Competitive reactivities determine the size and composition of multimetallic nanocrystals

 

Multimetallic nanocrystals (NCs) have attracted considerable attention due to their physical, chemical, and catalytic properties, which often surpass those of their monometallic counterparts. The distinctive properties of NCs are determined by the synergistic interactions among their constituent metals.

Synthesizing these materials with precise control over size and composition remains a major challenge because of the differences in the reactivities of the metal precursors. Owing to these differences, one would expect that increasing the number of metal precursors would enhance the formation of heterogeneous products (mixtures of particles with different sizes and compositions).

However, a multinational team of researchers demonstrated a counterintuitive effect in the synthesis of multimetallic nanocrystals: differences in the reactivities of metal precursors can actually promote the formation of highly uniform multimetallic nanocrystals.

Ru nanoparticles (≈ 4.5 nm) and precursor solutions of Fe, Co, Ni, and Cu were used as seeds. Upon introducing five metals (RuFeCoNiCu), a uniform product was obtained: pentametallic nanocrystals of ≈ 14.1 ± 1.4 nm with a narrow size distribution. This effect persisted even when the seed size, precursor ratios, and additional metals (Cr, In) were varied.

The mechanism underlying this remarkable process was elucidated through time-lapse analysis of intermediate products and tomography. As shown in the Figure, the formation of pentametallic nanocrystals proceeded through three distinct stages: (i) predominant reduction of Cu on previously formed Ru seeds, (ii) onset of Co, Ni, and Fe reduction accompanied by partial surface-layer formation, and (iii) complete reduction and integration of all constituent metals into fully formed RuFeCoNiCu nanocrystals.

When the pentametallic nanocrystals supported on Al2O3 were used as catalysts, they exhibited a reaction rate more than four times higher than that of monometallic Ru in ammonia decomposition (NH3 → N2 + 3H2), while maintaining comparable activation energy and thermal stability.

This work proposes a new principle for the design of complex multimetallic nanocrystals: rather than suppressing the competition among metal precursor reactivities, it can be harnessed. This finding leads the way toward libraries of nanomaterials with unique synergistic properties for applications such as catalysis and sustainable energy technologies.

For further information go to: Science

Self-assembled DNA micelles with Gold Nanoparticles for the Detection of miRNAs Associated with Alzheimer’s Disease

 

Alzheimer’s disease is a progressive neurodegenerative disorder that represents one of the greatest challenges in modern medicine. The disease is characterized by the abnormal accumulation of beta-amyloid (Aβ) plaques and tau protein in the brain, leading to inflammation, neuronal damage, and cognitive decline. One of the major challenges is that clinical symptoms typically emerge only after the brain is substantially damaged, thereby limiting the effectiveness of current treatments. Consequently, early detection has become a primary objective.

A research group in China developed an innovative strategy based on lateral flow assays (LFAs), a diagnostic tool for the sensitive, specific, and accessible detection of biomarkers, with the aim of identifying microRNA (miRNA) strands associated with the early stages of Alzheimer’s disease. miRNAs are small non-coding RNA molecules that regulate gene expression by binding to specific messenger RNAs and inhibiting their translation or promoting their degradation.

The proposed method employs DNA micelles functionalized with

gold nanoparticles (AuNPs) and equipped with miRNA strands.

A key feature of this approach is the use of self-assembled DNA micelles, namely nanostructures that spontaneously organize into spherical aggregates in aqueous solution. The DNA micelles were functionalized with gold nanoparticles (AuNPs) and mixed with strands of the target miRNA. When the sample is applied to the LFA test strip, the DNA–AuNP–miRNA complex migrates by capillary action toward the test line, where it is captured by a second probe containing a sequence complementary to the target miRNA and immobilized by a biotin/streptavidin interaction. The accumulation of AuNPs on the test strip produces a visible red band due to their plasmonic properties, with an intensity proportional to the concentration of miRNA present in the sample.

Since target miRNAs coexist with other miRNA species in real samples, it is essential for the system to exhibit high specificity toward the targets of interest. To evaluate this, the authors assessed cross-reactivity against other miRNAs and observed that no signal was produced at the test lines in the presence of interfering species. Red bands appeared only when the corresponding target miRNA (miR-34a, miR-125b, or miR-15a) was present.

Overall, the results demonstrate that the LFA enables the simultaneous detection of multiple miRNAs in serum with greater sensitivity and selectivity than conventional assays. This performance is attributed to the use of nanostructures that function as highly efficient recognition platforms capable of amplifying signals that would otherwise remain undetectable.

For further details, consult: Biosensors and bioelectronics