Poly thickness resonance

Thickness of the barrier layer, optimized at 220 nm [133], played a crucial role with respect to the chemosensor sensitivity, selectivity and LOD. So, eventually, the chemosensor architecture comprised a gold-film electrode, sputtered onto a 10-MHz resonator, coated with the poly(bithiophene) barrier layer, which was then overlaid with the MIP film. This architecture enabled selective determination of the amine at the nanomole concentration level. LOD for histamine was 5 nM and the determined stability constant of the MIP-histamine complex, XMn> = 57.0 M 1 [131], compared well with the values obtained with other methods [53, 136, 137]. Moreover, due to the adopted architecture, the dopamine chemosensor could determine this amine with the stability constant for the MIP-dopamine complex, XMip = (44.6 4.0) x 106 M-1 and LOD of 5 nM [133], which is as low as that reached by electroanalytical techniques [138]. The MIP-QCM chemosensor for adenine [132] also featured low, namely 5 nM, LOD and the stability constant determined for the MIP-adenine complex, XMIP = (18 2.4) x 104 M, was as high as that of the MIP-adenine complex prepared by thermo-induced co-polymer-ization [139]. The linear concentration range for determination of these amines extended to at least 100 mM. 

Fig. 21 Changes in resonant frequency (panel A) and resonant resistance (panel B) for a poly(vinylferrocene-co-/ /-isopropylacrylamide) film (VF NIPAA = 1 13 dry film thickness ca. 5 pm) as a function of temperature, with the film maintained in the reduced state ( = 0.0 V dashed line) and in the oxidized state (E = 0.5 V full line). Electrode Pt (area = 0.2 cm ) on 9-MHz AT-cut quartz crystal. Solution 0.1 moldm NaCl04. Temperature scanned from 35 to 10 °C over the course of ca. 1 h. (Reproduced from Ref [137] with permission from the American Chemical Society.)...

In Sect. 2.7.2.1.2, the phenomenon of film resonance was discussed. In this special situation, the film thickness corresponds to one quarter of the acoustic wavelength, that is, the acoustic phase shift defined by Eq. (11) has the numerical value = 7t/2. For a film of given shear modulus, progressive increase in thickness will eventually result in this condition being satisfied. This phenomenon is illustrated in Fig. 27 [41] for a poly(3-hexylthiophene) film as a function of the polymerization charge during deposition. As can be seen, the resonant frequency transiently moves sharply upwards and the peak amplitude... 

Fluorescence. We have also measured fluorescence produced by two-photon excitation for thick films of polysilane. For this experiment, the laser was a Spectra-Physics sub-picosecond dye laser system, focussed onto the polymer films to produce intensities of =440 MW/cm. Emission was focussed into a 0.5 m spectrometer and spectra were collected using an optical multichannel analyzer and analyzed on an IBM PC. For poly(di-n-hexylsilane), the two-photon induced emission is broadband (AXpwHM -10 nm at room temperature), with line center at =380 nm, as shown in figure 10. The emission spectrum is identical to that observed for this compound by UV excitation, and the average degree of fluorescence anisotropy (=0.2) produced at the two-photon resonance (579 nm) is quite similar to that oteerved for on-resonance UV excitations in polysilanes [26]. 

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