Optical fiber-assisted enzymatic recombinase amplification: A label-free biosensing platform for ultrasensitive DNA...

Enzymatic recombinase amplification (ERA) allows rapid nucleic acid detection under isothermal conditions but typically requires fluorescence labeling and specialized equipment. Here, a label-free, optical fiber-assisted ERA(FaERA) platform that integrates a tapered microfiber (TMF) evanescent field sensor modified with a polydopamine (PDA) nanointerface is proposed. The PDA coating enables efficient immobilization of primers, which initiate the amplification process upon recognition of the target DNA. Amplification induces refractive index changes at the fiber surface, resulting in a measurable spectral shift. The centrosomal protein 55(CEP55) gene, which is associated with various cancers, was selected as a representative target. Successful amplification was achieved over a concentration range from 1 aM to 10⁴ aM within 15 min, with a detection limit of 1 aM. The system can distinguish between target and non-target samples even in the presence of potential interfering substances. FaERA simplifies detection by eliminating fluorescence, and its fiber-based design enables remote signal transmission, enhancing flexibility for decentralized testing. This work demonstrates the feasibility of integrating biosensing with ERA for real-time, label-free nucleic acid detection, offering a promising approach for point-of-care and field diagnostics.