DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering

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 × 10¹⁰ and 8 × 10⁹, 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

Self-Assembled Bimetallic Au–Ag Nanorod Vertical Array for Single-Molecule Plasmonic Sensing

Ordered plasmonic nanoparticle arrays are highly desirable for optical sensing as they provide uniformly distributed plasmonic hotspots due to their periodic order and near-field coupling. Anisotropic-shaped bimetallic nanoparticles are of particular interest, as their hybridized plasmonic modes enable precise tuning of plasmonic resonance and optical responses. However, the controlled assembly of large-scale arrays of bimetallic nanoparticles with uniformly distributed hotspots remains a challenge. In this study, we present a highly robust and reproducible method for creating large-area vertically aligned arrays of bimetallic Au–Ag nanorods by epitaxially growing Ag over preassembled Au nanorods. Structural characterization using electron microscopy and X-ray photoelectron spectroscopy confirms the formation of a uniform thin layer of Ag, creating a bimetallic Au–Ag nanorod array. We also demonstrate the efficacy of the designed nanoarrays for surface-enhanced Raman scattering (SERS) spectroscopy. Our experimental and computational studies show considerably enhanced optical responses of bimetallic Au–Ag nanorods compared to their monometallic counterparts. The scalability, cost-effectiveness, and reproducibility of this method make it a versatile platform for creating various structures by varying guest nanoparticles in suspensions with broad applications in biomedical research, food safety surveillance, and environmental monitoring

Cell-Penetrating and Enzyme-Responsive Peptides for Targeted Cancer Therapy: Role of Arginine Residue Length on Cell Penetration and In Vivo Systemic Toxicity

For the improved delivery of cancer therapeutics and imaging agents, the conjugation of cell-penetrating peptides (CPPs) increases the cellular uptake and water solubility of agents. Among the various CPPs, arginine-rich peptides have been the most widely used. Combining CPPs with enzyme-responsive peptides presents an innovative strategy to target specific intracellular enzymes in cancer cells and when combined with the appropriate click chemistry can enhance theranostic drug delivery through the formation of intracellular self-assembled nanostructures. However, one drawback of CPPs is their high positive charge which can cause nonspecific binding, leading to off-target accumulation and potential toxicity. Hence, balancing cell-specific penetration, toxicity, and biocompatibility is essential for future clinical efficacy. We synthesized six cancer-specific, legumain-responsive RnAANCK peptides containing one to six arginine residues, with legumain being an asparaginyl endopeptidase that is overexpressed in aggressive prostate tumors. When conjugated to Alexa Fluor 488, R1–R6AANCK peptides exhibited a concentration- and time-dependent cell penetration in prostate cancer cells, which was higher for peptides with higher R values, reaching a plateau after approximately 120 min. Highly aggressive DU145 prostate tumor cells, but not less aggressive LNCaP cells, self-assembled nanoparticles in the cytosol after the cleavage of the legumain-specific peptide. The in vivo biocompatibility was assessed in mice after the intravenous injection of R1–R6AANCK peptides, with concentrations ranging from 0.0125 to 0.4 mmol/kg. The higher arginine content in R4–6 peptides showed blood and urine indicators for the impairment of bone marrow, liver, and kidney function in a dose-dependent manner, with instant hemolysis and morbidity in extreme cases. These findings underscore the importance of designing peptides with the optimal arginine residue length for a proper balance of cell-specific penetration, toxicity, and in vivo biocompatibility