TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Group: The sensing end group is halide, nitride, amide, amine or ketone. The attaching end group is trichlorosilyl groups, amine or carboxylic acid group. The monolayer comprises a pentacene film having a thickness of 10 nm, preferably 3-10 nm and is deposited using microcontact printing. Preferred Process: The sensing end group generates an atomically sharp interface for differentiating the molecules, and the substance is detected when the sensing end group adsorbs the threshold amount of desired molecule. The adsorbed molecules was selectively removed from the sensing end group by heating the monolayer by current pulses. The energy required to heat 3x10-13 cm3 of the monolayer is 15 pJ. The charge carrier density or charge mobility of the sensing end group are changed according to the adsorption of vapor molecules. The sensing end group is removed and replaced without removing conjugated segment or attaching end group.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The substrate is silicon substrate, contacts or metals chosen from gold, aluminum, silver, platinum, copper, lithium, calcium and their combinations, and the gate insulator is high dielectric constant oxide having a dielectric constant of more than 4.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Properties: The processing module monitors differentiates responses from the transistors in the array, and detects the changes in differential responses associated with the adsorption of vapor molecules. The silicon circuitry is configured such that transistor sensors are packaged as integrated circuit where the sensors are exposed to testing atmosphere. The monolayer comprises individual organic monolayer molecules for self assembly covalently bonded to other molecules, and provides maximum response even at a low concentration of less than 10-16 moles of analyte molecules. SPECIFIC COMPOUNDS - The gate insulator is yttria stabilized zirconia. The conjugated segment is phenyl-acetylene or phenylene-vinylene.