Porous Gold Nanocubes Particle-Sensitized U-Shaped Fiber-Optic Surface Plasmon Resonance Sensor for Ultra-Sensitive Detection of Virus RNA

A novel sensitized U-shaped fiber-optic sensor based on the localized surface plasmon resonance (LSPR) principle was proposed to detect virus RNA, especially COVID-19 RNA sequences. To accomplish ultrahigh sensitivity for detecting COVID-19 RNA sequences, a novel porous gold nanocube particle was proposed for the first time to sensitize a U-shaped fiber made of multimode fiber (MMF)-no-corefiber (NCF)-MMF. The sensor first coats a gold film on the surface of the fiber to excite surface plasmon resonance (SPR). Then, it coats a porous gold nanocube particle on the surface of the gold nanofilm to excite the LSPR, which improves the sensitivity of the sensor. Gold nanoparticles can form tip structures on the sensor surface, causing a hot spot effect. This increases the sensitivity of the fiber-optic sensor compared to the conventional U-shaped fiber-optic sensor without sensitization treatment and the U-shaped fiber-optic sensor combined with spherical gold nanoparticles for sensitization. The experimental results showed that the sensor’s refractive index (RI) sensitivity reached 3893 nm/RIU. The reverse-transcribed complementary DNA (cDNA) of one piece of COVID-19 RNA was used as the sample to be detected in this article to demonstrate the performance of the sensor. The specific detection of cDNA was achieved by chemical modification of the sensor’s surface and DNA hybridization technology. The sensor’s sensitivity is 0.41 nm/nM, significantly improving over conventional fiber-optic biosensors regarding RNA concentration detection sensitivity. In the experimental process, the sensor demonstrated high sensitivity, rapid response time, high stability, compact size, and portability, all crucial for viral RNA detection and other biomass detection and measurement.