MicroRNAs (miRNAs) in exosomes can be transferred from parental cells to recipient cells by trafficking exosomes, and they are effective in regulating the gene expression of the recipient cells. Therefore, exosomal miRNAs play a vital role in cancer biology and could be potential biomarkers for cancer diagnosis and therapeutic responses. However, accurate detection of exosomal miRNAs is still challenging due to the low abundance of any given miRNA in exosomes. Herein, a surface-enhanced Raman scattering (SERS)-based sensor was developed for the quantitative determination of let-7a miRNAs in MCF-7 cell-derived exosomes (MCF-7 exosomes) using a close-packed and ordered Au octahedral array as a sensing platform. Au octahedra in the array uniformly stand on their triangular face. This kind of orientation produces “hot surfaces” rather than “hot spots” and greatly improves the detection sensitivity and uniformity. Let-7a detection with single-base specificity was thus achieved from the SERS intensity change induced by the structural switch of the probing DNA from a hairpin to a duplex in the presence of the target. The sensor showed a broad linear range (10 aM to 10 nM) and a low detection limit (5.3 aM) without using any signal amplification strategy. Moreover, this sensor could accurately detect target let-7a in MCF-7 exosomes and further value the impact of drug treatment on exosomal let-7a expression, indicating promising applications of the developed sensor for cancer diagnostics and therapy.

The development of an effective method for identifying severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) via direct viral protein detection is significant but challenging in combatting the COVID-19 epidemic. As a promising approach for direct detection, viral protein detection using surface-enhanced Raman scattering (SERS) is limited by the larger viral protein size compared to the effective electromagnetic field (E-field) range because only the analyte remaining within the E-field can achieve high detection sensitivity. In this study, we designed and fabricated a novel long-range SERS (LR-SERS) substrate with an Au nanoplate film/MgF 2 /Au mirror/glass configuration to boost the LR-SERS resulting from the extended E-field. On applying the LR-SERS to detect the SARS-CoV-2 spike protein (S protein), reagent-free detection achieved a low detection limit of 9.8 × 10 −11 g mL −1 and clear discrimination from the SARS-CoV S protein. The developed technique also allows testing of the S protein in saliva with 98% sensitivity and 100% specificity.

A fundamental challenge, particularly, in surfaceenhanced Raman scattering (SERS) analysis is the detection of analytes that are distant from the sensing surface. To tackle this challenge, we herein report a long-range SERS (LR-SERS) substrate supporting an extension of electric field afforded by long-range surface plasmon resonance (LRSPR) excited in symmetrical dielectric environments. The LR-SERS substrate has a sandwich configuration with a triangle-shaped gold nanohole array embedded between two dielectrics with similar refractive indices (i.e., MgF 2 and water). The finite-difference time-domain simulation was applied to guide the design of the LR-SERS substrate, which was engineered to have a wavelength-matched LRSPR with 785 nm excitation. The simulations predict that the LR-SERS substrate exhibits great SERS enhancement at distances of more than 10 nm beyond its top surface, and the enhancement factor (E F ) has been improved by three orders of magnitude on LR-SERS substrates compared to that on conventional substrates. The experimental results show good agreement with the simulations, an E F of 4.1 × 10 5 remains available at 22 nm above the LR-SERS substrate surface. The LR-SERS substrate was further applied as a sensing platform to detect microRNA (miRNA) let-7a coupled with a hybridization chain reaction (HCR) strategy. The developed sensor displays a wide linear range from 10 aM to 1 nM and an ultralow detection limit of 8.5 aM, making it the most sensitive among the current detection strategies for miRNAs based on the SERS−HCR combination to the best of our knowledge.

Detection of methyltransferase (MTase) activity is of great significance in methylation-related disease diagnosis and drug screening. Herein, we present a dual-amplification sensing strategy that is assisted by plasmonically enhanced Raman intensity at engineered nanoholes array, along with signal amplification by the hybridization chain reaction (HCR) for the ultrasensitive detection of M.SssI MTase activity and inhibitor screening. An engineered surface-enhanced Raman scattering (SERS) substrate, namely, a structured nanoholes array (NHA) with wavelengthmatched surface plasmon resonance (SPR) at the wavelength of laser excitation (785 nm), was rationally designed through finitedifference time-domain (FDTD) simulations, precisely fabricated through master-assisted replication, and then used as a sensing platform. Uniform and intense SERS signals were achieved by turning on the plasmonic enhancement under the excitation of SPR. Probe DNA was designed to hybridize with target DNA (a BRCA1 gene fragment), and the formed dsDNA with the recognition site of M.SssI was assembled on the NHA. In the presence of M.SssI, the HCR process was triggered upon adding DNAs labeled with the Raman reporter Cy5, leading to an amplified SERS signal of Cy5. The intensity of Cy5 increases with increasing M.SssI activity, which establishes the basis of the assay for M.SssI. The developed assay displays an ultrasensitivity that has a broad linear range (0.002−200 U/mL) and a low detection limit (2 × 10 −4 U/mL), which is superior to that of the reported SERS-based detection methods. Moreover, it can selectively detect M.SssI in human serum samples and evaluate the efficiency of M.SssI inhibitors.

The use of coral-shaped Au nanostructures as a heater to selectively induce apoptosis in photothermal therapy of cancer is reported.