Highly sensitive and highly selective tests are important for the early detection of disease, the detection of environmental toxins, or for the detection of explosives at airports. Increased selectivity for the target analytes helps to avoid false-positive results.
In the journal Angewandte Chemie, Indian scientists have now introduced a specific detection method for the explosive TNT that can be used to detect even a single molecule.
Thalappil Pradeep, Ammu Mathew, and P. R. Sajanlal at the Indian Institute of Technology Madras use an ingenious combination of micro- and nanostructures as sensors: gold mesoflowers, flower-shaped gold particles about 4 µm in size, act as supports for silver clusters, tiny clumps of exactly 15 silver atoms embedded in the protein bovine serum albumin. When irradiated with light of the right wavelength, the silver clusters luminesce, giving off red light. The gold of the mesoflower supports intensifies the fluorescence. Their unique shape is a particular advantage, because it is easy to unambiguously identify under an optical microscope, unlike spherical particles.
If a drop of a solution containing TNT is applied, it reacts with the amino groups of the bovine serum albumin to make a Meisenheimer complex—a reaction specific to TNT. This extinguishes the red glow of the silver clusters. In order to make this reaction even more distinct, the researchers also embedded a green fluorescing dye, which was adsorbed on a silicon dioxide layer grown on the gold flowers. As long as the silver clusters glow red, the green fluorescence is suppressed. When TNT molecules switch off the red light, the green dye begins to glow. The color change from red to green can be observed with a fluorescence microscope.
A TNT concentration of one ppb (part per billion) extinguishes the fluorescence, one ppt (part per trillion), reduces it markedly. The researchers supplemented their luminescence technique with a second analytical method, SERS (surface-enhanced Raman scattering), which also functions extremely well with a version of the flower-shaped sensors. “This allowed us to attain detection limits as low as the sub-zeptomole range (10-21 mol),” explains Pradeep. Just one “flower” is enough to operate as a sensor. It reacts when it comes into contact with as few as nine molecules. A device based on this principle is under development.The researchers were also able to detect mercury with similar sensitivity by using the same sensor strategy. Says Pradeep: “Our concept could also be used for the ultra-trace analysis of other substances through the incorporation of specific ligands on the sensors.”
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
Transforming plant cells from generalists to specialists
07.12.2016 | Duke University
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine