Black phosphorus thin film integrated long-period fiber grating for highly refractive index and biomolecules detection

Abstract We have developed a sensing platform using a long-period fiber grating (LPFG) integrated black phosphorus (BP) thin film from the numerical simulation analysis and experimental process verification. Due to the high optical absorption of BP, the attenuated depth of the cladding mode in the BP coated LPFG (named BP-LPFG) sensor can be varied by the change of external environment. Benefited from the BP film, the sensing system shows a superior enhancement in the refractive index (RI) detection compared to the use of bare LPFG. The sensitivity can reach 122.1 dB/RIU, 139.5 dB/RIU, and 931.9 dB/RIU in the RI regions of 1.33–1.38, 1.39–1.44, and near 1.455, respectively. Moreover, this sensing system has been applied to implement the highly sensitive and label-free detection for the bovine hemoglobin (BHb) molecules, with a sensitivity of 5.6 dB/(mg/mL) and a detection limit of 0.05 mg/mL achieved. The detection limit is 2600 times lower than the hemoglobin threshold for the confirmation of men’s anemia illness, defined by the World Health Organization (WHO). This newly sensing platform is promising in the early clinical diagnose for anemia illness.