Ultrasensitive Detectors Research Articles

Radiative Recombination of Spatially Extended Excitons in (ZnSe/CdS)/CdS Heterostructured Nanorods

We report on organometallic synthesis of luminescent (ZnSe/CdS)/CdS semiconductor heterostructured nanorods (hetero-NRs) that produce an efficient spatial separation of carriers along the main axis of the structure (type II carrier localization). Nanorods were fabricated using a seeded-type approach by nucleating the growth of 20-100 nm CdS extensions at [000 +/- 1] facets of wurtzite ZnSe/CdS core/shell nanocrystals. The difference in growth rates of CdS in each of the two directions ensures that the position of ZnSe/CdS seeds in the final structure is offset from the center of hetero-NRs, resulting in a spatially asymmetric distribution of carrier wave functions along the heterostructure. Present work demonstrates a number of unique properties of (ZnSe/CdS)/CdS hetero-NRs, including enhanced magnitude of quantum confined Stark effect and subnanosecond switching of absorption energies that can find practical applications in electroabsorption switches and ultrasensitive charge detectors.

Fluorescence correlation spectroscopy to study the degradation of oligonucleotides, both naked and complexed, to cationic carriers

The degradation of double-labeled oligonucleotides (ONs) was followed by the disappearance of Fluorescence Energy Transfer between the rhodamine green and Cy5 fluorophores attached to the 3′ and 5′ end of the oligonucleotides. The fluorescence intensities after rhodamine green excitation were recorded using the ultra-sensitive detectors of a dual-color FCS setup. The ratio of the Cy5 to rhodamine green fluorescence showed to give accurate information on the integrity of the oligonucleotides and could be easily used to follow the degradation of naked or complexed double-labeled oligonucleotides, both in buffer and in living cells.

Nanotechnology-based electrochemical sensors for biomonitoring chemical exposures.

The coupling of dosimetry measurements and modeling represents a promising strategy for deciphering the relationship between chemical exposure and disease outcome. To support the development and implementation of biological monitoring programs, quantitative technologies for measuring xenobiotic exposure are needed. The development of portable nanotechnology-based electrochemical (EC) sensors has the potential to meet the needs for low cost, rapid, high-throughput, and ultrasensitive detectors for biomonitoring an array of chemical markers. Highly selective EC sensors capable of pM sensitivity, high-throughput and low sample requirements (<50 microl) are discussed. These portable analytical systems have many advantages over currently available technologies, thus potentially representing the next generation of biomonitoring analyzers. This paper highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are presented. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are discussed.

Application and New Developments in Fluorescence Spectroscopic Techniques in Studying Individual Molecules

Techniques based on fluorescence have played a variety of roles in chemistry, physics, spectroscopy, medicine, nanotechnology, and biotechnology due to their high selectivity, sensitivity, simplicity, and fastness in spectroscopic and imaging measurements. While detecting fluorescence from individual molecules by fluorescence‐based techniques, poor signal, limited lifespan of fluorophores, trade‐off between time resolution, and the level of detail of information were few major concerns. Ultrasensitive detectors permit the combination of the high time resolution of single photon counting devices with the large field of view and spectral resolution allowed by two‐dimensional detectors. Photobleaching and on‐off blinking of fluorophores can be improved dramatically by chemical modifications or changing the reagents. New ways of controlling local fields such as optic, electric, magnetic, chemical, or biochemical environments take advantage of the noninvasiveness and high temporal and spatial resolution of single‐molecule fluorescence (SMF) to get a direct feedback of events at the nanometer scale in various domains of research. Some of the applications and new developments in fluorescence spectroscopic techniques in detecting, investigating, and/or manipulating individual molecules have been discussed.

Ultrasensitive proximity Josephson sensor with kinetic inductance readout

We propose a mesoscopic kinetic-inductance radiation detector based on a long superconductor-normal metal-superconductor Josephson junction. The operation of this proximity Josephson sensor relies on large kinetic inductance variations under irradiation due to the exponential temperature dependence of the critical current. Coupled with a dc superconducting quantum interference device readout, the PJS is able to provide a signal to noise (S/N) ratio up to ∼103 in the terahertz regime if operated as calorimeter, while electrical noise equivalent power as low as ∼7×10−20W∕Hz at 200mK can be achieved in the bolometer operation. The high performance together with the ease of fabrication make this structure attractive as an ultrasensitive cryogenic detector of terahertz electromagnetic radiation.

The application of inductively coupled plasma mass spectrometry in clinical pharmacological oncology research

Metal-based anticancer agents are frequently used in the treatment of a wide variety of cancer types. The monitoring of these anticancer agents in biological samples is important to understand their pharmacokinetics, pharmacodynamics, and metabolism. In addition, determination of metals originating from anticancer agents is relevant to assess occupational exposure of health care personnel working with these drugs. The high sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) has resulted in an increased popularity of this technique for the analysis of metal-based anticancer drugs. In addition to the quantitative analysis of the metal of interest in a sample, ICP-MS can be used as an ultrasensitive metal selective detector in combination with speciation techniques such as liquid chromatography. In the current review we provide a systematic survey of publications describing the analysis of platinum- and ruthenium-containing anticancer agents using ICP-MS, focused on the determination of total metal concentrations and on the speciation of metal compounds in biological fluids, DNA- and protein-adducts, and environmental samples. We conclude that ICP-MS is a powerful tool for the quantitative analysis of metal-based anticancer agents from multiple sample sources.

Lumped Element Kinetic Inductance Detectors

Kinetic Inductance Detectors (KIDs) provide a promising solution to the problem of producing large format arrays of ultra sensitive detectors for astronomy. Traditionally KIDs have been constructed from superconducting quarter-wave resonant elements capacitively coupled to a co-planar feed line [1]. Photon detection is achieved by measuring the change in quasi-particle density caused by the splitting of Cooper pairs in the superconducting resonant element. This change in quasi-particle density alters the kinetic inductance, and hence the resonant frequency of the resonant element. This arrangement requires the quasi-particles generated by photon absorption to be concentrated at positions of high current density in the resonator. This is usually achieved through antenna coupling or quasi-particle trapping. For these detectors to work at wavelengths shorter than around 500 μm where antenna coupling can introduce a significant loss of efficiency, then a direct absorption method needs to be considered. One solution to this problem is the Lumped Element KID (LEKID), which shows no current variation along its length and can be arranged into a photon absorbing area coupled to free space and therefore requiring no antennas or quasi-particle trapping. This paper outlines the relevant microwave theory of a LEKID, along with theoretical and measured performance for these devices.

Importance of the Debye screening length on nanowire field effect transistor sensors.

Nanowire field effect transistors (NW-FETs) can serve as ultrasensitive detectors for label-free reagents. The NW-FET sensing mechanism assumes a controlled modification in the local channel electric field created by the binding of charged molecules to the nanowire surface. Careful control of the solution Debye length is critical for unambiguous selective detection of macromolecules. Here we show the appropriate conditions under which the selective binding of macromolecules is accurately sensed with NW-FET sensors.

Evaluation of a Microwave SQUID Multiplexer Prototype

As large arrays of ultrasensitive cryogenic detectors of radiant energy are developed, multiplexing schemes are required to manage system complexity. Any such scheme must also meet stringent sensitivity, bandwidth, dynamic range and power dissipation specifications. We describe preliminary tests of a microwave frequency-division multiplexed readout of SQUID amplifiers. From these initial tests we estimated the number of SQUIDs that can be multiplexed with this scheme and the sensitivity and bandwidth of each SQUID amplifier.

Ultrasensitive Quantum-Limited Far-Infrared STJ Detectors

We describe recent work at Yale on Superconducting Tunnel Junction (STJ) direct detectors that have been developed for submillimeter astronomy. To monitor the response of the detector with large readout bandwidth and excellent sensitivity, we use a novel readout based on radio frequency (RF) reflectometry, like the readout invented for the RF-SET. For calibration of the detector, we have developed an in-situ, on-chip, hot-cold photon source. This is a voltage biased gold microbridge. Noise emitted by the microbridge couples via a coplanar stripline to the detector. This provides a calibrated blackbody photon source with near unity coupling, fast chopping, and calculable output. We present recent detection results in the range 100-160 GHz. These demonstrate the expected good responsivity, high sensitivity, and fast response. This approach is easily used with a frequency-multiplexed readout, allowing economy of cold electronics. Ultimate sensitivity is in the range 1 times 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> .

The Promise of Plasmonics

A technology that squeezes electromagnetic waves into minuscule structures may yield a new generation of superfast computer chips and ultrasensitive molecular detectors

Unpredictability and chance in scientific progress

It is much easier to interpret the past than to predict the future, and especially so when dealing with the vicissitudes of science. The laser, for example, which did not emerge until 1960, could have been assembled decades earlier by perspicacious physicists following Einstein’s classic paper in 1917 on population inversion in electronic energy levels. Equally, a widely read, mathematically-oriented engineer or computer scientist, knowing Radon’s work in Leipzig, also in 1917, could have foreseen and accelerated the arrival of the technique of tomography, with all that it has done to revolutionize medicine. In this article, I cite examples of devices, techniques, procedures, and theories that exhibit a variety of different origins and subsequent development. In some instances progress had been extraordinary rapid, in others extremely slow; and in several the element of chance and coincidence has played a vital role. With the exception of the computer itself few electronic devices have had a more profound impact on the progress of experimental science and on social interaction among human beings than the charge coupled device, otherwise known as the CCD. It has fundamentally transformed the whole of observational astronomy and very large sections of terrestrial and marine biology. The study and application of nanoscience no less than progress in nanotechnology have likewise been revolutionized by the CCD, which is an ultrasensitive detector that picks up extremely low levels of light ranging from the infra red to the visible, the ultra violet and even X-rays. It is more than a thousand times more sensitive than the most sensitive photographic plate, which is why it is nowadays the basis of modern digital and video cameras, optical scanners and camcorders, as well as spectrometers, fax machines and other high performance imaging facilities that are these days a part of mobile phones. (One million chil-

Catalyzed Radical Polymerization of Styrene Vapor on Nanoparticle Surfaces and the Incorporation of Metal and Metal Oxide Nanoparticles within Polystyrene Polymers

We present a novel approach to polymerize olefin vapors on the surfaces of metallic and semiconductor nanoparticles. In this approach, a free radical initiator such as AIBN is dissolved in a volatile solvent such as acetone. Selected nanoparticles (prepared separately using the laser vaporization-controlled condensation method) are used to form initiator-coated nanoparticles placed on a glass substrate. The olefin (styrene) vapor is polymerized by the thermally activated initiator on the nanoparticle surfaces. Our approach also provides structural and mechanistic information on the early stages of catalyzed gas-phase polymerization, which can be used to correlate the gas-phase structural properties with the bulk properties and the performance of the polymer nanocomposites. This correlation is the key step in controlling the properties of the polymer nanocomposites. Our results clearly demonstrate the success of this method in preparing polymer coated nanoparticles for a variety of interesting applications. The precise control of the chemical functionality, thickness, and morphology of the polymer film and the size, size distribution, and properties of the core nanoparticles (photoluminescence, magnetic) may lead to major technological breakthroughs in a variety of applications including drug delivery, ultrasensitive detectors, and chemical and biological sensors.

Theory of a Josephson junction parallel array detector sensitive to very weak signals

An array of coupled short junctions (Josephson junction parallel array) is shown to be able to response to ultra-weak signals when it is worked at the onset of nonlinear supratransmission in the hysteresis loop of bistability. The theory is based on the fundamental solutions of the continuous limit (the sine-Gordon equation on the finite interval submitted to Neuman boundary conditions) that result from synchronization and adaptation to the external driving. This provides the solution to a problem that dates back to 1986 [O. H. Olsen and M. R. Samulsen, Phys. Rev. B34, 3510 (1986)], namely the complete analytical understanding of the bistability in a long Josephson junction or in an array of short junctions. The property allows to conceive ultrasensitive detectors or else, by convenient modulation of the seed, efficient digital amplifiers. Numerical simulations reveal that such a bistable behavior occurs also in two-dimensional lattices where no theory is available yet.

Polymer-Silicon Microcantilevers Serve as Ultrasensitive IR Detectors

Polymer-Silicon Microcantilevers Serve as Ultrasensitive IR Detectors

Kinetic Inductance Detectors for Mass Spectroscopy

Mass Spectroscopy (MS) is a powerful analysis tool used for the study of DNA and Proteins. Recently, Time of Flight (ToF) MS instrumentation based on superconductive detectors, namely Transition Edge Sensors (TES) or Superconducting Tunnel Junctions (STJ), have been proposed because they feature a good efficiency even for high masses molecules, which have very low speed. This is due to the fact that both STJ and TES provide a signal that is proportional to the kinetic energy rather than the speed. However, TES and STJ require a low operating temperature (0.1 K) and are relatively slow, which in a ToF-MS translates directly to degraded mass resolution. We propose a different type of detector: the Kinetic Inductance Detector, which has been successfully investigated as an ultra-fast and ultra-sensitive optical detector. This detector has a very fast time response (sub ns), thus providing a very good mass resolution, and shares with the other superconductive detectors the independence on the mass value. Moreover, it could operate at higher temperature (in the 2-4 K range). We have investigated different configurations of kinetic inductance detectors for MS, alone and in combination with Josephson devices, and report on the expected performances.

Ultrasensitive femtosecond two-photon detector with resonantly enhanced nonlinear absorption

We report on two-photon detection based on nonlinear absorption between subbands in quantum wells. Resonantly enhanced nonlinear absorption, 6 orders of magnitude higher than that of typical bulk semiconductors, leads to a threshold power density for quadratic detection as low as 0.1 W/cm2 and to femtosecond time resolution. The approach facilitates dynamic characterization of the optical light field of infrared emitters with unprecedented sensitivity. We also present a new method for determining the intersubband and intrasubband scattering times by means of autocorrelation measurements.

FRET-FCS as a tool to evaluate the stability of oligonucleotide drugs after intracellular delivery

The intracellular degradation of single-stranded, double-labeled oligonucleotides (ONs) was studied by following the disappearance of Fluorescence Resonance Energy Transfer (FRET) between the rhodamine green and Cy5 fluorophores attached to respectively the 3′ and 5′ end of the ONs. The green and red fluorescence intensities upon rhodamine green excitation were monitored using the ultra-sensitive detectors of a dual-color Fluorescence Correlation Spectroscopy (FCS) instrument. The ratio of the red to green fluorescence (R/G ratio) as obtained from such FRET-FCS measurements showed to give accurate information on the integrity of the ONs, without the need for additional auto- or cross-correlation analysis of the registered fluorescence intensity fluctuations. Intracellular measurements revealed that most of the 40mer phosphodiester ONs were degraded before they entered the nucleus. For the 20mer phosphodiester ONs, this degradation occurred more slowly, and both intact and degraded ONs entered the nucleus. For the 20mer phosphorothioate ONs, no intracellular degradation was observed during the measured time period. The sensitive detection of the intracellular fluorescence by the FCS setup will be particularly useful in situations where the expected fluorescence is too low to be detected by FRET-imaging as may occur after intracellular delivery of ONs by cationic carriers.

Development and operation of the twin radio frequency single electron transistor for cross-correlated charge detection

Ultrasensitive detectors and readout devices based on the radio frequency single electron transistor (rf-SET) combine near quantum-limited sensitivity with fast operation. Here we describe a twin rf-SET detector that uses two superconducting rf-SETs to perform fast, real-time cross-correlated measurements in order to distinguish subelectron signals from charge noise on microsecond time scales. The twin rf-SET makes use of two tuned resonance circuits to simultaneously and independently address both rf-SETs using wavelength division multiplexing and a single cryogenic amplifier. We focus on the operation of the twin rf-SET as a charge detector and evaluate the cross talk between the two resonance circuits. Real-time suppression of charge noise is demonstrated by cross correlating the signals from the two rf-SETs. For the case of simultaneous operation, the rf-SETs had charge sensitivities of δqSET1=7.5μe∕Hz and δqSET2=4.4μe∕Hz.

A low-angle X-ray scatter breast-imaging system based on a novel multi-element Si-pad array operated in spectroscopic mode

A novel multi-element Si-pad array operated in spectroscopic mode was designed in collaboration with Sintef to measure low-angle X-ray scattered photons in the energy range of 12–45 keV with an FWHM energy resolution of about 4 keV. This detector is used as the ultra-sensitive diffraction detector in a dual-sensor X-ray breast-imaging scanning system. Each detector is wire-bonded to a high-density low-noise XA1.3 readout chip designed by IDE AS. A new DAQ system was also developed to be used in conjunction with the detector and the readout electronics. Results regarding the characterization of this new Si-pad detector and its performance to measure scattering signatures of several materials of interest are presented.