Advanced DNA Detection via Multispectral Plasmonic Metasurfaces

Abstract

We propose and demonstrate a sensing platform based on plasmonic metasurfaces for the detection of very low concentrations of deoxyribo-nucleic acid (DNA) fragments. The platform relies on surface-enhanced infrared absorption spectroscopy, implemented via a multispectral metasurface. Specifically, different regions (“pixels”) are engineered so as to separately cover the medium-infrared range of the electromagnetic spectrum extending from the functional-groups to the fingerprint region of a single analyte. In conjunction with a suitable bio-functionalization, this enables univocal and label-free recognition of specific molecules. For experimental validation, we fabricate a large-area gold metasurface on a silicon chip, and functionalize it with a recognition layer of peptide nucleic acid (PNA). Our experimental results indicate the possibility to detect complementary DNA fragments in concentrations as low as 50 fM, i.e., well below the value attained by standard methods, with additional advantages in terms of processing time, versatility and ease of implementation/operation.

Probing Denaturation of Protein A via Surface-Enhanced Infrared Absorption Spectroscopy

“…The basic geometry is schematized in Figure 1 a,b: we consider cross-shaped gold NAs (of thickness t = 50 nm, arm length L , and arm width W ) arranged on a 2-D periodic square grid (of period P ), laid on a silicon substrate, embedded in air. Such geometry has already been successfully utilized in previous studies [ 37 , 38 , 39 ], demonstrating very good performance in terms of field enhancement and robustness with respect to polarization. Assuming, for simplicity, infinite periodicity in the transverse plane and normally incident plane-wave illumination from the air region, we can reduce our study to a single 3-D unit-cell (shown in Figure 1 a), with the lateral walls terminated with periodic boundary conditions.…”

“…In a series of ongoing studies [ 37 , 38 , 39 ], we have focused on the optimized design and fabrication of plasmonic MSs for SEIRA spectroscopy. For the design, we have developed some accurate and effective forward- and inverse-modeling strategies for selecting the NA shape and spatial arrangement, aimed at maximizing the detection sensitivity even for extremely small molecules.…”

“…For the design, we have developed some accurate and effective forward- and inverse-modeling strategies for selecting the NA shape and spatial arrangement, aimed at maximizing the detection sensitivity even for extremely small molecules. For the fabrication, we have developed a manufacturing process that is reproducible, highly homogeneous (<10% variability), versatile, fast, and provides reusable devices [ 37 , 38 , 39 ]. Specifically, our fabricated sensors were able to determine amounts of immobilized small molecules (molecular weight (MW) < 300 g/mol) equal to 0.7 fmoles, with a SEIRA EF of [ 37 ].…”

“…In this case, we adopted an innovative design based on a multiresonant MS made of different pixels (covering an area of 500 × 500 μm 2 ) each one designed to match a specific vibrational band, so that the whole MS could recognize different vibrational bands occurring within different parts of the MIR spectrum, from the region of functional groups to that of the fingerprint. By exploiting a similar approach, together with a specific bio-functionalization, we were also able to attain univocal and label-free recognition of complementary deoxyribonucleic acid (DNA) fragments in concentrations as low as 50 fM, i.e., well below the value attained by standard methods, with additional advantages in terms of processing time [ 39 ].…”

H3 (Hydrogel‐Based, High‐Sensitivity, Hybrid) Plasmonic Transducers for Biomolecular Interactions Monitoring

“…All these transduction mechanisms are based on the localized surface plasmon resonance (LSPR) exhibited by noble‐metal NPs. [ 20,21 ] Refractometric biosensors exploit the LSPR shifts as a function of a target analyte when properly interacting with the biorecognition element adhered on the surface of the NPs; [ 22,23 ] Surface‐enhanced infrared absorption (SEIRA) and surface‐enhanced raman scattering (SERS) exploit the LSPR to enhance infrared and Raman signals of molecules onto plasmonic substrates; [ 24–26 ] Metal‐enhanced fluorescence (MEF), also referred to as plasmon‐enhanced fluorescence (PEF), exploit the LSPR to increase the signal intensity of fluorescent dyes, depending on the spectral overlapping between plasmonic absorption and fluorescent dye extinction/emission and their separation distance. [ 27–30 ] Moreover, the combination of plasmonic nanoparticles with polymers has been enabling novel functionalities and transduction mechanisms based on the different mechanical properties of flexible substrates.…”