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Fabrication of Plasmonic nanoantennas based on DNA origami.

Exploiting the unique spatial addressability offered by DNA origami, we synthesize a variety of plasmonic nanoantenna metamolecules. Anisotropic nanostructures like Silver/Gold Nanostars, Silver/Gold Nanorods, Silver/Gold Nanobipyramids, etc. are employed for the formation of nanoantennas. Plasmonic hotspots are generated at precise positions in these gold and silver dimer nanoantennas to achieve several hundred folds of electromagnetic enhancement.

Single Molecule Fluorescence Enhancement

Plasmonic nanoantennas provide a viable platform for emission manipulation of quantum emitters through unprecedented control of light-matter interactions in the deep subwavelength regime, substantially improving the weal emitters quantum efficiency. Nanoantenna geometries are rationally designed to realize precise engineering of metal nanostructures and deterministic positioning of a single emitter specifically at the plasmonic hotspot. This thus generates huge fluorescence enhancement enabling application of these nanoantennas as highly sensitive biosensing platforms.

SERS-based label-free single molecule detection of clinically relevant biomolecules.

Single clinically relevant biomarkers are precisely placed in the hotspots engineered in the plasmonic nanoantennas. Intense field enhancement is generated in the plasmonic hotspots which enable SERS-based application of the structures for single molecule detection. This can pave the way for the fabrication of highly sensitive biosensors with significant improvements in detection limits.

Single Molecule Fluorescence Spectroscopy

Single molecule experiments offer new perspectives to study the behaviour of individual molecules which are often concealed in ensemble measurements due to averaging out. In this direction, plasmonic nanoantennas are fabricated which can produce several folds of fluorescence enhancements of single dye molecule. Our plan is to use these highly capable nanostructures as tools in single molecule fluorescence spectroscopy to study Nano-Bio dynamics using our PicoQuant MicroTime 200 Confocal setup.

Photocatalysis

The novel ways to carry out chemical reactions are one of the ultimate challenges for sustainable development in modern industry. For the generation of effective light-harvesting systems and photocatalytic reactions, unidirectional energy transfer in nanostructured materials is designed. The strong light–matter interactions produce highly energetic hot electrons and holes that possess immense power for transforming light energy into chemical energy and carrying out photocatalytic reactions and single-particle photocatalysis. These energetic charge carriers are more localized at the sharp points known as hot spots or active areas.

DNA Origami-Template Bimetallic Core-Shell Nanostructures for Enhanced Oxygen Evolution Reaction

We presented the design of Ag-coated Au nanostar (core–shell-type Au@Ag nanostar) monomer structures assembled on rectangular DNA origami and studied their electrocatalytic activities through OER, which remains unexplored. Our designed DNA origami-template bimetallic nanostar catalyst showed excellent OER activity and high stability without using any external binder and exhibited a current density of 10 mA cm–2 at a low overpotential of 266 mV, which was smaller than those of ss-DNA-functionalized Au@Ag nanostars and DNA origami-templated pure Au nanostars. Our results revealed that DNA origami-assembled core–shell Au@Ag nanostars show better electrocatalytic performance as compared to pure-core Au nanostars immobilized on DNA origami, owing to the presence of a highly conductive Ag layer. Such controlled assembly of bimetallic nanostructures on a DNA origami template can provide additional electrochemical surface area and a higher density of active sites resulting in enhanced electrocatalysis.

More Info: https://doi.org/10.1021/acs.jpcc.2c00007

Broadband SERS Enhancement by DNA Origami Assembled Bimetallic Nanoantennas with Label-Free Single Protein Sensing

Plasmonic dimer nanoantennas with a tunable gap decorated with Ag-coated Au nanostars on origami were constructed. The single-molecule SERS enhancement of three dyes with emission in different spectral regions after the incorporation of single dye molecules in between two nanostars was demonstrated. The enhancement factors (EFs) achieved in the range of 10⁹–10¹⁰ for all the single dye molecules, under both resonant and non-resonant excitation conditions, would enable enhanced photostability during time-series measurement. The potential of our designed nanoantennas was further explored to accommodate and detect a single thrombin protein molecule after selective placement in the wide nanogap of 10 nm. Our results suggest that such nanoantennas can serve as a broadband SERS enhancer and enable specific detection of target biological molecules with single-molecule sensitivity.

More Info:  https://doi.org/10.1021/acs.jpclett.1c02272

Selective recognition of amyloid marker single Thioflavin T using DNA origami-based gold nanobipyramids nanoantenna

In our recent publication in Nanoscale, the design of gold bipyramid monomer and dimer structures with precise nanogap assembled on a rectangular DNA origami template was demonstrated for the first time. An amyloid marker ThT, a SERS‐active dye, was incorporated on DNA origami using G-rich DNA sequence modified branching staple in the junction of the origami. The stoichiometry of the ThT dye molecule bound to the G-quadruplex complex was estimated by using a single molecule fluorescence confocal microscope which suggested the presence of a single ThT molecule incorporated on DNA origami. We further utilized our designed nanoantennas for specific detection of ThT using SERS-based technique for achieving the goal of ultrasensitive detection of amyloid fibrils. Our experimental findings prove that our developed platform was able to sense a single ThT molecule through extraordinary enhancement of ThT Raman signal by the plasmonic hotspot created in the nanogap of Au bipyramid dimer nanoantennas. To the best of our knowledge, this is the first report on specific detection of single ThT using metallic nanoantennas based on DNA origami.

More Info: https://doi.org/10.1039/D2NR06389A 

Single-Molecule Fluorescence Enhancement-Based Detection of ATP Using DNA Origami-Assembled Au@Ag Nanostar Optical Antennas

In our recent report published in the Journal of Physical Chemistry C, bimetallic Au@Ag nanostars (NSs) nanoantenna site-specifically arranged by DNA origami technique was employed for the fluorescence enhancement of a single Cy3 dye positioned at the interparticle gap between the nanostructures. A maximum of ∼65-fold enhancement of Cy3 dye was observed using fabricated dimeric assemblies of Au@Ag NSs. Additionally, to expand the utility of ultrasmall detection volumes of assembled dimer nanoantenna, the fluorescence enhancement of a small biologically relevant molecule, ATP was explored using crystal violet dye as the probe, attaining a maximum of ∼42-fold enhancement. The fluorescence measurements of the designed system using CV dye indicated the detection of ATP molecules down to the sensitivity of two molecules. The present work adds a new tool in the design of coupled nanoantennas exhibiting fluorescence enhancement and can be further developed for emerging applications in point of care diagnosis.

More Info: https://doi.org/10.1021/acs.jpcc.3c00020