Silver nanoparticles have possibility of a significant change in the optical characteristics, and tunable properties, which make them to be used as unique analytical reagents in UV-Vis spectrometry and test-methods of analysis. Non-spherical nanoparticles, due to their developed morphology, can provide us with novel properties unavailable for the spherical nanoparticles made of the same material, and thus they have attracted remarkable attention as promising analytical reagents in optical molecular spectroscopy. One of the interesting types of non-spherical nanoparticles is silver triangular nanoplates (AgTNPs). Moreover, the special blue color of AgTNPs compared to other types of silver nanoparticles may play a remarkable role for the naked-eye detection and the sensitivity of AgTNPs to the vast majority of analytes is higher than that of nanoparticles of other morphologies. Thus, they are frequently utilized for sensitive probes for detection of various analytes. In this regard, the preparation, stabilization and analytical use of AgTNPs are of particular interest. Here, Alfa Chemistry describes in detail the preparation of AgTNPs and their application as an analytical reagent in optical molecular spectroscopy according to the previous report [1].
Synthesis
There are many methods for the synthesis of AgTNPs. According to the literature data, three fundamentally different approaches are most often used to prepare AgTNPs: chemical reduction methods, photochemical methods, as well as biological and biochemical methods.
- Chemical reduction methods: In the methods, silver(I) ions are reduced in the presence of a stabilizer (such as organic molecules, polymers, or surfactants), which results in the formation of small prismatic seed nanoparticles in solution. Then these nanoparticles are kept in the mother liquor at a specific temperature and pH, which leads to the formation of larger triangular structures. At present, various anions of polybasic carboxylic acids or their mixtures with citrate ion in a specific ratio can be used as stabilizer to produce AgTNPs such as citrate, acetate, oxalate, malonate, succinate, citramalate, tartrate, glutarate, adipate, isocitrate, cis-aconate and tricarballylate, thereinto, citrate is most frequently used.
- Photochemical methods: In the methods, a solution containing spherical silver nanoparticles is exposed to electromagnetic radiation of a certain spectral range, resulting in the formation of AgTNPs with desired morphology, size, and size distribution by selecting the energy of an electromagnetic radiation source. The most widely used methods utilize electromagnetic radiation in the visible region of spectrum. Less often, ultraviolet (UV) irradiation and radiolysis are used to prepare AgTNPs. The methods can be used to prepare monodisperse AgTNPs samples.
- Biological and biochemical methods: The methods involve reducing silver(I) ions with the help of various biological systems (such as microorganisms, plant cells, and bacteria) using peptide macromolecules, biopolymers and nucleic acids as stabilizers to synthesis of AgTNPs.
Applications
A change in the morphology of AgTNPs leads to a change in the color of their solution from blue to red or yellow. Upon aggregation of AgTNPs, the formation of brown or grey solutions is observed. These color transitions are quite contrasted and can be used both for the spectrophotometric determination of various compounds and for their visual or colourimetric detection. Recently, AgTNPs as analytical reagents were increasingly used for the spectrophotometric determination of metal ions, anions as well as organic and inorganic compounds. The high molar absorption coefficients as well as substantial changes in their spectral characteristics in different conditions (such as presence of substances that affect their geometric parameters or cause aggregation) make AgTNPs a promising alternative to traditional spectrophotometric reagents.
