Ultrathin-film oscillator biosensors excited by ultrafast light pulses

Novel thin-film oscillator biosensors are developed using picosecond ultrasound method. 100-nm silicon-nitride thin films and 16-nm Pt thin films are used, and ultrashort light pulses are focused on their surfaces to excite the through-thickness resonance vibrations, which are detected by the delayed probe-light pulses using the optoelastic effect. Their fundamental resonance frequencies are 45 and 132 GHz, corresponding to theoretical mass sensitivities of 5.0 × 10−5 and 2.2 × 10−5 pg/cm2/Hz, respectively. These thin-film biosensors are used for detecting human immunoglobulin G (hIgG) with staphylococcus aureus protein A nonspecifically immobilized on the film surfaces. Injection of a 5 nM analyte caused 2% decrease in the resonance frequency.