared to image middle ear pathologies
Full text linkVisualizing structures deep inside opaque biological tissues is one of the central challenges in biomedical imaging. Optical imaging with visible light provides high resolution and sensitivity; however, scattering and absorption of light by tissue limits the imaging depth to superficial features. Imaging with shortwave infrared light (SWIR, 1–2 μm) shares many advantages of visible imaging, but light scattering in tissue is reduced, providing sufficient optical penetration depth to noninvasively interrogate subsurface tissue features. However, the clinical potential of this approach has been largely unexplored because suitable detectors, until recently, have been either unavailable or cost prohibitive. Here, taking advantage of newly available detector technology, we demonstrate the potential of SWIR light to improve diagnostics through the development of a medical otoscope for determining middle ear pathologies. We show that SWIR otoscopy has the potential to provide valuable diagnostic information complementary to that provided by visible pneumotoscopy. We show that in healthy adult human ears, deeper tissue penetration of SWIR light allows better visualization of middle ear structures through the tympanic membrane, including the ossicular chain, promontory, round window niche, and chorda tympani. In addition, we investigate the potential for detection of middle ear fluid, which has significant implications for diagnosing otitis media, the overdiagnosis of which is a primary factor in increased antibiotic resistance. Middle ear fluid shows strong light absorption between 1,400 and 1,550 nm, enabling straightforward fluid detection in a model using the SWIR otoscope. Moreover, our device is easily translatable to the clinic, as the ergonomics, visual output, and operation are similar to a conventional otoscope.United States. National Institutes of Health (9-P41-EB015871-26A1)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-13-D-0001
Two-Photon Oxygen Sensing with Quantum Dot-Porphyrin Conjugates
No full textSupramolecular assemblies of a quantum dot (QD) associated to palladium(II) porphyrins have been developed to detect oxygen (pO[subscript 2]) in organic solvents. Palladium porphyrins are sensitive in the 0–160 Torr range, making them ideal phosphors for in vivo biological oxygen quantification. Porphyrins with meso pyridyl substituents bind to the surface of the QD to produce self-assembled nanosensors. Appreciable overlap between QD emission and porphyrin absorption features results in efficient Forster resonance energy transfer (FRET) for signal transduction in these sensors. The QD serves as a photon antenna, enhancing porphyrin emission under both one- and two-photon excitation, demonstrating that QD-palladium porphyrin conjugates may be used for oxygen sensing over physiological oxygen ranges.National Cancer Institute (U.S.) (Grant R01-CA126642)National Science Foundation (U.S.). Graduate Research Fellowshi
Dual-band ultraviolet-short-wavelength infrared imaging via luminescent downshifting with colloidal quantum dots
No full textThe performance of short-wavelength infrared (SWIR) cameras in the visible and ultraviolet (UV) regions is limited by the absorption of high-energy photons in inactive regions of the imaging array. Dual-band UV-SWIR imaging can be achieved by using PbS colloidal quantum dots (CQD) to downshift incident UV light to the SWIR band. The CQD downshifting layer has minimal impact on the SWIR imaging performance and greatly increases the UV sensitivity of an InGaAs camera. A dual-lens design in which the QDs are incorporated on a removable substrate is demonstrated, which provides UV sensitivity without modification of the InGaAs camera focal plane array. A single-lens design in which the QDs are deposited directly on the focal plane array is demonstrated using both a standard InGaAs focal plane and a substrate-thinned focal plane. Higher UV resolution for the substrate-thinned focal plane is observed.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-07-D-004)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowshi
Biexciton Quantum Yield of Single Semiconductor Nanocrystals from Photon Statistics
No full textBiexciton properties strongly affect the usability of a light emitter in quantum photon sources and lasers but are difficult to measure for single fluorophores at room temperature due to luminescence intermittency and bleaching at the high excitation fluences usually required. Here, we observe the biexciton (BX) to exciton (X) to ground photoluminescence cascade of single colloidal semiconductor nanocrystals (NCs) under weak excitation in a g(2) photon correlation measurement and show that the normalized amplitude of the cascade feature is equal to the ratio of the BX to X fluorescence quantum yields. This imposes a limit on the attainable depth of photon antibunching and provides a robust means to study single emitter biexciton physics. In NC samples, we show that the BX quantum yield is considerably inhomogeneous, consistent with the defect sensitivity expected of the Auger nonradiative recombination mechanism. The method can be extended to study X,BX spectral and polarization correlations.United States. Dept. of Energy (grant no. DE-FG02-07ER46454)Massachusetts Institute of Technology. George R. Harrison Spectroscopy Laboratory (grant no. NIH P41 RR02594)United States. Dept. of Energy. Office of Basic Energy Sciences (award no. DE-SC0001088
Multispectral imaging via luminescent down-shifting with colloidal quantum dots
No full textThe high infrared quantum yield, continuous absorption spectrum, and band edge tunability of colloidal quantum dots (QD) has opened up new opportunities to use luminescent down shifting for multispectral imaging in the infrared. We demonstrate a QD sensitized short wavelength infrared (SWIR) camera which is capable of UV-SWIR multispectral imaging. The application of multispectral cameras for UV tagging applications is demonstrated and the extension of this technology to the mid infrared spectral region is discussed.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-07-D-0004)United States. Air Force Office of Scientific Research (FA9550-11-C-0028)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowship (32 CFR 168a
Energy transfer of CdSe/ZnS nanocrystals encapsulated with rhodamine-dye functionalized poly(acrylic acid)
No full textEnergy transfer between a CdSe/ZnS nanocrystal (NC) donor and a rhodamine isothiocyanate (RITC) acceptor has been achieved via a functionalized poly(acrylic acid) (PAA) encapsulating layer over the surface of the NC. The modification of PAA with both N-octylamine (OA) and 5-amino-1-pentanol (AP) [PAA–OA–AP], allows for the simultaneous water-solubilization and functionalization of the NCs, underscoring the ease of synthesizing NC–acceptor conjugates with this strategy. Photophysical studies of the NC–RITC constructs showed that energy transfer is efficient, with kFRET approaching 10⁸ s⁻¹. The ease of the covalent conjugation of molecules to NCs with PAA–OA–AP coating, together with efficient energy transfer, makes the NCs encapsulated with PAA–OA–AP attractive candidates for sensing applications.
Graphical abstract
The modification of poly(acrylic acid) (PAA) with both N-octylamine (OA) and 5-amino-1-4 pentanol (AP) [PAA–OA–AP] allows for the simultaneous water-solubilization and 5 functionalization of the NCs for applications derived from energy transfer. Highlights
► Poly(acrylic acid) (PAA) has been modified with both N-octylamine (OA) and 5-amino-1-pentanol (AP) [PAA–OA–AP]. ► This modification furnishes a water-soluble and functionalized overcoating for conjugation to CdSe/ZnS nanocrystals (NCs). ► Photophysical studies establish energy transfer between the NC and a conjugated rhodamine isothiocyanate (RITC) dye. ► These properties together establish NC–PAA–OA–AP conjugates as attractive candidates for sensing applications.National Cancer Institute (U.S.) (R01-CA126642)International Society for Neurochemistry (W911NF-07-D-0004
Slow-Injection Growth of Seeded CdSe/CdS Nanorods with Unity Fluorescence Quantum Yield and Complete Shell to Core Energy Transfer
Full text linkA two-step process has been developed
for growing the shell of
CdSe/CdS core/shell nanorods. The method combines an established fast-injection-based
step to create the initial elongated shell with a second slow-injection
growth that allows for a systematic variation of the shell thickness
while maintaining a high degree of monodispersity at the batch level
and enhancing the uniformity at the single-nanorod level. The second
growth step resulted in nanorods exhibiting a fluorescence quantum
yield up to 100% as well as effectively complete energy transfer from
the shell to the core. This improvement suggests that the second step
is associated with a strong suppression of the nonradiative channels
operating both before and after the thermalization of the exciton.
This hypothesis is supported by the suppression of a defect band,
ubiquitous to CdSe-based nanocrystals after the second growth
Mechanistic Insights into the Formation of InP Quantum Dots
No full textThe molecular mechanism of InP colloidal quantum dot (QD) syntheses was investigated by NMR spectroscopy. Unlike methods for monodisperse PbSe and CdSe, existing InP syntheses result in total depletion of molecular phosphorous species following nucleation, so QD growth is due exclusively to non-molecular ripening. Amines inhibit precursor depletion by solvation (see picture), contrary to previous reports.MIT-Harvard Center for Cancer Nanotechnology Excellence (National Institutes of Health (U.S.) 1U54-CA119349)United States. Army Research Office (ISN W911NF-07-D-0004)Massachusetts Institute of Technology. Dept. of Chemistry Instrumentation Facility (CHE-980806)Massachusetts Institute of Technology. Dept. of Chemistry Instrumentation Facility (DBI-9729592)National Science Foundation (U.S.). Graduate Research Fellowship Progra
Tissue- and Organ-Selective Biodistribution of NIR Fluorescent Quantum Dots
No full textA significant portion of the field of nanomedicine is predicated on being able to target nanoparticles to sites of disease. However, in vivo biodistribution and clearance of nanoparticles are poorly understood. In this study, a novel formulation of near-infrared fluorescent InAs(ZnS) quantum dots was synthesized and coated with a systematically increasing chain length of PEG. We found that varying PEG chain length resulted in major changes in organ/tissue-selective biodistribution and clearance from the body.National Science Foundation (U.S.) (Massachusetts Institute of Technology. Biophysical Instrumentation Facility 0070319)National Institutes of Health (U.S.) (Massachusetts Institute of Technology. Biophysical Instrumentation Facility GM68762)National Institutes of Health (U.S.) (Grant R33-EB-000673)National Institutes of Health (U.S.) (MIT-Harvard NanoMedical Consortium U54-CA-119349
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