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A new electrochemical DNA biosensor based on mercaptopropionic acid (MPA)-capped ZnS quantum dots (MPA-ZnS QDs) immobilization matrix for covalent binding with 20-base aminated oligonucleotide has been successfully developed. Prior to the modification, screen-printed carbon paste electrode (SPE) was self-assembled with multilayer gold nanoparticles (AuNPs) and cysteamine (Cys). The inclusion of MPA-ZnS QDs semiconducting material in modified electrodes has enhanced the electron transfer between the SPE transducer and DNA leading to improved bioanalytical assay of target biomolecules. Electrochemical studies performed by cyclic voltammetry (CV) and differential pulsed voltammetry (DPV) demonstrated that the MPA-ZnS QDs modified AuNPs electrode was able to produce a lower charge transfer resistance response and hence higher electrical current response. Under optimal conditions, the immobilized synthetic DNA probe exhibited high selectivity towards synthetic target DNA. Based on the DPV response of the reduction of anthraquinone monosulphonic acid (AQMS) redox probe, the MPA-ZnS QDs-based electrochemical DNA biosensor responded to target DNA concentration from 1 × 10−9 μM to 1 × 10−3 μM with a sensitivity 1.2884 ± 0.12 µA, linear correlation coefficient (R2) of 0.9848 and limit of detection (LOD) of 1 × 10−11 μM target DNA. The DNA biosensor exhibited satisfactory reproducibility with an average relative standard deviation (RSD) of 7.4%. The proposed electrochemical transducer substrate has been employed to immobilize the aminated Arowana fish (Scleropages formosus) DNA probe. The DNA biosensor showed linearity to target DNA from 1 × 10−11 to 1 × 10−6 µM (R2 = 0.9785) with sensitivity 1.1251 ± 0.243 µA and LOD of 1 × 10−11 µM. The biosensor has been successfully used to determine the gender of Arowana fish without incorporating toxic raw materials previously employed in the hazardous processing conditions of polypyrrole chemical conducting polymer, whereby the cleaning step becomes difficult with thicker films due to high levels of toxic residues from the decrease in polymerization efficacy as films grew. [ABSTRACT FROM AUTHOR]

Increasing public awareness of food quality and safety has prompted a rapid increase in food authentication of halal food, which covers the production method, technical processing, identification of undeclared components, and species substitution in halal food products. This urges for extensive research into analytical methods to obtain accurate and reliable results for monitoring and controlling the authenticity of halal food. Nonetheless, authentication of halal food is often challenging because of the complex nature of food and the increasing number of food adulterants that cause detection difficulties. This review provides a comprehensive and impartial overview of recent studies on the analytical techniques used in the analysis of halal food authenticity (from 1980 to the present, but there has been no significant trend in the choice of techniques for authentication of halal food during this period). Additionally, this review highlights the classification of different methodologies based on validity measures that provide valuable information for future developments in advanced technology. In addition, methodological developments, and novel emerging techniques as well as their implementations have been explored in the evaluation of halal food authentication. This includes food categories that require halal authentication, illustrating the advantages and disadvantages as well as shortcomings during the use of all approaches in the halal food industry. [ABSTRACT FROM AUTHOR]

The evaluation of chilli hotness using amperometric capsaicin biosensor-based enzyme that was immobilized covalently to the surface of modified acrylic microspheres is the first of its kind presented in this work. The immobilization of enzyme covalently to the surface of microspheres via succinimide groups prevented the leaching of the enzyme. The enzymatic reaction between horseradish peroxidase-capsaicin in the presence of hydrogen peroxide, which was mediated by vinyl ferrocene, enabled the current measurement at a low potential (0.22 V). Besides, the pungency level of the chilli that was proportional to the capsaicin concentration was measured using this method. This biosensor gave a linear response range towards capsaicin from 0.75–24.94 μM (R 2 = 0.992) with a detection limit at 0.39 μM. Moreover, the relative standard deviation (RSD) for reproducibility study was 8.2% (n = 7). Therefore, this biosensor was successfully applied for evaluation of chilli hotness in chilli sample, as well as in comparison with a standard method that employed the HPLC method. [ABSTRACT FROM AUTHOR]

Abstract: 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 505nm. The colour intensity of the product was found to increase in proportion to the capsaicin concentration after 20–30s of exposure. The linearity of the biosensor towards capsaicin was in the concentration range of 0.2–4.0mM with detection limit of 0.17mM. 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. [Copyright &y& Elsevier]

[Display omitted] • Optical enzymatic biosensor based on MB28 copolymer and sol–gel stacked membranes. • NBCM-doped polyacrylate H+ ion transducer optically sensitive towards changes of pH. • Protonated MB28 optode membrane gives distinct color change via H+ ion transfer. • Indirect formaldehyde quantification by determining H+ ion at pH optode membrane. 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. [ABSTRACT FROM AUTHOR]

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

New acrylic microspheres were synthesised by photopolymerisation where the succinimide functional group was incorporated during the microsphere preparation. An optical biosensor for urea based on reflectance transduction with a large linear response range to urea was successfully developed using this material. The biosensor utilized succinimide-modified acrylic microspheres immobilized with a Nile blue chromoionophore (ETH 5294) for optical detection and urease enzyme was immobilized on the surface of the microspheres via the succinimide groups. No leaching of the enzyme or chromoionophore was observed. Hydrolysis of the urea by urease changes the pH and leads to a color change of the immobilized chromoionophore. When the color change was monitored by reflectance spectrophotometry, the linear response range of the biosensor to urea was from 0.01 to 1,000 mM (R2 = 0.97) with a limit of detection of 9.97 μM. The biosensor response showed good reproducibility (relative standard deviation = 1.43%, n = 5) with no interference by major cations such as Na+, K+, NH4+ and Mg2+. The use of reflectance as a transduction method led to a large linear response range that is better than that of many urea biosensors based on other optical transduction methods. [ABSTRACT FROM AUTHOR]

An amperometric electrochemical biosensor has been developed for ammonium (NH4 +) ion detection by immobilising alanine dehydrogenase (AlaDH) enzyme in a photocurable methacrylic membrane made up of poly(2-hydroxyethyl methacrylate) (pHEMA) on a screen-printed carbon paste electrode (SPE). The current detected was based on the electrocatalytic oxidation of nicotinamide adenine dinucleotide reduced (NADH) that is proportional to the consumption of NH4 + ion whilst enzymatic amination of AlaDH and pyruvate is taking place. The biosensor was operated amperometrically at a potential of +0.6V and optimum pH 7. The NH4 + biosensor demonstrated linear response to NH4 + ion concentration in the range of 0.03-1.02 mg/L with a limit of detection (LOD) of 8.52 μg/L. The proposed method has been successfully applied to the determination of NH4 + ion in river water samples without any pretreatment. The levels of possible interferents in the waters were negligible to cause any interference on the proposed method. The analytical performance of the biosensor was comparable to the colorimetric method using Nesslerisation but with much lower detection limit and linear response range at ppb level. [ABSTRACT FROM AUTHOR]

The use of multilayer of gold nanoparticles (AuNPs) attached on gold electrode surface via thiol chemistry to fabricate an ammonium (NH4+) ion biosensor based on alanine dehydrogenase (AlaDH) was investigated. The approach of the study was based on construction of biosensor by direct deposition of AuNPs and 1,8-octanedithiol (C8-DT) onto the gold electrode surface. For the immobilisation of enzyme, 2-mercaptoethanol (2BME) was first covalently attached to AlaDH via esther bonding and then followed by chemically attached the 2BME-modified AlaDH (2BME-AlaDH) moiety onto the AuNPs electrode via the exposed thiol group of 2BME. The resulting biosensor response was examined by means of amperometry for the quantification of NH4+ ion. In the absence of enzyme attachment, the use of three layers of AuNPs was found to improve the electrochemistry of the gold electrode when compared with no AuNPs was coated. However, when more than three layers of AuNPs were coated, the electrode response deteriorated due to excessive deposition of C8-DT. When AlaDH was incoporated into the AuNPs modified electrode, a linear response to NH4+ ion over the concentration range of 0.1-0.5mM with a detection limit of 0.01mM was obtained. In the absence of AuNPs, the NH4+ ion biosensor did not exhibit any good linear response range although the current response was observed to be higher. This work demonstrated that the incorporation of AuNPs could lead to the detection of higher NH4+ ion concentration without the need of dilution for high NH4+ ion concentration samples with a rapid response time of <1 min. [ABSTRACT FROM AUTHOR]

Abstract: An optical biosensor based on glutamate dehydrogenase (GLDH) immobilized in a chitosan film for the determination of ammonium in water samples is described. The biosensor film was deposited on a glass slide via a spin-coating method. The ammonium was measured based on β-nicotinamide adenine dinucleotide (NADH) oxidation in the presence of α-ketoglutaric acid at a wavelength of 340nm. The biosensor showed optimum activity at pH 8. The optimum chitosan concentrations and enzyme loading were found to be at 2% (w/v) and 0.08mg, respectively. Optimum concentrations of NADH and α-ketoglutaric acid both were obtained at 0.15mM. A linear response of the biosensor was obtained in the ammonium concentration range of 0.005 to 0.5mM with a detection limit of 0.005mM. The reproducibility of the biosensor was good, with an observed relative standard deviation of 5.9% (n =8). The biosensor was found to be stable for at least 1month when stored dry at 4°C. [Copyright &y& Elsevier]

Abstract: The development of an optical biosensor based on immobilization of 3-methyl-2-benzothiazolinone hydrazone (MBTH) in hybrid nafion/sol–gel silicate film and tyrosinase in chitosan film for the detection of phenolic compounds has been described. Tyrosinase was immobilized in chitosan film deposited on the hybrid nafion/sol–gel silicate film containing MBTH. The enzymatic oxidation product of phenolic compounds were stabilized through formation of adduct with MBTH to produce a maroon color adduct. The color intensity of adduct was found to increase proportionally with the increase of the substrate concentrations after 5min exposure. The linearity of the biosensor towards phenol, catechol and m-cresol were in the respective concentration range of 0.5–7.0, 0.5–10.0 and 1.0–13.0mg/L with detection limit of 0.18, 0.23 and 0.43mg/L, respectively. The biosensor shows a good stability for at least 3 months. [Copyright &y& Elsevier]

Abstract: An optical biosensor based on the immobilized tyrosinase enzyme in a chitosan film is described for the detection of phenol. The film was prepared by depositing a chitosan solution containing tyrosinase onto a microscope glass slide via spin coating technique. The quinone produced from the enzymatic oxidation of phenol was reacted with 3-methyl-2-benzothiazolinone hydrazone (MBTH) to produce a maroon color adduct. The color intensity of the adduct was found to increase proportionally with the increase of the substrate concentrations after 15min exposure to the substrate. The optimum enzyme loading and chitosan concentrations were found to be 0.9mg and 2% (w/v), respectively. The biosensor also demonstrated optimum activity at pH 6–7, optimum temperature of 45°C and a linear response in the phenol concentration range of 2.5–70.0μM. The response characteristics of the biosensor towards different phenolic compounds were determined. It was found that the biosensor gave a linear response in the concentration range of 2.5–50.0μM for 4-chlorophenol, 2.5–100.0μM for m-cresol and 12.5–400.0μM for p-cresol. The limit of detection and the apparent Michaels–Menten constant (K m) of the biosensor were 0.9, 1.0, 1.0, 3.0μM and 0.038, 0.037, 0.056, 0.201mM for 4-chlorophenol, phenol, m-cresol and p-cresol, respectively. It showed good stability for at least 2 months. [Copyright &y& Elsevier]

[Display omitted] • p n BA-NAS membrane as both enzyme supporting matrix and pH-sensitive transducer. • Loading of NAS monomer enhanced elasticity and flexibility of the sensing membrane. • Rapid detection via direct formaldehyde accessibility at AOX catalytic film surface. • Potentiometric quantification of formaldehyde by ion transfer reaction at the interface. 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. [ABSTRACT FROM AUTHOR]

A regenerable electrochemical DNA biosensor based on a new type of acrylic microspheres and gold nanoparticles (AuNPs) composite coated onto a screen printed electrode (SPE) has been successfully developed for specific determination of the 35 S promoter from cauliflower mosaic virus (CaMV 35S) gene in soybean. DNA probe was immobilised onto acrylic microspheres via covalent bonding. The presence of modified gene in soybean can be detected via hybridisation of CaMV 35S gene-modified DNA with immobilised DNA probe, which was monitored by differential pulse voltammetry of anthraquinone-2-sulfonic acid monohydrate sodium salt (AQMS) as redox indicator during hybridisation event. The peak current signal of AQMS was linearly related to the target CaMV 35S gene concentration over the range of 2×10−15 to 2×10−9 M (R 2 =0.982) with a very low concentration detect limit (7.79×10−16 M). The recovery test showed satisfactory results of 94.6±5.1–105.4±4.9% (n =5) when the biosensor was used for the determination of genetically modified (GM) DNA sequences extracted from GM soybean samples. The DNA biosensor showed good reproducibility (relative standard deviation (RSD) below 5.0%, n =5) and regenerability (RSD below 5.0%, n =7). The biosensor response was stable up to 45 days of storage period at 4°C. The main advantages of this biosensor design are very low detection limit and capability of reusing the biosensor for at least seven times after regeneration with mild sodium hydroxide. [ABSTRACT FROM AUTHOR]

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 1.0−100.0µM. The slope of the calibration curve was 56.10mV/decade with detection limit of 1.00µM. The relative standard deviation for the sensor reproducibility was 4.86%. The response time of the sensor was 5min at optimum pH 8.0 with 1.00mg/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. [ABSTRACT FROM AUTHOR]

Abstract: Ferrocene and its derivatives have been widely used as mediators in biosensor and it is of interest to produce ferrocene-containing (or its derivatives) polymeric films for biosensor application and to prevent leaching of the mediator. In this paper, we report photocurable polymer films for the physical immobilization of ferrocene and vinylferrocene in a low hydrophilicity methacrylate polymer. The hydrophobic–hydrophilic properties of the polymers and its effect on the leaching of the entrapped ferrocene and enzyme were studied. The entrapped ferrocene compounds showed good redox behaviour in these photocured films and the films were used to fabricate a biosensor for the detection of glucose, where the enzyme glucose oxidase (GOD) was incorporated together with the mediator during the photocuring step. Very little or no leaching of the entrapped ferrocene and glucose oxidase was observed. Upon immobilization of the enzyme, the biosensor demonstrated rapid response towards glucose at low potential, yielding a linear glucose response range of 4–17 and 5–42 mM, respectively, for ferrocene and vinylferrocene films. Both glucose biosensors gave reproducibility of &#60;10% relative standard deviations (n=6). The simple and single-step fabrication of the biosensor film is a major advantage when compared to other ferrocene-containing glucose biosensor films. [Copyright &y& Elsevier]

Abstract: A single-step fabrication of a glucose biosensor with simultaneous immobilization of both ferrocene mediator and glucose oxidase in a photocurable methacrylic film consisting of poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) was reported. The entrapped ferrocene showed reversible redox behaviour in the photocured film and no significant leaching of both entrapped ferrocene and enzyme glucose oxidase was observed because of the low water absorption properties of the co-polymer films. From electrochemical studies, ferrocene entrapped in the co-polymer film demonstrated slow diffusion properties. A linear glucose response range of 2–11 mM was obtained at low applied potential of +0.25 V. The glucose biosensor fabricated by this photocuring method yielded sensor reproducibility and repeatability with relative standard deviation of &#60;10% and long-term stability of up to 14 days. The main advantage of the use of photocurable procedure is that biosensor membrane fabrication can be performed in a single step without any lengthy chemical immobilization of enzyme. [Copyright &y& Elsevier]