Acrylamide: New Organic Solvent with Chemically Tunable Viscosity for Rapid Gram-Scale Synthesis of Gold Nanoparticles.

Noble metal nanoparticles have demonstrated various biomedical, optical, and electronic applications owing to their unique chemical and physical properties. However, their gram-scale synthesis remains a challenge. We have developed a method for the gram-scale synthesis of gold nanoparticles (AuNPs) using acrylamide (AAm) as a solvent. AAm possesses unique properties such as low melting temperature, high solvating power, and high solubility of its polymer (polyacrylamide(pAAm)) in water. The viscosity of the AAm solvent can be chemically tuned by the polymerization of AAm and addition of a low-volatile diluent, which can stabilize highly concentrated as-synthesized AuNPs in gram quantities. The synthesized AuNPs are substantially stable and catalytically active under high ionic strength conditions owing to the pAAm protection on the particle surface. Further, the synthesis mechanism of the AuNPs has been thoroughly investigated. The versatility of the synthesis method is proved by synthesizing other mono-(Ag and Pd) and bimetallic (Au + Pd and Ag + Pd) nanoparticles using the AAm solvent with controlled viscosity. Importantly, the productivity of this synthetic strategy is the highest among the previously reported gram-scale synthesis methods of AuNPs. To the best of our knowledge, our study presents the use of acrylic monomer as a solvent for the gram-scale synthesis of noble metal nanoparticles for the first time. This study significantly extends the list of solvents with chemically tunable viscosity by including other acrylic reagents for nanomaterial synthesis, functionalization, and catalytic, optical, and electrical reactions under highly localized reaction conditions.

Interfacial interactions of SERS-active noble metal nanostructures with functional ligands for diagnostic analysis of protein cancer markers.

Noble metal nanostructures with designed hot spots have been widely investigated as surface-enhanced Raman spectroscopy (SERS)-active substrates, particularly for selective and sensitive detection of protein cancer markers. For specific target recognition and efficient signal amplification, SERS probe design requires a choice of SERS-active nanostructures as well as their controlled functionalization with Raman dyes and target recognition entities such as antibodies. However, the chemical conjugation of antibodies and Raman dyes to SERS substrates has rarely been discussed to date, despite their substantial roles in detection schemes. The interfacial interactions of metal nanostructures with functional ligands during conjugation are known to be strongly influenced by the various chemical and physical properties of the ligands, such as size, molecular weight, surface charge, 3-dimensional structures, and hydrophilicity/hydrophobicity. In this review, we discuss recent developments in the design of SERS probes over the last 4 years, focusing on their conjugation chemistry for functionalization. A strong preference for covalent bonding is observed with Raman dyes having simpler molecular structures, whereas more complicated ones are non-covalently adsorbed. Antibodies are both covalently and non-covalently bonded to nanostructures, depending on their activity in the SERS probes. Considering that ligand conjugation is highly important for chemical stability, biocompatibility, and functionality of SERS probes, this review is expected to expand the understanding of their interfacial design, leading to SERS as one of the most promising spectroscopic analytical tools for the early detection of protein cancer markers.

A facile single-step synthesis of polyvinylpyrrolidone-silver nanocomposites using a conventional spray dryer.

We have developed a facile single-step synthesis of silver nanocomposite using a conventional spray dryer. We investigated the synthetic conditions by controlling the concentrations of the chemical reactants. Further, we confirmed the effect of the molecular weight of polyvinylpyrrolidones, and revealed that the molecular weight significantly affected the properties of the resultant silver nanocomposites. The long-term stability of the silver nanocomposites was tested, and little change was observed, even after storage for three months. Most of all, the simple commercial implementation, in combination with large-scale synthesis, possesses a variety of advantages, compared to conventional complicated and costly dry-process synthesis methods. Thus, our method presents opportunities for further investigation, for both lab-scale studies and large-scale industrial applications.

Pyridine: a Denaturant or Stabilizer of Spherical Nucleic Acids?

The spotlighted dual functions of pyridine as a denaturant and as a stabilizer for duplex DNA are thoroughly investigated using spherical nucleic acids (SNAs). At neutral pH, pyridine destabilizes the duplex interconnects of assembled SNAs, resulting in a gradual decrease in their melting temperature (Tm) as a function of the pyridine concentration. This result is in good agreement with the conventional role of pyridine as a powerful denaturant for free duplex DNA. On the contrary, the addition of pyridine dramatically increases the Tm of hybridized SNAs under acidic conditions, which could be a striking result of pyridine's stabilizing effect for DNA duplex as previously suggested on the basis of the pyridine-nucleobase interactions. After comprehensive and quantitative investigation based on the analysis of the sharp melting transitions of SNAs, however, we report that, in fact, the pH increase induced by pyridine is also an essential parameter accounting for pyridine's DNA-stabilizing effects under acidic conditions. Importantly, we prove that pyridine, particularly at a low concentration, does not increase the Tm of hybridized SNAs even under acidic conditions, if the pH increase by pyridine is corrected to maintain the same initial pH.