Sandwich Electrochemical Immunosensor Research Articles

Early Detection of Carcinoembryonic Antigen Using Hollow Nanospheres Improves the Outcome of Pediatric Solid Tumors

A sandwich electrochemical immunosensor was developed for sensitive detection of carcinoembryonic antigen (CEA) using hollow nanospheres composite material loaded with gold nanoparticles as the signal tag and gold triangular nanoplate as the substrate material. Samples obtained from pediatric solid tumor tissue and their blood samples were used to detect CEA using this nanoparticle. The hollow nanospheres constructed in this study, provided abundant reaction sites and high catalytic activity, while the loading of Au NPs enhances conductivity and biocompatibility. The immunosensor has good analytical ability in detecting CEA in the mass concentration range of 1 pg/mL to 50 ng/mL, with a low detection limit (LOD) of 0.37 pg/mL. This novel method provides a valuable tool for rapid clinical detection of CEA in the context of pediatric solid tumors.

Immunosensing of neuron-specific enolase based on signal amplification strategies via catalysis of ascorbic acid by heteropolysate COF

In view of the importance of quantification of neuron-specific enolase (NSE), an electrochemical NSE immunosensor was developed. The sandwich voltammetric immunosensor utilized vinyl-functionalized crystalline covalent organic framework (COFTAPT-Dva) modified electrode to load lots of Ab1 via thiol-ene “click” reaction as matrix. A crystalline cationic EB-COF:Br was used to load Au nanoparticles (AuNPs) and H3[PMo12O40] (PMo12) as immunoprobe. The AuNPs with the size of about 30 nm were firstly grown on EB-COF:Br and then a large number of electroactive PMo12 were uniformly assembled on AuNPs/EB-COF:Br via ion exchanging reaction. The AuNPs not only facilitated the bonding of Ab2 based on Au–S bond, but also improved performance of Ab2/AuNPs/EB-COF:PMo12 immunoprobe. The sensitivity of sandwich electrochemical immunosensor could be primarily amplified based on loaded abundant PMo12. Secondary sensitivity amplification of immunosensor could be achieved by using PMo12 to catalyze ascorbic acid. The linear range of sandwich voltammetric immunosensor based on current change of differential pulse voltammetry is 500 ± 36 fg mL−1 - 100 ± 8 ng mL−1. Thanks to the dual sensitivity amplification strategy, the sensitivity is as high as 54.06 ± 3.2 μA cm−2/lg(cNSE/ng mL−1), and the detection limit is as low as 166 ± 10.8 fg mL−1. It proves that it is completely feasible to amplify sensitivity of sandwich voltammetric immunosensors using polyoxometalate-COF and its catalytic substrate.

A sandwich electrochemical immunosensor based on MXene@dual MOFs for detection of tumor marker CA125.

The detection signal of carbohydrate antigen 125 (CA125) can be quantitatively amplified via the dual metal-organic framework (MOF) sandwich strategy. We propose a versatile method for synthesizing uniform MXene and MIL-101(Fe)-NH2 composites that combine the advantages of both materials to build a base layer with superb performance. MXene exhibits excellent electrical conductivity and high surface area. The mesoporous MIL-101(Fe)-NH2 not only increases the loading capacity of the primary antibody but also possesses the catalytic activity of the metal center (Fe). UiO66 loaded with methylene blue (MB) was fabricated as an electrochemical immunosensor signal tag to enable the detection of CA125. The mixture of MXene and MIL-101(Fe)-NH2 prepared as the substrate was fixed by chitosan rich in amino groups. As the signal amplification sector, UiO66@MB enhanced secondary antibody loading capacity and generated a redox signal enabling the detection of antigenic substances. The proposed electrochemical immunosensor demonstrated high sensitivity with a low limit of detection (LOD) of 0.006 U/mL. Therefore, the dual MOF sandwich-based immunosensor provides a novel method for the early diagnosis of CA125.

An Enzyme-Free Sandwich Amperometry-Type Immunosensor Based on Au/Pt Nanoparticle-Functionalized Graphene for the Rapid Detection of Avian Influenza Virus H9 Subtype

Avian influenza virus H9 subtype (AIV H9) has contributed to enormous economic losses. Effective diagnosis is key to controlling the spread of AIV H9. In this study, a nonenzymatic highly electrocatalytic material was prepared using chitosan (Chi)-modified graphene sheet (GS)-functionalized Au/Pt nanoparticles (GS-Chi-Au/Pt), followed by the construction of a novel enzyme-free sandwich electrochemical immunosensor for the detection of AIV H9 using GS-Chi-Au/Pt and graphene–chitosan (GS-Chi) nanocomposites as a nonenzymatic highly electrocatalytic material and a substrate material to immobilize capture antibodies (avian influenza virus H9-monoclonal antibody, AIV H9/MAb), respectively. GS, which has a large specific surface area and many accessible active sites, permitted multiple Au/Pt nanoparticles to be attached to its surface, resulting in substantially improved conductivity and catalytic ability. Au/Pt nanoparticles can provide modified active sites for avian influenza virus H9-polyclonal antibody (AIV H9/PAb) immobilization as signal labels. Upon establishing the electrocatalytic activity of Au/Pt nanoparticles on graphene towards hydrogen peroxide (H2O2) reduction for signal amplification and optimizing the experimental parameters, we developed an AIV H9 electrochemical immunosensor, which showed a wide linear range from 101.37 EID50 mL−1 to 106.37 EID50 mL−1 and a detection limit of 100.82 EID50 mL−1. This sandwich electrochemical immunosensor also exhibited high selectivity, reproducibility and stability.

Electrochemical Immunoassay of Melanoma Biomarker CPEB4 Based on Cobalt Porphyrin Functionalized Graphene Oxide

Rapid and early detection of cytoplasmic polyadenylate element-binding protein 4 (CPEB4) can protect against advanced malignant melanoma. Herein, we developed a sandwich electrochemical immunosensor based on GO-CoPP as a signal amplifier for the highly sensitive quantitative detection of the melanoma biomarker CPEB4. The sensor used gold nanoparticles (AuNPs) as a substrate enhancer and graphene oxide (GO) polymer modified with cobalt protoporphyrin (CoPP) as a signal carrier (GO-CoPP). The AuNPs were used to capture large amounts of primary antibodies and accelerated the electron transfer rate of the substrate, while GO-CoPP can be used to provide large amounts of the signal unit CoPP and secondary antibodies. These features of the composites conferred high sensitivity and the current response of the proposed immunosensor to CPEB4. Under optimal conditions, the developed immunosensor performed well over a wide linear range of 0.1 pg ml−1 to 10 ng ml−1 with a detection limit of 0.074 pg ml−1 (S/N = 3). In summary, the sensor showed promise for a wide range of applications in the quantitative detection of other tumor markers, with good reproducibility, high selectivity, and simple and sensitive operation.

A sandwich-type electrochemical immunosensor using trimetallic nanozyme as signal amplification for NT-proBNP sensitive detection

Heart failure (HF) is a major public health problem trigged by a heart circulation disorder. Early detection and diagnosis are conducive to the prevention and treatment of HF. N-terminal B-type natriuretic peptide precursor (NT-proBNP) is considered to be a sensitive diagnostic biomarker of HF. In this study, we constructed a NT-proBNP sandwich electrochemical immunosensor by using electroplated gold nanoparticles (Au NPs) as the substrate and utilizing rough-surfaced trimetallic Au@PdPt nanozymes (Au@PdPt RTNs) as current signal amplification. The Au NPs as substrate material modified glassy carbon electrode (GCE) have excellent conductivity and biocompatibility, which not only accelerate electron transfer rate, but also improve the loading capacity of primary antibody (Ab1). Moreover, the Au@PdPt RTNs were synthesized by a one-pot method and used as the labels to bound with secondary antibodies (Ab2) via the Pt-N. The large specific surface area and excellent catalytic properties for H2O2 of Au@PdPt RTNs can effectively enhance the stability and sensitivity of the immunosensor. With the favorable cooperation of Au NPs and Au@PdPt RTNs, the constructed immunosensor exhibited a wide concentration range from 0.1 pg mL−1 to 100 ng mL−1 and a low detection limit of 0.046 pg mL−1. Furthermore, the accuracy of the analysis of NT-proBNP in diluted human serum samples was satisfactory. The results revealed the electrochemical immunosensor has a prospective application in clinical detection.

An Electrochemical Sandwich Immunosensor Based on Signal Amplification Technique for the Determination of Alpha-Fetoprotein.

The synthesis of Au nanocubes is used to label alpha-fetoprotein antibody (anti-AFP) and horseradish peroxidase (HRP) to form an immune complex for antibody detection. Graphene oxide-methylene blue-gold nanoparticles (GO-MB-AuNPs) nanocomposites were used as the immunosensing platform. This proposed sandwich-type immunoassay shows good performance. This method establishes a feasible amperometric immunoassay method for sensitive analysis of AFP in serum samples. Under the optimal experimental conditions, the DPV current response of the immunosensor is proportional to the logarithmic value of the AFP concentration. The linear detection range can achieve to 0.005–20 ng/mL with a detection limit of 1.5 pg/mL. The proposed immunosensor has good precision, selectivity and stability, and can be used for AFP determination in clinical tests.

An electrochemical sandwich immunosensor of vascular endothelial growth factor based on reduced graphene oxide/gold nanoparticle composites

An electrochemical immunosensor is described for the detection of vascular endothelial growth factor–A (VEGF). Anti VEGF antibody was obtained from Pichia pastoris through expressing the nucleotide sequence. To self-assembly decoration of anti-body on the surface of the electrode, reduced graphene oxide/Au nanoparticles (RGO/Au NPs) was used that caused increase the conductivity and active surface area of the electrode. Instrument characterization were used for structural analysis of RGO/Au NPs. The results show that Au NPs distributed on the surface of RGO sheets uniformly with an average size of 60 nm. Different electric signal transduction modes were used to study the electrochemical performance of the prepared nanoprobe for the detection of VEGF. For the determination of VEGF in buffer media, another anti-VEGF antibody conjugated with Horseradish peroxidase as a secondary antibody that attached and made a sandwich probe on the surface of the electrode was used. Electrochemical studies show that the nanoprobe has suitable selectivity among other biological macromolecules and a good electrochemical response to Anti VEGF by limit of detection about 6 fg.ml−1.

A sandwich electrochemical immunosensor based on antibody functionalized-silver nanoparticles (Ab-Ag NPs) for the detection of dengue biomarker protein NS1

Dengue, a viral disease caused by a flavivirus belonging to family. Flaviviridae, is a serious threat to human health in tropical and subtropical regions worldwide. Herein, we design a sandwich-type immunosensor based on a nano-probe maintaining antibody functionalized‑silver-nanoparticles (Ab-Ag NPs) as a trace tag for simple, sensitive, and selective detection of dengue biomarker NS1. Diazonium assisted immobilization of antibody on graphite pencil electrodes provided a selective and specific platform for analyte (NS1) recognition, sandwiched by Ab-Ag NPs. Well defined and sharp electrochemical signals by Ag NPs, characteristics of their oxidation, probed the specific detection of NS1. A proportional increase in the faradic current for the oxidation of Ag NPs is observed with an increase in analyte NS1 concentration. This sandwiched based immunosensor facilitated to achieve a linear range of 3–300 ng/mL with a detection limit of 0.5 ng/mL for NS1 detection. The studies evaluating possible interference with analog analytes are carried to demonstrate the specificity of the designed immunosensor. The applicability of the method is also evaluated to monitor NS1 in spiked human serum samples analysis. The designed sandwich-type immunosensor strategy integrating nano trace tag may find wide-spread clinical applications for early and rapid detection of biomarkers.

Sensitive competitive label-free electrochemical immunosensor for primal detection of ovarian cancer

A simple, sensitive and one-step electrochemical technique was employed for the development of sandwich electrochemical immunosensor for the detection of CA 125 antigen. A unique three-dimensional gold nanostructure grown substrate is developed by electrodeposition technique to immobilize a large amount of anti-CA 125 through functionalization of gold nanostructures to immobilize cancer biomarker CA 125 and in human serum as well. The prepared immunosensor can directly amplify the electrochemical signal by making use of silicon nanoparticles conjugated with target antibody to achieve a detection limit of 1 pg ml−1 in human serum. However, a comparative low detection limit of 1 fg ml−1 with wide dynamic range from 1 μg ml−1 to 1 fg ml−1 was obtained in cancer biomarker CA 125 solution. The immunosensor is sensitive, stable and reproducible in clinical serum samples. This gold nanostructures-based sandwich immunosensor can be mass manufactured, which may offer great potential to fabricate economical and sensitive immunosensor for broad applications in clinical diagnosis.

Amperometric immunoassay for the carcinoembryonic antigen by using a peroxidase mimic consisting of palladium nanospheres functionalized with glutathione-capped gold nanoparticles on graphene oxide.

A composite nanoenzyme was used in a sandwich-type electrochemical immunoassay for the carcinoembryonic antigen (CEA). Hierarchically porous palladium nanospheres (Pd NPs) were functionalized with glutathione-capped gold nanoparticles (G-Au NPs) and then loaded onto graphene oxide (GO) to obtain a peroxidase mimicking nanoenzyme of type GO-supported G-Au/Pd. The composite can catalyze the oxidation of the substrate tetramethylbenzidine (TMB) by H2O2 to give blue-colored oxidized TMB within only 20s. This strong peroxidase activity, good conductivity and high specific surface area of the material make it a useful label for secondary antibodies (Ab2) for the detection of CEA. The cotton-like electrodeposited gold nanoparticles with good electrical conductivity were used to immobilize primary antibody (Ab1). The amperometric immunoassay has a detection range that extends from 10fg·mL-1 to 100ng·mL-1 at a working potential of -0.4V with addition of 5mmol·L-1 H2O2 as electrochemically active substrate, and the detection limit is as low as 3.2fg·mL-1 (S/N= 3). Graphical abstract Schematic of sandwich electrochemical immunosensor for the carcinoembryonic antigen. Electrodeposited gold used as substrate material, and Graphene oxide supported G-Au NPs functionalized porous Pd nanospheres (GO supported G-Au/Pd) as signal amplification platform, which catalyze the oxidation of tetramethylbenzidine (TMB).

Dual-signal sandwich electrochemical immunosensor for amyloid β-protein detection based on Cu–Al2O3-g–C3N4–Pd and UiO-66@PANI-MB

Combining of amperometric and square wave voltammetric methods (SWV), the dual-signal sandwich electrochemical immunosensor was developed for quantitative determination of amyloid β-protein (Aβ). Cu was doped into Al2O3 lattice (Cu–Al2O3) and reacts with graphite carbon nitride (g-C3N4) to generate Cu–Al2O3-g-C3N4 with internal dual-reaction center structure, which has good catalytic properties of hydrogen peroxide (H2O2). Subsequently, palladium nanoparticles (Pd NPs) was introduced into Cu–Al2O3-g-C3N4 (Cu–Al2O3-g–C3N4–Pd) that not only synergistically catalyzed H2O2 but also immobilized anti-Aβ (Ab1) via Pd–NH2. The Cu–Al2O3-g–C3N4–Pd was used as matrix material to modify the electrode, which can produce obviously electrochemical signals through Amperometry i-t curve. Meanwhile, the Zr6O4(OH)4(CO2)12 (UiO-66) modified with polyaniline (PANI) has the large specific surface, good conductivity and adsorption capacity, which can support methylene blue (MB) as signal label of anti-Aβ (Ab2). Therefore, the UiO-66@PANI-MB can provide an obviously electrochemical signal about MB through SWV. Under optimal conditions, the dual-signal sandwich electrochemical immunosensor has salient analytical performance and both signal platforms provide more accurate results. The linear range of detection obtained by the immunosensor was 10 fg/mL-100 ng/mL, and the detection limit was 3.3 fg/mL. This method not only provided a reliable guarantee for the experimental detection but also provided an effective strategy for the detection of other biological.

An Electrochemical Sandwich Immunosensor for the Detection of HER2 using Antibody-Conjugated PbS Quantum Dot as a label

A facile electrochemical sandwich immunosensor for the detection of a breast cancer biomarker, the human epidermal growth factor receptor 2 (HER2), was designed, using lead sulfide quantum dots-conjugated secondary HER2 antibody (Ab2-PbS QDs) as a label. Using Ab2-PbS QDs in the development of electrochemical immunoassays leads to many advantages such as straightforward synthesis and well-defined stripping signal of Pb(II) through acid dissolution, which in turn yields better sensing performance for the sandwiched immunosensor. In the bioconjugation of PbS QDs, the available amine and hydroxyl groups from secondary anti-HER2 and capped PbS QDs were bound covalently together via carbonyldiimidazole (CDI) acting as a linker. In order to quantify the biomarker, SWV signal was obtained, where the Pb2+ ions after acid dissolution in HCl was detected. The plated mercury film SPCE was also detected in situ. Under optimal conditions, HER2 was detected in a linear range from 1–100 ng/mL with a limit of detection of 0.28 ng/mL. The measures of satisfactory recoveries were 91.3% to 104.3% for the spiked samples, displaying high selectivity. Therefore, this method can be applied to determine HER2 in human serum.

An electrochemical sandwich immunosensor for cardiac troponin I by using nitrogen/sulfur co-doped graphene oxide modified with Au@Ag nanocubes as amplifiers.

A voltammetric sandwich immunoassay is described for the biomarker cardiac troponin I (cTnI). The gold nanocube-functionalized graphene oxide (AuNC/GO) is employed as a substrate to accelerate the electron transfer and to immobilize more primary antibodies. It also employs composite materials prepared from bimetallic gold/silver core-shell nanocubes and nitrogen and sulfur co-doped reduced graphene oxide as the signal amplifier. The introduction of N and S into GO enlarges the active surface and accelerates the electron transfer rate. Such unique characteristics render the material an effective support substrate to load more Au@AgNC and to immobilize an increasing number of second antibodies via Ag-N bonds. After specific binding with cTnI, the immunosensor was incubated in a labeled cTnI secondary antibody solution. The amperometric signal change is then measured at 0.34V (vs. SCE) using o-phenylenediamine and hydrogen peroxide as an electrochemical probe. Response is linear in theconcentration range from 100fg∙mL-1 to 250ng∙mL-1, and the detection limit is 33fg∙mL-1. Graphical abstract Schematic presentation of cardiac troponin I (cTnI) electrochemical immunosensor based on gold nanocube-functionalized graphene oxide (AuNC/GO) as substrate material, bimetallic gold/silver core-shell nanocubes and nitrogen and sulfur co-doped reduced graphene oxide (Au@AgNC/N, S-rGO) as signal amplifier, and hydrogen peroxide (H2O2) and o-phenylenediamine (o-PD) as redox probe.

Development of a Sandwich Immunosensor for concurrent detection of carcinoembryonic antigen (CEA), vascular endothelial growth factor (VEGF) and α-fetoprotein (AFP) biomarkers

Cancer Biomarkers are important biological molecules which provide early detection, diagnosis and classification of cancer cells. In this work, nanoparticle tags with different redox potentials have been used as an electrochemical coding technology for the simultaneous detection of carcinoembryonic antigen (CEA), vascular endothelial growth factor (VEGF) and α-fetoprotein (AFP) biomarkers. As far as we know, this is the only work that covers the simultaneous detections of these biomarkers. For this purpose, basically, an electrochemical sandwich immunosensor, which was fabricated from carbon screen printed electrode, was utilized as a diagnostic platform. As nanoparticle tags, PbAu@ɣFe2O3, CuAu@ɣFe2O3 and ZnAu@ɣFe2O3 hybrid nanolabels were synthesized and used for labelling anti-CEA, anti-VEGF and anti-AFP, respectively. By monitoring differential pulse voltammetric oxidation peaks of labeling metals (Pb, Cu, Zn), CEA, VEGF and AFP biomarkers were detected at the same time.

Sandwich Electrochemical Immunosensor for Early Detection of Tuberculosis Based on Graphene/Polyaniline-Modified Screen-Printed Gold Electrode.

A rapid and sensitive sandwich electrochemical immunosensor was developed based on the fabrication of the graphene/polyaniline (GP/PANI) nanocomposite onto screen-printed gold electrode (SPGE) for detection of tuberculosis biomarker 10-kDa culture filtrate protein (CFP10). The prepared GP/PANI nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The chemical bonding and morphology of GP/PANI-modified SPGE were studied by Raman spectroscopy and FESEM coupled with energy dispersive X-ray spectroscopy, respectively. From both studies, it clearly showed that GP/PANI was successfully coated onto SPGE through drop cast technique. Cyclic voltammetry was used to study the electrochemical properties of the modified electrode. The effective surface area for GP/PANI-modified SPGE was enhanced about five times compared with bare SPGE. Differential pulse voltammetry was used to detect the CFP10 antigen. The GP/PANI-modified SPGE that was fortified with sandwich type immunosensor exhibited a wide linear range (20–100 ng/mL) with a low detection limit of 15 ng/mL. This proposed electrochemical immunosensor is sensitive, low sample volume, rapid and disposable, which is suitable for tuberculosis detection in real samples.

Rapid screening drug susceptibility test in tuberculosis using sandwich electrochemical immunosensor

Drug susceptibility testing (DST) for Mycobacterium tuberculosis currently faces multiple challenges, including lengthy ineffective standard methods, the expensive cost of molecular tests, and large bulky diagnostic machines. In this work, a disposable MPT64 sensor was developed to rapidly determine drug susceptibility (DS-TB) and multidrug resistant tuberculosis (MDR-TB) using an electrochemical sandwich-immunosensor for the detection of MPT64 as an indicator of Mycobacterium tuberculosis growth. Anti-MPT64 (as capture antibody; cAb) was immobilised on screen printed carbon electrodes to specifically bind with MPT64 target protein. A reporter probe of anti-MPT64 conjugated with horseradish peroxidase (HRP labeled rAb) then completed the sandwich immunocomplex. The current signals were received from the catalytic reaction between 3,3′-5,5′-tetramethylbenzidine (TMB), H2O2 and HRP labeled rAb using the chronoamperometric mode on a portable potentiostat. Increasing MPT64 concentration was taken as an indicator of growth, which was measured by the disposable MPT64 sensor. This sensor shows the possibility of determining DST by comparing the signals of DS-TB and MDR-TB growth in drug-free and drug-containing liquid medium. The time required to identify DS-TB and MDR-TB in pure culture MTB and leftover sputum sediments from patients are 3 days and 4–6 days, respectively. Therefore, using this sensor is significantly rapid and inexpensive and has the potential to be used for drug susceptibility testing of tuberculosis in middle to low income countries.

Electrochemical Sandwich Immunosensor for Determination of Exosomes Based on Surface Marker-Mediated Signal Amplification

Extracellular vesicles (EVs), namely, exosomes and microvesicles, are important mediators of intercellular communication pathways. Since EVs can be detected in a variety of biofluids and contain a specific set of biomarkers which are reminiscent of their parental cells, they show great promise in clinical diagnostics as EV analysis can be performed in minimally invasive liquid biopsies. However, reliable, fast and cost-effective methods for their determination are still needed, especially if decentralized analysis is intended. In this study, we developed an electrochemical biosensor which works with 1.5 μL sample volume and can detect as low as 200 exosomes per microliter, with a linear range spanning almost 4 orders of magnitude. The sensor is specific and readily differentiates exosomes from microvesicles in samples containing 1000-fold excess of the latter. Capability of detecting exosomes in real samples (diluted serum) was shown. This was achieved by immobilizing rabbit antihuman CD9 antibodies on gold substrates and using monoclonal antibodies against CD9 for detection of captured exosomes. Signal amplification is presumably obtained from the fact that multiple detector antibodies bind to the surface of each captured vesicle. Detection is performed based on electrochemical reduction of 3,3',5,5'-tetramethyl benzidine (TMB) after addition of horseradish peroxidase (HRP)-conjugated anti-IgG antibodies. This amperometric biosensor can be easily incorporated into future miniaturized and semiautomatic devices for EV determination.

Electrochemical immunoassay for the cancer marker LMP-1 (Epstein-Barr virus-derived latent membrane protein 1) using a glassy carbon electrode modified with Pd@Pt nanoparticles and a nanocomposite consisting of graphene sheets and MWCNTs

We describe an electrochemical sandwich immunosensor with enhanced sensitivity for the determination of the tumor marker LMP-1. The capture antibody (Ab1) was immobilized on a composite consisting of graphene sheets and carboxylated multiwalled carbon nanotubes (GS-MWCNTs) in a chitosan matrix that was placed on the surface of glassy carbon electrodes (GCE). The detection antibody (Ab2) marked with thionine was fixed on a composite of HRP/Pd@Pt-MWCNTs. Following exposure to the antigen (LMP-1), an amplified signal was observed in differential pulse voltammetry because of the synergistic effect between the Pd@Pt NPs and HRP in the presence of added H2O2. The differential pulse voltammetry signal is best acquired at a working potential of −250 mV (vs. Ag/AgCl) in the presence of H2O2. Under optimized conditions, the calibration range extends from 0.01 to 40 ng mL−1 of LMP-1, and the detection limit is 0.62 pg mL−1 (S/N = 3). Hence, this immunosensor provides a promising tool for an early diagnosis of nasopharyngeal carcinoma.

A sandwich electrochemical immunosensor for Salmonella pullorum and Salmonella gallinarum based on a screen-printed carbon electrode modified with an ionic liquid and electrodeposited gold nanoparticles

This article describes an electrochemical immunosensor for rapid determination of Salmonella pullorum and Salmonella gallinarum. The first step in the preparation of the immunosensor involves the electrodeposition of gold nanoparticles used for capturing antibody and enhancing signals. In order to generate a benign microenvironment for the antibody, the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate was used to modify the surface of a screen-printed carbon electrode (SPCE). The single steps of modification were monitored via cyclic voltammetry and electrochemical impedance spectroscopy. Based on these findings, a sandwich immunoassay was worked out for the two Salmonella species by immobilizing the respective unlabeled antibodies on the SPCE. Following exposure to the analytes, secondary antibody (labeled with HRP) is added to form the sandwich. After adding hydrogen peroxide and thionine, the latter is oxidized and its signal measured via CV. A linear response to the Salmonella species is obtained in the 104 to 109 cfu · mL−1 concentration range, and the detection limits are 3.0 × 103 cfu · mL−1 for both species (at an SNR of 3). This assay is sensitive, highly specific, acceptably accurate and reproducible. Given its low detection limit, it represents a promising tool for the detection of S. pullorum, S. gallinarum, and - conceivably - of other food-borne pathogens by exchanging the antibody.