Smart packaging: sensors for monitoring of food quality and safety

The development of chemical sensors and biosensors over several decades has been investigated resulting in novel and very interesting sensor devices with great promise for many areas of applications including food technology. The incorporation of such sensors into the food packaging technology has resulted what we call smart or intelligent packaging. These are truly integrated and interdisciplinary systems that invoke expertise from the fields of chemistry, biochemistry, physics and electronics as well as food science and technology. Smart packaging utilises chemical sensor or biosensor to monitor the quality & safety of food from the producers to the costumers. This technology can result in a variety of sensor designs that are suitable for monitoring of food quality and safety, such as freshness, pathogens, leakage, carbon dioxide, oxygen, pH, time or temperature. Thus, this technology is needed as on-line quality control and safety in term of consumers, authorities and food producers, and has great potential in the development of new sensing systems integrated in the food packaging, which are beyond the existing conventional technologies, like control of weight, volume, colour and appearance.     

Analysis of reflectance spectra of tropical seagrass species and their value for mapping using multispectral satellite images

ABSTRACT

Mapping of the distribution of individual seagrass species is essential for any attempts to manage seagrass ecosystems. It is therefore important to understand how the spectra of different seagrass species vary, in order to establish their unique absorption features and how these can be utilised for mapping by making use of remote-sensing images. This paper presents measurements of the reflectance spectra between 400 and 900 nm for nine tropical species of seagrass. Continuum removal and multispectral resampling procedures were applied to the spectra. Dendrogram analysis was carried out to identify species clustering as the basis for a mapping scheme. Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) approaches were employed for the classification of seagrass species using WorldView-2 images and measured spectra as the input endmember. Classification Tree Analysis (CTA) and an image segmentation approach using CTA (Object-Based Image Analysis – OBIA) were performed as a means of comparison. The results indicate that the absorption features and overall shape of the spectra for all seagrass species are relatively similar, and implied that the major differences are attributable to the absolute reflectance values. Consequently, SAM and SID produced results of low accuracy (<30%), whereas, CTA and OBIA delivered results exhibiting higher accuracy (60–92%). The use of a spectral-based classification algorithm was ineffective for the classification and mapping of seagrass species using multispectral images. The utilisation of absolute reflectance values was beneficial for the classification of seagrass species having similar spectral shape.     

Effects of different metals on the synthesis and properties of waterborne polyurethane composites containing pyridyl units

This study used dicyclohexylmethane 4,4-diisocyanate, polybutylene adipate, polyether-1,3-diol, and 2,6-pyridinedimethanol to synthesize a novel water-based polyurethane (WPU) that contained pyridyl units. To enhance the thermal, mechanical, swelling, and antimicrobial properties of the WPU, various metals (silver nitrate, copper acetate, cobalt acetate, and zinc acetate) were incorporated to form WPU/metal composites. In addition, the study investigated the effects of the metal types on the WPU properties. Fourier transform infrared spectroscopy was used to confirm the synthesis of the WPU containing pyridine. Atomic force microscopy illustrated that the added metals increased the WPU surface roughness. The contact angle and degree of swelling tests demonstrated that the added metal reduced the WPU hydrophilicity, and with the addition of other metal types, the hydrophobicity increased considerably. Thermal gravimetric analysis indicated that the initial decomposition temperature of the highest WPU thermal stability was attributed to zinc. In addition, the results of differential scanning calorimetry and dynamic mechanical analysis showed that adding a small amount of metal increased the hard and soft segment glass transition temperatures. A universal strength tester validated that the WPU mechanical properties varied with the different metal additives and that the WPU strength increased. However, the WPU toughness and ductility decreased with the addition of metals; silver provided the highest mechanical strength. An antimicrobial test indicated that silver enhanced the antimicrobial property. The moisture permeability and waterproof property of the WPU coating was also analyzed.     

Interdiffusion effect on GaAsSbN/GaAs quantum well structure studied by 10-band k•p model

The effect of annealing on the photoluminescence (PL) in GaAsSbN/GaAs quantum well (QW) grown by solid-source molecular-beam epitaxy (SS-MBE) has been investigated. Low-temperature (4 K) PL peaks shift to higher energy sides with the increase of annealing temperature. An As-Sb atomic interdiffusion at the heterointerface is proposed to model this effect. The compositional profile of the QW after interdiffusion is modeled by an error function distribution and calculated with the 10-band k•p method. When the diffusion length equals to 1.4 nm, a corresponding transition energy blueshift of 36 meV is derived. This agrees with the experimental result under the optimum condition (750 °C at 5 min).     

Application of fluorescence emission ratio technique for transformer oil monitoring

In this work a new fluorescence emission measurement technology was introduced and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate it for the oil oxidation measurement of electrical insulating oil. The oxidation characteristics of insulating oil were found to be fairly represented by the titration method and IR spectroscopy, and the results are comparable to a change in the fluorescence emission ratio that is defined as the shift in fluorescence intensity in the measured wavelength range. The result also shows that by the measurement of fluorescence emission ratio, it is possible to detect the oxidation of oil relatively earlier than by other methods. This study suggests that the developed technology can provide sufficient information for evaluating the insulating oil quality, and that the developed FER sensor can be used as an effective condition monitoring device of electrical insulating oil oxidation.     

Growth of 1‐eV GaNAsSb‐based photovoltaic cell on silicon substrate at different As/Ga beam equivalent pressure ratios

We report the performance of 1‐eV GaNAsSb‐based photovoltaic samples grown on a Si substrate using molecular beam epitaxy at different As/Ga beam equivalent pressure (BEP) ratios. The light current–voltage curve and spectral response of the samples were measured. The sample grown at an As/Ga BEP ratio of 10 showed the highest energy conversion efficiency with an open circuit voltage (V_OC) of 0.529 V and a short circuit current density of 17.0 mA/cm². This measured V_OC is the highest ever reported value in GaNAsSb 1‐eV photovoltaic cell, resulting in the lowest ever reported E_g/q‐V_OC of 0.50 eV. The increase in the As/Ga BEP ratio also resulted in an increase in the bandgap‐voltage offset value (E_g/q‐V_OC) and a decrease in quantum efficiency up to As/Ga BEP ratio of 18. Copyright © 2015 John Wiley & Sons, Ltd.     

High-Gain Low Turn-On Voltage AlGaAs/GaAsNSb/GaAs Heterojunction Bipolar Transistors Grown by Molecular Beam Epitaxy

AlGaAs/GaAsNSb heterojunction bipolar transistors (HBTs) with low turn-on voltage have been fabricated. The turn-on voltage of the device fabricated from an as-grown sample is ~180 mV lower than that of a conventional AlGaAs/GaAs HBT. The effect of rapid thermal annealing on device performance is an increase in the gain from ~8.5 to ~20. However, the knee voltage of the annealed sample (~3 V), as well as the turn-on voltage, is also higher compared with that of the as-grown sample (~1.5 V).     

A proposed mechanism of action of textile/Al2O3–TiO2 bimetal oxide nanocomposite as an antimicrobial agent

The textile/Al₂O₃–TiO₂ bimetal oxide nanocomposite has been developed as an antimicrobial agent, but its antimicrobial mechanism has still not been clarified. The Al₂O₃–TiO₂ bimetal oxide nanoparticle has been reported as a radical scavenger. This study focuses on investigating the antimicrobial mechanism of the textile/Al₂O₃–TiO₂ bimetal oxide nanocomposite against Escherichia coli and their interaction with cell envelope biomolecules. L-α-Phosphatidyl ethanolamine (PE) is used as a model of bacteria to investigate the antimicrobial mechanism of this nanocomposite. The antimicrobial activity of the textile/Al₂O₃–TiO₂ bimetal oxide nanocomposite was investigated by using attenuated total reflectance/Fourier transform infrared (ATR-FTIR) and UV–Vis, while the toxicity of this nanocomposite was also examined through tissue culture test against a fibroblast skin cell. The ATR-FTIR used was able to confirm the destroyed cell envelope of the bacteria. The amounts of reactive oxygen species (ROS) were analyzed by UV–Vis spectroscopy and the toxicity of this nanocomposite was also examined by reacting tissue culture against the fibroblast skin cell. Overall, the antimicrobial mechanism of this textile nanocomposite was first by the attachment of this nanocomposite through the attachment of this nanoparticle to the surface of PE (as the model of bacteria) by hydrogen binding, and then nanoparticles can destroy the cell wall of bacteria through oxidation reaction by the produced ROS. Finally, these nanoparticles scavenged the ROS free radical. Therefore, the attached nanoparticles attached on textile can kill bacteria without any ROS free radical remaining in human body. These results suggest that the antimicrobial mechanism of this nanocomposite is mostly different due to the scavenger ability of this nanocomposite and its lower toxicity.     

Mangrove biomass carbon stock mapping of the Karimunjawa Islands using multispectral remote sensing

Among vegetated coastal habitats, mangrove forests are among the densest carbon pools. They store their organic carbon in the surrounding soil and thus the sequestered carbon stays in the sediment for a long time and cannot be easily returned to the atmosphere. Additionally, mangroves also provide various important ecosystem services in coastal areas and surroundings. Accordingly, it is important to understand the distribution of biomass carbon stock in mangrove habitats in a spatial and temporal context, not only to reduce CO₂ concentrations in the atmosphere, but also for their sustainability. The objectives of this research are to map the mangrove carbon stock and estimate the total biomass carbon stock sheltered by mangrove forests, with the Karimunjawa Islands as a study site, using the widely available passive remote sensing system ALOS AVNIR-2. The modelling and mapping of mangrove carbon stock incorporates the integration of image pixel values and mangroves field data via empirical modelling. Vegetation indices and PC bands at different levels of radiometric corrections were all used as the input in the mangrove carbon stock modelling so that the effectiveness and sensitivity of different image transformations to particular radiometric correction levels could be analysed and understood. Afterward, the accuracy and effectiveness of each mangrove carbon stock-mapping routine was compared and evaluated. The accuracy of the best mangrove above-ground carbon stock (AGC) map modelled from vegetation index is 77.1% (EVI1, SE 5.89 kg C m^?2), and for mangrove below-ground carbon stock (BGC) it is 60.0% (GEMI, SE 2.54 kg C m^?2). The mangrove carbon stock map from ALOS AVNIR-2 PC bands showed a maximum accuracy of 77.8% (PC2, SE 5.71 kg C m^?2) and 60.8% (PC2, SE 2.48 kg C m^?2) for AGC and BGC respectively. From the resulting maps, the Karimunjawa Islands are estimated to shelter 96,482 tonnes C of mangroves AGC with a mean value of 21.64 kg C m^?2 and 24,064 tonnes C of mangroves BGC with a mean value of 5.39 kg C m^?2. Potentially, there are approximately 120,546 tonnes C of mangrove biomass carbon stock in the Karimunjawa Islands. Remote-sensing reflectance can successfully model mangrove carbon stock based on the relationship between mangrove canopy properties, represented by leaf area index (LAI) and the tree or root biomass carbon stock. The accuracy of the mangrove carbon stock map is subject to errors, which are sourced mainly from: (1) the absence of a species-specific biomass allometric equation for several species present in the study area; (2) the generalized standard conversion value of mangrove biomass to mangrove carbon stock; (3) the relationship between mangrove reflectance and mangrove LAI; (4) the relationship between mangrove reflectance and above-ground mangrove biomass and carbon stock due to its relationship with LAI; (5) the relationship between mangrove LAI and mangrove below-ground parts; (6) the inability to perform mangrove carbon stock modelling at the species level due to the complexities of the mangrove forest in the study area; (7) background reflectance and atmospheric path radiance that could not be completely minimized using image radiometric corrections and transformations; and (8) spatial displacement between the actual location of the mangrove forest in the field and the corresponding pixel in the image. The availability of mangrove biomass carbon stock maps is beneficial for carrying out various management activities, and is also very important for the resilience of mangroves to changing environments.