Capacitance immunosensors based on an array biotape

A new array immunosensing system with high-throughput has been developed, based on the principle of a biotape that could be used to make a biocassette recorder.     

Label-free capacitive immunosensors for ultra-trace detection based on the increase of immobilized antibodies on silver nanoparticles

Detection of ultra-trace amounts of antigens by label-free capacitive immunosensors was investigated using electrodes modified with silver nanoparticles (AgNPs) that allows for an increase in the amount of immobilized antibodies. The optimal amount of AgNPs that provided the highest immobilization yield was 48 pmol (in 2.0 mL). The performances of immunosensor electrodes for human serum albumin prepared with AgNPs, were compared to electrodes prepared with gold nanoparticles. The two systems provided the same linear range (1.0 × 10⁻¹⁸ to 1.0 × 10⁻¹⁰ M) and detection limit (1.0 × 10⁻¹⁸ M). The system with AgNPs was used to analyze albumin in urine samples and the results agreed well with the immunoturbidimetric assay (P > 0.05). Electrodes modified with AgNPs and appropriate antibodies were tested for their performances to detect analytes of different sizes. For a macromolecule (human serum albumin) the incorporation of AgNPs improved the detection limit from 100 to 1 aM. For small molecules, microcystin-LR and penicillin G, the detection limits were lowered from 100 and 10 fM to 10 and 0.7 fM, respectively. The high sensitivity and very low detection limits are potentially useful for the analysis of toxins or residues present in samples at ultra-trace levels and this method could easily be applied to other affinity pairs.     

The immunosensors for measurement of 2,4-dichlorophenoxyacetic acid based on electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) was evaluated for the direct determination of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Specific antibody against 2,4-D was immobilised onto different gold electrodes. Several methods of antibody immobilisation by covalent linkage to modified surface were studied. Self-assembled monolayers formed using thiocompounds as cystamine, 4-aminothiophenol (ATPh), 3,3'-dithiopropionic acid di-(N-succinimidyl ester) (DTSP) and 11-mercaptoundecanoic acid (MUA) were chosen for the sensing surface activation. Three different sensor types were tested: screen-printed disc and finger-like structures and interdigitated array (IDA) electrodes produced by lithography. The measurements were carried out in a stationary arrangement, and the reaction between hapten and the immobilised antibody was observed online. Changes of impedance parameters were evaluated, and the best immobilisation technique (using 4-aminothiophenol) was chosen for further measurements. Impedance changes due to immunocomplex formation were evaluated, and the possibility of direct monitoring of 2,4-D binding to the antibody was demonstrated at a fixed frequency. For the strip sensor, the calibration curves were constructed in concentration range from 45 nmol l(-1) to 0.45 mmol l(-1) of 2,4-D.     

Structure of the receptor layer in electrochemical immunosensors. Modern trends and prospects of development

Literature data on the modern state and prospects for the development of research in the area of receptor layer immobilization in electrochemical immunosensors were examined and systematized. The first section of the review is devoted to structural features and functions of biological immunoreceptors, viz., antibodies or their fragments. The main methods of antibody immobilization on the working electrode surface are considered in detail in the second section. The prospects for the development of electrochemical immunosensors are discussed in the third section of the review.     

Polymer based RIFS sensing: an approach to the indirect measurement of organic pollutants in water

Organic pollutants in water originating from industrial sources are a major problem. For their detection, the application of thin film polymer transducers is described. The reflectometric interference spectroscopy (RIFS) technique was used as a method of detection. Sampling is achieved by an FIA system which allows the determination of concentrations of hydrocarbons in water. The experimental set-up is outlined in detail. The sensitivities for toluene and different chlorinated hydrocarbons are given. The sensors used show a linear dependence on the analyte concentration over a wide concentration range. The limit of detection achieved with this system is discussed.     

Immobilization of Protein A on SAMs for the elaboration of immunosensors

Binary mixtures of 11-mercaptoundecanoic acid (MUA) and other thiols of various lengths and terminal functions were chemisorbed on gold-coated surfaces via S–Au bonds to form mixed self-assembled monolayers (SAMs). Several values of the mole fraction of MUA in the thiol mixtures were tested and the structure and composition of the resulted thin films were characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The results made it clear that co-adsorption of MUA with thiols of similar chain length led to well-ordered monolayers whereas the co-adsorption of MUA with shorter thiols yielded less crystalline-like thin films, but with more reactive carboxylic acid terminal groups. This criterion appeared decisive for efficient covalent binding of Staphylococcus aureus Protein A (PrA), a protein that displays high affinity for the constant fragment (Fc) of antibodies of the IgG type from various mammal species. The ability of immobilized Protein A to recognize and bind a model IgG appeared to be optimal for the mixed SAM of MUA and the short-chain, ω-hydroxythiol 6-mercaptohexanol in the proportion 1–3.     

Nanoparticle-based immunosensors and immunoassays for aflatoxins

Aflatoxins are naturally existing mycotoxins produced mainly by Aspergillus flavus and Aspergillus parasiticus, present in a wide range of food and feed products. Because of their extremely high toxicity and carcinogenicity, strict control of maximum residue levels of aflatoxins in foodstuff is set by many countries. In daily routine, different chromatographic methods are used almost exclusively. As supplement, in several companies enzyme immunoassay-based sample testing as primary screening is performed. Recently, nanomaterials such as noble metal nanoparticles, magnetic particles, carbon nanomaterials, quantum dots, and silica nanomaterials are increasingly utilized for aflatoxin determination to improve the sensitivity and simplify the detection. They are employed either as supports for the immobilization of biomolecules or as electroactive or optical labels for signal transduction and amplification. Several nanoparticle-based electrochemical, piezoelectric, optical, and immunodipstick assays for aflatoxins have been developed. In this review, we summarize these recent advances and illustrate novel concepts and promising applications in the field of food safety.     

Detection of pathogenic Staphylococcus aureus bacteria by gold based immunosensors

We describe the elaboration of ultra-sensitive immunosensors, to detect the bacterial pathogen Staphylococcus aureus. We utilized commercially available polyclonal anti-S. aureus antibody as receptor. Immunosensors were elaborated by building a self-assembled monolayer (SAM) of thiolamine onto planar gold-coated sensor chips. Then, Protein A was covalently linked to the thiolated SAM using glutaraldehyde as cross-linking agent. After a blocking step by Bovine Serum Albumin (BSA), the antibody was immobilized by affinity to Protein A. This step-by-step construction was monitored by Polarization Modulation Reflection Absorption Infrared Spectroscopy (PM-RAIRS) and Quartz Crystal Microbalance with Dissipation (QCM-D). In a first stage, the parameters of immunosensor elaboration were optimized using a model rabbit IgG. The accessibility of receptors and the homogeneity of their distribution were checked by PM-RAIRS, QCM-D, and by immuno-gold scanning electron microscopy. Then, the specific rabbit anti-S. aureus antibody was immobilized and the resulting sensing layer was applied to the detection of the pathogen target. Independent detection of bacteria immobilized on the sensors by fluorescent imaging allowed validation of the specificity of recognition toward the pathogen as well as a quantitative response of the sensor. Using PM-RAIRS as transducing technique allowed us to enhance sensitivity and reach a very competitive detection level (10⁵ CFU mL^?1).     

Microfluidic flow transducer based on the measurement of electrical admittance

A new flow transducer for measuring the flow rate of a conducting fluid in a microchannel is reported. In this paper, the measure of flow of such fluid under laminar flow conditions based on the change of electrical admittance is established with the aid of a pair of electrodes parallel to the line of flow in a glass-PDMS microfluidic device. This flow sensor is simple in design and can be integrated to most of the microfluidic platforms. The effect of flow rate of the electrolyte, the frequency of the applied ac voltage, the voltage applied across the detector electrodes, and the conductivity of the electrolyte are varied to optimize for high sensitivity. The optimized values are then used to demonstrate the measurements of very low flow rates (<1 nL s(-1)). This flow sensor can be extended towards the measurement of chemical and biochemical buffers and reagents.     

A portable solid-state electrochemical sensor based on N-doped graphite as a transducer layer for determination of a multiple sclerosis managing medication in biological fluids

Journal of Solid State Electrochemistry - Solid-state electrochemical sensors have shown tremendous promise for portable and reliable ion detection, thanks to implementing new functional materials...     

Development of piezoelectric immunosensors for measurement of albuminuria

The development of piezoelectric immunosensors for human serum albumin (HSA) is reported. The piezoelectric crystals were modified either with monoclonal antibody AL-01 (direct assay) or with HSA (competitive assay). Measurements were carried out in the flow-through mode. Affinity interaction between albumin and the antibody was characterised. With immobilised antibody and HSA in solution, the kinetic association rate constant k(a) was 18 100 l mol(-1) s(-1) and the dissociation constant k(d) was 0.00369 s(-1). For the opposite arrangement (immobilised HSA), a slower dissociation was observed, k(d) was 0.00085 s(-1). A competitive assay for HSA was developed with working range of 1-5 mug ml(-1) and a total time for one analysis equal to 17 min. Samples of urine were analysed after tenfold dilution. The developed system was successfully evaluated on real samples from diabetic patients and the obtained results correlated well with the standard reflectometric assay of proteins in urine.     

Potentiometric transducer based biomimetic sensors for priority envirotoxic markers--an overview

Most of the potentiometric sensing electrodes offer detection limits of the order of approximately 1 micromol L(-1) rarely stretching down to 0.1 micromol L(-1). Recent advances have made it possible to bring these levels down to 0.01-10 nmol L(-1) for some inorganic ions. Most of these electrodes (barring a few) have come up to expectations in terms of selectivity in spite of significant strides made in the design and synthesis of novel chemical receptors. Imprinted polymers or plastic antibodies which rely on lock and key mechanism can, in principle, selectively rebind and sense a particular analyte in a host of other analogous species of similar size, shape and geometry. Thus, the integration of imprinted polymers with potentiometric transducers has immense potentialities in the fabrication of commercial sensing devices. This review gives an overview of research efforts made so far in this direction, critically discusses the virtues and vices and presents the futuristic scenario on imprinted polymer based potentiometric sensors.     

Biocatalytic precipitation induced by an affinity reaction on dendrimer-activated surfaces for the electrochemical signaling from immunosensors

We have developed a strategy of signal generation for immunosensors that transduces biospecific affinity recognition reactions into electrochemical signals. The cyclic voltammetric method, tracking the precipitation of insoluble products onto the sensing surface and the subsequent decrement in the electrode area, was chosen for signal registration. Precipitation of insolubilities was induced by the catalytic reaction of enzymes, which were labeled to the biospecifically attached protein or antibody molecules. As a model system for affinity recognition, we have investigated the functionalization of biotin groups to the sensing monolayer and their biospecific interactions with anti-biotin antibody molecules. The immunosensing interface was developed onto the dendrimer-activated self-assembled monolayers (SAMs), as the base template for the functionalization of the antigen moiety and signal generation. The advantages of using dendrimer-activated SAMs in comparison to the plain modified thiolate SAMs for the sensing surface were shown in terms of sensing performances, and the analytical characteristics of the resulting immunosensor were examined. Additionally, the sensing system was applied for biotin/(strept)avidin couples, extending the applicability of the developed strategy.     

Stable photoalignment layer for nematic liquid crystals based on ladder-like polysilsesquioxanes

A new kind of aligning material for liquid crystal cells, ladder-like polysilsesquioxanes (LPS) grafted with cinnamoyl side groups, has been developed to improve the thermal stability of the photoalignment layer. The LC aligning ability of the LPS-based alignment layers, fabricated by linearly polarized UV-induced polymerization (LPP), was characterized by polarizing optical microscopy, conoscopic observations and electro-optic response measurements. In particular, a practical and severe annealing test was adopted to examine the thermal stability of the alignment layer; this showed that even when LC cells were annealed at 100 C (much higher than the clearing point of the LC) for several hours, good LC orientation could remain when the cell was cooled to a constant measurement temperature. The results confirmed that the photoalignment layers exhibited not only good LC aligning ability, but also excellent thermal stability, so heralding their potential application in LCDs.     

Towards the fabrication of label-free amperometric immunosensors using SWNTs

A label-free immunosensor based on the modulation of the electrochemistry of a surface bound redox species, to detect the presence of antibodies, is demonstrated. In this proof of concept study the model epitope was biotin and the model antibody was anti-biotin IgG. Glassy carbon (GC) electrode surfaces were first modified with 4-nitrophenyl groups by electrochemical reductive adsorption of the corresponding aryl diazonium salt. Subsequently, the nitro group was reductively converted into an amine, giving 4-aminophenyl groups. Oxidatively shortened single walled carbon nanotubes (SWNTs) were then covalently attached to the electrode via self-assembly; a procedure that has previously been shown to give SWNTs aligned normal to the surface. 1,1-Di(aminomethyl)ferrocene was attached to the carboxylic acid terminated SWNTs followed by attachment of biotin to the remaining free amine of the ferrocene derivative. Binding of anti-biotin IgG to the surface bound epitope resulted in attenuation of the ferrocene electrochemistry. This label-free immunosensor was successfully able to detect anti-biotin between 30 and 450 ng mL⁻¹.     

Photosensitive systems for microlithography based on organometallic photoinitiators

The photodecomposition of the Ar-laser sensitive photo-initiator bis(pentafluorophenyl)titanocene 1 was investigated. Two intermediate species were postulated: a pentafluorophenylcyclopentenyl radical 16 which acts as quencher and a ketene acetal radical of the structure CH₂-CH=C(OCH₃)OTiR_x 17 which could initiate the polymerization.     

Multilayered separator based on porous polyethylene layer,Al2O3 layer,and electro-spun PVdF nanofiber layer for lithium batteries

With an aim to enhance the thermal stability and electrolyte wetting of a polyethylene porous separator, an Al₂O₃ nano-powder layer and an electro-spun PVdF nanofiber layer were successively formed on both sides of the polyethylene separator. The Al₂O₃ layer provides excellent thermal stability as indicated by thermal shrinkage of only 7.8 % in area at 180 °C and absence of a meltdown up to 200 °C. The electrolyte uptake of the multilayer separator was increased with the thickness of the nanofiber layer. As a result, discharge capacity, rate capability, and cycle life of the lithium ion batteries employing the PVdF nanofiber layers were improved, overcompensating for a loss of performance caused by the Al₂O₃ layer. Therefore, the multilayer approach is highly effective in improving both the performance and safety of lithium ion batteries.