Search

A novel and simple optical biosensor to detect triglycerides (TGs) has been successfully constructed by using pectin hydrogel membrane as the indicator pH and chromoionophore ETH 5294 (CI), with lipase as the catalyst. The enzymatic working system against TGs releasing H+ ions will affect the color absorbance of CI. The characterization results show that a TG biosensor has the optimum condition and sensitivity at the phosphate buffer concentration of 50 mM, pH 7, and enzyme loading of 60 &mu, g. The biosensor works at the tripalmitin (TP) concentration range of 100&ndash, 400 mg/dL. With the sensitivity of 0.001 (∆A/(mg/dL)), the biosensor response reaches stability after five minutes, and the limit of detection (LOD) of the TG optical biosensor is 15 mg/dL. Relative standard deviation (RSD) in a reproducibility test was 2.5%, with a 15-day lifespan.

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.

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.

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.

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.

Fish are an important source of proteins and healthy lipids. However, they can accumulate nonpolar pollutants such as polycyclic aromatic hydrocarbons (PAHs) from their aquatic environment through absorption and/or adsorption. Human exposure to parent PAHs by fish consumption has not yet been determined. This study aims to assess the exposure of Malaysians to PAHs through fish ingestion and to estimate the lifetime cancer risk using the cancer risk assessment guidelines set by the U.S. Environmental Protection Agency (US EPA) and previous studies. Giant sea perch (barramundi) were collected from a fish farm on Langkawi Island. The mean concentration of 18 PAHs in the giant sea perch was 573.66 ± 47.56 ng g−1 dry weight. The abundance of low-molecular-weight PAHs (63%) was higher than that of high-molecular-weight PAHs (37%), indicating that petrogenic inputs were higher than pyrogenic inputs. The average daily intake of the 18 PAHs through giant sea perch consumption was 294.47 [ng/kg bwt/day]−1. ...

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 IC 50 = 1236.54±12.83 µ g/mL in the DPPH radical scavenging activity, 22.76% inhibition in the β-carotene bleaching test at 1000 µ g/mL, and IC 50 = 878±16.54 µ g/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 .

A new optical urea biosensor based on urease (Urs) physically attached to a pH optode made from Nile Blue (NB) chromoionophore-doped kappa-carrageenan (KC) membrane is described in this paper. The immobilized Urs on the biosensor surface catalyzed the hydrolytic decomposition of urea into ammonium hydroxide, a pH changed to a more basic condition, and resulted in a colour change of the pH sensor membrane from blue to violet, which can be quantified reflectometrically using a fibre optic reflectance spectrophotometer. A linear relationship was perceived between the reflectance intensity of the KC membrane-based biosensor and the urea concentration in the range of 0.001–100 mM with the detection limit calculated at 0.001 mM. The response time of the urea biosensor was 10 min, and no significant discrepancy was noted for the results obtained from the direct analysis of urine samples by both the reflectance catalytic biosensor and the UV–vis spectrophotometric standard method based on the p -dimethylaminobenzaldehyde (DMAB) reagent.

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.

Spectrophotometric determination of hydroxymethylfurfural (HMF) based on p-toluidine as a reagent has been studied. The absorption intensities were measured at a wavelength range of 250 to 500 nm to record the absorption spectra before and after reaction with the HMF. The solution response was obtained at pH 3. The concentration of HMF was 5 × 10-3M, whereas for p-toluidine was 8 × 10-3M .The relative standard deviation (R.S.D.) of reproducibility was 3.33% when concentration of p-toluidine 3 × 10-3M was used .The photostability was found to be good with 1.9 %. M was used . The photostability was found to be good with 1.9 %.

Biogenic amines (BA) are chemistry compounds shaped by amino acids decarboxylation and exist in protein food and beverages. They are labelled toxic if consumed and some countries prohibit to consume them in high level especially histamine. Two major methods have been used and developed well such as chromatography methods and sensors methods. The common method applied for chromatography namely liquid chromatography (LC) and gas chromatography (GC) while for sensor methods such as optical, chemical and bio sensor. These methods have advantages and disadvantages. For chromatography methods, derivatization methods are required in order to improve their sensitivity and selectivity, nevertheless these methods are very expensive and time-consuming. During derivatization step, it needs more time and bear the risk of an only partial detection due to an incomplete derivatization. Furthermore, sensor methods exist to solve these issues, while they do not require derivatization step, generate a direct signal that can be interpreted by anyone, very fast and simple, yet they have disadvantages in several aspects such as sensitivity, accuracy and selectivity compared to chromatography methods. This review is based on studies about biogenic amines detection from the last decades until now and related to food and beverage samples. Although biogenic amines commonly found in protein-food for decades, new approaches and technical possibilities still required in order to increase the sensitivity, selectivity and accuracy of analytical methods to tackle the complexity by their matrices. The rationale of this study is also to provide data about the comparison of the analytical techniques between conventional and sensor methods. Furthermore, the various approaches of biogenic amines determination and the most applied analytical methods have been reviewed.

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

Toxicity Identification Evaluation (TIE) is a useful method for the classification and identification of toxicants in a composite environment water sample. However, its extension to a larger sample size has been restrained owing to the limited throughput of toxicity bioassays. Here we reported the development of a high-throughput method of TIE Phase I. This newly developed method was assisted by the fluorescence-based cellular oxidation (CO) biosensor fabricated with roGFP2-expressing bacterial cells in 96-well microplate format. The assessment of four river water samples from Langat river basin by this new method demonstrated that the contaminant composition of the four samples can be classified into two distinct groups. The entire toxicity assay consisted of 2338 tests was completed within 12 h with a fluorescence microplate reader. Concurrently, the sample volume for each assay was reduced to 50 μL, which is 600 to 4700 times lesser to compare with conventional bioassays. These imply that the throughput of the CO biosensor-assisted TIE Phase I is now feasible for constructing a large-scale toxicity monitoring system, which would cover a whole watershed scale.

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 developed colorimetric pH sensor film based on edible materials for real-time monitoring of food freshness is described. The mixed natural dyes from edible plants Clitoria sp and Brassica sp were extracted and incorporated into &iota, carrageenan film as a colorimetric pH sensor film for monitoring food spoilage and its freshness. The color changes of the developed colorimetric sensor film were measured with chromametry and UV-vis spectroscopy, respectively. Experimental results show that colorimetric pH sensor film demonstrated statistically significant differences (p &lt, 0.05) between CIE-L*a*b* coordinates color system indicated that the developed colorimetric sensor film was able to give a gradual change in color over a wide pH range. The color of the colorimetric sensor film also changes discretely and linearly with factors that contribute to food spoilage using shrimp and durian samples. Moreover, the developed colorimetric pH sensor film has the potential to be used as a safe, non-destructive testing and also a flexibly visual method for direct assessment of food freshness indicator during storage.

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 thiourea compound, 2,2-oxybis(ethyl)-4-(1-naphthyl)-3-thiourea 3 has been synthesized and characterized by using FTIR, 1 H-NMR, 13 C-NMR, and MS spectroscopy. The binding properties of with various cations were also carried out using ‘naked eye’, UV-vis and 1 H-NMR titration experiments. This compound exhibited effective binding for Hg 2+ in the presence of other cations, such as Ag + , Ni 2+ , Sn 2+ , Zn 2+ , Fe 2+ , Cu 2+, and Pb 2+ . Continuous variation titration experiments were conducted in order to determine the binding behavior for Hg 2+ . Stoichiometry of the host and guest binding interactions were also determined using continuous variation titration experiments and plotting molar-ratio curves. Pearson Product moment method was employed to calculate the correlation coefficient, and non-linear regression equation was used to calculate dissociation constant K d . Molar-ratio and binding constant data substantiated the presence of binding sites for the compound 3 .

The growth of microbes in biofilms are associated with repeated and chronic human infections and are extremely resistant to antimicrobial agents. The purpose of this study was to determine the diversity of bacteria from necrotic roots canals of teeth and to detect their biofilm formation ability. A total of 42 bacterial isolates were isolated and identified as belonging to 11 genera. These are Enterococcus sp. (21.4%) followed by Streptococcus sp. (16.8%), Bacillus sp. (11.9%), Peptostreptococcus sp. (9.5%), Staphylococcus sp. (9.5%), Bacteroides sp. (7.1%), Clostridium sp. (7.1%), Actinomyces sp. (7.1%), Fusobacterium sp. (4.76%), Provotella sp. (2.4%) and Chromobacterium sp. (2.4%). Three screening methods for biofilm forming ability were used. Congo Red Agar method (CRA), Tube method (TM) and Microtitre Plate (MTP). From the results, MTP method is a more reliable and quantitative method for the screening and detection of microorganism’s ability to form biofilm. This method can be recommended and sugges...

The development of indicator label for detection of total volatile basic nitrogen (TVB-N) is described. Dye extract from edible plants containing anthocyanins was immobilized onto iota-carrageenan as polymer matrix. TVB-N detection worked based on pH increase as the basic deterioration volatile amines generated in the package headspace. Results showed that the indicator label has changed color from blue to green after 12 hours of storage at ambient conditions. The TVB-N value was 38.9648 mg /100 g which is exceeded of acceptability level for seafood products. The pH value of squid flesh has also increased during storage. The colour values of L * and a * negative increases while b* negative decrease with increasing storage time. The indicator label is potentially used as freshness indicator for squid at ambient conditions.

The basic concept of environmental toxicity and its importance in the evaluation of ecosystem health will be introduced. Toxicity evaluation theory and practice will be briefly discussed. Traditional techniques such as bioassays for environmental toxicity evaluation will be introduced where the advantages and disadvantages will be presented. But the main focus of environmental toxicity evaluation will be on the use of more recent techniques for rapid environmental toxicity assessments such as toxicity biosensor and its basic concept, current applications, and future prospects.

A new thiourea derivative, N1,N3-bis[[3,5-bis(trifluoromethyl)phenyl]carbamothioyl]isophthalamide (TPC), as a potential copper ionophore was investigated. TPC was immobilized via drop casting method into poly(n-butyl acrylate) pBA membrane and the sensor was characterized by potentiometric method. The sensor fabricated based on TPC showed a Nernstian response towards copper ion with the slope of 27.07±2.84 mV/decade in the range of 1.0×10-6 - 1.0-10-4 M and limit of detection of 6.24 × 10-7 M. In addition, based on the separate solution method (SSM), the logarithm selectivity coefficients were less than -3.00 for monovalent, divalent and trivalent cations that are present in the environmental water samples such as K+, Ca2+, Mg2+ and Fe3+. This confirmed that the sensor fabricated with TPC exhibited good sensitivity and selectivity towards copper ion.A new thiourea derivative, N1,N3-bis[[3,5-bis(trifluoromethyl)phenyl]carbamothioyl]isophthalamide (TPC), as a potential copper ionophore was investigated. TPC was immobilized via drop casting method into poly(n-butyl acrylate) pBA membrane and the sensor was characterized by potentiometric method. The sensor fabricated based on TPC showed a Nernstian response towards copper ion with the slope of 27.07±2.84 mV/decade in the range of 1.0×10-6 - 1.0-10-4 M and limit of detection of 6.24 × 10-7 M. In addition, based on the separate solution method (SSM), the logarithm selectivity coefficients were less than -3.00 for monovalent, divalent and trivalent cations that are present in the environmental water samples such as K+, Ca2+, Mg2+ and Fe3+. This confirmed that the sensor fabricated with TPC exhibited good sensitivity and selectivity towards copper ion.

An enzyme-based electrochemical biosensor was investigated for the analysis of Sunset Yellow synthetic food dye. A glassy carbon electrode was coated with a poly(acrylamide-co-ethyl methacrylate) membrane to immobilize laccase using a single-step photopolymerization procedure. Poly(acrylamide-co-ethyl methacrylate) membrane was demonstrated to have acceptable water absorption and suitable for biosensor application. Sunset Yellow biosensor exhibited a linear response range from 0.08 to 10.00 µM with a detection limit of 0.02 µM. This biosensor was successfully used to determine Sunset Yellow in soft drinks with recoveries of 99.0–101.6%. The method was validated using high-performance liquid chromatography, indicating the biosensor can be as a promising alternative method for Sunset Yellow detection.

A new approach for the development of a highly sensitive aluminium(III) ion sensor via the preconcentration of aluminium(III) ion with a self-assembled monolayer on a gold nanoparticles modified screen-printed carbon electrode and current mediation by potassium ferricyanide redox behavior during aluminium(III) ion binding has been attempted. A monolayer of mercaptosuccinic acid served as an effective complexation ligand for the preconcentration of trace aluminium; this led to an enhancement of aluminium(III) ion capture and thus improved the sensitivity of the sensor with a detection limit of down to the ppb level. Under the optimum experimental conditions, the sensor exhibited a wide linear dynamic range from 0.041 to 12.4 μM. The lower detection limit of the developed sensor was 0.037 μM (8.90 ppb) using a 10 min preconcentration time. The sensor showed excellent selectivity towards aluminium(III) ion over other interference ions.

A novel approach for the determination of Al3+ from aqueous samples was developed using an optode membrane produced by physical inclusion of Al3+ selective reagent, which is morin into a plasticized poly(vinyl chloride). The inclusion of Triton X-100 was found to be valuable and useful for enhancing the sorption of Al3+ ions from liquid phase into the membrane phase, thus increasing the intensity of optode’s absorption. The optode showed a linear increase in the absorbance at λmax = 425 nm over the concentration range of 1.85 × 10−6–1.1 × 10−4 mol L−1 (0.05–3 μg mL−1) of Al3+ ions in aqueous solution after 5 min. The limit of detection was determined to be 1.04 × 10−6 mol L−1 (0.028 μg mL−1). The optode developed in the present work was easily prepared and found to be stable, has good mechanical strength, sensitive and reusable. In addition, the optode was tested for Al3+ determination in lake water, river water and pharmaceutical samples, which the result was satisfactory.

The complexation reaction of Co2+ (M) and the 1,1-diethyl-3-(4-methoxybenzoyl)thiourea (L) ligand in the binary mixtures: acetonitrile–dimethylsulfoxide (MeCN–DMSO), acetonitrile–dichloromethane (MeCN–DCM), water–dimethylsulfoxide (H2O–DMSO) and acetonitrile–water (MeCN–H2O), was investigated using a conductometric method at temperatures of (288.15, 298.15, 308.15 and 318.15) K. In all cases, the conductance data showed that the stoichiometry of the neutral complex formed between M and L is 1:3 [M:3L], which indicates that the Co2+ ion was oxidized to Co3+ during the reaction. The best estimate of the stability constant, log10 K f, = 3.31 for the [CoL3] complex, was observed with the MeCN–DCM (20:80 %) binary mixture at 298.15 K. The values of the thermodynamic parameters (i.e., $$ \Delta G_{\text{c}}^{^\circ } $$ and $$ \Delta S_{\text{c}}^{^\circ } $$ ) for the formation of the [CoL3] complex were obtained from the temperature dependence of the stability constant via van’t Hoff plots. The results show that, in most cases, the [CoL3] complexes are enthalpy destabilized but entropy stabilized. The values and signs of the thermodynamic parameters are affected by the nature and composition of the mixed solvents but are independent of the temperature.

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.

In the title benzoyl­thio­urea derivative (MPiCB), the piperidine ring has a chair conformation and its mean plane is inclined to the 4-meth­oxy­benzene ring by 63.0 (3)°., 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.

The presence of carcinogens in food is a major food safety concern. A nanocomposite-based electrochemical DNA biosensor was constructed for potential carcinogen detection in food samples by immobilizing amine terminated single stranded DNA onto silica nanospheres deposited onto a screen-printed electrode modified using gold nanoparticles. The effect of three different DNA sequences: 15-base guanine, 24-base guanine and 24-base adenine-thymine rich DNA on carcinogen (formaldehyde and acrylamide) detection was evaluated. The competitive binding of the DNA with the carcinogen and electroactive indicator, Methylene blue (MB) was measured using differential pulse voltammetry. Optimization studies were conducted for MB concentration and accumulation time, DNA concentration, buffer concentration, pH and ionic strength. Overall, the 24-base guanine rich DNA yielded the best results with a detection limit of 0.0001 ppm, linear range between 0.0001 ppm and 0.1 ppm and reproducibility below 5% R.S.D. Finally, the results obtained using the biosensor were validated using Ames test.

The successful integration of nanotechnology as a platform for food sensors offers tremendous benefits in detecting contaminants, particularly in their applications for food quality and safety. The sensors based on nanomaterials (nanosensor), both chemical sensors (chemical nanosensors) and biosensors (nanobiosensors), can be used online and integrated into existing manufacturing process and distribution line or off-line as rapid, simple, and portable, as well as disposable, sensors for food contaminants. Food contaminants could be residues of pesticides, veterinary and human drugs, microbial toxins, preservatives, contaminants from food processing and packaging, and other residues. This milieu of compounds can pose difficulties in the detection of food contaminants. Nanosensors with their novel uses are the emerging method that could be used for the detection of many food contaminants, even mycotoxins and many food allergens. Whether it used as online or off-line, the nanosensor can be integrated with wireless technology and used for real-time transmission of contaminant alarm or test results to remote servers, providing rapid screening and reporting. Thus nanosensors are more cost-effective, rapid, and more sensitive than instrumental and conventional procedures. Recent developments in nanosensors may provide more applications for their use in food contaminant detection. The future role of these nanosensors will become even more important as the food laboratory is faced with the increasing pressure to reduce cost, time, and complexity. The objective of this chapter is to give a general overview of the possible application of nanosensors in the food contaminant detection and analysis.

A highly sensitive and simple reagent immobilization procedure for a non-plasticized fluorescence optode based on polymer inclusion membranes (PIM) has been developed. The preparation procedure is based on physical immobilization procedure, namely encapsulation technique which produces an optical sensing membrane. The sensitive PIM contains poly (vinyl chloride) (PVC) as the base polymer, Aliquat 336 as an extractant and sodium morin-5-sulphonate (NaMSA) as the reagent. The use of PIM has increased the response of the PIM based optode about five-fold enhancement compared to the non-PIM optode. The optimized optode was characterized by a linear calibration curve in the range from 5.19 × 10 −7 to 6.00 × 10 −5 mol L −1 of aluminium(III) (Al(III)), with a detection limit of 4.07 × 10 −7 mol L −1 . The response of the optode was three minutes and it was also found to be reproducible. The optode has been successfully tested for the determination of Al(III) in natural water samples and result obtained is comparable to atomic absorption spectrometry method.

This paper reports the use of a polymer inclusion membranes (PIMs) for direct determination of Al(III) ions in natural water by using a fluorescence based optode. The best composition of the PIMs consisted of 60 wt.% (m/m) poly (vinyl chloride) (PVC) as the base polymer, 20 wt.% (m/m) triton X-100 as an extractant, 20 wt.% (m/m) dioctyl phthalate (DOP) as plasticizer and morin as the reagent, was used in this study. The inclusion of triton X-100 was used for enhancing the sorption of Al(III) ions from liquid phase into the membrane phase, thus increasing the optode fluorescence intensity. The optimized optode was characterized by a linear calibration curve in the range from 7.41 × 10(-7) to 1.00 × 10(-4) molL(-1) of Al(III), with a detection limit of 5.19 × 10(-7) molL(-1). The response of the optode was 4 min and reproducible results were obtained for eight different membranes demonstrated good membrane stability. The optode was applied to the determination of Al(III) in natural water samples. The result obtained is comparable to atomic absorption spectrometry method.

Median enterococci counts of beach water samples gradually increased at statistically significant levels (χ2: 26.53, df: 4; p0.0001) with increasing proximity to river influx. The difference in proportion of antibiotic resistant enterococci in beach water and river water samples was statistically significant (p0.05) for the tested antibiotics with river isolates generally presenting higher resistance frequencies. Virulence genes cyl, esp, gelE and asa were detected at varying frequencies (7.32%, 21.95%, 100% and 63.41% respectively) among river isolates. On the other hand, the prevalence of these genes was lower (0%, 20%, 67.27% and 41.82% respectively) among beach water isolates. Multi-Locus-Sequence-Typing analysis of Enterococcus faecalis presented four sequence types (ST) one of which shared six out of seven tested loci with ST6, a member of the clonal complex of multi-drug resistant strains associated with hospital outbreaks.

Studies were conducted to understand the complexation behavior of carrageenans and methylene blue (MB) under immobilized conditions to build a novel carrageenan sensor. The sensor was an optical device based on reflectance changes due to the change of MB color (blue to purple) on exposure to carrageenan. MB was immobilized on poly(n-butylacrylate-co-N-acryloxysuccinimide) [poly(nBA-NAS)] microspheres and were coated onto a plastic support to fabricate the sensor. The sensor response was found to be related to the formation of the MB-carrageenan complexes and was more selective to Iota-carrageenan when compared with other types of carrageenans, e.g. Lambda- and Kappa-carrageenans. Besides, the sensor also showed no response to other gelling agents such as alginate and agar. Thus, the sensor exhibited a linear response range to Iota-carrageenan from 80 to 5000 ppm with a sensitivity of 377.5 ± 1.37 ΔIntensity/decade ( R 2 = 0.980). Lower detection limit of the sensor was 80 ppm, whilst repeatability and reproducibility were 0.36% and 0.31% relative standard deviation, respectively. Moreover, the sensor was useful in analyzing carrageenan in real samples with 83–117% recovery values.

A K + ion-sensitive optical sensor based on Nile Blue (chromoionophore ETH5294) incorporated into poly(n-butyl acrylate) [poly(nBA)] microspheres was successfully developed. A combination of acrylic spheres and optical reflectometry had enhanced the sensing performance of the optical K + ion sensor, as the former provides large surface area for better loading capacity and higher reaction rate, while the latter offers simple and rapid measurements. The sensing mechanism involves ion-exchange reaction, which occurs at the surface of the microspheres where influx of K + ions and efflux of H + ions take place. The sensor response was a result of the total deprotonation of chromoionophore immobilized within poly(nBA) microspheres in response to the formation of K + ion–ionophore complex. The change of the response in the presence of K + ions was studied via reflectance spectroscopy using an optical fibre probe. The K + ion sensor based on these microspheres exhibited sensitivity slope of 43.15 ΔIntensity/decade ( R 2 = 0.961) in a range 0.01–1000 mM of KCl with a lower detection limit of 0.01 mM. Sensor response time was 10 min with good reproducibility (relative standard deviation, %RSD = 5.71). Analysis of urine samples for K + ions gave 87–115% recovery and the results were comparable with established method for K + ions analysis. Leaching tests and life time study revealed that acrylic microspheres worked well as an immobilization matrix for hydrophobic chromoionophore.

The fabrication of an optical biosensor based on stacked immobilisation of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in sol–gel/butyl acrylate hybrid film and horseradish peroxidase (HRP) in chitosan film for capsaicin detection was studied. The optimum volume ratio of sol–gel to butyl acrylate was 1:0.5 (v/v). Peroxidase was immobilised in chitosan film deposited on top of the hybrid sol–gel/butyl acrylate film containing MBTH. The reaction between capsaicin and MBTH in the presence of HRP and hydrogen peroxide as oxidative agent was studied. The finding indicated that HRP catalysed the oxidative coupling reaction between MBTH and capsaicin thus producing red-coloured azo-dye compounds that could be observed at the wavelength of 505 nm. The colour intensity of the product was found to increase in proportion to the capsaicin concentration after 20–30 s of exposure. The linearity of the biosensor towards capsaicin was in the concentration range of 0.2–4.0 mM with detection limit of 0.17 mM. Relative standard deviation (RSD) values of reproducibility were 5.57–6.33%. The developed biosensor correlated well with the standard method, HPLC for the determination of capsaicin concentration in real samples.

In many electrochemical DNA based biosensors, a redox indicator is required to be introduced separately to indicate the DNA hybridization event. In this work, we have developed a simple procedure for voltammetric determination of CaMV 35S gene modified DNA without the need for introduction of a redox indicator. The DNA biosensor contains an immobilized DNA probe and also a methylene blue redox indicator that is able to slow release during the hybridization event. The biosensor was constructed from a screen printed carbon paste electrode (SPE) coated with an acrylic microsphere (AM)–gold nanoparticle (AuNP) composite immobilized with single-stranded DNA probes, whilst methylene blue (MB) was immobilized in the hydrogel poly(2-hydroxyethyl methacrylate) membrane located next to the electrode. Genetically modified (GM) DNA was examined based on the reduction in the MB cathodic peak current (ipc) signal, which was ascribed to the DNA hybridization event, via the differential pulse voltammetry (DPV) method. The ipc current signal of MB after DNA hybridization with target CaMV 35S gene DNA was linearly related to the logarithmic target DNA concentration ranging from 2.0 × 10−12 to 2.0 × 10−7 M (R2 = 0.989) with a limit of detection (LOD) at 1.40 × 10−13 M. The proposed AM–AuNP composite DNA electrode gave satisfactory reproducibility performance with

The characteristics of a potentiometric biosensor for the determination of permethrin in treated wood based on immobilised cells of the fungus Lentinus sajor-caju on a potentiometric transducer are reported this paper. The potentiometric biosensor was prepared by immobilisation of the fungus in alginate gel deposited on a pH-sensitive transducer employing a photocurable acrylic matrix. The biosensor gave a good response in detecting permethrin over the range of 1.0−100.0 µM. The slope of the calibration curve was 56.10 mV/decade with detection limit of 1.00 µM. The relative standard deviation for the sensor reproducibility was 4.86%. The response time of the sensor was 5 min at optimum pH 8.0 with 1.00 mg/electrode of fungus L. sajor-caju. The permethrin biosensor performance was compared with the conventional method for permethrin analysis using high performance liquid chromatography (HPLC), and the analytical results agreed well with the HPLC method (at 95% confidence limit). There was no interference from commonly used organophosphorus pesticides such as diazinon, parathion, paraoxon, and methyl parathion.