Smart app-based on-field colorimetric quantification of mercury via analyte-induced enhancement of the photocatalytic activity of TiO₂–Au nanospheres Rini Ravindranath, Arun Prakash Periasamy, Prathik Roy, Yu-Wen Chen, Huan-Tsung Chang Jun 4, 2018 mercury detection TiO₂–Au nanospheres