Conducting polymer-based optical sensor for heavy metal detection in drinking water

Polyaniline (PAni), the conducting polymer, has been investigated for decades, and has been explored extensively for electrochemical applications based on the fact that the conductivity and conformation of PAni changes with its protonation-deprotonation effects. We studied a phenomenon, i.e. change in the optical characteristics of PAni without explicit protonation or de-protonation, rather due to interaction of immunoglobulin (IgG) with heavy metal ions on its surface. The present study aims to incorporate PAni as a detection matrix to develop evanescent wave absorbance based fibre-optic sensor for detection of heavy metals in drinking water. Empirical study showed heat treated IgG exhibits more affinity towards heavy metal ions compared to native IgG. Binding of heavy metals (arsenic, lead, mercury and cadmium) to IgG showed spectroscopic alteration of PAni which was utilized to develop a cost-effective fibre-optic heavy metal sensor. The study was accomplished using an experimental set up consisting of a white light source, optical fiber and a spectrometer. The preliminary experiments were carried out with 10 ppb of arsenic, lead, mercury and cadmium and significant response was observed for each of the heavy metals. Interference of the sensor with other normal ions for e.g. potassium, sodium, magnesium, manganese, iron and zinc were also tested. The current investigation represents a significant step to fabricate highly sensitive optical