Fiber Optic Sensor for HCG Detection

Fiber optic sensors can detect hCG by measuring changes in optical properties, using tapered fibers or photonic crystal fibers enhanced with nanoparticles or interferometric techniques.Tapered Optical Fiber BiosensorsTapered optical fibers decorated with gold nanoparticles (Au-NPs) are widely used for hCG detection. The fiber is stretched to a diameter of around 3–3.5 µm using a flame-brushing technique, creating a narrow waist where the evanescent field is amplified. Gold nanoparticles are deposited on the taper via photodeposition using a laser source (typically 1535–1550 nm). When hCG is present in a sample, it interacts with the nanoparticles, causing measurable changes in optical power or spectral shift. Detection ranges can cover 1 mIU/mL to 100,000 mIU/mL, with limits of detection as low as 0.03–0.04 mIU/mL in water or urine, demonstrating high sensitivity and specificity without requiring additional bioreceptors (antigens) for recognition .Photonic Crystal Fiber-Based Interferometric SensorsAnother approach uses photonic crystal fibers (PCF) integrated into a Mach-Zehnder interferometer (MZI). Sections of PCF are collapsed and spliced with single-mode fibers to create high-sensitivity regions. The presence of hCG in urine alters the refractive index and absorption, which changes the intensity and phase of the transmitted laser light. Sensitivity depends on the PCF length, with longer fibers (e.g., 1.5 cm) providing higher sensitivity. This method allows quantitative detection of pregnancy hormones and can be adapted for other biomedical assays .Advantages and ApplicationsHigh sensitivity and specificity: Both tapered fiber and PCF sensors can detect clinically relevant hCG concentrations.Rapid and label-free detection: Optical changes are measured directly without chemical labeling.Versatility: Can be applied to water, urine, or other biological fluids.Biomedical and industrial potential: Useful for early pregnancy tests, cancer biomarker detection, and research on hormone levels .SummaryFiber optic sensors detect hCG by exploiting optical interactions between the hormone and the sensor surface. Tapered fibers with gold nanoparticles amplify the evanescent field, while photonic crystal fibers use interferometry to detect refractive index changes. Both approaches provide highly sensitive, reproducible, and non-invasive detection, making them promising tools for clinical diagnostics and biomedical research .