The use of an alumina-coated ZnSe internal reflection element (IRE) to detect spores by attenuated total reflection infrared spectroscopy (FTIR-ATR) was investigated. Two methods for coating the IRE with alumina are described. It is shown that the adsorption proceeds through an interaction of the carboxylate groups on <i>Bacillus globigii</i> (BG) and positively charged sites on the alumina. The amount adsorbed is highly dependent on solution pH and passes through a maximum value near pH 5, which is dictated by the charge density on the spores and the charge density on the alumina surface. Furthermore, it is shown that lateral–lateral repulsion between the spores limits the maximum adsorbed amount, giving rise to a detection limit of 10<sup>7</sup> spores per cm<sup>2</sup> of the IRE.

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