The present invention relates to the use asymmetric monolayer forming species and electroconduit forming species to detect target analytes. 
There are a number of assays and sensors for the detection of the presence and/or concentration of specific substances in fluids and gases.  Many of these rely on specific ligand/antiligand reactions as the mechanism of detection.  That is, pairs of substances (i.e. the binding pairs or ligand/antiligands) are known to bind to each other, while binding little or not at all to other substances.  This has been the focus of a number of techniques that utilize these binding pairs for the detection of the complexes.  These generally are done by labeling one component of the complex in some way, so as to make the entire complex detectable, using, for example, radioisotopes, fluorescent and other optically active molecules, enzymes, etc. 
Other assays rely on electronic signals for detection.  Of particular interest are biosensors.  At least two types of biosensors are known; enzyme-based or metabolic biosensors and binding or bioaffinity sensors.  See for example U.S. Pat.  Nos.  4,713,347; 5,192,507; 4,920,047; 3,873,267; and references disclosed therein.  While some of these known sensors use alternating current (AC) techniques, these techniques are generally limited to the detection of differences in bulk (or dielectric) impedance. 
The use of self-assembled monolayers (SAMs) on surfaces for binding and detection of biological molecules has recently been explored.  See for example WO98/20162; PCT US98/12430; PCT US98/12082; PCT US99/01705; PCT/US99/21683; PCT/US99/10104; PCT/US99/01703; PCT/US00/31233; U.S. Pat.  Nos.  5,620,850; 6,197,515; 6,013,459; 6,013,170; and 6,065,573; and references cited therein. 
Accordingly, it is an object of the invention to provide novel methods and compositions for the electronic detection of target analytes using self-assembled monolayers. 
In accordance with the objects outlined above, the present invention provides compositions comprising metallic surfaces comprising asymmetric monolayer forming species comprising two components.  One of the components is a standard monolayer forming species, such an alkyl chain.  The other component is an electroconduit forming species.  Electroconduit forming species are short chain alkyl groups, which may be branched. 
In a further embodiment, the invention provides methods of detecting a target analyte in a test sample comprising attaching said target analyte to a metallic surface comprising asymmetric monolayer forming species via binding to a capture binding ligand.  Recruitment linkers, or label probes are directly or indirectly attached to the target analyte to form an assay complex.  The method further comprises detecting electron transfer between an electron transfer moiety and an electrode.