Ultrahigh sensitivity fiber laser integrated biosensor for TNF-α detection in human blood sample

A label-free fiber biosensor based on Erbium-doped fiber laser (EDFL) integrated singlemode – tapered quad-core -singlemode fiber (STQS) structure is proposed and demonstrated for the detection of TNF-α. An excessive level of TNF-α in the body is an indicator for a number of serious health conditions. The sensor head structure is constructed by splicing and tapering a short section quad-core fiber (length 20 mm, diameter 5.45 µm) between two single-mode fibers. Antibodies of tumor necrosis factor-α (TNF-α) are then immobilized on the surface of the STQS structure to realize specifical binding with TNF-α. An EDFL is integrated to the sensor system to improve sensor resolution due to its high Quality (Q) factor of laser. Experimental result shows that the EDFL integrated STQS biosensor can detect TNF-α in solution with a concentration as low as 10 pg/mL (diluted by phosphate buffered saline) with an average wavelength shift of 0.59 nm. Human blood samples from three patients (TNF-α concentrations vary from 10 to 30 pg/mL) have been tested using the developed biosensor and the results agree well with standard method of flow immunofluorescence luminescence assay used in a hospital setting.