The original QTL technology was invented by David Whitten, Duncan McBranch, and co-workers in the course of their research at Los Alamos National Laboratory. A broad technology and intellectual property platform (QTL Lightspeed™) has since been developed at QTLBiosystems. The QTL Technology provides a simple “lock-and-key” approach to selective identification of biological molecules.  The “key” portion of this invention consists of a tailored molecule comprising three essential components: Quencher-Tether-Ligand (QTL™).

 
The ligand is the portion of the molecule which binds selectively to a given biological molecule to be detected (the “lock,” or receptor).  The tether connects it to the quencher, which binds weakly to a fluorescent polymer, quenching or “turning off” the light emission from the polymer.

The QTL quenching can be reversed; “Recognition” of a biological species (e.g. a virus) at a receptor site causes strong binding between the receptor and the ligand.  As a result, the QTL is pulled away from the polymer, and the strong fluorescence of the polymer is turned back on.  This is one approach to a QTL Biosensor™.

The QTL approach provides a single-step, instantaneous, homogeneous assay where the amplification step is intrinsic to the fluorescent polymer. The polymer QTL approach provides a system for effective sensing of biological agents by observing fluorescence changes. The key scientific basis is the amplification of quenching of fluorescence that can be obtained with certain charged conjugated polymers and small molecule quenchers.

A fluorescent polyelectrolyte-based superquenching assay has been shown to offer several advantages over conventional small molecule based fluorescence assays. For example, conjugated polyelectrolytes, dye pendant polyelectrolytes, etc. can "harvest" light effectively both by absorption and by superquenching. The enhanced absorbing power of the polymers is indicated by the observation that even sub nanomolar solutions of some of these materials are visibly colored. The fluorescence of these polymers can be detected at even lower concentrations. Superquenching occurs in the presence of small molecules capable of serving as electron transfer or energy transfer quenchers to the polymer or one of its repeat units.

» QTL Technology Overview (pdf)