Label-free DNA biosensing by topological light confinement

Abstract

Large-area and transparent all-dielectric metasurfaces sustaining photonic bound states in the continuum (BICs) provide a set of fundamental advantages for ultrasensitive biosensing. BICs bridge the gap of large effective mode volume with large experimental quality factor. Relying on the transduction mechanism of reactive sensing principle, herein, we first numerically study the potential of subwavelength confinement driven by topological decoupling from free space radiation for BIC-based biosensing. Then, we experimentally combine this capability with minimal and low-cost optical setup, applying the devised quasi-BIC resonator for PNA/DNA selective biosensing with real-time monitoring of the binding event. A sensitivity of 20 molecules per micron squared is achieved, i.e. ≃0.01 pg. Further enhancement can easily be envisaged, pointing out the possibility of single-molecule regime. This work aims at a precise and ultrasensitive approach for developing low-cost point-of-care tools suitable for routine disease prescreening analyses in laboratory, also adaptable to industrial production control.

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

“…In a similar approach, a SOI metasurface of titled nanoellipsoids functionalized for the detection of the biotoxin microcystin-LR (MC-LR) yielded a bulk sensitivity S = 788 nm/RIU, measured Q ∼ 170 (FoM∼ 100) and a very low detection limit for MC-LC of 0.002 ng/mL 91 . Label-free biosensing of DNA was demonstrated by functionalizing an A-BIC-SiN metasurface, detecting a concentration of 20 molecules/µm 2 paving the way for single-molecule regime 92 . Moreover, Wang et al 93 introduced a new type of Si-on-glass qBIC metasurface composed of asymmetric crescent-shapes metaatoms, experimentally measuring a bulk sensitivity of 326 nm/RIU for a Q ∼ 120, as well as biomolecular layer sensing of streptavidin at sub-nM concentrations after biotin functionalization of the metasurface.…”

“…91 Label-free biosensing of DNA was demonstrated by functionalizing an A-BIC-SiN metasurface, detecting a concentration of 20 mol μm −2 paving the way for a single-molecule regime. 92 Moreover, Wang et al 93 introduced a new type of Si-on-glass qBIC metasurface composed of asymmetric crescent-shapes meta-atoms, experimentally measuring a bulk sensitivity of 326 nm RIU −1 for a Q ∼ 120, as well as biomolecular layer sensing of streptavidin at sub-nM concentrations after biotin functionalization of the metasurface. In another recent experimental study of an asymmetric Si nanopillar qBIC metasurface bulk sensitivity and FoM values of 608 nm RIU −1 and 46 were demonstrated.…”

Label-Free Bound-States-in-the-Continuum Biosensors

“…All-dielectric structures that support BICs have been widely used in the design of high- Q biosensors based on their advantages of low loss and high functionality. In this section, some all-dielectric BICs biosensors are introduced, including BICs gratings [ 57 , 58 , 59 , 60 , 61 , 62 , 63 ], symmetry-broken [ 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 ] and topological-boundary-states-governed [ 78 ] BICs metasurfaces, and BICs PhCSs [ 56 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ].…”

“…Two quasi-BIC modes excited by Si 3 N 4 PhCSs are used respectively for the laser input amplification and the RI probe to achieve 2D RI imaging for PC3 cells. Furthermore, Figure 5 b shows the Si 3 N 4 PhCS proposed by Zito et al [ 83 ] for DNA biodetection. A FW-BIC can be excited when the light source is incident at a small angle, and the FW-BIC could be utilized for the real-time specific biodetection of DNA.…”

“… BIC biosensors composed of all-dielectric PhCSs. ( a ) A Si 3 N 4 PhCS utilized to recognize the interaction between tumor suppressor protein p53 and cancer protein MDM2 (reprinted with permission from [ 80 ], ©2018, Silvia Romano et al, CC BY license); ( b ) accidental BICs in PhCS for DNA detection (reprinted with permission from [ 83 ], ©2021, Gianluigi Zito et al, CC BY license). …”