Analytical and Bioanalytical Chemistry, Nov, 2010, Vol.398(5), p.2133(8)
Byline: Chongxiao Tan (1), Nenad Gajovic-Eichelmann (1), Rainer Polzius (2), Niko Hildebrandt (3), Frank F. Bier (1) Keywords: THC; Saliva; Homogeneous; Immunoassay; FITC Abstract: The detection of the major active component of cannabis, I9-tetrahydrocannabinol (THC), becomes increasingly relevant due to its widespread abuse. For control purposes, some easy-to-use, sensitive and inexpensive test methods are needed. We have developed a fluorescence immunoassay utilising THC--fluorescein conjugate as tracer. Fluorescence spectroscopy of the conjugate revealed an unusual property: The relatively weak fluorescence of a dilute tracer solution was increased by a factor of up to 5 after binding of a THC-specific antibody. Fluorescence lifetime measurements in aqueous solutions suggested two different tracer conformations both associated with quenching of fluorescein fluorescence by the intramolecular THC moiety. After antibody binding, the tracer enters a third conformation in which fluorescence quenching of fluorescein is completely suppressed. Utilising this property, we established a homogeneous competitive immunoassay (homogeneous increasing fluorescence immunoassay) with low detection limits. The test requires only two reagents, the new tracer molecule and an anti-THC antibody. A single test takes only 8 min. The dynamic detection range for THC is 0.5 to 20 ng/mL in buffer, with a limit of detection (LOD) of 0.5 ng/mL. The test also works in diluted saliva samples (1:10 dilution with buffer) with an LOD of 2 ng/mL and a dynamic range of 2--50 ng/mL. Author Affiliation: (1) Group Biosensors, Fraunhofer Institute for Biomedical Engineering, Am Muhlenberg 13, 14476, Potsdam-Golm, Germany (2) Research Unit, Dragerwerk AG & Co. KGaA, Moislinger Allee 53-55, 23558, Lubeck, Germany (3) Group NanoPolyPhotonics, Fraunhofer Institute for Applied Polymer Research, Wissenschaftspark Golm, Geiselbergstrasse 69, 14476, Potsdam-Golm, Germany Article History: Registration Date: 07/08/2010 Received Date: 05/05/2010 Accepted Date: 06/08/2010 Online Date: 26/08/2010 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00216-010-4109-6) contains supplementary material, which is available to authorized users.
Marijuana ; Detection Equipment ; Fluorescence ; Reagents ; Tracers (Biology) ; Antibodies ; Fluorescein
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