Analytical methods for the detection of organophosphates (OPs) are of interest on the basis that many nerve agents possess the basic OP structure (Figure 1). In this work we have used UV/vis absorption spectroscopy to examine the interaction of selected OPs with Zn(II), Fe(III) and Co(II) tetraphenyl porphines, three metalloporphyrins that are typically used as surface substrates for array-based optical sensors. The non-polarizable solvent cyclohexane was employed. Shifting patterns of the Soret band for Zn(II) tetraphenyl porphine (ZnTPP) as a function of ligand concentration, molecular size and thermodynamic binding properties for a homologous series of OP ligands are presented. Based on our results for ZnTPP, we hypothesize that OP size along with steric factors play a role in detection and sensitivity, where changes to the spectral band constitute the signal of interest. These aspects must be a consideration in the design of any metalloporphyrin-based sensor for OP detection.

Figure 1. General OP structure