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Alzheimer's disease is the most prevalent form of dementia and is primarily characterized by the accumulation of β-amyloid and phosphorylated tau proteins in the brain, along with the degeneration of nerve cells, which leads to impairment of various cognitive functions. A significant biomarker of Alzheimer's disease is the decreased level of soluble β-amyloid peptide (1–42) (Aβ1-42) in cerebrospinal fluid (CSF), as pathology progresses when CSF-Aβ1-42 levels drop below 192 pg mL−1. In this study, we developed an amperometric immunosensor based on magnetic beads as the platform for constructing the immunosensor. Monoclonal antibodies are immobilized on the MBs, enabling selective detection of Aβ1-42. The detection antibody is conjugated with the enzyme horseradish peroxidase, which, in the presence of H2O2 and hydroquinone, catalyzes the decomposition of H2O2 and the oxidation of hydroquinone to p-quinone, generating an electric current measured at a potential of −200 mV (vs. the Ag pseudo-reference electrode) using screen-printed carbon electrodes. The amperometric sandwich-type immunosensor demonstrates a linear response in the concentration range of 10 to 10,000 pg mL−1, with a detection limit of 7.4 pg mL−1, exhibiting excellent selectivity against the assessed interferents. These findings suggest the potential application of this immunosensor in the early diagnosis of Alzheimer's disease, offering a sensitive and specific tool for clinical analysis. Despite its high performance, further studies are required to validate its robustness and applicability in complex clinical samples. [ABSTRACT FROM AUTHOR]

Alzheimer’s disease is the most prevalent form of dementia and is primarily characterized by the accumulation of β-amyloid and phosphorylated tau proteins in the brain, along with the degeneration of nerve cells, which leads to impairment of various cognitive functions. A significant biomarker of Alzheimer’s disease is the decreased level of soluble β-amyloid peptide (1–42) (Aβ1-42) in cerebrospinal fluid (CSF), as pathology progresses when CSF-Aβ1-42 levels drop below 192 pg mL−1. In this study, we developed an amperometric immunosensor based on magnetic beads as the platform for constructing the immunosensor. Monoclonal antibodies are immobilized on the MBs, enabling selective detection of Aβ1-42. The detection antibody is conjugated with the enzyme horseradish peroxidase, which, in the presence of H2O2 and hydroquinone, catalyzes the decomposition of H2O2 and the oxidation of hydroquinone to p-quinone, generating an electric current measured at a potential of −200 mV (vs. the Ag pseudo-reference electrode) using screen-printed carbon electrodes. The amperometric sandwich-type immunosensor demonstrates a linear response in the concentration range of 10 to 10,000 pg mL−1, with a detection limit of 7.4 pg mL−1, exhibiting excellent selectivity against the assessed interferents. These findings suggest the potential application of this immunosensor in the early diagnosis of Alzheimer’s disease, offering a sensitive and specific tool for clinical analysis. Despite its high performance, further studies are required to validate its robustness and applicability in complex clinical samples.

Herein, we have manufactured a newly designed bifunctional impedimetric and amperometric immunosensor for rapidly detecting erythromycin (ERY) in complicated environments and food stuffs. For this, bimetallic cobalt/cerium-layered double hydroxide nanosheets (CoCe-LDH NSs), which was derived from Co-based zeolite imidazole framework via the structure conversion, was simultaneously utilized as the bioplatform for anchoring the ERY-targeted antibody and for modifying the gold and screen printed electrode. Basic characterizations revealed that CoCe-LDH NSs was composed of mixed metal valences, enrich redox, and abundant oxygen vacancies, facilitating the adhesion on the electrode, the antibody adsorption, and the electron transfers. The manufactured impedimetric and amperometric immunosensor based on CoCe-LDH has showed the comparable sensing performance, having a wide linear detection range from 1.0 fg mL−1 to 1.0 ng mL−1 with the ultralow detection limit toward ERY. Also, the portable, visualized, and efficient analysis of ERY was then attained at the smartphone-assisted CoCe-LDH-based SPE. [Display omitted] • Portable smartphone-assisted amperometric immunosensor, detection of erythromycin. • CoCe-LDH with abundant oxygen vacancies, rapid electron transfer, high bioaffinity toward antibody. • Ultra-low limitation of detection of 0.40 fg mL−1, good reproducibility, stability, and acceptable practicality. [ABSTRACT FROM AUTHOR]

The global expand of SARS-CoV-2 has highlighted the importance of early and rapid detection to control the spread of a pandemic. In this study, specific and high-affinity monoclonal antibodies (mAbs) were developed against the conserved nucleocapsid protein of the virus among variants. Appropriate antibody pairs were selected to develop a lateral flow immunoassay (LFIA) and an unconventional application of an amperometric biosensor using unmodified screen-printed electrodes and external magnetic bead preparation. In the study, the LFIA we developed detected the SARS-CoV-2 virus at 10 4 PFU/mL, while the amperometric biosensor enabled sensitive detection of inactivated SARS-CoV-2 with an LOD of 5.5 PFU/mL. After validating the developed systems, it is considered that the mAbs we have obtained will enable the sensitive and selective detection of SARS-CoV-2 in LFIA and amperometric immunosensor platforms for clinical diagnosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

A facile and highly sensitive determination of prostate-specific antigen (PSA) is of great significance for the early diagnosis, monitoring and prognosis of prostate cancer. In this work, a disposable and label-free electrochemical immunosensing platform was demonstrated based on chitosan–graphene-modified indium tin oxide (ITO) electrode, which enables sensitive amperometric determination of PSA. Chitosan (CS) modified reduced graphene oxide (rGO) nanocomposite (CS–rGO) was easily synthesized by the chemical reduction of graphene oxide (GO) using CS as a dispersant and biofunctionalizing agent. When CS–rGO was modified on the patterned ITO, CS offered high biocompatibility and reactive groups for the immobilization of recognition antibodies and rGO acted as a transduction element and enhancer to improve the electronic conductivity and stability of the CS–rGO composite film. The affinity-based biosensing interface was constructed by covalent immobilization of a specific polyclonal anti-PSA antibody (Ab) on the amino-enriched electrode surface via a facile glutaraldehyde (GA) cross-linking method, which was followed by the use of bovine serum albumin to block the non-specific sites. The immunosensor allowed the detection of PSA in a wide range from 1 to 5 ng mL−1 with a low limit of detection of 0.8 pg mL−1. This sensor also exhibited high selectivity, reproducibility, and good storage stability. The application of the prepared immunosensor was successfully validated by measuring PSA in spiked human serum samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Smartphone-assisted portable biosensor for rapid and visualized detection of TYL. • Bimetallic CoMn-ZIF derived electroactive layered double hydroxide (CoMn-LDH) • High specific surface area, electrochemical activity, and affinity toward antibody. • Ultralow limit of detection, good practicality toward TYL in diverse real samples. The precise and rapid analysis of antibiotics containing in food stuffs is essential for guaranteeing the safety of food products and drinking water. Thus, the sensitive determination of antibiotics is highly urgent. Herein, CoMn-LDH derived from bimetallic CoMn-ZIF was utilized as the sensitive material and ink for modifying the screen-printed electrode (SPE) to manufacture the visualized amperometric immunosensor to detect tylosin (TYL) with the smartphone assistance. Benefiting to the features of CoMn-ZIF, the achieved CoMn-LDH exhibited large specific surface area and pore size, abundant oxygen vacancies, rich and exposed metal sites, high functionality, and core–shell nanostructure with thin shell thickness. Thus, CoMn-LDH illustrated the high adhesive force with the SPE, the improved affinity toward the TYL-targeted antibody and fast electronic response. Thereby, the manufactured CoMn-LDH-based amperometric immunosensor displayed the wide linear range from 1.0 fg mL−1 to 1.0 ng mL−1 with an ultralow detection limit of 0.89 fg mL−1 toward TYL. Also, the developed amperometric immunosensor has demonstrated the good sensing ability of high selectivity, good reproducibility and stability, and accepted regenerated performance, as well as the great potential for the electronic visualized analysis of TYL containing in diverse real samples. This work has provided a new amperometric immunosensing strategy for the efficient analysis of antibiotics in food samples through the visual way. [ABSTRACT FROM AUTHOR]

Carcinoembryonic antigen levels in the human body reflect the conditions associated with a variety of tumors and can be used for the identification, development, monitoring, and prognosis of lung cancer, colorectal cancer, and breast cancer. In this study, an amperometric immunosensor with CuCo/carbon nanocubes (CuCo/CNC) as the signal label is constructed. The bimetal-doped carbon skeleton structure has a high specific surface area and exhibits good electrocatalytic activity. In addition, Au/g-C3N4 nanosheets (Au/g-C3N4 NSs) are used to modify the substrate platform, facilitating the loading of more capture antibodies. The reaction mechanism was explored through electrochemical methods, X-ray powder diffraction, X-ray photoelectron spectroscopy, and other methods. Kinetic studies have shown that CuCo/CNC have good peroxidase-like activity. In addition, the electrocatalytic reduction ability of CuCo/CNC on hydrogen peroxide can be monitored using amperometric i–t curve (− 0.2 V, vs. SCE), and the response current value is positively correlated with the CEA antigen concentration. The prepared electrochemical immunosensor has good selectivity, precision, and stability. The dynamic range of the sensor was 0.0001–80 ng/mL, and the detection limit was 0.031 pg/mL. In addition, the recovery and relative standard deviation in real serum samples were 97.7–103 % and 3.25–4.13 %, respectively. The results show that the sensor has good analytical capabilities and can provide a new method for the clinical monitoring of CEA. [ABSTRACT FROM AUTHOR]

In this work, the authors reported the hybrid architecture of carbon nanotube (CNT)–zinc oxide (ZnO) nanowire as a multi‐functional probe in amperometric immunosensor for the detection of urine albumin. Low‐cost substrate such as glass is possible because of novel low‐temperature growth process of CNT/ZnO nanowires as a multi‐function electrode in this sensor. Based on Schottky like behaviour this structure exhibit excellent high current density to achieve higher performance. Measurement of urine albumin is a new way for early detection of diabetic and also low concentration of it in culture media is also considered in order to verify the conversion of stem cells to liver cells. Human albumin serum antibody is used as a selective and sensitive part. The amperometric performance of immunosensor is studied and showed excellent performance for detection of albumin in urine samples. Very high linear range (from 3.3 ng/µl to 3.3 mg/µl) with a correlation coefficient of 0.825 and low detection limit (3.3 ng/µl or 4.96 × 10−8 mol l−1) are the main characteristics of this sensor. Due to the high dynamic range and sensitivity, this sensor was also used in medical diagnosis and biomedical applications. [ABSTRACT FROM AUTHOR]

• ZIF-8 was elaborately employed as a template to synthesize MB-PDA smart labels. • pH responsive smart labels were vastly elevated sensitivity of immunosensor. • Immunosensor for CA 125 exhibited an ultralow detection limit of 0.336 μU mL−1. A sandwich-type amperometric immunosensor based on pH responsive sensitivity amplifiable route was elaborately designed for determination of carcinoma antigen 125 (CA 125). The sensitivity of amperometric immunosensor depends on a change of current response (ΔI) attributed to antigen to be tested per unit concentration. Employing zeolitic imidazolate framework (ZIF-8) as the template, the hollow-structured polydopamine framework with high specific surface area can be fabricated and it can enrich large amounts of signal molecules. The pH responsive hollow polydopamine composites which loaded methylene blue (MB) covalently coupled with antibodies (Ab 2) were implemented as smart labels and the Au-rGO with high absorption capacity was served as substrate to capture signal molecules. Different from traditional electrochemical immunosensor, HCl led to the destruction of the labels and disassociation of antibody-antigen interaction layer. The impedance of modified interface was dramatically decreased and the distance between signal molecules and the sensing interface was shortened, giving rise to the improvement of electron transfer efficiency and amplification of current response. With the help of pH responsive strategy, ΔI caused by antigen was effectively elevated, leading to the sensitivity amplification of immunosensor. Under optimum conditions, the amperometric immunosensor with good reproducibility, high sensitivity and specificity exhibited an ultralow detection limit of 0.336 μU mL−1 (S/N = 3) and a wide linear range from 0.0001 to 100 U mL−1 for CA 125 detection. [ABSTRACT FROM AUTHOR]

Abstract Reducing background signal is an effective method to improve the sensitivity of amperometric immunosensors, which are significant in the detection of cancer. Herein, a novel immunosensor probe was synthesised using zeolitic imidazolate framework-hydroquinone-bovine serum albumin (ZIF-8-HQ-BSA). Based on the probe, an "off-on" strategy was applied in the immunosensor to amplify ΔI, the current signal "turn off and on". The ZIF-8-HQ-BSA probe initially showed little current signal since ZIF-8 and BSA exhibit poor conductivity. To amplify the current signal "turn on", the structure of ZIF-8 was broken after treatment with HCl, releasing hydroquinone to be absorbed by the polyaniline hydrogel substrate. Hydroquinone can produce a strong signal and also exhibits strong catalytic ability for H 2 O 2 to further enhance the signal. Following this method, the immunosensing platform was used to detect cytokeratins antigen 21-1 (CYFRA21-1) in human serum and revealed a wide liner range from 0.1 pg mL−1 to 100 ng mL−1 with a low detection limit of 0.65 pg mL−1 (S/N = 3), demonstrating good consistency with an electrochemiluminescence immunoassay. Thus, the amperometric immunosensing platform discussed in this work has high potential for application in healthcare monitoring, clinical diagnostics, and biomedical devices. Highlights • ZIF-8-HQ-BSA as new immunoprobe was fabricated for amperometric immunoassay. • "off-on" strategy was used to amplify sensitivity in amperometric sensor. • The immunosensor showed ultrawide linear range from 0.1 pg mL−1 to 100 ng mL−1. [ABSTRACT FROM AUTHOR]

Abstract Based on multifunctionalized zeolitic imidazolate frameworks (ZIFs)-initiated cascade reaction triggered signal amplification strategy, a novel sandwich-type amperometric immunosensor was constructed for ultrasensitive detection of carbohydrate antigen 24-2 (CA 242). The methylene blue-glucose oxidase-ZIF-8/reduced graphene oxide-Au (MB-GOx-ZIF-8/Au-rGO) was synthesized by a facile coprecipitation method for enzyme immobilization and redox species loading. The multifunctionalized ZIFs conjugated with labeling antibodies were employed as immunoprobe. In the presence of glucose, tandem reaction was driven by the immunoprobe to catalyze the glucose oxidation to yield H 2 O 2. Simultaneously, the generated H 2 O 2 induced the decomposition of poly(anilineboronicacid) (PABA)/poly(vinyl alcohol) (PVA) films on substrate, which made the PVA chains breaking away from PABA polymer. Due to the poor conductivity of PVA chains, this decomposition reaction can amplify the current signal. The current difference (ΔI) caused by per unit concentration target with tandem reaction amplification was elevated prominently, resulting in ultrasensitive analytical performance of the immunosensor. Under optimal conditions, the proposed immunosensor displayed wide linear range from 0.001 to 1000 U mL−1 with an ultralow limit of detection 69.34 μU mL−1 (S/N = 3). This method successfully implemented functionalized ZIFs in immunoprobe construction for sensitivity amplification, providing a promising strategy to construct ultrasensitive immunosensing platform for analysis of other tumor marker. Highlights • Multifunctional ZIFs were synthesized for enzyme and redox species loading. • Glucose-triggered cascade reaction was used for signal amplification. • The immunosensor displayed ultralow limit of detection 69.34 μU mL−1. [ABSTRACT FROM AUTHOR]

Nanogel as a multifunctional carrier was used to fabricate immunoprobe. The obtained immunoprobe was applied in a competitive amperometric immunosensor and exhibited an excellent analytical performance for the detection of tumor marker. The nanogel was easily fabricated by irradiation of the mixture of glucose, sodium citrate and sodium alginate by microwave, which exhibits excellent adsorbent ability for multivalence metal ions. The immunoprobe was constructed by functionalizing such uniform nanogels with multivalence metal ions (Cu 2+ as model) as redox species and gold nanoparticles for immobilizing antibody. The signal of Cu 2+ from the nanogel can be directly measured without acid dissolution and pre-concentration, which substantially simplified the detection steps. Besides, the response current can be amplified by glucose because Cu 2+ is an electro-catalyst for the oxidation of glucose. Polyaniline hydrogel with a three dimensional network structure and π–π conjugated structure was used to fabricate immunosensing substrate, which extremely improved the specific surface area and conductivity of the modified electrode. Under optimal conditions, the current changes of square wave voltammetry were used to detect neuron specific enolase (as a model analyte) with a broad linear ranging from 0.01 to 1000 ng mL −1 and a ultralow detection limit of 4.6 pg mL -1 (S/N = 3). This work provides a new strategy for designing multifunctional immunoprobes. [ABSTRACT FROM AUTHOR]

Sensitivity amplification strategy by implementing click chemistry in the construction of biosensing interface can efficiently improve the performance of immunosensor. Herein, we developed a sandwich-type amperometric immunosensor for ultrasensitive detection of carbohydrate antigen 24-2 (CA 242) based on pH responsive label-assisted click chemistry triggered sensitivity amplification strategy. The sensitivity of amperometric immunosensor relies on the current response differences (ΔI) caused by per unit concentration target analyte. The pH responsive Cu 2+ -loaded polydopamine (CuPDA) particles conjugated with detection antibodies were employed as labels, which can release Cu(II) ions by regulating pH. In the presence of ascorbic acid (reductant), Cu(II) ions were reduced to Cu(I) ions. Azide-functionalized double-stranded DNA (dsDNA) as signal enhancer was immobilized on the substrate through Cu + -catalyzed azide/alkyne cycloaddition reaction. With the help of the click reaction, the ΔI caused by target was elevated prominently, resulting in sensitivity amplification of the immunosensor. Under optimal condition, the proposed immunosensor exhibited excellent performance with linear range from 0.0001 to 100 U mL −1 and ultralow detection limit of 20.74 μU mL −1 . This work successfully combines click chemistry with pH-responsive labels in sandwich-type amperometric immunosensor, providing a promising sensitivity amplification strategy to construct immunosensing platform for analysis of other tumor marker. [ABSTRACT FROM AUTHOR]

This paper describes the first immunosensor reported so far for the highly sensitive determination of the egg white allergen, ovomucoid (OM). The approach involves the selective capture of sandwich immunocomplexes formed by capture antibody-target protein allergen-HRP-labeled detector antibody onto carboxylic acid-functionalized magnetic beads (HOOC-MBs). The resulting magnetic bioconjugates were captured on the surface of disposable screen-printed carbon electrodes (SPCE) to perform amperometric detection at −0.20 V vs . the Ag pseudo-reference electrode in the presence of hydroquinone (HQ) and H 2 O 2 . The as prepared electrochemical immunoplatform showed a wide range of linearity (0.3–25 ng mL −1 ), a LOD of 0.1 ng mL −1 , which is much lower than those claimed for commercial ELISA kits, and a great selectivity against other white egg allergenic proteins. The developed immunosensor was successfully employed for the simple and accurate determination of trace amounts of OM in unprocessed (eggs and wheat flour) and baked (bread) food samples. [ABSTRACT FROM AUTHOR]

Antivenom allergy disease mediated by patient IgE is an important public health care concern. To improve detection of hypersensitive individuals prior to passive antibody therapy, an amperometric immunosensor was developed to detect reactive human IgE. Whole horse IgG3 (hoIgG3) was immobilized onto the surface of carbon or gold screen-printed electrodes through a cross-linking solution of glutaraldehyde on a chitosan film. Sera from persons with a known allergic response to hoIgG3 or non-allergic individuals was applied to the sensor. Bound human IgE (humIgE) was detected by an anti-humIgE antibody through a quantitative amperometric determination by tracking via the electrochemical reduction of the quinone generated from the hydroquinone with the application of a potential of 25 mV. The optimal immunosensor configuration detected reactive humIgE at a dilution of 1:1800 of the human sera that represent a detection limit of 0.5 pg/mL. Stability testing demonstrated that through 20 cycles of a scan, the specificity and performance remained robust. The new immunosensor successfully detected humIgE antibodies reactive against hoIgG3, which could allow the diagnosis of potential allergenic patients needing therapeutic antivenom preparations from a horse. [ABSTRACT FROM AUTHOR]

In this paper, an amperometric immunosensor for the detection of carbofuran was developed. Firstly, multiwall carbon nanotubes (MWCNTs) and graphene sheets-ethyleneimine polymer-Au (GS-PEI-Au) nanocomposites were modified onto the surface of a glass carbon electrode (GCE) via self-assembly. The nanocomposites can increase the surface area of the GCE to capture a large amount of antibody, as well as produce a synergistic effect in the electrochemical performance. Then the modified electrode was coated with gold nanoparticles-antibody conjugate (AuNPs-Ab) and blocked with BSA. The monoclonal antibody against carbofuran was covalently immobilized on the AuNPs with glutathione as a spacer arm. The morphologies of the GS-PEI-Au nanocomposites and the fabrication process of the immunosensor were characterized by X-ray diffraction (XRD), ultraviolet and visible absorption spectroscopy (UV-vis) and scanning electron microscopy (SEM), respectively. Under optimal conditions, the immunosensor showed a wide linear range, from 0.5 to 500 ng/mL, with a detection limit of 0.03 ng/mL (S/N = 3). The as-constructed immunosensor exhibited notable performance features such as high specificity, good reproducibility, acceptable stability and regeneration performance. The results are mainly due to the excellent properties of MWCNTs, GS-PEI-Au nanocomposites and the covalent immobilization of Ab with free hapten binding sites for further immunoreaction. It provides a new avenue for amperometric immunosensor fabrication.

In this paper, an amperometric immunosensor modified with protein A/deposited gold nanocrystals (DpAu) was developed for the ultrasensitive detection of carbofuran residues. First, DpAu were electrodeposited onto the Au electrode surface to absorb protein A (PA) and improve the electrode conductivity. Then PA was dropped onto the surface of DpAu film, used for binding antibody Fc fragments. Next, anti-carbofuran monoclonal antibody was immobilized on the PA modified electrode. Finally, bovine serum albumin (BSA) was employed to block the possible remaining active sites avoiding any nonspecific adsorption. The fabrication procedure of the immunosensor was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), respectively. With the excellent electroconductivity of DpAu and the PA’s oriented immobilization of antibodies, a highly efficient immuno-reaction and detection sensitivity could be achieved. The influences of the electrodeposition time of DpAu, pH of the detection solution and incubation time on the current response of the fabricated immunosensor were investigated. Under optimized conditions, the current response was proportional to the concentration of carbofuran which ranged from 1 to 100 ng/mL and 100 ng/mL to 100 μg/mL. The detection limit was 0.1924 ng/mL. The proposed carbofuran immnuosensor exhibited high specificity, reproducibility, stability and regeneration performance, which may open a new door for ultrasensitive detection of carbofuran residues in vegetables and fruits.

An amperometric magnetoimmunosensor for the determination of human p53 protein is described in this work using a sandwich configuration involving the covalent immobilization of a specific capture antibody onto activated carboxylic-modified magnetic beads (HOOC-MBs) and incubation of the modified MBs with a mixture of the target protein and horseradish peroxidase-labeled antibody (HRP-anti-p53). The resulting modified MBs are captured by a magnet placed under the surface of a disposable carbon screen-printed electrode (SPCE) and the amperometric responses are measured at 0.20 V (vs. an Ag pseudo-reference electrode), upon addition of hydroquinone (HQ) as a redox mediator and H2O2 as the enzyme substrate. The magnetoimmunosensing platform was successfully applied for the detection of p53 protein in different cell lysates without any matrix effect after a simple sample dilution. The results correlated accurately with those provided by a commercial ELISA kit, thus confirming the immunosensor as an attractive alternative for rapid and simple determination of this protein using portable and affordable instrumentation. [ABSTRACT FROM AUTHOR]

A highly sensitive disposable amperometric magnetoimmunosensor for the rapid determination of Ara h 2 protein, one of the major peanut allergens, is reported. The approach uses a sandwich configuration involving selective capture and detector antibodies and carboxylic acid-modified magnetic beads (HOOC-MBs). Detector antibodies are labeled with HRP-conjugated secondary antibodies and the MBs bearing the immunoconjugates are magnetically captured on surface of a disposable screen-printed carbon electrode (SPCE). The affinity reactions are monitored amperometrically at −0.20 V (vs a Ag pseudo-reference electrode) in the presence of hydroquinone (HQ) as electron transfer mediator and upon addition of H 2 O 2 as the enzyme substrate. The developed magnetoimmunosensor exhibits a wide range of linearity between 87 and 10,000 pg mL −1 Ara h 2 with a detection limit of 26 pg mL −1 as well as a great selectivity against other non-target proteins. The magnetoimmunosensing platform was successfully applied for the detection of Ara h 2 in different food extracts. After an appropriate sample dilution no matrix effects were observable. The developed methodology was able to detect trace amounts of the peanut allergen (0.0005% or 5.0 mg kg −1 ) in wheat flour spiked samples. The results correlated properly with those provided by a commercial ELISA kit. [ABSTRACT FROM AUTHOR]

A sensitive and rapid method for the determination of the clinically relevant biomarker human endoglin (CD105) in serum samples is presented, involving a magneto-actuated immunoassay and amperometric detection at disposable screen-printed carbon electrodes (SPCEs). Micro-sized magnetic particles were modified with a specific antibody to selectively capture the target protein which was further sandwiched with a secondary HRP-labeled antibody. The immunocomplexes attached to the magnetic carriers were amperometrically detected at SPCEs using the hydroquinone (HQ)/H 2 O 2 /HRP system. The magneto-actuated immunosensing platform was able to detect 5 pmoles of endoglin (in 25 μL of sample, 0.2 μM) in 30 min providing statistically similar results to those obtained using a commercial ELISA kit for the determination of endogenous content of endoglin in human serum samples. [ABSTRACT FROM AUTHOR]

A highly sensitive disposable amperometric immunosensor based on the use of magnetic beads (MBs) is described for determination of Ara h 1, the major peanut allergen, in only 2 h. The approach uses a sandwich configuration involving selective capture and biotinylated detector antibodies and carboxylic acid-modified MBs (HOOC-MBs). The MBs bearing the immunoconjugates are captured by a magnet placed under the surface of a disposable screen-printed carbon electrode (SPCE) and the affinity reactions are monitored amperometrically at −0.20 V (vs a Ag pseudo-reference electrode) in the presence of hydroquinone (HQ) as electron transfer mediator and upon addition of H 2 O 2 as the enzyme substrate. The developed immunosensor exhibits a wide range of linearity between 20.8 and 1000.0 ng mL −1 Ara h 1, a detection limit of 6.3 ng mL −1 , a great selectivity, a good reproducibility with a RSD of 6.3% for six different immunosensors and a useful lifetime of 25 days. The usefulness of the immunosensor was demonstrated by determining Ara h 1 in different matrices (food extracts and saliva). The results correlated properly with those provided by a commercial ELISA method offering a reliable and promising analytical screening tool in the development of user-friendly devices for on-site determination of Ara h 1. [ABSTRACT FROM AUTHOR]

Detection of Mycobacterium bovis (M bovis) is important for prevention of a cattle tuberculosis outbreak. In this study, a nanobiosensor modified by gold nanoparticles for detection of M bovis in milk was developed. The biosensor was fabricated firstly by dropping the mix solution of chitosan (Ch), Au nanoparticles (AuNPs), and alkaline phosphatase labeled goat anti-mouse IgG (ALP-IgG) on glassy carbon electrode (GCE) to form a robust film with good biocompatibility, then antibody against Mycobacterium tuberculosis (anti-M.TB), which could identify M bovis, was immobilized on the composite film through the reaction with ALP-IgG. The biosensor was able to detect M bovis with the detection limit 3.5×103 cfu/ml and a linear range from 104 to 106 cfu/ml. This strategy could be applied as a rapid platform for detection of M. bovis for cattle tuberculosis infection. [ABSTRACT FROM AUTHOR]

An amperometric magnetoimmunosensor for the determination of human p53 protein is described in this work using a sandwich configuration involving the covalent immobilization of a specific capture antibody onto activated carboxylic-modified magnetic beads (HOOC-MBs) and incubation of the modified MBs with a mixture of the target protein and horseradish peroxidase-labeled antibody (HRP-anti-p53). The resulting modified MBs are captured by a magnet placed under the surface of a disposable carbon screen-printed electrode (SPCE) and the amperometric responses are measured at −0.20 V (vs. an Ag pseudo-reference electrode), upon addition of hydroquinone (HQ) as a redox mediator and H2O2 as the enzyme substrate. The magnetoimmunosensing platform was successfully applied for the detection of p53 protein in different cell lysates without any matrix effect after a simple sample dilution. The results correlated accurately with those provided by a commercial ELISA kit, thus confirming the immunosensor as an attractive alternative for rapid and simple determination of this protein using portable and affordable instrumentation.

In this work, a novel magnetic beads (MBs)-based immunosensing approach for the rapid and simultaneous determination of the main peanut allergenic proteins (Ara h 1 and Ara h 2) is reported. It involves the use of sandwich-type immunoassays using selective capture and detector antibodies and carboxylic acid-modified magnetic beads (HOOC-MBs). Amperometric detection at −0.20 V was performed using dual screen-printed carbon electrodes (SPdCEs) and the H2O2/hydroquinone (HQ) system. This methodology exhibits high sensitivity and selectivity for the target proteins providing detection limits of 18.0 and 0.07 ng/mL for Ara h 1 and Ara h 2, respectively, with an assay time of only 2 h. The usefulness of the approach was evaluated by detecting the endogenous content of both allergenic proteins in different food extracts as well as trace amounts of peanut allergen (0.0001% or 1.0 mg/kg) in wheat flour spiked samples. The developed platform provides better Low detection limits (LODs) in shorter assay times than those claimed for the allergen specific commercial ELISA kits using the same immunoreagents and quantitative information on individual food allergen levels. Moreover, the flexibility of the methodology makes it readily translate to the detection of other food-allergens.

A new amperometric immunosensor based on the covalent immobilization of tissue transglutaminase enzyme in its open conformation (open-tTG) was developed and optimized for determination of anti-tissue transglutaminase antibodies (anti-tTG) in human serum. Experimental design allowed us to find the optimal conditions for quantification of both IgA and IgG isotypes of anti-tTG in order to assess suitability of the device for diagnostic purposes. The glassy carbon electrodic substrate was electrochemically functionalized with gold nanoparticles and subsequently derivatized with a self-assembled monolayer of 11-mercaptoundecanoic acid for the covalent anchoring of the enzyme. This step was performed under carefully controlled conditions in order to keep the open conformation of the tTG. The immunosensor showed good analytical performance with limit of detection levels (1.7AUmL−1 for IgA and 2.7AUmL−1 for IgG) below the diagnostic threshold value (3.0AUmL−1) and inter-sensor reproducibility giving RSD lower than 10%. The developed sensor was validated in serum samples from pediatric patients for clinical applications, using two ELISA kits specific for the determination of anti-tTG IgA and IgG antibodies as reference methods; good recovery rates ranging from 74% to 117% were calculated. [ABSTRACT FROM AUTHOR]

A chip format sandwich-type immunoassay based on Nanobodies® (Nbs) with the Human Epidermal Growth Factor Receptor (HER2) extracellular domain as antigen model has been developed. The HER2 is considered as an important biomarker because its overexpression causes an aggressive type of breast cancer. Nbs are single domain antigen-binding fragments derived from camelid heavy-chain antibodies. The strategy of the presently developed sandwich immunoassay takes advantage of the small size of Nbs for the detection of the electroactive redox tracer onto the screen printed electrode (SPE). A capture anti HER2 Nb was covalently immobilized onto the SPE, and the detection Nb, raised against another epitope of HER2, was labeled with horseradish peroxidase (HRP). The biosensor signal corresponded to the electroreduction of para-quinone generated at the SPE by the HRP in the presence of hydroquinone and hydrogen peroxide. The best performing and optimized immunoassay conditions consisted of 2 and 20 min for the first and the second incubation times, respectively. The amperometric signal obtained was proportional to the logarithm of HER2 concentration between 1 and 200 µg/mL and the modified SPE storage stability lasted for at least three weeks. Determination of HER2 in human cells has been realized. [ABSTRACT FROM AUTHOR]

A novel label-free amperometric immunosensor is proposed for the ultrasensitive detection of zearalenone (ZEN) based on mesoporous carbon (MC) and trimetallic nanorattles (core/shell particles with movable cores encapsulated in the shells). The nanorattles are composed of special Au-core and imperfect AgPt-shell structure (Au@AgPt). The Au@AgPt nanorattles are loaded onto the MC by physical adsorption. The structure of the Au@AgPt nanorattles was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) confirmed the composition of the synthesized nanorattles. Compared with monometallic and bimetallic nanoparticles (NPs), Au@AgPt nanorattles show a higher electron transfer rate due to the synergistic effect of the Au, Ag and Pt NPs. MC further improves the sensitivity of the immunosensor because of its extraordinarily large specific surface area, suitable pore arrangement and outstanding conductivity. The large specific surface area of MC and MC@Au@AgPt were characterized by the BET method. ZEN antibodies are immobilized onto the nanorattles via Ag–NH 2 bonds and Pt–NH 2 bonds. Cyclic voltammetry and square wave voltammetry were used to characterize the recognizability of ZEN. Under optimum experimental conditions, the proposed immunosensor exhibited a low detection limit (1.7 pg mL −1 ), a wide linear range (from 0.005 to 15 ng mL −1 ) as well as good stability, reproducibility and selectivity. The sensor can be used in clinical analysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] Functionalized-graphene nanocomposites was synthesized by a chemical method. [•] The sensitivity of immunosensor was improved by functionalized-graphene lable. [•] The immunosensor exhibited good precision, reproducibility and specificity. [Copyright &y& Elsevier]

Highlights: [•] An amperometric immunosensor was developed for the detection of MA. [•] PB could catalyze the reduction of H2O2 to amplify the amperometric signal. [•] The immunosensor exhibited high selection, stabilization and sensitivity. [Copyright &y& Elsevier]

Abstract: A conducting long-chain polythiols (poly (2-aminothiophenol), PATP) was synthesized by a chemical polymerization process and combined with Au nanoparticles (AuNPs) to prepare a novel, sensitive and label-free electrochemical biosensor by adsorption of carcinoembryonic antibody (anti-CEA) on the PATP–AuNPs modified gold electrode. Differential pulse voltammetry (DPV) was used to characterize the recognition of carcinoembryonic antigen (CEA). Under the optimized conditions, the proposed immunosensor displayed a good amperometric response to CEA with linear range from 1fgmL−1 to 10ngmL−1 and a detection limit of 0.015fgmL−1 (signal/noise=3). The results demonstrated that the immunosensor has advantages of high sensitivity, wide linear range, good repeatability, and good selectivity. Importantly, the results of the detection of clinical serum specimens with the proposed sensor were well consistent with the data determined by micropartical enzyme immunoassay (MPEI), showing that the present work provides a promising ultrasensitive immunoassay strategy for clinical applications. [Copyright &y& Elsevier]

Abstract: A novel immunoassay protocol for simultaneous electrochemical determination of alpha-fetoprotein (AFP), carcinoembryonic (CEA) and streptococcus suis serotype 2 (SS2) was designed. As standard sandwich-type immunoassay format, three primary antibodies (Ab1), anti-CEA and anti-AFP and anti-SS2, were immobilized via protein A (PA) adsorbed by Nafion modified electrodes, and functionalized graphene sheets (GS), containing abundant gold nanoparticles (AuNPs) and carboxyl group, were used to immobilize secondary antibody@redox-probe so as to act as tracer. Concentration of each analyte was quantitatively related to the reduction peak current of corresponding redox-probe in differential pulse voltammetry (DPV) scan. The resulting immunosensor exhibited high selectivity and sensitivity in simultaneous determination of three analytes. The linear range was from 0.016 to 50ng/mL for AFP with a detection limit of 5.4pg/mL, 0.010 to 50ng/mL for CEA with a detection limit of 2.8pg/mL and 0.012 to 50ng/mL for SS2 with a detection limit of 4.2pg/mL (S/N=3). [Copyright &y& Elsevier]

We report a highly sensitive competitive-type assay for multiplexing electrochemical detection of clenbuterol in pig urine using a 16-sensor array. In this design, the clenbuterol was first conjugated with bovine serum albumin (BSA), and then the conjugates were immobilized on the electrode surface to compete with the free clenbuterol in the sample for specific antibody. Under the optimal conditions, the reproducibility of the clenbuterol electrochemical immunosensor was evaluated to be 3.4 % (coefficient of variation, CV) and the limit of detection was estimated to be 1.3 pg/mL. The very low detection limit was probably derived from the higher efficiency of the competitive immunoreaction caused by appropriate quantities of the clenbuterol immobilized on the 16-sensor array and the suitable amount of anti-clenbuterol antibody in the assay system. [ABSTRACT FROM AUTHOR]

An amperometric immunosensor for glycosylated hemoglobin (HbA1c) is reported. A glassy carbon electrode is modified with gold nanoparticles (AuNPs) bearing a ferrocene derivative and a glycosylated pentapeptide (GPP) as an epitope to which anti-HbA1c IgG can selectively bind. The rest of the electrode is passivated with an oligo(ethylene oxide) species to give the electrode resistant to nonspecific adsorption of proteins. Complexation of anti-HbA1c IgG with the surface bound epitope resulted in attenuation of the ferrocene electrochemistry. The immunosensor can detect HbA1c in the range of 4.6 %-15.1 % of total hemoglobin in human blood by a competitive inhibition assay. [ABSTRACT FROM AUTHOR]

In this paper, an amperometric immunosensor for the detection of carbofuran was developed. Firstly, multiwall carbon nanotubes (MWCNTs) and graphene sheets-ethyleneimine polymer-Au (GS-PEI-Au) nanocomposites were modified onto the surface of a glass carbon electrode (GCE) via self-assembly. The nanocomposites can increase the surface area of the GCE to capture a large amount of antibody, as well as produce a synergistic effect in the electrochemical performance. Then the modified electrode was coated with gold nanoparticles-antibody conjugate (AuNPs-Ab) and blocked with BSA. The monoclonal antibody against carbofuran was covalently immobilized on the AuNPs with glutathione as a spacer arm. The morphologies of the GS-PEI-Au nanocomposites and the fabrication process of the immunosensor were characterized by X-ray diffraction (XRD), ultraviolet and visible absorption spectroscopy (UV-vis) and scanning electron microscopy (SEM), respectively. Under optimal conditions, the immunosensor showed a wide linear range, from 0.5 to 500 ng/mL, with a detection limit of 0.03 ng/mL (S/N = 3). The as-constructed immunosensor exhibited notable performance features such as high specificity, good reproducibility, acceptable stability and regeneration performance. The results are mainly due to the excellent properties of MWCNTs, GS-PEI-Au nanocomposites and the covalent immobilization of Ab with free hapten binding sites for further immunoreaction. It provides a new avenue for amperometric immunosensor fabrication. [ABSTRACT FROM AUTHOR]

Abstract: Within the framework of research carried out by our team aimed at developing new immunological methods to determine proteins such as immunoglobulins G in different biological matrixes, for instance, serum and milk, tests were performed on several immunosensors based on different transducer types, i.e. amperometric (classical or screen-printed) electrodes for hydrogen peroxide. Lastly the feasibility of constructing immunosensors based on surface plasmon resonance (SPR) was investigated. “Competitive” immunological procedures were used in the first two cases. Conversely, the surface plasmon resonance transduction technique allowed a “direct” measurement. Applications were performed on human serum, powdered milks for babies and particularly on several animal milks, in the case of buffalo milk seeking a routine control method to identify possible inflammatory affections in the animals. [Copyright &y& Elsevier]

Abstract: In this paper, a novel label-free amperometric immunosensor for the detection of carbofuran residues was developed. The deposited gold nanocrystals (DpAu)/4,4′-thiobisbenzenethiol (DMDPSE) multilayers ({DpAu/DMDPSE} n ) membranes were used for modifying Au electrode to fabricate amperometric immunosensor. DpAu/DMDPSE multilayers were modified alternatively to form multiple membranes by layer-by-layer self-assembly technology. The sensitive steps of surface modification were characterized by cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS), respectively. The immunoreaction between anti-carbofuran monoclonal antibody and carbofuran directly triggered a signal via different pulse voltammetry (DPV). Under the optimized conditions, a linear relationship between the relative change in peak current of DPV (%ΔI) and the logarithm of carbofuran solution was obtained in the range from 0.1 to 1.0×106 ng/mL with a detection limit of 0.06ng/mL. The advantages of the immunosensor were exhibited in its wider linear range, better reproducibility, stability, selectivity and regeneration. Using lettuces, cabbages, green peppers, tomatoes, Chinese chives and strawberries as model samples, acceptable recovery of 82.0–109.2% was obtained. The proposed method was proven to be a feasible quantitative method for carbofuran analysis, which may open a new door for ultrasensitive detection of carbofuran residues in vegetables and fruits. [Copyright &y& Elsevier]

An electrochemical immunosensor has been developed for the determination of carbofuran based on gold nanoparticles (DpAu), prussian blue-multiwalled carbon nanotubes-chitosan (PB-MWCNTs-CTS) nanocomposite film and protein A (SPA) layer-by-layer assemble technology. DpAu and PB-MWCNTs-CTS incorporated films were used to enhance the electroactivity and stability of the immunosensor. The porous three-dimensional PB-MWCNTs-CTS nanocomposite film provided many amino groups and carboxyl groups to cross-link SPA and offered a large specific surface area to immobilize SPA. The formation of a self-assembled SPA layer was employed onto the electrode surface to increase the binding capacity of the antibody. The conformational process of the immunosensor and electrochemical performance of immunoreaction between carbofuran and the anti-carbofuran monoclonal antibody were characterized by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Effects of experimental variables, such as the concentration of the SPA and antibody, the adsorption time of DpAu, the pH of supporting electrolyte and the incubation time, were investigated in details. Under optimum operating conditions, the system provided a wide linear range between 0.1 and 1 μg/mL with a low detection limit of 0.021 ng/mL. The proposed immunosensor exhibited high sensitivity, high stability and good reproducibility, and it can be used for the detection of carbofuran pesticide. [ABSTRACT FROM AUTHOR]

In this study, anti-carbofuran monoclonal antibodies (Ab) were immobilized onto a gold electrode surface modified with multilayers of L-cysteine and gold colloidal nanoparticles (GNPs). Furthermore, horseradish peroxidase (HRP) as enzyme membrane was used for blocking unspecific sites and amplifying signal. The conformational properties of the immunosensor were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The concentration of antibody solution, pH of working buffer and incubation time were studied in detail for optimization of analytical performance. Under optimal conditions, the variation of current response was proportional to the concentration of carbofuran which ranged from 0.01 ng/mL to 50 ng/mL with a correlation coefficient of 0.9912. The detection limit was 0.01 ng/mL (S/N = 3). The proposed immunosensor exhibited good reproducibility and stability and it can be used for the rapid detection of carbofuran pesticide. [ABSTRACT FROM AUTHOR]

A new label-free immunosensor for the determination of carbofuran was proposed in this paper. Saturated thiourea (TU) and gold nanoparticles (GNPs) were modified onto the glassy carbon electrode surface to form a GNPs/TU film, which provided an interface containing-NH2 to assemble the second GNPs for the immobilization of anti-carbofuran antibody. Bovine serum albumin was used for blocking the non-specific adsorption sites. Thus, a novel amperometric immunosensor for carbofuran was prepared. The electrochemical properties of the modified processes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Under the optimal conditions, the current response was proportional to the concentration of carbofuran ranging from 1.0 ng/mL to 100.0 ng/mL and from 100.0 ng/mL to 200 μg/mL with the detection limit 0.11 ng/mL. The proposed amperometric immunosensor exhibited high sensitivity, low cost and simplified procedures, which provided a new promising tool for the detection of pesticides residues in food and environment. [ABSTRACT FROM PUBLISHER]

Abstract: Okadaic acid (OA), a lipophilic phycotoxin is mainly produced by toxigenic dinoflagellates. The need to develop high performing methods for OA analysis able to improve the traditional ones is evident. In this work, a novel experimental methodology for label-free detection of OA was developed. Protein G magnetic beads (protein-G-MBs) modified gold electrode was used to immobilize anti-OA monoclonal antibody (anti-OA-MAb). Preliminary, colorimetric tests were performed in order to validate protein-G-MBs and anti-OA-MAb reaction. Electrochemical detection was carried out by differential pulse voltammetry in ferri/ferrocyanide solution. The limit of detection value obtained (0.5μgL−1) validated the developed electrochemical immunosensor as a promising tool for routine use. The matrix effect and the recovery rate were also assessed with real samples, showing a good percentage of recovery. [Copyright &y& Elsevier]

Abstract: A novel electrochemical sensing interface, electrodeposition of gold–platinum alloy nanoparticles (Au–PtNPs) on carbon nanotubes, was proposed and used to fabricate a label-free amperometric immunosensor. On the one hand, the multiwalled carbon nanotubes (MWCNTs) could increase active area of the electrode and enhance the electron transfer ability between the electrode and redox probe; on the other hand, the Au–PtNPs not only could be used to assemble biomolecules with bioactivity kept well, but also could further facilitate the shuttle of electrons. In the meanwhile, horseradish peroxidase (HRP) instead of bovine serum albumin (BSA) was employed to block the possible remaining active sites and avoid the nonspecific adsorption. With the synergetic catalysis effect of Au–PtNPs and HRP towards the reduction of hydrogen peroxide (H2O2), the signal could be amplified and the sensitivity could be enhanced. Using alpha-fetoprotein (AFP) as model analyte, the fabricated immunosensor exhibited two wide linear ranges in the concentration ranges of 0.5–20ngmL−1 and 20–200ngmL−1 with a detection limit of 0.17ngmL−1 at a signal-to-noise of 3. Moreover, the immunosensor exhibited good selectivity, stability and reproducibility. The developed protocol could be easily extended to other protein detection and provided a promising potential in clinical diagnosis application. [Copyright &y& Elsevier]

Abstract: A new label-free amperometric immunosensor was developed for detection of carcinoembryonic antigen (CEA) based on chitosan-ferrocene (CS-Fc) and nano-TiO2 (CS-Fc+TiO2) complex film and gold nanoparticles–graphene (Au–Gra) nanohybrid. CS-Fc+TiO2 composite membrane was first modified on a bare glass carbon electrode. Then Au–Gra nanohybrid was formed on the CS-Fc+TiO2 membrane by self-assembly strategy. Next, further immobilization of anti-CEA was constructed according to the strong interaction between Au–Gra and the amido groups of anti-CEA. Since Au–Gra nanohybrid films provided a congenial microenvironment for the immobilization of biomolecules, the surface coverage of antibody protein could be enhanced and the sensitivity of the immunosensor has been improved. The good electronic conductive characteristic might be attributed to the synergistic effect of graphene nanosheets and Au NPs. The modified process was characterized by scanning electron microscope (SEM) and cyclic voltammetry (CV). Under optimized conditions, the resulting biosensor displayed good amperometric response to CEA with linear range from 0.01 to 80ng/mL and a detection limit of 3.4pg/mL (signal/noise=3). The results demonstrated that the immunosensor has advantages of high conduction, sensitivity, and long life time. This assay approach showed a great potential in clinical applications and detection of low level proteins. [Copyright &y& Elsevier]

n amperometric immunosensor has been developed for sensitive determination of hepatitis B surface antigen as a model protein. A glassy carbon electrode was modified with an assembly of positively charged poly(allylamine)-branched ferrocene (PAA-Fc) and negatively charged gold nanoparticles (Au NPs). The formation of PAA-Fc effectively avoids the leakage of Fc, retains its electrochemical activity, and enhances the conductivity of the composite. The adsorption of Au NPs onto the PAA-Fc matrix provides sites for the immobilization of the antigen and a favorable micro-environment to maintain its activity. The morphologies and electrochemistry of the sensing film were investigated via scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Factors influencing the performance of the immunosensor were studied in detail. The concentration of the antigen can be quantitated (by measuring the decrease of the amperometric response resulting from the specific binding between antigen and antibody) in the range between 0.1 and 150 ng mL, with a detection limit of 40 pg mL (S/N = 3). The method is economical, efficient, and potentially attractive for clinical immunoassays. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The hepatotoxic microcystins, especially microcystin-LR (MC-LR), are causing serious problems to public health and fisheries. We describe here a label-free amperometric immunosensor for rapid determination of MC-LR in water sample. The sensor was prepared by immobilizing antibody on a gold electrode coated with L-cysteine-modified gold nanoparticles. The stepwise self-assembly of the immunosensor was monitored and characterized by means of electrochemical impedance spectroscopy and differential pulse voltammetry. A 0.60 mmol L solution of hydroquinone was used as the electron mediator. The immunosensor was incubated with MC-LR at 25 °C for 20 min, upon which the differential pulse voltammetric current changed linearly over the concentration range from 0.05 to 15.00 μg L, with a detection limit of 20 ng L. The developed biosensor was used to determine MC-LR in spiked crude algae samples. The recovery was in the range from 95.6 to 105%. This method is simple, economical and efficient, this making it potentially suitable for field analysis of MC-LR in crude algae and water samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]