Infrared Plasmonic Biosensor with Tetrahedral DNA Nanostructure as Carriers for Label‐Free and Ultrasensitive Detection of miR‐155

MicroRNAs play an important role in early development, cell proliferation, apoptosis, and cell death, and are aberrantly expressed in many types of cancers. To understand their function and diagnose cancer at an early stage, it is crucial to quantitatively detect microRNA without invasive labels. Here, a plasmonic biosensor based on surface‐enhanced infrared absorption (SEIRA) for rapid, label‐free, and ultrasensitive detection of miR‐155 is reported. This technology leverages metamaterial perfect absorbers stimulating the SEIRA effect to provide up to 1000‐fold near‐field intensity enhancement over the microRNA fingerprint spectral bands. Additionally, it is discovered that the limit of detection (LOD) of the biosensor can be greatly improved by using tetrahedral DNA nanostructure (TDN) as carriers. By using near‐field enhancement of SEIRA and specific binding of TDN, the biosensor achieves label‐free detection of miR‐155 with a high sensitivity of 1.162% pm (−1) and an excellent LOD of 100 × 10(−15) m. The LOD is about 5000 times lower than that using DNA single strand as probes and about 100 times lower than that of the fluorescence detection method. This work can not only provide a powerful diagnosis tool for the microRNAs detection but also gain new insights into the field of label‐free and ultrasensitive SEIRA‐based biosensing.