Chemiluminescence (CL) detection is seldom used in two-dimensional solid support microarray platforms because adequate sensitivity and spatial resolution is difficult to achieve. The three-dimensional ordered microchannels of the Flow-thru Chip increase both the sensitivity and spatial resolution required for quantitative CL measurements on microarrays. Enzyme-catalyzed CL reactions for the detection of hybridizations on microchannel glass were imaged using a CCD camera. Signal uniformity, sensitivity, and dynamic range of the detection method were determined. The relative standard deviation of signal intensities across an array of 64 spots was 8.1%. A detection limit of 250 amol of target with a linear dynamic range of 3 orders of magnitude was obtained for a 3-h assay. Similar to two-color fluorescence measurements, multiple enzyme labels were employed to demonstrate two-channel chemiluminescence. A unique method for measuring the relaxation time of a chemiluminescent species is also described.

Two sensing mechanisms utilizing Langmuir monolayer flow, the pressure-driven movement of a Langmuir film into a hydrophobic surface−liquid interface, have been investigated and involve analyte interaction with either the flowing monolayer or stationary film. The sensing aspect is achieved through modulation of the bilayer formation rate. A sensor using this novel transduction mechanism was developed for Cd2+, based on the interaction of divalent cations with the carboxylic headgroup of the flowing monolayer. Aqueous divalent cations associate with an oleic acid monolayer, increasing its viscosity. As a result, the flow rate of the associated monolayer is slower than for the unassociated monolayer. A rudimentary pH sensor was also developed to exemplify flow-based sensing, in which oleyl alcohol flows into the interface between a mixed methyl-carboxylic acid terminated self-assembled monolayer modified gold electrode and water. The flow rate for this system was sensitive to subphase pH. Attenuation of the monolayer flow rate is dependent upon the relative surface concentration of the carboxylic acid moiety in the multicomponent surface monolayer. The major contribution to the modulation of the monolayer flow rate in this system is attributed to solvation thermodynamics of the carboxylate anion macroscopically averaged across the modified electrode surface.

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The bilayer formation properties of single-component acyl chains of varying length and extent of unsaturation are compared using Langmuir monolayer flow. Four series of structural motifs in the flowing film were considered: linked oleyl chains; chains with a single cis double bond over a range of total chain lengths; chains of the same length with 1-5 cis double bonds; molecules which flow that do not have the standard cis double bond in the chain. Slower flow rates were observed for Langmuir films with increased numbers of linked oleyl chains due to the enhanced interlayer coupling between the flowing and stationary films. Slower flow rates were also observed with increased acyl chain length due to the increased intralayer coupling between the flowing molecules. More rapid flow rates were observed as the number of double bonds within the film forming material was increased, due to both the decreased inter-and intralayer coupling. While no single structural feature is common to molecules that undergo monolayer flow, all molecules that have been observed to flow exist at a liquid expanded phase state at the equilibrium spreading pressure.