Solution-phase sensor arrays

Solution-Phase Sensor Arrays with Boronie Aeid-Appended Bipyridinium Salts... 

Chitosan-clay bio-nanocomposites are very stable materials without significant desorption of the biopolymer when they are treated with aqueous salt solutions for long periods of time. In this way, they act as active phases of electrochemical sensors for detection of ions (Figure 1.8). The particular nanostructuration of the biopolymer in the interlayer region drives the selective uptake of monovalent versus polyvalent anions, which has been applied in electrode arrays of electronic tongues [132]. 

Polymer films have been very widely applied to modify the surfaces of chemical sensors both for solution and gas phase measurements. Solution coating has been used to coat quartz crystal oscillators [91-93, 112] and SAW devices [113, 114] with various polymeric adsorbates and polymer/lipid mixtures [90, 94] to prepare arrays of sensors for use in gas sensing and odor evaluation and discrimination. 

A directional SHM transducer that does not require either phase-array delays or connection switching to achieve steering is described in Xu et al. [63]. This directional sensor achieves tuning into preferential direction at certain discrete frequencies, which are the solution of a firequency-wavenumber equation. The transducer consists of a skew array of piezo-wafer active sensors placed at pitch values d, d.2 and angles a, 5 about the 1 and 2 axes, respectively (Figure 16.29(a)). The transducer achieves directivity at certain fi equencies Figure 16.29(b) illustrates the directionality measured with SLDV on an isotropic aluminum 45° at 105 kHz, 120° at 150 kHz, — 17° at 200 kHz, 88° at 280 kHz. Thus, the transducer directionality is controlled by the excitation firequency in discrete steps. 

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