Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties.
Clusters comprising up to few tens of atoms are an intermediate state of matter. Unlike molecules and crystalline particles, clusters do not have a regular structure. A cluster of a given size may have many different isomers, some of which may be close in energy.
The most exciting thing is that the atomic clusters of sub-nano or nano-scale are often show drastic change in the physical and chemical properties compared to that of their bulk material, due to the effect of quantum confinement. This different behavior of nano-scale materials is found to be very useful in various kinds of applications to the mankind for the last two decades.
Clusters offer exciting prospects for designing new materials, owing to the strong dependence of their electronic properties on their size and structure. The cluster assembled materials are solids where atomic clusters serve as the fundamental units. The exciting thing for these solids is that they takes the advantage of the exotic properties of clusters due to the effect of quantum confinement and make them accessible in a bulk material with a tunable chemical, electronic, optical and magnetic properties. The cluster assembled materials are formed with a network by linking the cluster motifs as building blocks with an atomic/molecular linker. Some of the special clusters of stable motif classified with aromatic, jellium and Zintl models possess potency to be used as building blocks in the cluster assembled materials.
Clusters are considered as promising catalysts because they exhibit a higher reactivity than bulk materials. Even noble metals such as gold and platinum become highly reactive as clusters. Clusters may also serve as models to elucidate the structure and function of catalytically active sites on surfaces.
Gold atomic clusters detect pesticide
A new sensor promises to detect extremely low concentrations of organophosphorous pesticides in environmental samples . Researchers have made the sensor using surfactant-modified gold atomic clusters.
Continuous exposure to organophosphorous compounds, used as pesticides, can cause headaches, dizziness, blurred vision, nausea, reduced heart rate, fever, coma and even death. Existing techniques for detecting such pesticides are time consuming and expensive. Some of them use enzymes that are unstable.
Previous studies have shown that clusters of gold atoms are better catalysts than bulk gold or gold nanoparticles. This is because the high surface-to-volume ratio of gold atomic clusters results in a large number of binding sites, which are accessible for catalysis and sensing.
To design a simple, fast and sensitive detection technique, the researchers fabricated the sensor by depositing gold atomic clusters on a gold electrode and stabilizing it using a surfactant compound. They then probed the efficacy of the sensor in detecting methyl parathion, an organophosphorous pesticide, at various concentrations.
Compared with bulk-gold and gold-nanoparticle-modified electrodes, the electrode containing gold atomic clusters exhibited enhanced activity for the reduction of methyl parathion. The atomic-cluster electrode gave a reduction current that was 480 and 150 times higher than those obtained using bulk-gold and gold-nanoparticle-modified electrodes, respectively.
The sensor showed excellent sensitivity and reproducibility for methyl parathion detection in environmental samples.