Ab initio investigation of functionalization of titanium carbide Ti3C2 MXenes to tune the selective detection of lung cancer biomarkers

Selected volatile organic compounds (VOCs), such as benzene (C6H6), cyclohexane (C6H12), isoprene (C5H8), cyclopropanone (C3H4O), propanol (C3H8O), and butyraldehyde butanal (C4H8O), in exhaled human breath can act as indicators or biomarkers of lung cancer diseases. Detection of such VOCs with low density would pave the way for an early diagnosis of the disease and thus early treatment and cure. In the present investigation, the density-functional theory (DFT) is applied to study the detection of the mentioned VOCs on Ti3C2TX MXenes, saturated with the functional groups Tx = O, F, S, and OH. For selectivity, comparative sensing of other interfering air molecules from exhaled breath, such as O2, N2, CO2, and H2O is further undertaken. Three functionalization (Tx = O, F, and S) are found promising for the selective detection of the studied VOCs, in particular Ti3C2O2 MXenes has shown distinct sensor response toward the C5H8, C6H6, C6H12, and C3H4O. The relatively strong physisorption (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${E}_{ads}\cong -0.45 to-0.65 {\text{eV}}$$\end{document}Eads≅-0.45to-0.65eV), triggered between VOC and MXene due to an enhancement of van der Waals interaction, is found responsible to affect the near Fermi level states, which in turn controls the conductivity and consequently the sensor response. Meanwhile, such intermediate-strength interactions remain moderate to yield small desorption recovery time (of order \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau \cong \mu {\text{s}}-{\text{ms}})$$\end{document}τ≅μs-ms) using visible light at room temperature. Thus, Ti3C2O2 MXenes are found promising candidate material for reusable biosensor for the early diagnosis of lung cancer diseases through the VOC detection in exhaled breath.

According to the World Health Organization, lung cancer (LC) accounted for 2.21 million new cases of cancer globally in 2020, making it the second most common cancer (after breast cancer) and the leading cause of cancer deaths 1 .Compared to LC diagnosed at a more advanced stage, early diagnosis improves survival and is crucially important for the start of a successful medical therapy and plausible high chance of curing before its spread in human body 2 .Different investigations of early-stage cancer have shed light on the alterations that take place during the early phases of tumor formation 2,3 .It was proven that for many cancer diseases, such as liver, lung, bowl and breast cancers, physiotherapeutic treatments exist provided early prognoses are achieved on time [4][5][6] .For instance, early diagnosis may yield good chance of survival ranging from 6/10 in lung cancer, to 9/10 in bowel cancer, and to 10/10 in breast cancer 6 .
More than half of number of patients with LC die within a year after being diagnosed, making it one of the leading causes of cancer deaths 7 , as attributed to the challenges in the therapy and diagnosis.The additional complications and high costs of examinations involving bronchoscopy and needle biopsies make them unsuitable for population screening 8 .Towards reducing the patient's mortality rate, early diagnosis of cancer through applicable and non-invasive techniques is vital, such as blood based liquid biopsies in capturing the circulating biomarkers 9 .Another non-invasive approach in the detection of cancers in the early stage is through the analysis of volatile organic compounds (VOCs) biomarkers existing within the exhaled breath of the patients 9,10 which should be more reliable as it is easy and cost effective.Statistics shows that only 16% of lung cancers can be detected at early stage 7 .From perspectives of VOCs' analysis, in 1971, Linus Pauling discovered that healthy human breath contains about 200 VOCs 11 .Hence, the question remains to which appropriate VOCs to select as lung-cancer biomarkers and beyond what critical density to decide about the cancer diagnosis, and finally what materials should be suitable for the detection.
In a statistical study, Michalis Koureas and co-workers 3 investigated the prospect of using breath analysis to differentiate between LC, other lung diseases, and the healthy control group.The levels of 19 VOCs were measured in research participants' exhaled breath.Significant differences in several substances between LC patients and healthy controls were discovered.Exogenous monoaromatic, 1-and 2-propanol biomarker sets predominately and effectively distinguished between LC patients and healthy controls.The quantities of these substances in the patient's breath may indicate changes in their physiological and biochemical status, and they may be employed as probes to examine LC 3 .
In another related work, Reji and coworkers 12 used density functional theory (DFT) calculations and presented a comparative adsorption study of six VOCs biomarkers (i.e., acetone, ethanol, acetonitrile, 2-propanol, isoprene, and toluene) on 2D Sc 2 CO 2 MXenes nanosheet.The authors reported that all VOCs can be detected via chemiresistive mechanism; while the weakly adsorbed species (e.g., toluene and isoprene) can also be detected based on the change in the work functions.Moreover, Wan and coworkers 13  Exploring defects versus doping in blue phosphorene (BlueP) to simulate experimental data, Sun and coworkers 14 used DFT to study the interaction mechanism towards the capture of some selected VOCs, such as acetone, ethanol and propanal.They focused on defects like single and multiple vacancies and on dopants like S/Si.They reported that only mono-vacancy and S-substitutional doping to have great potential for the detection of their studied VOCs.In a further exploration of 2D materials for the detection of biomarkers, Hussain and coworkers 15 presented a spin-polarized DFT study on nitogenated holey graphene (C 2 N), graphdiyne (GDY), and their hetero-structure (C 2 N•••GDY) to detect selected VOCs, such as acetone, ethanol, propanal, and toluene.They found that the incorporation of C 2 N in hetero-structure (C 2 N•••GDY) is necessary to enhance the van der Waals interactions with VOCs.They further applied thermodynamic analysis to study the sensing characteristics of VOCs under ambient conditions.They proposed C 2 N•••GDY hetero-structure as promising material for sensing certain VOCs.
After the breakthrough synthesis of MXenes by Yuri Gogotsi and coworkers in 2011 16,17 , these 2D materials subsequently found their applications in several fields, such as gas-sensing [18][19][20][21] , biosensing 12,22 , energy-storage 23 , and metal-ion batteries 24,25 .Since their invention date, Ti 3 C 2 T x MXenes 16,17 have been well characterized both experimentally 26 and theoretically 27 by being thermodynamically very stable.For instance, recently, Lu et al. 27 presented a combination of experimental and simulation studies of Ti 3 C 2 T x MXenes (T = F, OH, and O) to demonstrate their relevance for energy storage applications.These authors 27 showed the phonon spectra lacking negative frequencies as an evidence of structural stability of these MXenes.Furthermore, the distinguished and unique characteristics of MXenes' families stem in the moderate interaction (predominantly van der Waals type) between the incident molecules and the polar surface of the functionalized MXenes.Such moderate interaction scales between strong physisorption, with ability to induce electric dipole moments in small molecules, such as in hydrogen molecules and thus making MXenes suitable for hydrogen storage, to weak chemisorption with metallic compounds making MXenes suitable for battery applications 24,28 .Hence, in the context of biomarker detection, it's worth noting that VOCs consist of organic molecules that are slightly larger than the small air interfering molecules of exhaled human breath.Consequently, MXenes have the potential to induce dipole moments in various regions of VOCs, leading to stronger physisorption compared to other ambient air molecules.Such characteristics renders MXenes well-suited for selective sensing of VOCs 12 .Nevertheless, the ongoing challenge is to evaluate and optimize the ideal passivation layer that can further enhance the selectivity for VOCs specific for LC diseases.
The scope of the present investigation is to employ the state-of-the-art DFT technique by using the Vienna Ab-initio Simulation Package (VASP) to study five Ti 3 C 2 T x {T x = O, F, S, (OH), and F(OH)} MXenes for the selective detection of six representative VOCs as lung-cancer biomarkers, such as C 5 H O from the exhaled healthy human breath have also been investigated.The study also comprises the electronic, magnetic, transport properties, and sensor response to explore the sensitivity and selectivity of the studied MXenes.

Structural properties
Figure 1 shows the relaxed structures before the adsorption processes.Top panels show the atomic structures of the 6 VOCs biomarkers, which were selected as lung cancer biomarkers.The relaxed structures of these VOCs are in good agreement with literature 13 .Lower four panels in Fig. 1  Furthermore, supported by the results of the electronic structure calculations below, these MXenes are paramagnetic having metallic characters.Their discrepancies are due to the passivation layers.Definitely, the passivation layers have great ability to make different populations of electric dipoles.The strongest dipoles should be attributed to the oxygen passivation.The electronegativity characters in descending order of strengths are: χ F = 3.98 > χ O = 3.44 > χ S = 2.58 Pauling 29 .Although F atom is more electronegative than O atom, in passivation layer, oxygen is divalent and having a coordination of 2 whereas fluorine is monovalent and having same coordination of 2. Such coordination yielded transfer of charge to oxygen more than that to fluorine (i.e., |q(O)|= 1.065 >|q(F )|= 0.692 >|q(S)|= 0.352).Consequently, the electric dipole moments originating on oxygen atoms are stronger than those on fluorine.Thus, the vdW interactions of oxygen passivation should be justified to be the strongest.

Adsorption properties
For the sake of selective gas sensing, the adsorptions of the six VOCs lung-cancer biomarkers are studied and compared to the adsorptions of other four interfering air molecules existing in the exhaled human breath (i.e., N 2 , O 2 , CO 2 , and H 2 O).Actually, the adsorption of the whole 10 molecules on five different MXenes systems were assessed: (i) Ti 3 C 2 O 2 , (ii) Ti 3 C 2 F 2 , (iii) Ti 3 C 2 S 2 , (iv) Ti 3 C 2 (OH) 2 , and (v) Ti 3 C 2 F(OH).The results of adsorption energies, VOC-substrate distances, charge transfers, and magnetizations for six VOCs biomarkers are shown in Table 1.On the other hand, Table 2 displays the results of adsorption energies of the interfering air molecules and compare them to those ab-initio results existing in literature for sake of benchmarking.The results of Table 1 clearly corroborate the relevance of three functionalized MXenes towards the adsorption selectivity of biomarkers (namely, O-, F-, and S-passivated Ti 3 C 2 MXenes).It should be emphasized that MXenes (iv-v) (i.e., Ti 3 C 2 (OH) 2 and Ti 3 C 2 F(OH)) demonstrated complete lack of selectivity.Besides, one noticed peculiar behaviors of oxygen molecule as to chemically react on the surfaces of these latter MXenes.For instance, on the surface of Ti 3 C 2 F(OH) MXenes, O 2 molecule attracts two hydrogen atoms and forms hydrogen peroxide H 2 O 2 .So, these configurations are excluded from further consideration.The relaxed structures due to the adsorption of 6 VOCs on particularly the Ti 3 C 2 O 2 MXenes are displayed in Fig. 2. While all the VOCs exhibit physisorption processes, those containing oxygen exhibit the strongest interactions as displayed by the close distances to the MXenes' surfaces; and they should consist best candidate biomarkers.
The results of adsorption energies of the 10 molecules (six VOCs and four air molecules) on four MXenes (i-iv) are displayed in Fig. 3. Furthermore, as being potential candidates for the selective detection of biomarkers, only three MXenes are selected for the rest of investigation: (i) Ti 3 C 2 O 2 , (ii) Ti 3 C 2 F 2 , and (iii) Ti 3 C 2 S 2 .One more remark about the behavior of oxygen molecule with Ti 3 C 2 O 2 MXene, as it is shown in the bar chart diagram, O 2 has a positive adsorption energy indicating that Ti 3 C 2 O 2 is more invulnerable to oxidation.This trend is also consistent with the finding of many other ab-initio simulations existing in literature [32][33][34] (see Table 2).Although our current findings reveal that the O 2 molecule does not get adsorbed on Ti 3 C 2 O 2 MXene, yet this trend is still in favor of aiming the selectivity towards the VOCs biomarkers.So, the oxygen data is just excluded in Fig. 3a.
For the case of Ti 3 C 2 O 2 , the logical rational contribution of vdW physical interactions has been evaluated.Intriguingly, our findings revealed that intrinsic vdW interactions account for 100% of the binding energy and are the main contributors to it.For instance, the VOCs were found to exhibit a positive adsorption energy (i.e., not interacting with the substrate) upon the switching off the vdW interactions in our simulations.
To demonstrate the selectivity of the detection of VOCs, the adsorption energies of four interfering air molecules (N 2 , O 2 , CO 2 , and H 2 O) are included in Table 2 and compared to those existing in literature.Our results are in excellent agreement with literature.For instance using Ti 3 C 2 O 2 MXenes, our results of adsorption energies It should be emphasized that these structures have been experimentally synthesized and proven to be thermodynamically stable.As described in the previous section, the relaxed structures are in good agreement with literature as well 18 .

Spin polarized density of states (DOS)
Figure 4 shows the spin-polarized total density of states (TDOS) of Ti 3 C 2 O 2 MXenes after the adsorption of the six VOCs in solid lines.The spin-polarized TDOS of MXenes without the VOCs is shown in shaded curve.The Fermi level is taken as an energy reference (i.e., E F = 0).All the results of TDOSs show that the MXenes exhibit metallic characters which is attributed to the d state of the titanium atoms (Ti).Subsequently, the difference between solid and shaded curves especially at the energy region near Fermi level should reveal the effect on transport rectification and consequently the sensor response.Focusing on the discrepancies in the region near Fermi level of Ti 3 C 2 O 2 , one may notice their existences in VOCs biomarkers number i-iii (i.e., Isoprene "C 5 H 8 ", Benzene "C 6 H 6 ", and Cyclohexane "C 6 H 12 ").Figure S1 (supplementary documents) displays the spin-polarized TDOS of other two MXenes, which are also selected to be candidates for selective gas-sensing of VOCs biomarkers.Namely, Figure S1-a and S1-b corresponding to MXenes Ti 3 C 2 F 2 and Ti 3 C 2 S 2 before and after the adsorption of six VOCs biomarkers.Once again, by focusing at energy region around Fermi level, one can notice some discrepancies between shaded and solid curves, especially being very pronounced in the three VOCs biomarkers on Ti 3 C 2 S 2 MXenes.Yet, these results of TDOS need further analysis to make them more useful.The calculations of the conductivity, using the Drude model, should follow below, as well as charge transfer through both Bader charge analysis and charge density difference (CDD).

Charge transfer and sensor response
Figure 5 shows the results of charge-density difference (CDD) of six VOCs biomarkers on three MXenes: (i)    The results confirmed that Ti 3 C 2 O 2 MXenes to be the best candidate for the selective sensing of at least four VOCs biomarkers (namely: isoprene "C 5 H 8 ", benzene "C 6 H 6 ", cyclohexane "C 6 H 12 ", and cyclopropanone "C 3 H 4 O"), which mostly act as reducing agents.The sensor response for these four molecules on Ti 3 C 2 O 2 MXenes are ranging from 52%, 60%, 47%, to 43%, respectively, as shown in Table S1.One recalls that the direct-current (DC) conductivity was estimated using the Drude formula, which is valid for a system of quasi-free electron gas, as in case of MXenes which have metallic characters.So, it is concluded that Ti 3 C 2 O 2 to be the best candidate for detecting four VOCs biomarkers.
In order to assess whether the sensor is useable or disposable, we have calculated the recovery time using Eq. ( 4) at room temperature and under the exposure of visible light.The results are shown in Table 3 in units of seconds.It is remarkable that the recovery time for our selected MXenes (i.e., O-, F-, and S-passivated Ti 3 C 2 MXenes) is small and ranging between μs and ms.Such results are very encouraging and rather corroborating    www.nature.com/scientificreports/ the suitability of these MXenes for the selective detection of the studied VOCs as they provide moderately strong physisorption interactions to alter the transport properties and sensor response while maintaining the recovery time small enough.So, they can be good candidates for platforms in reusable biosensors for efficient detection of lung cancer biomarkers.

Conclusions
An ab-initio method based on VASP was employed to search for the suitable functionalization of Ti , and H 2 O} were considered in the investigation of the adsorption, transport and gas sensing properties.While all molecules were found to exhibit physisorption processes on the studied Ti 3 C 2 T x MXenes (with T x = O, F, S, (OH), or F(OH)) groups), the interactions between the VOC biomarkers and, particularly, the O-, F-, and S-passivated MXenes are found to be relatively strong (with E ads ∼ = −0.45to− 0.65eV ) and to yield higher sensitivity.The reason behind such enhanced physisorption is attributed to the formation of strong electric dipole moments in the VOCs which in turn strengthen the van der Waals interactions to the extend to affect the states near Fermi level of the adsorbent.Such effects can rectify the conductivity and consequently the sensor response.Furthermore, such scenario or trend is more pronounced in the case of interaction between the O-passivated Ti 3 C 2 MXenes and the O-containing VOCs.Equally importantly, the calculated recovery time at room temperature under the visible light exposure was found small at the order ranging between few μs to ms.It is concluded that, among the studied systems, Ti 3 C 2 O 2 was the best candidate as platform of efficient reusable biosensor the selective detection of lung cancer biomarkers, thus, enabling early diagnosis of lung cancer diseases.

Computational methodology
The computational supercell is composed of 3 × 3 primitive cells (PCs) of Ti 3 C 2 T x MXenes with periodic boundary conditions applied along the x and y directions and vacuum space of 20 Å along the z direction to enable the simulation of a single isolated monolayer (ML).The passivation layer on Ti .Furthermore, the VOCs biomarkers were also relaxed in their free standing states and the results of relaxations are displayed in Fig. 1.The relaxed structures are found to be in good agreement with literature vis-à-vis morphology and bond lengths 13 .The computational method is based on DFT as implemented in VASP package.This code is worldwide popular and very reliable in predicting the ground state properties of solids and molecules and should be the most suitable for the adsorption properties.It solves the Kohn-Sham equations iteratively using plane wave basis set with periodic conditions.Projected-augmented plane waves were employed to describe the electron-ion interaction 37 .The exchange and correlation interaction is handled using the Perdew-Burke-Ernzerhof formula of the generalized gradient approximation (GGA) approach 38 .Plane wave basis set is used up to an energy cutoff of 520 eV.The sampling of the Brillouin zone is carried out using the special-k point technique due to the Monkhorst-Pack scheme 39 .For the atomic relaxations and density of states calculations, grids of 4 × 4 × 1 and 6 × 6 × 1 were used, respectively.In the DFT self-consistent cycle, convergence criteria of 10 -6 eV on total energy and 0.01 eV/Å on force per atom were used.The inclusion of van der Waals (vdW) interaction is essential and was implemented using DFT-D3 method of Grimme scheme 40 .The atomic charge transfers are evaluated using the Bader charge analysis 41 .
To study the adsorption, the VOCs and interfering air molecules were individually brought close to the surface of functionalized MXenes within a distance of about 2.0 Å and atomic relaxations started.Initial configurations of molecules on different sites and in different orientations were tested.The results of total energy calculations are explored to calculate the molecular adsorption energy: where E MXene−Mol tot , E MXene tot , and E Mol tot are total energies of molecule adsorbed on MXene, MXene, and the free molecule, respectively.The ratio (R) of the contribution of vdW interactions to the molecular adsorption energy can be evaluated using the following formula: where E vdW ads and E NovdW ads are the adsorption energies with and without vdW interactions, respectively.After the adsorption process, the MXenes maintain their metallic characters.So, one can evaluate the DC conductivity using Drude formula (see reference 42 for details).Then, the sensor response can be estimated as follows 42 : In order to decide about whether the sensor should be reusable or disposable, one may estimate the recovery time 43 given by: where υ o is the attempt frequency factor, having values 10 12 and 10 16 Hz under visible and UV light situations, respectively 44,45 .E ads is the adsorption energy, k B and T are the Boltzmann constant and the absolute temperature, respectively.
Figure1shows the relaxed structures before the adsorption processes.Top panels show the atomic structures of the 6 VOCs biomarkers, which were selected as lung cancer biomarkers.The relaxed structures of these VOCs are in good agreement with literature13 .Lower four panels in Fig.1display the relaxed structures of pristine MXenes monolayers samples of: (1) Ti 3 C 2 O 2 , (2) Ti 3 C 2 F 2 , (3) Ti 3 C 2 S 2 , and (4) Ti 3 C 2 (OH) 2 MXenes.Furthermore, supported by the results of the electronic structure calculations below, these MXenes are paramagnetic having metallic characters.Their discrepancies are due to the passivation layers.Definitely, the passivation layers have great ability to make different populations of electric dipoles.The strongest dipoles should be attributed to the oxygen passivation.The electronegativity characters in descending order of strengths are: χ F = 3.98 > χ O = 3.44 > χ S = 2.58 Pauling29 .Although F atom is more electronegative than O atom, in passivation layer,

Figure 1 .
Figure 1.Relaxed atomic structures of six VOCs biomarkers in their free-standing states, and four Ti 3 C 2 T x MXenes functionalized with T = O, F, S, and OH group, respectively.Atom Colors: C (grey), H (white), Ti (orange), O (red), F (green), and S (yellow).(a) Ti 3 C 2 O 2 , (b) Ti 3 C 2 F 2 , (c) Ti 3 C 2 S 2 , and (d) Ti 3 C 2 (OH) 2 .It should be emphasized that these structures have been experimentally synthesized and proven to be thermodynamically stable.As described in the previous section, the relaxed structures are in good agreement with literature as well18 .

Figure 3 .
Figure 3. Binding energies of 10 molecules deposited on four Ti 3 C 2 T x MXenes functionalized with T = O, F, S, and OH group.10 molecules comprise six VOCs lung-cancer biomarkers and four air molecules existing in healthy exhaled breath (i.e., N 2 , O 2 , CO 2 , H 2 O).If E ads > 0, then it should indicate that the molecule does not bind to the surface of MXenes.

Figure 6
shows the results of both (a) the absolute values of the adsorption energies and (b) charge transfers, which are originally summarized in Table 1 for the adsorption processes of 10 molecules (i.e., six VOCs biomarkers + four air molecules) on the three MXenes (1) Ti 3 C 2 O 2 , (2) Ti 3 C 2 F 2 , and (3) Ti 3 C 2 S 2 .From the perspective of the adsorption energies, VOCs biomarkers possess much higher values than the four interfering air molecules existing in the exhaled breath (N 2 , O 2 , CO 2 and H 2 O).Whereas, from the perspective of charge transfer, the values are larger on the side of VOCs biomarkers but not as pronounced as the adsorption energies.

Figure 4 . 6 Figure 7
Figure 4. Spin-polarized TDOS of 6 systems due to the interactions of 6 VOCs lung-cancer biomarkers with Ti 3 C 2 O 2 MXenes.Shaded curves are due to the substrate whereas the solid curves are attributed to the VOC-MXenes systems.Fermi level is take as an energy reference (E F = 0).

Figure 5 .
Figure 5. Charge density difference (CDD) of 6 VOCs lung-cancer biomarkers after getting relaxed on 3 Ti 3 C 2 T x MXenes functionalized with T = O, F, or S. Colors of atoms: Ti (sky blue), C (brown), O (red), and H (white). Gain (deficit) of charge is indicated by color yellow (cyan).

Figure 6 .
Figure 6.adsorption energy (a) and charge transfer (b) attributed to the relaxation of 10 molecules (comprising 6 VOCs lung-cancer biomarkers + 4 air molecules interfering the healthy exhaled breath) on 3 Ti 3 C 2 T x MXenes functionalized with T = O, F, or S.

Figure 7 .
Figure 7. Sensor responses of 6 VOCs lung-cancer biomarkers after their adsorption on 3 Ti 3 C 2 T x MXenes functionalized with T = O, F, or S. Ti 3 C 2 O 2 MXenes is shown to have distinguished selectivity toward at least four VOCs biomarkers.Thus, it should be the best candidate for platform of reusable biosensor with promising early diagnosis of lung cancer diseases.
3 C 2 T x MXenes, in both side and top views, are shown in Fig. 1.Pristine Ti 3 C 2 MXenes has a triangular lattice constant a = 3.050 Å, which is in good agreement with the experimental value of 3.057 Å 36 .Lattice parameters of Ti 3 C 2 T x MXenes with T x = O, F, S, and OH are a = 3.027, 3.062, 3.124 Å, and 3.067 Å, respectively.Accordingly, for instance the supercell of Ti 3 C 2 O 2 has the dimensions A = B = 9.081 Å, C = 30 Å and contains 63 atoms (27 Ti + 18 C + 18 O atoms)

Table 2 .
35r calculated Adsorption energies (eV) of air interfering molecules (N 2 , O 2 , CO 2 , H 2 O) on three MXenes of interest are shown and compared to data available in literature for sake of benchmarking.A Ref.30, B Ref.31, C Ref.32, D Ref.33, E Ref.34, F Ref.35.

Table 3 .
Recovery time of VOCs' desorption on the selected MXenes (unit of second), calculated at room temperature and exposed to visible light.
3 C 2 -based MXenes as platform for biosensor for selective detection of lung cancer biomarkers.Six VOC biomarkers {namely,