Impedimetric Aptasensor Research Articles

Electrospun zirconium oxide embedded in graphene-like nanofiber for aptamer-based impedimetric bioassay toward osteopontin determination.

An impedimetric bioassay was constructed based on a nanohybrid of zirconium oxide nanoparticles and graphene-like nanofiber (denoted by ZrO2@GNF) for the determination of osteopontin (OPN). A series of ZrO2@GNF nanohybrids with different morphologies and nanostructures were derived from zirconium-based metal-organic frameworks (UiO-66) entrapped within the electric spun polyacrylonitrile (PAN) fiber (represented by UiO-66@PAN) by calcination at different temperatures. The basic characterizations revealed that the UiO-66@PAN nanofibers were collapsed into short nanorods. As such, homogeneously distributed ZrO2 nanoparticles were found to be embedded within the GNF nanostructure. This transition in the chemical structure and nanostructure not only can greatly enhance the electrochemical conductivity of the nanohybrid but also can strengthen the adsorbed bioaffinity toward OPN aptamer strands. As compared with bioassays based on ZrO2@GNF calcined at 500°C and 900°C, the ZrO2@GNF nanohybrid obtained at 700°C (ZrO2@GNF700) demonstrated superior sensing performance, showing a determination limit of 4.76fgmL-1 within a OPN concentration ranging 0.01pgmL-1 to 2.0ngmL-1. It also displayed high selectivity, accompanied by good reproducibility and stability, acceptable applicability, and excellent repeatability. Graphical abstractSchematic representation of an impedimetric aptasensor based on nanohybrids of zirconium oxide nanoparticles and graphene-like nanofiber (ZrO2@CNF) was constructed for osteopontin detection. The ZrO2@CNF700 nanohybrid-based aptasensor demonstrated superior sensing performances, providing a promising tool for detecting cancer markers in biomedical diagnosis.

Ultrasensitive detection of amoxicillin by TiO2-g-C3N4@AuNPs impedimetric aptasensor: Fabrication, optimization, and mechanism

The trace amount of antibiotics in water can be enriched in the human body through the food chain, leading to extremely harmful effects on people's health. Therefore, it is urgent to develop new methods to detect trace pollutants in various aquatic phase. An analytical method utilizing the synergistic effect between the sensing strategy and catalytic material with high electron transfer capacity can be used to detect trace antibiotics. In this paper, an ultrasensitive impedimetric aptasensor was fabricated by the synergy between functionalized materials (TiO2-g-C3N4) and gold nanoparticles (Au NPs). Due to the formation of the ‘Au-S’ bond between the thiol-aptamer and Au NPs, amoxicillin and the aptamer can be specifically recognized on the modified glassy carbon electrode (GCE), and the impedance signal increased rapidly. Meanwhile, the Box-Behnken Design (BBD) strategy was used to reduce the random error of the experiment, so that the prepared aptasensor has the highest sensitivity to the detection of amoxicillin. Under optimized conditions, the sensor successfully achieved the detection of amoxicillin in the ultra-low detection range (0.5–3 nM) and reached the ultra-low detection limit (0.2 nM). The detection strategy has good selectivity, reproducibility, and stability, and thus has good potential to detect amoxicillin in actual wastewater.

AgNPs/QDs@GQDs nanocomposites developed as an ultrasensitive impedimetric aptasensor for ractopamine detection.

Developing easy-to-use and miniaturized sensors for in-field monitoring of targets which is related to human health is necessary. Ractopamine (RAC) is a feed additive with serious side effects that is forbidden in many countries. This study reports the fabrication of an impedimetric aptasensor for ultrasensitive and selective detection of the RAC in human biological fluids. Accordingly, an efficient nanocomposites was synthesized by a beneficial combination of graphene quantum dots (GQDs), quantum dots (QDs) and silver nanoparticles (AgNPs) for modifying a glassy carbon electrode (GCE). This nanocomposite is promising to present a synergistic effect in the increase of the active surface area of the modified electrode to more load the biocapture of the target. Next, the RAC-binding aptamer (Apt) was attached to the AgNPs/QDs@GQDs/GCE surface and a sensitive layer for the RAC detection was embedded. A RAC-Apt complex was formed upon adding the RAC and the changes of the electrochemical behavior were studied by some electrochemical techniques such as electrochemical impedance spectroscopy (EIS). Under optimal conditions, the charge transfer resistance (Rct) value was increased linearly with increasing of the RAC concentrations in the range of 1 fM to 901.4nM. Limit of detection (LOD) was calculated to be 330 aM which is superior by other reported electrochemical methods in the RAC sensing. The applicability of the aptasensor was tested in human urine and blood serum as the real samples and satisfactory results of specificity were achieved. It seems that the proposed strategy not only provides a new ultrasensitive strategy for RAC detection but also expands the application of the sensing interface to develop other aptasensors by changing the Apt sequence.

Chitosan-carbon quantum dots as a new platform for highly sensitive insulin impedimetric aptasensor

Considering the importance of measuring insulin in the prevention and diagnosis of diabetes-related illnesses, here we introduced an ultrasensitive electrochemical aptamer-based sensor for detection of insulin in human blood serum. In this research, carbon quantum dots (CQDs) were synthesized using simple, fast and cheap methods from candle soot. By dispersion of the CQDs in chitosan (Chi) matrix, homogenous CQD-Chit nano-composite was obtained. The experimental results demonstrate the good advantages of proposed CQD-Chit nano-composite, such as homogeneity, high stability and multiple amino groups for covalent immobilization of aptamer and fabrication of highly selective insulin aptasensor. CQD-Chit nano-composite was characterized by the transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDAX), Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques. Under the optimized conditions with electrochemical impedance spectroscopy technique, a linear response ranges from 0.5 nM to 10 nM with the sensitivity of 80.07 Ω/nM and the very low detection limit of 106.8 pM was obtained for insulin detection. The fabricated aptasensor is validated in comparison with standard methods for detection of insulin in human blood serum. Also, the analytical performances of the fabricated aptasensor can be a superiority compared to the current insulin electrochemical biosensors.

Electrochemical detection of lipopolysaccharide based on rolling circle amplification assisted formation of copper nanoparticles for enhanced resistance generation

In this work, a novel sandwich-type impedimetric biosensor was fabricated for highly sensitive and selective detection of lipopolysaccharide (LPS) from E. coli O55:B5. LPS aptamer I was immobilized onto electrodeposited gold nanoparticles (Au) modified electrode for capturing LPS in buffer and serum. LPS aptamer II and rolling circle amplification (RCA) primer were conjugated with gold nanoparticles (AuNPs) to use as signal tags. LPS was sandwiched between AuNPs/primer/aptamer II bioconjugates and aptamer I. This was followed by extension of RCA, which resulted in long poly-thymine (T) single strand (ssDNA) sequences to adsorb copper ions (Cu2+) into the skeleton of poly-T sequences. Thus, poly-T ssDNA directly served as the specific template for copper nanoparticles (CuNPs) formation with the aid of ascorbic acid (VC). Finally, the formed CuNPs@ssDNA complex promoted the oxidation of pyrocatechol violet (PCV) to insoluble bulky oligomer (precipitation) in the presence of H2O2. The reaction significantly enhanced the resistance signal of LPS quantitative determination. The impedimetric aptasensor exhibited a wide dynamic working range of 0.01 pg/mL ˜ 100 ng/mL with a detection limit of 4.8 fg/mL. This method also showed good selectivity and reproducibility, and demonstrated the applicability of LPS detection in human serum samples, offering a promising avenue for sensitive LPS detection.

Bifunctional bioplatform based on NiCo Prussian blue analogue: Label-free impedimetric aptasensor for the early detection of carcino-embryonic antigen and living cancer cells

A novel bifunctional electrochemical aptasensor based on bimetallic NiCo Prussian blue analogue (NiCoPBA) nanocubes has been constructed for detecting carcino-embryonic antigen (CEA) and corresponding living cancer cells. The NiCoPBA exhibits a regular cubic shape of 100 nm size, with fluorescence and excellent biocompatibility. In view of the intrinsic cavities, metallic coordination centers, rich CN groups, and π-π* interactions of NiCoPBA, the CEA-targeted aptamer strands can be strongly anchored on the surface of nanocubes. Given that the CEA cancer marker is overexpressed on the H460 cell surface of carcinomas, the developed NiCoPBA-based aptasensor not only can be employed to determine CEA in human serum via the formation of stable G-quadruplex between aptamer strands and CEA, but also can be utilized to directly detect cancer cells due to the strong binding force between CEA aptamer and cancer cell. The fabricated sensor shows superior sensing performance toward CEA compared with other reported CEA aptasensors, providing an extremely low limit of detection (LOD) of 0.74 fg mL−1 (1.62 fM) (S/N = 3) in a wide linear range of 1.0 fg mL−1 to 5.0 ng mL−1, as well as an LOD of 47 cells mL–1 for H460 cells. Thereby, the proposed aptasensor may be further used as a promising platform for detecting other cancer markers when anchoring different kinds of aptamers, with potential bifunctional applications in early diagnosis of tumor markers and cancer cells.

An impedimetric aptasensor for ultrasensitive detection of Penicillin G based on the use of reduced graphene oxide and gold nanoparticles.

The authors describe an impedimetric aptasensor for Penicillin G (PEN) which is an important antibiotic. The method is based on the use of a pencil graphite electrode (PGE) modified with reduced graphene oxide (RGO) and gold nanoparticles (GNPs) for ultrasensitive detection of PEN. The morphology of a bare PGE, RGO/PGE, and GNP/RGO/PGE, and the functional groups on graphene oxide (GO) and RGO were studied using scanning electron microscopy and Fourier transform infrared spectroscopy. Electrochemical impedance spectroscopy was used for detection of PEN by measuring the charge transfer resistance (Rct). Also, cyclic voltammetry was recorded at potential range of 0.30 to +0.70V for PGE treatment. This aptamer-based assay has a wide linear range that extends from 1.0 fM to 10μM, and a limit of detection as low as 0.8 fM. The method was applied to the determination of PEN in spiked milk from cow, sheep, goat and water buffalo. Recoveries ranged from 92% to 104%. The assay is fast, ultrasensitive, high reproducible, and selective over antibiotics such as streptomycin, tetracycline, and sulfadiazine. Graphical abstract Schematic presentation of an impedimetric aptasensor for Penicillin G antibiotic using a pencil graphite electrode (PGE) modified with reduced graphene oxide (RGO) and gold nanoparticles (GNPs). This aptamer based assay has limit of detection as low as 0.8 fM.

Computational analysis and optimization of carcinoembryonic antigen aptamers and experimental evaluation

Carcinoembryonic antigen (CEA), a highly glycosylated protein, overexpresses in many cancers. In this study, computational methods were used to optimize CEA aptamers. Experimental evaluvation of selected aptamers were conducted through electrochemical impedance spectroscopy. After two and three-dimensional structure modeling, the complexes of twelve reported aptamers against CEA were simulated using the ZDOCK server. Based on docking scores, two aptamer sequences (CSR59 and CSR57.1) were selected and used to create a new library. This ssDNA aptamer library consisting of 91 sequences was created using diverse in silico mutational methods. We obtained seventeen sequences having higher binding scores than reported sequences. Based on ZDOCK scores, the interaction domain of CEA, and steric hindrance due to glycosylation, two aptamer sequences (G3S1.5 and G2S2.2) were selected. An impedimetric aptasensor was designed, and selected aptamers were used as biorecognition elements. Resistance to charge transfer (Rct) quantities confirmed the bioinformatic approach and molecular docking scores. The result showed that the interaction ability of selected aptamers was about 13.5 fold higher than the control. It can be concluded that the selected aptamers have good potential for detection of carcinoembryonic antigen biomarker.

Impedimetric aptasensor for the label-free and selective detection of Interleukin-6 for colorectal cancer screening

Despite the fact that cancer research has experienced important advances and remarkable improvement in the curing processes during the last decades, this disease still occupies a leading position among the causes of death worldwide. It has been demonstrated that there is an interconnection between the overexpression of interleukin-6 cytokine and the tumor growth, metastasis, and therapeutic resistance in several types of malignancies. Herein, a highly sensitive and selective aptasensor for quantitative detection of interleukin-6 was developed by using a glassy carbon electrode modified with p-aminobenzoic acid, p-aminothiophenol and gold nanoparticles. A thio-terminated aptamer specific for interleukin-6 was immobilized on the surface of the modified electrode via the formation of gold-sulfur bonds. This DNA oligonucleotide was then used as a detection probe to capture the target protein at the biosensor surface allowing label-free detection by electrochemical impedance spectroscopy. The developed aptasensor showed a good linear response from 5 pgmL-1 to 100 ngmL-1 with a detection limit of 1.6 pgmL-1, within the range of physiological concentration of the protein. The biosensor exhibited high selectivity and has been successfully used to detect interleukin-6 in blood samples collected from patients suffering of colorectal cancer, with excellent recoveries after the addition of known amount of the target protein.

Selection of high affinity aptamer-ligand for dexamethasone and its electrochemical biosensor

A high specificity aptamer-ligand biorecognition and binding system to monitor of dexamethasone (DXN) was developed. The detection principle was based on a label-free electrochemical aptasensor. The selection of the aptamer was successfully performed by the systematic evolution of ligands through exponential enrichment technique (SELEX). From a random library of 1.08 × 1015 single-stranded DNA, an aptamer designated as DEX04 showed a highest affinity with a dissociation constant of 18.35 nM. It also showed a good conformational change when binding with DXN. In addition, the aptamer DEX04 did not show any cross-reactivity with other commonly used hormones. An impedimetric aptasensor for DXN was then developed by immobilizing DEX04 on a gold electrode. The binding upon to DXN was monitored by following the change in the charge transfer resistance (Rct) of the [Fe(CN)6]4−/3− redox couple. The aptasensor exhibited a linear range from 2.5 to 100 nM with a detection limit of 2.12 nM. When applied aptasensor to test in water samples, it showed good recovery percentages. The new DXN aptamer can be employed in other biosensing applications for food control and the diagnosis of some diseases in medicine as a cost-effective, sensitive and rapid detection method.

An ultra-sensitive aptasensor based on carbon nanohorns/gold nanoparticles composites for impedimetric detection of carbendazim at picogram levels

We reported a carbon nanohorns/gold nanoparticles composites-based impedimetric aptasensor for carbendazim (CBZ) detection in lettuce and orange juice at picogram levels. The increased electron-transfer resistance, resulting from the formation of CBZ-aptamer complex, was recorded by electrochemical impedance spectroscopy as the aptasensor response for CBZ. Under the optimal conditions, the proposed aptasensor displayed a linear response for CBZ ranging from 1 to 1000 pg mL−1 with a detection limit of 0.5 pg mL−1. Noteworthy, the as-developed aptasensor displayed the lowest detection limit for CBZ among the previously reported methods. Common pesticides (atrazine, thiamethoxam, etc.) with 100-fold concentration did not interfere the CBZ detection. For CBZ detection in lettuce and orange juice, satisfactory recoveries were obtained with standard addition method. Statistics demonstrated that no significant differences were found between the data provided by standard HPLC-MS reference method and developed aptasensing method in term of accuracy and precision. We believe that the proposed aptasensor possesses a potential application for CBZ monitoring in agricultural product and food.

Development of an Impedimetric Aptasensor for Label Free Detection of Patulin in Apple Juice.

In the present work, an aptasensing platform was developed for the detection of a carcinogenic mycotoxin termed patulin (PAT) using a label-free approach. The detection was mainly based on a specific interaction of an aptamer immobilized on carbon-based electrode. A long linear spacer of carboxy-amine polyethylene glycol chain (PEG) was chemically grafted on screen-printed carbon electrodes (SPCEs) via diazonium salt in the aptasensor design. The NH2-modified aptamer was then attached covalently to carboxylic acid groups of previously immobilized bifunctional PEG to build a diblock macromolecule. The immobilized diblocked molecules resulted in the formation of long tunnels on a carbon interface, while the aptamer was assumed as the gate of these tunnels. Upon target analyte binding, the gates were assumed to be closed due to conformational changes in the structure of the aptamer, increasing the resistance to the charge transfer. This increase in resistance was measured by electrochemical impedance spectroscopy, the main analytical technique for the quantitative detection of PAT. Encouragingly, a good linear range between 1 and 25 ng was obtained. The limit of detection and limit of quantification was 2.8 ng L−1 and 4.0 ng L−1, respectively. Selectivity of the aptasensor was confirmed with mycotoxins commonly occurring in food. The developed apta-assay was also applied to a real sample, i.e., fresh apple juice spiked with PAT, and toxin recovery up to 99% was observed. The results obtained validated the suitability and selectivity of the developed apta-assay for the identification and quantification of PAT in real food samples.

Novel chitosan-Nafion composite for fabrication of highly sensitive impedimetric and colorimetric As(III) aptasensor

In the present work, for the first time we takes the advantages of chitosan-Nafion (Chit-Naf) composite as a highly conductive surface platform and a novel CNT-based signal amplification strategy to develop a lable-free impedimetricaptamer-based sensor for highly sensitive detection of As(III). The electrochemical impedance spectroscopy (EIS) investigations surprisingly revealed that the glassy carbon electrode (GC) electrode modified with Chit-Naf composite had higher electron transfer kinetics compared the bare GC, GC/Naf and GC/Chit electrodes, which promises a great potential as an efficient platform in construction of biosensing assays. In this work, we employed a signal amplification strategy based on carbon nanotube-bovine serum albumin (CNT-BSA) hybrid system, by which sensitivity and detection limit of the aptasensor for the detection of As(III) were obtained to be 100.82 Ω nM−1 and a of 74 pM, respectively. This protocol provided one of the lowest limits of detection for As(III) on aptamer-based electrodes recently described in the literature. Moreover, the change of the optical absorptive properties of CNTs upon biorecognition interactions provides a way to detect the biorecognition process and thus allowed us to design an optical As(III) aptasensor using the UV–Vis spectroscopic method. The discrimination capability of the fabricated aptasensor for recognizing As(III) in the presence of other metal ions and a complex matrix of waste water samples was successfully investigated. This protocol provided a new method for sensitive detection of As(III) with considerable advantages in terms of reproducibility, selectivity, being mediator free and regenerability of the sensing interface.

Rapid Determination of Ochratoxin A in Grape and Its Commodities Based on a Label-Free Impedimetric Aptasensor Constructed by Layer-by-Layer Self-Assembly.

A simple and sensitive label-free impedimetric aptasensor for rapid determination of ochratoxin A (OTA) has been developed, which was based on the combination between thiolated aptamer and gold nanoparticles by layer-by-layer self-assembly. Because of the interaction between aptamer and OTA, the relative normalized electron-transfer resistance (ΔRct) values obtained by electrochemical impedance spectroscopy (EIS) was proportional to the concentration of OTA and showed a good linear relationship from 0.1 to 10.0 ng/mL, with a lower detection limit (0.030 ng/mL) than one-step thiolated DNA aptasensor. The established method was successfully applied to detect and analyze OTA in table wine and grape juice, and the recovery was 90.56%–104.21% when PVP effective removed of phenolic substances. The label-free impedimetric aptasensor was used for rapid detection and quantitation of OTA in the inoculated grapes with the Aspergillus Nigri (H1), and the production of OTA (62.4 μg/kg, 20 μg/kg) far exceeded the maximum levels of 2 μg/kg after inoculation for three days. The developed method exhibited a good specificity, high sensitivity, time-efficient, and it could be applied to detect the OTA concentration in grape and its commodities.

Target-inspired Zn2+-dependent DNAzyme for ultrasensitive impedimetric aptasensor based on polyacrylic acid nanogel as amplifier

In general, the traditional impedimetric aptasensor for detecting protein is based on its high molecular weight and low dielectric constant. Yet, the efficiency of these aptasensors is hindered by the slight resistance change in the trace concentration range because of the high initial resistance (the electrostatic repulsion between the compact negatively charged DNA on the electrode and [Fe(CN)6]3-/4-). To effectively and simply circumvent this issue and improve the detection sensitivity, we design an impedimetric aptasensor by reducing the substrate DNA's density on the electrode through the target-inspired recycling DNA cleavage. In order to enlarge the differences in resistance, the polyacrylic acid (PAA) nanogel is implemented as amplifier due to its poor conduction and negative charge that can hinder electron transfer and repulse the mediator [Fe(CN)6]3-/4-, respectively. Based on the target-inspired DNAzyme and PAA nanogel as amplifier, the ultrasensitive impedimetric aptasensor of carcinoembryonic antigen (CEA) in the buffer solution possesses a wide dynamic range of 10 fg mL−1 to 10 ng mL−1 and ultra-low detection limit of 7.9 fg mL−1 (10-fold relative to equivalent aptasensors). When tested in human serum, the proposed aptasensor exhibits good performance with an ultra-low detection limit of 1.4 fg mL−1, which is slightly higher than that in buffer solution.

Impedimetric aptasensor for kanamycin by using carbon nanotubes modified with MoSe2 nanoflowers and gold nanoparticles as signal amplifiers.

An aptamer based impedimetric method is described for the determination of kanamycin. A hydrothermal route was applied to synthesize molybdenum selenide nanoflowers (MoSe2) which are promising materials for use in sensing interfaces due to their high specific surface and excellent electrical conductivity. Carbon nanotubes were then decorated with the MoSe2 nanoflowers and gold nanoparticles (AuNP/CNT/MoSe2) and placed on a glassy carbon electrode to serve as a signal amplifier. An amino-terminal kanamycin-specific aptamer was covalently linked to carboxy groups of acid-oxidized CNTs on the electrode to act as the signalling probe. The various steps during the construction of the modified electrode were monitored by scanning electron microscopy, wavelength-dispersive and energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The change in electrochemical signal was quantified by electrochemical impedance spectroscopy, typically at a working voltage of 0.22V vs. Ag/AgCl. The calibration plot is linear in the 1 pM-0.1nM and 100nM-10μM kanamycin concentration range and has a 0.28 pM detection limit. The assay is outstandingly selective, sensitive, stable and reproducible. Graphical abstract ᅟ.

An impedimetric aptasensor for Shigella dysenteriae using a gold nanoparticle-modified glassy carbon electrode.

This work describes an aptasensor for the foodborne pathogen Shigella dysenteriae (S. dysenteriae). A glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs) by electrodeposition. Then, thiolated aptamer for S. dysenteriae detection was self-assembled on the surface of the modified GCE, and any free residual AuNPs were blocked with 6-mercapto-1-hexanol. The size, morphology, and distribution of the AuNPs were characterized by field emission scanning electron microscopy. Detection of S. dysenteriae was performed measurement of the charge transfer resistance (Rct) before and after addition of S. dysenteriae using hexacyanoferrate as an electrochemical probe. The interaction between the aptamer and outer-membrane proteins of S. dysenteriae lead to an increase in the Rct of the sensor. The assay has a linear dynamic range that extends from 101 to 106CFU.mL-1 and a limit of detection of 100CFU.mL-1. It can differentiate between alive S. dysenteriae and other pathogens. Dead S. dysenteriae cells do not have any effect on selectivity. Unpasteurized and pasteurized skim milk and some water samples were spiked with S. dysenteriae and then successfully examined by this method. The results were validated by real-time PCR. The method is fast, low-cost, highly sensitive, and specific. Hence, it represents a valuable tool in food quality control. Graphical abstract Schematic presentation of a label free impedimetric aptasensor for Shigella dysenteriae using a glassy carbon electrode modified with gold nanoparticles (AuNPs) and 6-mercapto-1-hexanol (MCH). The limit of detection of this aptasensor is as low as 1CFU.mL-1 for target bacteria.

Reduced graphene-oxide transducers for biosensing applications beyond the Debye-screening limit

In the field of label-free biosensing, various transducer materials and strategies are under investigation to overcome the Debye-screening limitation of charged biomolecules. We demonstrate an in-line, impedimetric aptasensor with reduced graphene-oxide (rGO) thin films as transducers to detect prostate specific antigens (PSA) in a physiological buffer solution. Unlike classical electrochemical impedance spectroscopy (EIS), this direct, label-free and fully-electronic biosensor approach does not need any redox markers. As specific capture molecules, short anti-PSA aptamers ensured a close binding of the target molecules to the transducer surfaces. Results showed a limit of detection smaller than 33 pM of PSA and a wide detection range from 0.033 to 330 nM fully covering the clinically relevant range of PSA (0.115–0.290 nM). This promising performance can be attributed to the bipolar electronic transport characteristics of the ultra-thin rGO layers similar to pristine graphene. The attachment of target biomolecules to the films changes the resistance of the rGO thin films. Such an in-line EIS configuration with rGO thin films opens promising prospects for biosensing beyond the Debye-screening limitation, which is a major challenge for conventional semiconductor field-effect devices towards clinical applications.

(Invited) Biomolecule Immobilization By Electrogenerated Polymers for Biosensing Applications

For four decades, the development of biointerfaces has been the subject of increasing research efforts in the field of biosensors and energy conversion. In particular, the functionalization of electrodes by biomaterials based on electrogenerated polymers and / or carbon nanotubes or graphene is widely used for the design of biosensors and biofuel cells. These nano-objects were successfully functionalized by electropolymerization of pyrrolic monomers or pyrene derivatives exhibiting affinity or covalent binding interactions towards biomolecules. Various biomolecule immobilization strategies have been explored involving photografting process, affinity and host-guest interactions. Some new approaches for developing nanostructured biomaterials based on supramolecular assemblies will be illustrated. In particular, an original versatile methodology for molecular grafting on different surfaces via a new photoactivatable diazirine derivative is reported. This pyrene-diazirine, which was electropolymerized onto various electrodes, enabled, under UV irradiation, the photografting of redox mediators and enzymes.1 Recent examples of electropolymerized films will be presented for the design of labeless immunosensors for dengue or cholera toxin antibody. 2,3 In particular, an original impedimetric immunosensor for the detection of cholera antibody was developed based on carbon nanotube deposits with different controlled thicknesses. These nanotube deposits were functionalized via electrocoating of polypyrrole-nitrilotriacetic acid (poly-NTA) followed by the formation of a Cu (II) complex with the NTA functions. The bioreceptor unit, cholera toxin B subunit, modified with biotin, was then immobilized via coordination of the biotin groups with the NTA-Cu(II) complex. The resulting impedimetric cholera Ab sensor shows a very satisfying detection limit of 10−13 g mL−1 and an exceptional linear range detection of 8 orders of magnitude. Following a similar elaboration strategy, an electrochemical highly sensitive aptasensor was developed based on electropolymerized poly-NTA film and a new aptamer functionalized by a pentahistidine peptide for the quantification of bisphenol A. A surface coverage of antibisphenol A aptamer of 1.84 10−10 molcm−2 was estimated from the electrochemical signal of the [RuIII (NH3 )6 ]3+ complex bound by electrostatic interactions onto the aptamer-modified electrode. The binding of bisphenol A onto the polymer film was successfully characterized by electrochemical methods as square wave voltammetry and electrochemical impedance spectroscopy measurements. The designed label-free impedimetric aptasensor displayed a wide linear range from 10−11 to 10−6 mol L−1 with a sensitivity of 372 Ω per unit of log of concentration and an excellent specificity toward interfering agents such as 4,4′ -dihydroxybiphenyl and bisphenol P.4 Finally, a simple, versatile, and rapid method for the fabrication of optically-transparent large-area carbon nanotube films via flotation assembly, will be described. After solvent-induced assembly, floating films were transferred to a flat supporting substrate to form conductive and transparent nanotube film electrodes. A proof-of-concept nanostructured bioelectrode demonstrating high sensitivity for glucose was developed with an electropolymerized poly(pyrene-adamantane) layer for host–guest immobilization of active b-cyclodextrin tagged GOx enzymes.5

Label-free detection of cytochrome C by a conducting polymer-based impedimetric screen-printed aptasensor

In this study we have introduced a new sensitive and selective biosensor for the determination of cytochrome C (Cyt C) as a biomarker for cell apoptosis.