Bioluminescent assays with immobilized firefly luciferase based on flow injection analysis

Immobilization of luciferase from a firefly lantern extract on glass strips as an alternative strategy for luminescent detection of ATP

The bioluminescent reaction catalysed by firefly luciferase has become widely established as an outstanding analytical system for assay of ATP. When used in solution, luciferase is unstable and cannot be re-used, a problem that can be partially circumvented by immobilizing the enzyme on solid substrates. Transparent glass is especially advantageous over alternative immobilizing matrices, since it allows most of the emitted photons to be detected. We report a new method for luciferase immobilization on glass which does not require prior silanization and glutaraldehyde activation, thus saving preparation time and minimizing enzyme inactivation. Our method is based on the co-immobilization by adsorption of luciferase (from a firefly lantern extract) and poly-L-lysine (PL) on non-porous glass strips. Luciferase immobilized in this way exhibits minimal variations in intersample activity, high sensitivity for ATP detection (linear luminescence responses down to 50 nmol/L) and good stability (full activity for at least 60 days when stored at -80 degrees C). PL-mediated immobilization of luciferase on glass strips provides an attractive strategy for the design of specific ATP biosensors, with potential in industry, environmental screening, medicine and biological research.

Chemiluminescent imaging of enzyme-labeled probes using an optical microscope-videocamera luminograph

A chemiluminescent system has been developed for ultrasensitive, quantitative analysis as well as visualization of the spatial distribution of biomolecules such as antigens, enzymes, antibodies, DNA probes in tissue, or cells. The system consists of a low-light imaging Vidicon videocamera connected to an optical microscope, able to measure light at the single photon level and perform 3D image analysis of the subcellular distribution of the analyte. The concentration and the spatial distribution of enzymes, or enzyme-labeled biospecific reagents can be determined using appropriate chemiluminescent substrates. Analytes are also determined with coupled enzymatic reactions terminating in light emission. Oxirane acrylic beads (250-micron-diameter macroporous particles) with immobilized horseradish peroxidase have been used as a model system to optimize the experimental conditions in terms of signal intensity and spatial resolution as a function of different chemiluminescent substrates such as luminol/enhancer/H2O2 and acridancarboxylate ester/H2O2. Localization of oxirane beads immobilized acetylcholinesterase has been also used to optimize a system in which the detection and localization of the primary enzyme involves two secondary enzymes in solution, choline oxidase and horseradish peroxidase, leading to a final light emission. Immunoenzymatic reactions for the detection of viral antigens and in situ hybridization assays for the detection of viral DNAs (cytomegalovirus, herpes simplex virus) have been performed in cells using peroxidase-labeled antibodies or cDNA probes and the analytical performance of different chemiluminescent substrates for the enzyme has been evaluated. The results obtained showed the possibility to sharply image the bioprobes in single cells and peroxidase is a suitable label when luminol/H2O2 system is used in conjunction with enhancer as in the ECL and SuperSignal Ultra reagents; other substrates such as Lumigen PS-3, despite adequate detectability, showed problems of localization of the signal as a result of the relatively long half-life of the excited emitting species and its diffusion in the chemiluminescent cocktail. The system has proven to be highly sensitive, able to perform quantitative analysis, and relatively simple.

Flow injection assays with chemiluminescence and bioluminescence detection--a review

This paper reviews publications that combine the technique of flow injection (FI) with chemiluminescence (CL) and bioluminescence (BL) detection, from the earliest papers in 1979/80 to mid-1992, and refers exclusively to reactions occurring in solution. Air-segmented systems and liquid chromatography with CL detection are not considered unless FI has been used to pre-optimize the system. The applications have been categorized in terms of the type of CL reaction; there are separate entries for luminol, peroxyoxalate, other CL reactions and BL reactions. Each of the four sections includes a table of applications that lists the analyte, the nature of the reaction, the sample matrix and the limit of detection.

Microdialysis and luminescent probe: analytical and clinical aspects

Immobilized enzymes are widely used in the clinical laboratory to assay several analytes and enzymes. The use of immobilized enzymes makes these reagents recoverable, disposable and in most cases increases their stability and catalytic activity. In conjunction with bioluminescent enzymes (firefly and bacterial luciferases) and chemiluminescent catalyst (peroxidase) we set up high-sensitive flow sensors based on the use of nylon tube coil or epoxy methacrylate column as solid support. For in-vivo determination a suitable microdialysis probe inserted directly into brain or blood allows continuous measurement of extracellular lactate levels by means of a bioluminescent flow detector system. This procedure performs more measurements in the same time interval than other systems (HPLC), e.g. to give a detailed description of the effects of ischemia, or other pathological events, on lactate concentration in the brain.

Design of luminescence photobiosensors

The potential of immobilized enzyme membranes in biosensors has been explored in our group for several years. Although part of our work has been mainly devoted to electrochemical transducers and oxidases for the design of enzyme electrodes, the demand for ultrasensitive and highly selective sensors led us to consider the use of luminescent enzyme systems associated to optical transduction. When considering the need for operational and reliable biosensors in biotechnology, immobilization and stability of the sensing element still remain, in most cases, an unavoidable problem. We recently proposed a very fast and reliable procedure for preparing enzymatic membranes from Pall (Biodyne Immunoaffinity membranes) supplied in a pre-activated form. Both the firefly and bacterial systems as well as peroxidase for the chemiluminescent determination of various analytes, could be bound to such a support. Based on this approach, a fibre-optic sensor with immobilized enzymes has been designed which permits bio- or chemiluminescent analysis of ATP, NADH or H2O2 respectively. With the NADH-based system, other analytes could be detected using coupled dehydrogenases. This device appears very promising and includes the convenience of both the luminescence sensitivity as well as the handling of the biosensor design.

Coupled reactions for the determination of analytes and enzymes based on the use of luminescence

Immobilized enzymes are widely used in the clinical laboratory in the assay of several analytes and enzymes. The use of immobilized enzymes makes these reagents recoverable and re-usable, and in most cases increases their stability and catalytic activity. In conjunction with bioluminescent enzymes (firefly and bacterial luciferases) and chemiluminescent catalyst (peroxidase) we set up high-sensitive flow methods based on the use of nylon tube coil or epoxy methacrylate column as solid support. All the NAD(P)/NAD(P)H-dependent dehydrogenases (bacterial luciferase), ATP-dependent enzymes (firefly luciferase) and oxidases producing H2O2 (peroxidase) can be immobilized and a large variety of analytes have been sensitively measured. As an alternative format we also reported a dry chemistry method in which all the enzymes, substrates and cofactors are ready to use, supported on dry cellulose disks. Methodological problems such as flow conditions, stability, pH, ionic strength and analytical performances are also reported.

Continuous-flow bioluminescent determination of ATP in platelets using firefly luciferase immobilized on epoxy methacrylate

Firefly luciferase was immobilized on epoxy methacrylate beads and used for a continuous-flow assay of ATP extracted from platelets. The immobilized luciferase had a half-life of 3 days at 25 degrees C; there was a 25% recovery of luciferase activity upon immobilization, and ca 50 reactors were made from 1 mg of commercial enzyme. The sensitivity of the assay was 0.3 pmol of ATP, and the response was linear between 1 and 500 pmol of ATP. The ATP content of platelets obtained with the present method correlated well with those obtained using soluble luciferase.

Novel strategies in flow-injection analysis

An overview of the most recent advances in flow-injection analysis, and the future trends and potential of this powerful technique are presented.

Determination of total cholesterol in serum by flow injection analysis with immobilized enzymes

Several photometric and fluorimetric methods are proposed for the determination of cholesterol by use of enzymes immobilized on controlled-pore glass and the normal and stopped-flow injection modes, achieving linear ranges of the calibration curves between 26-776 mumol/l and 5-265 mumol/l with excellent regression coefficients and good coefficients of variation. The methods have been applied to the determination of this analyte in serum with excellent results.