Liposome immunoblotting assay using a substrate-forming precipitate inside immunoliposomes

Efficient and robust isolation of rabbit scFv antibodies using antigen-coupled multilamellar vesicles

We demonstrated an efficient screening method for rabbit scFv antibodies using antigen-coupled multi-lamellar vesicles (Ag-MLVs) as solid supports. Model phages displaying mouse anti-human IgG scFv at a probability of 10^-4-10^-5% were successfully isolated by Ag-MLVs after 3 or less rounds of biopanning, whereas they could not be isolated using conventional antigen-coated immunotubes. This screening method was applied to isolate rabbit antigen-specific scFvs from 4 different phage libraries. Biopanning procedures employing Ag-MLVs yielded positive phages in the 3rd round or earlier, and specific antigen-binding of scFvs was observed after the 1st round in two biopanning selections. The dissociation rate constants (k_off) of isolated scFv clones tended to decrease with progressing biopanning rounds. The average dissociation constants (K_D) of the isolated scFvs ranged between 1.7 and 87 nM, whereas the lowest K_D of 12 pM was recorded for anti-CRP scFv. Comprehensive characterization of 355 different clones of the isolated rabbit scFvs presented a relatively low isoelectric point, and most of these were more thermo-stable than the conventional mouse scFvs, based on their instability and aliphatic indices. These results clearly indicate the advantages and potential of a combination of rabbit scFv-displaying phage library and biopanning using Ag-MLVs for antibody discovery. In addition, the results obtained in this study support the suitability of rabbit scFvs for several applications, including the development of diagnostic agents and affinity ligands for molecular diagnosis and bioseparation.

Liposome-Based Bioassays

This review highlights the potential of using liposomes in bioassays. Liposomes consist of nano- or micro-sized, synthetically constructed phospholipid vesicles. Liposomes can be loaded with a number of reporting molecules that allow a dramatic amplification of the detection threshold in bioassays. Liposome-based sensors bind or react with the biological components of targets through the introduction of properly tailored vectors anchored on their external surface. The use of liposome-based formulations allows the set-up of bioassays that are rapid, sensitive, and often suitable for in-field applications. Selected applications in the field of immunoassays, as well as recognition/assessment of corona proteins, nucleic acids, exosomes, bacteria, and viruses are surveyed. The role of magnetoliposomes is also highlighted as an additional tool in the armory of liposome-based systems for bioassays.

Nanostructured porous Si optical biosensors: effect of thermal oxidation on their performance and properties

The influence of thermal oxidation conditions on the performance of porous Si optical biosensors used for label-free and real-time monitoring of enzymatic activity is studied. We compare three oxidation temperatures (400, 600, and 800 °C) and their effect on the enzyme immobilization efficiency and the intrinsic stability of the resulting oxidized porous Si (PSiO2), Fabry-Pérot thin films. Importantly, we show that the thermal oxidation profoundly affects the biosensing performance in terms of greater optical sensitivity, by monitoring the catalytic activity of horseradish peroxidase and trypsin-immobilized PSiO2. Despite the significant decrease in porous volume and specific surface area (confirmed by nitrogen gas adsorption-desorption studies) with elevating the oxidation temperature, higher content and surface coverage of the immobilized enzymes is attained. This in turn leads to greater optical stability and sensitivity of PSiO2 nanostructures. Specifically, films produced at 800 °C exhibit stable optical readout in aqueous buffers combined with superior biosensing performance. Thus, by proper control of the oxide layer formation, we can eliminate the aging effect, thus achieving efficient immobilization of different biomolecules, optical signal stability, and sensitivity.

Preparation of monodisperse and size-controlled poly(ethylene glycol) hydrogel nanoparticles using liposome templates

Liposomes were used as templates to prepare size-controlled and monodisperse poly(ethylene glycol) (PEG) hydrogel nanoparticles. The procedure for the preparation of PEG nanoparticles using liposomes consists of encapsulation of photopolymerizable PEG hydrogel solution into the cavity of the liposomes, extrusion through a membrane with a specific pore size, and photopolymerization of the contents inside the liposomes by UV irradiation. The size distributions of the prepared particles were 1.32+/-0.16 microm (12%), 450+/-62 nm (14%), and 94+/-12 nm (13%) after extrusion through membrane filters with pore sizes of 1 microm, 400 nm, and 100 nm, respectively. With this approach, it is also possible to modify the surface of the hydrogel nanoparticles with various functional groups in a one-step procedure. To functionalize the surface of a PEG nanoparticle, methoxy poly(ethylene glycol)-aldehyde was added as copolymer to the hydrogel-forming components and aldehyde-functionalized PEG nanoparticles could be obtained easily by UV-induced photopolymerization, following conjugation with poly-L-lysine-FITC through amine-aldehyde coupling. The prepared PEG particles showed strong fluorescence from FITC on the edge of the particles using confocal microscopy. The immobilization of biomaterials such as enzymes in hydrogel particles could be performed with loading beta-galactosidases during the hydration step for liposome preparation without additional procedures. The resorufin produced by applying resorufin beta-D-galactopyranoside as the substrate showed the fluorescence under the confocal microscopy.

Characteristics of a liposome immunoassay on a poly(methyl methacrylate) surface

Liposome immunoassay (LIA) is based on enzyme immunoassay (EIA) but the detection sensitivity could be significantly enhanced by using antibody-coupled immunoliposomes encapsulating HRP (horse radish peroxidase). Here, we applied LIA to non-porous poly(methyl methacrylate) (PMMA) and polystyrene (PS) surfaces to compare its detection sensitivity with that of EIA, using rabbit IgG (a ligand molecule) and anti-rabbit IgG antibody (a capture molecule) as the model system. LIA developed much stronger color signals than EIA, especially at a lower concentration range (< ca. 1 microg mL(-1)). PMMA showed higher affinity toward rabbit IgG than the PS surface, and the anti-rabbit IgG antibody adsorbed on PMMA was more stable than that on PS. Furthermore, the effects of spot volume and antibody concentration on the signal density were analyzed. The signal density increased as the antibody concentration increased, but it was not significantly affected by the spot volume (2.5-20 microL). In conclusion, LIA on PMMA as a solid support is a very useful, highly sensitive microarray detection system.

Amperometric immunosensor for direct detection based upon functional lipid vesicles immobilized on nanowell array electrode

An original electrochemical immunosensor has now been developed that is based upon the spontaneous immobilization of biotinylated, functional lipid vesicles (FLVs) on a polymeric resist layer. An electrode was fabricated utilizing a form of electron-beam (e-beam) that has been used to fabricate 200 nm (nanoscale) wells in the resist layer covering of the gold electrode. The stability of adhered FLVs upon the nanowell (NW) electrode was observed by atomic force microscopy (AFM). From these observations, we were able to determine that the assembled FLVs primarily adhered as individual molecules, that is, without the aggregation or fusion noted in earlier designs. Additionally, these immobilized FLVs demonstrated clearly defined redox activity in electrochemical measurements. Streptavidin, biotinylated capture antibody, and target proteins were consequently injected in order to set up the immunoassay environment. Electrochemical immunoassay experimentation was performed on the NW array electrode with model proteins, such as human serum albumin (HSA) and carbonic anhydrase from bovine (CAB). We observed a notable current decrease, following the redox path, interrupted by the target HSA, indicating the binding of the capture antibody with the target antigen. On the basis of these results, we propose a new type of immunosensor incorporating this mechanism of spontaneous immobilization of FLVs.

Characteristics of microblotting assay using immunoliposomes

To clarify the applicability of a liposome immunoblotting assay to microassay systems, the effects of the sample volume blotted on polyvinylidiene fluoride (PVDF) membrane on the sensitivity and signal intensity were studied and compared with those in a conventional immunoblotting assay utilizing enzyme-labeled antibody. In the liposome immunoblotting assay, signal intensities per unit area (signal density) were almost the same or increased slightly with decreasing blotted sample volume (from 20 to 2 microl) at the same concentration of analyte (human IgM) adsorbed on PVDF membrane. A substrate, 4-chloro-1-naphtol, for color development formed colored precipitates inside the liposomes. Thus, the colored signal was detected without loss of intensity. On the other hand, in the conventional immunoblotting assay, signal densities decreased with decreasing sample volume at the same concentration of analyte. This is caused by partial losses of the colored signal into the substrate solution by diffusion, because the fraction of loss increases with decreasing sample volume. These results show that the liposome immunoblotting assay is a promising method for the detection of analytes blotted in small areas, because its sensitivity is higher than that of the conventional blotting assay.

Development of Liposome Immune Lysis Assay for the Herbicide Atrazine

A homogeneous complement-mediated liposome immune lysis assay (LILA) was developed for determination of the herbicide atrazine. To dispose the antigen on the surface of lipid bilayer the atrazine was conjugated to a dimirystoylphosphatidylethanolamine (DMPE) carrier. Calcein was compared with sulforhodamine 101 as a fluorophore label for entrapping into the antigen-sensitized liposomes. The liposomes were incubated with rabbit anti-atrazine antibodies in the presence of guinea pig complement. Formation of the antigen-antibody complexes on the liposomal surface initiated the lytic action of the complement. As free competing atrazine inhibited the lytic reaction, the amount of calcein released was inversely proportional to the atrazine content in the probe. Concentration and kinetic dependences of the immunoassay were characterized to reach its maximal sensitivity. The developed assay allows detecting atrazine in concentrations up to 0.13 ng mL(-1) in the sample (0.04 ng mL(-1) in the final reaction mixture). The named sensitivity is two orders higher than those for the microplate enzyme-linked immunosorbent assay (ELISA) with the same antibodies which allows us to recommend LILA for environmental monitoring.

Horseradish peroxidase: a valuable tool in biotechnology

Peroxidases have conquered a prominent position in biotechnology and associated research areas (enzymology, biochemistry, medicine, genetics, physiology, histo- and cytochemistry). They are one of the most extensively studied groups of enzymes and the literature is rich in research papers dating back from the 19th century. Nevertheless, peroxidases continue to be widely studied, with more than 2000 articles already published in 2002 (according to the Institute for Scientific Information). The importance of peroxidases is emphasised by their wide distribution among living organisms and by their multiple physiological roles. They have been divided into three superfamilies according to their source and mode of action: plant peroxidases, animal peroxidases and catalases. Among all peroxidases, horseradish peroxidase (HRP) has received a special attention and will be the focus of this review. A brief description of the three super-families is included in the first section of this review. In the second section, a comprehensive description of the present state of knowledge of the structure and catalytic action of HRP is presented. The physiological role of peroxidases in higher plants is described in the third section. And finally, the fourth section addresses the applications of peroxidases, especially HRP, in the environmental and health care sectors, and in the pharmaceutical, chemical and biotechnological industries.