Development of an unmodified screen-printed graphene electrode for nonenzymatic histamine detection

The high requirement for food quality control has inspired the creation of high-performance sensing, cost-effectiveness, and ease to use. Therefore, the aim of this work is to develop nonenzymatic electrochemical platforms for direct detection of histamine using unmodified screen-printed graphene electrodes (SPGEs) for their applications such as evaluation of fish freshness. In alkaline media (0.2 M NaOH), unmodified SPGEs showed a very low oxidation potential of histamine at +0.58 V (vs. Ag/AgCl) avoiding perturbations from other biogenic amines. The developed method offers an excellent selectivity, sensitivity (a limit of detection (at 3SD/slope) of 0.62 mg L^-1) and wide working linear range (5-100 mg L^-1) for histamine detection. In addition, the proposed method was successfully applied to detect histamine in canned fish samples with recovery values ranging from 90.72% to 101.21%. Therefore, this newly proposed method is promising as an alternative choice for the determination of histamine in fish samples and related food products.

Synthesis of Multifunctional Electrically Tunable Fluorine-Doped Reduced Graphene Oxide at Low Temperatures

Doping with heteroatoms is a well-established method to tune the electronic properties and surface chemistry of graphene. Herein, we demonstrate the synthesis of a fluorine-doped reduced graphene oxide (FrGO) at low temperatures that offers multiple opportunities in applied fields. The as-synthesized FrGO product shows a better electrical conductivity of 750 S m^-1 than that of undoped rGO with an electrical conductivity of 195 S m^-1. To demonstrate the multifunctional applications of the as-synthesized FrGO, it was examined for electromagnetic interference shielding and electrochemical sensing of histamine as an important food biomarker. A laminate of FrGO delivered an EMI shielding effectiveness value of 22 dB in Ku band as compared with 11.2 dB for an rGO laminate with similar thickness. On the other hand, an FrGO modified sensor offered an excellent sensitivity (∼7 nM), wide detection range, and good selectivity in the presence of similar biomarkers. This performance originates from the better catalytic ability of FrGO as compared with rGO, where fluorine atoms play the role of catalytic active sites owing to their high electronegativity. The fluorination reaction also helps to improve the reduction degree of the chemically synthesized graphene, consequently enhancing the electrical conductivity, which is a prime requirement for increasing the electromagnetic and electrochemical properties of graphene.

Ultratrace Detection of Histamine Using a Molecularly-Imprinted Polymer-Based Voltammetric Sensor

Rapid and cost-effective analysis of histamine, in food, environmental, and diagnostics research has been of interest recently. However, for certain applications, the already-existing biological receptor-based sensing methods have usage limits in terms of stability and costs. As a result, robust and cost-effective imprinted polymeric receptors can be the best alternative. In the present work, molecularly-imprinted polymers (MIPs) for histamine were synthesized using methacrylic acid in chloroform and acetonitrile as two different porogens. The binding affinity of the MIPs with histamine was evaluated in aqueous media. MIPs synthesized in chloroform displayed better imprinting properties for histamine. We demonstrate here histamine MIPs incorporated into a carbon paste (CP) electrode as a MIP-CP electrode sensor platforms for detection of histamine. This simple sensor format allows accurate determination of histamine in the sub-nanomolar range using an electrochemical method. The sensor exhibited two distinct linear response ranges of 1 × 10^-10-7 × 10^-9 M and 7 × 10^-9-4 × 10^-7 M. The detection limit of the sensor was calculated equal to 7.4 × 10^-11 M. The specificity of the proposed electrode for histamine is demonstrated by using the analogous molecules and other neurotransmitters such as serotonin, dopamine, etc. The MIP sensor was investigated with success on spiked serum samples. The easy preparation, simple procedure, and low production cost make the MIP sensor attractive for selective and sensitive detection of analytes, even in less-equipped laboratories with minimal training.

Electrocatalysis in DNA Sensors

Electrocatalysis is often thought of solely in the inorganic realm, most often applied to energy conversion in fuel cells. However, the ever-growing field of bioelectrocatalysis has made great strides in advancing technology for both biofuel cells as well as biological detection platforms. Within the context of bioelectrocatalytic detection systems, DNA-based platforms are especially prevalent. One subset of these platforms, the one we have developed, takes advantage of the inherent charge transport properties of DNA. Electrocatalysis coupled with DNA-mediated charge transport has enabled specific and sensitive detection of lesions, mismatches and DNA-binding proteins. Even greater signal amplification from these platforms is now being achieved through the incorporation of a secondary electrode to the platform both for patterning DNA arrays and for detection. Here, we describe the evolution of this new DNA sensor technology.

Small electron-transfer proteins as mediators in enzymatic electrochemical biosensors

Electrochemical mediators transfer redox equivalents between the active sites of enzymes and electrodes and, in this way, initiate bioelectrocatalytic redox processes. This has been very useful in the development of the so-called second-generation biosensors, in which they transduce a catalyzed reaction into an electrical signal. Among other pre-requisites, redox mediators must be readily oxidized and/or reduced at the electrode surface and readily interact with the biorecognition component. Small chemical compounds (e.g. ferrocene derivatives, ruthenium, or osmium complexes and viologens) are frequently used for this purpose but, lately, small redox proteins (e.g. horse heart cytochrome c) have also been used as redox partners in biosensing applications. In general, docking between two complementary proteins introduces a second level of selectivity to the biosensor and enlarges the list of compounds analyzed. Moreover, electrochemical interferences are frequently minimized owing to the small overpotentials achieved. This paper provides an overview of enzyme biosensors that are mediated by electron-transfer proteins. The paper begins with a brief discussion of mediated electrochemistry in biosensing systems and proceeds with a detailed description of relevant work on the cooperative use of redox enzymes and biological electron donors and/or acceptors.

Selective histamine piezoelectric chemosensor using a recognition film of the molecularly imprinted polymer of bis(bithiophene) derivatives

A histamine piezoelectric (acoustic) sensor using a molecularly imprinted polymer (MIP) film has been devised and tested. The sensor comprises an electrodeposited MIP film as the recognition element and a 10 MHz AT-cut shear-thickness-mode bulk-acoustic-wave quartz crystal resonator with Pt film electrodes as the signal transducer. Preparation of the sensing film involved two consecutive electrochemical polymerizations, performed under cyclic voltammetric conditions, with the use of a supporting electrolyte of 0.1 M tetra-n-butylammonium perchlorate in acetonitrile. First, a poly(bithiophene) barrier film was deposited by electropolymerization on the Pt/quartz resonator to prevent histamine electro-oxidation and avoid possible contamination of the Pt electrode surface. Next, the histamine-templated MIP film was deposited by electropolymerization on top of this barrier film. For that purpose, two functional monomers of bis(bithiophene) derivatives, i.e., one bearing the 18-crown-6 and the other dioxoborinane substituent, were copolymerized in the presence of the histamine template. The consecutive growth of both these overlaid films was monitored with an electrochemical quartz crystal microbalance (EQCM). Subsequently, the histamine was extracted from MIP with 0.01 M NaOH for 12 h. The UV-vis and X-ray photoelectron spectroscopic measurements confirmed the completeness of the removal of the histamine template from the MIP film. The analytical performance of the chemosensor was assessed under flow injection analysis (FIA) conditions using the carrier 0.5 M HEPES buffer (pH = 7.5) solution and the piezoelectric microgravimetry detection at QCM. The negative peaks of resonant frequency linearly decreased with the increase of the histamine concentration in the range 10-100 mM for 150 microL/min flow rate, and 100 microL volume of the injected sample. The sensitivity of the chemosensor (0.33 Hz/mM) was more than twice as that of the chemosensor without the poly(bithiophene) barrier film (0.15 Hz/mM). The chemosensor performance was superior for selective histamine recognition if the poly(bithiophene) barrier film thickness exceeded 200 nm. The chemosensor discriminated histamine from functionally or structurally similar compounds, such as dopamine, tryptamine, and imidazole. Stability constants of the affinity complexes of MIP and analyte or the interfering agent were determined from kinetic studies. For the MIP-histamine complex, the stability constant thus evaluated was equal to 57.0 M(-1) being much higher than those for the MIP-tryptamine and MIP-dopamine complexes determined to be 10.7, and 6.4 M(-1), respectively. The concentration limit of detection was as low as 5 nM histamine if the carrier solution flow rate was as low as 35 microL/min and the injection sample volume as large as 1 mL.

Histamine dehydrogenase from Rhizobium sp.: gene cloning, expression in Escherichia coli, characterization and application to histamine determination

The gene encoding histamine dehydrogenase in Rhizobium sp. 4--9 has been cloned and overexpressed in Escherichia coli. The coding region of the gene was 2,079 bp and encoded a protein of 693 amino acids with a calculated molecular mass of 76,732 Da. This histamine dehydrogenase was related to histamine dehydrogenase from Nocardioides simplex (54.5% identical), trimethylamine dehydrogenase from Methylophilus methylotrophus (39.3% identical) and dimethylamine dehydrogenase from Hyphomicrobium X (38.1% identical), which have a covalent 6-S-cysteinyl flavin mononucleotide and a [4Fe--4S] cluster as redox cofactors. Sequence alignment and a UV-visible absorption spectrum supported the presence of these cofactors in this histamine dehydrogenase. The investigation of the enzymatic properties suggested that this enzyme exhibited the most excellent substrate specificity toward histamine among all amine oxidases or dehydrogenases found to date. The recombinant enzyme was able to be used for the colorimetric determination of histamine, which gave a linear calibration curve and identical data with conventional methods.

Bioelectrocatalysis-based application of quinoproteins and quinoprotein-containing bacterial cells in biosensors and biofuel cells

Electrochemical studies on the applied aspects of quinoproteins are briefly reviewed. Catalytic reactions of quinoprotein enzymes can be connected to electrochemical reactions directly or by the mediation of molecules functioning as electron acceptors of the enzymes. Such an enzyme-electrochemical reaction is called bioelectrocatalysis. It provides a novel method of kinetic analysis of enzyme catalysis and even whole bacterial cell catalysis. The principle of bioelectrocatalysis is first described, then, the bioelectrocatalysis-based application of quinoproteins in biosensors is mentioned. Characteristics and performance of this type of biosensor is explained by citing our own work. Possible application in bioreactors and biofuel cells is also mentioned.

Redox properties of quinohemoprotein amine dehydrogenase from Paracoccus denitrificans

Paracoccus denitrificans produces two primary enzymes for the amine oxidation, tryptophan-tryptophylquinone (TTQ)-containing methylamine dehydrogenase (MADH) and quinohemoprotein amine dehydrogenase (QH-AmDH). QH-AmDH has a novel cofactor, cysteine tryptophylquinone (CTQ) and two hemes c. In this work, the redox potentials of three redox centers in QH-AmDH were determined by a mediator-assisted continuous-flow column electrolytic spectroelectrochemical technique. Kinetics of the electron transfer from QH-AmDH to three kinds of metalloproteins, amicyanin, cytochrome c(550), and horse heart cytochrome c were examined on the basis of the theory of mediated-bioelectrocatalysis. All these metalloproteins work as a good electron acceptor of QH-AmDH and donate the electron to the terminal oxidase of P. denitrificans, which was revealed by reconstitution of the respiratory chain. These properties are in marked contrast with those of MADH, which shows high specificity to amicyanin. These electron transfer kinetics are discussed in terms of thermodynamics and structural property.