3-(4-Aminophenyl)-1,5-diphenylpent-2-ene-1,5-dione (PDO) is a colorimetric sensor of Lewis acid cations that has been covalently attached to a poly(ethylene glycol) (PEG) scaffold. The resulting PDO-PEG is soluble in water and other organic solvents and acts as a colorimetric sensor of Lewis acid cations by undergoing cyclization into the triarylpyrylium form. In water, PDO-PEG also undergoes the colorimetric change in the presence of Brönsted acids, which may limit its usefulness. This modified PEG is recoverable by precipitation from cold ethanol and reusable after reopening of the triarylpyrylium heterocycle to the active pentenedione form. The testing-recovery-reuse cycle has been performed five times without noticeable differences in the response. In contrast to PDO-PEG, PDO on its own is insoluble in water and remains completely soluble in ethanol. This solubility behavior of PDO makes the molecule unsuitable for use as a reusable and recoverable sensor.