Multiresonant plasmonic nanostructure for ultrasensitive fluorescence biosensing

Abstract

A novel metallic nanostructure for efficient plasmon-enhanced fluorescence readout of biomolecular binding events on the surface of a solid sensor chip is reported. It is based on gold multiperiod plasmonic grating (MPG) that supports spectrally narrow plasmonic resonances centered at multiple distinct wavelengths. They originate from diffraction coupling to propagating surface plasmons (SPs) forming a delocalized plasmonic hotspot associated with enhanced electromagnetic field intensity and local density of optical states at its surface. The supported SP resonances are tailored to couple with the excitation and emission transitions of fluorophores that are conjugated with the biomolecules and serve as labels. By the simultaneous coupling at both excitation and emission wavelengths, detected fluorescence intensity is enhanced by the factor of 300 at the MPG surface, which when applied for the readout of fluorescence immunoassays translates to a limit of detection of 6 fM within detection time of 20 min. The proposed approach is attractive for parallel monitoring of kinetics of surface reactions in microarray format arranged on a macroscopic footprint. The readout by epi-fluorescence geometry (that inherently relies on low numerical aperture optics for the imaging of the arrays) can particularly take advantage of the reported MPG. In addition, the proposed MPG nanostructure can be prepared in scaled up means by UV-nanoimprint lithography for future practical applications.

Responsive Hydrogel Binding Matrix for Dual Signal Amplification in Fluorescence Affinity Biosensors and Peptide Microarrays

“…The pNIPAAm-based thermoresponsive biointerface platform was employed on a sensor chip for surface plasmon-enhanced fluorescence measurements, which in conjunction with specific metallic nanostructures can provide optical enhancement in the acquired fluorescent signal by a factor of 300. , Compared to our previous studies with large-molecular-weight antibody ligands, post-modification with low-molecular-weight peptides offers the advantage of preserving the thermoresponsive properties of pNIPAAm-based polymer networks, and it translates into a pronounced increase in the fluorescence intensity by a large factor of 5. The combination of optical- and analyte-compaction-based amplification holds the potential to benefit from both the high binding capacity of the swollen HG binding matrix and probing with the tightly confined electromagnetic field associated with the excitation of SPs on metallic thin films and nanostructures.…”

Plasmon–Exciton Coupling Effect in Nanostructured Arrays for Optical Signal Amplification and SARS-CoV-2 DNA Sensing

“…The emission quenching that typically occurs when emitters are in close or direct contact with metals is prevented here since the dyes are sandwiched between the high electric fields generated by the adjacent walls and the bottom of the nanoslit . There are other approaches that attempt to provide optical enhancement due to plasmon–exciton coupling in nanostructures, such as core–shell nanoparticles or nanocone cavities. − Nevertheless, there is a need to have a better understanding of the underlying reaction mechanism of different NS designs, thus improving the optical signal enhancement. To address the need, we investigated the impact of excitation and emission wavelengths of fluorophores with excited plasmons in the nanoslit array.…”

State-of-the-Art Optical Devices for Biomedical Sensing Applications—A Review

“…The incident EM field is also concentrated around the nanostructure by LSPR. Plasmon-enhanced fluorescence (PEF) [68,69], surface-enhanced Raman scattering (SERS) [70,71], and surface-enhanced infrared absorption spectroscopy (SEIAS) [72,73] are all examples of how the local EM field can affect optical effects like fluorescence, Raman scattering, and infrared absorption. The LSPR-related EM field stretches into the ambient medium (usually 30 nm) and deteriorates exponentially for a dipole.…”