Amperometric tyrosinase biosensor based on Fe3O4 nanoparticles–chitosan nanocomposite

Magnetic loading of tyrosinase-Fe3O4/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N(2) adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10(-9) to 1.0×10(-5) M, a high sensitivity of 78 μA mM(-1), a low detection limit of 1 nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.

Chitosan: an integrative biomaterial for lab-on-a-chip devices

Chitosan is a naturally derived polymer with applications in a variety of industrial and biomedical fields. Recently, it has emerged as a promising material for biological functionalization of microelectromechanical systems (bioMEMS). Due to its unique chemical properties and film forming ability, chitosan serves as a matrix for the assembly of biomolecules, cells, nanoparticles, and other substances. The addition of these components to bioMEMS devices enables them to perform functions such as specific biorecognition, enzymatic catalysis, and controlled drug release. The chitosan film can be integrated in the device by several methods compatible with standard microfabrication technology, including solution casting, spin casting, electrodeposition, and nanoimprinting. This article surveys the usage of chitosan in bioMEMS to date. We discuss the common methods for fabrication, modification, and characterization of chitosan films, and we review a number of demonstrated chitosan-based microdevices. We also highlight the advantages of chitosan over some other functionalization materials for micro-scale devices.

An amperometric immunosensor based on a polyelectrolyte/gold magnetic nanoparticle supramolecular assembly--modified electrode for the determination of HIV p24 in serum

A novel supramolecular amperometric immunosensor for the determination of Human Immunodeficiency Virus antigen p24 (HIV p24) was built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode with HIV p24 antibody (anti-p24) being immobilized on polyelectrolyte/gold nanoparticle multilayer films. The multilayer films were composed of poly(L-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized Fe₃O₄(core)/gold(shell) nano particles (GMPs).The immunosensor preparation steps were monitored by X-ray fluorescence spectrometry (XRFS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In pH 6.5 PBS, after the immunosensor was incubated with HIV p24 solution at 25 °C for 5 min, the electron transfer access of FeCN is partially inhibited, which leads to a linear decrease of peak current. In addition, the performance of the immunosensor was studied in detail. It offers high-sensitivity for the detection of p24 and has good correlation for the detection of p24 in the range of 0.1 to 100.0 ng/mL with a detection limit of 0.05 ng/mL estimated at a signal-to-noise ratio of 3. The proposed immunosensor was used to analyze p24 in human serum specimens and the results showed the developed immunosensor provides a promising alternative approach for detecting p24 in the early diagnosis of AIDS patients.

Amperometric detection of dopamine in vivo with an enzyme based carbon fiber microbiosensor

We developed a novel implantable enzyme-based carbon fiber biosensor for in vivo monitoring of dopamine. The biosensor is fabricated using tyrosinase immobilized in a biocompatible matrix consisting of a biopolymer, chitosan and ceria-based metal oxides, deposited onto the surface of a carbon fiber microelectrode with a diameter of approximately 100 microm. Tyrosinase catalyzes the conversion of dopamine to o-dopaquinone, and the reduction of o-dopaquinone, which requires a low potential difference, was detected electrochemically. The role of each component in the sensing layer was systematically investigated in relation to the analytical performance of the biosensor. In its optimal configuration, the biosensor demonstrated a detection limit of 1 nM dopamine, a linear range of 5 orders of magnitude between 10 nM and 220 microM, a sensitivity of 14.2 nA x microM(-1), and good selectivity against ascorbic acid, uric acid, serotonin, norepinephrine, epinephrine, and 3,4-dihydroxy-l-phenylalanine (L-DOPA). The system provided continuous, real time monitoring of electrically stimulated dopamine release in the brain of an anesthetized rat. Levels of dopamine up to 1.69 microM were measured. This new implantable dopamine biosensor provides an alternative to fast scan cyclic voltammetry for in vivo monitoring of dopamine.

Amperometric biosensor based on tyrosinase immobilized onto multiwalled carbon nanotubes-cobalt phthalocyanine-silk fibroin film and its application to determine bisphenol A

An amperometric bisphenol A (BPA) biosensor was fabricated by immobilizing tyrosinase on multiwalled carbon nanotubes (MWNTs)-cobalt phthalocyanine (CoPc)-silk fibroin (SF) composite modified glassy carbon electrode (GCE). In MWNTs-CoPc-SF composite film, SF provided a biocompatible microenvironment for the tyrosinase to retain its bioactivity, MWNTs possessed excellent inherent conductivity to enhance the electron transfer rate and CoPc showed good electrocatalytic activity to electrooxidation of BPA. The cyclic voltammogram of BPA at this biosensor exhibited a well defined anodic peak at 0.625 V. Compared with bare GCE, the oxidation signal of BPA significantly increased; therefore, this oxidation signal was used to determine BPA. The effect factors were optimized and the electrochemical parameters were calculated. The possible oxidation mechanism was also discussed. Under optimum conditions, the oxidation current was proportional to BPA concentration in the range from 5.0 x 10(-8) to 3.0 x 10(-6) M with correlation coefficient of 0.9979 and detection limit of 3.0 x 10(-8) M (S/N=3). The proposed method was successfully applied to determine BPA in plastic products and the recovery was in the range from 95.36% to 104.39%.

An electrochemical impedimetric immunosensor for label-free detection of Campylobacter jejuni in diarrhea patients' stool based on O-carboxymethylchitosan surface modified Fe3O4 nanoparticles

A novel electrochemical impedimetric immunosensor based on O-carboxymethylchitosan surface modified Fe(3)O(4) nanoparticles (denoted as OCMCS-Fe(3)O(4) nanoparticles) was developed for rapid detection of Campylobacter jejuni, which is becoming the most common cause of gastroenteritis in developed countries and raising major public health concerns worldwide. In the present study, anti-FlaA monoclonal antibodies 2D12 (denoted as 2D12McAbs) were immobilized on OCMCS-Fe(3)O(4) nanoparticles. The detection was performed by measuring relative change in impedance before and after 2D12McAbs-Campylobacter jejuni reaction with the technique of electrochemical impedance spectroscopy. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of Campylobacter jejuni concentrations in the range of 1.0x10(3) to 1.0x10(7) CFU/mL (r=0.991). The advantages of the OCMCS-Fe(3)O(4) nanoparticle-based immunosensor are simplicity of use, fast response, wide linear range, acceptable reproducibility and long stability. Moreover, the immunosensor could be regenerated by being treated with glycine-HCl buffer solution (pH 2.8). We demonstrate the convenient application of the novel immunosensor for the detection of Campylobacter jejuni in diarrhea patients' stool samples.

Direct monitoring of pollutants based on an electrochemical biosensor with novel peroxidase (POX1B)

A biosensor for the monitoring of phenolic compounds based on a new protein named POX(1B) purified from garlic which demonstrates similar biochemical properties to peroxidase is investigated. The enzyme was immobilized into chitosan microspheres with covalent link. The properties of the biosensor were analyzed with Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and cyclic voltammetry (CV). FT-IR demonstrates the covalent attachment of POX(1B) into chitosan and SEM shows high dispersion of the POX(1B) into the chitosan microspheres. The redox potential of POX(1B) in chitosan is 147 mV vs. SCE, which is much higher than reported works using HRP, demonstrating excellent direct electrochemical behaviour of the POX(1B). The electrocatalytic activity of the obtained biosensor towards chlorophenols derivatives in a large range from 10 pM to 10 microM was demonstrated. The mediator free POX(1B)-based biosensor exhibited high sensitivity towards 2,6-dichlorophenol, 4-chlorophenol and pentachlorophenol. A detection limit of 1 pM in the case of 4-chlorophenol was demonstrated with kinetic constant K(m,app) of 0.42 microM with high rapidity of electrochemical response of the biosensor of 1 s.

Magnetic microbead-based electrochemical immunoassays

This review provides a summary of recent works concerning electrochemical immunoassays using magnetic microbeads as a solid phase. Recent research activity has led to innovative and powerful detection strategies that have been resulted in sensitive electrochemical detection. Coupling of magnetic microbeads with highly sensitive electrochemical detection provides a useful analytical method for environmental evaluation and clinical diagnostics, etc. The huge surface area and high dispersion capability of magnetic microbeads strongly contributes towards the development of new sensitive, rapid, user-friendly, and miniaturized electrochemical immunoassay systems. Moreover, the immunocomplexes formed on the magnetic microbead surface can be easily detected without pretreatment steps such as preconcentration or purification, which are normally required for standard methods. The discussion in this review is organized in two main subjects that include magnetic-microbead-based assays using enzyme labels and nanoparticle tags.

Highly sensitive amperometric biosensors for phenols based on polyaniline-ionic liquid-carbon nanofiber composite

A novel polyaniline-ionic liquid-carbon nanofiber (PANI-IL-CNF) composite was greenly prepared by in situ one-step electropolymerization of aniline in the presence of IL and CNF for fabrication of amperometric biosensors. The scanning electron micrographs confirmed that the PANI uniformly grew along with the structure of CNF and the PANI-IL-CNF composite film showed a fibrillar morphology with the diameter of around 95 nm. A phenol biosensor was constructed by immobilizing tyrosinase on the surface of the composite modified glassy carbon electrode via the cross-linking step with glutaraldehyde. The biosensor exhibited a wide linear response to catechol ranging from 4.0 x 10(-10) to 2.1 x 10(-6)M with a high sensitivity of 296+/-4 AM(-1)cm(-2), a limit of detection down to 0.1 nM at the signal to noise ratio of 3 and applied potential of -0.05 V. According to the Arrhenius equation, the activation energy for enzymatic reaction was calculated to be 38.8 kJmol(-1) using catechol as the substrate. The apparent Michaelis-Menten constants of the enzyme electrode were estimated to be 1.44, 1.33, 1.16, 0.65 microM for catechol, p-cresol, phenol, m-cresol, respectively. The functionalization of CNF with PANI in IL provided good biocompatible platform for biosensing and biocatalysis.

Use of Fe₃O₄ Nanoparticles for Enhancement of Biosensor Response to the Herbicide 2,4-Dichlorophenoxyacetic Acid

Magnetic nanoparticles of Fe₃O₄ were synthesized and characterized using transmission electron microscopy and X-ray diffraction. The Fe₃O₄ nanoparticles were found to have an average diameter of 5.48 ±1.37 nm. An electrochemical biosensor based on immobilized alkaline phosphatase (ALP) and Fe₃O₄ nanoparticles was studied. The amperometric biosensor was based on the reaction of ALP with the substrate ascorbic acid 2-phosphate (AA2P). The incorporation of the Fe₃O₄ nanoparticles together with ALP into a sol gel/chitosan biosensor membrane has led to the enhancement of the biosensor response, with an improved linear response range to the substrate AA2P (5-120 μM) and increased sensitivity. Using the inhibition property of the ALP, the biosensor was applied to the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The use of Fe₃O₄ nanoparticles gives a two-fold improvement in the sensitivity towards 2,4-D, with a linear response range of 0.5-30 μgL^-1. Exposure of the biosensor to other toxicants such as heavy metals demonstrated only slight interference from metals such as Hg²⁺, Cu²⁺, Ag²⁺ and Pb²⁺. The biosensor was shown to be useful for the determination of the herbicide 2, 4-D because good recovery of 95-100 percent was obtained, even though the analysis was performed in water samples with a complex matrix. Furthermore, the results from the analysis of 2,4-D in water samples using the biosensor correlated well with a HPLC method.