Rapid response optical ion/gas sensors using dimer–monomer metalloporphyrin equilibrium in ultrathin polymeric films coated on waveguides

Optical sensors with rapid response times (1–2 s) toward solution phase chloride and gas phase amine species are described. The sensors are based on the incorporation of indium(III) octaethylporphyrin (In(III)[OEP]) within ultrathin polymeric films (<0.5 μm) deposited via spin coating on a planar fused silica waveguide. The In(III)[OEP] forms a hydroxide ion bridged dimer when anion sites in the form of a lipophilic borate derivative (i.e., potassium tetrakis([3,5-bis(trifluoromethyl)phenyl]borate (KTFPB)) are added to the plasticized films. Selective chloride or amine extraction into the films results in a change in the optical absorption spectrum of the metalloporphyrin owing to ligation of these species to the In(III) center, forcing the formation of monomeric In(III)[OEP] species. These ligation reactions are completely reversible. The use of the waveguide sensing configuration enables very fast response times without loss in sensitivity since the optical pathlength is significant (e.g., absorbance is enhanced about 20 times even when 0.3 μm thick film is employed). The fast response times of the sensors makes such devices potentially useful as detectors in flow-through analytical systems such as flow-injection analysis (FIA) or gas/liquid phase chromatography.