PubMed · 9775543
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B J Roth, J P Wikswo. 1998. Comments on "Hall effect imaging".. https://doi.org/10.1109/10.720207
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To probe directly the analyte/film interactions that characterize molecular recognition in gas sensors, we recorded changes to the in situ surface vibrational spectra of specifically functionalized surface acoustic wave (SAW) devices concurrently with analyte exposure and SAW measurement of the extent of sorption. Fourier transform infrared external-reflectance spectra (FT-IR-ERS) were collected from operating 97-MHz SAW delay lines during exposure to a range of analytes as they interacted with thin-film coatings previously shown to be selective: cyclodextrins for chiral recognition, nickel camphorates for Lewis bases such as pyridine or organophosphonates, and phthalocyanines for aromatic compounds. In most cases where specific chemical interactions--metal coordination, "cage" compound inclusion, or pi-stacking--were expected, analyte dosing caused distinctive changes in the IR spectra, together with anomalously large SAW sensor responses. In contrast, control experiments involving the physisorption of the same analytes by conventional organic polymers did not cause similar changes in the IR spectra, and the SAW responses were smaller. For a given conventional polymer, the partition coefficients (or SAW sensor signals) roughly followed the analyte fraction of saturation vapor pressure. These SAW/FT-IR results support earlier conclusions derived from thickness-shear mode resonator data.
Acoustic wave based immunosensors have proven to facilitate the in situ detection of marker-free proteins in real time. However, the vast majority of these studies focuses on the interaction of a single type of antigen with immobilized receptors in pure buffer solutions. In an effort to evaluate the potential of acoustic plate mode immunosensors for operation in more complex biological environments, antigen/antibody reactions have been studied in pure buffer solution, in the presence of cells, and in human serum. It has been observed that the devices do not respond to cell adsorption and that antigen/antibody reactions can successfully be detected even if a thick layer of cells is deposited on the sensing surface. By varying the frequency of operation, it was shown that the sensitivity of the devices toward nonspecific protein adsorption is reduced at high frequencies of operation. Thus, spurious immunosensor response caused by non-specific adsorption processes can be suppressed by appropriately selecting device frequency. Using immunoglobulin G with minimum cross reactivity with human serum proteins, antigen/antibody reactions have also been monitored in human serum. While the observed frequency shifts are comparable to those measured in pure buffer solutions, the binding process is accompanied by additional acoustic loss, indicating changes in the viscoelastic properties of the interfacial layer.
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