Ultrahigh-Sensitivity Detection of TNF-α Based on U-Shape Single Mode-Tapered Four Core-Single Mode Fiber Biosensor

In this paper, a high sensitivity U-shape single mode- tapered four core-single mode (STFS) optical fiber biosensor is proposed and investigated for tumor necrosis factor-alpha (TNF-α) detection in both Phosphate Buffered Saline (1x) (PBS) and diluted serum. The surface of U-shape STFS biosensor is immobilized with TNF-α antibody (10 μg/mL), which will specifically bind with target TNF-α. The results demonstrate a Hill curve relationship between wavelength shift and TNF-α concentration (from 10 ¹ to 10 ⁴ pg/mL diluted in PBS). The lowest concentration of TNF-α detected in the experiment is 10 pg/mL, with an average wavelength shift of 0.389 nm. The average wavelength fluctuation of the sensor in PBS is 0.099 nm, and the corresponding limit of detection (LOD) is 4.35 pg/mL. Results for the detection of TNF-α in blood sample is also presented. It is found that the deviation of detected TNF-α concentrations (13.00–15.03 pg/mL, calibrated by measured results in PBS) is -0.7%~14.7% compared to standard TNF-α concentration of 13.09 pg/mL in blood. This biosensor, with its simple structure and high sensitivity, has the potential to serve as a valuable reference in disease diagnosis and medical drug usage, offering promising application prospects.