Concave-Tip Optical Fiber Apta-Biosensor Based on Localized Surface Plasmon Resonance for the Detection of Dopamine

This paper presents an enhanced concave tip optical fiber (CTOF) probe for dopamine (DA) detection based on localized surface plasmon resonance (LSPR) and DNA aptamers as sensing elements. The CTOF probe was fabricated using chemical etching and optimized for the confinement factor to improve the refractive index (RI) sensitivity by enhancing the LSPR field. The RI sensitivity of the LSPR-CTOF sensor, measured in the range of 1.3332-1.3604 RIU, was obtained at 1716 nm/RIU, demonstrating a 323.9% increase compared to the conventional flat tip fiber (FTF) structure. Fiber optic sensing probes were created by immobilizing the Au nanoparticles (AuNPs) and specific DNA aptamers on the tip of the fiber. The DA sensitivity of the sensor was obtained at 1.78 nm/log(M) across a wide concentration range of 100 fM-1mM. Additionally, the limit of detection and quantification were achieved at 2.5 fM and 16.3 fM, respectively. The selectivity of the sensor was evaluated using ascorbic acid and epinephrine. Moreover, repeatability and stability were studied in detail. These findings show that these Apta-biosensors based on LSPR are good candidates for in-vivo DA detection.