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Posted: May 15, 2014
Nanoparticle ink for rapid diagnosis
(Nanowerk News) Science is taking decisive steps to incorporate the potential of new technical applications to real life. The latest is the incorporation of nanoparticles of gold or silver into conventional ink, the same ink as in our ballpoints or pens, and is an advanced solution in identifying molecules in fields such as medical diagnosis, biology, the environment, safety, etc.
That is to say, the ink is not only a conductor of messages, emotions, tests or trials, or news in the daily papers, but also, at the same time, it can be an optimum tool, cheap and easy to use, so that a researcher or doctor can extract molecular-scale conclusions and which to date have required large-scale and high-cost technical instrumentation. A fountain pen and an A4 sheet of paper is all that is needed.
Research undertaken in Dr. Luis Liz Marzán’s laboratory at the Biomaterials Research Centre (CIC biomaGUNE), which he directs in the Basque city of Donostia-San Sebastián, and published in Small ("Pen-on-Paper Approach Toward the Design of Universal Surface Enhanced Raman Scattering Substrates"), puts forward a new technique the principal contribution of which lies in facilitating and reducing the cost of creating the chemical substrates used to identify molecules in any field of activity, molecules which are analysed and described employing spectroscopy equipment. In effect, it is expected that this technique will, for example, contribute to the rapid diagnosis of illnesses.
The basis of the project carried out by Dr. Liz Marzán’s team and led by Dr. Lakshminarayana Polavarapu (post-doctorate researcher from the team), lies in a technique known as dispersive raman spectroscopy, discovered by Indian scientist Sir C.V. Raman, who was awarded the Nobel Prize for Physics in 1930. In the 1970s, when measurements with a silver electrode were being made, it was accidentally discovered that the signal obtained was much greater than usual, giving rise to a modification of the technique which we know today as surface-enhanced raman spectroscopy (SERS). We now know that this phenomenon is due to the existence of plasmon electronic oscillations which cause strong electric fields in the silver grains present in such a surface.
This technique is commonly used in chemistry, given that the vibrational information is highly specific for the chemical links in molecules and, in this way, provides a "fingerprint" of the molecule which thus can be identified. The technique is used in a multitude of fields, such as medical diagnosis, environmental control, etc., albeit having certain limitations, above all due to the difficulty in obtaining substrates that are sufficiently reliable and reproducible and that at the same time, are not too expensive or complicated to produce.
To overcome problems of this nature - involving conventional SERS substrates -, a lot of attention has been paid to paper-based SERS substrates. Paper is cheap, flexible, biodegradable, disposable and light, and is widely used in our everyday lives.
A pen and a sheet of paper
The proposal from Dr. Liz Marzán’s team is a qualitative leap, obviating prefabricated substrates and, thus, overcoming their limitations and difficulties, and substituting them by an ink containing nanoparticles.
“In this way, using any pen the ink of which is made with gold or silver conducting nanoparticles, we can draw, on a white sheet of paper, a series of small squares for example – Sudoku-style – or any sentence and, the concrete substance we wish to analyse being deposited on this ink, we can put this through the spectrometer, which gives us the signal (fingerprint) of what we are analysing”, stated Dr. Liz Marzán. Moreover, it will be a highly important boost to rapid diagnosis.
“The advantage is that the operative does not need to acquire substrates. Inks can be bought at the moment when undertaking the experiment, the pen is loaded with the special ink, the paper is drawn or painted on, depending how the analysis is to be carried out, a sample of the substance requiring analysis is placed on it, and we have the result”, explained the scientist. The result could be a medical diagnosis, a contaminant in water, pesticides, applications in matters of safety, etc.
Each line of the drawing contains about a million nanoparticles, giving it great potential when generating the signal for analysing the molecules, being augmented 10 million times. At the same time, one gram of gold enables manufacturing ink for many thousands of tests, the production of this type of ink not being complicated, and the quantities involved being very small.
“We have employed very sophisticated spectrometers but there are also portable spectrometers which can be carried to a reservoir, for example, and possible contaminants measured, i.e. you take your notebook and ink, paint on the paper, place the drop of water on it and then put it through the spectrometer, and you have the test on the spot”, concluded Dr. Liz Marzán.