Pushing Down the Limit of NH₃ Detection of Graphene-Based Chemiresistive Sensors through Functionalization by Thermally Activated Tetrazoles Dimerization

Abstract

An easy and cost-effective method is presented to functionalize graphene through thermally activated dimerization of 2,5-diaryltetrazoles. Consistently with the experimental spectroscopic results, theoretical calculations demonstrate that during the thermal treatment a dimerization process to tetrazine is energetically more favorable than covalent grafting. Since both the functionalization method by thermal activation and the use of tetrazoles have never been considered before to prepare graphene-based chemiresistors, this represents a promising approach to develop graphene-related sensing platforms. Five different 2,5-diaryltetrazoles have been tested here for the effective functionalization of low-defect graphene layers on silicon nitride. Based on these layers, an array of sensors has been prepared for testing upon ammonia exposure. The tests on the sensing performances clearly show sensitivity to ammonia, extending the current range of ammonia detection with a graphenebased chemiresistor down to the sub-ppm range, as results from a benchmarking with data available in the literature. Furthermore, all sensors perform better than bare graphene. Density functional theory (DFT) calculations, carried out on a model of the best performing layer of the array, provided the theoretical framework to rationalize the sensing mechanism and disclose a dual role played by the tetrazine molecules, (i) acting as ammonia concentrators and (ii) mediating the electron transfer between ammonia and graphene.

Targeting biomarkers in the gas phase through a chemoresistive electronic nose based on graphene functionalized with metal phthalocyanines

“…A comparison with literature works has been performed in terms of sensitivity ( i.e. sensor response percentage normalized over the concentration: (Δ R / R 0 × 100)/[NH 3 ]) and detection limit: the results obtained for the five developed sensors are in line with both graphene-based sensors, 28,29,73–80 and reduced graphene oxide functionalized with metal phthalocyanine molecules, 81–84 as can be found in Table SVII †…”

“…A comparison with literature works has been performed in terms of sensitivity (i.e. sensor response percentage normalized over the concentration: (DR/R 0 × 100)/[NH 3 ]) and detection limit: the results obtained for the ve developed sensors are in line with both graphene-based sensors, 28,29,[73][74][75][76][77][78][79][80] and reduced graphene oxide functionalized with metal phthalocyanine molecules, [81][82][83][84] as can be found in Table SVII. † As for the sensing mechanisms, the resistance increase upon ammonia exposure indicates that the Gr, Gr_FePc, Gr_NiPc, and Gr_ZnPc layers are p-type, consistently with the fact that the electron injection from ammonia reduces the density of holes in these layers.…”

“…26,27 In this perspective Gr represents a more reliable layer to develop sensing platforms, provided that proper and effective functionalization strategies are introduced to enhance Gr sensing properties. In particular, recent studies have demonstrated the possibility to develop highly sensitive Gr layers upon functionalization, [28][29][30][31][32] disclosing important progress in the eld of specic molecule sensing in the gas phase that, in turn, can be considered as a promising starting point for the development of graphene-based e-noses. So far only few Gr-based enoses driven in a FET conguration have been reported, [33][34][35] which requires micro-electronic grade preparation of the device, or e-noses based on capacitors.…”

A Chemiresistor Sensor Array Based on Graphene Nanostructures: From the Detection of Ammonia and Possible Interfering VOCs to Chemometric Analysis

“…Carbon nanotubes have been largely studied as single sensors [ 26 , 27 , 28 ] and, even to a lesser extent, also as electronic noses [ 17 , 29 ], while, only in the past few years, graphene, thanks to its high sensitivity to the surface adsorption of gas molecules [ 30 ], its high in-plane conductivity, and its low electrical intrinsic noise [ 31 ], has attracted the interest or researchers working in the sensors field. Although recent studies have clearly demonstrated the possibility to develop highly sensitive graphene sensors after proper functionalization [ 32 , 33 , 34 , 35 , 36 , 37 ], still few are the works exploiting graphene to develop sensors array [ 38 , 39 , 40 ], especially in a chemiresistor configuration [ 41 ].…”

Imine Bond-Based Fluorescent Nanofilms toward High-Performance Detection and Efficient Removal of HCl and NH3

“…To address the problems, various techniques such as chemosensors, − colorimetric sensors, − electrochemical methods, − and sol–gel-based visualization have been used for the monitoring of them. These techniques, however, are hard to be widely used because they may suffer from some of the shortcomings such as a bulky instrument, slow response, low sensitivity, unfavorable reversibility, specially trained personnel, high cost, etc. − Recently, metal–organic frameworks (MOFs), − nanofibrous membranes, , and polymers were used to conduct the detection.…”