Differences in DNA Probe-Mediated Aggregation Behavior of Gold Nanomaterials Based on Their Geometric Appearance.

Nanoparticles are used extensively to detect nucleic acid biomarkers due to their analytical applicability and sensitivity. Systems employing the surface plasmon resonance of gold nanomaterials are overwhelmingly considered to be candidates. The aggregation of gold nanomaterials mediated by the hybridization of target DNA at the interface causes a change in the surface plasmon resonance inherent in gold nanomaterials. Such changes can be measured by spectroscopy or even visualized by the naked eye, enabling effective and positive detection. The optical properties of gold nanoparticles are affected by their shape. The geometric appearance of the nanoparticles also affects their colloidal stability and aggregation behavior. In this study, we examined the effect of the geometric appearance of gold nanomaterials on DNA-mediated aggregation behavior through comparative experiments. Experimental and theoretical methods were used concurrently to derive accurate results and to support the hypotheses. Coarse-grained molecular dynamics simulations were performed with a large-scale atomic/molecular massively parallel simulator to understand the aggregation of nanoparticles with the same surface area and various aspect ratios. As a result, we confirmed that the aggregation sensitivity of nanoparticles was affected by the shape of the contact point with the gold nanomaterials. This study demonstrates that the design of a detection system should be accompanied by an in-depth review of the morphology of the nanoparticle.

Assemblies of Colloidal CdSe Tetrapod Nanocrystals with Lengthy Arms for Flexible Thin-Film Transistors.

Herein, we report unique features of the assemblies of tetrapod-shaped colloidal nanocrystals (TpNCs) with lengthy arms applicable to flexible thin-film transistors. Due to the extended nature of tetrapod geometry, films made of the TpNC assemblies require reduced numbers of inter-NC hopping for the transport of charge carriers along a given channel length; thus, enhanced conductivity can be achieved compared to those made of typical spherical NCs without arms. Moreover, electrical conduction through the assemblies is tolerant against mechanical bending because interconnections between TpNCs can be well-preserved under bending. Interestingly, both the conductivity of the assemblies and their mechanical tolerance against bending are improved with an increase in the length of tetrapod arms. The arm length-dependency was demonstrated in a series of CdSe TpNC assemblies with different arm lengths (l = 0-90 nm), whose electrical conduction was modulated through electrolyte gating. From the TpNCs with the longest arm length included in the study (l = 90 nm), the film conductivity as high as 20 S/cm was attained at 3 V of gate voltage, corresponding to electron mobility of >10 cm2/(V s) even when evaluated conservatively. The high channel conductivity was retained (∼90% of the value obtained from the flat geometry) even under high bending (bending radius = 5 mm). The results of the present study provide new insights and guidelines for the use of colloidal nanocrystals in solution-processed flexible electronic device applications.

Molecular dynamics study on microstructures of diblock copolymer melts with soft potential and potential recovery.

Various microstructures are obtained through the self-assembly of block copolymers on the basis of the compositional fractions and repulsive interactions among different types of beads. The inhomogeneity of block copolymers can be studied by molecular dynamics. However, preparing initial configurations of various self-assembled structures directly by molecular dynamics requires extensive computational time because of topological constraints. Furthermore, manual preparation often becomes a complicated and time-consuming procedure even for the simplest structures, such as a lamellar phase, not to mention three-dimensional bicontinuous cubic phases such as a gyroid phase. In this paper, this difficulty is overcome by using a soft potential, which allows the system to reach a self-assembled state quickly (within 3τ_{d}). Once a self-assembled microstructure is obtained, the normal potential is restored and equilibration steps are performed to enable the calculation of various properties of the microstructures. Various equilibrated phase structures-including S (spherical), H (hexagonal), G (gyroid), and L (lamellar) phases-are obtained by this approach. To verify our method, static and dynamic properties of the lamellar phase are examined and compared with previous results.