Metal nano layer coating for increasing the sensitivity of spectroscopic measurements is proposed and experimentally demonstrated in this paper. The metal nano layer will attract the micro-poisons from any measured aqueous sample increasing the concentration of the micro-poison in the vicinity of the surface and significantly improves the sensitivity of the spectroscopic measurement. The demonstration was carried out using Fourier Transform Infra-Red (FTIR) operating in the MIR 400 cm -1 - 4000 cm -1 and 5 nm Gold layer which was grown on silicon oxide substrate. In the experimental demonstration Malathion organophosphate pesticide was used as micro-poison. The spectroscopic measurement proves that Malathion was attracted to the metal nano layer. Furthermore, the absorption lines of Malathion were detected and recognized. This proof of principle can be applied to any Internal Reflection Elements (IRE) and it can be used to purify any aqueous solutions and atmosphere from micro-poisons which will be attracted to the metal Nano layer.
Pollution of the environment caused by industrialization, domestic waste, massive use of insecticides, pesticides and herbicides, antibiotics remains and microorganisms, results in increasing the numbers of environment contaminations. On the other hand, deliberate contamination as act of terror should be taken into account. Those contaminations are potentially dangerous to humans and to the ecosystem. Recent investigations indicate that the influence of micro poisons, especially Organophosphates, on humans can be expressed as long term damage and diseases [
Organophosphates which are widely used micro poisons in agriculture and domestic use, can be detected in aqua solutions samples using very sensitive gas or liquid chromatographic [
Pre-concentration is well known method [
Biosensors are another group of micro poisons detectors in which the bioreceptor is designed to interact with the specific analyte to produce a measurable signal. This can be carried out using enzymes [
Optical sensors based on spectroscopic properties of the micro-poisons are of particular interest compared with chemical sensing mentioned above due to: 1) uniqueness of spectral signature in MIR and Far Infrared (FIR) spectral region enabling multicomponent detection; 2) robustness; 3) remote sensing capability; and 4) can be contentious and real time. Attenuated Total Reflection (ATR) which is an Internal Reflection Element (IRE), is well known and it is wildly used in infrared spectroscopic measurements and spectroscopic research [
The penetration depth, dp, of the evanescent wave into the sample is given by [
where l is the beam wavelength, q is the angle of the incidence beam and n1 and n2 are the indices of refraction of the ATR crystal and the sample respectively. The combination of Fourier Transform Infra-Red (FTIR) system [
In order to detect and recognize a micro-poison in aqueous solution, a good knowledge of its absorptions spectral lines (spectroscopic signature) is required. Using a radiation source and a detector operating in the
absorption line wavenumber (see
An example of using metal nano particles in spectroscopic measurements is the Surface-Enhanced Infrared Absorption (SEIRA) method [
Nano particles research has intense scientific interest due to many potential application in versatile fields such as biomedical, optics and electronic fields [
In order to demonstrate this method of pre-concentration using metal nano layer coatings, we choose micro- poison Malathion from the organophosphate (OP) group [
The First step of the demonstration includes ATR-FTIR spectroscopic signature analysis of the pure Malathion. The measurements were conducted in the MIR range using ISF 113 FTIR (Bruker Inc.) configured to operate with Globar source, Ge/KBr beam-splitter and DTGS detector. The ATR accessory was MVP-pro STAR ATR (Harrick Inc.).
The second step in the demonstration is to investigate the interaction between metal nano particles coatings and electromagnetic radiation in the MIR. This investigation was carried out using thin metal nano layer coating on silicon oxide substrate. Thin metal nano layers with different thickness were grown using sputtering machine on a regular silicon oxide substrates. Those samples were experimentally tested using the FTIR system in the MIR band for their spectroscopic signature.
From
In order to demonstrate the attraction of Malathion organophosphate to the metal nano particles and the feasibility of detecting and recognizing it using Circular ATR, we prepared two silicon oxide substrates. One of them was coated using sputtering machine with 5 nm layer of Gold nano particles and the second without coating that was used as control. A drop of pure Malathion was put on each of those two silicon substrates for two days in close cell until the drops were dried. After two days a FTIR reflection measurement in MIR band was carried out for the two substrates. The FTIR beam was directed to the location of the dried Malathion drops on the substrate surface. The results are shown in
From the spectral signature results of
The concept of pre-concentration using Circular ATR crystal coated with Gold nano particles was presented and demonstrated in this study. The result of
preparations are needed and the results are in real time. Thus, this new concept can be used to control and monitor drinking water and/or other aqua solutions and/or agriculture food products. Remote control spectral measurements can be carried out using the above experimental set-up and the circular ATR configuration (with nano metal coating) shown in
The authors would like to thanks Dr Amos Sharoni from the Nano technology center of Bar Ilan University (BIU) for is help with the preparation of metal Nano particles coatings and discussions.