An Optical-Fiber-Based Airborne Particle Sensor.

A new optical-fiber-based airborne particle counter is reported. Unlike traditional light-scatter-based techniques, the particle is detected through the drop in optical fiber coupling efficiency as the particle disrupts the electromagnetic mode of the optical beam. The system is simple, substantially smaller than traditional systems, and does not require high power laser input. This makes it attractive for wearable air quality monitors where size is a premium. There is close agreement between theoretical model and experimental results for solid and liquid particles in the 1 to 10 µm range.

VO(2) based waveguide-mode plasmonic nano-gratings for optical switching.

In this paper, we present one dimensional plasmonic narrow groove nano-gratings, covered with a thin film of VO(2) (Vanadium Dioxide), as novel optical switches. These narrow groove gratings couple the incident optical radiation to plasmonic waveguide modes leading to high electromagnetic fields in the gaps between the nano-gratings. Since VO(2) changes from its semiconductor to its metallic phase on heating, on exposure to infra-red light, or on application of voltage, the optical properties of the underlying plasmonic grating also get altered during this phase transition, thereby resulting in significant switchability of the reflectance spectra. Moreover, as the phase transition in VO(2) can occur at femto-second time-scales, the VO(2)-coated plasmonic optical switch described in this paper can potentially be employed for ultrafast optical switching. We aim at maximizing this switchability, i.e., maximizing the differential reflectance (DR) between the two states (metallic and semiconductor) of this VO(2) coated nano-grating. Rigorous Coupled Wave Analysis (RCWA) reveals that the switching wavelengths - i.e., the wavelengths at which the values of the differential reflectance between VO(2) (S) and VO(2) (M) phases are maximum - can be tuned over a large spectral regime by varying the nano-grating parameters such as groove width, depth of the narrow groove, grating width, and thickness of the VO(2) layer. A comparison of the proposed ideal nano-gratings with various types of non-ideal nano-gratings - i.e., nano-gratings with non-parallel sidewalls - has also been carried out. It is found that significant switchability is also present for these non-ideal gratings that are easy to fabricate. Thus, we propose highly switchable and wide-spectra VO(2) based narrow groove nano-gratings that do not have a complex structure and can be easily fabricated.

A Wearable Hydration Sensor with Conformal Nanowire Electrodes.

A wearable skin hydration sensor in the form of a capacitor is demonstrated based on skin impedance measurement. The capacitor consists of two interdigitated or parallel electrodes that are made of silver nanowires (AgNWs) in a polydimethylsiloxane (PDMS) matrix. The flexible and stretchable nature of the AgNW/PDMS electrode allows conformal contact to the skin. The hydration sensor is insensitive to the external humidity change and is calibrated against a commercial skin hydration system on an artificial skin over a wide hydration range. The hydration sensor is packaged into a flexible wristband, together with a network analyzer chip, a button cell battery, and an ultralow power microprocessor with Bluetooth. In addition, a chest patch consisting of a strain sensor, three electrocardiography electrodes, and a skin hydration sensor is developed for multimodal sensing. The wearable wristband and chest patch may be used for low-cost, wireless, and continuous monitoring of skin hydration and other health parameters.

Custom visible to infrared, multi-wavelength light emitters for pulse oximeter applications.

Compact multi-wavelength light sources have been developed to provide flexibility in pulse oximeter device design. Advantages of these light sources include emitting light of multiple wavelengths with a constant ratio of intensity, and a co-linear light propagation path through tissue. These devices can function as normal pulse oximeter to determine oxygen saturation and pulse rate, but this approach potentially reduces circuit complexity, reduces motion artifacts and enables multi-wavelength sensing of different forms of hemoglobin or other blood products.

Patterned hybrid nanohole array surfaces for cell adhesion and migration.

We report the fabrication of hybrid nanohole array surfaces to study the role of the surface nanoevironment on cell adhesion and cell migration. We use polystyrene beads and reactive ion etching to control the size and the spacing between nanoholes on a tailored self-assembled monolayer inert gold surface. The arrays were characterized by scanning electron microscopy and brightfield microscopy. For cell adhesion studies, cells were seeded to these substrates to study the effect of ligand spacing on cell spreading, stress fiber formation, and focal adhesion structure and size. Finally, comparative cell migration rates were examined on the various nanohole array surfaces using time-lapse microscopy.

Plasmon resonances of gold nanoparticles incorporated inside an optical fibre matrix.

Metallic nanoparticles were incorporated into the core of standard telecommunication grade optical fibres. This creates a simple, yet robust, platform which can be used to investigate the properties of nanoparticles, for sensing, spectroscopy, and optical switching applications. The optical response of gold nanoparticles embedded in the optical fibre matrix was evaluated as a function of temperature and the use of the structure as an inline fibre-optic temperature sensor is described. A redshift in the localized surface plasmon (LSP) resonance related peak, as well as broadening of the plasmon resonance, was observed upon increasing the temperature of the nanoparticle containing fibre. The shift and broadening of the plasmon resonance were attributed to the temperature dependence of dielectric constants of metallic nanoparticles and the silica matrix and to plasmon-phonon interactions.