A New Strategy for Silver Deposition on Au Nanoparticles with the Use of Peroxidase-Mimicking DNAzyme Monitored via a Localized Surface Plasmon Resonance Technique.

Peroxidase-mimicking DNAzyme was applied as a catalyst of silver deposition on gold nanoparticles. This DNAzyme is formed when hemin binds to the G-quadruplex-forming DNA sequence. Such a system is able to catalyze a redox reaction with a one- or two-electron transfer. The process of silver deposition was monitored via a localized surface plasmon resonance technique (LSPR), which allows one to record scattering spectrum of a single nanoparticle. Our study showed that DNAzyme is able to catalyze silver deposition. The AFM experiments proved that DNAzyme induced the deposition of silver shells of approximately 20 nm thickness on Au nanoparticles (AuNPs). Such an effect is not observed when hemin is absent in the system. However, we noticed non-specific binding of hemin to the capture oligonucleotides on a gold NP probe that also induced some silver deposition, even though the capture probe was unable to form G-quadruplex. Analysis of SEM images indicated that the surface morphology of the silver layer deposited by DNAzyme is different from that obtained for hemin alone. The proposed strategy of silver layer synthesis on gold nanoparticles catalyzed by DNAzyme is an innovative approach and can be applied in bioanalysis (LSPR, electrochemistry) as well as in material sciences.

Hyperspectral imaging of plasmon resonances in metallic nanoparticles.

The spectroscopy of metal nanoparticles shows great potential for label-free sensing. In this article we present a hyper-spectral imaging system combined with a microfluidic system, which allows full spectroscopic characterization of many individual nanoparticles simultaneously (>50 particles). With such a system we were able overcome several limitations that are present in LSPR sensing with nanoparticle ensemble. We experimentally quantified (incorporating atomic force microscopy as well) the correlation between geometry, position of plasmon resonance (λPeak) and sensitivity of the particles (Sb=1.63λPeak-812.47[nm/RIU]). We were able to follow the adsorption of protein layers and determined their spatial inhomogeneity with the help of the hyperspectral imaging.

Localized surface plasmon resonance (LSPR) biosensing using gold nanotriangles: detection of DNA hybridization events at room temperature.

We present a proof-of-concept of the application of gold nanotriangles in sequence specific DNA detection, using localized surface plasmon resonance (LSPR) spectroscopy and dark-field optical microscopy. The sensing platform comprises gold nanotriangles immobilized on a glass chip and oligonucleotides as probes. Probe formation and testing complementary and non-complementary targets followed common chip technology protocols. Gold nanotriangles showed a remarkable sensitivity of 468 nm per RIU and allowed detection of 20-mer targets. When the target sequence was part of a 50-mer synthetic DNA oligonucleotide, LSPR shifts as high as 35 nm were observed. Conversely, when the target was present in PCR products of ca. 350 bp, obtained from clinical samples, LSPR shifts larger than 20 nm were observed. Moreover, LSPR shifts were less than ±1 nm for the respective non-complementary targets. These results with gold nanotriangles as sensors are a notable improvement to the LSPR shifts of less than 5 nm usually obtained for spherical gold nanoparticles of comparable sizes. Optimal conditions for the detection of synthetic and PCR product targets using gold nanotriangles and oligonucleotide probes were achieved with low percentages of intercalating thioalkanes; target hybridization at room temperature, 3 hours of incubation, and 2× SSC buffer stringency conditions.