New, bioluminescence-enhanced detection systems for use in enzyme activity tests, enzyme immunoassays, protein blotting and nucleic acid hybridization

A bifunctional luminogenic substrate for two luminescent enzymes: firefly luciferase and horseradish peroxidase

Horseradish peroxidase (HRP) catalyzes the oxidative chemiluminescent reaction of luminol, and firefly luciferase catalyzes the oxidation of firefly D-luciferin. Here we report a novel substrate, 5-(5'-azoluciferinyl)-2,3-dihydro-1,4-phthalazinedione (ALPDO), that can trigger the activity of HRP and firefly luciferase in solution because it contains both luminol and luciferin functionalities. It is synthesized by diazotization of luminol and its subsequent azo coupling with firefly luciferin. NMR spectral data show that the C5' of benzothiazole in luciferin connects the diazophthalahydrazide. The electronic absorption and fluorescence properties of ALPDO are different from those of its precursor molecules. The chemiluminescence emission spectra of the conjugate substrate display biphotonic emission characteristic of azophthalatedianion and oxyluciferin. It has an optimum pH of 8.0 for maximum activity with respect to HRP as well as luciferase. At pH 8.0 the bifunctional substrate has 12 times the activity of luminol but has 7 times less activity than the firefly luciferin-luciferase system. The specific enhancement of light emission from the cyclic hydrazide part of ALPDO helped in the sensitive assay of HRP down to 2.0 x 10(-13) M and of ATP to 1.0 x 10(-14) mol. Addition of enhancers such as firefly luciferin and p-iodophenol (PIP) to the HRP-ALPDO-H2O2 system enhanced the light output.

Bioluminescent fusion conjugates and bioluminescent immunoassays: 1988-1998

The first part of this survey focuses on immunoassays and related ligand:binder assays (receptor:ligand, DNA probe) that use either a luciferase or a photoprotein as a label. In addition, references to assays that use a conventional label detected using a bioluminescent assay are included. The second part of the survey collects together references to publications on recombinant fusion proteins in which one of the fused proteins is bioluminescent (e.g., a luciferase or a photoprotein). References are cited by year and then alphabetically by first author. Copyright 1999 John Wiley & Sons, Ltd.

Ultrasensitive enzyme immunoassay

Ultrasensitive enzyme immunoassay methods are reviewed not only for antigens but also for antibodies and haptens with emphasis on factors which limit the sensitivity. Ultrasensitive immunoassays can be developed by noncompetitive solid phase assay systems rather than competitive ones for antigens and antibodies. However, no noncompetitive immunoassays have been available for hapten molecules which cannot be bound simultaneously by two different antibody molecules. This has been overcome by developing methods to derivatize haptens with amino groups so that the derivatized haptens may be measured by two-site noncompetitive assays. For ultrasensitive noncompetitive solid phase immunoassays, the nonspecific binding of labeled reactants (background noise) should be minimized. This has been achieved by developing methods to transfer the complex of analytes and labeled reactants from solid phase to solid phase with minimal dissociation of the complex. Thus, the sensitivity for antigens, haptens and antibodies has been markedly improved and some applications have been made.

Comparison of seven bio- and chemiluminescent reagents for in situ detection of antigens and nucleic acids

Bio- and chemiluminescence have proved sensitive enough to compete with chromogenic and radioisotopic tracers for in situ detection. However, they must also provide a discriminant morphological analysis of the specific signal. We have tested seven bio- or chemiluminescent reagents for tissue antigen and nucleic acid detection by immunocytochemistry (ICC) or in situ hybridization (ISH). They were based on luminescent detection of peroxidase, alkaline phosphatase, beta-galactosidase or xanthine oxidase. We also explored whether high molecular weight polymers could increase the spatial definition of the photon emission. An ICCD camera was used to collect the light signal provided by immunolabelling of endothelial cells and by ISH of human papilloma virus on cell smears. Among the enzyme-luminescent substrate combinations tested, the enhanced luminol chemiluminescence (ECL) gave the best resolution of the specific signal. The other systems were mainly hampered by a high diffusion of the reaction product over the tissue section. Unfortunately, in this case, the high molecular weight polymers tested were inefficient. However, the addition of polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP) significantly improved respectively the definition and intensity of ECL photon emission. We demonstrate that chemiluminescence gives a morphological resolution allowing histological examination. The extension of this new application, now depends on physicochemical adaptation of chemiluminescent reagents to the constraints of tissue detection.

Low-light imaging technology in the life sciences

Photon imaging is an increasingly important technique for the measurement and analysis of chemiluminescence and bioluminescence. New high-performance low-light level imaging systems have recently become available for the life sciences. These systems use advances in camcera design and digital image processing and are now being used for a wide range of luminescence applications. They offer good sensitivity for photon detection and large dynamic range, and are suitable for quantitative analysis. This is achieved using a range of software techniques including image arithmetic, histogramming or summing regions of interest, feature extraction and multiple image processing for kinetics or assay screening. Improvements in image-processing hardware and software have increased the usefulness of these systems in the biosciences. Low-light imaging is a rapid and non-invasive method for the sensitive detection and analysis of luminescent assays. As such it offers a powerful and sensitive tool for investigating processes, both at the cellular level (luc and lux reporter genes, intracellular signalling) and for measurement of macro samples (immunoassays, gels and blots, tissue sections).

A new ultrasensitive bioluminogenic enzyme substrate for beta-galactosidase

A derivative of D-luciferin, D-luciferin-O-beta-galactoside, was synthesized and used as highly sensitive substrate for beta-galactosidase. The substrate was physicochemically characterized. Enzymatic cleavage of the new compound by beta-galactosidase was demonstrated and kinetic constants Km, Vmax, kcat and kcat/Km have been determined. The compound has been proved to be a highly sensitive substrate for beta-galactosidase, permitting a limit of detection of 3.7 x 10(-19) mol of enzyme per assay.

The digoxigenin:anti-digoxigenin (DIG) technology--a survey on the concept and realization of a novel bioanalytical indicator system

A review is given on the novel non-radioactive digoxigenin:anti-digoxigenin (DIG) bioanalytical indicator system. After a general introduction on direct and indirect indicator systems based on previous non-radioactive indicator reactions as well as in vitro and in vivo amplification procedures the principle of the new digoxigenin:anti-digoxigenin technology is demonstrated. The novel system is based on the specific high-affinity interaction between the cardenolide digoxigenin from Digitalis plants and a digoxigenin-specific antibody coupled with a reporter group. A variety of methods for digoxigenin modification of nucleic acids, proteins and glycans are presented. In addition, various applications of the novel non-radioactive indicator system in a variety of direct or indirect detection approaches with either insoluble or soluble substrates are described. It is also shown that with these applications alternative reaction formats are used which are partly characterized by additional amplification steps.

Development of ultrasensitive enzyme immunoassay reviewed with emphasis on factors which limit the sensitivity

Development of ultrasensitive enzyme immunoassays for antigens, haptens and antibodies is reviewed with emphasis on factors which limit the sensitivity. One of the most important conditions for ultrasensitive immunoassays is the use of non-competitive solid phase assay systems rather than competitive ones. Although non-competitive immunoassays are available for antigens and antibodies, there are only competitive immunoassays for hapten molecules which can not be bound simultaneously by two different antibodies. In order to overcome this difficulty, methods have been developed to derivatize haptens with amino groups so that the derivatized haptens may be measured by two-site assays. The other condition for ultrasensitive immunoassays is to minimize the non-specific binding of labelled reactants. This has been achieved by developing methods to transfer the complex of analytes and labelled reactants from solid phase to solid phase without dissociation. Thus, the sensitivity for antigens, haptens and antibodies has been markedly improved. However, the sensitivity for the detection of label enzymes remains to be improved.

Ultrasensitive enzyme immunoassay

Ultrasensitive enzyme immunoassay methods not only for antigens but also for antibodies and haptens are reviewed. These methods are based on a noncompetitive type of assay using solid phase rather than a competitive one. One of the greatest obstacles limiting the sensitivity of noncompetitive immunoassay methods using solid phase is the nonspecific binding of labeled reactants to solid phase. A novel method (immune complex transfer immunoassay method) to overcome this difficulty has been developed. In the initially developed method, antibodies in test serum were reacted with dinitrophenylated biotinylated antigen. The complex formed was trapped onto (anti-dinitrophenyl group) IgG-coated solid phase. The solid phase was washed to eliminate nonspecific immunoglobulins. The complex was eluted from the solid phase with dinitrophenyl-L-lysine, again trapped onto avidin(streptavidin)-coated solid phase and finally measured by reaction with (anti-immunoglobulin) Fab'-enzyme conjugate. Namely, the complex of antibodies and dinitrophenylated biotinylated antigen was transferred from one solid to another, effectively eliminating nonspecific immunoglobulins nonspecifically adsorbed onto the first solid phase. By this method with and without further modifications, the sensitivity for antibodies in serum has been considerably improved. The same principle of immune complex transfer has been applied to the detection of antigens, and one milliattomole (600 molecules) of human ferritin has been detected. Ultrasensitive, noncompetitive immunoassay methods to measure haptens with amino groups have also been developed to measure attomole amounts of haptens.

Firefly luciferase, synthesized to very high levels in caterpillars infected with a recombinant baculovirus, can also be used as an efficient reporter enzyme in vivo

Trichoplusia ni and Spodoptera littoralis larvae were infected with a recombinant AcNPV, having the viral polyhedrin gene replaced with the cDNA encoding firefly luciferase. Both S. littoralis and T. ni synthesized very high levels of luciferase representing greater than or equal to 25% and greater than or equal to 15%, respectively of the total Coomassie blue stainable protein. Luciferase was apparently not secreted into the hemolymph but was contained within the body tissue. Expression in S. littoralis larvae suggests that luciferase can be an excellent reporter enzyme to study virus infection, dissemination and expression in different tissues, host range determination, insect physiology and also to monitor the release of recombinant virus in the environment when used as a biocide.