FRET enhancement in aluminum zero-mode waveguides.

Zero-mode waveguides (ZMWs) can confine light into attoliter volumes, which enables single molecule fluorescence experiments at physiological micromolar concentrations. Of the fluorescence spectroscopy techniques that can be enhanced by ZMWs, Förster resonance energy transfer (FRET) is one of the most widely used in life sciences. Combining zero-mode waveguides with FRET provides new opportunities to investigate biochemical structures or follow interaction dynamics at micromolar concentrations with single-molecule resolution. However, prior to any quantitative FRET analysis on biological samples, it is crucial to establish first the influence of the ZMW on the FRET process. Here, we quantify the FRET rates and efficiencies between individual donor-acceptor fluorophore pairs that diffuse into aluminum zero-mode waveguides. Aluminum ZMWs are important structures thanks to their commercial availability and the large amount of literature that describe their use for single-molecule fluorescence spectroscopy. We also compared the results between ZMWs milled in gold and aluminum, and found that although gold has a stronger influence on the decay rates, the lower losses of aluminum in the green spectral region provide larger fluorescence brightness enhancement factors. For both aluminum and gold ZMWs, we observed that the FRET rate scales linearly with the isolated donor decay rate and the local density of optical states. Detailed information about FRET in ZMWs unlocks their application as new devices for enhanced single-molecule FRET at physiological concentrations.

Nanophotonic enhancement of the Förster resonance energy-transfer rate with single nanoapertures.

Tailoring the light-matter interaction and the local density of optical states (LDOS) with nanophotonics provides accurate control over the luminescence properties of a single quantum emitter. This paradigm is also highly attractive to enhance the near-field Förster resonance energy transfer (FRET) between two fluorescent emitters. Despite the wide applications of FRET in nanosciences, using nanophotonics to enhance FRET has remained a debated and complex challenge. Here we demonstrate enhanced energy transfer within single donor-acceptor fluorophore pairs confined in single gold nanoapertures. Experiments monitoring both the donor and the acceptor emission photodynamics clearly establish a linear dependence of the FRET rate on the LDOS in nanoapertures, demonstrating that nanophotonics can be used to intensify the near-field energy transfer. Strikingly, we observe a significant six-fold increase in the FRET rate for large donor-acceptor separations exceeding 13 nm. Exciting opportunities are opened to investigate biochemical structures with donor-acceptor distances much beyond the classical Förster radius. Importantly, our approach is fully compatible with the detection of single biomolecules freely diffusing in water solution under physiological conditions.

Nonreciprocal switching thresholds in coupled nonlinear microcavities.

A concept for the design of nonlinear optical diodes is proposed that uses the multistability of coupled nonlinear microcavities and the dependence of switching thresholds on the direction of incidence. A typical example of such a diode can be created by combining two mirror-symmetric microcavities where modes of the opposite parity dominate. It is shown that a strong nonreciprocal behavior can be achieved together with a negligible insertion loss. To describe the dynamical properties of such systems, a model based on the coupled-mode theory is developed, and a possible implementation in the form of multilayered structures is considered.

Exact analytical representations for broadband transmission properties of quarter-wave multilayers.

The formalism of the scattering matrix is applied to describe the transmission properties of multilayered structures with deep variations of the refractive index and arbitrary arrangements of the layers. We show that there is an exact analytical formula for the transmission spectrum, which is valid for the full spectral range and which contains only a limited number of parameters for structures satisfying the quarter-wave condition. These parameters are related to the poles of the scattering matrix, and we present an efficient algorithm to find them, which is based on considering the ray propagation inside the structure and subsequent application of the harmonic inversion technique. These results are significant for analyzing the reshaping of ultrashort pulses in multilayered structures.

Method to determine the tracking angles of heliostats.

The heliostats with two tracking axes are considered, and the method is presented to find the tracking angles for reflection of sun light to a given target. An important advantage of the method is that the tracking axes are not required to be orthogonal like in azimuth-elevation, tilt-roll or target-aligned heliostats. All of these configurations are covered in a unified way, and the presented solution is valid even for arbitrary orientation of tracking axes. The ability to have such a general solution is very valuable, because the orthogonality condition may not hold precisely for manufacturing reasons or due to degradation of heliostats. These deviations need to be corrected properly to achieve a high concentration of sun light. The offsets between tracking axes are also taken into account. However, the targeting problem for heliostats in this case becomes considerably different from the inverse kinematic problems for robotic arm manipulators. It is shown that the tracking angles can be found iteratively, and the convergence of results is very fast for a typical set of parameters used in solar thermal plants. To simplify the use of the method, a Python-library HelioK was developed, and it is demonstrated how to work with it in a Jupyter-notebook. To explain the kinematics of heliostats better, a 3D model of heliostat is provided, which was made and animated in an open-source 3D editor Blender. The main highlights of the method:•The tracking axes and the facet of heliostat can have an arbitrary orientation, and there can be offsets between them.•The tracking problem is solved both for targets attached to heliostat (local aiming) and for separated targets (global aiming).•The single-axis trackers are included as a limiting case.

Determinants of vitamin D levels in men receiving androgen deprivation therapy for prostate cancer.

PURPOSE: Studies found an association between decreased 25-OH vitamin D blood level and prostate cancer progression. Vitamin D supplementation is controversial and dosage recommendations inconsistent. This study identified factors associated with 25-OH vitamin D levels and whether vitamin D supplementation with 800 IU/day raised vitamin D levels in prostate cancer patients receiving androgen deprivation therapy (ADT). DATA SOURCES: We recruited 108 men treated with ADT for ≥9 months from eight cancer and urology practices. Sections of the NHANES 2005-2006 questionnaire and Canadian Fitness Survey were completed identifying age, ethnicity, length of ADT use, calcium supplementation ≥1000 IU mg/day, body mass index, exercise, alcohol and tobacco use, and vitamin D supplementation ≥800 IU/daily. Blood was collected for 25-OH vitamin D analysis. CONCLUSIONS: The majority of men (66%) had blood levels of 25-OH vitamin D <32 ng/mL. Regression analysis showed vitamin D supplementation (ß = 6.556, CI 1.463, 11.650; p = .012) and African American ethnicity (ß = -7.816, CI -12.996, -2.635; p = .003) is associated with 25-OH vitamin D level after controlling age and tobacco use. PRACTICE IMPLICATIONS: Findings support current recommendations for supplementation with ≥800 IU vitamin D/day for men receiving ADT. Nurse practitioners caring for prostate cancer patients receiving ADT should include vitamin D monitoring and supplementation.

Plasmonic antennas and zero-mode waveguides to enhance single molecule fluorescence detection and fluorescence correlation spectroscopy toward physiological concentrations.

Single-molecule approaches to biology offer a powerful new vision to elucidate the mechanisms that underpin the functioning of living cells. However, conventional optical single molecule spectroscopy techniques such as Förster fluorescence resonance energy transfer (FRET) or fluorescence correlation spectroscopy (FCS) are limited by diffraction to the nanomolar concentration range, far below the physiological micromolar concentration range where most biological reaction occur. To breach the diffraction limit, zero-mode waveguides (ZMW) and plasmonic antennas exploit the surface plasmon resonances to confine and enhance light down to the nanometer scale. The ability of plasmonics to achieve extreme light concentration unlocks an enormous potential to enhance fluorescence detection, FRET, and FCS. Single molecule spectroscopy techniques greatly benefit from ZMW and plasmonic antennas to enter a new dimension of molecular concentration reaching physiological conditions. The application of nano-optics to biological problems with FRET and FCS is an emerging and exciting field, and is promising to reveal new insights on biological functions and dynamics.

Self-reported exercise and bone mineral density in prostate cancer patients receiving androgen deprivation therapy.

PURPOSE: Men with prostate cancer receiving androgen deprivation therapy (ADT) are at increased risk for decreased bone mineral density (BMD). This study evaluates the relationship between self-reported daily activity, endurance and resistance exercise, and BMD measured by dual-energy x-ray absorptiometry (DEXA) in prostate cancer patients receiving ADT. DATA SOURCES: We recruited 96 men treated with ADT for ≥9 months from urology and cancer practices. The Canadian Fitness Survey assessed daily activity and exercise. Data on demographic and lifestyle characteristics and calcium and vitamin D supplementation were collected. Blood was collected for analysis of 25-OH vitamin D. A DEXA scan was performed. CONCLUSIONS: A positive association between endurance exercise and DEXA T-scores of the hip was shown. Regression analysis showed endurance exercise of medium to heavy intensity (measured as energy expenditure in MET-hours/week) was associated with T-scores of the hip (ß = 0.048; 95% CI 0.003, 0.112; p = .040) but not with spinal T-scores after controlling for age, body mass index, and alcohol use. IMPLICATIONS FOR PRACTICE: Findings are cross-sectional, but if confirmed in prospective studies suggest that increased endurance exercise is a practical measure nurse practitioners can institute to prevent low bone density in the hip of men treated with ADT.