Solid-State Chemiresistors from Two-Dimensional MoS2 Nanosheets Functionalized with l-Cysteine for In-Line Sensing of Part-Per-Billion Cd2+ Ions in Drinking Water

Paul Bazylewski; Sheldon Van Middelkoop; Ranjith Divigalpitiya; Giovanni Fanchini

doi:10.1021/acsomega.9b03246

Solid-State Chemiresistors from Two-Dimensional MoS₂ Nanosheets Functionalized with l-Cysteine for In-Line Sensing of Part-Per-Billion Cd²⁺ Ions in Drinking Water

ACS Omega. 2019 Dec 26;5(1):643-649. doi: 10.1021/acsomega.9b03246. eCollection 2020 Jan 14.

Authors

Paul Bazylewski^{1

2}, Sheldon Van Middelkoop¹, Ranjith Divigalpitiya², Giovanni Fanchini^{1

3}

Affiliations

¹ Department of Physics & Astronomy, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada.
² 3M Canada Company, 1840 Oxford St., London, Ontario N5V 3R6, Canada.
³ Department of Chemistry, University of Western Ontario, 1151 Richmond Street., London, Ontario N6A 5B7, Canada.

Abstract

Sensing of metal contaminants at ultralow concentrations in aqueous environments is vital in today's overpopulated world, with an extremely stringent limit (<5 ppb) for Cd²⁺ ions in drinking water. Here, we utilize sonochemically exfoliated molybdenum disulfide (MoS₂) nanosheets functionalized with l-cysteine (Cys) as highly sensitive and selective two-dimensional (2D) materials for solid-state chemiresistors. We specifically targeted Cd²⁺ ions due to their high toxicity at low concentrations. MoS₂-Cys nanosheets are fabricated using an ad hoc, low-complexity, one-pot synthesis method. Porous MoS₂-Cys thin films with a high surface area are assembled from these nanosheets. Two-terminal chemiresistors incorporating MoS₂-Cys films are demonstrated to be preferentially sensitive to Cd²⁺ ions at neutral pH, irrespective of other metal ions present in water flowing through the device. A 5 ppb concentration of the Cd²⁺ ions in the water stream increases the device resistivity by 20 times. Our devices operate at broad (1-500 ppb) range and fast (∼1 s) response times. Cd²⁺ is selectively detected because of preferential, size-driven adsorption at the interstitials between l-cysteine functional groups, combined with pH-controlled charge transfer that removes electronic gap states from MoS₂. MoS₂-Cys-based chemiresistors can be deployed in-line to detect metal ions without any need for additional offline measurements.