Ultrahigh Sensitivity Label-Free Microfiber Biosensor for Rapid Detection of C-Reactive Protein

C-reactive protein (CRP) is a rapidly rising protein in acute phase reactions such as inflammation and infection, which is commonly used in clinical diagnosis and monitoring of inflammatory diseases. This study tackles the critical issue by developing a single mode-tapered multimode-single mode (STMS) microfiber biosensor for CRP detection. The tapered multimode fiber significantly enhances the evanescent field. By immobilizing antibodies onto its surface, the sensor achieves high sensitivity and selective detection of CRP. Furthermore, robust sensor encapsulation combined with bovine serum albumin (BSA) blocking ensures excellent stability and minimizes nonspecific binding. The experimental data demonstrate that the developed STMS microfiber biosensor exhibits excellent stability (0.0411 nm). When the CRP antibodies were functionalized with $50~\mu $ g/mL, the limit of detection (LoD) can achieve as reduced as 0.1 pg/mL within 20 min. Furthermore, the proposed STMS microfiber biosensor also has good specificity and reusability, and when the proposed STMS microfiber biosensor was immersed in a mixture with high-concentration solutions of other proteins (IL-6, TNF- $\alpha $ , BSA, and EGF), the target CRP can still be detected. In addition, if the proposed STMS microfiber biosensor is stored in a refrigerator at $4~^{\circ } $ C, the detection of CRP is almost unaffected within five days. These results suggest that the STMS microfiber biosensor proposed in this study has significant application prospects for CRP detection.