Development of Non-Labeled QCM Biosensor for the Detection of <i>β</i>-Galactosidase: A Comparative Study of Gold and Polystyrene Nanoparticles

The performance of gold and polystyrene nanoparticles was investigated using quartz crystal microbalance (QCM) as sensor platform; β-Galactosidase antibody with corresponding antigen was utilized for the immunoreaction. The development of the immunosensor included: 1) formation of self assembled monolayers on quartz crystals; 2a) immobilization of p-aminothiophenol functionalized gold nanoparticles on carboxyl-terminated self assembled monolayer, or 2b) immobilization of polystyrene nanoparticles on crystals modified with p-aminothiophenol self assembled monolayer; 3) attachment of monoclonal anti β-Gal on nanoparticles; and 4) detection of target analyte. The nanoparticles used were synthesized in house and characterized by transmission electron microscopy and infrared spectroscopy. The results revealed that antibodies were strongly attached to functionalized gold nanoparticles; the weaker immobilization of antibodies to polystyrene nanoparticles provoked their detachment during antigen detection. When cross reactivity of polystyrene nanoparticles was checked using a different antigen (Brucella), displacement of antibody was not recorded, demonstrating specificity of the reaction. To the best of our knowledge this is the first direct comparison between behaviors of biosensors developed with two commonly used nanoparticles. The results showed that both nanoparticles produced biosensors capable to detect β-Gal. Nevertheless biosensors developed using polystyrene nanoparticles are simpler, cheaper and more eco-friendly than those developed using gold nanoparticles.