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We present a chemical sensor based on a microfabricated array of eight silicon cantilevers actuated at their resonance-frequency and functionalized by polymer coatings. The operating principle relies on transduction of chemical or physical processes into a mechanical response. After exposure to analyte vapor, analyte molecules diffuse into the cantilever coating, which begins to swell. Jointly with the mass increase, a change of interfacial stress between coating and cantilever occurs, resulting in a bending of the cantilevers. Our setup allows the simultaneous detection of cantilever oscillation and bending of eight cantilevers by time-multiplexed optical beam deflection readout. The ac component of the cantilever response is demodulated, and the cantilever resonance-frequency is tracked by a custom-built phase-locked loop. By filtering out the ac component (oscillation), the dc signal (bending) is extracted, yielding information on mass as well as surface stress changes simultaneously. Detection results of water, primary alcohols, alkanes and perfumes are presented.

An array of microcantilever beams, coated with a self-assembled monolayer of bistable, redox-controllable [3]rotaxane molecules, undergoes controllable and reversible bending when it is exposed to chemical oxidants and reductants. Conversely, beams that are coated with a redox-active but mechanically inert control compound do not display the same bending. A series of control experiments and rational assessments preclude the influence of heat, photothermal effects, and pH variation as potential mechanisms of beam bending. Along with a simple calculation from a force balance diagram, these observations support the hypothesis that the cumulative nanoscale movements within surface-bound “molecular muscles” can be harnessed to perform larger-scale mechanical work.

The interfacial stress of self-assembled monolayers on Au exposed to buffers of various pH values and ionic strengths is measured as a function of the liquid environment. The method uses two thiol-modified Au-covered silicon cantilevers and a differential method to compensate for thermal and refractive index changes of the liquid environment. Increasing pH and ionic strength leads to a bending, i.e., a compressive stress, of a mercaptohexadecanoic acid-covered cantilever compared to a hexadecanethiol-covered reference cantilever. In addition, the interfacial stress is found to be highly dependent on the surface density of the ionizeable mercaptohexadecanoic acid molecules when they are coadsorbed with hexadecanethiols on Au.

Raman detection of nitrogen gas is very difficult without a multi-pass arrangement and high laser power. Hollow-core photonic bandgap fibers (HC-PBF) provide an excellent means of concentrating light energy in a very small volume and long interaction path between gas and laser. One particular commercial fiber with a core diameter of 4.9 microns offers losses of about 1dB/m for wavelengths between 510 and 610 nm. If 514nm laser is used for excitation, the entire Raman spectrum up to above 3000 cm -1 will be contained within the transmission band of the fiber. A standard Raman microscope launches mW level 514nm laser light into the PBF and collects backscattered Raman signal exiting the fiber. The resulting spectra of nitrogen gas in air at ambient temperature and pressure exhibit a signal enhancement of about several thousand over what is attainable with the objective in air and no fiber. The design and fabrication of a flow-through cell to hold and align the fiber end allowed the instrument calibration for varying concentrations of nitrogen. The enhancement was also found to be a function of fiber length. Due to the high achieved Raman signal, rotational spectral of nitrogen and oxygen were observed in the PBF for the first time to the best of our knowledge.

We present quantitative and qualitative detection of analyte vapors using a microfabricated silicon cantilever array. To observe transduction of physical and chemical processes into nanomechanical motion of the cantilever, swelling of a polymer layer on the cantilever is monitored during exposure to the analyte. This motion is tracked by a beam-deflection technique using a time multiplexing scheme. The response pattern of eight cantilevers is analyzed via principal component analysis (PCA) and artificial neural network (ANN) techniques, which facilitates the application of the device as an artificial chemical nose. Analytes tested comprise chemical solvents, a homologous series of primary alcohols, and natural flavors. First differential measurements of surface stress change due to protein adsorption on a cantilever array are shown using a liquid cell.

We present a novel chemical sensor based on a microfabricated array of silicon cantilevers. Individual cantilevers are sensitized for the detection of analytes using metal coatings. Analyte molecules chemisorbing or physisorbing on the cantilever coating and chemical reactions produce a change in interfacial stress between analyte molecules and cantilever. This leads to a nanomechanical response of the cantilever, i.e. bending. The bending is read out using a time-multiplexed optical beam-deflection technique. From magnitude and temporal evolution of the bending, quantitative information on analyte species and concentration is derived. Here, we demonstrate the detection of ethene and water vapor with such a nanomechanical nose.

We present a novel chemical sensor based on a micromechanical array of silicon cantilevers sensitized for the detection of analytes using cantilever coatings such as metals, self-assembled monolayers, or polymers. Chemical reactions are transduced into a mechanical response and read out using an optical beam-deflection technique. Detection of primary alcohols, natural flavors, and water vapor is demonstrated.