Label-free tapered optical fiber plasmonic biosensor.

We designed and fabricated a novel label-free ultrasensitive tapered optical fiber (TOF) plasmonic biosensor that successfully detected a five panel of microRNAs with good selectivity. The biosensing platform integrates three different metallic nanoparticles: gold spherical nanoparticles (AuNPs), gold nanorods (AuNRs), and gold triangular nanoprisms (AuTNPs) laminated TOF to enhance the evanescent mode. The dip in the intensity profile of the transmission spectrum corresponded to the specific wavelength of the nanoparticle. The AuTNPs laminated TOF was found to exhibit the highest refractive index sensitivity and was therefore used to assay the panel of microRNAs. Single stranded DNA probes were self-assembled on the AuTNPs TOF plasmonic biosensors to achieve the highest sensitivity from the formation of hydrogen bonds between the ssDNAs and the target microRNAs. Experimentally, we observed that by measuring the spectral shifts, a limit of detection (LOD) between 103 aM and 261 aM for the panel of microRNAs can be achieved. Additionally, the ssDNA layer immobilized on the TOF plasmonic biosensor resulted in an extended dynamic range of 1 fM - 100 nM. In human serum solution, clinically relevant concentration of the panel of microRNAs were successfully detected with a LOD between 1.097 fM to 1.220 fM. This is the first report to demonstrate the applicability of our TOF plasmonic biosensor approach to detect a panel of microRNAs. This simple yet highly sensitive approach can provide a high-throughput and scalable sensor for detecting and quantifying large arrays of microRNAs, thereby expanding the applications of biosensors.