New antibody immobilization method via functional liposome layer for specific protein assays

Research advances and applications of biosensing technology for the diagnosis of pathogens in sustainable agriculture

Plant diseases significantly impact the global economy, and plant pathogenic microorganisms such as nematodes, viruses, bacteria, fungi, and viroids may be the etiology for most infectious diseases. In agriculture, the development of disease-free plants is an important strategy for the determination of the survival and productivity of plants in the field. This article reviews biosensor methods of disease detection that have been used effectively in other fields, and these methods could possibly transform the production methods of the agricultural industry. The precise identification of plant pathogens assists in the assessment of effective management steps for minimization of production loss. The new plant pathogen detection methods include evaluation of signs of disease, detection of cultured organisms, or direct examination of contaminated tissues through molecular and serological techniques. Laboratory-based approaches are costly and time-consuming and require specialized skills. The conclusions of this review also indicate that there is an urgent need for the establishment of a reliable, fast, accurate, responsive, and cost-effective testing method for the detection of field plants at early stages of growth. We also summarized new emerging biosensor technologies, including isothermal amplification, detection of nanomaterials, paper-based techniques, robotics, and lab-on-a-chip analytical devices. However, these constitute novelty in the research and development of approaches for the early diagnosis of pathogens in sustainable agriculture.

Biosensors for plant pathogen detection

Infectious plant diseases are caused by pathogenic microorganisms such as fungi, bacteria, viruses, viroids, phytoplasma and nematodes. Worldwide, plant pathogen infections are among main factors limiting crop productivity and increasing economic losses. Plant pathogen detection is important as first step to manage a plant disease in greenhouses, field conditions and at the country boarders. Current immunological techniques used to detect pathogens in plant include enzyme-linked immunosorbent assays (ELISA) and direct tissue blot immunoassays (DTBIA). DNA-based techniques such as polymerase chain reaction (PCR), real time PCR (RT-PCR) and dot blot hybridization have also been proposed for pathogen identification and detection. However these methodologies are time-consuming and require complex instruments, being not suitable for in-situ analysis. Consequently, there is strong interest for developing new biosensing systems for early detection of plant diseases with high sensitivity and specificity at the point-of-care. In this context, we revise here the recent advancement in the development of advantageous biosensing systems for plant pathogen detection based on both antibody and DNA receptors. The use of different nanomaterials such as nanochannels and metallic nanoparticles for the development of innovative and sensitive biosensing systems for the detection of pathogens (i.e. bacteria and viruses) at the point-of-care is also shown. Plastic and paper-based platforms have been used for this purpose, offering cheap and easy-to-use really integrated sensing systems for rapid on-site detection. Beside devices developed at research and development level a brief revision of commercially available kits is also included in this review.

High-sensitivity detection of oxytetracycline using light scattering agglutination assay with aptasensor

We present an aptamer-based biosensor (aptasensor) for rapid and high-sensitive detection of oxytetracycline (OTC) antibiotic in PBS inside a Y-channel PDMS microfluidic device. The detection was made by real-time monitoring of the agglutination assay of ssDNA aptamer-conjugated polystyrene latex microspheres with proximity optical fibers. The agglutination assay was performed with serially diluted OTC antibiotic solutions using highly carboxylated polystyrene particles of 920 nm diameter conjugated with OTC-binding ssDNA aptamer. Proximity optical fibers were used to measure the increase in 45° forward light scattering of the aggregated particles by fixing them around the viewing cell of the device with stable angle and distance to the detector. The detection limit was around 100 ppb for the current aptasensor system with the detection time less than 3 min.

Liposome characterization by quartz crystal microbalance measurements and atomic force microscopy

This chapter reviews liposome characterization by quartz crystal microbalance (QCM) measurements and atomic force microscopy (AFM). In many studies, AFM imaging is simply used to image liposomes with resolution often that does not allow morphological analysis. Although liposome size can be obtained by processing AFM images, it is found that liposomes flatten upon surface adsorption or immobilization. Liposome stability and stiffness have been characterized by using AFM imaging or AFM force measurements, although the latter method, using a microsphere attached on the AFM cantilever, seems more appropriate to limit liposome damage and to obtain more quantitative analysis, such as the Young's modulus. Investigation of liposome layers by QCM revealed that liposomes can be detected from a combined analysis of frequency and bandwidth shifts. However, QCM by itself provides only limited information on liposomes. QCM can be used to assess the presence of a layer and also to discriminate between rigid and viscoelastic ones. Liposome properties have been derived from QCM curves, but often this requires making hypotheses that are difficult to assess. AFM and QCM analyses need to be combined with other techniques to provide complementary information.

Characterization for binding complex formation with site-directly immobilized antibodies enhancing detection capability of cardiac troponin I

The enhanced analytical performances of immunoassays that employed site-directly immobilized antibodies as the capture binders have been functionally characterized in terms of antigen-antibody complex formation on solid surfaces. Three antibody species specific to cardiac troponin I, immunoglobulin G (IgG), Fab, and F(ab')(2) were site-directly biotinylated within the hinge region and then immobilized via a streptavidin-biotin linkage. The new binders were more efficient capture antibodies in the immunoassays compared to randomly bound IgG, particularly, in the low antibody density range. The observed improvements could have resulted from controlled molecular orientation and also from flexibility, offering conditions suitable for binding complex formations.

Quantitation of surface coverage of oligonucleotides bound to chip surfaces: a fluorescence-based approach using alkaline phosphatase digestion

Silanized chip surfaces provide a reliable substrate for immobilization of oligonucleotides. The ability for rapid and sensitive detection of oligonucleotide surface coverage on these chips is crucial for their wide and effective applications in biotechnology. In this paper, two different silanization procedures were used to covalently bind fluorescent-labeled single-stranded DNA onto silicon dioxide or nitride chip surfaces. Effects of surface functionalization techniques for different surfaces, and immobilization conditions, including buffers and solution ionic strength, on surface probe coverage were investigated, quantifying the endpoint probe density by fluorescent measurement upon digestion with alkaline phosphatase (ALP). Digestion of surface-immobilized oligonuleotides with ALP released the fluorophore-tagged probe fragments back into the solution. The detection of DNA was accomplished by laser-induced fluorescence detection of the solution containing those cleaved fragments. The probe surface density on gold thin film, determined by ALP-digestion, was found to coincide well with that measured using the conventional alkanethiol-based fluorescence-displacement technique for the same system. The developed method has important implications for evaluating the performance of different oligonucleotide immobilization strategies. Also, it has the potential to serve as a sample-thrifty, time saving, and therefore routine tool to realize more realistic, practical quantification of the surface coverage of oligonucleotides immobilized on any solid surfaces.

An ultrasensitive chemiluminescence biosensor for cholera toxin based on ganglioside-functionalized supported lipid membrane and liposome

A novel chemiluminescence biosensor based on a supported lipid layer incorporated with ganglioside GM1 was developed for the detection of cholera toxin. The planar supported lipid membrane was prepared as biosensing interface via spontaneous spread of ganglioside-incorporated phospholipid vesicles on the octadecanethiol-coated gold surface. The specific interaction of multivalent CT by ganglioside GM1 molecules enables the biosensor to be implemented via a sandwiched format using a liposome probe functionalized with GM1 and horseradish peroxidase (HRP). Then, the presence of the target CT could be determined via the HRP-catalyzed enhanced chemiluminescence reaction. The developed strategy offers several unique advantages over conventional biosensors in that it allows for an easy construction and renewal of the sensing interface, a small background signal due to low non-specific adsorption of serum constituents on the lipid membrane, and effective immobilization of multiple biocatalytic amplifiers and recognition components via common phospholipid reagents. The developed biosensor was shown to give chemiluminescence signal in linear correlation to CT concentration within the range from 1pgmL(-1) to 1ngmL(-1) with readily achievable detection limit of 0.8pgmL(-1).

Endothelial targeting of semi-permeable polymer nanocarriers for enzyme therapies

The medical utility of proteins, e.g. therapeutic enzymes, is greatly restricted by their labile nature and inadequate delivery. Most therapeutic enzymes do not accumulate in their targets and are inactivated by proteases. Targeting of enzymes encapsulated into substrate-permeable polymer nano-carriers (PNC) impermeable for proteases might overcome these limitations. To test this hypothesis, we designed endothelial targeted PNC loaded with catalase, an H(2)O(2)-detoxifying enzyme, and tested if this approach protects against vascular oxidative stress, a pathological process implicated in ischemia-reperfusion and other disease conditions. Encapsulation of catalase (MW 247 kD), peroxidase (MW 42 kD) and xanthine oxidase (XO, MW 300 kD) into approximately 300 nm diameter PNC composed of co-polymers of polyethylene glycol and poly-lactic/poly-glycolic acid (PEG-PLGA) was in the range approximately 10% for all enzymes. PNC/catalase and PNC/peroxidase were protected from external proteolysis and exerted enzymatic activity on their PNC diffusible substrates, H(2)O(2) and ortho-phenylendiamine, whereas activity of encapsulated XO was negligible due to polymer impermeability to the substrate. PNC targeted to platelet-endothelial cell (EC) adhesion molecule-1 delivered active encapsulated catalase to ECs and protected the endothelium against oxidative stress in cell culture and animal studies. Vascular targeting of PNC-loaded detoxifying enzymes may find wide medical applications including management of oxidative stress and other toxicities.

Fluorometric immunoassay based on pH-sensitive dye-encapsulating liposomes and gramicidin channels

This article describes a new method for direct fluorometric immunoassay with a liposome array using pH-sensitive dye (BCECF [2',7'-bis(carboxyethyl)-4 or 5-carboxyfluorescein])-encapsulating liposomes immobilized on an avidin slip and gramicidin channels. The liposomes were composed of phosphatidylcholine (PC), cholesterol (Chol), biotinylated phosphatidylethanolamine (B-cap-PE), and recognition sites (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(2,4-dinitrophenyl) [DNP-PE], Fab' fragment of anti-substance P, and Fab' of anti-neurokinin A). The addition of gramicidin induced release of H(+) ions from the inner solution (pH 5.5) to the outer one (pH 7.8), enhancing fluorescence of BCECF (1.0mM) encapsulated in liposome. The binding of an analyte (anti-dinitrophenyl [anti-DNP], avidin, substance P, or neurokinin A) to the membrane-bound recognition sites caused further enhancement of fluorescence of BCECF due to a local distortion of the bilayer structure that affects the channel kinetics of gramicidin. The intensity of fluorescence from the immobilized liposomes 60 min after the addition of gramicidin (10 ng/ml) increased with an increase in the concentration of anti-DNP ranging from 1.2 x 10(-8) to 1.2 x 10(-6)g/ml, avidin ranging from 1.0 x 10(-8) to 1.0 x 10(-6)g/ml, substance P ranging from 1.0 x 10(-8) to 1.0 x 10(-6)g/ml, and neurokinin A ranging from 1.0 x 10(-8) to 1.0 x 10(-6)g/ml. The direct fluorometric immunoassay with a liposome array is simple and easy to carry out. The intensity of fluorescence emitted from the immobilized liposomes is directly measured after incubation with a sample solution and a gramicidin solution in sequence without washing steps. The assay allows simultaneous quantification of multiple components without labeling of antibody or antigen with a fluorescent tag. The liposome-based assay is discussed in terms of principle, sensitivity, and selectivity.

Site-directed biotinylation of antibodies for controlled immobilization on solid surfaces

Site-directed biotinylation of antibodies at the hinge region was developed to immobilize antibodies in an oriented manner via biotin-streptavidin linkage. When intact antibody was biotinylated with maleimide-activated biotin after reduction, the reaction preferentially occurred at the sulfhydryl groups between the C(H1) and the C(L) domains and, provided that the reagent concentration exceeded a certain level, at those between the C(H2) and the C(H2) domains at the hinge. Based on this result, we devised an approach in which free maleimide was added to compete with the activated biotin for the preferential sites between the C(H1) and the C(L) domains. Since the smaller molecular size of free maleimide made it more accessible for the reaction than biotin, maleimide bound to the groups between the C(H1) and the C(L) domains first and thus conceded the groups between the C(H2) and the C(H2) domains to biotin under optimal conditions. In an alternative approach, selective biotinylation at the hinge was also achieved by reacting activated biotin with F(ab')(2) fragment prepared by enzymatic cleavage. This result indicated that, when free of Fc, the hinge structure, which contains the functional groups, of the fragment was open, allowing easy access to the biotin derivative from the aqueous medium. Both site-directed biotinylation preparations were tested as capture antibodies in sandwich-type immunoassays and compared to whole antibody randomly biotinylated at amino groups on the molecule. Preparations of both the intact antibody and the F(ab')(2) showed consistently enhanced detection capabilities that were 2.6 and 20 times that of the control, respectively.

Phospholipid-based artificial viruses assembled by multivalent cations

Self-assembled DNA delivery systems based on cationic lipids are simple to produce and weakly hazardous in comparison with viral vectors, but possess a significant toxicity at high doses. Phospholipids are in contrast intrinsically safe; yet their association with DNA is problematic because of unfavorable electrostatic interactions. We achieve the phospholipid-DNA complexation through the like-charge attraction induced by cations. Monovalent cations are inappropriate due to their poor binding affinity with lipids as inferred from electrophoretic mobility, whereas x-ray diffractions reveal that with multivalent cations, DNA is complexed within an inverted hexagonal liquid-crystalline phase. Coarse-grained Monte Carlo simulations confirm the self-assembly of a DNA rod wrapped into a lipid layer with cations in between acting as molecular glue. Transfection experiments performed with Ca2+ and La3+ demonstrate efficiencies surpassing those obtained with optimized cationic DOTAP-based systems, while preserving the viability of cells. Inspired by bacteriophages that resort to polycations to compact their genetic materials, complexes assembled with tetravalent spermine achieve unprecedented transfection efficiencies for phospholipids. Influence of complex growth time, lipid/DNA mass ratio, and ion concentration are examined. These complexes may initiate new developments for nontoxic gene delivery and fundamental studies of biological self-assembly.

Using Capacitance Measurements as the Detection Method in Antigen-Containing Layer-by-Layer Films for Biosensing

The layer-by-layer technique is employed here to immobilize antigen-containing liposomes, so-called proteoliposomes, onto Au-interdigitated substrates, which are capable of molecular recognition of anti-pasteurellosis antibodies. Detection was carried out using a novel strategy entirely based upon capacitance measurements, and to enhance sensitivity, we combine the response of three different sensing units in a similar procedure used for taste sensors. With the three-electrode array immunoglobulin G (IgG) against pasteurellosis is detected at concentrations as low as nanograms per milliliter. Furthermore, because of the molecular recognition capability, a distinction can be made between specific and nonspecific IgG. The concepts behind the biosensors reported here may have a large impact for clinical tests, as the procedures to detect the antibody take only a few minutes and the biosensors are relatively low cost.

Immobilization of fibronectin onto a large area nanoimprinted polystyrene patterns

A well known fibrous protein, fibronectin was successfully immobilized onto well-fabricated nanopatterns of polystyrene (PS) substrates. The nanopatterns with finely-defined physical dimensions were obtained by nanoimprinting lithography (NIL) using anodized aluminum oxide (AAO) molds of which the pore sizes were controlled in nanometer scale; 45 nm, 250 nm and 410 nm for the widths and 110 nm and 500 nm for the pitches. Discrete changes of the surface images before and after the protein-adsorption on the patterns were demonstrated by scanning electron microscope (SEM), and the effect of the patterned features on the immobilization has been investigated and discussed.

Biochemical and immunochemical characterization of the antigen–antibody reaction on a non-toxic biomimetic interface immobilized red blood cells of crucian carp and gold nanoparticles

A special protein assay system based on a highly hydrophilic, non-toxic and conductive biominetic interface has been demonstrated. To fabricate such assay system, red blood cells of crucian carp (RBC) was initially grown on a glassy carbon electrode surface (GCE) deposited nano-sized gold particles (GPs), a second gold nanoparticle layer (NG) was then absorbed on the RBC surface, and finally mammary cancer 15-3 antibody (anti-CA15-3) was attached on the functional RBC surface. A competitive immunoassay format was employed to detect CA15-3 with horseradish peroxidase (HRP)-labeled CA15-3 as tracer and hydrogen peroxide as enzyme substrate. When the immunosensor was incubated into a mixture solution containing HRP-labeled CA15-3 and CA15-3 sample for 1h at 37 degrees C, the amperometric response decreased with the increment of CA15-3 sample concentration. AFM images of the modified layer revealed a uniform distribution of protein and nanogold. In situ QCM and electrochemical measurements demonstrated that the wanted antibody-antigen reactions should occur with high specificity and selectivity. The specific immunoassay system can be developed further to yield sophisticated structures for other proteins.