Humidity Sensing Properties of Flower‐Like VO2(B) and VO2(M) Nanostructures

VO₂(B) nanoflowers were synthesized via hydrothermal method, and VO₂(M) nanoflowers were obtained through heat‐transformation. Two sensors based on VO₂(B) and VO₂(M) nanoflowers were fabricated and their humidity characteristics were studied. It was found that these sensors exhibited fast response and recovery, perfect reproducibility and good stability. The VO₂(M) type sensor is more sensitive at high RH and can be used for high humidity detection. On the contrary, the VO₂(B) type sensor has a higher sensitivity at low RH, and can be used for low humidity detection, which is difficult for humidity sensors based on many other semiconductor oxides.     

Discourse on the utilization of polyaniline coatings for surface plasmon resonance sensing of ammonia vapor

Surface plasmon resonance spectroscopy is sensitive to near-surface (<300 nm) chemical and physical events that result in refractive index changes. The non-specific nature of the stimulus implies that chemical selectivity in SPR sensing configurations entirely relies upon the chemical recognition scheme employed. Biosensing applications commonly use surface layers composed of antibodies or enzymes for biomolecular recognition. Monitoring of volatile compounds with SPR spectroscopy, however, has not been widely discussed due to the difficulty in selectively responding to small molecules (<100 Da) in addition to the limited refractive index changes resulting from the interaction between the plasmon wave and volatile compounds.Different strategies explored thus far for sensing of small molecules have relied on optical and electrical changes of the recognition layer upon exposure to the analyte, yielding an indirect measurement. Examples of coatings used for gas-phase sensing with SPR include conducting metal oxides, polymers and organometallic dyes. Electrically conducting polymers, like polyaniline and polypyrrole, display dramatic conductivity changes in the presence of certain compounds. This property has resulted in their routine incorporation into different sensing schemes. However, application of electrically conducting polymers to SPR gas-phase sensing has been limited to a few examples, despite encouraging results.The emeraldine salt form of polyaniline (PAni) demonstrates a decreased electrical conductivity correlated to NH₃ concentration. In this contribution, PAni doped with camphorsulfonic acid (PAni-CSA) was applied to gas-phase sensing of NH₃ by way of SPR spectroscopy. Spectroscopic ellipsometry was used to determine the optical constants (n and k) for emeraldine salt and emeraldine base forms of PAni, confirming the wavelength-dependent response observed via SPR. The analytical performance of the coatings show that a limit of detection of 32 ppm NH₃ based on precision of the mass-flow controllers used and an estimated method limit of detection of ∼0.2 ppm based on three standard deviations of the blank. This is directly comparable to other, more established sensing architectures.     

Rhodamine-based chemosensing monolayers on glass as a facile fluorescent “turn-on” sensing film for selective detection of Pb

Rhodamine-based chemosensors 1 and 2 were synthesized and self-assembled onto glass surfaces for the selective fluorescent sensing of Pb²⁺. The immobilized chemosensors showed fluorescent responses that were turned-on with Pb²⁺ in CH₃CN, selectively over various metal ions. The Pb²⁺-selective fluorescent switch of the immobilized chemosensors was also reversible, allowing for repeated use for Pb²⁺ detection.     

Helical binuclear Co complexes of pyriporphyrin analogue for sensing homochiral carboxylic acids

A hybrid macrocycle composed of two bipyridines and two dipyrrins gave biscobalt complexes of figure eight macrocycle conformation with κ²-carboxylate ligands and water ligands at the axial sites. The axial acetate ligands of the biscobalt complex are readily exchanged with carboxylates of α-hydroxyl acids and α-amino acids. The chiral center of the axial carboxylate ligands controls the helical handedness of the macrocycle as evidenced by a typical CD couplet at 550 nm. The substitution labile nature of the biscobalt complex plays a key role for helical chirality induction on the macrocycle upon co-ordination of chiral carboxylate anions.     

PDMS-based gold electrode for sensing ascorbic acid

Electrode with optical shapes is appreciated in microfluidics. In this article, we reported a flexible poly(dimethylsiloxane) (PDMS)-based gold electrode for ascorbic acid detection. Gold nanoparticles were chemically deposited on PDMS and the composite film was applied as working electrode. The electrode could undergo deformation and display good response performance without damage. This biosensor could give quick response to ascorbic acid (AA) (<5s) and the currents were linear with concentrations of AA in range of 0.023-7.00 mM and 30-100 mM, respectively. Limit of detection was 0.008 mM (S/N=3). This biosensor has been applied to determine ascorbic acid content in vitamin C tablets and the results were consistent with traditional iodometric method.     

水中油对水体上行辐亮度光谱的影响

目前,学者主要关注利用遥感技术探测海面油膜。然而,经海洋物理过程或人为喷洒化学分散剂处理形成的水中油对海洋生境也具有危害作用。水体上行辐亮度是水色传感器的重要信号源,通过分析含油水体的上行辐亮度光谱特征,探索快速有效地遥测水中油的方法对保护海洋生境具有重要意义。基于大连港海域现场实测数据及Hydrolight模拟含油水体水下光场,通过分析上行辐亮度随波长、水深及太阳天顶角的变化特征,剖析水中油对上行辐亮度光谱的影响及水中油的敏感光谱特性。结果表明水中油的主要波谱响应区间位于可见光波段（380~760 nm）。随着水中油浓度的增加,上行辐亮度光谱峰值有逐渐向长波方向移动及蓝光波段辐亮度量值逐渐降低的趋势,这些变化处于水色遥感的探测光谱范畴,为利用水色遥感技术探测水中油提供了光谱依据。其次,上行辐亮度随水深逐级递减,并在接近水体下界面前不降反升的现象说明刚好在水面之上的上行辐亮度由各深度水体组分的后向散射及下界面的反射共同贡献,再经水汽界面上行透射而得,属于水体辐射传输的核心机理。这与水面油膜通过油类物质改变海表反射率而产生与自然海表不同反射光谱的探测机理具有本质上的差别。再者,与含水中油水体后向散射产生的上行辐亮度相比,海表对太阳光的反射属于强信号,会掩盖水体组分信息。水色卫星搭载的水色传感器具有一定的侧摆能力,能避开太阳辐射反射信号并接收到含水中油水体的上行辐亮度;水色卫星的当地过境时间一般为10至14点,且水色传感器具有高信噪比特征,满足含水中油水体的暗像元探测要求。该研究揭示了水色遥感探测含水中油水体的光谱和机理依据,表明可以视水中油为一种新的水体组分,基于光在水体中的辐射传输过程,开展含水中油水体的水色遥感反演研究。     

Spectrum sensing in cognitive radio networks and metacognition for dynamic spectrum sharing between radar and communication system: A review

The massive growth in mobile users and wireless technologies has resulted in increased data traffic and created demand for additional radio spectrum. This growing demand for radio spectrum has resulted in spectrum congestion and mandated the need for coexistence between radar and interfering communication emitters. To address the aforementioned issues, it is critical to review existing policies and evaluate new technologies that can utilize spectrum in an efficient and intelligent manner. Cognitive radio and cognitive radar are two promising technologies that exploit spectrum using dynamic spectrum access techniques. Additionally, introducing the bio-inspired concept ‘metacognition’ in a cognitive process has shown to increase the effectiveness and robustness of the cognitive radio and cognitive radar system. Metacognition is a high-order thinking agent that monitors and regulates the cognition process through a feedback and control process called the perception–action cycle. Extensive research has been done in the field of spectrum sensing in cognitive radio and spectral coexistence between radar and communication systems. This paper provides a detailed classification of spectrum sensing schemes and explains how dynamic spectrum access strategies share the spectrum between radar and communication systems. In addition to this, the fundamentals of cognitive radio, its architecture, spectrum management framework, and metacognition concept in radar are discussed. Furthermore, this paper presents various research issues, challenges, and future research directions associated with spectrum sensing in cognitive radar and dynamic spectrum access strategies in cognitive radar.