Abstract
Carbon nanotubes (CNTs) combine high electrical conductivity with high surface area and chemical stability, which makes them very promising for chemical sensing. While water quality monitoring has particularly strong societal and environmental impacts, a lot of critical sensing needs remain unmet by commercial technologies. In the present review, we show across 20 water monitoring analytes and 90 references that carbon nanotube-based electrochemical sensors, chemistors and field-effect transistors (chemFET) can meet these needs. A set of 126 additional references provide context and supporting information. After introducing water quality monitoring challenges, the general operation and fabrication principles of CNT water quality sensors are summarized. They are sorted by target analytes (pH, micronutrients and metal ions, nitrogen, hardness, dissolved oxygen, disinfectants, sulfur and miscellaneous) and compared in terms of performances (limit of detection, sensitivity and detection range) and functionalization strategies. For each analyte, the references with best performances are discussed. Overall, the most frequently investigated analytes are H+ (pH) and lead (with 18% of references each), then cadmium (14%) and nitrite (11%). Micronutrients and toxic metals cover 40% of all references. Electrochemical sensors (73%) have been more investigated than chemistors (14%) or FETs (12%). Limits of detection in the ppt range have been reached, for instance Cu(II) detection with a liquid-gated chemFET using SWCNT functionalized with peptide-enhanced polyaniline or Pb(II) detection with stripping voltammetry using MWCNT functionalized with ionic liquid-dithizone based bucky-gel. The large majority of reports address functionalized CNTs (82%) instead of pristine or carboxyl-functionalized CNTs. For analytes where comparison is possible, FET-based and electrochemical transduction yield better performances than chemistors (Cu(II), Hg(II), Ca(II), H2O2); non-functionalized CNTs may yield better performances than functionalized ones (Zn(II), pH and chlorine).
Highlights
While fresh water represents 3% of the total water on Earth, only 0.01% is available for human consumption [1]
After a brief overview of the design, fabrication and operating principles of CNTbased chemical sensors, we present exhaustively the various electrical and electrochemical sensors reported in the literature from 2000 to mid-2021
For Hg(II), the limit of detection (LOD) achieved with voltammetry is three orders of magnitude better than that obtained with FET, the latter being two orders of magnitude better than with chemistor
Summary
While fresh water represents 3% of the total water on Earth, only 0.01% is available for human consumption [1]. Unsustainable water use in agriculture and industry and climate changes are bringing about hydric stress worldwide. While drink water availability decreases, its quality degrades: World Health Organization (WHO) reports that, in developing countries, 80% of human diseases, are water borne [2]. Drinking water quality in numerous countries does not meet WHO standards [3,4]. The presence of water contaminants critically impacts human beings and ecosystem. It is of vital importance to be able to analyze fresh water, whether it is groundwater, irrigation water or tap water
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