Optical methods combine the wide availability of molecular indicators with simple and contactless measurements. In this context, indicator-displacement assay is a viable strategy for developing optical chemosensors with synthetic receptors. Such approach may be used to overcome the limits of sensing molecules and to widen the range of detectable compounds. In this paper, it is shown that proper blends of porphyrins and Lewis acid-base indicators can give rise to sensitive units whose properties exceed those of single components. (C) 2011 Published by Elsevier Ltd.