Novel gas sensor using polymer-film-coated quartz resonator for environmental monitoring

4-Hydroxy-2-nonenal, a lipid peroxidation product, as a biomarker in diabetes and its complications: challenges and opportunities

Over 30 million Americans are diagnosed with diabetes and this number is only expected to increase. There are various causes that induce complications with diabetes, including oxidative stress. In oxidative stress, lipid peroxidation-derived reactive carbonyl species such as 4-hydroxy-2-nonenal (4-HNE) is shown to cause damage in organs that leads to diabetic complications. We provided evidence to show that 4-HNE or/and 4-HNE-protein adducts are elevated in various organ systems of diabetic patients and animal models. We then discussed the advantages and disadvantages of different methodologies used for the detection of 4-HNE in diabetic tissues. We also discussed how novel approaches such as electrochemistry and nanotechnology can be used for monitoring 4-HNE levels in biological systems in real-time. Thus, this review enlightens the involvement of 4-HNE in the pathogenesis of diabetes and its complications and efficient methods to identify it. Furthermore, the article presents that 4-HNE can be developed as a biomarker for end-organ damage in diabetes such as diabetic cardiac complications.

Deep Reactive Ion Etching of Z-Cut Alpha Quartz for MEMS Resonant Devices Fabrication

Quartz is widely used in microelectromechanical systems (MEMS). Especially, MEMS quartz resonators are applied to sensors and serve as sensitive elements. The capability of deep etching is a limitation for the application. Presented in this paper is a deep and high accuracy reactive ion etching method applied to a quartz resonator etching process with a Cr mask. In order to enhance the capability of deep etching and machining accuracy, three kinds of etching gas (C₄F₈/Ar, SF₆/Ar and SF₆/C4F₈/Ar), bias power, inductively coupled plasma (ICP) power and chamber pressure were studied in an industrial reactive ion etching machine (GDE C200). Results indicated that the SF₆/C₄F₈/Ar chemistry gas is the suitable and optimal choice. Experiment results indicate that Cr (chromium) mask can obtain a higher selectivity than aluminum and titanium mask. A “sandwich” structure composed of Al layer-Cr layer-Al layer-Cr layer was proposed. The Al (aluminum) film can play the role of releasing stress and protecting gold electrodes, which can enhance the thickness of metal mask. An optimized process using SF₆/C₄F₈/Ar plasmas showed the quartz etching rate of 450 nm/min. Meanwhile, a microchannel with a depth of 75.4 µm is fabricated, and a nearly vertical sidewall profile, smooth surface is achieved.

Array-Assisted SERS Microfluidic Chips for Highly Sensitive and Multiplex Gas Sensing

A novel kind of array-assisted surface-enhanced Raman spectroscopy (SERS) microfluidic chip (ArraySERS chip) is demonstrated for gas sensing, which has the advantages of both ultrahigh sensitivity and multiplex sensing ability. On the one hand, the introduction of a microstructured triangular array can greatly increase the multiple collision probability between gas molecules and sensing interfaces in the channel. Compared with traditional gas sensors using sealed boxes, where gaseous molecules move only by diffusion, the ArraySERS chip exhibits significantly improved sensitivity. On the other hand, a composite nanoparticle is fabricated as a SERS probe for reading out the fingerprint spectral data, which consists of metal-organic framework (MOF) materials [Zeolitic Imidazolate framework-8 (ZIF-8)] and Au@Ag nanocubes, as well as cysteamine (CA) that serves as the gas-capturing agent. The experimental results show that such a structure of the SERS probe can further increase the sensing ability because of better adsorption of ZIF-8 for gas and the lower SERS background of CA itself. In addition, the simultaneous detection of multiplex gases was easily performed according to their own intrinsic SERS signals. Taking aldehyde gas as a model of a typical air pollutant, trace and multicomponent detection was realized using the ArraySERS chip. The limit of detection value was as low as 1 ppb, which is 2 magnitudes lower than that obtained by traditional methods. This strategy can be well extended for the detection of universal gases and help unleash the potential of existing gas sensors, especially for samples at low concentrations in air.

Optical Odor Imaging by Fluorescence Probes

Odor gas detection is important for the detection of explosives, environmental sensing, biometrics, foodstuffs and a comfortable life. Such odor-source localizations is an active research area for robotics. In this study, we tried to detect odor chemicals with an optical method that can be applied for the spatiotemporal detection of odor. We used four types of fluorescence dyes; tryptophan, quinine sulfate, acridine orange, and 1-anilinonaphthalene-8-sulfonate (ANS). As analyses, we measured the following four odor chemicals, 2-furaldehyde, vanillin, acetophenone, and benzaldehyde. The fluorescence-quenching mechanism of PET (Photoinduced Electron Transfer) or FRET (Fluorescence Resonance Electron Transfer), which occur between fluorescence dyes and odor compounds, could prevent unintended detection of various odorants that is caused by their unspecific adsorption onto the detecting materials. The fluorescence changes were then observed. Thus, we could detect the odor substances through fluorescent quenching by using the fluorescence dyes. Odor information could be obtained by response patterns across all the fluorescence dyes. Moreover, we captured odor images with a cooled CCD camera. Shapes of the targets that emitted odor could be roughly recognized by the odor-shape images. From the spatiotemporal images of odors, twodimensional odor expanse could be obtained.

Optical characterizations of ZnO, SnO2, and TiO2 thin films for butane detection

The optogeometric properties of various sensitive thin films involved in gas sensing applications are investigated by using the m-line technique and atomic force microscopy. Variations of these optical properties are studied under butane and ozone exposure.