Assays for detecting potentially toxicdanalytes utilize a preparation of eukaryotic or prokaryotic cells which have signal-generating metabolic activity. The sensitivity of such assays is significantly improved by the employment of a particulate solid-phase adsorbent e.g. silica gel, which can be preliminarily mixed either with the suspected toxic analyte or with the cellular reagent. It is found that the presence of either the adsorbent-analyte combination or the adsorbent-cellular reagent combination results in an amplification of the decrease of the intensity of the generated signal, thereby improving the detection capability of the assay, particularly with respect to low concentrations of toxicants.