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Organic thin-film transistor (OTFT) sensors based on a diketopyrrolopyrrole–thiophene polymer (PDQT) were fabricated to detect putrescine (PUT) vapors in air. Electrical properties and film characteristics of the sensors were examined with IV characterization, AFM and XRD. Upon PUT exposure, PDQT sensors showed fast responses and quick recovery. Two groups of sensors with different active layer thickness were compared for stability and sensitivity. Although with less stability under ambient conditions, sensors with thinner layers showed high sensitivity toward PUT with detection limit of 3 ppb. The group with thicker layers exhibited ideal long-term stability through 8 weeks of air storage along with proper reusability and reproducibility. The PDQT sensors showed a selectivity toward ammonia and biogenic amines. A preliminary test with food samples was carried out where PDQT sensors gave promising responses toward food-emitted vapors. Such sensors might be used in real-time freshness monitoring with further modification to lower the operational voltage and improve the stability. [ABSTRACT FROM AUTHOR]

A honeycomb-like micro-needle sensor with gold nanoparticles embedded for the determination of hexavalent chromium in seawater. [Display omitted] • A stainless steel micro-needle sensor with honeycomb-like structure was fabricated. • The honeycomb-like holes were embedded with gold nanoparticles. • The sensor showed high sensitivity and stability for the determination of Cr (VI). • The sensor was adopted for the determination of Cr (VI) in real seawater samples. As one of the most toxic heavy metals, hexavalent chromium (Cr(VI)) is a typical environmental pollutant that directly affects human health. In this work, a novel micro-needle sensor with honeycomb-like structure and embedded gold nanoparticles was proposed for the stable and sensitive determination of Cr(VI). The honeycomb-like structure provided larger specific surface area to support more gold nanoparticles which exhibited excellent catalytic activity towards the electrochemical reduction of Cr(VI) to Cr(Ⅲ). In addition, gold nanoparticles were embedded into the holes of the honeycomb-like structure, which can effectively prevent them from falling off from the electrode surface due to the protection of the holes. Combining the honeycomb-like structure of micro-needle electrode with the excellent catalytic activity of gold nanoparticles, the fabricated sensor exhibited outstanding stability and sensitivity for the cathodic stripping determination of Cr(VI). A linear range of Cr(VI) from 0.5 to 300 μmol/L was obtained, with the detection limit of 0.15 μmol/L. The recovery of the sensor for the determination of hexavalent chromium in seawater samples was also investigated. Moreover, the sensor might be further adapted for the determination of other heavy metals with different nanoparticles embedded. [ABSTRACT FROM AUTHOR]

Copper (Cu), a natural micronutrient with ecotoxicological significance, is involved in the carbon and nitrogen cycles occurring in marine ecosystems. Here, we developed a novel, antifouling gel-protected iridium (Ir) needle electrode modified with gold nanoparticles (G-IrNS) for long-term continuous and steady Cu monitoring. The gel formed an efficient membrane that effectively prevented the fouling of the sensing surface and displayed anti-convective properties, ensuring that mass transport toward the sensor surface was wholly controlled via diffusion. The repeatability, reproducibility, and stability of G-IrNS showed that it was suitable for long-term and on-site monitoring of Cu in seawater. Cu concentrations were successfully measured via fixed-point continuous monitoring for >2 weeks and onboard continuous monitoring in Bohai Sea using one sensor. Moreover, the relationship between Cu concentrations measured on-site via G-IrNS and its dissolved concentration in Bohai Sea was evaluated. G-IrNS can be applied to other metal ions as well, especially for long-term automatic on-site monitoring, thereby providing a basis for further research. [Display omitted] • An agarose gel-based antifouling iridium needle sensor was fabricated. • The sensor showed excellent long-term repeatability, reproducibility, and stability. • The long-term, on-site detection of Cu in seawater was realized using the sensor. • The speciation analysis of Cu in Bohai Sea based on the sensor was achieved. [ABSTRACT FROM AUTHOR]