A new concept in chemical sensing has been introduced that uses change
s in density of a cross-linked polymer to physically signal changes in
solution composition. Prototype systems that have now been developed
are based on Amberlite IRA 400 (Cl), where anion exchange provides a d
riving force for the resin's emergence from, and submergence into, wat
er due to changes in bead density. The potential utility of such senso
rs is briefly described.