Spectral characteristics and interrogation of a fiber-optic ball resonator biosensor modulated by a tilted fiber Bragg grating

•We investigate a fiber-optic refractive index sensor made by a tip ball resonator modulated by a tilted fiber Bragg grating (BR/TFBG).•The BR/TFBG sensor achieves sensitivity up to 274.0 dB/RIU for intensity detection.•A spectral profile correlation method is proposed, achieving RI sensitivity of 154.67 nm/RIU.•The probe was biofunctionalized for demonstration of HER2 cancer biomarker in the range 0.5–128 ng/mL.•The BR/TFBG requires simple manufacturing, and improves the sensitivity and interrogation over stand-alone BR and TFBG sensors.