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MXene-based sensors and biosensors: next-generation detection platforms
MXene-based sensors and biosensors: next-generation detection platforms
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Ankita Sinha1, Dhanjai2,3,4, Samuel M. Mugo3, Jiping Chen4 and Koodlur S. Lokesh5 1 Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, China), School of Environmental Science and Technology, Dalian University of Technology, Dalian, P.R. China, 2Department of Mathematical and Physical Sciences, Concordia University of Edmonton, Edmonton, AB, Canada, 3Department of Physical Sciences, MacEwan University, Edmonton, AB, Canada, 4CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian P.R. China, 5Department of Chemistry/Industrial Chemistry, Vijayanagara Sri Krishnadevaraya University, Ballari, India
14.1
Introduction
In current times, two-dimensional (2D) layered materials have withdrawn considerable attention due to their morphological resemblance with graphene. So far, 2D materials such as transition metal dichalcogenides and boron nitride have been extensively studied for their significant applications in the fields of electronics, catalysis, energy etc. [14]. Recently, MXene has emerged as a unique 2D material that mainly includes early transition metal carbides, nitrides, and carbonitrides [59]. MXene possesses layered morphology and are produced by etching layers of sp elements from three-dimensional (3D) MAX phases [9]. MAX phases are layered hexagonal with P63/mmc symmetry with general formula Mn11AXn (n 5 1, 2, 3) where M represents d-block transition metals, A represents main group 13 and 14 elements, and X is either C or N atoms [57]. The MX bond holds covalent/metallic/ionic character, whereas MA bond is of pure metallic nature [5]. Therefore, at high temperatures, MA bond decomposes into Mn11Xn, which results into recrystallization and formation of 3D Mn11Xn rocksalt-like structure [6]. Selective etching of reactive A layers from their MAX phases can be done using suitable chemicals without destroying MX layers (Fig. 14.1A) [6,8]. The process leads to the formation of highly stable closely packed Mn11XnTx layers, where Tx is the surface-terminating functional group such as oxygen (O), fluorine (F), or hydroxyl (OH) (Fig. 14.1B) [5,6,10]. For example, preparation of 2D Ti3C2 can be performed by exfoliation
Handbook of Nanomaterials in Analytical Chemistry. DOI: https://doi.org/10.1016/B978-0-12-816699-4.00014-1 Copyright © 2020 Elsevier Inc. All rights reserved.
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Figure 14.1 (A) Exfoliation of MAX phases and preparation of 2D MXene sheets, (B) Ti3C2Tx structure showing terminating groups on the surface of Ti3C2Tx nanosheets, (C) SEM, (D) TEM, (E) HRTEM, (F) SAED, (G) XRD, (H) FTIR of Ti3C2 MXene [6,10]. Source: Reprinted with permission from M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, et al., Two dimensional transition metal carbides, ACS Nano 6 (2012) 13221331; E. Lee, A.V. Mohammadi, B.C. Prorok, Y.S. Yoon, M. Beidaghi, D.J. Kim, Room temperature gas sensing of two-dimensional titanium carbide (MXene), ACS Appl. Mater. Interfaces, 9 (2017) 3718437190.
of Ti3AlC2 in 50% hydrogen fluride (HF) at room temperature for 2 h as per the following reactions [5,6]; Mn11 AlXn 1 3HF 5 AlF3 1 Mn11 Xn 1 1:5 H2
(14.1)
Mn11 Xn 1 2H2 O 5 Mn11 Xn ðOHÞ2 1 H2
(14.2)
Mn11 Xn 1 2HF 5 Mn11 Xn F2 1 H2
(14.3)
In the aqueous environment of HF solutions, the Al atoms are replaced by O, F, or OH functional groups and hence the outer surfaces of the exfoliated MX layers are chemically terminated [1114]. Thus, the interactions between the Mn11Xn layers become weak making their separation easy. Replacement of AlM bond through hydrogen or van der Waals bonds allows delamination of MXene by the
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ultrasonication of HF-treated MAX phases in suitable solvents such as isopropyl alcohol or methanol. This surface functionalization leads to significant impacts on the electronic and ion-transport properties of MXenes. The microscopic (scanning electron microscopic (SEM), transmission electron microscopic (TEM), high resolution TEM (HRTEM), selected area electron diffration (SAED) and spectroscopic (x-ray diffraction (XRD), Fourier transform infrared (FTIR)) characterization of 2D-layered MXene has been shown in Fig. 14.1(CH) [6,10]. MXenes show variable electronic activity depending upon their functionalization [11]. Since their discovery in 2011, MXenes have gained significant attraction due to their unique layered structure and extraordinary catalytic properties. MXenes offer extremely exceptional chemical, electrical, and ion-transport properties that promise for a wide range of potential applications in various fields [1517]. Recently, MXene has been applied as a sensitive platform for sensing and biosensing applications, which has been discussed in the present chapter. Moreover, future prospects in developing MXene-based detection devices have been focused at the end.
14.2
MXene-based sensing and biosensing for various analytes
MXene has emerged as a high-performance detection platform for various analytes. Sensing strategies based on MXene have been considered as highly advanced detection schemes with great utility in health, environment, medicine, and social security. Various analytical state-of-the-art methodologies have been developed exploiting unique sensing characteristics of MXene. Titanium carbide (Ti3C2) is the most explored MXene, which has been extensively applied for analytical sensing. The present section includes MXene-based detection of multiple analytes such as biomolecules, organic contaminants, using various analytical methods.
14.2.1 MXenes for detection of biomolecules Taking advantages of electrochemical techniques, different MXene sensors have been developed and exploited for sensing purposes which have been summarised as Table 14.1 [1830]. MXene-modified electrodes have been reported to be effective transducers for immobilization of biological receptors (e.g., enzymes) onto its surface. MXene biosensors enhance the catalytic performances toward electrochemical determination of different biomolecules [1824]. For example, nanocomposite of nafion-gold nanoparticles (Au-NP)-MXene was reportedly acted as a suitable surface for immobilization of glucose oxidase (GOx). The developed nafion-AuNPs-MXene biosensor was applied for amperometric detection of glucose [18]. In the developed biosensing matrix, MXene (Ti3C2Tx) showed improved electron-transfer reactions between active redox center (FAD) of GOx and electrode interface, showing direct electrochemistry between GOx and fabricated biosensor during glucose oxidation. Similarly, hemoglobin (Hb)-immobilized Ti3C2 was
Table 14.1 Electrochemical detection performance of MXene sensors and biosensors. Analyte
Electrochemical method
Detection limit
Detection range
References
Glucose H2O2 NO2 2 H2O2 H2O2 H2O2 AA, DA, UA, APAP H2O2 DA P53 gene Phenol Cd21, Pb21, Cu21, Hg21 BrO2 3 Malathion
Amperometry Amperometry Amperometry Amperometry Voltammetry (DPV) Amperometry Voltammetry (DPV)
5.9 µM 0.02 µM 0.12 µM 14.0 nM 1.95 µM 448 nM 0.25 µM, 0.26 µM, 0.12 µM, 0.13 µM 0.7 nM 100 3 1029 M 5 nM 12 nM 98 nM, 41 nM, 32 nM, 130 nM 41 nM 0.3 3 10214 M
0.118 mM 0.1260 µM 0.5 µM11.8 mM 0.1380 µM 2 µM1 mM 490 µM53.6 mM Upto 750 µM
[18] [19] [20] [21] [22] [23] [23]
100 3 102950 3 1026 M 10 nM1 mM 0.0515.5 µM 0.11.5 µM
[24] [25] [26] [27] [28]
50 nM5 µM 1 3 102141 3 1028 M
[29] [30]
Chronoamperometry FET ECL Amperometry Voltammetry (SWASV)
Voltammetry (DPV) Voltammetry (DPV)
DPV, differential pulse voltammetry; ECL, electrochemiluminescence; FET, field effect transistor; SWASV, square-wave stripping voltammetry.
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explored for its mediator-free biosensing activity toward H2O2 [19] and NaNO2 [20]. The prepared Hb-nafion-MXene-modified glassy carbon electrode (GCE) sensor was successfully applied to study the direct electrochemistry between Hb and the working electrode using amperometry. Furthermore, nanocomposites of metal/ metal oxides nanoparticles and MXene have also been reported for sensing applications. Decoration of titanium oxide (TiO2) nanoparticles on Ti3C2-MXene biosensor was successfully performed and exploited for H2O2 detection using amperometry [21]. Furthermore, in a recent study, voltammetric sensor based on Ti3C2Tx-PtNPs/ GCE was reported, which was used for the detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), and acetaminophen (APAP) biomolecules [23]. The sensor showed high electroactivity, which was ascribed to the synergistic effects of PtNPs and MXene. In another example, application of large anodic potential (1200 mV) to Ti3C2Fx resulted in the oxidation of its outer surface and utilized for oxidation studies of nicotinamide adenine dinucleotide (NADH) [23]. Furthermore, sensing of H2O2 was performed by exposing large cathodic potential (2500 mV) to Ti3C2Fx using chronoamperometry. The study showed great potential applicability of MXene-based biosensors, which exhibited dehydrogenase and oxidase-like activity suitable for sensing of NADH and H2O2, respectively. MXene-based field effect transistor (FET) sensor was developed for DA in spiked hippocampal neurons [25]. The conductance of Ti3C2Tx-MXene FET sensor was measured by ultrathin MXene micropatterns and different gating controls. The MXene sensor acted as an n-type FET when gate voltage was above 10.3 V and as p-type FET when gate potential level was below 10.3 V. The ππ interactions between DA and functionalized surface of MXene led to the efficient sensing of DA (Table 14.1). MXene-based quantum dots (MQDs) have also been utilized for bioimaging applications [31]. For example, Ti3C2-MQDs were synthesized and utilized as photoluminescent sensor. The prepared MQDs were applied as a biocompatible multicolor imaging probe for photoluminescent detection of RAW264.7 cell lines. Further, Ti3C2-MQDs were reported for sensing metabolism of MCF-7 cells [32]. Ti3C2-MQDs exhibited excitation wavelength due to size-dependant interband transition of carriers and surface defect sites. Furthermore, Ti3C2Tx was used as electroluminescent (ECL) sensor for the detection of nucleotide mismatch in human urine samples [26]. Practical applicability of the sensor for p53 gene single-nucleotide mismatch sensing showed high utility of MXene in biomedical applications.
14.2.2 MXene for detection of environmental contaminants MXenes have demonstrated promising applications toward environmental safety by the detection of potential contaminants. For example, Ti3C2-tyrosinase biosensor was used for the detection of phenol [27]. The MXene biosensor catalyzed the oxidation of phenol to corresponding o-quinone that was studied by amperometry. The biosensor showed high sensitivity toward phenol that was attributed to the highly compatible MXene surface, which retained tyrosinase activity even after its immobilization. Moreover, an alkaline (KOH) intercalated Ti3C2-MXene was prepared for voltammetric sensing of toxic heavy metals, using square-wave stripping voltammetry
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Figure 14.2 (A) Schematic preparation of Ti3C2 MXene from MAX phase and alkaline treatment, (B) SWASV response of the alk-Ti3C2/GCE sensor for individual analysis of (i) Pb21, (ii) Cd21, (iii) Cu21, (iv) Hg21; inset: corresponding linear calibration plots of peak current against Pb21, Cd21, Cu21, and Hg21concentrations, respectively [28]. Source: Reprinted with permission from X. Zhu, B. Liu, H. Hou, Z. Huang, K.M. Zeinu, L. Huang, et al., Alkaline intercalation of Ti3C2 MXene for simultaneous electrochemical detection of Cd(II), Pb(II), Cu(II) and Hg(II), Electrochim. Acta 248 (2017) 4657.
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(Fig. 14.2) [28]. Electroactivity of alk-Ti3C2/GCE was compared with pristine Ti3C2/GCE sensor toward detection of Cd21, Pb21, Cu21, and Hg21. Existence of [Ti-O]-H1 and [Ti-O]-K1 moieties in alk-Ti3C2 accelerated the cation exchange and thus the adsorption and reduction of heavy metal ions into their metallic form during stripping analysis. Furthermore, substitution of F2 ions with hydroxyl groups after alkaline treatment of Ti3C2 led to enhanced hydrophilicity and high conductivity for electron-transfer processes. Furthermore, a Ti3C2Tx/GCE sensor was prepared for the detection of bromate ions (BrO32). The sensor showed unique electrocatalytic properties toward BrO32 reduction using voltammetry [29]. In addition, MXene biosensors have been successfully applied for pesticide detection. An amperometric biosensor based on acetocholinesterase enzyme-immobilized Ti3C2Tx nanosheets was prepared for detection of organophosphate pesticide malathion [30]. The sensor showed high voltammetric performances toward malathion determination with low detection limit, high reproducibility, and stability. Furthermore, Ti3C2Tx-based surface-enhanced Raman spectroscopic (SERS) method was developed [33]. A SERS substrate based on Ti3C2Tx was prepared for Raman signal enhancement of dye Rhodamine 6 G, which is also a potent organic contaminant. The synergy between electromagnetic and chemical enhancements of Ti3C2Tx substrates showed high possibilities of MXenes in biochemical molecular sensing using SERS sensors. Ti3C2Tx demonstrated SERS effect in aqueous colloidal solutions of Rhodamine 6 G at 1027 M concentration.
14.2.3 MXene for detection of gaseous molecules MXene has been highly useful for the detection of toxic gases and applied as gas sensors. MXene can detect acetone (CH3COCH3) and ammonia (NH3), which are highly useful in medical diagnosis of diseases such as diabetes or peptic ulcers, respectively. MXenes show low electrical noise and strong signal intensity toward gaseous molecules. For example, Ti3C2OH2 MXene was used to study gases such as CH3COCH3, NH3, ethanol (C2H5OH), nitrogen oxide (NO2), propanal (C2H5CHO), and sulfur dioxide (SO2) at room temperature. The sensor exhibited a positive change in the resistance of the sensing channel over absorption of gases. The sensing response varied depending on the electronic properties of gases and semiconducting properties of the charge carrier (p- or n-type) [34]. Further, a Ti2CO2 MXene was prepared for NH3 sensing. Adsorption of various gases such as NH3, H2, CH4, CH3COCH3, CO2, N2, NO2, and O2 on Ti2CO2 surface was investigated to exploit its potential application as gas sensor. A significant change in the adsorption energy of MXene was observed with operating biaxial strain to capture NH3 molecules on its surface. The electronic interactions of NH3 with MXene resulted in the orbital overlap and large charge transfer. The conductivity of MXene was considerably enhanced after adsorption of NH3 under strain suggesting strong interaction and high sensitivity toward NH3 [35]. Moreover, MXene was further proved as a strong sensor for NH3 with high regenerating ability by reversible release and capture through control on the charge state of the system [36]. Introduction of two extra electrons to ZrCO2 resulted in the release of NH3 from MXene and led the conversion of chemisorption to physisorption. Furthermore,
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Figure 14.3 (A) Schematic illustration of Ti3C2Tx synthesis procedure, solution deposition at electrode and gas sensing equipment, (B) Ti3C2Tx-based sensing of ethanol, methanol, acetone, and ammonia gas at room temperature [10]. Source: Reprinted with permission from E. Lee, A.V. Mohammadi, B.C. Prorok, Y.S. Yoon, M. Beidaghi, D.J. Kim, Room temperature gas sensing of two-dimensional titanium carbide (MXene), ACS Appl. Mater. Interfaces 9 (2017) 3718437190.
adsorption of NH3 on functionalized groups of Ti3C2Tx such as O2 or OH2 led to the generation of electrons, which minimized the concentration of charge on MXene film and thus increased the resistance of the device [10]. 2D sheets of Ti3C2Tx were prepared and were integrated on flexible polyimide platforms with solution casting method as shown in Fig. 14.3A. The Ti3C2Tx sensor showed a p-type behavior and successfully detected ethanol, methanol, acetone, and ammonia gas at room temperature (Fig. 14.3B).
14.2.4 MXene for detection of motion and physical stimuli In recent times, MXenes have been used as strain sensors due to their high sensitivity (GF B772.6) and tunable sensing range (30%130% strain). MXenes have been applied for detection of phonations and substantial movements such as walking, jumping, running, or other human activities like coughing, and joint bending [37,38]. For example, Ti3C2Tx MXene nanocomposite with single-walled carbon nanotubes (CNTs) was prepared (Fig. 14.4A) and utilized as a strain sensor with
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Figure 14.4 (A) Preparation of Ti3C2Tx/CNT sensor, (B) Ti3C2Tx/CNT nanocompositebased peizoresistive strain sensor for phonation and substantial movement detection; (i) Ti3C2Tx-MXene/CNT strain sensor attached to human throat, (iiiv) responsive curves recorded while speaking “carbon”, “sensor”, and “MXene”, (v) Ti3C2Tx-MXene/CNT sensor attached to the human knee, (vi 2 viii) resistance responses of the sensor in detecting human leg movement walking, running, and jumping [37]. Source: Reprinted with permission from Y. Cai, J. Shen, G. Ge, Y. Zhang, W. Jin, W. Huang, et al., Stretchable Ti3C2Tx MXene/carbon nanotube composite based strain sensor with ultrahigh sensitivity and tunable sensing range, ACS Nano 12 (2018) 5662.
detection limit as low as 0.1% [37] The nanocomposite strain sensor (Ti3C2Tx/ CNTs) was utilized as skin attachable wearable devices for real-time applications such as capturing physiological signal and motion monitoring (Fig. 14.4B). The tunneling distances between MXene layers and interconnected CNTs changed their overlapping areas and distances when external pressure was applied. Furthermore, a peizoresistive sensor based on Ti3C2 MXene was developed, in which the distance between two MXene interlayers was decreased when external pressure was applied [38]. The fabricated sensor was applied to human body such as on cheek, eye corner, and throat to study the physical stimuli such as cheek bulging, eye blinking, and throat swallowing. Moreover, knee-bending release movement was also monitored through change in current over the function of time. Thus, MXene sensor demonstrated peizoresistive behavior in detecting subtle human activities.
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14.2.5 MXene for terahertz sensing MXene materials have shown their great potential in terahertz (THz) sensing. Potential of MXenes as THz sensor was studied by performing density functional theory calculations on Ti3C2 [39]. In particular, optical properties of THz, the electronic band structures, and the thermoelectric figure of merit (ZT) of monolayer and stacked Ti3C2Tx were studied. Excellent light extinction and optical absorption was observed in Ti3C2 in the THz range (0.00120.012 eV). Furthermore, stacked Ti3C2-MXene exhibited superior THz absorption and a high ZT value sufficiently enough to be applied in THz detectors. Such extraordinary features enable MXene for their potential application in fabricating THz sensing devices, terahertz bolometers, and photothermoelectric detectors.
14.3
Conclusion
MXenes are a developing class of 2D materials, which are based on transition metal carbides, nitrides, or carbon nitrides. MXenes are produced by etching out A layer from a 3D structure consisting of MAX (Mn11AXn), where M is an early d-transition metal, A is the main group sp element, and X is C or N. MXenes are mechanically very strong materials composed of mostly MC or MN bonds. Chemical functionalization of the MXene surface is done with terminating groups such as O, F, and OH in order to be able to achieve chemical applications including sensing. MXenes have demonstrated promising features for sensing and biosensing applications. Titanium carbide is the most explored MXene in the field of sensing, and therefore exploitation of other transition metal-based MXenes is highly anticipated. High biocompatibility of MXene drives great motivation to design advance biosensing systems based on aptamers, antibodies, and protein molecules. However, achieving stability of MXene biosensors is of great challenge. Development of MXene-based wearable electronics contributes greatly to various healthcare diagnostics and environmental sensing applications. Overall, MXene materials hold multiple promising features to be applied in diverse sectors of technology. Thus, MXenes provide great enthusiasm toward their implementation as next-generation detection devices.
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[3] K. Huang, Z. Li, J. Lin, G. Han, P. Huang, Two-dimensional transition metal carbides and nitrides (MXenes) for biomedical applications, Chem. Soc. Rev. (2018). Available from: https://doi.org/10.1039/c7cs00838d. [4] C.M. Hussain, Handbook of Nanomaterials for Industrial Applications, Elsevier, 2018. [5] M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, MXenes: a new family of two-dimensional materials, Adv. Mater. 26 (2014) 9921005. [6] M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, et al., Two dimensional transition metal carbides, ACS Nano 6 (2012) 13221331. [7] B. Anasori, Y. Xie, M. Beidaghi, J. Lu, B.C. Hosler, L. Hultman, et al., Two dimensional, ordered, double transition metals carbides (MXenes), ACS Nano 9 (2015) 95079516. [8] M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J. Niu, M. Heon, et al., Two dimensional nanocrystals produced by exfoliation of Ti3AlC2, Adv. Mater. 23 (2011) 42484253. [9] A. Sinha, Dhanjai, H. Zhao, Y. Huang, X. Lu, J. Chen, et al., MXene: an emerging material for sensing and biosensing, TrAC Trends Anal. Chem 105 (2018) 424435. [10] E. Lee, A.V. Mohammadi, B.C. Prorok, Y.S. Yoon, M. Beidaghi, D.J. Kim, Room temperature gas sensing of two-dimensional titanium carbide (MXene), ACS Appl. Mater. Interfaces 9 (2017) 3718437190. [11] M. Khazaei, M. Arai, T. Sasaki, C.Y. Chung, N.S. Venkataramanan, M. Estili, et al., Novel electronic and magnetic properties of two-dimensional transition metal carbides and nitrides, Adv. Funct. Mater. 23 (2013) 21852192. [12] I.R. Shein, A.L. Ivanovskii, Graphene-like nanocarbides and nanonitrides of d metals (MXenes): synthesis, properties and simulation, Micro Nano Lett. 8 (2013) 5962. [13] P. Paul, P. Chakraborty, T. Das, D. Nafday, T.S. Dasgupta, Properties at the interface of graphene and Ti2C MXene, Phys. Rev. B 96 (2017) 035437. [14] G.R. Berdiyorov, Effect of surface functionalization on the electronic transport properties of Ti3C2 MXene, Exploring Front. Phys. 111 (2015) 67002. [15] J. Zhu, E. Ha, G. Zhao, Y. Zhou, D. Huang, G. Yue, et al., Recent advance in MXenes: a promising 2D material for catalysis, sensor and chemical adsorption, Coord. Chem. Rev. 352 (2017) 306327. [16] V.M.H. Ng, H. Huang, K. Zhou, P.S. Lee, W. Que, J.Z. Xu, et al., Recent progress in layered transition metal carbides and/or nitrides (MXenes) and their composites: synthesis and applications, J. Mater. Chem. A 5 (2017) 30393068. [17] J.C. Lei, X. Zhang, Z. Zhou, Recent advances in mxene: preparation, properties and applications, Front. Phys. 10 (2015) 107303107311. [18] R.B. Rakhi, P. Nayak, C. Xia, H.N. Alshareef, Novel amperometric glucose biosensor based on MXene nanocomposite, Sci. Rep. 6 (2016) 36422. [19] F. Wang, C. Yang, C. Duan, D. Xiao, Y. Tang, J. Zhu, An organ-like titanium carbide material (mxene) with multilayer structure encapsulating hemoglobin for a mediatorfree biosensor, J Electrochem. Soc. 162 (2015) B16B21. [20] H. Liu, C. Duan, C. Yang, W. Shen, F. Wang, Z. Zhu, A novel nitrite biosensor based on the direct electrochemistry of hemoglobin immobilized on MXene-Ti3C2, Sens. Actuat. B 218 (2015) 6066. [21] F. Wang, C. Yang, M. Duan, Y. Tang, J. Zhu, TiO2 nanoparticle modified organlikeTi3C2 MXene nanocomposite encapsulating hemoglobin for a mediator free biosensor with excellent performances, Biosens. Bioelectron. 74 (2015) 10221028. [22] J. Zheng, J. Diao, Y. Jin, A. Ding, B. Wang, L. Wu, et al., An inkjet printed Ti3C2-GO electrode for the electrochemical sensing of hydrogen peroxide, J. Electrochem. Soc. 165 (2018) B227B231.
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[23] L. Lorencova, T. Bertok, J. Filip, M. Jerigova, D. Velic, P. Kasak, et al., Highly stable Ti3C2Tx-(MXene)/Pt nanoparticles modified glassycarbon electrode for H2O2 and small molecules sensing applications, Sensors Actuat. B Chem. 263 (2018) 360368. [24] L. Lorencova, T. Bertok, E. Dosekova, A. Holazova, D. Paprckova, A. Vikartovska, et al., Electrochemical performance of Ti3C2Tx MXene in aqueous media: towards ultrasensitive H2O2 sensing, Electrochim. Acta 235 (2017) 471479. [25] B. Xu, M. Zhu, W. Zhang, X. Zhen, Z. Pei, Q. Xue, et al., Ultrathin MXene micropattern based field-effect transistor for probing neural activity, Adv. Mater. 28 (2016) 33333339. [26] Y. Fang, X. Yang, T. Chen, G. Xu, M. Liu, J. Liu, et al., Two-dimensional titanium carbide (MXene)-based solid-state electrochemiluminescent sensor for label-free single-nucleotide mismatch discrimination in human urine, Sens. Actuat. B 263 (2018) 400407. [27] L. Wu, X. Lu, Dhanjai, Z.S. Wu, Y. Dong, X. Wang, et al., 2D transition metal carbide MXene as a robust biosensing platform for enzyme immobilization and ultrasensitive detection of phenol, Biosens. Bioelectron. 107 (2018) 6975. [28] X. Zhu, B. Liu, H. Hou, Z. Huang, K.M. Zeinu, L. Huang, et al., Alkaline intercalation of Ti3C2 MXene for simultaneous electrochemical detection of Cd(II), Pb(II), Cu(II) and Hg(II), Electrochim. Acta 248 (2017) 4657. [29] P.A. Rasheed, R.P. Pandey, K. Rasool, K.A. Mahmoud, Ultra sensitive electrocatalytic detection of bromate in drinking water based on Nafion/Ti3C2Tx (MXene) modified glassy carbon electrode, Sensors Actuat. B Chem. 265 (2018) 652659. [30] L. Zhou, X. Zhang, L. Ma, J. Gao, Y. Jiang, Acetylcholinesterase/chitosan-transition metal carbides nanocomposites based biosensor for the organophosphate pesticides detection, Biochem. Engineer. J 128 (2017) 243249. [31] Q. Xue, H. Zhang, M. Zhu, Z. Pei, H. Li, Z. Wang, et al., Photoluminescent Ti3C2 MXene quantum dots for multicolor cellular imaging, Adv. Mat. 29 (2017) 1604847. [32] X. Chen, X. Sun, W. Xu, G. Pan, D. Zhou, J. Zhu, et al., Ratiometric photoluminescence sensing based on Ti3C2 MXene quantum dots as an intracellular pH sensor, Nanoscale 10 (2018) 11111118. [33] A. Sarycheva, T. Makaryan, K. Maleski, E. Satheeshkumar, A. Melikyan, H. Minassian, et al., Two dimensional titanium carbide (MXene) as surface-enhanced raman scattering substrate, J. Phys. Chem. C 121 (2017) 1998319988. [34] S.J. Kim, H.J. Koh, C.E. Ren, O. Kwon, K. Maleski, S.Y. Cho, et al., Metallic Ti3C2Tx MXene gas sensors with ultrahigh signal-to-noise ratio, ACS Nano 12 (2018) 986993. [35] X. Yu, Y. Li, J. Cheng, Z. Liu, Q. Li, W. Li, et al., Monolayer Ti2CO2: a promising candidate for NH3 sensor or capturer with high sensitivity and selectivity, ACS Appl. Mater. Interfaces 7 (2015) 1370713713. [36] B. Xiao, Y. Li, X. Yu, J. Cheng, MXenes: reusable materials for NH3 sensor or capturer by controlling the charge injection, Sens. Actuat. B 235 (2016) 103109. [37] Y. Cai, J. Shen, G. Ge, Y. Zhang, W. Jin, W. Huang, et al., Stretchable Ti3C2Tx MXene/carbon nanotube composite based strain sensor with ultrahigh sensitivity and tunable sensing range, ACS Nano 12 (2018) 5662. [38] Y. Ma, N. Liu, L. Li, X. Hu, Z. Zou, J. Wang, et al., A highly flexible and sensitive piezoresistive sensor based on MXene with greatly changed interlayer distances, Nat. Commun. 8 (2017) 1207. [39] Y.I. Jhon, M. Seo, Y.M. Jhon, First-principles study of a MXene terahertz detector, Nanoscale 10 (2018) 6975.
14
Ankita Sinha1, Dhanjai2,3,4, Samuel M. Mugo3, Jiping Chen4 and Koodlur S. Lokesh5 1 Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, China), School of Environmental Science and Technology, Dalian University of Technology, Dalian, P.R. China, 2Department of Mathematical and Physical Sciences, Concordia University of Edmonton, Edmonton, AB, Canada, 3Department of Physical Sciences, MacEwan University, Edmonton, AB, Canada, 4CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian P.R. China, 5Department of Chemistry/Industrial Chemistry, Vijayanagara Sri Krishnadevaraya University, Ballari, India
14.1
Introduction
In current times, two-dimensional (2D) layered materials have withdrawn considerable attention due to their morphological resemblance with graphene. So far, 2D materials such as transition metal dichalcogenides and boron nitride have been extensively studied for their significant applications in the fields of electronics, catalysis, energy etc. [14]. Recently, MXene has emerged as a unique 2D material that mainly includes early transition metal carbides, nitrides, and carbonitrides [59]. MXene possesses layered morphology and are produced by etching layers of sp elements from three-dimensional (3D) MAX phases [9]. MAX phases are layered hexagonal with P63/mmc symmetry with general formula Mn11AXn (n 5 1, 2, 3) where M represents d-block transition metals, A represents main group 13 and 14 elements, and X is either C or N atoms [57]. The MX bond holds covalent/metallic/ionic character, whereas MA bond is of pure metallic nature [5]. Therefore, at high temperatures, MA bond decomposes into Mn11Xn, which results into recrystallization and formation of 3D Mn11Xn rocksalt-like structure [6]. Selective etching of reactive A layers from their MAX phases can be done using suitable chemicals without destroying MX layers (Fig. 14.1A) [6,8]. The process leads to the formation of highly stable closely packed Mn11XnTx layers, where Tx is the surface-terminating functional group such as oxygen (O), fluorine (F), or hydroxyl (OH) (Fig. 14.1B) [5,6,10]. For example, preparation of 2D Ti3C2 can be performed by exfoliation
Handbook of Nanomaterials in Analytical Chemistry. DOI: https://doi.org/10.1016/B978-0-12-816699-4.00014-1 Copyright © 2020 Elsevier Inc. All rights reserved.
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Figure 14.1 (A) Exfoliation of MAX phases and preparation of 2D MXene sheets, (B) Ti3C2Tx structure showing terminating groups on the surface of Ti3C2Tx nanosheets, (C) SEM, (D) TEM, (E) HRTEM, (F) SAED, (G) XRD, (H) FTIR of Ti3C2 MXene [6,10]. Source: Reprinted with permission from M. Naguib, O. Mashtalir, J. Carle, V. Presser, J. Lu, L. Hultman, et al., Two dimensional transition metal carbides, ACS Nano 6 (2012) 13221331; E. Lee, A.V. Mohammadi, B.C. Prorok, Y.S. Yoon, M. Beidaghi, D.J. Kim, Room temperature gas sensing of two-dimensional titanium carbide (MXene), ACS Appl. Mater. Interfaces, 9 (2017) 3718437190.
of Ti3AlC2 in 50% hydrogen fluride (HF) at room temperature for 2 h as per the following reactions [5,6]; Mn11 AlXn 1 3HF 5 AlF3 1 Mn11 Xn 1 1:5 H2
(14.1)
Mn11 Xn 1 2H2 O 5 Mn11 Xn ðOHÞ2 1 H2
(14.2)
Mn11 Xn 1 2HF 5 Mn11 Xn F2 1 H2
(14.3)
In the aqueous environment of HF solutions, the Al atoms are replaced by O, F, or OH functional groups and hence the outer surfaces of the exfoliated MX layers are chemically terminated [1114]. Thus, the interactions between the Mn11Xn layers become weak making their separation easy. Replacement of AlM bond through hydrogen or van der Waals bonds allows delamination of MXene by the
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ultrasonication of HF-treated MAX phases in suitable solvents such as isopropyl alcohol or methanol. This surface functionalization leads to significant impacts on the electronic and ion-transport properties of MXenes. The microscopic (scanning electron microscopic (SEM), transmission electron microscopic (TEM), high resolution TEM (HRTEM), selected area electron diffration (SAED) and spectroscopic (x-ray diffraction (XRD), Fourier transform infrared (FTIR)) characterization of 2D-layered MXene has been shown in Fig. 14.1(CH) [6,10]. MXenes show variable electronic activity depending upon their functionalization [11]. Since their discovery in 2011, MXenes have gained significant attraction due to their unique layered structure and extraordinary catalytic properties. MXenes offer extremely exceptional chemical, electrical, and ion-transport properties that promise for a wide range of potential applications in various fields [1517]. Recently, MXene has been applied as a sensitive platform for sensing and biosensing applications, which has been discussed in the present chapter. Moreover, future prospects in developing MXene-based detection devices have been focused at the end.
14.2
MXene-based sensing and biosensing for various analytes
MXene has emerged as a high-performance detection platform for various analytes. Sensing strategies based on MXene have been considered as highly advanced detection schemes with great utility in health, environment, medicine, and social security. Various analytical state-of-the-art methodologies have been developed exploiting unique sensing characteristics of MXene. Titanium carbide (Ti3C2) is the most explored MXene, which has been extensively applied for analytical sensing. The present section includes MXene-based detection of multiple analytes such as biomolecules, organic contaminants, using various analytical methods.
14.2.1 MXenes for detection of biomolecules Taking advantages of electrochemical techniques, different MXene sensors have been developed and exploited for sensing purposes which have been summarised as Table 14.1 [1830]. MXene-modified electrodes have been reported to be effective transducers for immobilization of biological receptors (e.g., enzymes) onto its surface. MXene biosensors enhance the catalytic performances toward electrochemical determination of different biomolecules [1824]. For example, nanocomposite of nafion-gold nanoparticles (Au-NP)-MXene was reportedly acted as a suitable surface for immobilization of glucose oxidase (GOx). The developed nafion-AuNPs-MXene biosensor was applied for amperometric detection of glucose [18]. In the developed biosensing matrix, MXene (Ti3C2Tx) showed improved electron-transfer reactions between active redox center (FAD) of GOx and electrode interface, showing direct electrochemistry between GOx and fabricated biosensor during glucose oxidation. Similarly, hemoglobin (Hb)-immobilized Ti3C2 was
Table 14.1 Electrochemical detection performance of MXene sensors and biosensors. Analyte
Electrochemical method
Detection limit
Detection range
References
Glucose H2O2 NO2 2 H2O2 H2O2 H2O2 AA, DA, UA, APAP H2O2 DA P53 gene Phenol Cd21, Pb21, Cu21, Hg21 BrO2 3 Malathion
Amperometry Amperometry Amperometry Amperometry Voltammetry (DPV) Amperometry Voltammetry (DPV)
5.9 µM 0.02 µM 0.12 µM 14.0 nM 1.95 µM 448 nM 0.25 µM, 0.26 µM, 0.12 µM, 0.13 µM 0.7 nM 100 3 1029 M 5 nM 12 nM 98 nM, 41 nM, 32 nM, 130 nM 41 nM 0.3 3 10214 M
0.118 mM 0.1260 µM 0.5 µM11.8 mM 0.1380 µM 2 µM1 mM 490 µM53.6 mM Upto 750 µM
[18] [19] [20] [21] [22] [23] [23]
100 3 102950 3 1026 M 10 nM1 mM 0.0515.5 µM 0.11.5 µM
[24] [25] [26] [27] [28]
50 nM5 µM 1 3 102141 3 1028 M
[29] [30]
Chronoamperometry FET ECL Amperometry Voltammetry (SWASV)
Voltammetry (DPV) Voltammetry (DPV)
DPV, differential pulse voltammetry; ECL, electrochemiluminescence; FET, field effect transistor; SWASV, square-wave stripping voltammetry.
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explored for its mediator-free biosensing activity toward H2O2 [19] and NaNO2 [20]. The prepared Hb-nafion-MXene-modified glassy carbon electrode (GCE) sensor was successfully applied to study the direct electrochemistry between Hb and the working electrode using amperometry. Furthermore, nanocomposites of metal/ metal oxides nanoparticles and MXene have also been reported for sensing applications. Decoration of titanium oxide (TiO2) nanoparticles on Ti3C2-MXene biosensor was successfully performed and exploited for H2O2 detection using amperometry [21]. Furthermore, in a recent study, voltammetric sensor based on Ti3C2Tx-PtNPs/ GCE was reported, which was used for the detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), and acetaminophen (APAP) biomolecules [23]. The sensor showed high electroactivity, which was ascribed to the synergistic effects of PtNPs and MXene. In another example, application of large anodic potential (1200 mV) to Ti3C2Fx resulted in the oxidation of its outer surface and utilized for oxidation studies of nicotinamide adenine dinucleotide (NADH) [23]. Furthermore, sensing of H2O2 was performed by exposing large cathodic potential (2500 mV) to Ti3C2Fx using chronoamperometry. The study showed great potential applicability of MXene-based biosensors, which exhibited dehydrogenase and oxidase-like activity suitable for sensing of NADH and H2O2, respectively. MXene-based field effect transistor (FET) sensor was developed for DA in spiked hippocampal neurons [25]. The conductance of Ti3C2Tx-MXene FET sensor was measured by ultrathin MXene micropatterns and different gating controls. The MXene sensor acted as an n-type FET when gate voltage was above 10.3 V and as p-type FET when gate potential level was below 10.3 V. The ππ interactions between DA and functionalized surface of MXene led to the efficient sensing of DA (Table 14.1). MXene-based quantum dots (MQDs) have also been utilized for bioimaging applications [31]. For example, Ti3C2-MQDs were synthesized and utilized as photoluminescent sensor. The prepared MQDs were applied as a biocompatible multicolor imaging probe for photoluminescent detection of RAW264.7 cell lines. Further, Ti3C2-MQDs were reported for sensing metabolism of MCF-7 cells [32]. Ti3C2-MQDs exhibited excitation wavelength due to size-dependant interband transition of carriers and surface defect sites. Furthermore, Ti3C2Tx was used as electroluminescent (ECL) sensor for the detection of nucleotide mismatch in human urine samples [26]. Practical applicability of the sensor for p53 gene single-nucleotide mismatch sensing showed high utility of MXene in biomedical applications.
14.2.2 MXene for detection of environmental contaminants MXenes have demonstrated promising applications toward environmental safety by the detection of potential contaminants. For example, Ti3C2-tyrosinase biosensor was used for the detection of phenol [27]. The MXene biosensor catalyzed the oxidation of phenol to corresponding o-quinone that was studied by amperometry. The biosensor showed high sensitivity toward phenol that was attributed to the highly compatible MXene surface, which retained tyrosinase activity even after its immobilization. Moreover, an alkaline (KOH) intercalated Ti3C2-MXene was prepared for voltammetric sensing of toxic heavy metals, using square-wave stripping voltammetry
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Figure 14.2 (A) Schematic preparation of Ti3C2 MXene from MAX phase and alkaline treatment, (B) SWASV response of the alk-Ti3C2/GCE sensor for individual analysis of (i) Pb21, (ii) Cd21, (iii) Cu21, (iv) Hg21; inset: corresponding linear calibration plots of peak current against Pb21, Cd21, Cu21, and Hg21concentrations, respectively [28]. Source: Reprinted with permission from X. Zhu, B. Liu, H. Hou, Z. Huang, K.M. Zeinu, L. Huang, et al., Alkaline intercalation of Ti3C2 MXene for simultaneous electrochemical detection of Cd(II), Pb(II), Cu(II) and Hg(II), Electrochim. Acta 248 (2017) 4657.
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(Fig. 14.2) [28]. Electroactivity of alk-Ti3C2/GCE was compared with pristine Ti3C2/GCE sensor toward detection of Cd21, Pb21, Cu21, and Hg21. Existence of [Ti-O]-H1 and [Ti-O]-K1 moieties in alk-Ti3C2 accelerated the cation exchange and thus the adsorption and reduction of heavy metal ions into their metallic form during stripping analysis. Furthermore, substitution of F2 ions with hydroxyl groups after alkaline treatment of Ti3C2 led to enhanced hydrophilicity and high conductivity for electron-transfer processes. Furthermore, a Ti3C2Tx/GCE sensor was prepared for the detection of bromate ions (BrO32). The sensor showed unique electrocatalytic properties toward BrO32 reduction using voltammetry [29]. In addition, MXene biosensors have been successfully applied for pesticide detection. An amperometric biosensor based on acetocholinesterase enzyme-immobilized Ti3C2Tx nanosheets was prepared for detection of organophosphate pesticide malathion [30]. The sensor showed high voltammetric performances toward malathion determination with low detection limit, high reproducibility, and stability. Furthermore, Ti3C2Tx-based surface-enhanced Raman spectroscopic (SERS) method was developed [33]. A SERS substrate based on Ti3C2Tx was prepared for Raman signal enhancement of dye Rhodamine 6 G, which is also a potent organic contaminant. The synergy between electromagnetic and chemical enhancements of Ti3C2Tx substrates showed high possibilities of MXenes in biochemical molecular sensing using SERS sensors. Ti3C2Tx demonstrated SERS effect in aqueous colloidal solutions of Rhodamine 6 G at 1027 M concentration.
14.2.3 MXene for detection of gaseous molecules MXene has been highly useful for the detection of toxic gases and applied as gas sensors. MXene can detect acetone (CH3COCH3) and ammonia (NH3), which are highly useful in medical diagnosis of diseases such as diabetes or peptic ulcers, respectively. MXenes show low electrical noise and strong signal intensity toward gaseous molecules. For example, Ti3C2OH2 MXene was used to study gases such as CH3COCH3, NH3, ethanol (C2H5OH), nitrogen oxide (NO2), propanal (C2H5CHO), and sulfur dioxide (SO2) at room temperature. The sensor exhibited a positive change in the resistance of the sensing channel over absorption of gases. The sensing response varied depending on the electronic properties of gases and semiconducting properties of the charge carrier (p- or n-type) [34]. Further, a Ti2CO2 MXene was prepared for NH3 sensing. Adsorption of various gases such as NH3, H2, CH4, CH3COCH3, CO2, N2, NO2, and O2 on Ti2CO2 surface was investigated to exploit its potential application as gas sensor. A significant change in the adsorption energy of MXene was observed with operating biaxial strain to capture NH3 molecules on its surface. The electronic interactions of NH3 with MXene resulted in the orbital overlap and large charge transfer. The conductivity of MXene was considerably enhanced after adsorption of NH3 under strain suggesting strong interaction and high sensitivity toward NH3 [35]. Moreover, MXene was further proved as a strong sensor for NH3 with high regenerating ability by reversible release and capture through control on the charge state of the system [36]. Introduction of two extra electrons to ZrCO2 resulted in the release of NH3 from MXene and led the conversion of chemisorption to physisorption. Furthermore,
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Figure 14.3 (A) Schematic illustration of Ti3C2Tx synthesis procedure, solution deposition at electrode and gas sensing equipment, (B) Ti3C2Tx-based sensing of ethanol, methanol, acetone, and ammonia gas at room temperature [10]. Source: Reprinted with permission from E. Lee, A.V. Mohammadi, B.C. Prorok, Y.S. Yoon, M. Beidaghi, D.J. Kim, Room temperature gas sensing of two-dimensional titanium carbide (MXene), ACS Appl. Mater. Interfaces 9 (2017) 3718437190.
adsorption of NH3 on functionalized groups of Ti3C2Tx such as O2 or OH2 led to the generation of electrons, which minimized the concentration of charge on MXene film and thus increased the resistance of the device [10]. 2D sheets of Ti3C2Tx were prepared and were integrated on flexible polyimide platforms with solution casting method as shown in Fig. 14.3A. The Ti3C2Tx sensor showed a p-type behavior and successfully detected ethanol, methanol, acetone, and ammonia gas at room temperature (Fig. 14.3B).
14.2.4 MXene for detection of motion and physical stimuli In recent times, MXenes have been used as strain sensors due to their high sensitivity (GF B772.6) and tunable sensing range (30%130% strain). MXenes have been applied for detection of phonations and substantial movements such as walking, jumping, running, or other human activities like coughing, and joint bending [37,38]. For example, Ti3C2Tx MXene nanocomposite with single-walled carbon nanotubes (CNTs) was prepared (Fig. 14.4A) and utilized as a strain sensor with
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Figure 14.4 (A) Preparation of Ti3C2Tx/CNT sensor, (B) Ti3C2Tx/CNT nanocompositebased peizoresistive strain sensor for phonation and substantial movement detection; (i) Ti3C2Tx-MXene/CNT strain sensor attached to human throat, (iiiv) responsive curves recorded while speaking “carbon”, “sensor”, and “MXene”, (v) Ti3C2Tx-MXene/CNT sensor attached to the human knee, (vi 2 viii) resistance responses of the sensor in detecting human leg movement walking, running, and jumping [37]. Source: Reprinted with permission from Y. Cai, J. Shen, G. Ge, Y. Zhang, W. Jin, W. Huang, et al., Stretchable Ti3C2Tx MXene/carbon nanotube composite based strain sensor with ultrahigh sensitivity and tunable sensing range, ACS Nano 12 (2018) 5662.
detection limit as low as 0.1% [37] The nanocomposite strain sensor (Ti3C2Tx/ CNTs) was utilized as skin attachable wearable devices for real-time applications such as capturing physiological signal and motion monitoring (Fig. 14.4B). The tunneling distances between MXene layers and interconnected CNTs changed their overlapping areas and distances when external pressure was applied. Furthermore, a peizoresistive sensor based on Ti3C2 MXene was developed, in which the distance between two MXene interlayers was decreased when external pressure was applied [38]. The fabricated sensor was applied to human body such as on cheek, eye corner, and throat to study the physical stimuli such as cheek bulging, eye blinking, and throat swallowing. Moreover, knee-bending release movement was also monitored through change in current over the function of time. Thus, MXene sensor demonstrated peizoresistive behavior in detecting subtle human activities.
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14.2.5 MXene for terahertz sensing MXene materials have shown their great potential in terahertz (THz) sensing. Potential of MXenes as THz sensor was studied by performing density functional theory calculations on Ti3C2 [39]. In particular, optical properties of THz, the electronic band structures, and the thermoelectric figure of merit (ZT) of monolayer and stacked Ti3C2Tx were studied. Excellent light extinction and optical absorption was observed in Ti3C2 in the THz range (0.00120.012 eV). Furthermore, stacked Ti3C2-MXene exhibited superior THz absorption and a high ZT value sufficiently enough to be applied in THz detectors. Such extraordinary features enable MXene for their potential application in fabricating THz sensing devices, terahertz bolometers, and photothermoelectric detectors.
14.3
Conclusion
MXenes are a developing class of 2D materials, which are based on transition metal carbides, nitrides, or carbon nitrides. MXenes are produced by etching out A layer from a 3D structure consisting of MAX (Mn11AXn), where M is an early d-transition metal, A is the main group sp element, and X is C or N. MXenes are mechanically very strong materials composed of mostly MC or MN bonds. Chemical functionalization of the MXene surface is done with terminating groups such as O, F, and OH in order to be able to achieve chemical applications including sensing. MXenes have demonstrated promising features for sensing and biosensing applications. Titanium carbide is the most explored MXene in the field of sensing, and therefore exploitation of other transition metal-based MXenes is highly anticipated. High biocompatibility of MXene drives great motivation to design advance biosensing systems based on aptamers, antibodies, and protein molecules. However, achieving stability of MXene biosensors is of great challenge. Development of MXene-based wearable electronics contributes greatly to various healthcare diagnostics and environmental sensing applications. Overall, MXene materials hold multiple promising features to be applied in diverse sectors of technology. Thus, MXenes provide great enthusiasm toward their implementation as next-generation detection devices.
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