Scientists from ITMO University and University. David Running-Gurion learned to determine chemical composition of various substances by means of setpowermode of gold nanoparticles.
Today, more attention is paid to the monitoring of air and water, the presence of harmful impurities. People realized that even a small number of hazardous compounds can negatively affect the health of humans and animals. In order to monitor the chemical composition of different substances, look for certain connections, you need sophisticated equipment. The most common technique used for this is a vibrational spectroscopy.
“you can use it easily to know the molecular composition of a completely unknown for you substances, – says the graduate of a joint educational program between the University ITMO and the University. David Ben-Gurion in the Negev Daler Dadajanov, fellow, International center for Physics of nanostructures. – How it works: there is an unknown chemical substance, which consists of a set of interacting atoms, for example, amino groups are hydrogen atoms, and nitrogen. If you fall on them the light radiation of the atoms begin to oscillate, absorbing some energy. As a result, the output energy will be less. In fact, at what frequency has absorbed energy, it is possible to judge which functional group contains the atoms of the molecule. You can make a "passport of molecules", against which the detector and determines which substance has the case.”
Today, these spectrographs operate in the middle infrared (IR) region of the spectrum which corresponds to radiation with a wavelength of 2.5-25 micrometers. In this range the differences between the falling energy and the energy has already been passed through the substance, clearly visible and suitable for analysis. However, the analyzers operating in the mid-IR spectrum, relatively large and bulky, not to mention their price. In addition, some bands in the mid-IR spectrum is so intense, for example, related to the oscillations of hydrogen atoms in the hydroxyl group (OH) which when detecting small amounts of substances result in total absorption. The presence of these bands makes it difficult to interpret other characteristic vibrational bands in the absorption spectrum.
The system could be done several times less if the work is not the mid-IR range, and in the middle, which corresponds to the shorter-wave radiation. Near infrared range is mastered much better than average, primarily due to the fact that this range has a modern Telecom.
“the key advantage of the near infrared region of the spectrum is that of the current date in this field is ��tion of energy-efficient and high-quality continuous radiation sources and reliable detectors, explains Dadajanov, they are cheaper than mid-IR zone, and more compact. So, the hardware for the mid-IR region can have dimensions one and a half meters, and for near it is likely to be able to fit on the human hand”.
However, there is a problem – reducing wavelength causes the difference between the trapped sample and the energy that passed through it is very small and difficult to grasp for the detector. As a result, qualitative analysis requires a greater amount of a substance that threatens the compaction of the entire installation. In addition, there is another complexity – the concept of many sensors is the detection of unknown substance with an extremely low concentration, for example, toxic molecules. When using the near-infrared range complicates the task.
Before you can create the device-analyzer on the basis of vibrational spectroscopy in the near infrared region, you need to figure out how to boost the signal obtained from the difference of the incident and passing through the substance of energy. On this project worked together specialists of the University. David Ben-Gurion in the Negev (Ben-Gurion University of the Negev, Israel) under the guidance of Dr. Alina Karabchevsky and their colleagues from ITMO University. Their work is published in the journal of Nanomaterials.
“In our work, we propose the following design on a substrate of a transparent dielectric, for example, borosilicate glass, formed a periodic array of gold nanoprecipitation. Such structures can be obtained by using electron-beam lithography, says Dadajanov. – After that, we cover the substrate with a thin layer of analyte and the recorded transmittance spectrum of the sample, which is caused by the joint excitation of plasmon resonance in gold nanoparticles and molecular vibrations of the analyte. Gold nonparallelity calculated shapes have plasmon resonance in the spectral region where absorption bands of the studied molecules. In addition, in close proximity to the metal surface there is an additional field amplification. This increases the sensitivity of the proposed sensor”.
This work is a theoretical study was conducted on numerical models. The next step will be to conduct real experiments to create such systems in laboratory conditions.
a Material provided by the press service of the ITMO
