Exploring the synergy of radiative coupling and substrate undercut in arrayed gold nanodisks for economical, ultra-sensitive label-free biosensing

Plasmonic nano-aperture label-free imaging of single small extracellular vesicles for cancer detection

BACKGROUND

Small extracellular vesicle (sEV) analysis can potentially improve cancer detection and diagnostics. However, this potential has been constrained by insufficient sensitivity, dynamic range, and the need for complex labeling.

METHODS

In this study, we demonstrate the combination of PANORAMA and fluorescence imaging for single sEV analysis. The co-acquisition of PANORAMA and fluorescence images enables label-free visualization, enumeration, size determination, and enables detection of cargo microRNAs (miRs).

RESULTS

An increased sEV count is observed in human plasma samples from patients with cancer, regardless of cancer type. The cargo miR-21 provides molecular specificity within the same sEV population at the single unit level, which pinpoints the sEVs subset of cancer origin. Using cancer cells-implanted animals, cancer-specific sEVs from 20 µl of plasma can be detected before tumors were palpable. The level plateaus between 5-15 absolute sEV count (ASC) per µl with tumors ≥8 mm3. In healthy human individuals (N = 106), the levels are on average 1.5 ASC/µl (+/- 0.95) without miR-21 expression. However, for stage I-III cancer patients (N = 205), nearly all (204 out of 205) have levels exceeding 3.5 ASC/µl with an average of 12.2 ASC/µl (±9.6), and a variable proportion of miR-21 labeling among different tumor types with 100% cancer specificity. Using a threshold of 3.5 ASC/µl to test a separate sample set in a blinded fashion yields accurate classification of healthy individuals from cancer patients.

CONCLUSIONS

Our techniques and findings can impact the understanding of cancer biology and the development of new cancer detection and diagnostic technologies.

Single-Exosome Counting and 3D, Subdiffraction Limit Localization Using Dynamic Plasmonic Nanoaperture Label-Free Imaging

Blood-circulating exosomes as a disease biomarker have great potential in clinical applications as they contain molecular information about their parental cells. However, label-free characterization of exosomes is challenging due to their small size. Without labeling, exosomes are virtually indistinguishable from other entities of similar size. Over recent years, several techniques have been developed to overcome the existing challenges. This paper demonstrates a new label-free approach based on dynamic PlAsmonic NanO-apeRture lAbel-free iMAging (D-PANORAMA), a bright-field technique implemented on arrayed gold nanodisks on invisible substrates (AGNIS). PANORAMA provides high surface sensitivity and has been shown to count single 25 nm polystyrene beads (PSB) previously. Herein, we show that using the dynamic imaging mode, D-PANORAMA can yield 3-dimensional, sub-diffraction limited localization of individual 25 nm beads. Furthermore, we demonstrate D-PANORAMA's capability to size, count, and localize the 3-dimensional, sub-diffraction limited position of individual exosomes as they bind to the AGNIS surface. We emphasize the importance of both the in-plane and out-of-plane localization, which exploit the synergy of 2-dimensional imaging and the intensity contrast.