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A microcantilever array sensor with cantilevers differentially functionalized with self-assembled monolayers (SAMs) of thiolated ligands is prepared by simultaneous capillary coating. This array is described for the detection of metal ions including [Li.sup.+], [Cs.sup.+], [Cu.sup.2+], [Co.sup.2+], [Fe.sup.3+], and [Al.sup.3+]. Binding of the charged metal cations to the surface of the microcantilever sensors produces surface stress that causes bending of the cantilevers that is detected as tip deflection using an array of vertical cavity surface emitting lasers and a position-sensitive detector. Optimization studies of the nanostructured deaUoyed surface were performed for SAMs based on their response to [Cu.sup.2+] cations. Sensor performance experiments demonstrate good sensitivity toward metal ions, with limits of detection as low as [10.sup.-8] molar. A multiplex capillary coating method for cantilever array creation is demonstrated and validated based on surface-enhanced Raman spectra obtained from adjacent cantilevers that were functionalized with different thiolated SAMs. The cantilever array coated with a range of thiolated ligands was exposed to the group of metal ions. The response characteristics of each metal ion show substantial diversity, varying not only in response magnitude, but response kinetics. A pattern recognition algorithm based on a combination of independent component analysis and support vector machines was able to validate that the sensor array response profiles produced enough information content that metal ions could be reliably classified with probabilities as high as 89%.

The very simple coupling of a standard, packed-column gas chromatograph with a microcantilever array (MCA) is demonstrated for enhanced selectivity and potential analyte identification in the analysis of volatile organic compounds (VOCs). The cantilevers in MCAs are differentially coated on one side with responsive phases (RPs) and produce bending responses of the cantilevers due to analyte-induced surface stresses. Generally, individual components are difficult to elucidate when introduced to MCA systems as mixtures, although pattern recognition techniques are helpful in identifying single components, binary mixtures, or composite responses of distinct mixtures (e.g., fragrances). In the present work, simple test VOC mixtures composed of acetone, ethanol, and trichloroethylene (TCE) in pentane and methanol and acetonitrile in pentane are first separated using a standard gas chromatograph and then introduced into a MCA flow cell. Significant amounts of response diversity to the analytes in the mixtures are demonstrated across the RP-coated cantilevers of the array. Principal component analysis is used to demonstrate that only three components of a four-component VOC mixture could be identified without mixture separation. Calibration studies are performed, demonstrating a good linear response over 2 orders of magnitude for each component in the primary study mixture. Studies of operational parameters including column temperature, column flow rate, and array cell temperature are conducted. Reproducibility studies of VOC peak areas and peak heights are also carded out showing RSDs of less than 4 and 3%, respectively, for intra-assay studies. Of practical significance is the facile manner by which the hyphenation of a mature separation technique and the burgeoning sensing approach is accomplished, and the potential to use pattern recognition techniques with MCAs as a new type of detector for chromatography with analyte-identifying capabilities.

A sensor for metal cations is demonstrated using single and binary mixtures of different thiolated ligands as self-assembled monolayers (SAMs) functionalized on silicon microcantilevers (MCs) with gold nanostructured surfaces. Binding of charged metal ions to the active surface of a cantilever induces an apparent surface stress, thereby causing static bending of the MC that is detected in this work by a beam-bending technique. A MC response mechanism based on changes in surface charge is discussed. The monodentated ligands arranged as SAMs on the MC surface are not expected to fully satisfy the coordination sphere of the detected metals. This leads to lower binding constants than would be expected for chelating ligands, but reversible responses. The modest binding constants are compensated in terms of the magnitudes of responses by the inherent higher sensitivity of the nanostructured approach as opposed to more traditional smooth surface MCs. Response characteristics are optimized in terms of SAM formation time, concentration of ligand solution, and pH of working buffer solution. Limits of detection for the tested mono-, di-, and trivalent metal ions are in low to submicromolar range. The results indicated that shapes and magnitudes of response profiles are characteristics of the metal ions and type of SAM. The response factors for a given SAM with the tested metal ions, or for a given metal with the tested SAMs, varied by roughly 1 order of magnitude. While the observed selectivity is not large, it is anticipated that sufficient ionic recognition contrast is available for selective metal ion identification when differentially functionalized arrays of MCs (different ligands on different cantilevers in the array) are used in conjunction with pattern recognition techniques.

It is shown that the performance of microcantilver-based chemical sensors in a liquid environment is affected by altering cantilever surface morphology and receptor phase type and thickness. Self-assembled monolayers of thiolated [beta]-cyclodextrin (HM-[beta]-CD) and thin films of vapor-deposited heptakis (2,3-O-diacetyl-6-O-tertbutyl-dimethylsilyl)-[beta]-cyclodextrin (HDATB-[beta]-CD) were studied on smooth and nanostructured (dealloyed) gold-coated microcantilever surfaces. The dealloyed surface contains nanometer-sized features that enhance the transduction of molecular recognition events into cantilever response, as well as increase film stability for thicker films. Improvements in the limits of detection of the compound 2,3-dihydroxynaphthalene as great as 2 orders of magnitude have been achieved by manipulating surface morphology and film thickness. The observed response factors for the analytes studied varied from 0.02-604 nm/ppm, as determined by cantilever deflection. In general, calibration plots for the analytes were linear up to several hundred nanometers in cantilever deflections.

Solid scintillating fibers, coated with a dual-mechanism bifunctional polymer shown to bind Cs(I) in alkaline solutions, were developed for measurement of (super 137)Cs. The effect of the epoxy-polymer coating thickness on attenuation of the signal from (super 137)Cs was evaluated. After optimal coating conditions were determined, both scintillation fiber and resin functions were retained, producing stable field-ready fibers. Temporal studies were performed to examine the kinetics of (super 137)Cs uptake into the resin. Calibration curves of the fiber response were generated by (beta)-emission from solutions of (super 137)Cs dissolved in 1 M sodium hydroxide. The plots exhibited a linear response over a range of 4-3200 nCi/mL(3.4 x 10(super -10)-2.7 x 10(super -7) M (super 137)Cs), with a limit of detection of 3.65 nCi/mL (approximately 42 parts per trillion (super 137)Cs). The distribution coefficient of Cs was determined to be 490 +/- 50 mL/g from these measurements. Selectivity studies of the resin were performed in the presence of 100 fold excess of Sr(II), A1(III), and nonradioactive Cs(I). Linear calibration plots were obtained in the presence of these potential interferences, but at a reduced sensitivity. The fibers were also used to evaluate the (super 137)Cs content of a mock tank waste sample to show the potential of the fibers in complicated matrixes.