Ultrasensitive Detectors Research Articles

Dark-Matter Mystery Nears Its Moment of Truth

Physicists working with an ultrasensitive particle detector deep underground reported three blips that could be particles of dark matter—suggesting that weakly interacting massive particles might not be far off.

Frequency, power and temperature dependence of the off-resonance magnetoresistance spike in irradiated 2D-electron systems

We present calculated results on frequency, power and temperature dependence of the recently discovered giant radiation-induced off-resonance magnetoresistance spike obtained in ultraclean two-dimensional electron systems. This spike shows up on the second harmonic of the cyclotron resonance. We apply the radiation-driven electron orbit model to this novel ultraclean scenario. In agreement with experiments, we obtain that the spike intensity is strongly dependent on temperature and radiation power. On the other hand, the spike position is mainly dependent on radiation frequency. These results would be of special interest from the application perspective, such as nanophotonics, ultrasensitive microwave detectors or solar cells given the strong translation of radiation energy into electrical current.

Improvement of the superconducting properties of NbN thin film on single-crystal silicon substrate by using a TiN buffer layer

Thin superconducting NbN film on silicon substrate is a promising material for use in some ultrasensitive sensors and detectors, such as the hot-electron bolometer mixer and the superconducting nanowire single-photon detector. Due to the large mismatch between NbN film and Si substrate, the NbN film has a lower critical temperature than NbN film on MgO substrate. TiN has been experimentally verified as a good buffer layer due to having the same face-centered-cubic crystallite structure as and a lattice constant close to that of the NbN film, i.e. the critical temperatures of NbN films (5–20 nm thickness) on TiN buffered silicon are about 1–3 K higher than those of NbN/Si. Such improvement can be ascribed not only to the reduction of the interface thickness in the NbN film, but also to the enlargement of the NbN grains, inherited from the TiN template layer.

Second-order optical coherence tomography: deeper and turbulence-free imaging

The superior resolution of optical coherence tomography (OCT) with respect to alternative imaging modalities makes it highly attractive, and some of its applications are already in extensive clinical use. However, one of the major limitations of OCT is that the tomographic picture it generates is depth-limited to approximately 1 mm in most biological tissues. This is mainly due to the spatially turbulent nature of the tissue, which leads to scattering. Moreover, this technique is extremely sensitive to temporal variations in the medium. We show that insensitivity to temporal and spatial turbulence may be gained by replacing the linear detector with an ultrasensitive two-photon detector. These results have striking implications on the attainable penetration depth of optical imaging and on its sensitivity to sample motion.

Capillary electrophoresis with three-color fluorescence detection for the analysis of glycosphingolipid metabolism

A capillary electrophoresis system with an ultrasensitive three-color laser-induced fluorescence detector was constructed for the simultaneous measurement of glycosphingolipids conjugated with a family of BODIPY fluorophores. The compounds were separated by capillary electrophoresis and detected by laser-induced fluorescence excited within a sheath-flow cuvette. Diode-pumped solid-state lasers operating at 473 nm and 532 nm, and a diode laser operating at 633 nm were used to excite glycosphingolipids tagged with BODIPY-FL, BODIPY-TMR, and BODIPY-650/665 fluorophores. Detection limits were 34 ± 1 molecules, 67 ± 7 molecules, and 36 ± 13 molecules of BODIPY-FL, BODIPY-TMR, and BODIPY-650/665 labeled glycosphingolipids. Separation efficiencies were typically one million theoretical plates. To test the ability of the system to analyze cellular contents in an in vitro biological model, differentiated PC12 cells were co-incubated with BODIPY-FL, BODIPY-TMR, and BODIPY-650/665 labeled lactosylceramide substrates. Cells were homogenized. The metabolic products originating from the glycosphingolipid substrates were simultaneously analyzed using the system.

Exploring the extreme universe with the Fermi Gamma-Ray Space Telescope

The Fermi orbiter, mapping the entire gamma-ray sky every three hours, monitors the cosmos for high-energy phenomena both fleeting and enduring.

A hybrid on-chip optomechanical transducer for ultrasensitive force measurements

Nanoscale mechanical oscillators are used as ultrasensitive detectors of force, mass and charge. Nanomechanical oscillators have also been coupled with optical and electronic resonators to explore the quantum properties of mechanical systems. Here, we report an optomechanical transducer in which a Si(3)N(4) nanomechanical beam is coupled to a disk-shaped optical resonator made of silica on a single chip. We demonstrate a force sensitivity of 74 aN Hz(-1/2) at room temperature with a readout stability better than 1% at the minute scale. Our system is particularly suited for the detection of very weak incoherent forces, which is difficult with existing approaches because the force resolution scales with the fourth root of the averaging time. By applying dissipative feedback based on radiation pressure, we significantly relax this constraint and are able to detect an incoherent force with a force spectral density of just 15 aN Hz(-1/2) (which is 25 times less than the thermal noise) within 35 s of averaging time (which is 30 times less than the averaging time that would be needed in the absence of feedback). It is envisaged that our hybrid on-chip transducer could improve the performance of various forms of force microscopy.

An ultrasensitive universal detector based on neutralizer displacement

Diagnostic technologies that can provide the simultaneous detection of nucleic acids for gene expression, proteins for host response and small molecules for profiling the human metabolome will have a significant advantage in providing comprehensive patient monitoring. Molecular sensors that report changes in the electrostatics of a sensor's surface on analyte binding have shown unprecedented sensitivity in the detection of charged biomolecules, but do not lend themselves to the detection of small molecules, which do not carry significant charge. Here, we introduce the neutralizer displacement assay that allows charge-based sensing to be applied to any class of molecule irrespective of the analyte charge. The neutralizer displacement assay starts with an aptamer probe bound to a neutralizer. When analyte binding occurs the neutralizer is displaced, which results in a dramatic change in the surface charge for all types of analytes. We have tested the sensitivity, speed and specificity of this system in the detection of a panel of molecules: (deoxy)ribonucleic acid, ribonucleic acid, cocaine, adenosine triphosphate and thrombin.

Ultrasensitive Far-Infrared Phototransistors Fabricated in Superlattice Structures

Charge sensitive infrared phototransistors (CSIPs), ultrasensitive detectors in the wavelength range of 10–50 µm, are fabricated in GaAs/AlGaAs superlattice structures. The superlattice structures consist of alternately grown 2-nm-thick Al0.3Ga0.7As tunnel barriers and thickness-modulated GaAs layers from 2 to 10 nm. The tilted miniband formed in a superlattice structure serves as a potential slope similar to formally used compositionally graded barriers. The utilization of the superlattice in a CSIP is expected to give advantages of easier design, less impurities, and better repeatability in crystal growth, and therefore provides more reliable device performance. The novel structure paves the way for the future mass production of CSIPs.

Ultrasensitive Far-Infrared Phototransistors Fabricated in Superlattice Structures

Charge sensitive infrared phototransistors (CSIPs), ultrasensitive detectors in the wavelength range of 10–50 µm, are fabricated in GaAs/AlGaAs superlattice structures. The superlattice structures consist of alternately grown 2-nm-thick Al0.3Ga0.7As tunnel barriers and thickness-modulated GaAs layers from 2 to 10 nm. The tilted miniband formed in a superlattice structure serves as a potential slope similar to formally used compositionally graded barriers. The utilization of the superlattice in a CSIP is expected to give advantages of easier design, less impurities, and better repeatability in crystal growth, and therefore provides more reliable device performance. The novel structure paves the way for the future mass production of CSIPs.

Colorful Molecular Diagnostics

Most diagnostic assays used daily in clinical laboratories are based on identifying and quantifying the presence of specific molecules that serve as markers of pathologic conditions and physiological status; however, these molecules are neither visualized nor counted directly. Instead, amplified signals generated through various strategies [e.g., real-time PCR, enzyme-linked assays (ELISAs), or simply blood culture] quantify the molecules of interest in an indirect fashion. These bioassays provide easy and robust detection on affordable instrumentation, but their amplification procedures also are usually associated with additional costs, additional time to results, increased labor, and a certain error rate. Furthermore, most of these methods monitor a single marker in a single sample. Consequently, methods that detect molecular markers directly are highly desirable. In most cases, this quest involves fluorescence spectroscopy and imaging, owing to its flexibility, low cost, and sensitivity in visualizing and characterizing single molecules in very small sample volumes (1). Until recently, single-molecule fluorescence detection was not a trivial task, because the signals generated from an individual molecule (for example, a fluorophore attached to a protein or DNA) were extremely weak. Only custom-built microscopes featuring the best combination of illumination sources, fluorescent probes, and ultrasensitive detectors could provide the sensitivity required to “see” and count single fluorescent molecules. Improvements introduced to facilitate studies of biological mechanisms in vitro and in vivo have made single-molecule microscopy instruments more sensitive, streamlined, and affordable. In fact, such instruments are leading the race for third-generation DNA sequencing (2, 3). In this issue of the Journal, Yim et al. (4) introduce a different application of single-molecule fluorophore …

The Global Coherence Initiative: Creating a Coherent Planetary Standing Wave

ABSTRACTThe much anticipated year of 2012 is now here. Amidst the predictions and cosmic alignments that many are aware of, one thing is for sure: it will be an interesting and exciting year as the speed of change continues to increase, bringing both chaos and great opportunity. One benchmark of these times is a shift in many people from a paradigm of competition to one of greater cooperation. All across the planet, increasing numbers of people are practicing heart-based living, and more groups are forming activities that support positive change and creative solutions for manifesting a better world. The Global Coherence Initiative (GCI) is a science-based, co-creative project to unite people in heart-focused care and intention. GCI is working in concert with other initiatives to realize the increased power of collective intention and consciousness.The convergence of several independent lines of evidence provides strong support for the existence of a global information field that connects all living systems and consciousness. Every cell in our bodies is bathed in an external and internal environment of fluctuating invisible magnetic forces that can affect virtually every cell and circuit in biological systems. Therefore, it should not be surprising that numerous physiological rhythms in humans and global collective behaviors are not only synchronized with solar and geomagnetic activity, but disruptions in these fields can create adverse effects on human health and behavior.The most likely mechanism for explaining how solar and geomagnetic influences affect human health and behavior are a coupling between the human nervous system and resonating geomagnetic frequencies, called Schumann resonances, which occur in the earth-ionosphere resonant cavity and Alfvén waves. It is well established that these resonant frequencies directly overlap with those of the human brain and cardiovascular system. If all living systems are indeed interconnected and communicate with each other via biological, electromagnetic, and nonlocal fields, it stands to reason that humans can work together in a co-creative relationship to consciously increase the coherence in the global field environment, which in turn distributes this information to all living systems within the field.GCI was established to help facilitate the shift in global consciousness from instability and discord to balance, cooperation, and enduring peace. A primary goal of GCI is to test the hypothesis that large numbers of people when in a heart-coherent state and holding a shared intention can encode information on the earth's energetic and geomagnetic fields, which act as carrier waves of this physiologically patterned and relevant information. In order to conduct this research, a global network of 12 to 14 ultrasensitive magnetic field detectors specifically designed to measure the earth's magnetic resonances is being installed strategically around the planet. More important is GCI's primary goal to motivate as many people as possible to work together in a more coherent and collaborative manner to increase the collective human consciousness.If we are persuaded that not only external fields of solar and cosmic origins but also human attention and emotion can directly affect the physical world and the mental and emotional states of others (consciousness), it broadens our view of what interconnectedness means and how it can be intentionally utilized to shape the future of the world we live in. It implies that our attitudes, emotions, and intentions matter and that coherent, cooperative intent can have positive effects.GCI hypothesizes that when enough individuals and social groups increase their coherence baseline and utilize that increased coherence to intentionally create a more coherent standing reference wave in the global field, it will help increase global consciousness. This can be achieved when an increasing number of people move towards more balanced and self-regulated emotions and responses. This in turn can help facilitate cooperation and collaboration in innovative problem solving and intuitive discernment for addressing society's significant social, environmental, and economic problems. In time, as more individuals stabilize the global field and families, workplaces, and communities move to increased social coherence, it will lead to increased global coherence. This will be indicated by countries adopting a more coherent planetary view so that social and economic oppression, warfare, cultural intolerance, crime, and disregard for the environment can be addressed meaningfully and successfully.

Chemical mapping at atomic resolution using energy-dispersive x-ray spectroscopy

Abstract

A simple model for the resonance shift of localized plasmons due to dielectric particle adhesion

Ultrasensitive detectors based on localized surface plasmon resonance refractive index sensing are capable of detecting very low numbers of molecules for biochemical analysis. It is well known that the sensitivity of such sensors crucially depends on the spatial distribution of the electromagnetic field around the metal surface. However, the precise connection between local field enhancement and resonance shift is seldom discussed. Using a quasistatic approximation, we developed a model that relates the sensitivity of a nanoplasmonic resonator to the local field in which the analyte is placed. The model, corroborated by finite-difference time-domain simulations, may be used to estimate the magnitude of the shift as a function of the properties of the sensed object - permittivity and volume - and its location on the surface of the resonator. It requires only a computation of the resonant field induced by the metal structure and is therefore suitable for numerical optimization of nanoplasmonic sensors.

The two dimensional electron system as a nanoantenna in the microwave and terahertz bands

We study the magnetoresistance of two-dimensional electron systems under several radiation sources of different frequencies for moderate power. We use the model of radiation-driven electron orbits extended to this regime. First, we consider the case of two different radiations and we find a regime of superposition or interference of harmonic motions, i.e., a modulated magnetoresistance response with pulses and beats. Finally, we consider a multiple photoexcitation case where we propose the two-dimensional electron system as a potential nanoantenna device or ultrasensitive detector for the microwave and terahertz bands. Thus, these results could be of special interest in nanophotonics and nanoelectronics.

Development of an ultra-sensitive radon detector for the SuperNEMO experiment

The SuperNEMO experiment is devoted to neutrinoless double beta decay detection and main R&D of the detector design is already finished. The crucial role in such low background experiments plays the suppression of background. One of the most important sources of radioactivity is the radon gas and its daughter products. The radon activity in the volume of the detector will be reduced significantly using the antiradon facility already installed in the Modane underground laboratory which provides air with a radon volume activity at the order of ∼ mBq/m3. To be able to measure low radon activities at the output of this antiradon facility in reasonable time of measurement the develoment of new ultra-sensitive radon detector is currently carried out. The detection is based on electrostatic collection of radon progenies (214Po, 218Po) on a Si PIN diode. Our idea is to increase the volume of the detector up to 1 m3 divided into smaller subdetectors (50–100 l) to improve the detection effectiveness and consequently the sensitivity. Two prototypes of sensitive radon detectors were constructed (50 l and 300 l). Preliminary results of the detection efficiency and the background measurement for the first prototype are also presented.

Picomolar Nitric Oxide Signals from Central Neurons Recorded Using Ultrasensitive Detector Cells

Nitric oxide (NO) is a widespread signaling molecule with potentially multifarious actions of relevance to health and disease. A fundamental determinant of how it acts is its concentration, but there remains a lack of coherent information on the patterns of NO release from its sources, such as neurons or endothelial cells, in either normal or pathological conditions. We have used detector cells having the highest recorded NO sensitivity to monitor NO release from brain tissue quantitatively and in real time. Stimulation of NMDA receptors, which are coupled to activation of neuronal NO synthase, routinely generated NO signals from neurons in cerebellar slices. The average computed peak NO concentrations varied across the anatomical layers of the cerebellum, from 12 to 130 pm. The mean value found in the hippocampus was 200 pm. Much variation in the amplitudes recorded by individual detector cells was observed, this being attributable to their location at variable distances from the NO sources. From fits to the data, the NO concentrations at the source surfaces were 120 pm to 1.4 nm, and the underlying rates of NO generation were 36-350 nm/s, depending on area. Our measurements are 4-5 orders of magnitude lower than reported by some electrode recordings in cerebellum or hippocampus. In return, they establish coherence between the NO concentrations able to elicit physiological responses in target cells through guanylyl cyclase-linked NO receptors, the concentrations that neuronal NO synthase is predicted to generate locally, and the concentrations that neurons actually produce.

Limits on the release of Rb isotopes from a zeolite based 83mKr calibration source for the XENON project

The isomer 83mKr with its half-life of 1.83 h is an ideal calibration source for a liquid noble gas dark matter experiment like the XENON project. However, the risk of contamination of the detector with traces of the much longer lived mother isotope 83Rb(T½ = 86.2 d) has to be ruled out. In this work the release of 83Rb atoms from a 1.8 MBq 83Rb source embedded in zeolite beads has been investigated. To do so, a cryogenic trap has been connected to the source for about 10 days, after which it was removed and probed for the strongest 83Rbγ-rays with an ultra-sensitive Germanium detector. No signal has been found. The corresponding upper limit on the released 83Rb activity means that the investigated type of source can be used in the XENON project and similar low-background experiments as 83mKr generator without a significant risk of contaminating the detector. The measurements also allow to set upper limits on the possible release of the isotopes 84Rb and 86Rb, traces of which were created alongside the production of 83Rb at the Rez cyclotron.

Nanobolometers for THz Photon Detection

This paper reviews the state of rapidly emerging terahertz hot-electron nanobolometers (nano-HEB), which are currently among of the most sensitive radiation power detectors at submillimeter wavelengths. With the achieved noise equivalent power close to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-19</sup> W/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and potentially capable of approaching NEP ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-20</sup> W/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , nano-HEBs are very important for future space astrophysics platforms with ultralow submillimeter radiation background. The ability of these sensors to detect single low-energy photons with high dynamic range opens interesting possibilities for quantum calorimetry in the midinfrared and even in the far-infrared parts of the electromagnetic spectrum. We discuss the competition in the field of ultrasensitive detectors, the physics and technology of nano-HEBs, recent experimental results, and perspectives for future development.

Detection of nonfluorescent molecules using differential interference contrast thermal lens microscope for extended nanochannel chromatography

An ultrasensitive absorbance detector, the differential interference contrast thermal lens microscope (DIC-TLM), was employed for a chromatography system using silica nanochannel. Recently, separation of ultrasmall volume sample has been strongly required for single-cell biological and chemical analysis. Previously, we have developed a chromatography system using nanochannels of ~100 nm scale (extended nanochannels) fabricated on a silica substrate. The extended nanochromatography realized highly efficient separation of samples <1 fL without packing materials. However, its detection method was limited to fluorescence method due to the small volume, and a new detector based on absorbance has been required. On the contrary, we have also developed DIC-TLM, a photothermal spectrometer based on absorption and thermal relaxation of sample for determination of concentration of nonfluorescent molecules in extended nanochannel. In this paper, we combined the extended nanochromatography and the DIC-TLM for separation and detection of nonfluorescent dyes. Particularly, basic performances of the DIC-TLM including quantitative performance and sensitivity were deliberated for injected samples of ~fL volume.