Detection of trace tumor markers in blood/serum is essential for the early screening and prognosis of cancer diseases, which requires high sensitivity and specificity of the assays and biosensors. A variety of label-free optical fiber-based biosensors has been developed and yielded great opportunities for Point-of-Care Testing (POCT) of cancer biomarkers. The fiber biosensor, however, suffers from a compromise between the responsivity and stability of the sensing signal, which would deteriorate the sensing performance. In addition, the sophistication of sensor preparation hinders the reproduction and scale-up fabrication. To address these issues, in this study, a straightforward lasso-shaped fiber laser biosensor was proposed for the specific determination of carcinoembryonic antigen (CEA)-related cell adhesion molecules 5 (CEACAM5) protein in serum. Due to the ultra-narrow linewidth of the laser, a very small variation of lasing signal caused by biomolecular bonding can be clearly distinguished via high-resolution spectral analysis. The limit of detection (LOD) of the proposed biosensor could reach 9.6 ng/mL according to the buffer test. The sensing capability was further validated by a human serum-based cancer diagnosis trial, enabling great potential for clinical use. The high reproduction of fabrication allowed the mass production of the sensor and extended its utility to a broader biosensing field.
Improving sensitivity is critical for the higher-order harmonic fiber Bragg grating sensors. To this aim, in this work, we have successfully introduced the phase-shift into the third harmonic fiber Bragg grating for tailoring a double-dip spectrum with a high finesse notch. The dual dips showed reversed responses for the intensity regarding the change of the temperature or axial strain, enabling a highly sensitive measuring regime using the intensity contrast between the two dips. Deduced from the sinusoidal responding curves, the highest temperature and the axial strain sensitivity could reach 0.964 dB/°C, and 0.0257 dB/
μ
ε
, three-fold times the other intensity-based fiber sensors. This work may promote the higher-order harmonic gratings into applications for enriching wavelength utilization.
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