Silver-polydiacetylene core–shell nanohybrids: From nano to mesoscale architectures

Hydrogen bonding reversibility in poly(10,12-pentacosadiynoic acid)/titanium dioxide composite analyzed by infrared spectroscopy

In this work, the chromatic behavior of a poly(10,12-pentacosadiinoic acid)/titanium dioxide (TiO₂) nanocomposite was studied. Infrared spectroscopy showed that above 55 °C the peak of the carboxyl groups undergoes a shift from 1690 cm^-1 (25-55° C) to 1710 cm^-1 (≥60 °C), which is reversible after cooling regardless of whether the sample was in the blue or red phase prior to heating. This indicates that the thermochromic behavior and the hydrogen bond shifting are not completely related, since the signal of the hydrogen bond is influenced by temperature, but is reversible; however, the color change is not. Importantly, TiO2 does favor thermochromic reversibility, unlike that indicated in previous reports. Computational chemistry showed that the effect of temperature on a polydiacetylene oligomer with three repeating units produces torsion, which directly impacts the strength of the hydrogen bonds between the carboxyl groups, coinciding with the experimental work.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Novel Color Change Film as a Time-Temperature Indicator Using Polydiacetylene/Silver Nanoparticles Embedded in Carboxymethyl Cellulose

Time-temperature indicators (TTIs) can be important tools in product applications to monitor food quality losses, especially for fruits and vegetables. In this context, the effects of silver nanoparticles (AgNPs) and glycerol on the color change of polydiacetylene/AgNPs (PDA/AgNPs) embedded in carboxymethyl cellulose (CMC) film as time-temperature indicators (TTIs) were investigated. A CMC film prepared with 30 mg/L AgNPs and a 1:3 (v/v) PDA:AgNP ratio exhibited a faster color change than under other conditions. At 35 °C, the films with PDA/AgNPs changed color from purplish-blue to purple and purple to reddish-purple over time due to the higher thermal conductivity of AgNPs and larger PDA surface area exposed to specific temperatures. The total color difference (TCD) of PDA/AgNP-embedded CMC film directly changed with regard to time and temperature. However, adding glycerol to the system resulted in a symmetrical chemical structure, a factor that delayed the color change. Scanning electron micrographs showed AgNPs embedded in the CMC films. Transmission electron micrographs indicated a core-shell structure of PDA/AgNP vesicles in the CMC matrix. PDA/AgNP vesicles were confirmed by second derivative Fourier transform infrared spectroscopy, with a new peak at 1390-1150 cm-1. The kinetics of TTIs from PDA/AgNP-embedded CMC films yielded an activation energy of 58.70 kJ/mol.

Chitosan-Stabilized Noble Metal Nanoparticles: Study of their Shape Evolution and Post-Functionalization Properties

Noble metal anisotropic nanostructures have achieved a growing interest in both academic and industrial domains mostly because of their shape-dependent plasmonic properties in the near-infrared region. In this paper, gold and gold-silver anisotropic nanostructures were synthesized in very high shape-yields through a wet, seed-mediated approach based on the use of nearly spherical silver nanoparticles as seeds and chitosan as stabilizing agent. Two chitosans of different origin and molecular properties were selected for the synthetic pathway, leading to the formation of variously sized and shaped end products. In detail, quite homogeneous nanoplatelets of about 25-nm size and 7-nm thickness or nearly spherical, highly porous nanocages of about 50-nm size were obtained, depending on the type of polysaccharide employed. The shape transition towards anisotropic morphologies occurred through a slow, spontaneous process, in which the chitosan nature seemed to play a key role. As expected, both nanoplatelets and nanocages exhibit shape-dependent plasmonic features and surface properties tunable for a variety of application fields. To prove this point, the nanostructures were successfully post-functionalized with poly(10,12-pentacosadiynoic acid) (PCDA), a carboxylic-endowed diacetylene able to anchor on noble metal substrates, to obtain versatile, chromic platforms suitable for sensing and spectroscopic purposes.

Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach

A flexible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted fluorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.

Use of a 4,5-dicyanoimidazolate anion based ionic liquid for the synthesis of iron and silver nanoparticles

Effects of cation and anion in the resulting ILs are influenced in the thermal transitions. Stable and better separated Fe- and Ag-NPs are obtained in newly designed nitrile functionalized 4,5-dicyanoimidazolate anion based IL.