High Surface Area Silica Particles as a New Vehicle for Ligand Immobilization on the Quartz Crystal Microbalance

This paper describes a new strategy for the immobilization of ligands on the surface of a quartz crystal microbalance for the purpose of producing piezoelectric sensors for selective detection of heavy metals in solution. Immobilization is achieved by reacting the ligand of choice with the interfacial Si-OH groups of micron-sized, porous, high surface area silica particles and then anchoring a monolayer of these particles onto the surface of the QCM. The particles thus act as the vehicle by which ligand immobilization is achieved. Detection of the metal occurs when it binds to the ligand, producing a mass change of the QCM/particle layer composite resonator. The method is demonstrated by detection of UO22+ with a phthalamic acid derivative immobilized on 3 μm diameter Hypersil silica particles. The mass gain of the particle layer as a function of the concentration of UO22+ (in the range 1-10 μM) constitutes an adsorption isotherm, from which a binding constant for the reaction of the immobilized ligand with UO22+ of 2 x 105 M-1 is calculated.