Competitive redox reaction of Au-NCs/MnO2 nanocomposite: Toward colorimetric and fluorometric detection of acid phosphatase as an indicator of soil cadmium contamination

Miao Xu; Ruixue Ma; Chunyu Huang; Guoyue Shi; Tianshu Zhou; Jingjing Deng

doi:10.1016/j.aca.2019.10.062

Competitive redox reaction of Au-NCs/MnO₂ nanocomposite: Toward colorimetric and fluorometric detection of acid phosphatase as an indicator of soil cadmium contamination

Anal Chim Acta. 2020 Feb 1:1096:174-183. doi: 10.1016/j.aca.2019.10.062. Epub 2019 Oct 31.

Authors

Miao Xu¹, Ruixue Ma¹, Chunyu Huang¹, Guoyue Shi², Tianshu Zhou¹, Jingjing Deng³

Affiliations

¹ School of Ecological and Environmental Sciences, Shanghai Key Lab for Urban Ecological Process and Eco-Restoration, East China Normal University, 500 Dongchuan Road, Shanghai, 200241, China; Institute of Eco-Chongming, 3663 Zhongshan Road, Shanghai, 200062, China.
² School of Chemistry and Molecular Engineering, East China Normal University, 500 Dongchuan Road, Shanghai, 200241, China.
³ School of Ecological and Environmental Sciences, Shanghai Key Lab for Urban Ecological Process and Eco-Restoration, East China Normal University, 500 Dongchuan Road, Shanghai, 200241, China; Institute of Eco-Chongming, 3663 Zhongshan Road, Shanghai, 200062, China. Electronic address: jjdeng@des.ecnu.edu.cn.

PMID: 31883584
DOI: 10.1016/j.aca.2019.10.062

Abstract

In this study, by rational regulating the competitive redox reaction of Au-NCs/MnO₂ nanocomposite between the dye indigo carmine (IC) and the enzymatic product L-ascorbic acid (AA), we have established a colorimetric and fluorometric double-channel responsive assay for acid phosphatase (ACP), which could serve as an indicator of soil cadmium (Cd) contamination. Initially, the gold nanoclusters (Au-NCs) were added to the suspension of MnO₂ nanosheets to form Au-NCs/MnO₂ nanocomposite with enhanced oxidative degradation ability. When IC was subsequently added, the blue color of IC faded due to oxidative degradation, and the mixture showed the yellow color of Au-NCs/MnO₂ nanocomposite. Meanwhile, based on the inner filter effect (IFE), the fluorescence of Au-NCs was suppressed by MnO₂ nanosheets during this process. However, with the presence of AA, hydrolyzed from L-ascorbic-2-phosphate (AAP) by ACP, the MnO₂ nanosheets in Au-NCs/MnO₂ nanocomposite were reduced to Mn²⁺ immediately. As a consequence, IC remained its blue color, in the meantime, the fluorescence of Au-NCs recovered, which essentially constituted a new mechanism for ACP detection with colorimetric and fluorometric double-channel response. With the method we developed, soil ACP activity can either be directly visualized by bare eyes or detected reliably through double channels. Furthermore, the dynamic changes of ACP activity during soil Cd contamination could also be monitored; the sharp increase of ACP activity at an appropriate time point could serve as a unique alarm for cadmium (Cd) contamination in soil, which is of great importance for soil quality evaluation and ecological risk assessment.

Keywords: Acid phosphatase; Au-NCs/MnO(2) nanocomposite; Competitive redox reaction; Dual-mode assay; Soil cadmium contamination.