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Optical biosensor for the detection of formaldehyde has been developed based on the transparent enzymatic stacked membranes system on the glass substrate, and employing optical absorption transducer with H+ ion-selective Nile Blue chromoionophore (NBCM) dye-doped methacrylic acrylic (MB28) copolymer membrane as the optode membrane. Alcohol oxidase (AOx) enzymes were entrapped within the biocompatible sol–gel matrix and deposited on top of the pH optode membrane. As the uppermost catalytic membrane catalyzes the oxidative conversion of formaldehyde to formic acid and hydrogen peroxide, the immobilized NBCM undergoes protonation reaction and forms HNBCM+, the dark blue ion-chromoionophore complex via H+ ion transfer reaction within the soft and flexible MB28 polymeric membrane. This rendered the enzymatic optode membrane absorbed a high yellow light intensity from the light source and exhibited maximum absorption peaks at 610 and 660 nm. Optical evaluation of formaldehyde by means on UV–vis absorption transduction of the enzymatic stacked membranes demonstrated rapid response time of 10 min with high sensitivity, good linearity and high reproducibility across a wide formaldehyde concentration range of 1 × 10−3–1 × 103 mM (R2 = 0.9913), and limit of detection (LOD) at 1 × 10−3 mM, which could be useful for formaldehyde assay in industrial, agricultural, environmental, food and beverages as well as medical samples. The formaldehyde concentration in snapper fish, pomfret fish and threadfin fish samples determined by the proposed optical enzymatic biosensor were very much close to the formaldehyde concentration values determined by the UV–vis spectrophotometric NASH standard method based on the statistical t-test. This suggests that the optical biosensor can be used as a reliable method for quantitative determination of formaldehyde levels in food samples.

The emergence of highly pathogenic and deadly human coronaviruses, namely SARS-CoV and MERS-CoV within the past two decades and currently SARS-CoV-2, have resulted in millions of human death across the world. In addition, other human viral diseases, such as mosquito borne-viral diseases and blood-borne viruses, also contribute to a higher risk of death in severe cases. To date, there is no specific drug or medicine available to cure these human viral diseases. Therefore, the early and rapid detection without compromising the test accuracy is required in order to provide a suitable treatment for the containment of the diseases. Recently, nanomaterials-based biosensors have attracted enormous interest due to their biological activities and unique sensing properties, which enable the detection of analytes such as nucleic acid (DNA or RNA), aptamers, and proteins in clinical samples. In addition, the advances of nanotechnologies also enable the development of miniaturized detection systems for point-of-care (POC) biosensors, which could be a new strategy for detecting human viral diseases. The detection of virus-specific genes by using single-stranded DNA (ssDNA) probes has become a particular interest due to their higher sensitivity and specificity compared to immunological methods based on antibody or antigen for early diagnosis of viral infection. Hence, this review has been developed to provide an overview of the current development of nanoparticles-based biosensors that target pathogenic RNA viruses, toward a robust and effective detection strategy of the existing or newly emerging human viral diseases such as SARS-CoV-2. This review emphasizes the nanoparticles-based biosensors developed using noble metals such as gold (Au) and silver (Ag) by virtue of their powerful characteristics as a signal amplifier or enhancer in the detection of nucleic acid. In addition, this review provides a broad knowledge with respect to several analytical methods involved in the development of nanoparticles-based biosensors for the detection of viral nucleic acid using both optical and electrochemical techniques.

An optical genosensor based on Schiff base complex (Zn2+ salphen) DNA label and acrylic microspheres (AMs) as polymer support of the capturing DNA probe (cpDNA) was developed for dengue virus serotype 2 (DEN-2) detection via reflectance spectrophotometric method. The solid-state optical DNA biosensor showed high selectivity and specificity up to one-base mismatch in the target DNA sequence owing to the salphen chemical structure that is rich in localized electrons, and allowed π-π stacking interaction between stacked base pairs of double-stranded DNA (dsDNA). The reflectometric DNA microsensor demonstrated a broad linear detection range towards DEN-2 DNA from 1 × 10–15 M to 1 × 10−3 M with a low limit of detection (LOD) obtained at 1.21 × 10–16 M. The DNA biosensor gave reproducible optical response with a satisfactory relative standard deviation (RSD) at 3.1%, (n = 3), and the reflectance response was stable even after four regeneration cycles of the DNA biosensor. The optical genosensor was proven comparable with standard reverse transcription polymerase chain reaction (RT-PCR) in detecting DEN-2 genome acquired from clinical samples of serum, urine and saliva of dengue virus infected patients under informed consent. The developed reflectometric DNA biosensor is advantageous in offering an early DEN-2 diagnosis, when fever symptom started to manifest in patient.

An optical biosensor employing immobilized haloalkane dehalogenase (HLD), the halide degrading enzyme for the detection of halogenated organic in environmental water and drinking water samples was developed. The enzymatic biosensor was fabricated by incorporating H+ ion selective chromoionophore ETH5294 and HLD enzyme in a stacked chitosan films system on a glass slide. Hydrolytic dehalogenation of dichloroethane (DCA) by the carbon-halide degrading HLD enzyme resulting in the release of a halogen, a proton and a primary alcohol. The halocarbon concentration was optically transduced by the pH transducer layer as a result of protonation reaction of the chromoionophore pH indicator dye embedded in the underneath layer. The resulting colour change of the protonated chromoionophore was measured by fiber optic reflectance spectrophotometry method. Under optimized conditions the detection limit of the proposed reflectance-based enzymatic biosensor membrane was estimated to be 1 mg L−1 with a wide dynamic linear concentration range of 5–60 mg L−1 DCA (R2 = 0.9792) and satisfactory reproducibility within the relative standard deviation (RSD) range of 3.4–4.3%. Validation test demonstrated that the optical halocarbon biosensor could be a promising tool for rapid (6 min) in situ and direct evaluation of organohalide in river water, tap water and bottled water samples without any sample pre-treatment or extraction steps.

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype ionotropic glutamate receptors are attractive antiepileptic targets responsible for mediating the majority of excitatory neurotransmission and plasticity. The noncompetitive antagonists obtain more and more attention as drug candidates for treatment of the neurological diseases involving excessive activity of AMPARs, due to they regulate AMPA receptors (AMPARs) activity independently of endogenous glutamate levels unlike the competitive antagonists. Development of novel AMPAR noncompetitive antagonists, which are safer and more efficacious than competitive antagonists, is highly under demand. Here, we present the discovery of novel antagonists against AMPAR through Structure-Based Virtual Screening (SBVS). Three compounds were successfully distinguished by several different filtering strategies, namely STOCK6S-10902, STOCK1N-49134 and STOCK5S-68665. The interaction mode of these compounds was further explored through molecular dynamics simulation, binding free energy calculation and the binding free energy decomposition. It is demonstrated that some residues within the binding pocket, which have been proved their importance in antagonist binding and gating, form strong hydrogen bond interactions with these three molecules. In particular, H-bond interactions with high occupancies between Ser516, Ser788 and STOCK6S-10902 and Ser516, Asn791 and STOCK1N-49134 were observed. The three hit compounds with new scaffolds and the detailed binding modes could potentially serve as a starting point for further optimization and development.

A reflectometric biosensor for enzymatic determination of halogenated organic pollutant in environmental water sample was developed. Polyacrylate microspheres modified with succinimide functional groups were employed as the substrate matrix for covalent immobilization of haloalkane dehalogenase (DhlA) enzyme, and ETH5294 Nile Blue chromoionophore (NBC) pH dye was physically immobilized on the acrylic micromatrix to function as an optical proton sensor. The hydrolytic dehalogenation of halocarbon catalyzed by the immobilized DhlA resulting in the release of a halogen and a proton, which protonated the immobilized NBC proton indicator, and a colour change of the biosensor from violet to blue was measured with a reflectance spectrophotometer for indirect quantification of the halogenated hydrocarbon concentration. The enzymatic halocarbon reflectance biosensor exhibited a dynamic linear response range of 1–30 mg L−1 1,2-dichloroethane (DCA) (R2 = 0.9762) with a detection limit of 0.3 mg L−1. The proposed enzymatic biosensor gave rapid response, within 2 min, towards the detection of 50 mg L−1 DCA at 662 nm, and demonstrated stable response up to 6 days of storage period at 4 °C and pH 8.0. Validation between the developed biosensor with standard gas chromatography–electron capture detector (GC-ECD) showed that both methods have a comparable accuracy in detecting halocarbon species.

Programmed cell death (PCD) plays a critical role throughout the lives of plants, it is regarded as a highly regulated and active process of plant cell death during the times of biotic or abiotic stress. This study aims to provide developmental anatomical characteristics of the interxylary cork formation in the roots of Astragalus. membranaceus var. mongholicus, and to subsequently show cytomorphological evidence that PCD is involved in the development of rhytidome and interxylary cork. The developmental anatomy of rhytidome and interxylary cork of the perennial fresh main root of A. membranaceus var. mongholicus was studied using light microscopy, whereas the PCD in the development of rhytidome and interxylary cork was studied using fluorescence microscopy and transmission electron microscopy. Histologically, it was observed that the parenchyma cells of secondary phloem and xylem in roots recovered their meristematic ability, and later developed into rhytidome and interxylary cork. Cytologically, ultrastructural characteristics such as nucleus malformation, vacuole disappearance, mitochondrial degeneration, and vesicle filling were observed. In roots, the nucleus of the phloem parenchyma cells were terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive from the pre-rhytidome stage to the formation of rhytidome stage and 4',6-diamidino-2-phenylindole dihydrochloride (DAPI)-negative during the mature rhytidome stage. The TUNEL assay of the xylem parenchyma cells showed positive characteristics from the early stage of interxylary cork formation to the interxylary cork formation stage, whereas DAPI-negative characteristics were observed in the mature interxylary cork. Gel electrophoresis showed that DNA cleavage was random. Our results indicated that the formation of the rhytidome and interxylary cork involved the PCD process.

Abundant of preparatory works have recognized that fluorescent sensors based on 8-aminoquinoline are popular tools to detect Zn2+ ions in environmental and biological applications. Along with these studies, researchers started to introduce a variety of carboxamido group into an 8-aminoquinoline molecule in forming 8-amidoquinoline derivatives. Therefore, this systematic review aims to introduce a general overview of the fluorophore 8-aminoquinoline as Zn2+ receptors and to provide comparisons of collected studies that related to 8-amidoquinoline derivatives as fluorophore probe of the sensor. According to PRISMA systematic searches strategy, 13 articles were analyzed for trends, research designs, results and discussion, subject samples, and remarks or conclusions. We found cross-sectional studies with four aspects in zinc sensing that have been targeted; binding studies via titration, detection's limit, interferences studies, and validation of the study. Hence, this paper also included assessments of those criteria and the trends of development of 8-amidoquinoline derivatives based-zinc fluorescent chemosensor. It also showed that most of the researches conducted in China. In conclusion, this study identified various research designs of fluorescent chemosensors based on 8-amidoquinoline prolong with the effectiveness and potential as a recognition probe to assist the detection of zinc. Hence, elucidation of those derivatives essential to be explored because more studies are needed to improve the sensing criteria of the zinc sensor

Carrageenans are linear sulphated polysaccharides that are commonly added into confectionery products but may exert a detrimental effect to human health. A new and simpler way of carrageenan determination based on an optical sensor utilizing a methylcellulose/poly(n-butyl acrylate) (Mc/PnBA) composite membrane with immobilized methylene blue (MB) was developed. The hydrophilic Mc polymer membrane was successfully modified with a more hydrophobic acrylic polymer. This was to produce an insoluble membrane at room temperature where MB reagent could be immobilized to build an optical sensor for carrageenan analysis. The fluorescence intensity of MB in the composite membrane was found to be proportional to the carrageenan concentrations in a linear manner (1.0–20.0 mg L−1, R2 = 0.992) and with a detection limit at 0.4 mg L−1. Recovery of spiked carrageenan into commercial fruit juice products showed percentage recoveries between 90% and 102%. The optical sensor has the advantages of improved sensitivity and better selectivity to carrageenan when compared to other types of hydrocolloids. Its sensitivity was comparable to most sophisticated techniques for carageenan analysis but better than other types of optical sensors. Thus, this sensor provides a simple, rapid, and sensitive means for carageenan analysis.

Graphene decorated with graphitic nanospheres functionalized with pyrene butyric acid (PBA) is used for the first time to fabricate a DNA biosensor. The electrode was formed by attaching a DNA probe onto PBA, which had been stacked onto a graphene material decorated with graphene nanospheres (GNSs). The nanomaterial was drop-coated onto a carbon screen-printed electrode (SPE) to create the GNS-PBA modified electrode (GNS-PBA/SPE). A simple method was used to produce GNS by annealing graphene oxide (GO) solution at high temperature. Field emission scanning electron micrographs confirmed the presence of a spherical shape of GNS with a diameter range of 40–80 nm. A stable and uniform PBA-modified GNS (GNS-PBA) was obtained with a facile ultrasonication step. Thus allowing aminated DNA probes of genetically modified (GM) soybean to be attached to the nanomaterials to form the DNA biosensor. The GNS-PBA/SPE exhibited excellent electrical conductivity via cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests using potassium ferricyanide (K3[Fe(CN)6]) as the electroactive probe. By employing an anthraquinone monosulfonic acid (AQMS) redox intercalator as the DNA hybridization indicator, the biosensor response was evaluated using the DPV electrochemical method. A good linear relationship between AQMS oxidation peak current and target DNA concentrations from 1.0 × 10−16 to 1.0 × 10−8 M with a limit of detection (LOD) of less than 1.0 × 10−16 M was obtained. Selectivity experiments revealed that the voltammetric GM DNA biosensor could discriminate complementary sequences of GM soybean from non-complementary sequences and hence good recoveries were obtained for real GM soybean sample analysis. The main advantage of using GNS is an improvement of the DNA biosensor analytical performance.

A DNA micro-optode for dengue virus detection was developed based on the sandwich hybridization strategy of DNAs on succinimide-functionalized poly(n-butyl acrylate) (poly(nBA-NAS)) microspheres. Gold nanoparticles (AuNPs) with an average diameter of ~20 nm were synthesized using a centrifugation-based method and adsorbed on the submicrometer-sized polyelectrolyte-coated poly(styrene-co-acrylic acid) (PSA) latex particles via an electrostatic method. The AuNP&ndash, latex spheres were attached to the thiolated reporter probe (rDNA) by Au&ndash, thiol binding to functionalize as an optical gold&ndash, latex&ndash, rDNA label. The one-step sandwich hybridization recognition involved a pair of a DNA probe, i.e., capture probe (pDNA), and AuNP&ndash, PSA reporter label that flanked the target DNA (complementary DNA (cDNA)). The concentration of dengue virus cDNA was optically transduced by immobilized AuNP&ndash, PSA&ndash, rDNA conjugates as the DNA micro-optode exhibited a violet hue upon the DNA sandwich hybridization reaction, which could be monitored by a fiber-optic reflectance spectrophotometer at 637 nm. The optical genosensor showed a linear reflectance response over a wide cDNA concentration range from 1.0 &times, 10&minus, 21 M to 1.0 &times, 12 M cDNA (R2 = 0.9807) with a limit of detection (LOD) of 1 &times, 29 M. The DNA biosensor was reusable for three consecutive applications after regeneration with mild sodium hydroxide. The sandwich-type optical biosensor was well validated with a molecular reverse transcription polymerase chain reaction (RT-PCR) technique for screening of dengue virus in clinical samples, e.g., serum, urine, and saliva from dengue virus-infected patients under informed consent.

A novel label-free electrochemical DNA biosensor was constructed for the determination of Escherichia coli bacteria in environmental water samples. The aminated DNA probe was immobilized onto hollow silica microspheres (HSMs) functionalized with 3-aminopropyltriethoxysilane and deposited onto a screen-printed electrode (SPE) carbon paste with supported gold nanoparticles (AuNPs). The biosensor was optimized for higher specificity and sensitivity. The label-free E. coli DNA biosensor exhibited a dynamic linear response range of 1 &times, 10&minus, 10 &micro, M to 1 &times, 5 &micro, M (R2 = 0.982), with a limit of detection at 1.95 &times, 15 &micro, M, without a redox mediator. The sensitivity of the developed DNA biosensor was comparable to the non-complementary and single-base mismatched DNA. The DNA biosensor demonstrated a stable response up to 21 days of storage at 4 ℃ and pH 7. The DNA biosensor response was regenerable over three successive regeneration and rehybridization cycles.

Biosensor optik berasaskan hemoglobin (Hb) terpegun pada mikrosfera poli(n-butil akrilat-co-N-akriloksisuksinimida) [poli(nBA-NAS)] telah dibangunkan bagi mengesan kepekatan ion nitrit (NO2-). Kompleks HEM ferum dalam Hb memangkinkan tindak balas penurunan ion NO2- kepada nitrik oksida (NO) lalu bergabung dengan deoksihemoglobin (HbFe2+) membentuk kompleks ferum-nitrosil-hemoglobin (HbFe2+-NO) yang berwarna hijau kekuningan. Spektrofotometer pantulan gentian optik digunakan untuk memantau kepekatan ion NO2- secara kuantitatif berdasarkan perubahan warna Hb terpegun pada mikrosfera poliakrilat daripada perang kemerahan ke hijau kekuningan pada panjang gelombang pantulan maksimum 668 nm. Pencirian terhadap biosensor nitrit reflektometrik melibatkan ujian kesan pH, kesan kepekatan Hb, julat rangsangan linear, kebolehasilan, jangka hayat dan kesan gangguan ion telah dijalankan. Biosensor ion NO2- optik terbangun memaparkan julat linear dinamik daripada 5 hingga 50 mg mL-1 (R2=0.9894) pada pH7.0 dengan had pengesanan (LOD) sebanyak 3.3 mg mL-1 dan nilai sisihan piawai relatif (RSD) kebolehasilan biosensor sebanyak 5.8%. Jangka hayat biosensor optik nitrit tersebut adalah selama 36 hari dan majoriti ion asing yang sering wujud bersama ion NO2- dalam sampel air semula jadi tidak menunjukkan kesan gangguan yang bererti terhadap penentuan ion NO2- menggunakan biosensor optik terbangun kecuali ion Hg2+, Ag+, Br- dan S2-.

In view of the growing need for rapid and non-destructive method for monitoring of fish freshness to secure the safety standard of food, a reflectometric biosensor kit has been developed for in situ and real-time analysis of creatine as freshness marker. The optical bienzymatic creatine biosensor was fabricated by covalent grafting of both creatinase (CI) and urease (Ur) on the pH chromoionophore ETH 5295-doped poly(styrene-co-acrylic acid) (PSA) latex microspheres via EDC/NHS coupling chemistry. An optical fiber reflectance spectrophotometer was employed for reflectance measurement of the biorecognition phase for quantification of creatine levels, which can be used as the indicator of the extent of fish spoilage for direct evaluation of fish freshness. The dynamic linear response range of the reflectance creatine biosensor was obtained from 16 to 48 mM, which corresponds to the physiological range of creatine in fish body surface metabolite with a reproducibility of less than 2% relative standard deviation (RSD). The biosensor response time was about 7 min and did not show interference by some important biogenic amines (BAs), amino acids and nitrogen compounds normally co-exist with creatine in the biofluid of fish surface such as histamine, phenylalanine, tyrosine and taurine except sarcosine and uric acid.

A microspheres-based microbial optosensor for NO 2 − ion quantitation was constructed by using immobilized Raoutella planticola ( R. planticola ), the bacterium expressing NAD(P)H nitrite reductase (NiR) enzyme, which was isolated from local edible bird’s nest (EBN) via microbial technique. The whole cells and the lipophilic Nile Blue chromoionophore (NBC) were physically adsorbed on the self-adhesive photocurable poly( n -butyl acrylate-co- N -acryloxysuccinimide) [poly(nBA-NAS)] microspheres, whilst the reduced co-enzyme NAD(P)H was covalently immobilized on the succinimide-functionalized acrylic microspheres via peptide link to produce a reagentless nitrite biosensing system. As the microbial bio-optode responded to nitrite through colour change from blue to pink, a facile reflectometric approach was adopted to measure reflectance intensity at 639 nm, before and after reaction with nitrite at optimum pH 8. The optosensor could quantify NO 2 − ion concentration within a dynamic linear response range of 0.5–400 mg L −1 with a limit of detection (LOD) of 0.2 mg L −1 . The large surface area to volume ratio of the acrylic microspheres allowed solid-state diffusional mass transfer of the substrate to occur at micro-bio-optode surface, and an equilibrium response was achieved within 5 min. The practical feasibility of using the bio-optode for nitrite assay in food matrix sample showed good agreement with standard ion chromatography method.

An electrochemical DNA biosensor for DNA determination of genetically modified (GM) soybean (CaMV 35S target genes) was developed utilizing a new detection concept based on the adsoption of anthraquinone‐2‐sulphonic acid (AQMS) on the reduced graphene oxide nano‐particles (rGO) during DNA hybridization events. The aminated DNA probe for CaMV 35S was immobilized onto poly(n‐butyl acrylate) film modified with succinimide functional groups [poly(nBA‐NAS)] via peptide covalent bond. Nanosheets of rGO were entrapped in the poly(nBA‐NAS) film to form a conducting [poly(nBA‐NAS)‐rGO] film of the DNA biosensor. Besides facilitating the electron transfer reactions, the rGO also functioned as an adsorbent for AQMS. The sensing mechanism of the proposed DNA biosensor involved measuring the oxidation current of the AQMS adsorbed on the electrode surface at −0.50 V using differential pulse voltammetry (DPV) before and after a DNA hybridization event. Under optimum conditions, the DNA biosensor demonstrated a linear proportionality between AQMS oxidation signal and logarithm cDNA concentration from 1.0×10−15 M to 1.0×10−8 M target DNA with a detection limit of 6.3×10−16 M. The electrochemical DNA biosensor possessed good selectivity and a shelf life of about 40 days with relative standard deviation of reproducibility obtained in the range of 3.7–4.6% (n=5). Evaluation of the DNA biosensor using GM soybean DNA extracts showed excellent recovery percentages of 97.2–104.0.

An optical enzymatic phenylalanine biosensor for non-invasive evaluation of fish freshness using biofluid from the fish body surface has been developed based on phenylalanine dehydrogenase (PDH) and nicotinamide adenine dinucleotide (NAD+) chemisorbed on the graphene oxide-chitosan (GO/CT) nanocomposites film. The immobilized PDH on the biosensor surface via EDC/NHS coupling strategy catalyzed the oxidative deamination of phenylalanine to phenylpyruvate, and concomitantly converted the cofactor NAD+ (oxidized form) to fluorophore NADH (reduced form), which can be quantified by using fluorescence spectrophotometer. The phenylalanine-responsive fluorescent biosensor showed a dynamic linear concentration range between 0.03 mM and 0.24 mM phenylalanine at 644 nm emission wavelength with an excitation wavelength of 320 nm. The limit of detection (LOD) of the fluorometric phenylalanine biosensor was estimated at 0.02 mM with a fast response time of 1 min. No significant interference by amines-synthesized amino acids, such as histamine, creatine, sarcosine, creatinine, tyrosine and uric acid at typical physiological levels commonly co-exist with phenylalanine in the biofluid metabolite of fish towards fresh fish quality grading. Validation study of the GO/CT catalytic film revealed excellent practicality of the biosensor in biological fluid sample of tuna fish (Euthynnus affinis) for detection of phenylalanine. The proposed GO/CT nanocomposites biofilm offers rapid test that can be assessed with an easy manner to rapidly analyze large number of samples in a short period of time.

The presence of mycotoxins in foodstuffs and feedstuffs is a serious concern for human health. The detection of mycotoxins is therefore necessary as a preventive action to avoid the harmful contamination of foodstuffs and animal feed. In comparison with the considerable expense of treating contaminated foodstuffs, early detection is a cost-effective way to ensure food safety. The high affinity of bio-recognition molecules to mycotoxins has led to the development of affinity columns for sample pre-treatment and the development of biosensors for the quantitative analysis of mycotoxins. Aptamers are a very attractive class of biological receptors that are currently in great demand for the development of new biosensors. In this review, the improvement in the materials and methodology, and the working principles and performance of both conventional and recently developed methods are discussed. The key features and applications of the fundamental recognition elements, such as antibodies and aptamers are addressed. Recent advances in aptasensors that are based on different electrochemical (EC) transducers are reviewed in detail, especially from the perspective of the diagnostic mechanism; in addition, a brief introduction of some commercially available mycotoxin detection kits is provided.

The presence of histamine in foods due to improper storage of foods is associated with toxicological risk and quality indicators. An impedimetric sensor was developed by immobilising fluoro-substituted hydroxyl functionalised Schiff base zinc(II) complex on the titanium dioxide nanoparticles-coated fluorine-doped tin oxide (nano-TiO2/FTO) electrode for sensitive and selective determination of histamine with high recovery ability. Elucidation of chemical structure for the Zn(II)-Schiff base complex has been conducted by employing NMR, FTIR and ESI-MS spectroscopic techniques, whilst Schiff base complex-histamine binding affinity was evaluated by means of Raman spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical impedimetric sensor showed charge-transfer resistance (Rct) response that is proportional to the logarithm of histamine concentration between 1.0 × 10−7 M and 1.0 × 10−2 M (R² = 0.9894), which is useful for the determination of typical histamine levels in food samples. The impedimetric sensor exhibited high selectivity towards histamine over other biogenic amines occurring in foods e.g. putrescine and cadaverine, and some other amine compounds e.g. ethanolamine (1˚ amine), 1,2-phenylenediamine (1,2-PDA, 2˚ amine) and triethylamine (TED, 3˚ amine). The Schiff base complex electrode is reusable, and rapid regeneration of the electrode within 30 s simply by using water allows high-throughput histamine assay. Impedimetric detection of histamine in salmon fillet at the Schiff base complex electrode has been validated with HPLC and showed high promise to be applied as an inexpensive and effective tool for food safety surveillance.

A solid-state DNA optode sensor has been developed based on the employment of glutaraldehyde (GD)-activated aminated silica nanoparticles (SiO2NPs-NH2) DNA carrier matrix, and the newly synthesized yellowish N,N’-bis-5-(hydroxysalicylidene)phenylene-diamine-zinc(II) (i.e. the Zn salphen complex) oligonucleotide label. Some three Schiff base complexes with three different transition metal ions (Zn2+, Ni2+, Cu2+) were synthesized through a simple one-pot reaction (5 h), and characterized by their physical and chemical properties based on FTIR, NMR and ESI–MS analyses. Due to the square planar geometry and aromatic ring structured characteristics of the metal complex intercalators, they could intercalate between DNA bases via π-π stacking interaction, and rendered a yellowish pink hue on the DNA biosensor surface. Reflectometric optimization revealed high selectivity of the nanosilica-based DNA biosensor in the detection of dengue serotype 2 DNA, which capable of discriminating even a single nucleotide mismatch. The optical DNA biosensor demonstrated a linear reflectance response between 1.0 × 10−15 M and 1.0 × 10−11 M cDNA (R2 = 0.9975) with a fast DNA hybridization time of 30 min and a limit of detectable (LOD) DNA concentration as low as 1 zM. In addition, this biosensor showed high shelf life stability with a 20-day operational duration and reusable for five consecutive DNA testings. The proposed optical DNA biosensor offers biosensing performance far superior to that of previously reported electrochemical DNA biosensor for early diagnosis of dengue infection with respect to dynamic linear range, LOD and response time.

Candida albicans and Cryptococcus neoformans, human-pathogenic fungi found worldwide, are receiving increasing attention due to high morbidity and mortality in immunocompromised patients. In the present work, 110 fungus pairs were constructed by coculturing 16 wood-decaying basidiomycetes, among which coculture of Trametes robiniophila Murr and Pleurotus ostreatus was found to strongly inhibit pathogenic fungi through bioactivity-guided assays. A combination of metabolomics and molecular network analysis revealed that 44 features were either newly synthesized or produced at high levels in this coculture system and that 6 of the features that belonged to a family of novel and unusual linear sesterterpenes contributed to high activity with MICs of 1 to 32 μg/ml against pathogenic fungi. Furthermore, dynamic 13C-labeling analysis revealed an association between induced features and the corresponding fungi. Unusual sesterterpenes were 13C labeled only in P. ostreatus in a time course after stimulation by the coculture, suggesting that these sesterterpenes were synthesized by P. ostreatus instead of T. robiniophila Murr. Sesterterpene compounds 1 to 3 were renamed postrediene A to C. Real-time reverse transcription-quantitative PCR (RT-qPCR) analysis revealed that transcriptional levels of three genes encoding terpene synthase, farnesyl-diphosphate farnesyltransferase, and oxidase were found to be 8.2-fold, 88.7-fold, and 21.6-fold higher, respectively, in the coculture than in the monoculture, indicating that biosynthetic gene cluster 10 was most likely responsible for the synthesis of these sesterterpenes. A putative biosynthetic pathway of postrediene A to postrediene C was then proposed based on structures of sesterterpenes and molecular network analysis. IMPORTANCE A number of gene clusters involved in biosynthesis of secondary metabolites are presumably silent or expressed at low levels under conditions of standard laboratory cultivation, resulting in a large gap between the pool of discovered metabolites and genome capability. This work mimicked naturally occurring competition by construction of an artificial coculture of basidiomycete fungi for the identification of secondary metabolites with novel scaffolds and excellent bioactivity. Unusual linear sesterterpenes of postrediene A to C synthesized by P. ostreatus not only were promising lead drugs against human-pathogenic fungi but also highlighted a distinct pathway for sesterterpene biosynthesis in basidiomycetes. The current work provides an important basis for uncovering novel gene functions involved in sesterterpene synthesis and for gaining insights into the mechanism of silent gene activation in fungal defense.

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.

A novel disposable electrochemical biosensor based on immobilized calf thymus double-stranded DNA (dsDNA) on the carbon-based screen-printed electrode (SPE) is developed for rapid biorecognition of carrageenan by using methylene blue (MB) redox indicator. The biosensor protocol for the detection of carrageenan is based on the concept of competitive binding of positively charged MB to the negatively charged dsDNA and carrageenan. The decrement in the MB cathodic peak current (ipc) signal as a result of the released MB from the immobilized dsDNA, and attracted to the carrageenan can be monitored via differential pulse voltammetry (DPV). The biosensor showed high sensitivity and selectivity to carrageenan at low concentration without interference from other polyanions such as alginate, gum arabic and starch. Calibration of the biosensor with carrageenan exhibited an excellent linear dependence from 1–10 mg L−1 (R2 = 0.98) with a detection limit of 0.08 mg L−1. The DNA-based carrageenan biosensor showed satisfactory reproducibility with 5.6–6.9% (n = 3) relative standard deviations (RSD), and possessing several advantages such as simplicity, fast and direct application to real sample analysis without any prior extensive sample treatments, particularly for seaweeds and food analyses.

Carbon dots (C-dots) were used to study the binding mechanisms with serum protein, bovine serum albumin (BSA) by using two notable binding systems known as non-covalent and covalent interaction. Interaction between C-dots and BSA were estimated by Stern-Volmer equation and Double Log Regression Model (DLRM). According to the fluorescent intensity, quenching of model carrier protein by C-dots was due to dynamic quenching for non-covalent and static quenching for covalent binding. The binding site constant, KA and number of binding site, for covalent interaction is 1754.7L/mol and n≈1 (0.6922) were determined by DLRM on fluorescence quenching results. The blue shift of the fluorescence spectrum, from 450nm to 421nm (non-covalent) and 430nm (covalent) and suggested that both the microenvironment of C-dots and protein changed in relation to the protein concentration. The fluorescence intensity results show that protein structure has a significant role in Protein-C-dots interactions and type of binding influence physicochemical properties of C-dots differently. Understanding to this bio interface is important to utilize both quantum dots and biomolecules for biomedical field. It can be a useful guideline to design further applications in biomedical and bioimaging.

A potentiometric whole cell biosensor based on immobilized marine bacterium, Pseudomonas carrageenovora producing κ-carrageenase and glycosulfatase enzymes for specific and direct determination of κ-carrageenan, is described. The bacterial cells were immobilized on the self-plasticized hydrogen ion (H+)-selective acrylic membrane electrode surface to form a catalytic layer. Hydrogen ionophore I was incorporated in the poly(n-butyl acrylate) [poly(nBA)] as a pH ionophore. Catalytic decomposition of κ-carrageenan by the bienzymatic cascade reaction produced neoagarobiose, an inorganic sulfate ion and a proton. The latter was detectable by H+ ion transducer for indirect potentiometric quantification of κ-carrageenan concentration. The use of a disposable screen-printed Ag/AgCl electrode (SPE) provided no cleaning requirement and enabled κ-carrageenan detection to be carried out conveniently without cross contamination in a complex food sample. The SPE-based microbial biosensor response was found to be reproducible with high reproducibility and relative standard deviation (RSD) at 2.6% (n = 3). The whole cell biosensor demonstrated a broad dynamic linear response range to κ-carrageenan from 0.2-100 ppm in 20 mM phosphate buffer saline (PBS) at pH 7.5 with a detection limit at 0.05 ppm and a Nernstian sensitivity of 58.78±0.87 mV/decade (R2 = 0.995). The biosensor showed excellent selectivity towards κ-carrageenan compared to other types of carrageenans tested e.g. ι-carrageenan and λ-carrageenan. No pretreatment to the food sample was necessary when the developed whole cell biosensor was employed for direct assay of κ-carrageenan in dairy product.

Previous studies have shown that waterlogging/ hypoxic conditions induce aerenchyma formation to facilitate gas exchange. Ethylene (ET) and reactive oxygen species (ROS), as regulatory signals, might also be involved in these adaptive responses. However, the interrelationships between these signals have seldom been reported. Herein, we showed that programmed cell death (PCD) was involved in aerenchyma formation in the stem of Helianthus annuus. Lysigenous aerenchyma formation in the stem was induced through waterlogging (WA), ethylene and ROS. Pre-treatment with the NADPH oxidase inhibitor diphenyleneiodonium (DPI) partially suppressed aerenchyma formation in the seedlings after treatment with WA, ET and 3-amino-1, 2, 4-triazole (AT, catalase inhibitor). In addition, pre-treatment with the ethylene perception inhibitor 1-methylcyclopropene (1-MCP) partially suppressed aerenchyma formation induced through WA and ET in the seedlings, but barely inhibited aerenchyma formation induced through ROS. These results revealed that ethylene-mediated ROS signaling plays a role in aerenchyma formation, and there is a causal and interdependent relationship during WA, ET and ROS in PCD, which regulates signal networks in the stem of H. annuus.

Background Butadiene is a platform chemical used as an industrial feedstock for the manufacture of automobile tires, synthetic resins, latex and engineering plastics. Currently, butadiene is predominantly synthesized as a byproduct of ethylene production from non-renewable petroleum resources. Although the idea of biological synthesis of butadiene from sugars has been discussed in the literature, success for that goal has so far not been reported. As a model system for methanol assimilation, Methylobacterium extorquens AM1 can produce several unique metabolic intermediates for the production of value-added chemicals, including crotonyl-CoA as a potential precursor for butadiene synthesis. Results In this work, we focused on constructing a metabolic pathway to convert crotonyl-CoA into crotyl diphosphate, a direct precursor of butadiene. The engineered pathway consists of three identified enzymes, a hydroxyethylthiazole kinase (THK) from Escherichia coli, an isopentenyl phosphate kinase (IPK) from Methanothermobacter thermautotrophicus and an aldehyde/alcohol dehydrogenase (ADHE2) from Clostridium acetobutylicum. The Km and kcat of THK, IPK and ADHE2 were determined as 8.35 mM and 1.24 s−1, 1.28 mM and 153.14 s−1, and 2.34 mM and 1.15 s−1 towards crotonol, crotyl monophosphate and crotonyl-CoA, respectively. Then, the activity of one of rate-limiting enzymes, THK, was optimized by random mutagenesis coupled with a developed high-throughput screening colorimetric assay. The resulting variant (THKM82V) isolated from over 3000 colonies showed 8.6-fold higher activity than wild-type, which helped increase the titer of crotyl diphosphate to 0.76 mM, corresponding to a 7.6% conversion from crotonol in the one-pot in vitro reaction. Overexpression of native ADHE2, IPK with THKM82V under a strong promoter mxaF in M. extorquens AM1 did not produce crotyl diphosphate from crotonyl-CoA, but the engineered strain did generate 0.60 μg/mL of intracellular crotyl diphosphate from exogenously supplied crotonol at mid-exponential phase. Conclusions These results represent the first step in producing a butadiene precursor in recombinant M. extorquens AM1. It not only demonstrates the feasibility of converting crotonol to key intermediates for butadiene biosynthesis, it also suggests future directions for improving catalytic efficiency of aldehyde/alcohol dehydrogenase to produce butadiene precursor from methanol. Electronic supplementary material The online version of this article (10.1186/s12934-018-1042-4) contains supplementary material, which is available to authorized users.

A membrane-based potentiometric biosensor has been fabricated from poly(n-butyl acrylate-co-N-acryloxysuccinimide as both enzyme supporting matrix and pH-sensitive transducer on the Ag/AgCl screen-printed electrode for rapid and facile determination of formaldehyde. Detection of formaldehyde was based on H+ ion transfer reaction at the electrode–electrolyte interface facilitated with immobilized hydrogen ionophore via ion-ionophore complexation at the interface. The potentiometric enzyme biosensor demonstrated a broad linear range to formaldehyde from 0.5 to 220.0 mM (R2 = 0.9982) with fast response time within 8 s and sensitivity of 59.23 ± 0.85 mV/decade (n = 5). The operational stability of the formaldehyde biosensor with covalently immobilized alcohol oxidase showed > 95% sensitivity throughout the biosensor lifetime experimental period of 80 days. The formaldehyde biosensor based on succinimide-functionalized polyacrylate ion-selective membrane sustained negligible interference of potential interferants, e.g. methanol, ethanol, glucose and glycerol, and its feasibility for accurate assay of formaldehyde in commercial fish samples has been validated with UV–Vis spectrophotometric Nash standard method.

Histamine is one of the important biomarkers for food spoilage in the food sectors. In the present study, a rapid and simple analytical tool has been developed to detect histamine as an indirect strategy to monitor food freshness level. Optical histamine sensor with carboxyl-substituted Schiff base zinc(II) complex with hydroxypropoxy side chain deposited onto titanium dioxide nanoparticles was fabricated and was found to respond successfully to histamine. The Schiff base zinc(II) complex-histamine binding generated an enhancement of the fluorescent signal. Under the optimal reaction condition, the developed sensor can detect down to 2.53 × 10−10 M in the range of between 1.0 × 10−9 and 1.0 × 10−5 M (R2 = 0.9868). Selectivity performance of the sensor towards histamine over other amines was confirmed. The sensor also displayed good reproducibility performances with low relative standard deviation values (1.45%–4.95%). Shelf-life studies suggested that the developed sensor remains stable after 60 days in histamine detection. More importantly, the proposed sensor has been successfully applied to determine histamine in salmon fillet with good recoveries. This strategy has a promising potential in the food quality assurance sectors, especially in controlling the food safety for healthy consumption among consumers.

Mass-spectrometry-based and X-ray fluorescence-based techniques have allowed the study of the distribution of Zn2+ ions at extracellular and intracellular levels over the past few years. However, there are some issues during purification steps, sample preparation, suitability for quantification, and the instruments’ availability. Therefore, work on fluorescent sensors based on 8-aminoquinoline as tools to detect Zn2+ ions in environmental and biological applications has been popular. Introducing various carboxamide groups into an 8-aminoquinoline molecule to create 8-amidoquinoline derivatives to improve water solubility and cell membrane permeability is also a recent trend. This review aims to present a general overview of the fluorophore 8-aminoquinoline and its derivatives as Zn2+ receptors for zinc sensor probes. Various fluorescent chemosensor designs based on 8-amidoquinoline and their effectiveness and potential as a recognition probe for zinc analysis were discussed. Based on this review, it can be concluded that derivatives of 8-amidoquinoline have vast potential as functional receptors for zinc ions primarily because of their fast reactivity, good selectivity, and bio-compatibility, especially for biological applications. To better understand the Zn2+ ion fluorophores’ function, diversity of the coordination complex and geometries need further studies. This review provides information in elucidating, designing, and exploring new 8-amidoquinoline derivatives for future studies for the improvement of chemosensors that are selective and sensitive to Zn2+.

An electrochemical Hg(II) ion sensor has been developed by using a miniaturized carbon paste screen-printed electrode (CSPE) modified with reduced graphene oxide (rGO) sheets and tris-thiourea (TTU) chelating ligand compound, i.e. N,N′,N″-((nitrilotris(ethane-2,1diyl))tris(azanediyl))tris(carbonothioyl))tribenz amide. In view of the strong cation-exchange characteristic and adsorption of aromatic TTU tridentate ligand on the graphene nanomaterial surface by non-covalent π–π stacking interaction, the differential pulse voltammetry (DPV) peak current response of the voltammetric sensor was linearly dependent on a broad Hg(II) ion concentration detection range from 0.1–00.0 mg L−1 with a limit of detection (LOD) estimated at 0.02 mg L−1 after accumulation for 10 min. The chemically modified miniaturized SPE showed high stability throughout the course of the sensor lifetime study for the detection of inorganic Hg(II) ion with a relative standard deviation (RSD) of the sensor response obtained at 1.2%. The electrochemical sensor is reusable up to three consecutive Hg(II) ion assays by using 0.05 M acetate buffer (pH 8) as the sensor regeneration solution with a reversibility RSD value of 3.9%. The voltammetric sensor based on TTU derivative element and rGO nanosheets revealed satisfactory selectivity for Hg(II) ion over a large number of potential interfering ions, e.g. Ca(II), Co(II), Cu(II), Fe(II), Ni(II), Na(I) and Zn(II), and demonstrated reliable quantitative results as compared to the results obtained with inductively coupled plasma-mass spectrometer (ICP-MS) standard method for Hg(II) ion detection in river water samples.

A fluorescence bi-enzyme optical arginine biosensor based on novel fluorophore carbon nanodots (C-dots) pH indicator derived from natural Gadong (Dioscorea hispida) tuber was developed. The brightly luminescent pH sensitive carbon-based quantum dots (QDs) exploited from exotic wild yam polysaccharides via aqueous-based synthesis method were immobilized on the acrylic-N-acryloxysuccinimide copolymer microspheres. Recombinant Glaciozyma antarctica arginase (GaArg) cloned in E. coli expression system and commercial urease were grafted on the acrylic microspheres (AMS) via peptide covalent link. During fluorescence arginine detection, the immobilized arginase catalyzed hydrolysis conversion of arginine to ornithine and urea, and subsequent enzymatic hydrolysis of urea by immobilized urease rendering deprotonation of starch-based C-dots, resulted in the heightening of C-dots’ photoluminescence intensity due to elevated localized pH. Under 380 nm excitation, the C-dots fluorescence intensity at 420 nm increased linearly with arginine over the concentration range of 1–10 mM, with the limit of detection (LOD) estimated at 0.9 mM. The Gadong starch-based C-dots, which prepared from different natural tuber samples showed high reproducible physico-chemical properties, and gave reproducible fluorescence intensity at different pH values with relative standard deviation (RSD) values obtained at

A reagentless, rapid and facile optical reflectance sensor has been fabricated based on immobilization of novel bis-thiourea (BT) ligand compound, N,N′-(((3,3′-dimethoxy-[1,1′-biphenyl]-4,4′-diyl)bis(azanediyl))bis(carbonothioyl))bis(4-methoxybenzamide) onto acrylic poly(n-butyl acrylate) [poly(nBA)] microspheres for sensitive and selective determination of Cu2+ ion in aqueous solution. Binding study of BT ionophore toward Cu2+ ions was performed via colorimetric detection and UV–Vis titration experiments. The stoichiometric binding ratio and binding constant (Ka) of BT to Cu2+ ion was determined to be 1:2 and 5.2 × 104 M−1, respectively, based upon Job's plot and Benesi–Hildebrand analyses. The optical reflectance chemosensor based on BT derivative element responded exclusively to Cu2+ ion while being almost irresponsive to the other interfering ions, and exhibited a dynamic linear response range from 7.80 × 10−7–1.60 × 10−4 M Cu2+ ion with a limit of detection (LOD) of 6.12 × 10−7 M, and fast response time of

An optical aptasensor-based sensing platform for rapid insulin detection was fabricated. Aminated porous silica microparticles (PSiMPs) were synthesized via a facile mini-emulsion method to provide large surface area for covalent immobilization of insulin-binding DNA aptamer (IGA3) by glutaraldehyde cross-linking protocol. A Nickel-salphen type complex with piperidine side chain [Ni(II)-SP] was synthesized with a simple one-pot reaction, and functionalized as an optical label due to strong π-π interaction between aromatic carbons of G-quadruplex DNA aptamer and planar aromatic groups of Ni(II)-SP to form the immobilized IGA3-Ni(II)-SP complex, i.e. the dye-labeled aptamer, thereby bringing yellow colouration to the immobilized G-quartet plane. Optical characterization of aptasensor towards insulin binding was carried out with a fiber optic reflectance spectrophotometer. The maximum reflectance intensity of the immobilized IGA3-Ni(II)-SP complex at 656 nm decreased upon binding with insulin as aptasensor changed to brownish orange colouration in the background. This allows optical detection of insulin as the colour change of aptasensor is dependent on the insulin concentration. The linear detection range of the aptasensor is obtained from 10 to 50 μIU mL−1 (R2 = 0.9757), which conformed to the normal fasting insulin levels in human with a limit of detection (LOD) at 3.71 μIU mL−1. The aptasensor showed fast response time of 40 min and long shelf life stability of >3 weeks. Insulin detection using healthy human serums with informed consent provided by participants suggests the DNA aptamer biosensor was in good agreement with ELISA standard method using BIOMATIK Human INS (Insulin) ELISA Kit.

A sensitive and selective optical DNA biosensor was developed for dengue virus detection based on novel square-planar piperidine side chain-functionalized N,N′-bis-4-(hydroxysalicylidene)-phenylenediamine-nickel(II), which was able to intercalate via nucleobase stacking within DNA and be functionalized as an optical DNA hybridization marker. 3-Aminopropyltriethoxysilane (APTS)-modified porous silica nanospheres (PSiNs), was synthesized with a facile mini-emulsion method to act as a high capacity DNA carrier matrix. The Schiff base salphen complexes-labelled probe to target nucleic acid on the PSiNs renders a colour change of the DNA biosensor to a yellow background colour, which could be quantified via a reflectance transduction method. The reflectometric DNA biosensor demonstrated a wide linear response range to target DNA over the concentration range of 1.0 × 10−16–1.0 × 10−10 M (R2 = 0.9879) with an ultralow limit of detection (LOD) at 0.2 aM. The optical DNA biosensor response was stable and maintainable at 92.8% of its initial response for up to seven days of storage duration with a response time of 90 min. The reflectance DNA biosensor obtained promising recovery values of close to 100% for the detection of spiked synthetic dengue virus serotypes 2 (DENV-2) DNA concentration in non-invasive human samples, indicating the high accuracy of the proposed DNA analytical method for early diagnosis of all potential infectious diseases or pathological genotypes.

A new biosensor for the analysis of nitrite in food was developed based on hemoglobin (Hb) covalently immobilized on the succinimide functionalized poly(n-butyl acrylate)-graphene [poly(nBA)-rGO] composite film deposited on a carbon-paste screen-printed electrode (SPE). The immobilized Hb on the poly(nBA)-rGO conducting matrix exhibited electrocatalytic ability for the reduction of nitrite with significant enhancement in the reduction peak at −0.6 V versus Ag/AgCl reference electrode. Thus, direct determination of nitrite can be achieved by monitoring the cathodic peak current signal of the proposed polyacrylic-graphene hybrid film-based voltammetric nitrite biosensor. The nitrite biosensor exhibited a reproducible dynamic linear response range from 0.05–5 mg L−1 nitrite and a detection limit of 0.03 mg L−1. No significant interference was observed by potential interfering ions such as Ca2+, Na+, K+, NH4+, Mg2+, and NO3− ions. Analysis of nitrite in both raw and processed edible bird’s nest (EBN) samples demonstrated recovery of close to 100%. The covalent immobilization of Hb on poly(nBA)-rGO composite film has improved the performance of the electrochemical nitrite biosensor in terms of broader detection range, lower detection limit, and prolonged biosensor stability.

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.

A label-free impedimetric DNA biosensor based on graphene nanosheets has been developed for the detection of Escherichia coli O157:H7 strain GZ-021210. Probe DNA (pDNA) of E. coli was immobilized onto graphene nanosheets by the surface functionalization of graphene with 1-pyrenebutyric acid (PyBA) followed by carbodiimide linkage. The hybridization of complementary DNA (cDNA) of E. coli with the immobilized pDNA increased the electron transfer resistance of the graphene nanosheets, as observed by electrochemical impedance spectroscopy (EIS). The E. coli DNA biosensor displayed a wide range of linear response (1.0 × 10−10 M to 1.0 × 10−14 M), low detection limit (0.7 × 10−15 M), single-base mismatch selectivity, high robustness and good reproducibility. The current work demonstrates an important advancement in the development of a sensitive biosensor for E. coli detection.

Magnesium (Mg)-deficiency is a widespread problem adversely affecting the quality and yield of crops, including citrus. 'Xuegan' [Citrus sinensis (L.) Osbeck] seedlings were irrigated every other day with nutrient solution at an Mg concentration of 0 mM (Mg-deficiency) or 1 mM (Mg-sufficiency) for 16 weeks. Thereafter, biomass, leaf mass per area, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), pigments in the upper and lower leaves, Mg, gas exchange, organic acids, nonstructural carbohydrates, total soluble proteins, amino acids, phenolics and anthocyanins, and key enzymes related to organic acid, amino acid and phenolic metabolisms in the roots, and upper and lower leaves were assayed in order to test the hypothesis that Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes may differ among the roots, and upper and lower leaves. Magnesium-deficiency affected the most measured parameters more in the lower than in the upper leaves except for the nonstructural carbohydrates, but the variation trends were similar between the two. Despite increased accumulation of nonstructural carbohydrates, the lower CO2 assimilation in the Mg-deficient leaves was not caused by the feedback inhibition mechanism via sugar accumulation. Both dark respiration and organic acid metabolism were elevated in the Mg-deficient lower leaves to 'consume' the excess carbohydrates, and inhibited in the Mg-deficient roots with less accumulation of nonstructural carbohydrates to keep the balance of net carbon. More total phenolics and fewer anthocyanins were accumulated in the Mg-deficient lower leaves, whereas the accumulation of both total phenolics and anthocyanins was reduced in the Mg-deficient roots. Interestingly, amino acid biosynthesis was repressed in the Mg-deficient roots and lower leaves, thus lowering the level of total free amino acids in these roots and leaves. To conclude, great differences existed in the Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes among the roots, and upper and lower leaves.

Seedlings of “Xuegan” (Citrus sinensis) and “Sour pummelo” (Citrus grandis) were irrigated daily with a nutrient solution at a pH of 2.5, 3, 4, 5, or 6 for 9 months. Thereafter, the following responses were investigated: seedling growth; root, stem, and leaf concentrations of nutrient elements; leaf gas exchange, pigment concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and chlorophyll a fluorescence; relative water content, total soluble protein level, H2O2 production and electrolyte leakage in roots and leaves. This was done (a) to determine how low pH affects photosynthesis, related physiological parameters, and mineral nutrient profiles; and (b) to understand the mechanisms by which low pH may cause a decrease in leaf CO2 assimilation. The pH 2.5 greatly inhibited seedling growth, and many physiological parameters were altered only at pH 2.5; pH 3 slightly inhibited seedling growth; pH 4 had almost no influence on seedling growth; and seedling growth and many physiological parameters reached their maximum at pH 5. No seedlings died at any given pH. These results demonstrate that citrus survival is insensitive to low pH. H+-toxicity may directly damage citrus roots, thus affecting the uptake of mineral nutrients and water. H+-toxicity and a decreased uptake of nutrients (i.e., nitrogen, phosphorus, potassium, calcium, and magnesium) and water were likely responsible for the low pH-induced inhibition of growth. Leaf CO2 assimilation was inhibited only at pH 2.5. The combinations of an impaired photosynthetic electron transport chain, increased production of reactive oxygen species, and decreased uptake of nutrients and water might account for the pH 2.5-induced decrease in CO2 assimilation. Mottled bleached leaves only occurred in the pH 2.5-treated C. grandis seedlings. Furthermore, the pH 2.5-induced alterations of leaf CO2 assimilation, water-use efficiency, chlorophylls, polyphasic chlorophyll a fluorescence (OJIP) transients and many fluorescence parameters, root and leaf total soluble proteins, H2O2 production, and electrolyte leakage were all slightly greater in C. grandis than in C. sinensis seedlings. Hence, C. sinensis was slightly more tolerant to low pH than C. grandis. In conclusion, our findings provide novel insight into the causes of low pH-induced inhibition of seedling growth and leaf CO2 assimilation.

Transcriptomic analysis of cultured fungi suggests that many genes for secondary metabolite synthesis are presumably silent under standard laboratory condition. In order to investigate the expression of silent genes in symbiotic systems, 136 fungi-fungi symbiotic systems were built up by co-culturing seventeen basidiomycetes, among which the co-culture of Trametes versicolor and Ganoderma applanatum demonstrated the strongest coloration of confrontation zones. Metabolomics study of this co-culture discovered that sixty-two features were either newly synthesized or highly produced in the co-culture compared with individual cultures. Molecular network analysis highlighted a subnetwork including two novel xylosides (compounds 2 and 3). Compound 2 was further identified as N-(4-methoxyphenyl)formamide 2-O-β-D-xyloside and was revealed to have the potential to enhance the cell viability of human immortalized bronchial epithelial cell line of Beas-2B. Moreover, bioinformatics and transcriptional analysis of T. versicolor revealed a potential candidate gene (GI: 636605689) encoding xylosyltransferases for xylosylation. Additionally, 3-phenyllactic acid and orsellinic acid were detected for the first time in G. applanatum, which may be ascribed to response against T.versicolor stress. In general, the described co-culture platform provides a powerful tool to discover novel metabolites and help gain insights into the mechanism of silent gene activation in fungal defense.

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 10–60 ppm and a fast response time of 2 min when compared with many commonly used coloured reagents. The limit of detection (LOD) of the optical NH4+ ion sensor was 7.9 ppm 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.

One of the major problems in the analysis of ammonia (NH 3 ) using spectrophotometric method is highly coloured water sample. A reflectometric NH 3 sensor based on a facile single-step immobilisation of cobalt(II) (Co 2+ ) ion onto high capacity Dowex HCR-W2 microspheres has been developed to enable the direct NH 3 determination in highly coloured water samples. The combination of Co 2+ 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 Co 2+ ion, when complexed with NH 3 gave a blue colouration of hexamminecobaltate(II) ([Co(NH 3 ) 6 ] 2+ ) complex at pH 13. The NH 3 sensor reached maximum colour intensity in ∼6 min at ambient conditions. The linear calibration curve was 60–290 mM NH 3 with a detection limit of 16 mM NH 3 , which is suitable for direct determination of NH 3 -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 NH 3 in heavily polluted sewage water. The results obtained were in good agreement with those produced by acidimetric reference method.

A new optosensor for visual quantitation of nitrite (NO2(-)) ion has been fabricated by physically immobilizing Safranine O (SO) reagent onto a self-adhesive poly(n-butyl acrylate) [poly(nBA)] microspheres matrix, which was synthesized via facile microemulsion UV lithography technique. Evaluation and optimization of the optical NO2(-) ion sensor was performed with a fiber optic reflectance spectrophotometer. Scanning electron micrograph showed well-shaped and smooth spherical morphology of the poly(nBA) microspheres with a narrow particles size distribution from 0.6 μm up to 1.8 μm. The uniform size distribution of the acrylic microspheres promoted homogeneity of the immobilized SO reagent molecules on the microspheres' surfaces, thereby enhanced the sensing response reproducibility (

Ammonia (NH3) has been widely used in the manufacture of fertilizers that applied to soil, but the high consumption of fertilizers will end up with water pollution. Owing to the deleterious effects of NH3 to human and environment, a new optosensor for NH3 has been fabricated based on silica pellet sensing material. Microsilica was synthesized by sol-gel method in the presence of cobalt(II) chloride hexahydrate (CoCl2·6H2O), followed by manual grinding process to obtain micro-sized silica particles. Due to the non-transparent pellet material used for NH3 sensing, a fiber optic reflectance spectrophotometer was employed for monitoring of reflectance signal transduction event as the pellet colour changed from pink to blue hue upon reaction with NH3 at optimum pH 13. Due to the high porosity and surface area of silica microparticles were used as immobilization matrix, the immobilized Co2+ ion demonstrated broad dynamic linear range from 18 to 100 ppm NH3 with a fast response time of 3 min. The reflectometric sensing protocol involves a single-step NH3 assay which merely requires dispensing small aliquots of NH3 onto the reaction surface of the pellet sensor. This makes on-site NH3 detection more user-friendly and convenient when compared to traditional electrochemical-, infrared- and gas chromatography-based methods.

The use of the enzyme alanine dehydrogenase (AlaDH) for the determination of ammonium ion (NH(4)(+)) usually requires the addition of pyruvate substrate and reduced nicotinamide adenine dinucleotide (NADH) simultaneously to effect the reaction. This addition of reagents is inconvenient when an enzyme biosensor based on AlaDH is used. To resolve the problem, a novel reagentless amperometric biosensor using a stacked methacrylic membrane system coated onto a screen-printed carbon paste electrode (SPE) for NH(4)(+) ion determination is described. A mixture of pyruvate and NADH was immobilized in low molecular weight poly(2-hydroxyethyl methacrylate) (pHEMA) membrane, which was then deposited over a photocured pHEMA membrane (photoHEMA) containing alanine dehydrogenase (AlaDH) enzyme. Due to the enzymatic reaction of AlaDH and the pyruvate substrate, NH(4)(+) was consumed in the process and thus the signal from the electrocatalytic oxidation of NADH at an applied potential of +0.55 V was proportional to the NH(4)(+) ion concentration under optimal conditions. The stacked methacrylate membranes responded rapidly and linearly to changes in NH(4)(+) ion concentrations between 10-100 mM, with a detection limit of 0.18 mM NH(4)(+) ion. The reproducibility of the amperometrical NH(4)(+) biosensor yielded low relative standard deviations between 1.4-4.9%. The stacked membrane biosensor has been successfully applied to the determination of NH(4)(+) ion in spiked river water samples without pretreatment. A good correlation was found between the analytical results for NH(4)(+) obtained from the biosensor and the Nessler spectrophotometric method.

To explore natural herbs to maintain the bactericidal activity of hydrogen peroxide (H).Eighteen extracts of Chinese herbs were prepared complying with the standard protocol. Each of the solutions was then mixed with 1% H2O2. The mixtures were handled with two approaches: autoclaved daily for one, two or three times; stored at room temperature from one through five years. Then the bactericidal activity were evaluated by assaying the minimal bactericidal concentration (MBC) and minimal inhibitory concentration (MIC) against Gram positive (Staphylococcus aureus, ATCC25923) and Gram negative (Escherichia coli, ATCC12421) bacteria.While mixed with 1% H2O2, 10 out of 18 kinds of assessed Chinese herbs displayed MBC values at 1:12800 or higher after three times of autoclaving, and 8 of them preserved such level of MBC value after stored at room temperature for three years. Some Chinese herbs, i.e. R. Scutellariae, R. Coptidis, R. Bupleuri, H. Epimedii, C. Phelledendri and F. Chrysanthemi, can significantly maintain the bactericidal activity of diluted H2O2.Certain Chinese herbs can effectively stabilize the bactericidal activity of H2O2 undergoing autoclave or long-term storage. This paper reported a brandnew pharmaceutical function of Chinese herbs and provided experimental data for the potential enhancement of H2O2 usage while its stability level is promoted.