Polymeric Membrane Marine Sensors with a Regenerable Antibiofouling Coating Based on Surface Modification of a Dual-Functionalized Magnetic Composite.

Environmentally compatible polymeric membrane marine sensors with excellent antiadhesive and antibacterial properties have recently been developed. However, the regeneration abilities of these sensors after fouling have rarely been investigated. Herein, a novel strategy for preparation of a regenerable antibiofouling coating via surface modification of a dual-functionalized magnetic composite is proposed. A zwitterionic polymer (i.e., poly(sulfobetaine methacrylate)) and a quaternary ammonium compound (i.e., 3-trimethoxysilylpropyl octadecyldimethyl ammonium chloride) are coated on the surface of Fe3O4 microspheres for antiadhesion and bacterial inactivation, respectively. The antifouling magnetic composite can readily be modified on the sensor's surface via the magnetically assisted self-assembly technology. Using a polymeric membrane calcium ion-selective electrode as a model sensor, the protection layer-coated electrode shows the markedly improved antibiofouling activities as compared to the unmodified sensor. More importantly, by altering the direction of the external magnetic field, the antifouling coating can easily be removed after fouling along with the removal of the adsorbed bacterial cells from the electrode's surface, which is followed by re-modifying a fresh coating for regeneration of the antifouling electrode. The proposed methodology for fabrication of a regenerable antibiofouling coating is promising to improve the durability of a marine sensor.

Potentiometric aptasensing of Escherichia coli based on electrogenerated chemiluminescence as a highly sensitive readout.

We introduce here a versatile approach to read out potentiometric aptasensors by electrogenerated chemiluminescence (ECL), which can amplify the small potential changes induced by the bacterial concentrations via ECL signals. In the present system, the electrode modified with single-walled carbon nanotubes (SWCNTs) and aptamer molecules acts as the reference electrode and is placed in the sample solution for sensing the bacterial concentration changes, while the Ru(bpy)32+ modified gold electrode serves as the working electrode for generating ECL signals and is placed in the detection solution containing tripropylamine (TPA) spatially separated from the sample solution by a salt bridge. Ru(bpy)32+ is immobilized on the gold electrode's surface for enhancement of luminous efficiency and reduction of reagent consumption. A moving-part-free fluid flowing system is introduced to promote the mass transport of TPA from the detection solution to the surface of the ECL generating electrode. When a constant potential is imposed between the working and reference electrodes, the potential changes at the SWCNTs-aptamer modified electrode induced by the bacterial concentrations can modulate the potentials at the Ru(bpy)32+ modified electrode, thus generating the ECL signals. The developed sensing strategy shows a highly sensitive response to E. coli O157: H7 in the linear range of 5-1000 CFU mL-1 with a low detection limit of 2 CFU mL-1. We believe that the proposed approach is promising to develop aptasensors for sensitive detection of bacterial cells.

Melatonin treatment delays ripening in mangoes associated with maintaining the membrane integrity of fruit exocarp during postharvest.

The effects of exogenous melatonin on postharvest ripening of mango (Mangifera indica L. cv. Keitt) were investigated after the fruit were dipped in 0 (as the control), 100, or 200 µM melatonin solution for 30 min, and then stored at room temperature (25 ± 1 °C). The results showed that melatonin treatments could delay the ripening process as indicated by inhibition to softening, respiration, color change and chlorophyll degradation in fruit during storage. Notably, 200 µM melatonin treatment delayed the degradation of phosphatidylglycerol (PG) and phosphatidylinositol (PI), and the accumulation of phosphatidylserine (PS) and phosphatidic acid (PA) in membrane phospholipids, inhibited the decrease in unsaturated fatty acids (IUFA) index and also decreased the contents of H2O2 and malondialdehyde (MDA) in the exocarp of the fruit, which might collectively contribute to the integrity of the membrane associated with the delay in the ripening process of mango fruit during postharvest.

Enhancing the Oil-Fouling Resistance of Polymeric Membrane Ion-Selective Electrodes by Surface Modification of a Zwitterionic Polymer-Based Oleophobic Self-Cleaning Coating.

Due to the frequent oil spill accidents and pollution of industrial oily wastewater, oil fouling has become a great challenge to polymeric membrane ion-selective electrodes (ISEs) for applications in oil-contaminated areas. Herein, a simple approach is proposed to enhance the oil-fouling resistance of polymeric membrane ISEs by surface modification of a zwitterionic polymer-based underwater oleophobic coating. As a proof-of-concept, a classical poly(vinyl chloride) membrane-based calcium ion-selective electrode (Ca2+-ISE) is chosen as a model sensor. The zwitterionic polymer-based coating can be readily modified on the sensor's surface by immersion of the electrode into a mixture solution of dopamine and a zwitterionic acrylate monomer (i.e., sulfobetaine methacrylate, SBMA). The formed poly(SBMA) (PSBMA) coating alters the oleophilic membrane surface to an oleophobic one, which endows the surface with excellent self-cleaning properties without loss of the sensor's analytical performance. Compared to the pristine Ca2+-ISE, the PSBMA-modified Ca2+-ISE exhibits an improved analytical stability when exposed to oil-containing wastewater. The proposed approach can be explored to enhance the oil-fouling resistance of other polymeric membrane-based electrochemical sensors for use in the oil-polluted environment.

An ultra-sensitive electrochemical sensor of Ni/Fe-LDH toward nitrobenzene with the assistance of surface functionalization engineering.

Hypersensitive detection of organic pollutions with high toxicity in drinking water always keeps its challenge in electroanalysis due to their low concentration and electrochemical redox inert. In this work, a novel nanomaterial modified electrode for the sensitive detection of nitrobenzene (NB) is presented, based on environmental friendly and cost-effective Ni/Fe layered double hydroxides functionalized with sodium dodecyl sulfate (Ni/Fe(SDS)-LDH). Such 2D layered composites were prepared and used to improve the sensitivity for NB detection, due to its good catalytic activity for NB reduction. Besides, the proposed electrode shows a remarkably promoted sensitivity to NB compared to Ni/Fe-LDHs modified one. It is because that the surface modifier SDS can provide more adsorption sites to significantly improve the adsorption of NB, which has been confirmed by the adsorption experiment and the characterization of Fourier transform infrared spectroscopy (FTIR). As a result, an impressive sensing behaviour is achieved at the proposed Ni/Fe(SDS)-LDHs modified electrode with a sensitivity of 15.79 µA µM-1 cm-2. This work provides a promising way to build more advanced nanomaterials to electrochemical detection of organic pollution based on energetically synergizing of adsorption by surface functionalization engineering.

Self-Sterilizing Polymeric Membrane Sensors Based on 6-Chloroindole Release for Prevention of Marine Biofouling.

A self-sterilizing strategy based on antimicrobial organic agent release is proposed for polymeric membrane sensors to prevent marine biofouling. A solid-contact polymeric membrane calcium ion-selective electrode (Ca2+-ISE) is selected as a model sensor. 6-Cholorindole (6-Cl indole) is utilized as the biocidal agent due to its potential antimicrobial activity and environmental friendliness. The plasticized polymeric membrane doped with 6-Cl indole shows a markedly improved antimicrobial activity against the bacterial cells collected from seawater and effectively prevents the formation of a biofilm on the sensor surface, while displaying response properties (i.e., linear range, selectivity, and response time) similar to those of the undoped membrane. Importantly, the present sensor can preserve an improved antimicrobial activity when kept in the artificial seawater for 45 days, indicating highly stable antibacterial properties of the membrane electrode. Additionally, the 6-Cl indole-doped Ca2+-ISE exhibits no significant loss of analytical performance after exposure to a rather concentrated bacterial suspension (∼109 colony-forming units per mL (CFU mL-1)) for 7 days. The proposed antimicrobial agent release methodology can be extended to develop polymeric membrane-based marine sensors with stable biofouling resistances against bacterial colonization.

Improving the Environmental Compatibility of Marine Sensors by Surface Functionalization with Graphene Oxide.

Improving the durability relating to biofouling resistance is still a major challenge for sensors applied in marine monitoring. Herein, a novel antifouling approach implementing biofouling resistance without compromising the sensor's performance is proposed. A polymeric membrane calcium ion-selective electrode (Ca2+-ISE) is chosen as a model sensor. An antifouling coating based on graphene oxide (GO) can be formed on the sensor's surface via the layer-by-layer technique in a simple and controllable manner. The GO coating works as a protection layer to impede the settlement of marine bacterial cells on the sensor surface due to its dual functionality of both antiadhesive and antimicrobial properties. The assembly of the GO coating does not influence the sensor's performance in terms of linear range and response slope. The biofouling resistance of the proposed sensor to marine bacterial cells is evaluated by using the colony-forming unit (CFU) counting method and confocal laser scanning microscopy analysis. An improved antimicrobial activity and a significant decrease in the adsorption of bacterial cells are observed for the GO-coated Ca2+-ISE. Moreover, negligible change is observed in the analysis performance of the GO-coated Ca2+-ISE after 7 day exposure to a rather high concentration marine bacterial suspension of ∼109 CFU mL-1. This work provides an efficient strategy of developing GO-based antifouling coatings to improve the environmental compatibility of marine sensors.

Effect of eugenol fumigation treatment on chilling injury and CBF gene expression in eggplant fruit during cold storage.

The effect of eugenol (EUG) on chilling injury (CI) to eggplant fruit (Solanum melongena L.) was investigated. Eggplant fruit were pre-treated with 25 µL/L EUG, and then stored at 4 °C for 12 days. Results showed that EUG fumigation treatment effectively retarded the CI development, reduced pulp browning, weight loss, and malondialdehyde (MDA) content, and sustained soluble solids content (SSC) and proline content. Moreover, the activities of polyphenol oxidase (PPO) and peroxidase (POD) were inhibited by EUG. C-repeat/dehydration-responsive element binding factors (CBF) genes are transcription factors playing a critical role in cold acclimation. To illuminate the molecular regulation of EUG on chilling tolerance in eggplant fruit, a 1151 bp SmCBF gene was identified and the effect of EUG on SmCBF expression was determined by RT-qPCR. EUG resulted in a higher SmCBF expression. These findings suggested that EUG treatment had potential effect on alleviating CI in eggplant fruit.

High Electrochemical Sensitivity of TiO2- x Nanosheets and an Electron-Induced Mutual Interference Effect toward Heavy Metal Ions Demonstrated Using X-ray Absorption Fine Structure Spectra.

Mutual interference is a severe issue that occurs during the electrochemical detection of heavy metal ions. This limitation presents a notable drawback for its high sensitivity to specific targets. Here, we present a high electrochemical sensitivity of ∼237.1 µA cm-2 µM-1 toward copper(II) [Cu(II)] based on oxygen-deficient titanium dioxide (TiO2- x) nanosheets. We fully demonstrated an atomic-level relationship between electrochemical behaviors and the key factors, including the high-energy (001) facet percentage, oxygen vacancy concentration, surface -OH content, and charge carrier density, is fully demonstrated. These four factors were quantified using Raman, electron spin resonance, X-ray photoelectron spectroscopy spectra, and Mott-Schottky plots. In the mutual interference investigation, we selected cadmium(II) [Cd(II)] as the target ion because of the significant difference in its stripping potential (∼700 mV). The results show that the Cd(II) can enhance the sensitivity of TiO2- x nanosheets toward Cu(II), exhibiting an electron-induced mutual interference effect, as demonstrated by X-ray absorption fine structure spectra.

Competitive adsorption behavior toward metal ions on nano-Fe/Mg/Ni ternary layered double hydroxide proved by XPS: Evidence of selective and sensitive detection of Pb(II).

Hypersensitive and highly selective nanomaterials for the measurement of heavy metal ions (HMIs) hold a key to electro-analysis. Various works improved the results of analysis but without scientific understanding. Herein, Fe/Mg/Ni-layered double hydroxide (LDH) has been successfully prepared and its electrochemical behavior for Pb(II) detection is also studied using square wave anodic stripping voltammetry (SWASV). The well performance of electrochemistry suggest that the modification with Fe/Mg/Ni-LDH significantly promotes the selectivity and sensitivity toward Pb(II). The sensitivity on Fe/Mg/Ni-LDH modified glassy carbon electrode (GCE) is 68.1µAµM-1 over the range from 0.03 to 1.0µM under the optimized conditions. Otherwise, the selectivity, anti-interference, stability measurements and practical implications of Fe/Mg/Ni-LDH modified GCE are also performed. What,s more, a reasonable mechanism of detection for Pb(II) including selectivity and sensitivity is proposed based on adsorption and characterized using XPS and XRD. These findings provide a potentially excellent material to improve the sensitivity and selectivity for toxic metal ions as well as a deep understanding of detection.

In Situ Underwater Laser-Induced Breakdown Spectroscopy Analysis for Trace Cr(VI) in Aqueous Solution Supported by Electrosorption Enrichment and a Gas-Assisted Localized Liquid Discharge Apparatus.

Traditional laser-induced breakdown spectroscopy (LIBS) always fails to directly detect target in aqueous solution due to rapid quenching of emitted light and adsorption of pulse energy by surrounding water. A method is proposed for the in situ underwater LIBS analysis of Cr(VI) in aqueous solution freed from the common problems mentioned above by combining a gas-assisted localized liquid discharge apparatus with electrosorption for the first time. In this approach, the introduction of the gas-assisted localized liquid discharge apparatus provides an instantaneous gaseous environment for underwater LIBS measurement (that is, the transfer of sampling matrix is not needed from aqueous solution to dry state). The preconcentration of Cr(VI) is achieved by electrosorption with a positive potential applied around adsorbents, which can promote the adsorption of Cr(VI) and inhibit that of the coexisting cations leading to a good anti-interference. Amino groups functionalized chitosan-modified graphene oxide (CS-GO) is utilized for Cr(VI) enrichment, which can be protonated to form NH3+ in acidic condition promoting the adsorption toward Cr(VI) by electrostatic attraction. The highest detection sensitivity of 5.15 counts µg-1 L toward Cr(VI) is found for the optimized electrosorption potential (EES = 1.5 V) and electrosorption time (tES = 600 s) without interference from coexisting metal ions. A corresponding limit of detection (LOD) of 12.3 µg L-1 (3σ method) is achieved, which is amazingly improved by 2 or even 3 orders of magnitude compared to the previous reports of LIBS.

Electrochemical Detection of Trace Arsenic(III) by Nanocomposite of Nanorod-Like α-MnO2 Decorated with ∼5 nm Au Nanoparticles: Considering the Change of Arsenic Speciation.

It has been reported that the majority of groundwater shows weak alkaline in which the As(III) species would be present as neutral H3AsO3 species and ionized H2AsO3- species. However, as most reported previously, electrochemical detection of As(III) has been operated under acidic conditions and the nonionic As(III) (H3AsO3) is the dominant species. Therefore, considering the change of As(III) speciation in different pH conditions, to develop a reliable method for the detection of As(III) in alkaline media might be more meaningful for practical applications. Here, combined the multilayer adsorption of nanorod-like α-MnO2 with the excellent electrocatalytic ability of ∼5 nm Au nanoparticles (AuNPs), an efficient and ultrahigh anti-interference electrochemical detection of As(III) with AuNPs/α-MnO2 nanocomposite in alkaline media (nearly real water environment) was developed. Notably, we have provided a thorough electrochemical analytical investigation to confirm the advantage of As(III) detection in alkaline media. The system was evaluated by a series of interference tests, and no obvious interference from commonly coexisting substances (referring to the groundwater, Togtoh region, Inner Mongolia, China) was observed in alkaline media. Furthermore, electrodes robust stability and excellent reproducibility were obtained. Under the optimized conditions, the limit of detection (3σ method) toward As(III) was 0.019 ppb, and the obtained sensitivity was 16.268 ± 0.242 µA ppb-1 cm-2. Finally, the proposed method has been successfully employed for detection of As(III) in a real water sample.

Iron Oxide with Different Crystal Phases (α- and γ-Fe2O3) in Electroanalysis and Ultrasensitive and Selective Detection of Lead(II): An Advancing Approach Using XPS and EXAFS.

Iron oxide with different crystal phases (α- and γ-Fe2O3) has been applied to electrode coatings and been demonstrated to ultrasensitive and selective electrochemical sensing toward heavy metal ions (e.g., Pb(II)). A range of Pb(II) contents in micromoles (0.1 to 1.0 µM) at α-Fe2O3 nanoflowers with a sensitivity of 137.23 µA µM(-1) cm(-2) and nanomoles (from 0.1 to 1.0 nM) at γ-Fe2O3 nanoflowers with a sensitivity of 197.82 µA nM(-1) cm(-2) have been investigated. Furthermore, an extended X-ray absorption fine structure (EXAFS) technique was applied to characterize the difference of local structural environment of the adsorbed Pb(II) on the surface of α- and γ-Fe2O3. The results first showed that α- and γ-Fe2O3 had diverse interaction between Pb(II) and iron (hydro)oxides, which were consistent with the difference of electrochemical performance. Determining the responses of Cu(II) and Hg(II) as the most appropriate choice for comparison, the stripping voltammetric quantification of Pb(II) with high sensitivity and selectivity at γ-Fe2O3 nanoflower has been demonstrated. This work reveals that the stripping performances of a nanomodifier have to be directly connected with its intrinsic surface atom arrangement.

Pre-harvest application of oxalic acid increases quality and resistance to Penicillium expansum in kiwifruit during postharvest storage.

Kiwifruit (Actinidia deliciosa cv. Bruno) fruits were sprayed with 5mM oxalic acid (OA) at 130, 137, and 144 days after full blossom, and then harvested at commercial maturity [soluble solid content (SSC) around 10.0%] and stored at room temperature (20 ± 1 °C). Pre-harvest application of OA led to fruit with higher ascorbic acid content at harvest, slowed the decreases in fruit firmness and ascorbic acid content and increase in SSC during storage, and also decreased the natural disease incidence, lesion diameter, and patulin accumulation in fruit inoculated with Penicillium expansum, indicating that the OA treatment increased quality and induced disease resistance in kiwifruit. It was suggested that the increase in activities of defense-related enzymes and in levels of substances related to disease resistance might collectively contribute to resistance in kiwifruit against fungi such as P. expansum in storage.

Electroadsorption-assisted direct determination of trace arsenic without interference using transmission X-ray fluorescence spectroscopy.

An analytical technique based on electroadsorption and transmission X-ray fluorescence (XRF) for the quantitative determination of arsenic in aqueous solution with ppb-level limits of detection (LOD) is proposed. The approach uses electroadsorption to enhance the sensitivity and LOD of the arsenic XRF response. Amine-functionalized carbonaceous microspheres (NH2-CMSs) are found to be the ideal materials for both the quantitative adsorption of arsenic and XRF analysis due to the basic amine sites on the surface and their noninterference in the XRF spectrum. In electroadsorptive X-ray fluorescence (EA-XRF), arsenic is preconcentrated by a conventional three-electrode system with a positive electricity field around the adsorbents. Then, the quantification of arsenic on the adsorbents is achieved using XRF. The electroadsorption preconcentration can realize the fast transfer of arsenic from the solution to the adsorbents and improve the LOD of conventional XRF compared with directly determining arsenic solution by XRF alone. The sensitivity of 0.09 cnt ppb(-1) is obtained without the interferences from coexisted metal ions in the determination of arsenic, and the LOD is found to be 7 ppb, which is lower than the arsenic guideline value of 10 ppb given by the World Health Organization (WHO). These results demonstrated that XRF coupled with electroadsorption was able to determine trace arsenic in real water sample.

Fumigation with essential oils improves sensory quality and enhanced antioxidant ability of shiitake mushroom (Lentinus edodes).

Several naturally occurring essential oils were evaluated for their effectiveness in maintaining sensory quality and increasing antioxidant levels and activities in shiitake (Lentinus edodes) mushrooms. Freshly harvested mushrooms were fumigated with 5 µl l(-)(1) clove, cinnamaldehyde and thyme oils at 10 °C for 1.5h and the antioxidant activities determined using assays of H2O2 content, O2(-) production rate, DPPH, and ABTS radical scavenging activity. The results showed that the antioxidant activities of the mushrooms fumigated with cinnamaldehyde were significantly increased when compared to the controls. Moreover, cinnamaldehyde fumigation significantly delayed losses of phenolic compounds and enhanced flavonoid content. The essential oil fumigation treatment also increased the antioxidant enzyme activities of CAT, SOD, APX and GR throughout the storage periods. All the fumigation treatments were effective in retarding mushroom sensory deterioration. These results indicate that postharvest application of essential oil fumigation can extend the shelf life and enhance the antioxidant capacity of shiitake mushrooms.

Browning inhibition and quality preservation of button mushroom (Agaricus bisporus) by essential oils fumigation treatment.

The effect of essential oil fumigation treatment on browning and postharvest quality of button mushrooms (Agaricus bisporus) was evaluated upon 16 days cold storage. Button mushrooms were fumigated with essential oils, including clove, cinnamaldehyde, and thyme. Changes in the browning index (BI), weight loss, firmness, percentage of open caps, total phenolics, ascorbic acid, microbial activity and activities of polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) were measured. The results indicated that all essential oils could inhibit the senescence of mushrooms, and the most effective compound was cinnamaldehyde. Fumigation treatment with 5 µl l⁻¹ cinnamaldehyde decreased BI, delayed cap opening, reduced microorganism counts, promoted the accumulation of phenolics and ascorbic acid. In addition, 5 µl l⁻¹ cinnamaldehyde fumigation treatment inhibited the activities of PPO and POD, and increased PAL activity during the storage period. Thus, postharvest essential oil fumigation treatment has positive effects on improving the quality of button mushrooms.

Effect of alginate/nano-Ag coating on microbial and physicochemical characteristics of shiitake mushroom (Lentinus edodes) during cold storage.

The effect of a novel alginate/nano-Ag coating material on the preservation quality of shiitake mushroom (Lentinus edodes) during 4±1°C storage was investigated. The results showed that the alginate/nano-Ag coating had quite a beneficial effect on the physicochemical and sensory quality, compared to the control treatment. After a 16-day storage, mushroom weight loss, softening, and browning of the alginate/nano-Ag coating were significantly inhibited. The lower microbial counts, including mesophilic, psychrophilic, pseudomonad, and yeasts and moulds, in treated mushrooms during storage should be attributed to the alginate/nano-Ag coating. Meanwhile, the contents of the reducing sugar, total sugar, total soluble solids and electrolyte leakage rate were increased to 3.9mg/g, 11.2mg/g, 5.1% and 16.5% for the alginate/nano-Ag coating and 3.7mg/g, 8.3mg/g, 6.3% and 31.7% for the control treatment. Therefore, the alginate/nano-Ag coating could be applied for preservation of the shiitake mushroom to expand its shelf life and improve its preservation quality.

Physicochemical responses and microbial characteristics of shiitake mushroom (Lentinus edodes) to gum arabic coating enriched with natamycin during storage.

Physicochemical responses and microbial characteristics of shiitake mushroom (Lentinus edodes) to gum arabic (GA) coating incorporating natamycin (NA) during storage were investigated. Mushroom weight loss, firmness, total soluble solids, total sugar, reducing sugar, ascorbic acid, and microbial and sensory quality were measured. Mushroom coated with gum arabic+natamycin (GANA) maintained tissue firmness and showed reduction in microbial counts from yeasts and moulds compared with the control. In addition, GANA coating also delayed changes in the soluble solids concentration, total sugar and ascorbic acid. Sensory evaluation proved the efficacy of GANA coating by maintaining the overall quality of shiitake mushroom during the storage period. The efficiency was better than that of GA or NA treatment alone. Our study suggests that GANA has the potential to improve the quality of shiitake mushroom and extend its shelf-life up to 16d.

Effects of tea polyphenol coating combined with ozone water washing on the storage quality of black sea bream (Sparus macrocephalus).

The present research evaluated the effects of tea polyphenol (TP) combined with ozone water (O(3)) on the quality of black sea bream (Sparus macrocephalus) over a period of 15 days storage at 4°C. A solution of TP (0.2%, w/v) was used to coat the fish after washing with ozone water (1mg/L). Fish physicochemical (pH, K value, peroxide value, thiobarbituric acid, total volatile basic nitrogen, trimethylamine, texture, and colour), sensory, and bacteriological characteristics were all analysed. TP+O(3) treatment effectively reduced nucleotide breakdown, lipid oxidation, protein decomposition, and microbial growth, and maintained better characteristics of texture, colour, and sensory compared with the control. The efficiency of TP+O(3) treatment was also better than that of TP treatment or O(3) treatment alone. Therefore, tea polyphenol coating combined with ozone water prewashing may be a promising method of maintaining the storage quality of black sea bream and of extending fish post-mortem shelf-life during 4°C storage.