Ultrasound-enhanced scintillation proximity assay for rapid diagnostics

Scintillation proximity assay (SPA) is a type of radioimmunoassay (RIA). We apply ultrasound enhancement to the general SPA. All assay procedures, including the antibody coating and radiolabeled antigen binding are achieved by simply mixing then standing for 5 min in an ultrasound chamber. No additional incubation time is required. To further demonstrate the capability of the UE-SPA, a quantitative measurement of CD55 in various grades of colon tumors was assessed on human tissue slides. The results showed a significant correlation between CD55 expression and tumorigenesis. In conclusion, we confirmed that UE-SPA is a reliable, rapid and alternative to RIA.

Mathematical Modeling of Bioassays

The high affinity and specificity of biological receptors determine the demand for and the intensive development of analytical systems based on use of these receptors. Therefore, theoretical concepts of the mechanisms of these systems, quantitative parameters of their reactions, and relationships between their characteristics and ligand-receptor interactions have become extremely important. Many mathematical models describing different bioassay formats have been proposed. However, there is almost no information on the comparative characteristics of these models, their assumptions, and predictive insights. In this review we suggested a set of criteria to classify various bioassays and reviewed classical and contemporary publications on these bioassays with special emphasis on immunochemical analysis systems as the most common and in-demand techniques. The possibilities of analytical and numerical modeling are discussed, as well as estimations of the minimum concentrations that may be detected in bioassays and recommendations for the choice of assay conditions.

Adaptive Focused Acoustics (AFA) Improves the Performance of Microtiter Plate ELISAs

We investigated the use of Adaptive Focused Acoustics (AFA) technology to improve the performance of microtiter plate enzyme-linked immunosorbent assays (ELISAs). Experiments were performed with commercially available AFA instrumentation and off-the-shelf 96-well microtiter plate sandwich ELISAs. AFA was applied over a range of acoustic energies, temperatures, and durations to the antigen/antibody binding step of an ELISA for measuring HIV-1 p24 in tissue culture samples. AFA-mediated antigen/antibody binding was enhanced up to 2-fold over passive binding at comparable temperatures and was superior or comparable at low temperature (8-10 °C) to passive binding at 37 °C. Lower nonspecific binding (NSB), lower inter- and intra-assay coefficients of variation (CVs), higher Z' factors, and lower limits of detection (LODs) were measured in AFA-mediated assays compared with conventional passive binding. In a more limited study, AFA enhancement of antigen/antibody binding and lower NSB was measured in an ELISA for measuring IGFBP-3 in human plasma. We conclude from this study that application of AFA to antigen/antibody binding steps in microtiter plate ELISAs can enhance key assay performance parameters, particularly Z' factors and LODs. These features render AFA-mediated binding assays potentially more useful in applications such as high-throughput screening and in vitro diagnostics than assays processed with conventional passive antigen/antibody binding steps.

Profiling RNA polymerase II using the fast chromatin immunoprecipitation method

The traditional method for determining the transcription rate of a gene, nuclear run-on, is time consuming, laborious, and involves the use of high levels of radio-labeled nucleotides. When combined with measurements of mRNA levels, RNA polymerase II (Pol II) chromatin immunoprecipitation (ChIP) is a simpler alternative to determine the transcription rate of genes. Moreover, this approach provides more information about the transcriptional regulation of a gene than nuclear run-on. The power of the ChIP assay is that it gives a researcher the ability to not only detect a specific protein-DNA interaction in vivo, for instance with Pol II, but also to determine the relative density of factors along genes or the entire genome. Though powerful, the conventional ChIP assay is time consuming (involving 2 days or more) and involves labor intensive steps. With Fast ChIP we simplified the assay to greatly reduce the time and labor involved. The improved assay is especially useful for studies which involve many samples, including the probing of multiple transcriptionally related factors simultaneously and/or looking at transcription events over several time points. Using Fast ChIP, 24 sheared chromatin samples can be processed to yield PCR ready DNA in 5 h.

The fast chromatin immunoprecipitation method

The chromatin immunoprecipitation assay (ChIP assay) has greatly facilitated the recent, dramatic expansion of our knowledge of the protein-DNA interactions involved in regulating gene expression, DNA repair, and cell division. The power of the assay is that it gives a researcher the ability to not only detect a specific protein-DNA interaction in vivo but also determine the relative density of factors along genes or the entire genome. Though powerful, the traditional assay is time consuming (involving 2 days or more) and laborious. With Fast ChIP, we simplified the assay to greatly reduce the time and labor involved. The improved assay is especially useful for studies which involve many samples, including the probing of multiple chromatin factors simultaneously and/or looking at genomic events over several time points. Using Fast ChIP, 24 sheared chromatin samples can be processed to yield PCR-ready DNA in 5 h.

Microplate-based chromatin immunoprecipitation method, Matrix ChIP: a platform to study signaling of complex genomic events

The chromatin immunoprecipitation (ChIP) assay is a major tool in the study of genomic processes in vivo. This and other methods are revealing that control of gene expression, cell division and DNA repair involves multiple proteins and great number of their modifications. ChIP assay is traditionally done in test tubes limiting the ability to study signaling of the complex genomic events. To increase the throughput and to simplify the assay we have developed a microplate-based ChIP (Matrix ChIP) method, where all steps from immunoprecipitation to DNA purification are done in microplate wells without sample transfers. This platform has several important advantages over the tube-based assay including very simple sample handling, high throughput, improved sensitivity and reproducibility, and potential for automation. 96 ChIP measurements including PCR can be done by one researcher in one day. We illustrate the power of Matrix ChIP by parallel profiling 80 different chromatin and transcription time-course events along an inducible gene including transient recruitment of kinases.

Protocol for the fast chromatin immunoprecipitation (ChIP) method

Chromatin and transcriptional processes are among the most intensively studied fields of biology today. The introduction of chromatin immunoprecipitations (ChIP) represents a major advancement in this area. This powerful method allows researchers to probe specific protein-DNA interactions in vivo and to estimate the density of proteins at specific sites genome-wide. We have introduced several improvements to the traditional ChIP assay, which simplify the procedure, greatly reducing the time and labor required to complete the assay. The simplicity of the method yields highly reproducible results. Our improvements facilitate the probing of multiple proteins in a single experiment, which allows for the simultaneous monitoring of many genomic events. This method is particularly useful in kinetic studies where multiple samples are processed at the same time. Starting with sheared chromatin, PCR-ready DNA can be isolated from 16-24 ChIP samples in 4-6 h using the fast method.

Ultrasound-accelerated formalin fixation of tissue improves morphology, antigen and mRNA preservation

Formalin fixation and paraffin embedding are conventional tissue preservation and processing methods used for histologic diagnosis in over 90% of cases. However, formalin fixation has three disadvantages: (1) slow fixation (16-24 h) hinders intraoperative decision making, (2) slow quenching of enzymatic activity causes RNA degradation, and (3) extensive molecule modification affects protein antigenicity. Applying high-frequency, high-intensity ultrasound to the formalin fixative cuts fixation time to 5-15 min. Fixation of various tissues such as lymph node, brain, breast, and prostate suggests that, compared to the conventional method, implementation of ultrasound retains superior and more uniform tissue morphology preservation. Less protein antigenicity is altered so that rapid immunohistochemical reactions occur with higher sensitivity and intensity, reducing the need for antigen retrieval pretreatment. Better RNA preservation results in stronger signals in in situ hybridization and longer RNA fragments extracted from fixed tissues, probably due to rapid inhibition of endogenous RNase activity. Molecules extracted from ultrasound-fixed tissues are of greater integrity and quantity compared to conventionally fixed tissues, and thus better support downstream molecular analyses. Overall, ultrasound-facilitated tissue preservation can provide rapid and improved morphological and molecular preservation to better accommodate both traditional and molecular diagnoses.

An amperometric enzyme-channeling immunosensor

This paper presents a new disposable amperometric, enzyme-channeling immunosensor for a quantitative, rapid, separation-free enzyme immunoassay (EIA) that can be used in clinical diagnostics, as well as in biomedical, biochemical, and environmental research. The sensor consists of a disposable, polymer-modified, carbon electrode on which enzyme 1 is coimmobilized with a specific antibody that binds the corresponding antigen in a test solution. The solution also contains a conjugate of enzyme 2. An immunological reaction brings the two enzymes into close proximity at the electrode surface, and the signal is amplified through enzyme channeling. The localization of both enzymes on the electrode surface limits the enzymatic reactions to the polymer/membrane/electrode interface. The sensor overcomes the problem of discriminating between the signal that is produced by the immuno-bound enzyme label on the electrode surface and the background level of signal that emerges from the bulk solution. Combining enzyme-channeling reactions, optimizing hydrodynamic conditions, and electrochemically regenerating mediators within the membrane layer of the antibody electrode significantly increased the signal-to-noise ratio of the sensor. The amperometric enzyme-channeling immunosensor enabled the performance of separation-free EIAs without washing steps, resulting in a relatively short assay time of 5-30 min for the complete immunoassay, compared with at least 1-3 h for ELISA methods. Model systems using peroxidase-antibody, biotin-avidin, viral antigens (CD4-gp120), and bacteria (Staphylococcus aureus) were investigated. S. aureus cells were detected in pure culture at concentrations as low as 1000 cells/ml.

A one-step, separation-free amperometric enzyme immunosensor

A new one-step, separation-free, amperometric enzyme immunosensor is described. The sensor consists of an antibody electrode that is low cost, disposable, and operates without washing or separation steps. The immunosensor combines the following signal-amplification systems: enzyme-channeling immunoassay; accumulation of the redox mediators (I2/I-); cyclic regeneration of an enzyme (peroxidase) substrate at the (polyethylenimine) polymer/electrode interface; and control of the hydrodynamic conditions at the interface of the antibody electrode. The immunological reactions were monitored electrochemically in situ, and the binding curves were directly visualized on a computer screen. The complete immunoassay can be performed in 5-20 min depending on the complexity of the immunological reactions. Model systems using rabbit IgG and human luteinizing hormone (hLH) in a 'sandwich' immunoassay revealed that the immunosensor can detect concentrations of hLH in human serum as low as 1 ng ml-1.

Detection of antibody to the PreS2 sequence of the hepatitis B virus envelope protein using an immuno-ligand assay with a silicon sensor detection system

Sensitive immunoassays are essential for establishing the efficacy of recombinant vaccines to hepatitis B virus (HBV). These experimental vaccines include the PreS2 and S domains of the HBV envelope protein. To facilitate measurement of antibody against HBV PreS2, we employed the immuno-ligand assay with silicon sensor-based detection. Labeling of immune reagents with the haptens biotin and fluorescein allows adaptation to the immunofiltration light addressable potentiometric sensor (LAPS) system. A biotinylated monoclonal anti-PreS2 antibody and anti-PreS2 in clinical serum samples competitively bind in liquid phase to a fluorescein labeled PreS2 + S antigen. Streptavidin mediates the immobilization on biotinylated nitrocellulose membranes. Fluorescein mediates binding of an anti-fluorescein urease conjugate to the immune complex. Urease serves as the signal-generating component which subsequently is measured in the LAPS reader. In comparison to a competitive RIA, the immuno-ligand assay demonstrated a four-fold improved sensitivity using a smaller sample volume. The higher sensitivity resulted in earlier detection of seroconversion during a clinical vaccine study.

Potentiometric enzyme channeling immunosensor for proteins

A potentiometric immunosensor for the detection of human IgG has been developed using an asymmetric, ion-selective membrane with immobilized adenosine deaminase and IgG. A protein A-alkaline phosphatase conjugate binds to the immobilized IgG, creating a bienzymatic catalytic layer. In the presence of sample IgG, the conjugate does not bind to the membrane. Instead, the intermediate in the two-step reaction (adenosine) must diffuse to the membrane surface, reducing the rate of product (ammonium) formation within the diffusion layer detected by the membrane. The immunosensor demonstrated is for the determination of IgG. A simplified model is described to predict the maximum rate enhancement for the 'channeled' versus 'unchanneled' reaction mechanisms.

Absorption-enhanced solid-phase immunoassay method via water-swellable poly(acrylamide) microparticles

Water-swellable hydrogel microspheres based on cross-linked polyacrylamide were used as solid supports in immunoassay formats. Capture antibody was covalently bound at the surfaces and the pore size of particles was such that these antibodies were excluded from the interiors. Upon contact with a solution containing immunological reactants, water molecules quickly penetrated the microspheres, causing them to swell, thereby concentrating analyte at the surface. Using swellable particles, the antigen capture rate during the first 5 min of incubation with antigen was two times that of antibody-coated 0.79 cm polystyrene beads. In addition, antibodies attached to lightly cross-linked swellable microparticles proved resistant to inactivation by ultrasonic energy, which can be used to accelerate immunological interactions.

ELISA for human IgG and IgM anti-lipopolysaccharide antibodies with indirect standardization

A new attempt to standardize ELISAs for the quantitation of human IgM and IgG anti-lipopolysaccharide antibodies (anti-LPS), without the use of a specific standard material, is described. Sandwich ELISAs for total IgG and IgM were combined with indirect ELISAs for anti-LPS IgG and IgM antibodies on a 96-well microtest plate using identical assay conditions. The concentration of specific IgG or IgM anti-LPS was read on the respective standard curve for total IgG or IgM. The results were corrected for residual immunoreactivity remaining unbound in the wells after one sample incubation in the combined assays. The quantitative results of IgG anti-LPS correlated well with results obtained using an ELISA with direct standardization (r = 0.969). 28 mg/l of IgM anti-LPS was found as median value among 121 blood donors using the described ELISA principle. Binding studies demonstrated a lower apparent affinity of donor anti-LPS IgM than anti-IgG.

Bioluminescent immunoassay for alpha-fetoprotein

A bioluminescent immunoassay of alpha-fetoprotein is described. It uses monoclonal antibodies labeled with glucose-6-phosphate dehydrogenase and polyclonal antibodies coimmobilized on Sepharose with bioluminescent enzymes from marine bacteria. The bioluminescent reaction which occurs in the immunosorbent is proportional to the amount of alpha-fetoprotein in the assay. The protocol is simple and rapid, and no separation step is required to remove the excess labeled antibodies. The assay can be performed directly on 25 microliters serum and it is as sensitive as other immunometric assays.

Bioluminescent immunosorbent for rapid immunoassays

We describe a bioluminescent immunoassay procedure which does not require a separation step to remove excess free label. A luminescent immunosorbent constituted of bacterial luciferase, FMN oxidoreductase, and an antibody coimmobilized on Sepharose is used to determine specifically the label enzyme (glucose-6-phosphate dehydrogenase, coupled to an antigen) bound by a specific antibody. The immunosorbent confines the bioluminescent reaction in a small volume, and the bound label produces NADH, which is directly used by the nearby luciferase FMN oxidoreductase enzyme system. On the contrary NADH produced by dehydrogenases in solution is directly oxidized without emitting light. Dehydrogenases contained in the biological sample do not interfere with the assay, which can be performed directly on 25 microliter of serum. In this paper we describe the general procedure and we analyze the different parameters that must be optimized.