Electrochemiluminescent enzyme biosensors
Electrochemiluminescent enzymes, their preparation and use as biosensors are disclosed. Specifically, two appendages are covalently attached to a desired dehydrogenase enzyme; (1) a nicotinamide adenine cofactor or analog thereof, and (2) a luminescent ruthenium complex. For example, glucose concentrations is the following way. A doubly-modified glucose dehydrogenase could oxidize glucose with concomitant reduction of the attached NAD + to NADH. Because NADH, but not NAD + , is able to interact with surface ruthenium to promote ECL, only enzyme molecules that have reacted with glucose will emit light from their ruthenium label in an ECL instrument. The relative close proximity of NADH and ruthenium on the enzyme surface enhances light emission as compared to the same concentrations in free solution. When NADH reduces ruthenium, it returns to become NAD + , permitting multiple cycles of ECL light emission from a single enzyme molecule. Such biosensors can be used in solution or bound to a solid surface. Assays employing the biosensor molecules can be performed on an IGEN Origen R Analyzer.
1. A method for the determination of the concentration of an enzyme substrate present in a specimen, comprising the steps of:
(a) contacting said specimen with an oxidoreductase conjugate under conditions which permit the oxidation of the enzyme substrate, said oxidoreductase conjugate comprising a co-factor and a species capable of generating an electrochemiluminescent signal separately linked in close proximity to an active site of said oxidoreductase in a manner which permits their electrochemical interaction with each other and a substrate also in close proximity to the active site;
(b) measuring the change in electrochemiluminescence from a base reading; and
(c) determining the concentration of enzymatic substrate based on the measured change in electrochemiluminescent signal.
2. The method according to claim 1 wherein the measurement and determination is done on a real time basis.
3. The method according to claim 1 wherein the determination of enzymatic substrate is deduced from a comparison with established kinetic parameters for the reaction.
4. The method according to claim 1 wherein the determination of enzymatic substrate concentration is determined based on rate measurements in the instrument.
5. The method of claim 1 wherein the steps are carried out simultaneously.
6. The method of claim 5 wherein the voltage necessary for electrochemiluminescence is pulsed so as to actively recycle said co-factor and said species caDable of generating an electrochemiluminescent signal.