Label-free and in situ detection of N -glycan expression on surface of cells is vital for understanding the progression of cancer. Herein, cytosensing based on U-shaped fiber optic local surface plasmon resonance (LSPR) was developed for cancer cell detection and N -glycan evaluation on cell surface. The U-shaped fiber optic LSPR has high refractive index sensitivity (RIS). Therefore, U-shaped fiber optic LSPR cytosensing afforded ultrasensitivity for cancer cell detection with the limit of detection (LOD) of 30 cells/mL and good linearity in a wide range of 1×10 2 -1×10 6 cells/mL under the optimal conditions of modified AuNPs size and Con A concentration. The U-shaped fiber optic LSPR cytosensing shows more than 29 times lower limit of detection than the straight ones. More importantly, the prepared U-shaped cytosensing was applied to evaluate the N -glycan expression level on the surface of cancer cells under different concentration external stimuli of inhibitor tunicamycin (TM). Noticeably, U-shaped fiber optic LSPR cytosensing showed an acceptable reproducibility, satisfactory anti-interference and good selectivity, and was also applied in the assessment of N -glycan expression on surface of six kinds of cell lines. Therefore, the U-shaped fiber optic LSPR offers a feasible tool in biophysical research and clinical diagnosis for cancer.
For human health and environmental protection, the identification of heavy metal ions in seawater is of great importance. Here, we presented and demonstrated a surface plasmon resonance (SPR) sensor for plug-and-play type copper ion (Cu2+) detection based on a U-shaped optical fiber. The suggested sensor is made of a U-shaped multi-single–multi (MSM) mode optical fiber coating with a gold film, which can produce a stronger evanescent field and greatly enhance the sensing characteristic of the SPR sensor. The maximum refractive index (RI) sensitivity of 7045.61 nm/RIU can be obtained by optimizing the relevant parameters of the sensor through simulation and experiment. The functionalization of the sensor was realized by chitosan and synthetic Schiff base in a simple way. The specific complexation of Cu2+ by Schiff base induces an RI change on the sensor surface, achieving a sensitivity of −35.35 nm/lg(mg/L) in the concentration range of the 0.07–1 mg/L. The developed sensor probe is capable of detecting Cu2+ concentration as low as $4.61\times 10^{-4}$ mg/L. Additionally, the repeatability, stability, specificity, and response time have been assessed to demonstrate that the sensor has significant capacity for future use in metal ions detection.
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