Single PbS Research Articles

Hydroxyapatite nanoparticles promote TLR4 agonist-mediated anti-tumor immunity through synergically enhanced macrophage polarization.

Macrophages represent the most prevalent immune cells in the tumor micro-environment, making them an appealing target for tumor immunotherapy. One of our previous studies showed that hydroxyapatite nanoparticles (HANPs) enhanced Toll-like receptor 4 (TLR4) signal transduction in macrophages. This study was proposed to investigate how HANPs manipulated the phenotype and function of macrophage against 4T1 breast tumors in the presence or absence of MPLA, a low toxic Toll-like receptor 4 (TLR4) agonist. The results demonstrated that the addition of HANPs to MPLA significantly promoted cytokine secretion and macrophage polarization toward a tumoricidal M1 phenotype. Further, the resulting supernatant from HANPs/MPLA co-stimulated macrophages enhanced 4T1 tumor cells apoptosis compared to that from macrophages treated with a single component or PBS control. In particular, we found HANPs elicited immunogenic cell death (ICD) indicated by the increased expression of "danger signals", including HMGB1, CRT and ATP in 4T1 cells. Subsequently, the ICD derivatives-containing supernatant from HANPs-treated 4T1 cells activated macrophage and shifted the phenotype of the cells toward M1 type. Moreover, in a tumor-bearing mice model, HANPs and MPLA synergistically delayed tumor growth compared to PBS control, which was positively associated with the promoted macrophage polarization and ICD induction. Therefore, our findings demonstrated a potential platform to modulate the function of macrophages, and shed a new insight into the mechanism involving the immunomodulatory effect of HANPs for tumor therapy. STATEMENT OF SIGNIFICANCE: Polarizing macrophage toward tumoricidal phenotype by harnessing Toll-like receptor (TLR) agonists has been proven effective for tumor immunotherapy. However, the immunomodulatory potency of TLR agonists is limited due to immune suppression or tolerance associated with TLR activation in immune cells. Herein, we introduced hydroxyapatite nanoparticles (HANPs) to MPLA, a TLR4 agonist. The results demonstrated that the addition of HANPs to MPLA promoted macrophage shift toward tumoricidal M1 phenotype, supported a "hot" tumor transformation, and delayed 4T1 tumor growth. Moreover, we found that HANPs elicited immunogenic cell death that produced "danger" signals from cancer cells thereby further facilitated macrophage polarization. This work is significant to direct the rational design of HANPs coupled with or without TLR agonists for tumor immunotherapy.

Ultrafast carrier dynamics of PbS quantum dots in glasses for light amplification

Lead sulfide quantum dots (PbS QDs) have a unique performance in the near-infrared (NIR) range. In-situ precipitation of PbS QDs in glass not only improves the stability, but also is easy to be fabricated fiber compatible with silicon photonics. In this work, we reveal that absorption cross sections of PbS QDs at 1040 nm are 4–13 × 10−16 cm2, the bi- and tri-excitons lifetime are∼60 and ∼10 ps due to the trap-assisted Auger recombination using transient absorption (TA). Furthermore, we demonstrate the broadband net gain in 1500–1600 nm in single PbS QDs embedded glass with a gain threshold of <N>= 4.1 (averaged number of excitons), and achieve the maximum gain time of ∼20 ps and gain coefficient of >120 cm−1. These results illustrate the existing obstacles to achieve the net gain in PbS QDs embedded glass, which is important for applications on fiber amplifiers, NIR laser and high-capacity telecommunication.

In vitro corrosion and in vivo behavior of high strength Mg-6Zn-1Mn alloy wire for gastrointestinal anastomosis nail application

Ti and its alloy staples can be retained in the human body for a long period because of their excellent corrosion resistance and thus requires revision surgery for removal. In this study, biodegradable Mg-6Zn-1Mn alloy staples were fabricated using ∼99.8 % area reduction cold drawing, whose service performance was evaluated by in vitro corrosion and in vivo tests. The high strength (∼340 MPa) of staples is mainly attributed to the formation of fine grains, nanoparticles, and additional dislocations. Moreover, owing to the effect of fine grains, as well as the high Schmid factor of prismatic ⟨a⟩ slip and pyramidal ⟨c+a⟩ slip, the staples also exhibit acceptable ductility (∼10 %). The in vitro corrosion results indicate that staple fractures occurred after immersion for 21 h in a single PBS solution. With the addition of ∼0.5 g/L bovine serum albumin (BSA), the time required to maintain the mechanical integrity of staples can expand to 90 h. This is mainly related to the adsorption and chelating effects between BSA and Mg matrix. After the implantation surgery, all rabbits fully recovered with normal oral intake, and Mg ions generated by degradation effectively promoted the absorption of the alimentary system. Therefore, the Mg-6Zn-1Mn alloy staples fabricated in this study exhibit desired effect, and excellent clinical application prospects.

Theoretical study of multi-band solar cells with a single PbS quantum dot superlattice film as a light absorption layer

Theoretical studies have predicted that quantum dot superlattice (QDSL) intermediate band solar cells (IBSC) have high power conversion efficiencies (PCE), but it has not been considered what intermediate band (IB) structure can actually be reproduced. We theoretically examined the characteristics of solar cells manufactured using a superlattice composed of colloidal PbS quantum dots (QDs), and found that PCE of 50% or more can be realized in a single junction structure with multi-step light absorption via IBs. PCE has been reported to increase as the number of IBs increases, but we found that this is not always the case due to the balance of the number of transition carriers in IBs.

Anharmonicity and correlated dynamics of PbTe and PbS studied by single crystal x-ray scattering

The lead chalcogenides with rocksalt structure, $\mathrm{Pb}X$ ($X$ = S, Se, Te), show great promise for thermoelectric applications in various doped and alloyed forms. Part of the explanation for this is their favorable low lattice thermal conductivities whose origin has been heavily debated. Powder x-ray diffraction experiments suggested Pb to be off-centered particularly in PbS. However, as shown here, single crystal x-ray diffraction shows the anharmonicity to be insignificant in PbS from 20 to 300 K, while it is significant from 100 to 622 K in PbTe although without leading to any Pb off-centering. Inelastic neutron scattering and anharmonic ab initio studies previously suggested the soft transverse optical mode to play an important role with respect to lowering the thermal conductivities of the lead chalcogenides. Here, the diffuse x-ray scattering of single crystal PbS is modeled from 20 to 300 K by correlated atomic displacements. The results indicate softening of the zone center transverse optical mode with decreasing temperature. From a chemical bonding perspective, the soft transverse optical mode can be rationalized by invoking the concepts of stereoactive lone pair formation and metavalent/resonant bonding.

Fast and ergonomic extraction of adherent mammalian cells for NMR-based metabolomics studies.

Cellular metabolomics has become key to elucidate mechanistic aspects in various fields such as cancerology or pharmacology, and is rapidly becoming a standard phenotyping tool accessible to the broad biological community. Acquisition of reliable spectroscopic datasets, such as nuclear magnetic resonance (NMR) spectra, to characterize biological systems depends on the elaboration of robust methods for cellular metabolites extraction. Previous studies have addressed many issues raised by these protocols, however with little pondering on ergonomic and practical aspects of the methods that impact their scalability, reproducibility and hence their suitability to high-throughput studies or their use by non-metabolomics experts. Here, we optimize a fast and ergonomic protocol for extraction of metabolites from adherent mammalian cells for NMR metabolomics studies. The proposed extraction protocol, including cell washing, metabolism quenching and actual extraction of intracellular metabolites, was first optimized on HeLa cells. Efficiency of the protocol, in its globality and for the different individual steps, was assessed by NMR quantification of 27 metabolites from cellular extracts. We show that a single PBS wash provides a seemly compromise between contamination from growth medium and leakage of intracellular metabolites. In HeLa cells, extraction using pure methanol, without cell scraping, recovered a higher amount of intracellular metabolites than the reference methanol/water/chloroform method with cell scraping, with yields varying across metabolite classes. Optimized and reference protocols were further tested on eight cell lines of miscellaneous nature, and inter-operator reproducibility was demonstrated. Our results stress the need for tailored extraction protocols and show that fast protocols minimizing time-consuming steps, without compromising extraction yields, are suitable for high-throughput metabolomics studies. Graphical abstract.

Mixed Lead Halide Passivation of Quantum Dots.

Infrared-absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead-halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX-PbS CQDs exhibit properties that exceed the best features of single lead-halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10-2 ± 3 × 10-3 cm2 V-1 s-1 vs 3 × 10-2 ± 3 × 10-3 cm2 V-1 s-1 in mobility). This translates into PV devices having a record IR open-circuit voltage (IR Voc ) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead-halide controls reported herein.

Mapping Charge Distribution in Single PbS Core - CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography.

We synthesized PbS core-CdS arm nanomultipod heterostructures (NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbS-CdS interface is chemically sharp as determined by aberration corrected transmission electron microscopy (TEM) and compared to density functional theory (DFT) calculations. Ensemble fluorescence measurements show quenching of the optical signal from the CdS arms indicating charge separation due to the heterojunction with PbS. A finite-element three-dimensional (3D) calculation of the Poisson equation shows a type-I heterojunction, which would prevent recombination in the CdS arm after optical excitation. To examine charge redistribution, we used off-axis electron holography (OAEH) in the TEM to map the electrostatic potential across an individual heterojunction. Indeed, a built-in potential of 500 mV is estimated across the junction, though as opposed to the thermal equilibrium calculations significant accumulation of positive charge at the CdS side of the interface is detected. We conclude that the NMH multipod geometry prevents efficient removal of generated charge carriers by the high energy electrons of the TEM. Simulations of generated electron-hole pairs in the insulated CdS arm of the NMH indeed show charge accumulation in agreement with the experimental measurements. Thus, we show that OAEH can be used as a complementary methodology to ensemble measurements by mapping the charge distribution in single NMHs with complex geometries.

Hydrothermal synthesis and thermoelectric properties of PbS

Abstract In this paper, hydrothermal approach combined with high pressure sintering method was employed to synthesize PbS. The X-ray diffraction results show that single phase PbS can be obtained by a simple hydrothermal method. The scanning electron microscope results show that the PbS sample has nearly cubic shape and preserves well crystallized and coarse grains after high pressure sintering. The thermoelectric performance of PbS obtained in this study is comparable to that of a PbS sample prepared by conventional method. The carrier type and concentration of PbS can be tuned effectively by doping with Bi. The maximum figure of merit for PbS doped with 1 mol% Bi reaches 0.44 at 550 K, which is about 30 % higher than that of undoped PbS. These results indicate that hydrothermal method provides a viable and controllable way of tuning the electrical transport and thermoelectric properties for PbS.

Photo Relaxation Change and Emission Quenching in Different Sizes of PbS‐Nanoparticles‐Protein Corona

AbstractIn this study, energy transfer from BSA to different size semiconductor nanoparticles PbS was analyzed by using photo Relaxation change and emission quenching analysis. Structures of thePbS NPs are studied by XRD, TEM, and FT‐IR measurements. The band gap and crystal size of PbS suggest the quantum confinement effect. Photo current of the BSA‐PbS NPs bioconjugate system increased compared to bare PbS nanoparticles from nA to μA. Change in photo relaxation life time of the bare PbS NP and PbS NPs‐BSA bioconjugate system is particle size dependent and interaction dependent. PbS NPs‐BSA bioconjugate were characterized by steady‐state fluorescence spectroscopy to determine the magnitude and mechanism of the energy transfer. It was found that the BSA fluorescence was quenched after the addition of PbS nanoparticles. Quenching of protein is large for larger size PbS nanoparticles. DLS study confirmed that BSA was adsorbed onto the surface of nanoparticles, creating a favourable geometry for quenching. Aggregation of BSA around a single PbS nanoparticle is size dependent. Larger nanoparticles are responsible for hard as well as soft corona due to interaction.Our results, which include photo relaxation times, energy transfer efficiencies showed that energy transferred take place via the Fluorescence Resonance Energy Transfer (FRET) mechanism. These energy transfer processes between protein molecules and PbS nanoparticles, will depend on the size of the particles involved.

Epitaxial 2D PbS Nanoplates Arrays with Highly Efficient Infrared Response.

2D nonlayered semiconductors attract intense interest due to their unique planar structure and various fascinating optoelectronic properties. Here, a method is developed to design orientation-controlled and well-defined single-crystalline PbS nanoplates arrays on mica. Furthermore, the single PbS nanoplate device displays great photoresponsivity, detectivity, and photogain values as high as 1621 A W-1 , 1.72 × 1011 Jones, and 2512, respectively.

Improving the Photocurrent in Quantum-Dot-Sensitized Solar Cells by Employing Alloy PbxCd1-xS Quantum Dots as Photosensitizers.

Ternary alloy PbxCd1−xS quantum dots (QDs) were explored as photosensitizers for quantum-dot-sensitized solar cells (QDSCs). Alloy PbxCd1−xS QDs (Pb0.54Cd0.46S, Pb0.31Cd0.69S, and Pb0.24Cd0.76S) were found to substantially improve the photocurrent of the solar cells compared to the single CdS or PbS QDs. Moreover, it was found that the photocurrent increases and the photovoltage decreases when the ratio of Pb in PbxCd1−xS is increased. Without surface protecting layer deposition, the highest short-circuit current density reaches 20 mA/cm2 under simulated AM 1.5 illumination (100 mW/cm2). After an additional CdS coating layer was deposited onto the PbxCd1−xS electrode, the photovoltaic performance further improved, with a photocurrent of 22.6 mA/cm2 and an efficiency of 3.2%.

Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

We present a tunnel spectroscopy study of single PbS quantum dots (QDs) as a function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the electron tunneling spectrum (ETS) of these QDs. In the shell-filling regime, the $8\ifmmode\times\else\texttimes\fi{}$ degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon blockade. From the data, a Huang-Rhys factor in the range $S\ensuremath{\sim}1.7\text{--}2.5$ is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS ${d}^{2}I/d{V}^{2}$.

SU‐E‐T‐101: An Arc Based Treatment Technique for Proton PBS Beam Utilizing Overlaid Bragg Peak Spots

Purpose:When Bragg peaks from proton PBS beams are overlaid from a large number of directions, it creates a localized dose distribution with rapid falloff. By positioning these overlaid Bragg peak (OBP) spots strategically throughout the targeted volume, a uniform and conformal dose distribution can be achieved. When PBS spots from all the directions are delivered in an arc fashion, it becomes the Volume Modulated Proton Therapy (VMPT) technique which corresponds to the VMAT technique in photon therapy.Methods:PBS beam from an IBA machine and a 20cm radius cylindrical phantom were simulated with GATE/GEANT4. To position the OBP spot at the center of the phantom, single energy PBS beam from 10/36/360 equally‐spaced directions around the phantom was used. To position the OBP spot at an off‐center position, PBS beams with various energies were used. To form a uniform dose distribution in 1D/2D, OBP spots are positioned in arrays with spot intervals and weight optimized.Results:Dose profile for single energy OBP spot improved when the number of beam angles increased from 10 to 36, but remained same from 36 to 360 angles. Multi‐energy OBP spot had a slightly non‐symmetrical profile due to the different energy proton beams used. By optimizing each OBP spot's weight, 11 OBP spots with 10mm interval size created a uniform dose distribution covering a length of 10cm. Similarly, 11×11 OBP spots in an array of 10mm interval size created a uniform dose distribution covering an area of 10×10cm2.Conclusion:We demonstrated the technique of using OBP spots to deliver uniform dose in 1D/2D. This technique can be easily extended through the optimization of position and weight of OBP spots in 3D and becomes the arc based VMPT technique. Further studies are needed to explore the optimization methods and full potential of the VMPT technique.

Thermoelectric Properties and Microstructure Studies of Spinodally Decomposed PbTe&lt;SUB&gt;0.38&lt;/SUB&gt;S&lt;SUB&gt;0.62&lt;/SUB&gt; Alloy

PbTe is a premiere mid-range temperature thermoelectric material and recent studies have proven nanostructing as an effective approach to reduce thermal conductivity of alloys. Whereas, little attention has been given to long-term thermal stability of secondary phases and microstructural evolution. Interestingly, replacing Te with S in PbTe provides an opportunity to form nanostructures in the bulk material through spinodal decomposition, which appears in binary phase diagrams of the PbTe–PbS system. Herein, the critical composition of PbTe_(0.38)S_(0.62) alloy is fabricated to n-type by chlorine doping. Thermoelectric transport properties of the alloy are investigated in the 300–850 K temperature range and the maximum zT achieved at 800 K is 0.75 with a predicted zT ∼ 0.85 at 750 K from single parabolic band model. The microstructure of the sintered samples was studied by FEG-SEM for both the as sintered and post transport properties measurement. The experimental results are compared with estimates from the parallel and series models for heterogeneous composites of single phase PbTe and PbS. The Seebeck coefficient is in agreement with the models predictions, but the resistivity is higher and the thermal conductivity is much lower than predicted values. We propose that this is attributed to the phonon and electron scattering on solute atoms in solid solutions and at interfaces.

Biotin-decorated silica coated PbS nanocrystals emitting in the second biological near infrared window for bioimaging.

Nanoparticles (NPs) emitting in the second biological near infrared (NIR) window of the electromagnetic spectrum have been successfully synthesized by growing a silica shell on the hydrophobic surface of OLEA/TOP PbS nanocrystals (NCs), by means of a reverse microemulsion approach, and subsequently decorated with biotin molecules. The fabrication of very uniform and monodisperse NPs, formed of SiO₂ shell coated single core PbS NCs, has been demonstrated by means of a set of complementary optical and structural techniques (Vis-NIR absorption and photoluminescence spectroscopy, transmission electron microscopy) that have highlighted how experimental parameters, such as PbS NC and silica precursor concentration, are crucial to direct the morphology and optical properties of silica coated PbS NPs. Subsequently, the silica surface of the core-shell NPs has been grafted with amino groups, in order to achieve covalent binding of biotin to NIR emitting silica coated NPs. Finally the successful reaction with a green-fluorescent labelled streptavidin has verified the molecular recognition response of the biotin molecules decorating the PbS@SiO₂ NP surface. Dynamic light scattering (DLS) and ζ-potential techniques have been used to monitor the hydrodynamic diameter and colloidal stability of both PbS@SiO₂ and biotin decorated NPs, showing their high colloidal stability in physiological media, as needed for biomedical applications. Remarkably the obtained biotinylated PbS@SiO₂ NPs have been found to retain emission properties in the 'second optical window' of the NIR region of the electromagnetic spectrum, thus representing attractive receptor-targeted NIR fluorescent probes for in vivo tumour imaging.

Surface chemistry of arenethiolate-capped PbS quantum dots and application as colloidally stable photovoltaic ink

Suitable post-synthesis surface modification of lead-chalcogenide quantum dots (QDs) is crucial to enable their integration in photovoltaic devices. We have developed a solution-phase ligand exchange strategy that exploits arenethiolate anions to replace the pristine oleate ligands on PbS QDs, while preserving the long-term colloidal stability of QDs and allowing their solution-based processability into photoconductive thin-films. Complete QD surface modification is demonstrated by IR spectroscopy analysis, whereas UV–Vis–NIR Absorption Spectroscopy provides quantitative evaluation of stoichiometry and thermodynamic stability of the resulting system. Arenethiolate ligands permit to reduce the inter-particle distance in PbS QD solids, leading to a drastic improvement of the photoinduced charge transport properties. Therefore, smooth dense-packed thin-films of arenethiolate-capped PbS QDs obtained via a single solution-processing step are integrated in heterojunction solar cells: such devices generate remarkable photocurrent densities (14mAcm−2) and overall efficiencies (1.85%), which are outstanding for a single PbS QD layer. Solution-phase surface modification of QDs thus represents an effective intermediate step towards low-cost processing for all-inorganic and hybrid organic/inorganic QD-based photovoltaics.

Spatially Resolved Optoelectronics in Lead Sulfide Nanowires

Spatially resolved optoelectronic investigation can reveal important information on charge transport and recombination in field-effect transistors (FETs) incorporating single nanowires (NWs). Scanning photocurrent microscopy (SPCM) was performed on single PbS NW FETs to extract diffusion length and lifetime of minority carriers as a function of gate voltage and excitation intensity. Interestingly, we observed a reverse of the photocurrent direction in gate-depleted PbS NW FETs under high intensity illumination. We attribute this effect to the back-gate induced carrier concentration gradient.

Formation, near-infrared luminescence and multi-wavelength optical amplification of PbS quantum dot-embedded silicate glasses

Optical properties of PbS quantum dot (QD)-embedded silicate glasses prepared through post annealing were investigated. By modulating the heat treatment condition, tunable near-infrared (NIR) photoluminescence (PL) was obtained. Noticeable optical amplification was achieved at both 1330nm and 1550nm windows with similar amplification characteristics in single PbS QD-embedded glass, which indicated that broadband optical amplification is expected at the entire PL band of PbS QD-embedded glass. The PbS QD-embedded glass with multi-wavelength optical amplification is promising as the gain medium of broadband fiber amplifiers and tunable fiber lasers.

Label-free detection of ovarian cancer biomarkers using whispering gallery mode imaging

Small optical microresonators that support whispering gallery mode (WGM) resonances are emerging as powerful new platforms for biosensing. These resonators respond to changes in refractive index and potentially offer many advantages for label-free sensing. Recently we reported an approach for detecting WGM resonances based on fluorescence imaging and demonstrated its utility by quantifying the ovarian cancer marker CA-125 in buffer. Here we extend those measurements by reporting a simplified approach for launching WGM resonances using excitation light coupled into a Dove prism. The enhanced phase matching enables significant improvements in signal-to-noise, revealing the mode structure present in each resonator. As with all label-free biosensing techniques, non-specific interactions can be limiting. Here we show that standard blocking protocols reduce non-specific interactions sufficiently to enable CA-125 quantification in serum samples. Finally, fluorescence imaging of WGM resonances offers the potential for large scale multiplexed detection which is demonstrated here by simultaneously exciting and imaging over 120 microsphere resonators. For multiplexed applications, analyte identity can be encoded in the resonator size and/or location. By encoding analyte identity into microresonator size, we simultaneously quantify the putative ovarian cancer markers osteopontin (38μm diameter sphere), CA-125 (53μm diameter sphere), and prolactin (63μm diameter sphere) in a single PBS assay. Together, these results show that fluorescence imaging of WGM resonances offers a promising new approach for the highly multiplexed detection of biomarkers in complex biological fluids.