design of optoelectronic tongue based on core-shell plasmonic nanostructures for visual detection and discrimination of halide ions

The purpose of this study is to provide an optoelectronic tongue for detection and discrimination of halide ions, one of the most important factors in environmental pollutants, using wide-color tonality of gold nanorods (aunrs). due to their high toxicity to mammals and organisms as well as corrosion ability, determination of halide ions in environmental waters are of high importance [1]. a group of nanostructures that are considered as sensory elements today due to their high absorption coefficient and sensitivity are aunr@ag. in these nanostructures, aunrs first synthesized and silver ions are reduced by a reducing agent and placed in the form of shells on the surface of aunrs. this sensor elements was used to determine many different analytes with growth or inhibition mechanism [2]. in this paper, inhibition of silver deposition on aunrs by the targets have been utilized for development of a colorimetric sensor array for simultaneous identification and determination of halide ions in water samples. at first aunrs with high lspr wavelengths are synthesized by a modified seed-mediated growth approach. then, at suitable ph condition, silver ions are reduced by ascorbic acid and coated on the surface of aunrs. this phenomenon leads to decrease in aspect ratio of aunrs and thus a blue shift in the longitudinal plasmon resonance of aunrs to shorter wavelength. these nanostructures are used in the next step to detection of the analytes. in the presence of the targets, due to different interaction tendency of halide ions towards silver ions in terms of their solubility constants, redox potentials and complex formation constants and their interaction with surface of aunrs as well, the thickness of silver deposited layer on the surface aunrs decreases at different levels. this alteration in the thickness of silver layer on aunrs; thus, a blue-shift in lspr peak of aunrs. these changes in the location of the lspr peak in the visible region provide a wide-range of color tonalities from red to green, blue, and purple, enabling discrimination of target anions. the fingerprint absorption profile of the aunrs@ag in the presence of halide anions analyzed by linear discriminant analysis (lda) and partial least squares (pls) regression were employed for the qualitative and quantitative determination.