We measured the elongation rate of PI3K-SH3 fibrils through immobilization of fibrils on a QCM sensor and subsequent incubation with monomer solution . To immobilize the fibrils on the sensor, chemical modification is necessary . We pelleted the fibrils, washed and resuspended them in 10 mM HCl twice, before mixing at a final concentration of 50 µM in buffer (10 mM HCl) with EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) (1M) and cystamine hydrochloride (0.5mg/ml). After pelleting and washing the chemically modified fibrils, we sonicated them in an Eppendorf tube in a volume of ca. 500 µl with a Bandelin Sonoplus using a MS72 probe (10% amplitude, 15 s, 1 s "on", 2 s "off"). We incubated gold sensors (Biolin Scientific, Gothenburg, Sweden) with the above-mentioned solution overnight in a 100% humidity environment. The measurements were performed with a QSense Pro QCM-D instrument (Biolin Scientific, Gothenburg, Sweden) by measuring the elongation rate as change in resonant frequency over time.