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

doi:10.1007/s00216-018-1114-7

Smart app-based on-field colorimetric quantification of mercury via analyte-induced enhancement of the photocatalytic activity of TiO₂-Au nanospheres

Anal Bioanal Chem. 2018 Jul;410(18):4555-4564. doi: 10.1007/s00216-018-1114-7. Epub 2018 Jun 4.

Authors

Rini Ravindranath^{1

2}, Arun Prakash Periasamy¹, Prathik Roy¹, Yu-Wen Chen¹, Huan-Tsung Chang^{3

4}

Affiliations

¹ Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei, 10617, Taiwan.
² Nanoscience and Technology Program, Taiwan International Graduate Program, Academia Sinica, Taipei, 11529, Taiwan.
³ Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei, 10617, Taiwan. changht@ntu.edu.tw.
⁴ Department of Chemistry, Chung Yuan Christian University, Chung Li District, Taoyuan City, 32023, Taiwan. changht@ntu.edu.tw.

PMID: 29862429
DOI: 10.1007/s00216-018-1114-7

Abstract

We have devised a unique strategy for highly sensitive, selective, and colorimetric detection of mercury based on analyte-induced enhancement of the photocatalytic activity of TiO₂-Au nanospheres (TiO₂-Au NSs) toward degradation of methylene blue (MB). Through electrostatic interactions, Au nanoparticles are attached to poly-(sodium 4-styreneulfonate)/poly(diallyldimethylammonium chloride) modified TiO₂ nanoparticles, which then form an Au shell on each TiO₂ core through reduction of Au³⁺ with ascorbic acid. Notably, the deposition of Hg species (Hg²⁺/CH₃Hg⁺) onto TiO₂-Au NSs through strong Au-Hg aurophilic interactions speeds up catalytic degradation of MB. The first-order degradation rates of MB by TiO₂-Au NSs and TiO₂-Au-Hg NSs are 1.4 × 10^-2 min^-1 and 2.1 × 10^-2 min^-1, respectively. Using a commercial absorption spectrometer, the TiO₂-Au NSs/MB approach provides linearity (R² = 0.98) for Hg²⁺ over a concentration range of 10.0 to 100.0 nM, with a limit of detection (LOD) of 1.5 nM. On the other hand, using a low-cost smartphone app that records the color changes (ΔRGB) of MB solution based on the red-blue-green (RGB) component values, the TiO₂-Au NSs/MB approach provides an LOD of 2.0 nM for Hg²⁺ and 5.0 nM for CH₃Hg⁺, respectively. Furthermore, the smartphone app sensing system has been validated for the analyses of various samples, including tap water, lake water, soil, and Dorm II, showing its great potential for on-line analysis of environmental and biological samples. Graphical Abstract ᅟ.

Keywords: Mercury; Methylene blue; Photo-degradation; Photocatalyst; Smartphone app; TiO2–Au nanospheres.