We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 × 10 and 8 × 10, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing.
Early‐stage detection of diseases caused by pathogens is a prerequisite for expedient patient care. Due to the limited signal‐to‐noise ratio, molecular diagnostics needs molecular signal amplification after recognition of the target molecule. In this present study, we demonstrate the design of plasmonically coupled bimetallic Ag coated Au nanostar dimers with controlled nanogap using rectangular DNA origami. We further report the utility of the designed nanostar dimer structures as efficient SERS substrate for the ultrasensitive and label‐free detection of the pyocyanin molecule, which is a biomarker of the opportunistic pathogenic bacteria, Pseudomonas aeruginosa. The experimental results showed that the detection limit of pyocyanin with such nanoantenna based biosensor was 335 pM, which is much lower than the clinical range of detection. Thus, fast, sensitive and label‐free detection of pyocyanin at ultralow concentration in an infected human body can pave a facile route for early stage warning for severe bacterial infections.
We
report a simple, green, and room temperature synthetic route
for the formation of Si quantum dots (Si QDs) and Au nanoparticle–Si
quantum dot (Au NP-Si QD) nanocomposites. Glucose was used as a reductant
for one-pot synthesis of water-dispersible blue emitting Si QDs. The
use of simple biomolecules for the generation of functional hybrid
materials is of great significance for both economic and environmental
benefits. The as prepared Si QDs have an average size of 2.7 nm with
emission maximum at 467 nm. These Si QDs showed a reversible thermoresponsive
emission in the temperature range of 20–80 °C in water
and excellent salt tolerance enabling the QDs to be extremely suitable
for biomolecular functionalization and use as probes for biological
fluorescence imaging. Further, the as prepared hydrophilic Si QDs
have been exploited as a reduction reagent to reduce Au3+ ions to Au NPs. The Si QDs also functioned as an effective stabilizer
by forming a thin layer over the Au NPs leading to the formation of
Au NP-Si QD nanocomposite. This composite material was found to exhibit
catalytic activity to reduce nitroarenes. Such multifunctional hybrid
nanomaterials are potential candidates for photocatalysis, bioimaging,
and sensing applications.
Engineering hotspots in surface-enhanced
Raman spectroscopy (SERS)
through precisely controlled assembly of plasmonic nanostructures
capable of expanding intense field enhancement are highly desirable
to enhance the potentiality of SERS as a label-free optical tool for
single molecule detection. Inspired by DNA origami technique, we constructed
plasmonic dimer nanoantennas with a tunable gap decorated with Ag-coated
Au nanostars on origami. Herein, we demonstrate the single-molecule
SERS enhancements of three dyes with emission in different spectral
regions after incorporation of single dye molecules in between two
nanostars. The enhancement factors (EFs) achieved in the range of
109–1010 for all the single dye molecules,
under both resonant and nonresonant excitation conditions, would enable
enhanced photostability during time-series measurement. We further
successfully explored the potential of our designed nanoantennas 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.
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