Room Temperature VOCs Sensing with Termination‐Modified Ti₃C₂T_x MXene for Wearable Exhaled Breath Monitoring

Abstract

not only played an indispensable role in environmental monitoring, but also been investigated in human healthcare and disease diagnosis. [1] Recent advances have explored the feasibility of using exhaled breath VOCs as biomarkers for monitoring of metabolic activities, [2] diabetes, [3] respiratory diseases, [4] as well as discrimination of cancer patients from health persons. [5] Compared with laborious gas chromatography, or conventional metal oxide sensors that require high operation temperature, VOCs sensors working at room temperature are rather appealing because of the low power consumption that greatly simplifies the fabrication of sensor devices. [6] Furthermore, the elimination of a heater can facilitate the integration of VOCs sensors to flexible electronics, where the flexible matrixes barely bear with high temperature. [6b,7] Thus, VOCs sensors operated at room temperature are ideal components to realize wearable gas sensing devices, [6b,8] which can provide in situ and real-time insights into variations of concerned targets within exhaled breath. However, the highly humidified exhaled breath inevitably results in dramatic background signals induced by respiration activities, casting shadow on the detection of exhaled VOCs.Nanoscale metal oxides, nanotubes, and 2D nanomaterials could all act as sensing layers in room temperature VOCs sensors. By doping of noble metal particles or forming of heterojunctions, these nanostructures may facilitate the covalent or ionic adsorption of VOCs molecules, thus the working temperature of metal oxides can be greatly decreased. [6a] The latter ones, however, rely more on physical absorption and intermolecular interactions, which can be promoted by increasing specific surface area and surface active sites via nanomaterial decoration. [9] Although promising nanomaterials including graphene and its derivatives, [10] transition metal dichalcogenides (TMDs), [9c,11] metal-organic frameworks (MOFs), [12] and carbon nanotubes [9b,13] have been intensively investigated in VOCs sensing, sensing materials with comprehensive merits of good conductivity, low noise, large surface area, and ample anchoring sites remain to be further exploited.2D transition metal carbides, carbonitrides, and nitrides, namely MXenes, have emerged as a promising family of 2D nanomaterials since its first report in 2011. [14] Etched from ternary precursor MAX (layered hexagonal-structure ternary Room temperature volatile organic compounds (VOCs) sensors usually suffer from severe humidity interference and insufficient sensitivity against VOCs, which greatly restricts its practical applications. Herein, the authors simultaneously reduce the hydrophilicity while improving the VOCs sensitivity of Ti 3 C 2 T x MXene by introducing hydrocarbon terminations. The terminationmodified Ti 3 C 2 T x (Ti 3 C 2 T x -M2) sensor demonstrates fivefold enhancement in ethanol sensitivity at room temperature, while response against water vapor has been reduced by 71% compared with pristine Ti 3 C 2 T x . ...

Ti3AlC2 MAX phase conversion to a novel 2D titanium carbo-oxide by an eco-friendly and low-cost method: highly selective gas sensing and supercapacitor evaluations

“…14,26 Although some reports have shown the use of MXene for VOC detection at room temperature, the selectivity still needs to be improved. 27 The problem of selectivity in VOCs detection is more difficult, especially against ethanol, because all of them are reducing gases and have the tendency to react in the same way with the sensing material.…”

Wafer-Level, High-Performance, Flexible Sensors Based on Organic Nanoforests for Human–Machine Interactions

“…As shown in Figure a, there is an abrupt change in the sensitivity curve of the sensor at 60% RH; this can be ascribed to the reach of the critical humidity condition. At this critical condition, the way the water molecules are absorbed changes from chemisorption to physisorption. − Especially when RH is below the critical condition, the number of water molecules is not large enough to form a continuous layer, whereas beyond the critical point, excess water molecules tend to form more layers on the sensing material. , In such a condition, the transfer of condensed water to the positions of electrodes becomes possible. Consequently, we obtained linear relationships between the capacitance and RH, one for each humidity range.…”

Flexible/wearable resistive gas sensors based on 2D materials

“…When integrated with a wearable detection tag, the sensor was successfully used for the in situ monitoring of exhaled ethanol. 84…”

“…When integrated with a wearable detection tag, the sensor was successfully used for the in situ monitoring of exhaled ethanol. 84 Hybrids of MXenes and other materials can also offer good opportunities for gas sensing applications. 85 For example, a Ti 3 C 2 T x MXene/rGO fiber gas sensor has been fabricated and shown to provide an almost constant resistance under 2000 bending cycles.…”