A simple and effective approach to the aqueous‐phase synthesis of crystalline silver nanorods and nanowires is demonstrated, using which their diameters and aspect ratios can be effectively controlled. The synthesis involves a template‐less and non‐seed process to high‐quality nanoparticles, which is low‐cost and proceeds at moderate temperatures. The nanorods and nanowires were synthesized by the reduction of silver nitrate with tri‐sodium citrate in the presence of sodium dodecylsulfonate. The concentration of tri‐sodium citrate plays a critical role while sodium dodecylsulfonate, as a capping agent, only plays an assistant role in controlling the diameters and aspect ratios of the products. High‐resolution transmission electron microscopy (HRTEM) and selected‐area electron diffraction (SAED) investigations show that the silver nanocrystals are generated with a twinned crystalline structure. We also put forward a primary experimental model to shed light on their growth mechanisms.
We report self-assembly of charge-stabilized gold and silver nanoparticles at water-air and water-oil interfaces, via manipulation of the interactions between the interfaces and the adsorbing nanoparticles. Nanoparticle adsorption from bulk colloids to an interface is an energy-favored, but finite sorption barrier-restrained (kinetics-controlled) process. Consequently, to successfully mediate self-assembly of nanoparticles, the finite sorption barrier should be decreased. That can be accomplished by manipulating its three controlling forces: the repulsive electrostatic force, the repulsive van der Waals force, and the attractive hydrophobic force between the interface and the adsorbing nanoparticles. It was found that hydrophobic coatings change nanoparticle hydrophobicity and greatly increase the attractive hydrophobic force. Surface active organic solvents (methanol, ethanol, isopropanol, and acetone) decrease the attractive hydrophobic force to some extent. However, they decrease the repulsive electrostatic force to a larger extent, via a "charge dilution" mechanism, due to their positive adsorption at the charged water-air and water-oil interfaces. Hydrophobic coatings and organic solvents consequently decrease the sorption barrier, facilitate nanoparticles overcoming the sorption barrier, and mediate the self-assembly of nanoparticles.
In our previous paper, a method for preparing enormous surface-enhanced Raman scattering (SERS) active substrates through the aggregation of silver particles trapped at an air-water interface was reported. Here, further efforts were devoted to investigate the origin of assembling silver particle films by adsorbing nanoparticles from bulk colloids to the air-water interface. It was revealed that it is thermodynamically favorable for a colloidal particle in bulk colloids to adsorb to the air-water interface; however, a finite sorption barrier between it and the nearby particles usually restrains the adsorption process. When an electrolyte such as KCl, which is commonly used as an activating agent for additional SERS enhancement, was added into silver colloids, it largely reduced the sorption barrier. Thus, silver nanoparticles can break through the sorption barrier, pop up, and be trapped at the air-water interface. The trapped silver particles are more inclined to aggregate at the interface than those in bulk colloids due to the increase of van der Waals forces and the reduction of electrostatic forces. The morphology of the as-prepared silver particle films was characterized by scanning electron microscope, and their SERS activity was tested using NaSCN as a probe molecule. The surface enhancement of the silver particle films is about 1-2 orders of magnitude higher compared with that of silver colloids, because most of the silver particles in the films are in the aggregation form that provides enormous SERS enhancement. Furthermore, the stability of such type of films is much better that of colloid solutions.
In the decade after being awarded the Nobel Prize in Chemistry in 2002, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been widely used as an analytical chemistry tool for the detection of large and small molecules (e.g., polymers, proteins, peptides, nucleic acids, amino acids, lipids, etc.) and for clinical analysis and research (e.g., pathogen identification, genetic disorders screening, cancer diagnosis, etc.). In view of the fast development of MALDI-TOF MS in clinical usage, this review systematically summarizes the most important applications of MALDI-TOF MS in clinical analysis and research by analyzing MALDI TOF MS-related reviews collected in the Web of Science database. On the basis of the analysis of keyword co-occurrence of over 2000 review articles, four themes consisting of “pathogen identification”, “disease diagnosis”, “nucleic acids analysis”, and “small molecules analysis” were found. For each theme, the review further outlined their application implications, analytical methods, and systems as well as limitations that need to be addressed. Overall, the review summarizes and elaborates on the clinical applications of MALDI-TOF MS, providing a comprehensive picture for researchers embarking on MALDI TOF MS-related clinical analysis and research.
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