Magnetic Bead/Gold Nanoparticle Double‐Labeled Primers for Electrochemical Detection of Isothermal Amplified Leishmania DNA

A novel methodology for the isothermal amplification of Leishmania DNA using labeled primers combined with the advantages of magnetic purification/preconcentration and the use of gold nanoparticle (AuNP) tags for the sensitive electrochemical detection of such amplified DNA is developed. Primers labeled with AuNPs and magnetic beads (MBs) are used for the first time for the isothermal amplification reaction, being the amplified product ready for the electrochemical detection. The electrocatalytic activity of the AuNP tags toward the hydrogen evolution reaction allows the rapid quantification of the DNA on screen‐printed carbon electrodes. Amplified products from the blood of dogs with Leishmania (positive samples) are discriminated from those of healthy dogs (blank samples). Quantitative studies demonstrate that the optimized method allows us to detect less than one parasite per microliter of blood (8 × 10^?3 parasites in the isothermal amplification reaction). This pioneering approach is much more sensitive than traditional methods based on real‐time polymerase chain reaction (PCR), and is also more rapid, cheap, and user‐friendly.     

Hybrid Structures for Surface‐Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene

A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface‐enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami–AuNP dimer–graphene hybrid structures.     

Modulation of Interparticle Distance in Discrete Gold Nanoparticle Dimers and Trimers by DNA Single‐Base Pairing

Self‐assembled structures of metallic nanoparticles with dynamically changeable interparticle distance hold promise for the regulation of collective physical properties. This paper describes gold nanoparticle dimers and trimers that exhibit spontaneous and reversible changes in interparticle distance. To exploit this property, a gold nanoparticle is modified with precisely one long DNA strand and approximately five short DNA strands. The long DNA serves to align the nanoparticles on a template DNA via hybridization, while the short DNAs function to induce the interparticle distance changes. The obtained dimer and trimer are characterized with gel electrophoresis, dynamic light scattering measurements, and transmission electron microscopy (TEM). When the complementary short DNA is added to form the fully matched duplexes on the particle surface in the presence of MgCl₂, spontaneous reduction of the interparticle distance is observed with TEM and cryo‐electron microscopy. By contrast, when the terminal‐mismatched DNA is added, no structural change occurs under the same conditions. Therefore, the single base pairing/unpairing at the outermost surface of the nanoparticle impacts the interparticle distance. This unique feature could be applied to the regulation of structures and properties of various DNA‐functionalized nanoparticle assemblies.