K. Li et al. [105], who developed a reversible optical fiber biosensor for the detection of a cancer biomarker (alpha-fetoprotein) in serum, also studied the relationship between the dimensions of the fiber and the Au NPs: their calculations indicated that, when using an unbent fiber, the sensitivity of the sensor could be enhanced by decreasing the diameter of the fiber or by increasing the size of the Au NPs. The gene discussed is AFP; the disease is cancer.