1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Materials Science inc. Nanomaterials & Polymers Nano Gold Hybrid Polyvinyl Alcohol Films for Sensing of Cu 2 + ions Deepak Sahu, Niladri Sarkar, Priyaranjan Mohapatra, and Sarat K Swain* [a] An efficient and eco-friendly approach is adopted for the synthesis of highly stable L-alanine assisted nano gold based polyvinyl alcohol nanocomposite hybrid films (Au/PVA).The – COOH groups of L-alanine and oxygeneous groups of polyvinyl alcohol are utilized for the synthesis of size controlled gold nanoparticles. The as-synthesized nanocomposites show rapid and selective detection of Cu 2 + ion in aqueous medium. With addition Cu 2 + ion to as-synthesized nanocomposites, the SPR peaks of Au NPs (538 nm) decrease with occurrence of a red shift as well as a new peak is observed at higher wavelength which is due to the aggregation of gold nanoparticles in the nanocomposites hybrid films. Scanning electron microscope (SEM) micrograph and energy dispersive spectroscopy (EDS) reveal the aggregation of gold nanoparticles in the nano- composite hybrid films. The limit of detection and limit of quantification for Cu 2 + ion are 40 nM and 133 nM respectively. This technique for detection of Cu 2 + ion in waste water samples is inexpensive and eco-friendly since no any toxic chemicals are used. In the presence of Cu 2 + ion, the colour of the hybrid film is changed hence, this method also involves visual detection of Cu 2 + ion without use of electrolyte or transducer. Further, many reported methods represent the in situ monitoring of Cu 2 + ion, but the present hybrid film can be used for in situ as well as ex situ monitoring of Cu 2 + ion. Introduction Recently, researchers are running behind the developing of nanosensor for the detection of toxic metal ions from the environmental and biological samples. Among different metal ions, Cu 2 + ion is one of the important environmental pollutant. Generally, Cu 2 + ions are third abundant metals in the human body. But excessive amount of Cu 2 + ion not only imbalance the cellular process that lead to Wilson’s disease, Parkinson’s disease but also causes many problems such as gastro intestinal disturbance, liver and kidney damage. [1–5] According to World Health Organization (WHO) maximum permissible limit is 20.5 μM in drinking water. [6] Moreover, copper ions are released from metallurgical plants and mixed with water, dust and fume that increase environmental pollution. Generally, 0.25 ppb (4 nM) and 3ppb (47 nM) of Cu 2 + ion are found in sea water and fresh water respectively. Although many sensitive techniques such as inductively coupled plasma optical emission spectroscopy(ICP-OES), [7] inductively coupled plasma mass spectrometry, [8] surface-enhanced Raman scattering spectro- scopy (SERS) [9] and atomic absorption spectroscopy [10] and are developed for the detection of Cu 2 + ion from aqueous, but these require difficult sample preparation and time consuming. Therefore, it is important to develop highly sensitive techniques that are cheap and do not require any difficult instruments. Over the past decades, various researchers are focused on the synthesis of nanostructured materials for the detection of copper ion on the basis of the high surface-to-volume ratio of nanomaterials. [11,12] Among all noble nanomaterial, gold nano- particles (Au NPs) have attracted much attention due to their different properties such as magnetic, catalytic properties, sensing properties, optical properties and electronic properties. [13–15] It gives a strong surface plasmon resonance (SPR) absorption peak in the UV-visible region. Therefore, it is used as sensor for detection of DNA, melamine, alkali metals and heavy metals ions. [16–21] Further, it has many applications in the field of catalysis and biology. Basically, SPR technique can be applied for the different studies such as bimolecular interactions detection, [22] plasma coagulation detection [23] and SPR imaging for protein/DNA, nucleic acids and protein–protein interactions. [24] For the detection of Cu 2 + ion in aqueous medium, gold nanoparticles based colorimetric and fluorescence sensor have been developed in many reports. Alizadeh et al. have synthesized pyridines-assisted Au NPs for colorimetric sensing of Cu 2 + and Ag + ions. [25] Formaldehyde modified hyper branched polyethylenimine capped Au NPs have been proposed for fluorescent and colorimetric detection of Cu 2 + . [26] Xu et al. has designed DNA modified gold nano- particle for sensing of Cu 2 + ion. [27] However, many toxic and costly chemicals are used for the synthesis of nanomaterial. Therefore, development of low cost and eco-friendly approach for the synthesis of gold nanoparticles is necessary towards sensing of heavy metal ion such as Cu 2 + ion in aqueous media. Basically, the absorption spectra of gold nanoparticles are shifted and the colour of the nanoparticles is changed due to change in their size and aggregation state. [28–31] The aggrega- [a] D. Sahu, N. Sarkar, Dr. P. Mohapatra, Prof. S. K Swain Department of Chemistry, Veer Surendra Sai University of Technology, Burla, Sambalpur- 768018, Odisha, India Tel.:91-9937082348 Fax: 91–663-2430204 E-mail: skswain_chem@vssut.ac.in swainsk2@gmail.com Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201902167 Full Papers DOI: 10.1002/slct.201902167 9784 ChemistrySelect 2019, 4,9784–9793 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim