Signal Enhancement of Pressure-Sensitive Film Based on Localized Surface Plasmon Resonance

Pressure-sensitive films have been used for measurement in micro flow, but thin films have very limited intensity, resulting in poor signal-noise ratio (SNR). This paper presents a pressure-sensitive film whose emission signal is enhanced by silver nanoparticles (AgNPs) based on localized surface plasmon resonance (LSPR). Electronic beam evaporator and annealing furnace are used to fabricate silver nanotexture surface. PtTFPP and polystyrene are dissolved in toluene and then spin-coated on the silver nanotexture surface to prepare the pressure-sensitive films. Signal enhancement of film with AgNPs due to LSPR is analyzed and enhancement effect of samples with different particle sizes and spacer thickness are compared. Pressure and temperature calibrations are performed to assess the sensing performance of pressure-sensitive films. Pressure-sensitive films with AgNPs demonstrate signal enhancement due to LSPR and show promise for measurement in micro flow.

The amount of light reaching the leaves in seagrass (Zostera marina) meadows

Seagrass meadows, and other submerged vegetated habitats, support a wide range of essential ecological services, but the true extents of these services are in many ways still not quantified. One important tool needed to assess and model many of these services is accurate estimations of the systems´ primary productivity. Such productivity estimations require an understanding of the underwater light field, especially regarding the amount of light that actually reaches the plants’ photosynthetic tissue. In this study, we tested a simple practical approach to estimate leaf light exposure, relative to incoming light at the canopy, by attaching light sensitive film at different positions on leaves of Zostera marina, eelgrass, in four seagrass meadows composed of different shoot density and at two different depths. We found that the light reaching the leaves decreased linearly down through the canopy. While the upper parts of the leaves received approximately the same level of light (photosynthetic photon flux density, PPFD) as recorded with a PAR meter at the canopy top, the average light that the seagrass leaves were exposed to varied between 40 and 60% of the light on top of the canopy, with an overall average of 48%. We recommend that actual light interception is measured when assessing or modelling light depending processes in submerged vegetation, but if this is not achievable a rough estimation for vegetation similar to Z. marina would be to use a correction factor of 0.5 to compensate for the reduced light due to leaf orientation and internal shading.

A Highly Sensitive Sensor of Methane and Hydrogen in Tellurite Photonic Crystal Fiber based on Four-Wave Mixing

A tellurite photonic crystal fiber (PCF) sensor structure is proposed for simultaneous measurements of the methane and hydrogen. The structure is a simple hexagonal three-cladding structure, and six air holes in the inner cladding are coated with methane-sensitive film and hydrogen-sensitive film respectively. Based on the degenerate four-wave mixing (DFWM) theory, the direct relationship between the wavelength shifts of Stokes spectrum or anti-Stokes spectrum and the variations of gas concentration can be established to realize the accurate detection of gas concentration. The influences of pump wavelength and gas-sensitive film thickness on the gas sensitivity are investigated, and the maximum sensitivity of methane and hydrogen after parameter optimization are -2.052nm/% and -0.236nm/%, respectively. The linearity of the fitting can reach up to 99.95%, and the low detection limit of methane is 450ppm and hydrogen is 2500ppm. The sensing method based on four-wave mixing in non-silica photonic crystal fiber also can be extended to other detections of gas-mixture in the mid-infrared field.

Thiol-Amine Functionalized Decorated Carbon Nanotubes for Biomarker Gases Detection

Thousands of gas molecules are expelled in exhaled breath, and some of them can reveal diseases and metabolomic disorders. For that reason, the development of fast, inexpensive, and reliable sensing devices has been attracting growing interest. Here, we present the development of different chemoresistors based on multi-walled carbon nanotubes (MWCNTs) decorated with platinum (MWCNT/Pt) and palladium (MWCNT/Pt) nanoparticles and also functionalized with a self-assembled monolayer (SAM) of 11-amino-1-undecanethiol (Thiol-amine). The nanocomposites developed are a proof-of-concept to detect some biomarker molecules. Specifically, the capability to identify and measure different concentrations of volatile organic compounds (VOCs), either aromatic (toluene and benzene) and non-aromatic (ethanol and methanol) was assessed. As a result, this paper reports the significant differences in sensing performance achieved according to the metal nanoparticle used, and the high sensitivity obtained when SAMs are grown on the sensitive film, acting as a receptor for biomarker vapours.

Hydrophobic Metal Organic Framework Enhanced Acoustic Wave Formaldehyde Sensor Based on Polyethyleneimine and Bacterial Cellulose Nanofilms

A surface acoustic wave (SAW) formaldehyde gas sensor was fabricated on a 42°75' ST-cut quartz substrate, with a composite sensing layer of zeolitic imidazolate framework (ZIF)-8 on polyethyleneimine (PEI)/ bacterial cellulose (BC) nanofilms. The addition of snowflake-like ZIF-8 structure on the PEI/BC sensitive film significantly improves the hydrophobicity of the SAW sensor and increases the sensor's sensitivity to formaldehyde gas. It also significantly increases the surface roughness of the sensitive film. Its hydrophobic nature prevents water molecules from entering into the internal pores of the BC film, thereby avoiding significant mass loading caused by the humidity change when the sensor is used to detect low-concentration formaldehyde gas. The Zn2+ sites at the surface of ZIF-8 improves the sensor's response to formaldehyde gas through enhancing the physical adsorptions. Experimental results show that the ZIF-8@PEI/BC SAW sensor has a response (e.g., frequency shift) of 40.3 kHz to 10 ppm formaldehyde gas at 25℃ and 30% RH. When the relative humidity was increased from 30% to 93%, the response (frequency shift) of the sensor drifts only ~5%, and there is negligible drift at a medium humidity level (~56% RH).