DNA‐Origami‐Based Assembly of Au@Ag Nanostar Dimer Nanoantennas for Label‐Free Sensing of Pyocyanin

Abstract

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.

DNA Origami-Templated Bimetallic Nanostar Assemblies for Ultra-Sensitive Detection of Dopamine

“…The synthetic strategy to prepare Au@Ag NSs was based on our recently reported method ( Kaur et al, 2021 ). Ag coating on seed-mediated synthesized Au NSs was achieved by the subsequent addition of AgNO 3 , ascorbic acid, and NH 4 OH solution.…”

“…To design nanoantenna assemblies, Au@Ag NSs were selectively assembled on dimerized DNA origami via hybridization between Au@Ag NSs prefunctionalized with DNA oligonucleotides and complementary dangling staples from DNA origami ( Scheme 1 ). The synthesized Au@Ag NSs were functionalized with thiolated DNA as explained in our previous report ( Kaur et al, 2021 ). Supplementary Figure S2A depicts a plasmonic shift of ∼7 nm observed in DNA functionalized Au@Ag NSs.…”

“…Au NSs were synthesized according to a previously reported modified protocol ( Tanwar et al, 2017 ). To achieve Ag coating, 1 μl of 0.1 M AgNO 3 , 1 μl of 0.1 M ascorbic acid, and 1 μl of NH 4 OH solution were subsequently added to 1 ml solution of Au NSs as described earlier ( Kaur et al, 2021 ). The washed Au@Ag NSs were then functionalized with 5′ thiol terminated DNA with sequence 5′-SH-CGTCGTATTCGATAGCTTAG-3′ using a previously described method ( Kaur et al, 2021 ).…”

“…To achieve Ag coating, 1 μl of 0.1 M AgNO 3 , 1 μl of 0.1 M ascorbic acid, and 1 μl of NH 4 OH solution were subsequently added to 1 ml solution of Au NSs as described earlier ( Kaur et al, 2021 ). The washed Au@Ag NSs were then functionalized with 5′ thiol terminated DNA with sequence 5′-SH-CGTCGTATTCGATAGCTTAG-3′ using a previously described method ( Kaur et al, 2021 ). Briefly, deprotected thiolated DNA was incubated with Au@Ag NSs overnight followed by slow salt addition until 750 mM final concentration.…”

“…More significantly, bimetallic Au–Ag nanostructures lead to extraordinary electromagnetic enhancements as they combine the plasmonic properties of both the metals in singular structure ( Cui et al, 2006 ; Fan et al, 2013 ; Feng et al, 2019 ). Recently, our group demonstrated assembly of bimetallic Ag coated Au nanostars (Au@Ag NSs) on DNA origami for the ultrasensitive SERS based detection of a bacterial biomarker, pyocyanin ( Kaur et al, 2021 ). In a very recent study, the designed bimetallic nanoantennas were utilized for the broadband SERS enhancement of single dye molecules emitting in different spectral region, and the specific and label-free detection of a single protein molecule placed in the junction of dimer nanoantenna ( Tanwar et al, 2021 ).…”