Development of label-free plasmonic Au-TiO2 thin film immunosensor devices

This work reports on the development of a label-free immunosensor technology, based on nanoplasmonic Au-
TiO2 thin films. The Au-TiO2 thin films were prepared by cost-effective reactive DC magnetron sputtering,
followed by a thermal annealing procedure. The latter promoted the growth of the Au nanoparticles throughout
the TiO2 matrix and induced some morphological changes, which are the base for the immunosensor device
functionality. A posterior plasma etching treatment was required to partially expose the nanoparticles to the
biological environment. It gave rise to a 6-fold increase of the total area of gold exposed, allowing further
possibilities for the sensor sensitivity enhancement. Experimental results demonstrated the successful functionalization
of the films' surface with antibodies, with the immobilization occurring preferentially in the exposed
nanoparticles and negligibly on the TiO2 matrix. Antibody adsorption surface coverage studies revealed antibody
low affinity to the film's surface. Nevertheless, immunoassay development experiments showed a strong and
active immobilized antibody monolayer at an optimized antibody concentration. This allowed a 236 signal-tonoise-
ratio in a confocal microscope, using mouse IgG and 100 ng/ml of Fab-specific anti-mouse IgG-FITC
conjugated. Label-free detection of the optimized antibody monolayer on Au-TiO2 thin films was also tested,
revealing an expected redshift in the LSPR band, which demonstrates the suitability for the development of costeffective,
label-free LSPR based immunosensor devices.