Application of Polypyrrole Multi-Walled Carbon Nanotube Composite Layer for Detection of Mercury, Lead and Iron Ions Using Surface Plasmon Resonance Technique

Lead and Iron Ions Using Surface Plasmon Resonance Technique. PLoS ONE 9(4): e93962. doi:10.1371/journal.pone.0093962 Application of Polypyrrole Multi-Walled Carbon Nanotube Composite Layer for Detection of Mercury, Lead and Iron Ions Using Surface Plasmon Resonance Technique Amir Reza Sadrolhosseini 0 A. S. M. Noor 0 Afarin Bahrami 0 H. N. Lim 0 Zainal Abidin Talib 0 Mohd. 0 Adzir Mahdi 0 Nikolai Lebedev, US Naval Reseach Laboratory, United States of America 0 1 Wireless and Photonics Networks Research Center of Excellence (WiPNET), Faculty of Engineering Universiti Putra Malaysia , Serdang, Selangor , Malaysia , 2 Department of Computer and Communication Systems Engineering, Faculty of Engineering , Universiti Putra Malaysia, Serdang, Selangor , Malaysia , 3 Faculty of Science, Islamic Azad University , Eslamshahr Branch, Tehran , Iran , 4 Department of Chemistry, Faculty of Science, Universiti Putra Malaysia , Serdang, Selangor , Malaysia , 5 Functional Device Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia , Serdang, Selangor , Malaysia , 6 Department of Physics, Faculty of Science, Universiti Putra Malaysia , Serdang, Selangor , Malaysia Polypyrrole multi-walled carbon nanotube composite layers were used to modify the gold layer to measure heavy metal ions using the surface plasmon resonance technique. The new sensor was fabricated to detect trace amounts of mercury (Hg), lead (Pb), and iron (Fe) ions. In the present research, the sensitivity of a polypyrrole multi-walled carbon nanotube composite layer and a polypyrrole layer were compared. The application of polypyrrole multi-walled carbon nanotubes enhanced the sensitivity and accuracy of the sensor for detecting ions in an aqueous solution due to the binding of mercury, lead, and iron ions to the sensing layer. The Hg ion bonded to the sensing layer more strongly than did the Pb and Fe ions. The limitation of the sensor was calculated to be about 0.1 ppm, which produced an angle shift in the region of 0.3u to 0.6u. - Funding: The authors would like to appreciate the Wireless and Photonics Networks Research Center of Excellence (WiPNET), Faculty of Engineering University Putra Malaysia for their continued supported throughout this project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Polypyrrole, polypyrrole-chitosan, polyanilin, and polythiophene [1] are conducting polymers so they have a good environmental stability and the ability to monitor the intrinsic affinity to heavy metal ions [2,3,4,], glucose [5,6,7], H2O2 [5,8], and they are sensitive to Cu, Pb, Hg, Au [9,10,11], Zn and Ni [12] ions. Hence, some researchers have considered the optical, electrical and thermal properties of conducting polymer. Polypyrrole (PPy) is a well-known conducting polymer and used for biosensors [13,14], composite materials [15,16], microelectronic devices [17], while a combination of polypyrrole and nanoparticles was used to enhance the sensing of biomolecules [18]. Carbon nanotubes (CNTs) enhance the electrical, thermal and optical properties of polymer and plastic materials [19]. CNTs are cylindrical shells with diameters in the 100 nm range and a high surface to volume ratio. High sensitivity, fast reaction time, and the modulation behavior of CNTs near biomaterials are the prominent properties to apply when considering sensor applications [19,20]. Hence, Sotiropoulou et al. [21] and Besteman et al. [22] sensed glucose using CNTs by immobilizing glucose-oxideenzymes on CNTs. Moreover, CNTs were used to detect heavy metals [23] such as Pb [24,25], U [26], and Cd [27] ions. Mercury, lead and iron ions have long been recognized as toxic and harmful environmental pollutants. Mercury has high vapor pressure and low stability. The Hg element can release into the environment and produce extreme toxicity, the Hg ion combines primarily with inorganic compounds and cannot be methylated. In contrast, the mercuric ion combines with both inorganic and organic ligands and can be methylated [6]. Mercury [28] and lead have toxic effects on humans [29] and can cause severe damage in the bones, kidneys, liver, brain [30] and the central nervous system [31,32,33]. The iron ion is a heavy metal and cause environmental pollution, while an over load is a cause of hemochromatosis [34]. Therefore, the detection and measurement of Hg, Pb, and Fe ions become more significant. Hence, as layer detector, such as polypyrrole and 2-mercaptobenzothiazole [6], polypyrrole chitosan composite [7], 1,6-hexanedithiol [35], and apo-metallothionein [36] were used to detection heavy metal ions in an aqueous solution using surface plasmon resonance with different sensitivity and selectivity. Ning et al. also used Ag and Au nanoparticles for detection of Hg ion in a water sample [37]. Panta et al. combined the conventional electrochemical method, surface plasmon resonance (SPR), and magnetohydrodynamic (MHD) convection to measure the concentration of the Hg ion [38]. They detected the Hg ion down to 1 fM concentration in aqueous solution but this method was combination of three methods. Hence, the mentioned sensor layer are sensitive to Hg or Pb and they cannot detect the Hg and Pb together with a high degree of accuracy. In 1994, Ajayan et al., reported synthesizing a carbon nanotube polymer nanocomposite [39]. Multi-walled carbon nanotubes (MWCNTs) have a conjugated p bond structure [40]. The delocalized p electrons in MWCNTs and PPy can bond together in a nanocomposite way to reduce the energy of the system and form a PPy/CNT nanocomposite [41,42,43], so polypyrrole with a MWCNT composite was used to improve the sensitivity and selectivity of sensors via interfacial interactions between MWCNTs and the conducting polymer [44, 45 and 46]. There are many techniques for analyzing trace metal, including atomic absorption, fluorescence spectrometry, inductively coupled plasma-mass spectrometry (ICP-MS), and electrochemical techniques. The application of these techniques suffers from disadvantages like the cost of the instrument, chemical knowledge, and nonlinearity of the calibration curve. A surface plasmon resonance (SPR) sensor is a versatile and effective optical technique to use to measure the concentration of ions and biomolecules. Good sensitivity, stability, reproducibility and portability are advantages of the SPR sensor. SPR is sensitive to a refractive index of analyte, and it exhibits change in real and imaginary parts of the refractive index [6,47]. In the present work, PPy-MWCNTs films were characterized using the Surface Plasmon Resonance (SPR) technique. As mentioned above, mercury, lead and iron are the most important heavy metals, and detection of them are the subject of certain environmental research, so the detection of Hg, Pb and Fe ions are presen (...truncated)