Optofluidic Plasmonics for Sensing Applications
Y. Fainman, Department of Electrical and Computer Engineering, 0407, University of California, San Diego, La Jolla, California 92093-0407
Next-generation optical sensing technologies are expected to have strong applications in biomedical, environmental, defense, chemical process control and manufacturing, and automotive markets. Surface plasmon resonance has been investigated and exploited for label-free detection of versatile biochemical reactions, but current approaches may not scale to the throughputs required by numerous applications. We conducted a study of surface plasmon resonance in two-dimensional nanohole arrays for high throughput sensing applications. We used ultrashort laser pulses for excitation, visualization and detection of surface plasmon polariton (SPP) waves amplitude and phase. For this study we investigate mode structures in metal-dielectric nanostructures made of nanohole arrays in metal films of different thickness (20-100 nm) and nanohole diameter (50-300 nm) for various substrates (glass, Si, GaAs). Specifically, we investigated ultrafast electrodynamics of SPPs and performed phase control of the surface wave via control of opticsl phase. Recently, the results of our studies on excitation, propagation and scattering of the SPP fields in 2-D nanohole arrays have been used in realizing a high spectral resolution surface plasmon polariton resonance sensor that operates at normal or near normal incidence facilitating high spatial resolution imaging. The samples for our SPP sensor experiments are fabricated by depositing gold films on a glass substrate followed by holographic lithography to achieve large usable areas (~1 cm2). A PDMS mold with microfluidic delivery channel 1cm x 2 mm x 100 m is then bonded to the substrate by oxygen plasma. The angular and spectral transmittance of the structure is modified from a Fano type to a pure Lorentzian lineshape with a parallel and orthogonal polarizer-analyzer pair. This change leads to a linewidth narrowing that maximizes the sensor resolution, which we show to be of O(10-5) refractive index units (RIU). We estimate the potential of this system to be better than O(10-6) RIU under optimal conditions. Most recent results on dynamic detection of biochemical reactions will be also presented.
Nanoscale Imaging of Excitons in Heterostructured Semiconductor Nanorods
Uri Banin, Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, Israel 91904; uri.banin@huji.ac.il
Semiconductor nanocrystals manifest unique size, shape and composition dependent properties with both basic and applied significance and are emerging building blocks of devices in Nanotechnology. An example concerns the use of highly emitting core/shell nanoparticles as targeted markers for cancer cells and as biological sensors. An important frontier in nanocrystal synthesis concerns the growth of heterostructures of different materials in the same nanostructure as means of increasing functionality. An interesting combination is that of two semiconductors where a seeded growth approach can be used to create rod shaped particles with either type I or type II band-alignment. Using different seed dot particles, we describe growth of either types of rod architectures. The use of optical spectroscopy along with STM and STS (scanning tunneling spectroscopy), was implemented to reveal the electronic properties and measure the band-offsets in these systems. Optically, the characteristics of these structures depend both on the seed and the shell. Whilst the absorption happens mostly in the shell, the emission wavelength is mostly determined by the band gap energy of the spherical seed. We also explore the characteristics of the exciton in a CdSe/CdS nanorod. In our samples, the seed size is approximately 3nm, and the rod length varies between 40-100nm, far below the optical diffraction limit. Therefore, apertureless near-field scanning optical microscopy (ANSOM), along with time resolving capabilities, is used to produce optical imaging and spectroscopy measurements of single nanorods. The strong distance dependent energy transfer between the excited particle and a metallic coated AFM tip provides a contrast mechanism for sub-diffraction limited optical imaging. These optical images are fully synchronized with the AFM scan, which enables us to correlate the optical image with the nanorod topography and resolve the exciton location with sub-20nm resolution.
Measurement of Membrane Potential with Ultrahigh Sensitivity and Resolution
Aaron Lewis, Department of Applied Physics, The Hebrew University of Jerusalem, Givat Ram, 91904, Jerusalem, Israel
This lecture will emphasize the importance of reduction in background for achieving new sensing capabilities. An interplay between methodologies based on spatial and spectral background reduction will be highlighted in order to reach the sensing goals that are the focus of this lecture.
The Unexplored Avenues of Human Skin Electromagnetic Properties in the Sub THz band
Yuri Feldman, Alexander Puzenko, Paul Ben Ishai, Andreas Caduff, and Aharon J. Agranat, Department of Applied Physics, The Hebrew University of Jerusalem, Givat Ram, 91904, Jerusalem, Israel
Recent studies of the minute morphology of the skin by optical coherence tomography showed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. This, together with the fact that the dielectric permittivity of the dermis is higher than that of the epidermis, brings forward the supposition that as electromagnetic entities, the sweat ducts could be regarded as imperfect helical antennas. Inherent to this supposition is the requirement that the duct possesses an electrical conductance mechanism, most probably proton hopping along H-bond networks that occurs in an extremely high frequency (EHF) range (75 – 600 GHz). Experimental evidence is presented that the spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure [Yu. Feldman, et al., PRL, 100, 128102 (2008).]. The results reported in this paper present a basis for an interpretation of these observations, to which no satisfactory explanation has hitherto been offered. Furthermore, these results lead to the conception of a generic technology for real time remote sensing of biometric parameters such as the pulse rate and the blood pressure. As such this technology can become the basis for applications in the homeland security and biomedical engineering arenas.
Dendritic spine-like gold protrusions improve the adherence and electrical coupling of neurons with the surface of micro-electronic devices
M.E. Spira and A. Hai, Department of Neurobiology. The Life Sciences Institute, The Hebrew University of Jerusalem, Israel
Integration of neurons with microelectronic devices has been a subject of intense studies over the last decade. One of the major problems in assembling efficient neuro-electronic hybrid systems is the weak electrical coupling between the components. This is mainly attributed to the fundamental property of living cells to form and maintain an extracellular cleft between the plasma membrane and any substrate to which they adhere. This cleft shunts the current generated by propagating action potentials and thus reduces the signal-to-noise ratio. Reducing the cleft thickness and thereby increasing the seal resistance formed between the neurons and the sensing surface is thus a challenge and could improve the electrical coupling coefficient. Using electron microscopy analysis and field potential recordings, we examined here the use of gold micro-structures which mimic dendritic spines in their shape and dimensions to improve the adhesion and electrical coupling between neurons and microelectronic devices. We found that neurons cultured on gold-spine, functionalized by a cysteine terminated peptide with a number of RGD repeats, readily engulf the spines, forming tight membrane-spine apposition. The field potentials generated by action potentials of cultured Aplysia neurons are significantly larger in neurons cultured on gold spines in comparison with the field potentials recorded by flat electrodes.
Whole-cell bacterial biochips for environmental monitoring
Shimshon Belkin, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
In recent years we have promoted the use of whole cell biosensors: natural or genetically engineered live cells that sensitively report on the presence of either pre-determined classes of chemicals, or on the general toxicity of the sample. By using live cells we are able to detect the very complex series of reactions that can exist only in an intact, functioning cell. Only a sensor of this type can report on the “well being” of a system, on the toxicity of a sample, the genotoxicity of a chemical or the bioavailability of a pollutant. No molecular recognition or chemical analysis can provide this type of information. To turn such cells into usable biosensors, they need to be immobilized onto a solid platform and coupled into a signal transduction apparatus. We have previously described the integration of the genetically engineered reporter cells into a disposable biochip, which is inserted into a prototype “toxicity analyzer”. The instrument is equipped with micro-fluidics components for water sampling, with optical systems for signal generation and imaging, and with the necessary electronics for data processing, analysis and communication. In the present communication we describe several new directions which were undertaken in the continuation of this research. These include the development of flow-through biochips for on-line water toxicity monitoring, printable microbial sensor arrays, the detection of toxic oxidative activity of CdSe quantum dots and electrochemical detectors of genotoxicity.
Compression, chemometrics and coherence in computational optical sensors
David Brady, Duke University, Durham NC, USA
Computational optical sensors based on co-design of physical coding and sampling interfaces and application specific signal estimation and analysis algorithms achieve revolutionary improvements in data efficiency, target specificity and multidimensional analysis. This talk describes fundamental limits for computational optical sensors and illustrates system capacity using as examples thin imagers developed under the DARPA MONTAGE program and coded aperture snapshot spectral imagers (CASSI). We focus in particular on SNR and chemometric fidelity of nonlinear estimation algorithms from parallel linear optical measurements and on the detailed structure of instrument functions for generalized sampling. We also focus on novel optical components (microlens arrays, plasmonic and thin film filters, coded apertures) in emerging computational sensor systems.
Real-time intraoperative navigation in neurosurgery
Prof. Leo Joskowicz, CASMIP Lab -- Computer-Aided Surgery and Medical Image Processing Laboratory, School of Engineering and Computer Science, The Hebrew University of Jerusalem, Israel.
This talk will address accuracy and uncertainty issues in a real-time intraoperative navigation system based on optical tracking currently in clinical use. We will briefly describe the system, the set-up and report our latest findings regarding the target and fiducial registration error. Joint work with PhD student Ruby Shamir and Dr. Yigal Shoshan from the Hadassah-Ein Karem University Medical Center.
Ultra-Miniature, Functional Endoscopy
Dvir Yelin, The Department of Biomedical Engineering, The Technion, Haifa, Israel
Small diameter endoscopes are limited in their ability to provide sufficient image quality and functionality for accurate medical diagnosis. Spectrally encoded endoscopy (SEE), a recently introduced approach for imaging through a single optical fiber, combines high quality imaging and sub-millimeter probe diameters by utilizing a miniature lens-grating combination at the distal end of an endoscope. With no rapid scanning mechanism inside the body, SEE enables three-dimensional, video-rate imaging through probes that can be as thin as the optical fiber itself. Utilizing low-coherence interferometry, SEE is capable of sub-surface Doppler imaging, which may be useful for many clinical applications that require safe, minimally invasive functional imaging of hard-to-reach locations in the body.
Coherence sensing – saving lives
Michal Balberg, Ornim Medical Ltd, Global Park, Lod, Israel
Non invasive optical sensing, based on near infrared spectroscopy, has revolutionized patient management by providing a quantitative measure of arterial blood oxygen saturation‐ i.e. pulse oximetry. In critical care, there is a need for a continuous, non invasive, and quantitative monitor of tissue vitality. Ornim Medical is developing a novel tissue vitality monitor, based on its proprietary technology: ultrasound‐tagged‐ light (UTLightTM) . The technology exploits the benefits of the acousto‐optic effect, spectroscopy, and coherence properties of light in tissue. This technology enables localized, non‐invasive measurement of oxygen saturation, blood flow and hemoglobin saturation that provide physicians with a multi‐modal assessment of tissue vitality. I will present the technology, the science behind it, and the clinical data we have collected demonstrating its benefits.