Showing papers by "Lynford L. Goddard published in 2017"

Plasmonic Sensing of Oncoproteins without Resonance Shift Using 3D Periodic Nanocavity in Nanocup Arrays

Abstract: A sensor design and sensing method based on plasmonic–photonic interactions that occur when a nanocavity array is embedded in a 3D tapered nanocup plasmonic substrate are reported. This device enables highly sensitive detection of refractive index changes based on changes to the transmission peak intensity without shift in the resonance wavelength. Unlike conventional plasmonic sensors, there is a consistent and selective change in the transmission intensity at the resonance peak wavelength with no spectral shift. In addition, there are wavelength ranges that show no intensity change, which can be used as reference regions. The fabrication and characterization of the plasmonic nanocavity sensor are described and also advanced biosensing is demonstrated. Simulations are carried out to better understand the plasmon–photonic coupling mechanism. This nanocavity plasmonic sensor design has a limit of detection of 1 ng mL−1 (5 × 10−12m) for the cancer biomarker carcinoembryonic antigen (CEA), which is a significant improvement over current surface plasmon resonance systems, and a dynamic range that is clinically relevant for human CEA levels.

Realization of palladium-based optomechanical cantilever hydrogen sensor.

Abstract: Hydrogen has attracted attention as an alternative fuel source and as an energy storage medium. However, the flammability of hydrogen at low concentrations makes it a safety concern. Thus, gas concentration measurements are a vital safety issue. Here we present the experimental realization of a palladium thin film cantilever optomechanical hydrogen gas sensor. We measured the instantaneous shape of the cantilever to nanometer-level accuracy using diffraction phase microscopy. Thus, we were able to quantify changes in the curvature of the cantilever as a function of hydrogen concentration and observed that the sensor’s minimum detection limit was well below the 250 p.p.m. limit of our test equipment. Using the change in curvature versus the hydrogen curve for calibration, we accurately determined the hydrogen concentrations for a random sequence of exposures. In addition, we calculated the change in film stress as a function of hydrogen concentration and observed a greater sensitivity at lower concentrations. Finding out the remaining capacity in a hydrogen fuel cell stands to become risk-free using a cantilever developed by a US team. Although hydrogen gas is a lightweight and renewable form of energy, its flammability poses issues for conventional electrical sensors. A safer approach developed by Steven McKeown, Xiaozhen Wang, Xin Yu, and Lynford Goddard at the University of Illinois at Urbana-Champaign uses the flex of microscopic planks to sense hydrogen gas in real time. Coating these cantilevers with palladium—a metal that expands in the presence of hydrogen—produced different mechanical curvatures that were detectable by an all-optical, phase-contrast microscope. The resulting near-instantaneous snapshots of the cantilever shape could accurately quantify hydrogen concentrations throughout a randomized series of exposures, with a minimum detection limit below 250 parts per million.

Plasmonic nanocone arrays for rapid and detailed cell lysate surface enhanced Raman spectroscopy analysis

Abstract: In this work, we develop, fabricate, and characterize a plasmonic nanocone array surface enhanced Raman spectroscopy (SERS) substrate with a uniform enhancement factor on the micron scale for qualitative and quantiative cell and cell lysate analysis. This work demonstrates how SERS substrates can be used as cell-based biosensors given that the enhancement factor of the substrate is sufficient for Raman detection and that the uniformity is high over the applicable surface area. These requirements allow accurate and quantitative comparisons between nonuniform samples under varying biochemical conditions. We apply the developed SERS substrate for Raman measurements and mapping of HeLa cells and cell lysate. This method is used for identification of UV-induced damage and detection of nanomolar concentrations of methylated guanine spiked in cell lysate samples.

Label-free cell-substrate adhesion imaging on plasmonic nanocup arrays.

Abstract: Cell adhesion is a crucial biological and biomedical parameter defining cell differentiation, cell migration, cell survival, and state of disease. Because of its importance in cellular function, several tools have been developed in order to monitor cell adhesion in response to various biochemical and mechanical cues. However, there remains a need to monitor cell adhesion and cell-substrate separation with a method that allows real-time measurements on accessible equipment. In this article, we present a method to monitor cell-substrate separation at the single cell level using a plasmonic extraordinary optical transmission substrate, which has a high sensitivity to refractive index changes at the metal-dielectric interface. We show how refractive index changes can be detected using intensity peaks in color channel histograms from RGB images taken of the device surface with a brightfield microscope. This allows mapping of the nonuniform refractive index pattern of a single cell cultured on the plasmonic substrate and therefore high-throughput detection of cell-substrate adhesion with observations in real time.

Reflective Palladium Nanoapertures on Fiber for Wide Dynamic Range Hydrogen Sensing

Abstract: We present detailed experimental results on a reflective fiber sensor that is capable of accurately quantifying the hydrogen concentration over a wide dynamic range that spans from 1% down to 90 ppm. The sensor consists of a “C” shaped nano-aperture etched into the facet of a palladium coated optical fiber. Hydrogen changes the intensity and phase delay of the field reflected by the aperture differently than for the surrounding film and thus it greatly affects the total reflected intensity that results from the interference of these two fields. The initial phase difference between the two regions can be tuned to increase the sensitivity by over-etching the aperture.

Low-cost electroluminescence imaging for automated defect characterization in photovoltaic modules

Abstract: Electroluminescence (EL) imaging is a fast, well-established, laboratory characterization technique for photovoltaic (PV) mod ules that typically requires expensive equipment. Here, we p resent a novel low-cost extensible EL imaging technique that utilizes a modifled camera and auxiliary hardware to automate EL imaging of field-deployed PV modules.

Enhanced parallel bridge defect inspection using a metalens assisted off-focus scanning imaging

Abstract: A near-field metalens is utilized to assist a conventional brightfield microscope for significantly enhancing the signal-to-noise ratio associated with a parallel bridge defect on a 7 nm node patterned wafer.

Focusing properties of a cascaded asymmetric microstructure under Gaussian beam illumination

Abstract: We compare the focusing of Gaussian and plane wave illumination for a cascaded asymmetric microstructure. Although the Gaussian beam generates a longer and wider photonic nanojet, it can still focus efficiently for non-optimal microstructure geometries.

Characterization of lithium niobate microdisk resonators with grating couplers

Abstract: We present the design and characterization of lithium photonic microdisk resonators with grating couplers fabricated in lithium niobate thin-films. The Q-factor was 7.4 × 104 for a 75 μm diameter microdisk.

Monolithic integration of vertical SiN x microrings on a ridge waveguide to achieve multi-channel photonic coupling

Abstract: Multi-channel vertical photonic coupling was observed, by integrating two different SiN x vertical microring couplers (VμRC) monolithically on a single ridge waveguide. This work represents a critical step to 3D photonic integration using VμRC's.

Diffraction phase microscopy imaging and multi-physics modeling of the nanoscale thermal expansion of a suspended resistor.

Abstract: We studied the nanoscale thermal expansion of a suspended resistor both theoretically and experimentally and obtained consistent results. In the theoretical analysis, we used a three-dimensional coupled electrical-thermal-mechanical simulation and obtained the temperature and displacement field of the suspended resistor under a direct current (DC) input voltage. In the experiment, we recorded a sequence of images of the axial thermal expansion of the central bridge region of the suspended resistor at a rate of 1.8 frames/s by using epi-illumination diffraction phase microscopy (epi-DPM). This method accurately measured nanometer level relative height changes of the resistor in a temporally and spatially resolved manner. Upon application of a 2 V step in voltage, the resistor exhibited a steady-state increase in resistance of 1.14 Ω and in relative height of 3.5 nm, which agreed reasonably well with the predicted values of 1.08 Ω and 4.4 nm, respectively.