Intracellular biocompatible hexagonal boron nitride quantum emitters as single-photon sources and barcodes

Color centers in hexagonal boron nitride (hBN) have been emerging as a multifunctional platform for various optical applications including quantum information processing, quantum computing and imaging. Simultaneously, due to its biocompatibility and biodegradability hBN is a promising material for biomedical applications. In this work, we demonstrate single-photon emission from hBN color centers embedded inside live cells and their application to cellular barcoding. The generation and internalization of multiple color centers into cells was performed via simple and scalable procedure while keeping the cells unharmed. The emission from live cells was observed as multiple diffraction-limited spots, which exhibited excellent single-photon characteristics with high single-photon purity of 0.1 and superb emission stability without photobleaching or spectral shifts over several hours. Due to different emission wavelengths and peak widths of the color centers, they were employed as barcodes. We term them Quantum Photonic Barcodes (QPBs). Each QPB can exist in one out of 470 possible distinguishable states and a combination of a few QPBs per cell can be used to uniquely tag virtually an unlimited number of cells. The barcodes developed here offer some excellent properties, including ease of production by a single-step procedure, biocompatibility and biodegradability, emission stability, no photobleaching, small size and a huge number of unique barcodes. This work provides a basis for the use of hBN color centers for robust barcoding of cells and due to the single photon emission, presented concepts could in future be extended to quantum-limited sensing and super-resolution imaging.

The Kondo Effect in CexLaLuScY (x = 0.05-1.0) High-Entropy Alloys

In the search for electronic phenomena in high-entropy alloys (HEAs) that go beyond the independent-electron description, we have synthesized a series of hexagonal rare earth (RE)-based HEAs: CexLaLuScY (x = 0.05-1.0). The measurements of electrical resistivity, magnetic susceptibility and specific heat have shown that the CexLaLuScY HEAs exhibit the Kondo effect, which is of a single impurity type in the entire range of employed Ce concentrations despite the alloys being classified as dense (concentrated) Kondo systems. A comparison to other known dense Kondo systems has revealed that the Kondo effect in the CexLaLuScY HEAs behaves quite differently from the chemically ordered Kondo lattices but quite similar to the RE-containing magnetic metallic glasses and randomly chemically disordered Kondo lattices of the chemical formula RE1xRE21-xM (with RE1 being magnetic and RE2 being nonmagnetic). The main reason for the similarity between HEAs and the metallic glasses and chemically disordered Kondo lattices appears to be the absence of a periodic 4f sublattice in these systems, which prevents the formation of a coherent state between the 4f-scattering sites in the T→ 0 limit. The crystal-glass duality of HEAs does not bring conceptually new features to the Kondo effect that would not be already present in other disordered dense Kondo systems. This study broadens the classification of HEAs to correlated electron systems.

Complex magnetism of single-crystalline AlCoCrFeNi nanostructured high-entropy alloy

We have investigated magnetism of the Al₂₈Co₂₀Cr₁₁Fe₁₅Ni₂₆ single-crystalline high-entropy alloy. The material is nanostructured, composed of a B2 matrix with dispersed spherical-like A2 nanoparticles of average diameter 64 nm. The magnetism was studied from 2 to 400 K via direct-current magnetization, hysteresis curves, alternating-current magnetic susceptibility, and thermoremanent magnetization time decay, to determine the magnetic state that develops in this highly structurally and chemically inhomogeneous material. The results reveal that the Cr-free B2 matrix of composition Al₂₈Co₂₅Fe₁₅Ni₃₂ forms a disordered ferromagnetic (FM) state that undergoes an FM transition at TC≈ 390 K. The Al- and Ni-free A2 nanoparticles of average composition Co₁₉Cr₅₆Fe₂₅ adopt a core-shell structure, where the shells of about 2 nm thickness are CoFe enriched. While the shells are FM, the nanoparticle cores are asperomagnetic, classifying into the broad class of spin glasses. Asperomagnetism develops below 15 K and exhibits broken-ergodicity phenomena, typical of magnetically frustrated systems.

Crystal Structure and Ferromagnetism of the CeFe9Si4 Intermetallic Compound

We have determined the crystal structure and the magnetic state of the CeFe₉Si₄ intermetallic compound. Our revised structural model (fully ordered tetragonal unit cell, I4/mcm) agrees with the previous literature report, except for some minor quantitative differences. Magnetically, the CeFe₉Si₄ undergoes a ferromagnetic transition at the temperature T_C ≈ 94 K. Ferromagnetism in the combined Ce-Fe spin system is a result of interplay between the localized magnetism of the Ce sublattice and the Fe band (itinerant) magnetism. Ferromagnetic ordering obeys the rather general rule that the exchange spin coupling between atoms possessing more than half-full d shells with atoms possessing less than half-full d shells is antiferromagnetic (where the Ce atoms are considered as light d elements). Since in rare-earth metals from the light half of the lanthanide series, the magnetic moment is directed opposite to the spin, this results in ferromagnetism. The magnetoresistance and the magnetic specific heat show an additional temperature-dependent feature (a shoulder) deep inside the ferromagnetic phase that is considered to originate from the influence of the magnetization on the electronic band structure via the magnetoelastic coupling, which alters the Fe band magnetism below T_C. The ferromagnetic phase of CeFe₉Si₄ is magnetically soft.

Electronic transport properties of the Al0.5TiZrPdCuNi alloy in the high-entropy alloy and metallic glass forms

High-entropy alloys (HEAs) are characterized by a simultaneous presence of a crystal lattice and an amorphous-type chemical (substitutional) disorder. In order to unravel the effect of crystal-glass duality on the electronic transport properties of HEAs, we performed a comparative study of the electronic transport coefficients of a 6-component alloy Al_0.5TiZrPdCuNi that can be prepared either as a HEA or as a metallic glass (MG) at the same chemical composition. The HEA and the MG states of the Al_0.5TiZrPdCuNi alloy both show large, negative-temperature-coefficient resistivity, positive thermopower, positive Hall coefficient and small thermal conductivity. The transport coefficients were reproduced analytically by the spectral conductivity model, using the Kubo-Greenwood formalism. For both modifications of the material (HEA and MG), contribution of phonons to the transport coefficients was found small, so that their temperature dependence originates predominantly from the temperature dependence of the Fermi–Dirac function and the variation of the spectral conductivity and the related electronic density of states with energy within the Fermi-level region. The very similar electronic transport coefficients of the HEA and the MG states point towards essential role of the immense chemical disorder.

The Effect of Scandium on the Structure, Microstructure and Superconductivity of Equimolar Sc-Hf-Nb-Ta-Ti-Zr Refractory High-Entropy Alloys

In this study, we investigate the scandium-containing Sc-Hf-Nb-Ta-Ti-Zr system of refractory high-entropy alloys (HEAs). Using the arc-melting method, we synthesized nine equimolar alloys (five 4-, three 5- and one 6-component), with all of them containing Sc. The alloys were characterized by XRD, electron microscopy and EDS, while superconductivity was investigated via electrical resistivity, specific heat and the Meissner effect. The results were compared to the parent Hf-Nb-Ta-Ti-Zr refractory HEAs, forming a single-phase body-centered cubic (bcc) structure and quite homogeneous microstructure. The addition of Sc produces a two-phase structure in the Sc-Hf-Nb-Ta-Ti-Zr alloys, with one phase being bcc and the other hexagonal close-packed (hcp). The hcp phase absorbs practically all Sc, whereas the Sc-poor bcc phase is identical to the bcc phase in the Hf-Nb-Ta-Ti-Zr parent system. Upon the Sc addition, the microstructure becomes very inhomogeneous. Large bcc dendrites (10–100 µm) are homogeneous in the central parts, but become a fine dispersion of sub-micron precipitates of the bcc and hcp phases close to the edges. The interdendritic regions are also a fine dispersion of the two phases. Superconductivity of the Sc-Hf-Nb-Ta-Ti-Zr alloys originates from the bcc phase fraction, which demonstrates identical superconducting parameters as the bcc Hf-Nb-Ta-Ti-Zr parent alloys, while the Sc-containing hcp phase fraction is non-superconducting.

Structure and Spin-Glass Magnetism of the MnxNi2Zn11-x Pseudobinary γ-Brasses at Low Mn Contents

The pseudobinary Mn_xNi₂Zn_11–x γ-brass-type phases at low Mn dopant levels (x = 0.1–0.5) were investigated. Crystal structures were determined for the two loading compositions of x = 0.3 and 0.5. The structures were solved in the cubic space group of I43m and are described in close analogy to the Ni₂Zn₁₁ parent γ-brass that is based on the 26-atom cluster, consisting of inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and cuboctahedron (CO). The refined site occupancies of the Mn_xNi₂Zn_11–x (x = 0.3, 0.5) reveal that the cluster center, which is empty in the Ni₂Zn₁₁, shows a partial occupation by Zn, with a partial depletion of Zn at the IT sites. The OH sites show a mixed Zn/Mn occupation. The OT and CO sites remain intact with respect to Ni₂Zn₁₁. Magnetic properties were studied for the Mn_0.3Ni₂Zn_10.7 composition. The temperature-dependent zero-field-cooled and field-cooled magnetization, the ac susceptibility, the M(H) hysteresis curves, the thermoremanent magnetization, and the memory effect demonstrate typical broken-ergodicity phenomena of a magnetically frustrated spin system below the spin freezing temperature T_f ≈ 16 K. The Mn_0.3Ni₂Zn_10.7 γ-brass phase classifies as a spin glass, originating predominantly from the random distribution of diluted Mn moments on the octahedral partial structure.

In a search for new pseudobinary/ternary γ-brass-type phases, we synthesized a series of Mn_xNi₂Zn_11−x compounds at low Mn doping levels (x = 0.1−0.5) and determined the structures for two compositions x = 0.3 and 0.5. Magnetic measurements show that the Mn_0.3Ni₂Zn_11.7 γ-brass is a spin glass.

Sterilization of polypropylene membranes of facepiece respirators by ionizing radiation

Ionizing radiation has been identified as an option for sterilization of disposable filtering facepiece respirators in situations where the production of the respirators cannot keep up with demand. Gamma radiation and high energy electrons penetrate deeply into the material and can be used to sterilize large batches of masks within a short time period. In relation to reports that sterilization by ionizing radiation reduces filtration efficiency of polypropylene membrane filters on account of static charge loss, we have demonstrated that both gamma and electron beam irradiation can be used for sterilization, provided that the respirators are recharged afterwards.

Ordering Effects and Percolation in the Structure Formation Process of the Oriented Polyolefin Porous Films

Structure transitions and mechanism of the formation of superlattices lamellae in microporous polyolefin (polyethylene and polypropylene) films obtained in the process based on polymer melt extrusion followed by annealing, uniaxial extension and thermal fixation have been studied by statistical analysis of electron microscopy images of the film surface. The structure of the porous films prepared in the multistage process has been studied by SEM, gravimetry and permeability measurements. It has been shown that the pore formation at the stage of uniaxial extension is accompanied by the ordering of lamellae and their self-organization controlled by spin draw ratio and annealing temperature. It was established that an increase of these parameters lead to the transition of disorder-order type. The effect of preparation conditions on the ordering process of regular spatial lattices of lamellae has been discussed.

Coronary stent as a tubular flow heater in magnetic resonance imaging

Background

A coronary stent is an artificial metallic tube, inserted into a blocked coronary artery to keep it open. In magnetic resonance imaging (MRI), a stented person is irradiated by the radio-frequency electromagnetic pulses, which induce eddy currents in the stent that produce Joule (resistive) heating. The stent in the vessel is acting like a tubular flow heater that increases the temperature of the vessel wall and the blood that flows through it, representing a potential hazard for the stented patient.

Methods

Heating of a metallic coronary stent in MRI was studied theoretically and experimentally. An analytical theoretical model of the stent as a tubular flow heater, based on the thermodynamic law of heat conduction, was developed. The model enables to calculate the time-dependent stent’s temperature during the MRI examination, the increase of the blood temperature passing through the stent and the distribution of the temperature in the vessel wall surrounding the stent. The model was tested experimentally by performing laboratory magnetic resonance heating experiments on a non-inserted stainless-steel coronary stent in the absence of blood flow through it. The model was then used to predict the temperature increase of the stainless-steel coronary stent embedded in a coronary artery in the presence of blood flow under realistic MRI conditions.

Results

The increase of the stent’s temperature and the blood temperature were found minute, of the order of several tenths of a degree, because the blood flow efficiently cools the stent due to a much larger heat capacity of the blood as compared to the heat capacity of the stent. However, should the stent in the vessel become partially re-occluded due to the restenosis problem, where the blood flow through the stent is reduced, the stent’s temperature may become dangerously high.

Conclusions

In the normal situation of a fully open (unoccluded) stent, the increase of the stent temperature and the blood temperature exiting the stent were found minute, of less than 1°C, so that the blood flow efficiently cools the stent. However, should the problem of restenosis occur, where the blood flow through the stent is reduced, there is a risk of hazardous heating.

Discovery of a superconducting high-entropy alloy

High-entropy alloys (HEAs) are multicomponent mixtures of elements in similar concentrations, where the high entropy of mixing can stabilize disordered solid-solution phases with simple structures like a body-centered cubic or a face-centered cubic, in competition with ordered crystalline intermetallic phases. We have synthesized an HEA with the composition Ta34Nb33Hf8Zr14Ti11 (in at. %), which possesses an average body-centered cubic structure of lattice parameter a=3.36  Å. The measurements of the electrical resistivity, the magnetization and magnetic susceptibility, and the specific heat revealed that the Ta34Nb33Hf8Zr14Ti11 HEA is a type II superconductor with a transition temperature Tc≈7.3  K, an upper critical field μ0H_c2≈8.2  T, a lower critical field μ0Hc1≈32  mT, and an energy gap in the electronic density of states (DOS) at the Fermi level of 2Δ≈2.2  meV. The investigated HEA is close to a BCS-type phonon-mediated superconductor in the weak electron-phonon coupling limit, classifying it as a "dirty" superconductor. We show that the lattice degrees of freedom obey Vegard's rule of mixtures, indicating completely random mixing of the elements on the HEA lattice, whereas the electronic degrees of freedom do not obey this rule even approximately so that the electronic properties of a HEA are not a "cocktail" of properties of the constituent elements. The formation of a superconducting gap contributes to the electronic stabilization of the HEA state at low temperatures, where the entropic stabilization is ineffective, but the electronic energy gain due to the superconducting transition is too small for the global stabilization of the disordered state, which remains metastable.

Is the ABCB1 gene associated with the increased risk of gastric cancer development?--preliminary research

One of the most common malignant diseases, both worldwide and in Poland, is gastric cancer. The pathogenesis of gastric cancer development is not entirely clear. Next to the environmental risk factors, such as Helicobacter pylori infection or dietary habits, the host genetic factors as predispositions to gastric cancer development are discussed. A transmembrane protein that could be associated with predisposition to cancer development is P-glycoprotein (P-gp). Physiologically, P-gp is present in normal tissue of the gastrointestinal tract, where it plays a protective role by transporting xenobiotics from a cell into extracellular environment. P-gp is encoded by the highly polymorphic ABCB1 gene. The most frequent polymorphisms at positions 1236, 2677, and 3435 may affect both the function and amount of protein, thereby leading to a loss of its physiological function, which could increase the predisposition to development of many diseases, including cancer. In this study, the potential significance of the ABCB1 gene in the development and progression of gastric cancer was evaluated. In 19 tissue samples collected from patients with gastric cancer, the ABCB1 gene polymorphisms were identified at positions 1236 and 2677 by automated sequencing and SNP 3435 by the RFLP method. The relative level of ABCB1 expression was measured in 10 samples of gastric cancer and morphologically normal tissues by real-time PCR. For SNPs at positions 1236, 2677, and 3435, no statistically significant differences in genotype frequencies between gastric cancer patients and healthy individuals were found. However, genotype TT for all studied polymorphisms occurred more frequently in the group of gastric cancer patients (31.6, 26.3, 42.1%, respectively) than in the group of healthy individuals (14.6, 13.5, 21.9%, respectively). The lowest relative expression levels of ABCB1 mRNA were observed for genotypes CC of SNP 1236, CC of SNP 3435, and GG of SNP 2677 (median: 0.215, 0.160, 0.160, respectively). There was a tendency that mutant homozygote TT for SNPs at positions 1236, 2677, and 3435 occurred more frequently in the subgroup of patients with Tis or stage I of TNM classification (SNP 1236 p = 0.0760; SNP 2677 p = 0.0813; SNP 3435 p = 0.0760) than in the subgroup of patients with stage II or III. Also the expression levels were lowest (median 0.740) in the group of patients with the less advanced clinical stage of cancer (Tis or I). Preliminary research showed that the ABCB1 gene polymorphisms at positions 1236, 2677, and 3435 were not related to an increased susceptibility of gastric cancer development. However, they may be associated with the inhibition of gastric cancer progression.

Quantitative determination of magnetic force on a coronary stent in MRI

PURPOSE

To introduce an analytical method for a quantitative determination of magnetic force on a coronary stent in the magnetic resonance imaging (MRI) magnet that is generally applicable to metallic implants. Magnetic forces on metallic implants in the MRI magnets are traditionally determined empirically by measuring deflection from the vertical plane at the central axis of the magnet and at the point of the largest force along the longitudinal axis of the magnet.

MATERIALS AND METHODS

Magnetic and chemical characterization of the stents was performed by a commercial magnetometer and energy-dispersive X-ray spectroscopy. Magnetic force on the stents fabricated of paramagnetic alloys (surgical stainless steel and cobalt-chromium) was determined by measuring the stent's magnetic dipole moment and employing the on-axis magnetic field profile of an MRI magnet.

RESULTS

The maximum force on the stainless steel stent was found to be F(S,max) = 0.18 mN, whereas on the cobalt-chromium stent it was F(C,max) = 0.06 mN.

CONCLUSION

The magnetic force on the investigated paramagnetic stents is even smaller than the gravitational force acting on the stents in the Earth's gravity field, so that it has no physiological impact on the stented vessels.

Abstract P4-09-02: Prognostic and Predictive Value of Centrally Reviewed Ki67 Labeling Index in Postmenopausal Women with Endocrine-Responsive Breast Cancer: Results from Austrian Breast and Colorectal Cancer Study Group Trial 8

Purpose: The aim of the present study was to assess the prognostic and predictive value of Ki67 labeling index in postmenopausal hormone receptor-positive early breast cancer patients who were treated with adjuvant tamoxifen or anastrozole after tamoxifen. Patients and Methods: We determined the expression of Ki67 by immunohistochemistry on whole tissue sections of breast carcinoma patients who had been enrolled in Austrian Breast and Colorectal Cancer Study Group (ABCSG) Trial 8 and received tamoxifen for 5 years or tamoxifen for 2 years followed by anastrozole for 3 years. Ki67 labeling index was evaluated as continuous variable or dichotomized at 10%. Distant recurrence and death were analyzed using Cox models adjusted for clinical and pathological factors.

Results: High Ki67 labeling index was observed in 394 of 1587 (23%) tumors and was associated with poor outcome. Patients with high Ki67 labeling index had a significantly shorter distant recurrence-free survival (adjusted hazard ratio [HR] for distant recurrence 2.16, 95% confidence interval [CI] 1.43-3.25, P < 0.001) and overall survival (adjusted HR for death 1.77, 95% CI 1.30-2.42, P < 0.001) as compared to patients with low Ki67 labeling index. No interaction between Ki67 labeling index and treatment was observed (P = 0.84).

Conclusion: High Ki67 labeling index is an independent poor prognostic factor for distant recurrence and death in postmenopausal women with early-stage, hormone receptor-positive breast cancer but is not predictive for outcome of adjuvant treatment with either tamoxifen or tamoxifen followed by anastrozole.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-09-02.

Abstract P3-10-07: T5 Is a New Molecular Predictor of Distant Recurrence in Estrogen Receptor-Positive, HER2-Negative Breast Cancer

Background: Molecular tests predicting outcome of breast cancer patients may be useful for treatment decisions in addition to standard clinicopathologic features.

Methods: Using human genome HG-U133A array and qRT-PCR datasets, we developed and validated a gene-expression signature predicting the likelihood of distant recurrence in postmenopausal, early-stage breast cancer patients with estrogen receptor-positive, HER2-negative tumors treated with adjuvant endocrine therapy. RNA levels assessed by qRT-PCR in formalin-fixed paraffin-embedded tumor specimens were used to calculate a risk score (T5) and to determine a risk group (low or high) for each patient. The prospectively defined T5 risk score was then validated independently in patients from two large randomized phase III trials. Distant recurrence-free survival and overall survival were analyzed with Cox models adjusted for clinicopathological factors. The primary endpoint was time to distant recurrence.

Results: In a training set of 964 tumors, we identified a gene-expression signature consisting of three proliferation-related genes (BIRC5, UBE2C, DHCR7), five estrogen-regulated genes (RBBP8, IL6ST, AZGP1, MGP, STC2), and three reference genes (CALM2, OAZ1, RPL37A). For the validation, RNA analysis was possible in 1702 of 1725 (99%) tumors of both validation sets. Women were classified as having low risk (n=832; 49%) or high risk (n=870; 51%) by the T5 risk score. The T5 risk score provided prognostic information independent from clinicopathologic risk as estimated by Adjuvant!Online or Ki67 labeling index. Patients with a higher T5 risk score had a significantly shorter time to distant recurrence (adjusted hazard ratio, 1.24; 95% confidence interval [CI], 1.15 to 1.33; P<0.001) and overall survival (adjusted hazard ratio, 1.13; 95% CI, 1.06 to 1.19; P<0.001) compared to patients with a lower T5 risk score. The addition of the risk characterized by the T5 risk score to the clinicopathological risk resulted in 10-year distant recurrence-free survival rates of 95% in combined low risk patients and 82% in combined high risk patients (P<0.001).

Conclusions: Using formalin-fixed paraffin-embedded tumor specimens, the multigene T5 risk score provides prognostic information independent of Adjuvant!Online or Ki67 labeling index. By combining the T5 risk score with clinicopathological risk, we were able to accurately identify breast cancer patients with low risk or high risk for distant recurrence. Using this new easy-to-use multigene tool in clinical practice will assist in optimizing adjuvant therapy by reducing both undertreatment and overtreatment and thus improves outcome and quality of life of patients with early-stage breast cancer.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-10-07.

Surface-spin magnetism of antiferromagnetic NiO in nanoparticle and bulk morphology

The surface-spin magnetism of the antiferromagnetic (AFM) material NiO in nanoparticle and bulk morphology was investigated by magnetic measurements (temperature-dependent zero-field-cooled (zfc) and field-cooled (fc) dc susceptibility, ac susceptibility and zfc and fc hysteresis loops). We addressed the question of whether the multisublattice ordering of the uncompensated surface spins and the exchange bias (EB) effect are only present in the nanoparticles, originating from their high surface-to-volume ratio or if these surface phenomena are generally present in the AFM materials regardless of their bulky or nanoparticle morphology, but the effect is just too small to be detected experimentally in the bulk due to a very small surface magnetization. Performing experiments on the NiO nanoparticles of different sizes and bulk NiO grains, we show that coercivity enhancement and hysteresis loop shift in the fc experiments, considered to be the key experimental manifestations of multisublattice ordering and the EB effect, are true nanoscale phenomena only present in the nanoparticles and absent in the bulk.

Isolation and characterization of a novel insecticidal crystal protein gene from Bacillus thuringiensis subsp. aizawai

Bacillus thuringiensis subsp. aizawai EG6346, a novel grain dust isolate, was analyzed by Southern blot hybridization for its insecticidal crystal protein (ICP) gene profile. Strain EG6346 lacks previously characterized cryIA ICP genes yet does possess novel cryI-related gene sequences. A recombinant genomic plasmid library was constructed for strain EG6346 in Escherichia coli. One recombinant plasmid, pEG640, isolated from the library contained a novel ICP gene on a 5.7-kb Sau3A insert. The sequence of this gene, designated cryIF, was related to, but distinct from, the published sequences for other cryI genes. A second novel cryI-related sequence was also located on pEG640, approximately 500 bp downstream from cryIF. Introduction of cryIF into a Cry- B. thuringiensis recipient strain via electroporation enabled sufficient production of CryIF protein for quantitative bioassay analyses of insecticidal specificity. The CryIF crystal protein was selectively toxic to a subset of lepidopteran insects tested, including the larvae of Ostrinia nubilalis and Spodoptera exigua.