Abstract
This study synthesized bare silver nanoparticles on paper and evaluated its response to copper (Cu(II)) ions to assess its potential as colorimetric sensing platform. The nanoparticles were synthesized in-situ on paper using silver nitrate and sodium borohydride as precursor and reducing agent, respectively. No stabilizer or functionalizing agent was added. A two-factor three-level full factorial design with varying concentration of reagents was employed in the synthesis process. The resulting sensor was successfully characterized using diffuse reflectance spectroscopy and scanning electron microscopy with elemental dispersive x-ray spectroscopy. The sensor was exposed to varying Cu(II) concentrations ranging from 1 to 30 mM and the developed color changes were analyzed using a computer imaging software. The changes in color were quantified using mean gray values from the imaging software. Based on the results, as the concentration of Cu(II) ions increased, the final mean gray value of the paper increased as well. The papers were observed to marginally lighten in color potentially due to the decrease in silver atoms or its interaction with copper. The relationship between Cu(II) concentration and the ratio of final and initial mean gray value was determined and although a weak linear relation existed from 1 to 30 mM, a positive slope supported the increase in mean gray value within the range tested. The changes in the elemental composition of the sensor due to exposure to Cu(II) ions were studied. Finally, the response of the sensor towards other metal ions was compared to that of Cu(II) in a selectivity study.