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Histamine is commonly present in food containing proteins, like in mackerel. Consuming fish is imperative for the improvement of human muscles. Nevertheless, some studies reported ingesting fish containing histamine more than 50 mg·kg-1 can cause toxicity. This study analyzed and determined the composition of histamine in mackerel and its products commonly consumed in Malaysia, especially on the East Coast of Malaysia. These included processed mackerel such as canned products, satay (skewed fish) and keropok lekor (fish cake/ cracker). Histamine analysis was performed using High Performance Liquid Chromatography (HPLC) equipped with a fluorescence detector. A derivatizing reaction was applied to increase the sensitivity of HPLC to histamine using 9-flourenilmethylchloroformate (FMOC-Cl). The chromatographic separation was achieved in 15 min. Method validation was in accordance to Commission Decision 657/2002/CE. The linear range was at 0.16 – 5.00 μg·mL-1 (histamine) with the LOD at 0.10 μg·mL-1 and LOQ at 0.30 μg·mL-1. Method applicability was checked on seven real samples involving raw, cooked, and dry products, yielding acceptable recovery. [ABSTRACT FROM AUTHOR]

A novel electrochemical DNA biosensor for ultrasensitive and selective quantitation of Escherichia coli DNA based on aminated hollow silica spheres (HSiSs) has been successfully developed. The HSiSs were synthesized with facile sonication and heating techniques. The HSiSs have an inner and an outer surface for DNA immobilization sites after they have been functionalized with 3-aminopropyltriethoxysilane. From field emission scanning electron microscopy images, the presence of pores was confirmed in the functionalized HSiSs. Furthermore, Brunauer-Emmett-Teller (BET) analysis indicated that the HSiSs have four times more surface area than silica spheres that have no pores. These aminated HSiSs were deposited onto a screen-printed carbon paste electrode containing a layer of gold nanoparticles (AuNPs) to form a AuNP/HSiS hybrid sensor membrane matrix. Aminated DNA probes were grafted onto the AuNP/HSiS-modified screen-printed electrode via imine covalent bonds with use of glutaraldehyde cross-linker. The DNA hybridization reaction was studied by differential pulse voltammetry using an anthraquinone redox intercalator as the electroactive DNA hybridization label. The DNA biosensor demonstrated a linear response over a wide target sequence concentration range of 1.0×10-12-1.0×10-2 μM, with a low detection limit of 8.17×10-14 μM (R2 = 0.99). The improved performance of the DNA biosensor appeared to be due to the hollow structure and rough surface morphology of the hollow silica particles, which greatly increased the total binding surface area for high DNA loading capacity. The HSiSs also facilitated molecule diffusion through the silica hollow structure, and substantially improved the overall DNA hybridization assay.Step-by-step DNA biosensor fabrication based on aminated hollow silica spheres [ABSTRACT FROM AUTHOR]

The attractive structural and mechanical properties of cellulose substrates (paper, cloth, and thread), including passive fluid transport, biocompatibility, durability, and flexibility, have attracted researchers in the past few decades to explore them as alternative microfluidic platforms. The incorporation of electrochemical (EC) sensing broadened their use for applications such as clinical diagnosis, pharmaceutical chemical analyses, food quality, and environmental monitoring. This article provides a review on the microfluidic devices constructed on paper, cloth, and thread substrates. It begins with an overview on paper-based microfluidic devices, followed by an in-depth review on the various applications of EC detection incorporated on paper-based microfluidic devices reported to date. The review on paper-based microfluidic devices attempts to convey a few perspective directions that cloth- and thread-based microfluidic devices may take in its development. Finally, the research efforts on the development and evaluation, as well as current limitations of cloth- and thread-based microfluidic devices are discussed. Microfluidic devices constructed on paper, cloth, and thread substrates are still at an early development stage (prototype) requiring several improvements in terms of fabrication, analytical techniques, and performance to become mature platforms that can be adapted and commercialized as real world products. However, they hold a promising potential as wearable devices. [ABSTRACT FROM AUTHOR]

A fluorescence-based fiber optic toxicity biosensor based on genetically modified Escherichia coli (E. coli) with green fluorescent protein (GFP) was developed for the evaluation of the toxicity of several hazardous heavy metal ions. The toxic metals include Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(III). The optimum fluorescence excitation and emission wavelengths of the optical biosensor were 400 ± 2 nm and 485 ± 2 nm, respectively. Based on the toxicity observed under optimal conditions, the detection limits of Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(III) that can be detected using the toxicity biosensor were at 0.04, 0.32, 0.46, 2.80, 100, 250, 400, 720 and 2600 μg/L, respectively. The repeatability and reproducibility of the proposed biosensor were 3.5%-4.8% RSD (relative standard deviation) and 3.6%-5.1% RSD (n = 8), respectively. The biosensor response was stable for at least five weeks, and demonstrated higher sensitivity towards metal toxicity evaluation when compared to a conventional Microtox assay. [ABSTRACT FROM AUTHOR]

Biosensors fabricated with whole-cell bacteria appear to be suitable for detecting bioavailability and toxicity effects of the chemical(s) of concern, but they are usually reported to have drawbacks like long response times (ranging from hours to days), narrow dynamic range and instability during long term storage. Our aim is to fabricate a sensitive whole-cell oxidative stress biosensor which has improved properties that address the mentioned weaknesses. In this paper, we report a novel high-throughput whole-cell biosensor fabricated by immobilizing roGFP2 expressing Escherichia coli cells in a κ-carrageenan matrix, for the detection of oxidative stress challenged by metalloid compounds. The E. coli roGFP2 oxidative stress biosensor shows high sensitivity towards arsenite and selenite, with wide linear range and low detection limit (arsenite: 1.0 × 10-3-1.0 × 10¹ mg·L-1, LOD: 2.0 × 10-4 mg·L-1; selenite: 1.0 × 10-5-1.0 × 10² mg·L-1, LOD: 5.8 × 10-6 mg·L-1), short response times (0-9 min), high stability and reproducibility. This research is expected to provide a new direction in performing high-throughput environmental toxicity screening with living bacterial cells which is capable of measuring the bioavailability and toxicity of environmental stressors in a friction of a second. [ABSTRACT FROM AUTHOR]

In this article a luminescence fiber optic biosensor for the microdetection of heavy metal toxicity in waters based on the marine bacterium Aliivibrio fischeri (A. fischeri) encapsulated in alginate microspheres is described. Cu(II), Cd(II), Pb(II), Zn(II), Cr(VI), Co(II), Ni(II), Ag(I) and Fe(II) were selected as sample toxic heavy metal ions for evaluation of the performance of this toxicity microbiosensor. The loss of bioluminescence response from immobilized A. fischeri bacterial cells corresponds to changes in the toxicity levels. The inhibition of the luminescent biosensor response collected at excitation and emission wavelengths of 287 ± 2 nm and 487 ± 2 nm, respectively, was found to be reproducible and repeatable within the relative standard deviation (RSD) range of 2.4-5.7% (n = 8). The toxicity biosensor based on alginate micropsheres exhibited a lower limit of detection (LOD) for Cu(II) (6.40 μg/L), Cd(II) (1.56 μg/L), Pb(II) (47 μg/L), Ag(I) (18 μg/L) than Zn(II) (320 μg/L), Cr(VI) (1,000 μg/L), Co(II) (1700 μg/L), Ni(II) (2800 μg/L), and Fe(III) (3100 μg/L). Such LOD values are lower when compared with other previous reported whole cell toxicity biosensors using agar gel, agarose gel and cellulose membrane biomatrices used for the immobilization of bacterial cells. The A. fischeri bacteria microencapsulated in alginate biopolymer could maintain their metabolic activity for a prolonged period of up to six weeks without any noticeable changes in the bioluminescence response. The bioluminescent biosensor could also be used for the determination of antagonistic toxicity levels for toxicant mixtures. A comparison of the results obtained by atomic absorption spectroscopy (AAS) and using the proposed luminescent A. fischeri-based biosensor suggests that the optical toxicity biosensor can be used for quantitative microdetermination of heavy metal toxicity in environmental water samples. [ABSTRACT FROM AUTHOR]

A new silica-gel nanospheres (SiO2NPs) composition was formulated, followed by biochemical surface functionalization to examine its potential in urea biosensor development. The SiO2NPs were basically synthesized based on sol-gel chemistry using a modified Stober method. The SiO2NPs surfaces were modified with amine (-NH2) functional groups for urease immobilization in the presence of glutaric acid (GA) cross-linker. The chromoionophore pH-sensitive dye ETH 5294 was physically adsorbed on the functionalized SiO2NPs as pH transducer. The immobilized urease determined urea concentration reflectometrically based on the colour change of the immobilized chromoionophore as a result of the enzymatic hydrolysis of urea. The pH changes on the biosensor due to the catalytic enzyme reaction of immobilized urease were found to correlate with the urea concentrations over a linear response range of 50-500 mM (R² = 0.96) with a detection limit of 10 mM urea. The biosensor response time was 9 min with reproducibility of less than 10% relative standard deviation (RSD). This optical urea biosensor did not show interferences by Na+, K+, Mg2+ and NH4+ ions. The biosensor performance has been validated using urine samples in comparison with a non-enzymatic method based on the use of p-dimethylaminobenzaldehyde (DMAB) reagent and demonstrated a good correlation between the two different methods (R² = 0.996 and regression slope of 1.0307). The SiO2NPs-based reflectometric urea biosensor showed improved dynamic linear response range when compared to other nanoparticle-based optical urea biosensors. [ABSTRACT FROM AUTHOR]

A novel method for the rapid modification of fullerene for subsequent enzyme attachment to create a potentiometric biosensor is presented. Urease was immobilized onto the modified fullerene nanomaterial. The modified fullerene-immobilized urease (C60 -urease) bioconjugate has been confirmed to catalyze the hydrolysis of urea in solution. The biomaterial was then deposited on a screen-printed electrode containing a non-plasticized poly(n-butyl acrylate) (PnBA) membrane entrapped with a hydrogen ionophore. This pH-selective membrane is intended to function as a potentiometric urea biosensor with the deposition of C60-urease on the PnBA membrane. Various parameters for fullerene modification and urease immobilization were investigated. The optimal pH and concentration of the phosphate buffer for the urea biosensor were 7.0 and 0.5 mM, respectively. The linear response range of the biosensor was from 2.31 x 10-3 M to 8.28 x 10-5 M. The biosensor's sensitivity was 59.67 ± 0.91 mV/decade, which is close to the theoretical value. Common cations such as Na+, K+, Ca2+, Mg2+ and NH4+ showed no obvious interference with the urea biosensor's response. The use of a fullerene-urease bio-conjugate and an acrylic membrane with good adhesion prevented the leaching of urease enzyme and thus increased the stability of the urea biosensor for up to 140 days. [ABSTRACT FROM AUTHOR]

Background: A novel optical sensor for the rapid and direct determination of permethrin preservatives in treated wood was designed. The optical sensor was fabricated from the immobilisation of 2,6-dichloro-p-benzoquinone-4- chloroimide (Gibbs reagent) in nafion/sol-gel hybrid film and the mode of detection was based on absorption spectrophotometry. Physical entrapment was employed as a method of immobilisation. Results: The sensor gave a linear response range of permethrin between 2.56-383.00 μM with detection limit of 2.5 μM and demonstrated good repeatability with relative standard deviation (RSD) for 10 μM at 5.3%, 100 μM at 2.7%, and 200 μM at 1.8%. The response time of the sensor was 40 s with an optimum response at pH 11. Conclusions: The sensor was useful for rapid screening of wood or treated wood products before detailed analysis using tedious procedure is performed. The validation study of the optical sensor against standard method HPLC successfully showed that the permethrin sensor tended to overestimate the permethrin concentration determined. [ABSTRACT FROM AUTHOR]

Whole cell biosensors always face the challenge of low stability of biological components and short storage life. This paper reports the effects of poly(2-hydroxyethyl methacrylate) (pHEMA) immobilization on a whole cell fluorescence biosensor for the detection of heavy metals (Cu, Pb, Cd), and pesticides (dichlorophenoxyacetic acid (2,4-D), and chlorpyrifos). The biosensor was produced by entrapping the cyanobacterium Anabaena torulosa on a cellulose membrane, followed by applying a layer of pHEMA, and attaching it to a well. The well was then fixed to an optical probe which was connected to a fluorescence spectrophotometer and an electronic reader. The optimization of the biosensor using several factors such as amount of HEMA and drying temperature were undertaken. The detection limits of biosensor without pHEMA for Cu, Cd, Pb, 2,4-D and chlorpyrifos were 1.195, 0.027, 0.0100, 0.025 and 0.025 μg/L respectively. The presence of pHEMA increased the limits of detection to 1.410, 0.250, 0.500, 0.235 and 0.117 μg/L respectively. pHEMA is known to enhance the reproducibility of the biosensor with average relative standard deviation (RSD) of ±1.76% for all the pollutants tested, 48% better than the biosensor without pHEMA (RSD = ±3.73%). In storability test with Cu 5 μg/L, the biosensor with pHEMA performed 11.5% better than the test without pHEMA on day-10 and 5.2% better on day-25. pHEMA is therefore a good candidate to be used in whole cell biosensors as it increases reproducibility and enhances biosensor storability. [ABSTRACT FROM AUTHOR]

This paper reports the levels of polycyclic aromatic hydrocarbons (PAHs) in the water around the Island and their probable sources. Water samples were collected from four jetties and three marine fish farms around the main Langkawi Island and analysed for 18 polycyclic aromatic hydrocarbons (PAHs) in December 2010. The total PAH concentrations ranged from 6.1 ± 0.43 to 46 ± 0.42 µgL-1, which exceed the maximum admissible concentrations of PAHs (0.20 µgL-1) for the water standard of European Union. The calculated diagnostic benzo [a] anthracene: benzo [a] anthracene + chrysene ratio of between 0.52 and 1.0 suggests that the sources of PAHs at the majority of the stations studied are derived primarily from pyrogenic sources, from incomplete fuel combustion of the boats and vehicle engines, with lesser amounts of PAHs contributed from petrogenic sources. Some stations displayed mixed sources. A significant positive correlation was found between total organic carbon (TOC) and the concentrations of the high-molecular-weight PAHs (r² = 0.86, P < 0.05), which suggests significant secondary sources of PAHs, such as those from atmospheric deposition. [ABSTRACT FROM AUTHOR]

Novel ionophores comprising various hydroxide and amine structures were immobilized onto poly(vinyl chloride) (PVC) matrices, and these were examined to determine Ti(III) selectivity. To predict the selectivity of Ti(III), a PVC membrane was used to investigate the binding of Ti(III) to c-methylcalix[4]resorcinarene (CMCR). The study showed that the chelating ligand, CMCR, was coordinated selectively to Ti(III) at eight coordination sites involving the oxygen atoms at the interface of the membrane/solution. The membrane was prepared, based on CMCR as an ionophore, sodium tetrakis(4-fluorophenyl) borate (NaTFPB) as a lipophilic ionic additive, and dioctylphthalate (DOP) as a plasticizer. The immobilization of the ionophore and surface characterization studies revealed that the performance of CMCR-immobilized PVC was equivalent to that of mobile ionophores in supported liquid membranes (SLMs). The strengths of the ion-ionophore (CMCR-Ti(OH)(OH2)52+) interactions and the role of ionophores on membranes were studied via UV-Vis, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and and X-ray diffraction (XRD). [ABSTRACT FROM AUTHOR]

An electrochemical microbiosensor for DNA has been fabricated based on new acrylic microspheres modified with reactive N-acryloxysuccinimide (NAS) functional groups. Hydrophobic poly(n-butylacrylate-N-acryloxysuccinimide) microspheres were synthesized in an emulsion form with a simple one-step photopolymerization technique. Aminated DNA probe was attached to the succinimde functional group of the acrylic microspheres via covalent bonding. The hybridization of the immobilized DNA probe with the complementary DNA was studied by differential pulse voltametry using anthraquninone-2-sulfonic acid monohydrate sodium salt (AQMS) as the electroactive hybridization label. The influences of many factors such as duration of DNA probe immobilization and hybridization, pH, type of ions, buffer concentrations, ionic strength, operational temperature and non-complementary DNA on the biosensor performance were evaluated. Under optimized conditions, the DNA microbiosensor demonstrated a linear response range to target DNA over a wide concentration range of 1.0 × 10-16 and 1.0 × 10-8 M with a lower limit of detection (LOD) of 9.46 × 10-17 M (R2 = 0.97). This DNA microbiosensor showed good reproducibility with 2.84% RSD (relative standard deviation) (n = 3). Application of the NAS-modified acrylic microspheres in the construction of DNA microbiosensor had improved the overall analytical performance of the resultant DNA microbiosensor when compared with other reported DNA biosensors using other nano-materials for membranes and microspheres as DNA immobilization matrices. [ABSTRACT FROM AUTHOR]

Explores the viability of the methacrylic-acrylic copolymers as self-plasticizing membrane matrixes for ion-selective electrodes (ISE) or other ion-sensor applications. Significance of polymer-type membrane in ISE construction; Experiments on several chemicals; Establishing polymer recipes for ion-sensor membranes; Immobilizing ionophores; Potentiometric behavior of copolymer membranes toward ions.

Chili hotness is very much dependent on the concentration of capsaicin present in the chili fruit. A new biosensor based on a horseradish peroxidase enzyme-capsaicin reaction mediated by ferrocene has been successfully developed for the amperometric determination of chili hotness. The amperometric biosensor is fabricated based on a single-step immobilization of both ferrocene and horseradish peroxidase in a photocurable hydrogel membrane, poly(2-hydroxyethyl methacrylate). With mediation by ferrocene, the biosensor could measure capsaicin concentrations at a potential 0.22 V (vs. Ag/AgCl), which prevented potential interference from other electroactive species in the sample. Thus a good selectivity towards capsaicin was demonstrated. The linear response range of the biosensor towards capsaicin was from 2.5-99.0 µM with detection limit of 1.94 µM. A good relative standard deviation (RSD) for reproducibility of 6.4%-09.9% was obtained. The capsaicin biosensor demonstrated long-term stability for up to seven months. The performance of the biosensor has been validated using a standard method for the analysis of capsaicin based on HPLC. [ABSTRACT FROM AUTHOR]

[Display omitted] • An electrochemical DNA biosensor has been effectively developed based on polyacrylic microspheres and gold nanoparticles (AuNPs) for the identification of the gene sequence of the harmful microalgae Alexandrium minutum. • Anthraquinone-2-sulfonic acid derivative (AQMS) works as a specific indicator for redox DNA hybridisation, enabling the identification of the harmful microalgae Alexandrium minutum for the first time. • The DNA biosensor, employing AQMS as a redox label for the detection of Alexandrium minutum demonstrated a minimal limit of detection and possessed an extensive linear range. • This new production of an electrochemical biosensor serves as a straightforward and rapid instrument for identifying Alexandrium minutum DNA in water samples tainted with this detrimental algae. Alexandrium species, including Alexandrium minutum (A. minutum) , are capable of producing paralytic shellfish toxins, which frequently adversely affect the aquaculture and fishing industries. Since it's critical, it needs to be precisely detected. This study addresses the development of an electrochemical DNA biosensor for detecting toxic microalga A. minutum gene sequence based on anthraquinone-2-sulfonic acid derivative (AQMS) as the redox DNA hybridisation indicator. DNA binding studies using UV–Vis and molecular docking were performed, confirming the intercalation behaviour. The binding constant (K b) of such interaction was 4.5 × 105 M−1 with the hyperchromicities shown are 13 % and 18 %, and the relative binding energies of the docked AQMS towards DNA was − 8.3 kcal mol−1. The RMSD value for AQMS was 0.2 Å, underscoring a remarkably close alignment and similarity with the redocked structure. The aminated DNA probe was then immobilised onto the screen-printed carbon electrode (SPCE) containing polyacrylic microspheres and gold nanoparticles (AuNPs). An excellent linear relationship of the response to DNA concentrations was obtained from 1 × 10−15 M to 1 × 10−5 M (R2 = 0.9908) with a limit detection (LOD) at 6.91 × 10−14 M. This lower detection limit is a significant improvement over several other electrochemical biosensors reported so far for A. minutum determinations. Selectivity experiments demonstrated that this new voltammetric DNA biosensor could distinguish between A. minutum target and non-target DNA and can regenerate after use for up to two cycles. This DNA biosensor has demonstrated its ability to early detect toxic microalgae by effectively differentiating among various non-target dinoflagellate species. Furthermore, the biosensor has been shown to successfully identify A. minutum in water samples from a river in Tumpat, Kelantan, with results comparable to standard polymerase chain reaction (PCR). [ABSTRACT FROM AUTHOR]

Abstract: A new optical sensor for fast screening of ammonium (NH4 +) ion was developed based on immobilisation of p-nitrobenzene-diazonium chloride (Riegler''s reagent) onto XAD-7 microbeads. In aqueous solution, the diazonium salt is unstable and will spontaneously decompose at room temperature but we have successfully stabilised this compound via immobilisation using physical adsorption to create a solid-state Riegler''s reagent for NH4 + ion determination with a storage period of one month. The quantification of NH4 + ion concentration was possible by using reflectance spectrophotometry method with an optical fibre probe. The solid-state Riegler''s reagent based optical sensor yielded a wide linear response range for NH4 + ion of 10–60ppm and a fast response time of 2min when compared with many commonly used coloured reagents. The limit of detection (LOD) of the optical NH4 + ion sensor was 7.9ppm NH4 + ion with optimum response at pH 7. The response of the sensor was reproducible (4.2–5.7% relative standard deviation, n =3) and can be regenerated using buffer pH 1. Except for Fe3+ ions, most common ions showed no serious interference. The sensor was also used for the determination of NH4 + ion in river water and the results obtained were comparable to those obtained by a standard titrimetric method. [Copyright &y& Elsevier]

Abstract: One of the major problems in the analysis of ammonia (NH3) using spectrophotometric method is highly coloured water sample. A reflectometric NH3 sensor based on a facile single-step immobilisation of cobalt(II) (Co2+) ion onto high capacity Dowex HCR-W2 microspheres has been developed to enable the direct NH3 determination in highly coloured water samples. The combination of Co2+ ion-immobilised microspheres via cation exchange chemical reaction and reflectometric technique has improved the optode sensing performance with respect to linear response range and response time. Immobilised Co2+ ion, when complexed with NH3 gave a blue colouration of hexamminecobaltate(II) ([Co(NH3)6]2+) complex at pH 13. The NH3 sensor reached maximum colour intensity in ∼6min at ambient conditions. The linear calibration curve was 60–290mM NH3 with a detection limit of 16mM NH3, which is suitable for direct determination of NH3-enriched leachate water samples. A good reproducibility between 5.4 and 5.9% relative standard deviation (RSD) was obtained with the probe and the sensing performance can be regenerated using buffer pH 1. The effect of potential interference ions has been investigated during the quantification of NH3 in heavily polluted sewage water. The results obtained were in good agreement with those produced by acidimetric reference method. [Copyright &y& Elsevier]

Anthropogenic emission is on the increase in urban cities due to increased human activities. However, the pollution level of heavy metals in urban environments due to emission from various anthropogenic sources could attain toxic levels to humans and biota. The roadside dust collected from Petaling Jaya, Malaysia was analysed for Pb, Cr, Cu, Cd, As, Ni, and Fe by using ZEE nit 650 P Graphite furnace atomic absorption spectroscopy. The contamination levels of these metals were assessed in terms of the geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (Cf), and integrated pollution index (IPI). The result of the principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed that the variations found in different concentrations of heavy metals were mainly due to industrial and traffic emissions. The computed results of Igeo and EF of heavy metals in urban dust suggested that there were pollutions of Cd, Cu, Pb, and As. Meanwhile, Igeo and EF of Ni, Cr, and Fe were very low and posed no serious pollution. The Cf and IPI assessments also indicated that Cd, Cu, and Pb were the major pollutants in Petaling Jaya urban dust. On the other hand, the potential ecological risks for single element (Er) confirmed the IPI results and the potential ecological risk index (RI) indicated that generally, the degree of pollution of heavy metals in roadside dust of PJ was considerable. These results could help in the development of suitable management strategies to minimise pollution by using various remediation methods in Petaling Jaya. [ABSTRACT FROM AUTHOR]

Biogenic amines have attracted interest among researchers because of their importance as biomarkers in determining the quality of food freshness in the food industry. A rapid and simple technique that is able to detect biogenic amines is needed. In this work, a new optical sensing material for one of the biogenic amines, histamine, based on a new zinc(II) salphen complex was developed. The binding of zinc(II) complexes without an electron-withdrawing group (complex 1) and with electron-withdrawing groups (F, complex 2; Cl, complex 3) to histamine resulted in enhancement of fluorescence. All complexes exhibited high affinity for histamine [binding constant of (7.14 ± 0.80) × 104, (3.33 ± 0.03) × 105, and (2.35 ± 0.14) × 105 M-1, respectively]. Complex 2 was chosen as the sensing material for further development of an optical sensor for biogenic amines in the following step since it displayed enhanced optical properties in comparison with complexes 1 and 3. The optical sensor for biogenic amines used silica microparticles as the immobilisation support and histamine as the analyte. The optical sensor had a limit of detection for histamine of 4.4 × 10-12 M, with a linear working range between 1.0 × 10-11 and 1.0 × 10-6 M (R2 = 0.9844). The sensor showed good reproducibility, with a low relative standard deviation (5.5 %). In addition, the sensor exhibited good selectivity towards histamine and cadaverine over other amines, such as 1,2-phenylenediamine, triethylamine, and trimethylamine. Recovery and real sample studies suggested that complex 2 could be a promising biogenic amine optical sensing material that can be applied in the food industry, especially in controlling the safety of food for it to remain fresh and healthy for consumption. [ABSTRACT FROM AUTHOR]

In the title compound, C14H18N2O2S, the piperidine ring has a chair conformation. Its mean plane is twisted with respect to the 4-methoxybenzoyl ring, with a dihedral angle of 63.0 (3)°. The central N--C(=S)--N(H)--C(=O) bridge is twisted with an N--C--N--C torsion angle of 74.8 (6)°. In the crystal, molecules are linked by N--H⋯O and C--H⋯O hydrogen bonds, forming chains along the c-axis direction. Adjacent chains are linked by C--H⋯π interactions, forming layers parallel to the ac plane. The layers are linked by offset π--π interactions [intercentroid distance = 3.927 (3) Å], forming a supramolecular three-dimensional structure. [ABSTRACT FROM AUTHOR]

Essential oils from fresh parts of Etlingera brevilabrum Valeton (Zingiberaceae) including rhizome, stolon, stem, and leaves were hydrodistilled, and studied for their chemical composition, antioxidant, and antibacterial activity. Characterization by GC-FID and GC-MS showed monoterpene hydrocarbons dominated the oils of the leaves and stems (57.3 and 73.4%) with oxygenated monoterpenes were dominant in the stolon and rhizomes (40.4 and 53.6%). The major compounds of the rhizome oil were perilla aldehyde (19.6%) and bornyl acetate (17.6%); the stolon oil, β-pinene (30.6%) and p-cymen-7-ol (25.0%); the stem oil, δ-3-carene (43.2%) and α-thujene (17.7%); and the leaf oil, α-thujene (38.1%) and p-cymen-7-ol (8.0%). The rhizome oil showed the highest antioxidant effects with IC50 = 1236.54±12.83 μg/mL in the DPPH radical scavenging activity, 22.76% inhibition in the β-carotene bleaching test at 1000 μg/mL, and IC50 = 878±16.54 μg/mL in the ferrous ion chelating ability. Antibacterial activity demonstrated by disc diffusion assay showed that the rhizome, stem and leaf oils inhibited Staphylococcus aureus and MRSA but not Bacillus subtilis and Bacillus thuringiensis. For Gram negative bacteria, the rhizome oil prevented the growth of Proteus mirabilis; the stem oil inhibited Escherichia coli and Proteus vulgaris; and the leaf oil was active against E. coli, P. vulgaris, and P. mirabilis. [ABSTRACT FROM AUTHOR]

A simple sticker sensor has been constructed using litmus paper and tests have been conducted to detect the freshness of beef samples. The results show that the sticker sensor can be used to determine the degree of beef freshness, since the color change of the litmus paper and the quality degradation of the beef during storage time had a similar trend, where the decay of the beef could be detected clearly (when the red litmus paper changed to blue). The sticker sensor reacted accurately to the beef's freshness in terms of pH change due to beef deterioration from pH 5.61 to 6.24 and from pH 5.67 to 6.02 as shown by its color change in real time at room and chiller temperature respectively. Thus, the sticker sensor can be used as an effective tool for monitoring the microbial quality of packaged fresh meat that correlates with the increased pH of the beef, where the total viable count (TVC) of 5 x 106 cfu/g or 6.698 log cfu/g correlates with a pH of 6.24. These levels were reached at 10 hrs and 7 days at room and chiller temperature respectively. This study provides a foundation for developing a simple sensor for beef freshness. [ABSTRACT FROM AUTHOR]

Vibrio cholerae is a Gram-negative bacterium that causes cholera, a diarrheal disease. Cholera is widespread in poor, under-developed or disaster-hit countries that have poor water sanitation. Hence, a rapid detection method for V. cholerae in the field under these resource-limited settings is required. In this paper, we describe the development of an electrochemical genosensor assay using lyophilized gold nanoparticles/latex microsphere (AuNPs–PSA) reporter label. The reporter label mixture was prepared by lyophilization of AuNPs–PSA–avidin conjugate with different types of stabilizers. The best stabilizer was 5% sorbitol, which was able to preserve the dried conjugate for up to 30 days. Three methods of DNA hybridization were compared and the one-step sandwich hybridization method was chosen as it was fastest and highly specific. The performance of the assay using the lyophilized reagents was comparable to the wet form for detection of 1 aM to 1 fM of linear target DNA. The assay was highly specific for V. cholerae , with a detection limit of 1 fM of PCR products. The ability of the sensor is to detect LAMP products as low as 50 ng µl −1 . The novel lyophilized AuNPs–PSA–avidin reporter label with electrochemical genosensor detection could facilitate the rapid on-site detection of V. cholerae . [ABSTRACT FROM AUTHOR]

A new cellulose nanocrystal–reduced graphene oxide (CNC–rGO) nanocomposite was successfully used for mediatorless electrochemical sensing of methyl paraben (MP). Fourier-transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM) studies confirmed the formation of the CNC–rGO nanocomposite. Cyclic voltammetry (CV) studies of the nanocomposite showed quasi-reversible redox behavior. Differential pulse voltammetry (DPV) was employed for the sensor optimization. Under optimized conditions, the sensor demonstrated a linear calibration curve in the range of 2 × 10−4–9 × 10−4 M with a limit of detection (LOD) of 1 × 10−4 M. The MP sensor showed good reproducibility with a relative standard deviation (RSD) of about 8.20%. The sensor also exhibited good stability and repeatability toward MP determinations. Analysis of MP in cream samples showed recovery percentages between 83% and 106%. Advantages of this sensor are the possibility for the determination of higher concentrations of MP when compared with most other reported sensors for MP. The CNC–rGO nanocomposite-based sensor also depicted good reproducibility and reusability compared to the rGO-based sensor. Furthermore, the CNC–rGO nanocomposite sensor showed good selectivity toward MP with little interference from easily oxidizable species such as ascorbic acid. [ABSTRACT FROM AUTHOR]