SALIANT aims to develop a hand-held device for real-time analysis of trace levels of explosives, chemicals and drugs. The key innovation is a positive detection lateral-flow test for small molecules that is highly sensitive and simple to use making it ideally suited to deployment by First Responders at crime scenes and terrorist incidents. Lateral flow immunodiagnostics has long offered the promise of fast, high quality testing for substances of low molecular weight. There have however been very real challenges to bringing the full power of such technology to bear in this area. The problem is simply size. Large analytes can support the simultaneous binding of both capture and detector antibodies, allowing typical excess-reagent sandwich immunoassays to be formatted in which increasing analyte concentration provides an increase of observable signal over a very low zero background. Small molecules are simply not large enough to support such simultaneous binding. Alternative systems in effect measure how much analyte is not present. This causes major problems in terms of precision, sensitivity and read-out where, classically, increasing concentration of analyte reduces the signal produced, making point-of-need devices often difficult to read. What is required is a robust system in which there is no observable signal in the absence of analyte, and even low level samples give an obvious observable signal over this zero background. SALIANT offers a system based on a small bindable moiety that is first conjugated close to the binding site of a primary antibody against the analyte such that when analyte binds the antibody, the moiety can still be bound by a labelled secondary antibody. A large reagent-analogue of the analyte is also introduced, binding analyte-unbound primary antibody, and thereby blocking binding of the secondary antibody to the moiety. Thus the more analyte present, the more binding of secondary antibody occurs and the more signal is produced.