Exfoliated 2D-MoS2 nanosheets on carbon and gold screen printed electrodes for enzyme-free electrochemical sensing of tyrosine

Journal Pre-proof Exfoliated 2D-MoS2 nanosheets on carbon and gold screen printed electrodes for enzyme-free electrochemical sensing of tyrosine R. Zribi, R. Maalej, E. Messina, R. Gillibert, M.G. Donato, O.M. Marag`o, P.G. Gucciardi, S.G. Leonardi, G. Neri

PII:

S0925-4005(19)31428-5

DOI:

https://doi.org/10.1016/j.snb.2019.127229

Reference:

SNB 127229

To appear in:

Sensors and Actuators: B. Chemical

Received Date:

11 April 2019

Revised Date:

28 August 2019

Accepted Date:

3 October 2019

Please cite this article as: Zribi R, Maalej R, Messina E, Gillibert R, Donato MG, Marag`o OM, Gucciardi PG, Leonardi SG, Neri G, Exfoliated 2D-MoS2 nanosheets on carbon and gold screen printed electrodes for enzyme-free electrochemical sensing of tyrosine, Sensors and Actuators: B. Chemical (2019), doi: https://doi.org/10.1016/j.snb.2019.127229

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

1

Exfoliated 2D-MoS2 nanosheets on carbon and gold screen printed electrodes for enzyme-free electrochemical sensing of tyrosine

R. Zribia,b,c, R. Maaleja, E. Messinad, R. Gillibertd, M. G. Donatod, O. M. Maragòd, P. G. Gucciardid,

ro of

S. G. Leonardib, G. Nerib,c,*

a

Georesources Materials Environment and Global Changes Laboratory (GEOGLOB), Faculty of Sciences of Sfax, University of Sfax, Tunisia. Department of Engineering, University of Messina, C.da Di Dio, I-98166 Messina, Italy

c

INSTM, Research unity of Messina

-p

b

CNR IPCF Istituto per i Processi Chimico-Fisici, viale F. Stagno D’Alcontres 37, I-98156 Messina, Italy

*

na

e-mail: [email protected]

lP

re

d

Research highlights 

Jo



Exfoliated two-dimensional molybdenum disulphide nanosheets (2D-MoS2) have been prepared; A simple enzyme-free 2D-MoS2 electrochemical sensor for the determination of tyrosine has been proposed for the first time; 2D-MoS2-SPCE electrode showed good performances toward tyrosine detection, reaching a maximum sensitivity of 1580 μA•mM−1•cm−2; Voltammetric method by using the proposed sensor provided satisfactory results for the detection of tyrosine in a real food integrator sample.

ur





Abstract We demonstrate a simple enzyme-free electrochemical sensor for tyrosine (Tyr) detection, based on the enhanced catalytical activity of two-dimensional molybdenum disulphide nanosheets (2DMoS2), prepared by liquid phase exfoliation and deposited on commercial screen-printed carbon and

2

gold electrodes (SPE). We first evaluate the electrochemical performances of the sensor by cyclic voltammetry (CV) in phosphate buffer solutions (PBS; pH = 7) as a function of the chemical nature and microscale texture of the working electrode, as well as the operating potential window. Results show that the modified-carbon (2D-MoS2-SPCE) and gold (2D-MoS2-SPAuE) electrodes display various anodic and cathodic peaks, whose potential and intensity depend on the potential window, electrode nature and 2D-MoS2 loading. 2D-MoS2 SPE electrodes are finally tested for voltammetric and amperometric detection of tyrosine. We show that 2D-MoS2-SPCE provide the best results, reaching a maximum sensitivity of 1580 μA·mM−1·cm−2 and a limit of detection (LOD) of 0.5 μM computed at a S/N = 3. The proposed method shows satisfactory results also for the detection of

ro of

tyrosine in a real food integrator sample. To our best knowledge, this is the first report demonstrating the use of 2D-MoS2 for the electrochemical determination of tyrosine.

-p

Keywords: Molybdenum disulphide nanosheets; Electrochemical sensors; Tyrosine.

re

1. Introduction

MoS2 is a transition metal disulphide (TMD) semiconductor with a direct band gap of about 1.9 eV and excellent charge carrier mobility. It finds useful implementations as electro-catalyst for

lP

many applications. Ultrathin two-dimensional MoS2 (2D-MoS2) flakes provide larger specific surface area, so their electrocatalytic properties are strongly enhanced with respect to bulk material.

na

The production of high quality mono- to few-layers MoS2 nanosheets is still a big challenge. Bottom-up methods include chemical vapor deposition (CVD) [1], physical vapor deposition [2], metal organic chemical vapor deposition MOCVD [3]. Top-down methods, such as

ur

micromechanical cleavage [4] and chemical intercalation methods [5-6], are also used. CVD, however, involves expensive equipment and harsh conditions; intercalation methods are critical

Jo

when MoS2 nanosheets structure integrity is a concern; micromechanical cleavage exhibits a low process yield. Following the methods for large scale production of graphene [7-8], liquid-phase exfoliation (LPE) has been tailored to prepare MoS2 nanosheets [9]. LPE is a scalable method for mass production of MoS2 as mono- and few-layers nanosheets. The process typically involves three steps [10]: (1) dispersion of the bulk microparticles in a solvent, (2) ultrasound-assisted exfoliation, and (3) purification. MoS2 flakes can be produced by surfactant-assisted [11] or surfactant-free exfoliation in organic solvents [9-13]. During ultrasonication, shear forces and cavitation act on the bulk material, leading to exfoliation of mono- to few-layers nanosheets with lateral dimensions of hundreds of nanometres. To prevent re-aggregation due to the inter-sheet attractive forces, solvents/

3

surfactants that minimize the interfacial tension between the liquid and flakes are used. LPE is a scalable process capable to produce industrial-scale volumes of materials [14]. In recent years MoS2 has gained tremendous attention as a material for sensing applications in the biomedical and food analysis fields [15]. Amino acids, the basic blocks of proteins, are essential in human body because of their important role in nutrition and metabolic regulation. Xia et al. reported an electrochemical sensor based on Ag-MoS2-Chitosan nanohybrid developed for the detection of tryptophan [16]. Tyrosine (Tyr) is an amino acid precursor of important neurotransmitters such as dopamine, being indispensable for humans. It is a biomarker for early detection of various brain diseases [17, 18].

ro of

Tyr is also one of the amino acids necessary for the maintenance of nutritional balance. Foods with high Tyr content, including cheese, egg and yogurt are in fact used in the diet of peoples with tyrosine deficiency [19]. Methods to detect tyrosine are, therefore, of great interest in both

fundamental and applicative research. The electrochemical determination of Tyr with standard

electrodes presents many limitations such as high over potentials, slow electron transfer reactions,

-p

low sensitivity and reproducibility [20]. A number of modified electrodes have been proposed,

featuring significant improvements of the electrocatalytic properties and stability of the electrode

re

response [21-28].

Sheets of highly defected MoS2 have shown enhanced catalytic activity in the activation of

lP

small molecules, such as hydrogen and oxygen, due to the large number of exposed edges [29]. No studies on the detection of tyrosine (Tyr) with MoS2-based sensor have been reported so far, to our best knowledge. In this paper, we investigate the use of 2D-MoS2 to improve the performances of a

na

simple, enzyme-free Tyr electrochemical sensor, by modification of the sensor electrodes. MoS2 nanoplatelets are prepared by LPE and deposited on commercial screen printed electrodes (SPE) in order to take advantage of the enhanced electrocatalytic reactivity of MoS2 in the detection of Tyr.

ur

We study the electrochemical response and the operating potential window of two sensors based on carbon and gold SPE modified with MoS2. Finally, we show the detection of Tyr in a commercially

Jo

available food integrator using optimized electrodes working in optimal operation conditions.

2. Experimental 2.1. 2D-MoS2 synthesis 2D-MoS2 nanosheets were prepared by surfactant-assisted liquid phase exfoliation of MoS2 microparticles in sodium cholate (SC), following the procedure detailed in ref. [11]. Exfoliation was

4

carried out by ultrasound treatment (30 minutes) with a horn ultrasonic bath (Branson 250) of an aqueous SC solution (0.045 mg/mL) into which MoS2 powder (0.15 mg/mL) was added. During sonication, the solution was kept in an ice bath to reduce detrimental heating effects. The dispersions were allowed to decant overnight in a flask. Then, the half top part (20 mL, typically) was taken and centrifuged at 1500 rpm for 15 minutes. The solution thus obtained was stable for months (see inset in Figure 1). Surfactants [30], as well as organic solvents [31], are fundamental to stabilize the 2D nanosheets solutions. Surfactants encapsulate the nanosheets so that electrostatic repulsions can be efficiently exploited (and even tuned) to avoid reaggregation [32]. The role of the organic solvent is to facilitate the delamination process and to sustain stable dispersions with high

ro of

concentrations of exfoliated 2D nanosheets. Best solvents are those that minimize the surface energy difference with the layered materials such N-methyl-2-pyrrolidone and Sodium Cholate [33].

-p

2.2. Characterizations

SEM images were acquired by means of a Zeiss CrossBeam 540. UV-Vis spectroscopy was

re

carried out with a Perkin Elmer Lambda 25. Raman spectroscopy was carried out with a Horiba XploRA setup at 638 nm and 785 nm. The laser beam was focused with a 10X objective (NA 0.25, WD 10.6mm). Experiments were carried out on the liquid solution (same samples used for UV-VIS,

lP

diluted 1:10 v/v). For comparison, measurements were carried out on the pristine powder and on the electrodes on which MoS2 flakes were cast. On the powder and the electrodes, laser power was kept

na

smaller than few hundreds of µW in order to prevent thermal effects. 2.3. Modified electrode fabrication

ur

Screen-printed electrodes (SPEs) were purchased from DropSens, Spain. The SPEs platforms used were: i) DRP-100, constituted of a 4-mm diameter carbon working electrode, a silver pseudoreference electrode and a carbon auxiliary electrode (named SPCE); ii) Low (C220AT) and high

Jo

surface area (C220BT) 4-mm diameter gold electrodes, having a silver pseudo-reference electrode and a gold auxiliary electrode (named SPAuE). Pictures of the bare SPEs platforms and their specifics are reported in the http://dropsens.com/ web site. To modify the bare SPEs, different volumes of a 2D-MoS2 dispersion at a concentration of 0.45 µg/mL, were directly drop cast onto the surface of working electrode and let dry at room temperature until further use. 2.4. Electrochemical tests

5

Electrochemical analyses, namely amperometric measurements and cyclic voltammetry, were performed by using a DropSens µStat 400 Potentiostat empowered by Dropview 8400 software. All sensors were characterized by cyclic voltammetry (CV) and chrono-amperometric tests in aerated 0.1 M PBS as electrolyte. CV was carried out at a scan rate of 50 mV/s in the potential range of 0 - 0.8 V. Tyr concentration was varied in the 0 – 600 µM range. Chrono-amperometric curves were obtained by recording the oxidation current while an appropriate volume of Tyr solution of certain concentration was added into the electrolyte solution maintained under magnetic stirring. Calibration curves were obtained by plotting the Faradaic current (the current values for

ro of

chronoamperometry, and the current peak for cyclic voltammetry) vs. concentration of tyrosine. The sensitivity was computed as the slope of the calibration curve. The Limit of Detection (LOD) was calculated at a signal-to-noise ratio S/N = 3. Both sensitivity and LOD were evaluated within

-p

the linear range of operation of the sensor. All experiments were performed at room temperature.

3. Results and discussion

re

3.1 2D-MoS2 characterization

lP

To investigate the properties of the as-synthesized 2D-MoS2 nanosheets, UV-VIS spectroscopy and Raman analyses were carried out on the MoS2 solutions. UV-Vis spectroscopy was carried out in the 250 - 900 nm wavelength range. To reduce the influence of (multiple) scattering in the

na

measurements and safely apply Beer’s law to estimate concentration, we diluted the sample 1:10 v/v in SC prior to analysis [34, 35]. The extinction spectrum of the diluted MoS2 solution (Fig. 1) shows the A- (680nm) and B- (622nm) exciton components, superposed to a scattering background,

Jo

ur

consistent to what expected for the 2H polytype of MoS2 [36].

6

Figure 1. Extinction spectrum of the MoS2 dispersion diluted 1:10 v/v. The absorbance normalized to the absorption length is reported on the vertical axis. Inset: picture of the MoS2 solution compared to the SC solution. The extinction spectrum provides information on the concentration, c, of the MoS2 flakes. Using the extinction coefficient  = 6820 L g-1 m-1 for the local minimum at 350 nm [36] we find c = 0.45 µg/mL for our sample. The comparison of the extinction peak at the B-exciton wavelength with the minimum extinction at 350 nm, considering also the position of the A-exciton, allows us to obtain information on the nanosheets length and thickness. The empirical formulas reported in refs. [36,14] were used to this aim. Here we find an average nanosheet length L = 450 nm and an average

ro of

number of layers per sheet Nlay comprised between 15 and 20. Raman spectroscopy at 638 nm (Fig. 2a) and 785 nm (Fig. 2b) was carried out to confirm the structure of the MoS2 nanosheets, evaluate the number of layers per particle and exclude

Jo

ur

na

lP

re

-p

contaminations and/or distortions of the crystalline matrix.

7

Figure 2: Raman spectra carried out at 638 nm (a) and 785 nm (b) on liquid dispersions (black lines), on the powder (red lines) and on the gold electrode after casting 150 µL of MoS2 solution (blue line). The Inset (b) represents the intensity of the 384 cm-1 band as a function of the amount of deposited MoS2 using 785 nm excitation. Experiments were carried by focusing the laser beam in the liquid solution and, for comparison, on the pristine powder. Measurements on the liquid dispersions were carried out with a laser power of 26 mW (638 nm) and 56 mW (785 nm) integrating 20 min. On the powder, as well as on the electrodes, laser powers were kept smaller than few hundreds of µW in order to avoid thermal effects that produce changes of the peaks positions and of the intensity ratios among the bands

ro of

1 [37,38]. We did not observe any relative shift between the two 𝐸2𝑔 (384 cm-1) and 𝐴𝑔1 (408 cm-1)

modes [37] (Fig. 2, black lines), neither in solution nor after deposition on the electrode (see Fig. 2b blue line and discussion in paragraph 3.2), between the nanosheets and the powder (Fig.2, red

lines). These two modes, were reported to shift one towards the other when the number of layers

-p

Nlay decreases below 7 [39,40]. Our results were therefore expected, given the number of average layers per flake estimated by UV-VIS and in agreement with the literature [14,11]. Interestingly, we

re

noted a different intensity ratio between the two modes in the spectra acquired at 785nm.

lP

3.2 Screen printed electrodes

Both carbon and gold electrodes were first tested as electrochemical platforms. The surface morphology of the bare electrodes was investigated by SEM (see Fig. 3a-c). The SPCE showed a

Jo

ur

a

na

rough surface with features’ size in the range from 10 to 50 nm (Fig. 3a).

c

b

8

d

e

-p

ro of

f

Figure 3. SEM images showing the surface of: a) SPCE; b, c) SPAuE ; d) 2D-MoS2(50µl)-SPCE; e,

re

f) 2D-MoS2(400µl)-SPAuE electrode. Insets in Figure a, b, c show a higher magnification of the electrode surface. Image b and c have been taken from DropSens web site.

lP

For what concerns the morphology of the gold electrodes, the low-surface area electrode (C220AT) presents a smooth surface with slight scratches (Fig. 3b), while the high-surface area one (C220BT) shows a rougher surface (Fig. 3c) with a three-dimensional structure. This latter platform

na

is expected to provide superior electron transfer rate at the electrode-electrolyte interface, because of the higher surface area, and thus lead to a superior electrocatalytic activity [41].

ur

SEM images in Fig. 3d,f show the 2D-MoS2 layer deposited on the carbon and gold electrodes. When depositing small volumes of the nanosheets solution (e.g. 50µl, as in the case of modified carbon electrode shown in Fig. 3d), the coverage of the surface is not complete. Vice versa, full

Jo

surface coverage is obtained with larger nanosheets volumes (400µl), as demonstrated by the 2DMoS2(400µl)-SPAuE electrodes shown in Figs. 3e, f. Raman analysis of the 2D-MoS2 layer deposited on the SPE was performed and compared with

2D-MoS2 before deposition. As an example, the Raman spectrum collected on the 2D-MoS2SPAuE is shown in Fig. 2b (blue line). The spectrum is similar to the one acquired in the 2D-MoS2 liquid solution (black line), suggesting that no transformation occurs when 2D-MoS2 is transferred from the solution to the electrode. For gold electrodes, the average Raman intensity of the 384 cm-1 mode is plotted (Fig. 2b, inset) as a function of the 2D-MoS2 volume cast on the electrode (50, 150

9

and 400 µl). The standard deviation over six measurements is used as error bar. As expected, the Raman intensity increases with the amount of deposited MoS2, up to saturation

3.3 Electrochemical tests 3.3.1 2D-MoS2-modified carbon electrode 3.3.1.1 Cyclic voltammetry in absence and presence of tyrosine The electrochemical behavior of unmodified carbon SPEs and 2D-MoS2-modified screen printed electrodes was assessed by CV in 0.1 M PBS electrolyte at a scan rate of 50 mV/s. First, the

ro of

electrodes were cycled in the potential range between 0 and 0.8 V. In these conditions, no peaks were observed on the unmodified carbon electrodes (Fig. 4a). 2D-MoS2-SPCE exhibited, instead, a larger CV cycle (Fig. 4b), likely due to the higher surface area compared to the bare carbon

electrodes. In the anodic direction, a process started to appear at about 0.6 V, likely due to oxygen

25

a)

bare SPCE

re

20

10

500 M Ty

lP

Current (uA)

15

5

PBS

0 -5

50mV/S 0,2

na

-10 0,0

0,4

0,6

0,8

Potential (V)

20

b)

500 M Ty

Jo

Current (uA)

15

MoS2 (100L) SPCE

ur

25

10 5

PBS

0

-5

50mV/S -10 0,0

-p

evolution reaction (OER). No peak was observed, instead, in the cathodic direction.

0,2

0,4

Potential (V)

0,6

0,8

10

Figure 4. Electrochemical behavior of a) unmodified SPEs and b) 2D-MoS2-modified electrodes in the 0 – 0.8 V potential window. CV was performed in air-saturated 0.1 M PBS electrolyte at a scan rate of 50 mV/s.

Subsequently, we investigated the effect of tyrosine addition. Upon addition of 500 µM of tyrosine, the unmodified SPCE showed an anodic wave at about 0.7 V, attributed to the irreversible oxidation of Tyr on the carbon nanostructured surface (Fig. 4a). On the modified 2D-MoS2-SPCE electrode (Fig. 4b), the tyrosine oxidation peak was characterized by a higher peak current and a lower potential (0.6 V). The better performances of the modified electrode can be associated with

ro of

an enhanced electrocatalytic oxidation activity toward tyrosine of the 2D-MoS2 sensing layer.

3.3.1.2 Effect of potential window

The effect of a wider potential window (-0.6 to 1.2 V) on the electrochemical behavior of the

-p

sensor was also evaluated (Fig. S2a). However, except for the rise of the anodic current due to the evolution of oxygen, appearing at a potential more positive than 0.8 V, no peak was noted on the unmodified SPCE and 2D-MoS2-SPCE. In presence of tyrosine, no evident enhancement of the

re

oxidation peak for this analyte was observed. This suggests that, for the 2D-MoS2-SPCE, a narrow potential window between 0 and 0.8 V is sufficient for the electroanalytical determination of

lP

tyrosine.

na

3.3.2 2D-MoS2-modified gold electrode

3.3.2.1 Cyclic voltammetry in absence and presence of tyrosine The electrochemical behavior of unmodified gold SPEs and 2D-MoS2-modified screen printed

ur

gold electrodes was assessed by CV in the same experimental conditions reported above. Preliminary tests showed that the high surface area electrode (C220BT) provided better

Jo

electrochemical characteristics compared to low surface area one (C220AT). In the following only data obtained with the C220BT gold electrode will be reported. In the potential range between 0 and 0.8 V, no peak was observed on the unmodified gold electrode (Fig. 5). During the first cycle with the modified-MoS2 electrodes, conversely, we measured a strong peak at 0.6 V, attributed to MoS2 (Fig. S1). The peak disappeared completely after few cycles, in agreement with findings reported by Banks et al. [42]. After this transitory regime, a state characterized by a stable CV cycle was reached (Fig. 5).

11

4 SPAuE 2D-MoS2-SPAuE (50 l)

Current (uA)

3

A1

2 1 0 -1 -2

C1 0,0

0,2

0,4

0,6

0,8

ro of

Potential (V)

Figure 5. Electrochemical behavior of unmodified SPEs and 2D-MoS2-modified electrodes in the 0 – 0.8 V potential window. CV was performed in air-saturated 0.1 M PBS electrolyte 50 mV/s.

The CV cycle evidenced the presence of a peak in the anodic direction (A1) followed, in the

-p

reverse scan, by a cathodic peak (C1) centered at about 0.28 V. We attribute this peaks couple to the reduction of oxidized gold species, formed on the surface of the modified gold electrode at a

re

positive potential higher than 0.5 V. Interestingly, we observed this peaks couple only on the 2D-

lP

MoS2-SPAuE, suggesting that the presence of 2D-MoS2 seems essential for its formation.

3.3.2.2 Evaluation of different MoS2 nanosheets loading

na

We investigated the effect of 2D-MoS2 nanosheets loading by adding increasing volumes of 2D-MoS2 nanosheets solution (50, 150, 400 µL) on the gold electrodes. The electrochemical

b) 2

 current (A)

Jo

ur

response is reported in Fig. 6.

1

0 0

100

200

MoS2 (l)

300

400

12

4

Current (uA)

3

Figure 6. a) Electrochemical

a)

AuBSPE 2D-MoS2-AuBSPE (50 l) 2D-MoS2-AuBSPE (150 l) 2D-MoS2-AuBSPE (400 l)

behavior in 0.1 M PBS at a

A1

2

scan rate of 50 mV/s of the

1

2D-MoS2-SPAuE in the 0 – 0.8

0

V potential window. b)

-1

Current variation of peak C1

-2

C1 0,0

0,2

0,4

0,6

vs. the volume of 2D-MoS2

0,8

nanosheets suspension used

Potential (V)

ro of

for the bare electrode modification.

The intensity of A1 and C1 peaks increased with the addition of 50 µl MoS2 (Fig. 6a, red line) Further addition leaded to a large decrease of the signal (blue and green lines). The plot of the C1

-p

peak current (Ip) vs. MoS2 loading (Fig. 6b) shows that there is an optimal MoS2 quantity that

maximizes the peak current. To explain this finding, we suppose that the peaks couple is related to

re

gold species at the interface with 2D-MoS2 nanosheets. Indeed, a certain coverage of 2D-MoS2 nanosheets is necessary to create interface sites. Increasing the coverage, however, they are

lP

gradually blocked by 2D-MoS2 nanosheets which progressively accumulate on the surface. The interface between the MoS2 nanosheets and Au seems then to play a peculiar role in the observed enhancement. It could be hypothesized that the charge-transfer efficiency between the MoS2

na

nanosheets and the conductive porous structure of the underlying metallic gold electrode SPAuE are factors which influence positively the oxidation-reduction processes. This is also in agreement with the better electrochemical characteristics found on the high-surface area electrode. Here, the more

ur

pronounced 3D texture (see SEM image in Fig. 3c) plays an important role in both exhibiting more exposed active MoS2 sites and preventing MoS2 nanosheets from aggregation.

Jo

The modified 2D-MoS2-(150 µl) SPAuE was tested at different tyrosine concentrations.

Differently from the 2D-MoS2-SPCE, on the modified gold electrode no obvious anodic peak for Tyr oxidation could be observed (Fig. 7). Indeed, in presence of Tyr the intensity of A1 and C1 peaks is noticeably decreased. The inhibition of the anodic and cathodic current peaks in presence of Tyr can be related to a strong affinity of this analyte to the electrode surface.

a)

0,0

M Tyr

a-0

b)

b -10 c -20

A1

d -50 e -70 f -100

h

g -200 h -500

0

h

a

h

a

h

Current (uA)

Current (uA)

1

-0,5

M Tyr

a-0 b -10 c -20 d -50 e -70

13

Figure 7. a) CV of MoS2-(150 µl) AuBSPE gold electrode, in the 0 – 0.8 V potential window, performed in 0.1 M PBS electrolyte and in the presence of different concentrations (0-500 µM) of

ro of

tyrosine, at a scan rate of 50 mV/s. b) Higher magnification of the C1 peak.

3.3.2.3 Effect of the potential window

We tested the unmodified and 2D-MoS2-SPAuE modified gold electrodes in a potential range

-p

from -0.6 to 1.2 V. On the unmodified electrode (Fig. S2,b) the C1 peak was more intense than the A1 peak. Its intensity was also higher compared to the same peak observed when cycling the electrode in a narrower potential range (0 - 0.8 V). Thus, this effect seems to be strongly linked to

re

the higher potential used. Other cathodic peaks also appeared at negative potentials, likely due to oxygen reduction on the gold surface. On the 2D-MoS2-SPAuE modified gold electrode (Fig. S3a-

lP

c), besides the peaks A1 and C1, other relevant peaks, named A2 and C2, were noted at 0.83V and 0.10 V, respectively. Their intensity increased with the nanosheets loading, suggesting that they come from redox processes involving Molybdenum species. The C2/C1 intensity ratio increased

na

with the MoS2 loading, which consequently reduced the free gold electrode surface, further confirming the surface coverage by MoS2 nanosheets.

ur

CV curves of the modified 2D-MoS2-SPAuE gold electrode at different loadings in presence of Tyr showed interesting features. First, the intensity of all peaks was much higher on the modified

Jo

electrode (Fig. 8, red, blue, green lines) than on the unmodified one (black line). The peaks A1 and C1 followed the same trend observed in the narrow potential range, while the intensity of the A2 and C2 peaks increased with increasing the 2D-MoS2 loading. These features further confirm the hypothesis made above about peaks attribution.

14

60 bare gold B in 500M of Tyr MoS2(50) in 500M of Tyr MoS2(150) in 500M of Tyr MoS2(400) in 500M of Tyr

Current (uA)

40

A2 A1

20 0 -20 -40

C1 C2

-60

-0,6 -0,4 -0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

ro of

Potential (V)

Figure 8. CV of 2D-MoS2-AuBSPE, in the -0.6 – 1.2 V potential window, performed in 0.1 M PBS electrolyte and in the presence of 500 µM of tyrosine, at a scan rate of 50 mV/s.

-p

3.3.2.4 Effect of scan rate

Studies were performed while monitoring the current peak as a function of scan rate () in the

re

range of 50-400 mV s-1 (see Fig. 9a). The peak current increased linearly with the scan rate (Fig. 9b), for all the peaks considered, indicating the occurrence of a surface-controlled process. As the

lP

scanning rate increased, the potential peak shifted positively for anodic processes and negatively for

200

a)

50 mV/s 100 mV/s 200 mV/s 300 mV/s 400 mV/s

150

0 -50 -100 -150

A1

100

C2

-250

-0,6

-0,4

-0,2

50 0 -50 -100

A2 A1 C1 C2

-150

C1

-200

b)

150

ur

50

Jo

Current (uA)

100

200

A2

Current (A)

250

na

cathodic processes, which is typical of irreversible reactions.

-200 MoS2 (50L) AuBSPE in 200 M of Tyr

0,0

0,2

0,4

Potential (V)

0,6

0,8

1,0

1,2

-250 0

50

100

150

200

250

300

350

400

scan rate (mV/S)

Figure 9. CV of 2D-MoS2-AuBSPE, in the -0.6 – 1.2 V potential window, performed in 0.1 M PBS electrolyte and in the presence of 200 µM of tyrosine, at different scan rate.

450

15

3.4 Electroanalytical detection of Tyr Tyr detection was carried out with carbon and gold electrodes, both unmodified and modified with MoS2. On both carbon electrodes the irreversible tyrosine oxidation current peak intensity increased with concentration (Fig. 10a). The modified electrodes featured, however, a larger signal variation. The calibration curves in Fig. 10b evidenced the enhancement of the current with the increase of the 2D-MoS2 loading. This is related to the intrinsic electrocatalytic activity of 2D-MoS2 [43-44]. In the linear range, between 0 and 100 µM, the sensitivity value was about 1400 μA·mM−1·cm−2.

30

Current (A)

40 35

25 20 15 10 5

40

0

30

0

200

400

MoS2 (l)

25

-p

current (A)

60

b)

35

45

0M 10M 20M 50M 70M 100M 200M 500M

80

Current (uA)

50

a)

Tyr conc

ro of

100

20

re

15 10

50mV/s 0,2

MoS2 (100 l) SPCE 0,4

lP

20

SPCE MoS2(100) MoS2(250) MoS2(400)

5

0,6

0,8

0 0

200

400

Tyrosine conc. (M)

na

Potential (V)

Figure 10. a) CV of 2D-MoS2 400µl-SPCE in 0.1 M PBS electrolyte and in the presence of different

ur

concentrations (0-500 µM) of tyrosine, at a scan rate of 50 mV/s. b) Calibration curve for the determination of tyrosine. The inset shows the current vs. the volume of the as-prepared 2D-MoS2

Jo

nanosheets suspension used for the bare electrode modification.

Subsequently, we tested the modified MoS2 400µl-SPAuE gold electrodes. Voltammetric

measurements with different Tyr concentrations were performed in the wider potential range (-0.6 1.2 V). The A2 and C2 peaks intensity (Fig. 11a) increased remarkably with tyrosine concentration. The current variation of the C2 peak at different Tyr concentration, is highlighted in Fig. 11b. Calibration curves for different loadings of 2D-MoS2 are displayed in Fig. 11c-d. Results on the modified gold electrodes confirm the behavior observed on the modified carbon electrodes. The current enhancement saturated when the loading overcomes 250 µl (Fig. 11c, blue and green

16

symbols). In the linear range (0-100 µM) the sensitivity is maximum (~ 1580 μA·mM−1·cm−2) if we consider the cathodic C2 peak variations (Fig. 11d). LOD, computed at a S/N = 3, is 0.5 μM. Sensitivity and LOD values compare well with previous reports [45-54].

50mV/S

A2

0M 10M 20M 50M 70M 100M 200M 500M

30 20 10

a)

b) -10

A1

-20

Current (uA)

40

0 -10 -20

Tyr conc

-30 -40

-30 C1

-40

-50

C2

-0,6 -0,4 -0,2

PBS

MoS2 (400L) SPAuE

0,0

0,2

0,4

0,6

0,8

1,0

-0,2

1,2

A2

na

10

0

ur

0 200

400

0,0

0,1

d)

0

Current (A)

20

c)

lP

50 l 150 l 250 l 400 l

-0,1

Potential (V)

re

Potential (V)

0M 10M 20M 50M 70M 100M 200M 500M

MoS2 (400L) SPAuE

50mV/S

-p

-50

Current (A)

-10

-20

50 l 150 l 250 l 400 l

-30

0

C2 200

400

(M)of different Tyrosine (2M) Figure 11. a) CV of 2D-MoS 400-SPAuE in 0.1 PBS electrolyte and in theTyrosine presence

concentrations (0-500 µM) of tyrosine, at a scan rate of 50 mV/s. b) Current variations of C1 peak

Jo

Current (uA)

PBS

Tyr conc

ro of

50

at different Tyr concentration. c-d) Calibration curves for the voltammetric determination of tyrosine at peak A2 and C2 with the modified 2D-MoS2-SPAuE electrodes.

17

Chronoamperometry was also applied to evaluate the determination capabilities of tyrosine with modified 2D-MoS2-SPCE carbon electrodes under a constant applied potential (0.6 V vs. Ag/AgCl). Fig. 12a displays the current response upon step-wise addition of tyrosine. The oxidation current rapidly increased with the Tyr concentration up to 617 µM.

10

617M

a)

b) 8

374M

6

196M

4

53M 44M 34M

2

102M

6

4

1,0

current (A)

8

Current (A)

Current (uA)

10

2

24M

ro of

12

0,5

0,0

0

0

0

800

1000

1200

40

concentration (M)

0

1400

20

100

200

300

400

500

600

Tyrosine (M)

-p

Time (s)

re

Figure 12. a) Current–time responses with successive addition of tyrosine at 2D-MoS2-SPCE electrode in 0.1 M PBS electrolyte at 0.6 V. b) Calibration curve for the determination of tyrosine.

lP

The inset displays the calibration curve in the lower concentration range. The corresponding calibration curve is reported in Fig. 12b. The plot in the inset highlight the dynamic linear range of Tyr (0 – 200 µM), which results wider compared to previous reports. A

na

linear fit of the current-concentration dependence in the very low concentration range (0-50 µM) yields a sensitivity of 148 μA·mM−1·cm−2. The modified 2D-MoS2 carbon electrode can therefore be used for determination of Tyr also by the amperometric method.

ur

In Table 1 we summarize the sensing performances toward dopamine detection with both MoS2 modified screen printed electrodes. The results indicate that MoS2 modified carbon and gold

Jo

provide similar performances. Further, is confirmed that the voltammetric method is preferable to chronoamperometry for the detection of Tyr, providing higher sensitivity and lower LOD. A comparison with Tyr sensors reported in literature is also made, demonstrating almost comparable performances.

18 Table1. Performances of the MoS2 modified screen printed electrodes proposed in this study for tyrosine detection. Performances of previous sensors for tyrosine detection are also reported for comparison [55].

LOD (µM)

Sensitivity

Technique Reference

Ura/GCE

0.8

-

DPV

[56]

Fe3+/ZMCPE

0.32

-

DPV

[57]

Nafion–CeO2–GCE

0.09

0.20 μA μM−1

DPV

[58]

2D-MoS2-SPCE

31.23

1400 μA·mM−1·cm−2

CV

This work

2D-MoS2-SPCE

1.4

148 μA·mM−1·cm−2

AMP

This work

2D-MoS2-AuBSPE

0.5

1580 μA·mM−1·cm−2

CV

This work

-p

3.5. Determination of Tyr in a commercial food integrator

ro of

Electrode

To demonstrate a practical application of our 2D-MoS2 based sensors, we performed

re

quantitative determination of Tyr in a commercial food integrator (Natural Point srl, 500 mg). A tablet was dissolved in water and further diluted with PBS. Both modified carbon and gold electrodes were tested, performing the CV tests and evaluating the peak current. Recovery values

lP

were evaluated as: Recovery (%) = (mg Tyr found/mg Tyr expected) ×100. The results obtained in three different measurements were averaged and the relative standard deviation (RSD) calculated

na

(Table 2). A good agreement is obtained between the Tyr quantity reported by the manufacturer and the one quantified by our sensors. Recovery values found were 98.2% (RSD = 4.3%) for the modified gold 2D-MoS2400-SPAuE sensor and 104.4% (RSD = 3.0%) for the modified carbon 2D-

ur

MoS2-SPCE one. The gold electrochemical platform provided the best performances.

Jo

Table 2. Determination of tyrosine in a real food integrator sample. Expected

Found

(mg Tyr/tablet)

(mg Tyr/tablet)

2D-MoS2-SPCE

500 mg

522 mg

104.4

4.3 (n=3)

2D-MoS2400-SPAuE

500 mg

491 mg

98.2

3.0 (n=3)

Sensor

Recovery (%)

RSD (%)

19

Finally, the stability of the sensor was evaluated, by performing tests after storage of the sensor for 1 month in ambient conditions. The sensor retained 93.6% of the initial response, which indicated a good long term stability.

4. Conclusions

2D-MoS2 nanosheets were prepared by liquid phase exfoliation and used to modify gold and carbon screen printed electrodes aimed at developing an enzyme-free electrochemical sensor for the determination of tyrosine. The performances improvement of these sensors in physiological pH

ro of

conditions are attributed to ultra-small size of MoS2 which provides an abundance of exposed edge sites, as well as to the morphological and textural properties of underlying carbon and gold

electrodes facilitating the electron and mass transfer. This study demonstrate that optimizing the potential window and 2D-MoS2 loading on carbon and gold SPE, the electroanalytical

-p

determination of tyrosine in real samples can be accomplished with good performances.

Acknowledgements

re

RZ acknowledges financial support from National Institute of Materials Science and Technology (INSTM), Italy. The Joint Bilateral Agreement CNR/The Czech Academy of Sciences

Jo

ur

na

lP

(CAS), Triennial Programme 2016-2018 is acknowledged for partial economic support.

20

References [1] X. Wang, H. Feng, Y. Wu, L. Jiao, Controlled Synthesis of Highly Crystalline MoS2 Flakes by Chemical Vapor Deposition, J. Am. Chem. Soc., 135 (2013) 5304-5307. [2] C. Muratore, J. J. Hu, B. Wang, Md Amanul Haque, J. E. Bultman, M. L. Jespersen, P. J. Shamberger, M. E. McConney, R. D. Naguy, A. A. Voevodin Continuous ultra-thin MoS2 films grown by low-temperature physical vapor deposition Appl. Phys. Lett. 104, 261604 (2014). [3] Kibum Kang, Saien Xie, Lujie Huang, Yimo Han, Pinshane Y. Huang, Kin Fai Mak, Cheol-Joo Kim, David Muller & Jiwoong Park High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity Nature 520, 656–660 (2015).

ro of

[4] K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, and A. K. Geim Two-dimensional atomic crystals PNAS, 102 (2005), 10451.

[5] J. Zheng, H. Zhang, S. Dong, Y. Liu, C. Tai Nai, H. Suk Shin, H. Y. Jeong, B. Liu, K. P. Loh, High yield exfoliation of two-dimensional chalcogenides using sodium naphthalenide Nature Communications volume 5, Article number: 2995 (2014)

-p

[6] Zeng Z, Yin Z, Huang X, Li H, He Q, Lu G, Boey F, Zhang H. Single-layer semiconducting nanosheets: high-yield preparation and device fabrication. Chem., 50 (2011), 11093

re

[7] Y. Hernandez, V. Nicolosi, M. Lotya, F. Blighe, Z. Sun, S. De, I. T. McGovern, B. Holland, M. Byrne, Y. Gunko, J. Boland, P. Niraj, G. Duesberg, S. Krishnamurti, R. Goodhue, J. Hutchison,

lP

V. Scardaci, A. C. Ferrari, J. N. Coleman High yield production of graphene by liquid phase exfoliation of graphite Nature nanotechnology 3.9 (2008) 563 [8] A. Ciesielski, P. Samorì, Graphene via sonication assisted liquid-phase exfoliation Chemical

na

Society Reviews, 43 (2014) 381-398.

[9] Coleman JN, Lotya M, O'Neill A, Bergin SD, King PJ, Khan U, Young K, Gaucher A, De S, Smith RJ, Shvets IV, Arora SK, Stanton G, Kim HY, Lee K, Kim GT, Duesberg GS, Hallam T,

ur

Boland JJ, Wang JJ, Donegan JF, Grunlan JC, Moriarty G, Shmeliov A, Nicholls RJ, Perkins JM, Grieveson EM, Theuwissen K, McComb DW, Nellist PD, Nicolosi V. Two-dimensional

Jo

nanosheets produced by liquid exfoliation of layered materials. Science, 331 (2011) 568

[10] A. Jawaid, D. Nepal, K. Park, M. Jespersen, A. Qualley, P. Mirau, L. F. Drummy, R. A. Vaia, Mechanism for Liquid Phase Exfoliation of MoS2 Chem. Mater., 2016, 28, 337–348

[11] R. J. Smith, P. J. King, M. Lotya, C. Wirtz, U. Khan, S. De, A. O'Neill, G. S. Duesberg, J. C. Grunlan, G. Moriarty, J. Chen, J. Wang, A. I. Minett, V. Nicolosi, J. N. Coleman, Large‐ Scale Exfoliation of Inorganic Layered Compounds in Aqueous Surfactant Solutions, Adv. Mater. 2011, 23, 3944–3948.

21

[12] M Mar Bernal, Lidia Álvarez, Emerson Giovanelli, Adriana Arnáiz, Luisa RuizGonzález,Santiago Casado, Daniel Granados, Ana M Pizarro, Andres Castellanos-Gomez, Emilio M Pérez, Luminescent transition metal dichalcogenide nanosheets through one-step liquid phase exfoliation, 2D Materials 3 (2016) 035014. [13] A. O’Neill, U. Khan, J. N. Coleman ,Preparation of High Concentration Dispersions of Exfoliated MoS2 with Increased Flake Size. Chem. Mater., 24 (2012), 2414 [14] E. Varrla, C. Backes, K. R. Paton, A. Harvey, Z. Gholamvand, J. McCauley, J. N. Coleman, Large-Scale Production of Size-Controlled MoS2 Nanosheets by Shear Exfoliation, Chem Mater. 27, 1129 (2015).

ro of

[15] A. Sinha, Dhanjai, B. Tan, Y. Huang, H. Zhao, X. Dang, J. Chen, R. Jain, MoS2 nanostructures for electrochemical sensing of multidisciplinary targets: A review, Trends in Analytical Chemistry 102 (2018) 75-90.

[16] X. Xia, Z. Zheng, Y. Zhang, X. Zhao, C. Wang, Synthesis of Ag-MoS2/chitosan

nanocomposite and its application for catalytic oxidation of tryptophan, Sens. Actuators B 192

-p

(2014) 42-50.

2015, 13: 345–354.

re

[17] M. An, Y. Gao, Urinary Biomarkers of Brain Diseases, Genomics Proteomics Bioinformatics.

[18] C.Y. Li, Voltammetric determination of tyrosine based on an l-serine polymer film electrode,

lP

Colloids Surf. B 50 (2006) 147-151.

[19] K. Varmira, G. Mohammadi, M. Mahmoudi, R. Khodarahmi, K. Rashidi, M. Hedayati, H. C. Goicoechea, A. R. Jalalvand, Fabrication of a novel enzymatic electrochemical

na

biosensor for determination of tyrosine in some food samples, Talanta 183, 2018, 1-10. [20] K. Huang, D. Luo, W. Xie, Y. Yu, Sensitive voltammetric determination of tyrosine using multi-walled carbon nanotubes/4-aminobenzeresulfonic acid film-coated glassy carbon

ur

electrode, Colloids Surf. B 61 (2008) 176-181. [21] A. Parsa, N. Akbarzadeh-Torbati, H. Beitollahi, Rapid and Sensitive Electrochemical

Jo

Monitoring of Tyrosine Using NiO Nanoparticles Modified Graphite Screen Printed Electrode Int. J. Electrochem. Sci., 14 (2019) 1556 – 1565.

[22] J.-L Zhang, R-Q. Li, Electrochemical Determination of Tyrosine and Nitrite Using CS/CMWNTs/GCE-modified Electrode Int. J. Electrochem. Sci., 13 (2018) 3527-3534. [23] A. Samadzadeh, I. Sheikhshoaie, H. Karimi-Maleh, Simultaneous Determination of Epinephrine and Tyrosine Using a Glassy Carbon Electrode Amplified with ZnO-Pt/CNTs Nanocomposite, Curr. Anal. Chem., 15, 2019 166 – 171.

22

[24] J. Zou, D. Mao, A. Thye, S. Wee, J. Jiang, Micro/nano-structured ultrathin g-C3N4/Ag nanoparticle hybrids as efficient electrochemical biosensors for L-tyrosine, Appl. Surf. Sci., 467, 2019, 608-618. [25] M. Rahman, N. S. Lopa, K. Kim, J.-Joon Lee, Selective detection of l-tyrosine in the presence of ascorbic acid, dopamine, and uric acid at poly(thionine)-modified glassy carbon electrode, J. of Electroanalytical Chemistry, 754, 2015, 87-93. [26] H. Heidari, E. Habibi, Lead-doped carbon ceramic electrode as a renewable surface composite electrode for the preparation of lead dioxide film and detection of l-tyrosine. J. Iranian Chem. Society, 2018, 15, 885–892.

ro of

[27] V. S. Krishnapillai, P. Prathish, T. P. Rao, In situ copper oxide modified molecularly imprinted polypyrrole film based voltammetric sensor for selective recognition of tyrosine, Talanta 85, 2011, 1056-1062.

[28] M. Taei, F. Hasanpour, H. Salavati, S.H. Banitaba, F. Kazemi, Simultaneous determination of cysteine, uric acid and tyrosine using Au-nanoparticles/poly(E)-4-(p-tolyldiazenyl)benzene-

-p

1,2,3-triol film modified glassy carbon electrode, Materials Science and Engineering C 59 (2016) 120–128.

re

[29] T. Y. Wang, D. L. Gao, J. Q. Zhuo, Z. W. Zhu, P. Papakonstantinou, Y. Li and M. X. Li, Size‐ Dependent Enhancement of Electrocatalytic Oxygen‐ Reduction and Hydrogen‐

lP

Evolution Performance of MoS2 Particles, Chem. - Eur. J., 2013, 19, 11939 -11948. [30]. F. Bonaccorso, T. Hasan, P. H. Tan, C. Sciascia, G. Privitera, G. Di Marco, P. G. Gucciardi, and A. C. Ferrari Density Gradient Ultracentrifugation of Nanotubes: Interplay of Bundling and

na

Surfactants Encapsulation J. Phys. Chem. C, 2010, 114 (41), pp 17267–17285 [31]. E. Messina, N. Leone, A. Foti, G. Di Marco, C. Riccucci, G. Di Carlo, F. Di Maggio, A. Cassata, L. Gargano, C. D’Andrea, B. Fazio, O. M. Maragò, B. Robba, C. Vasi, G. M. Ingo, P.

ur

G. Gucciardi Double-Wall Nanotubes and Graphene Nanoplatelets for Hybrid Conductive Adhesives with Enhanced Thermal and Electrical Conductivity, ACS Appl. Mater. Interfaces,

Jo

2016, 8 (35), pp 23244–23259

[32]. Amit Gupta, Vaishali Arunachalam, and Sukumaran Vasudevan Water Dispersible, Positively and Negatively Charged MoS2 Nanosheets: Surface Chemistry and the Role of Surfactant Binding J. Phys. Chem. Lett., 2015, 6 (4), pp 739–744 [33]. Amit Gupta, Vaishali Arunachalam, and Sukumaran Vasudevan Liquid-Phase Exfoliation of MoS2 Nanosheets: The Critical Role of Trace Water J. Phys. Chem. Lett. 2016, 7, 4884−4890 [34]. K. R. Paton, J. N. Coleman, Relating the optical absorption coefficient of nanosheet dispersions to the intrinsic monolayer absorption, Carbon 107, 733 (2016).

23

[35] A. Quirantes, F. Arroyo, J. Quirantes-Ros, Multiple Light Scattering by Spherical Particle Systems and Its Dependence on Concentration: A T-Matrix Study. J Colloid Interface Sci 240, 78 (2001). [36] C. Backes, R. J. Smith, N. McEvoy, N. C. Berner, D. McCloskey, H. C. Nerl, A. O’Neill, P. J. King, T. Higgins, D. Hanlon, N. Scheuschner, J. Maultzsch, L. Houben, G. S. Duesberg, J. F. Donegan, V. Nicolosi, J. N. Coleman, Edge and confinement effects allow in situ measurement of size and thickness of liquid-exfoliated nanosheets, Nat. Commun. 5:4576 (2014). [37] B. C. Windom, W. G. Sawyer, D. W. Hahn, A Raman Spectroscopic Study of MoS2 and MoO3: Applications to Tribological Systems, Tribol. Lett 42:301 (2011).

ro of

[38] S. Sahoo, A. P. S. Gaur, M. Ahmadi, M. J.-F. Guinel, R. S. Katiyar, Temperature-Dependent Raman Studies and Thermal Conductivity of Few-Layer MoS2, J. Phys. Chem C 117, 9042 (2013).

[39] B. Chakraborty, H. S. S. Ramakrishna Matte, A. K. Sood, C. N. R. Rao, Layer‐ dependent resonant Raman scattering of a few layer MoS2, J. Raman Spectrosc. 44, 92 (2013).

-p

[40] L. Liang, V. Meunier, First-principles Raman spectra of MoS2, WS2 and their heterostructures, Nanoscale 6, 5394 (2014).

re

[41] X. Ge, R. Wang, P. Liu, Y. Ding, Platinum-Decorated Nanoporous Gold Leaf for Methanol Electrooxidation, Chem. Mater. 2007, 19, 5827.

lP

[42] S. J. Rowley-Neale, D. A. C. Brownson, G. C. Smith, D. A. G. Sawtell, P. J. Kelly, C. E. Banks, 2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction, Nanoscale, 2015, 7, 18152.

na

[43] X. Chia, A. Yong Sheng, A. Ambrosi, S. Min Tan, M. Pumera, Electrochemistry of Nanostructured Layered Transition-Metal Dichalcogenides, Chemical Reviews 115 (2015) 11941.

ur

[44] G Neri, Thin 2D: the new dimensionality in gas sensing, Chemosensors 5 (2017) 21. [45] K. Huang, D. Luo, W. Xie, Y. Yu, Sensitive voltammetric determination of tyrosine using

Jo

multi-walled carbon nanotubes/4-aminobenzeresulfonic acid film-coated glassy carbon electrode, Colloids Surf. B 61 (2008) 176-181.

[46] J. Xu, Y. Wang, Y. Xian, L. Jin, Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography, Talanta 60 (2003) 1123-1130. [47] L. Liu, F. Zhao, F. Xio, B. Zeng, Improved voltammetric response of L-tyrosine on multiwalled carbon nanotubes-ionic liquid composite coated glassy electrodes in the presence of cupric ion, Electroanalysis 20 (2008) 2148-2152.

24

[48] H. Liang, T. Ling, J.F. Rick, T. Chou, Molecularly imprinted electrochemical sensor able to enantroselectivly recognize d and l-tyrosine, Anal. Chim. Acta. 542 (2005) 83-89. [49] L. Wang, C. Ma, X. Zang, Y. Ren, Y. Yu, Determination of tyrosine traces by adsorption voltammetry of its copper (II) complex, Fresenius J. Anal. Chem. 351 (1995) 689-691. [50]. A. Babaei, S. Mirzakhani, B. Khalilzadeh, A sensitive simultaneous determination of epinephrine and tyrosine using an iron(III) doped zeolite-modified carbon paste electrode, J. Braz. Chem. Soc. 20 (2009) 1862-1869. [51] G. Zhao, Y. Qi, Y. Tian, Simultaneous and direct determination of tryptophan and tyrosine at boron-doped diamond electrode, Electroanalysis 18 (2006) 830-834.

ro of

[52] Q. Xu, S. Wang, Electrocatalytic oxidation and direct determination of L-tyrosine by square wave voltammetry at multi-wall carbon nanotubes modified glassy carbon electrodes, Microchim. Acta 151 (2005) 47-52.

[53] V. Saumya, K. P. Prathish, T.P. Rao, In situ copper oxide modified molecularly imprinted polypyrrole film based voltammetric sensor for selective recognition of tyrosine, Talanta 85

-p

(2011) 1056-1062.

[54] P. Kanchana, N. Lavanya, C. Sekar, Development of amperometric L-tyrosine sensor based on

re

Fe-doped hydroxyapatite nanoparticles, Materials Science and Engineering C 35 (2014) 85-91. [55] N. H. Arani, S. M. Ghoreishi, A. Khoobi, Increasing the electrochemical system performance

lP

using a magnetic nanostructured sensor for simultaneous determination of L-tyrosine and epinephrine, Anal. Methods, 11 (2019) 1192-1198. [56] X.-Q. Lin, G.-F. Kang and X.-H. Zhu, Uracil Grafted Carbon Electrode: Electrocatalytic Behavior

na

of Tryptophan, Tyrosine, Catecholamine and Related Compounds Chin. J. Chem., 26 (2008) 681. [57] A. Babaei, S. Mirzakhani, B. Khalilzadeh, J. Braz, A sensitive simultaneous determination of epinephrine and tyrosine using an iron(III) doped zeolite-modified carbon paste electrode Chem. Soc.,

ur

20 (2009) 1862.

[58] A. S. Razavian, S. M. Ghoreishi, A. S. Esmaeily, M. Behpour, L. M. A. Monzon, J. M. D. Coey,

Jo

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles, Microchim. Acta, 181 (2014) 1947.

25

ro of

G. Neri received a degree in Chemistry in1980. From 1987 to 1998, he was a researcher at the University of Reggio Calabria. From 1991 to1996, he spent several years conducting research at the University of Michigan (USA). In 1998, he moved to the University of Messina, where since 2001 he has been a Full Professor of Chemistry. From 2004 to 2007, he was the Director of the Department of Industrial Chemistry and Materials Engineering at the University of Messina. In 2013 he has been awarded a grant by Samsung SAIT Global Research Outreach program for the project “Smart sensors for breath analysis”. His research activities cover many aspects of the synthesis and characterization of materials and the study of their sensing properties. His recent research has been focused on the application of gas sensors composed of nanostructured metal oxides and novel organic–inorganic hybrid nanocomposites and enzyme-free electrochemical sensors. Prof. Neri is author of more than 300 scientific publications in international journals. The total number of citations as reported in Scopus is around 8200, with an h-index of 48.

re

-p

Ramzi Maalej is presently a full professor of Physics at the University of Sfax, Tunisia. He received MS degree in Physics from the University of Sfax in 1995 and PhD in Quantum Physics from University of Tunis El Manar in 2001 and Habilitaion HDR in 2007. He has supervised nine PhD theses, and co-authored more than 58 peer-reviewed scientific journals. He is leading a research team “Photonic and Advanced Materials” composed of 13 researchers and associate professors. He has been invited professor in different universities in KSA, South Korea, Germany, and Portugal and given invited talks at several conferences. His research interests cover theoretical and experimental studies of lanthanide-doped materials for emerging applications as laser technologies, optoelectronic, nanosensors and forensic science. He is actually associate editor of IEEE transactions on nanobiosciences Journal and organizer of the International Conference of Engineering Sciences in Biology and Medicine ESBM for three editions.

Jo

ur

na

lP

R. Zribi obtained a master degree in Physics with honors in 2018, at the University of Sfax, Tunisia. Presently, is a first year PhD student at University of Sfax, in cotutele with the University of Messina, Italy. PhD research activity is devoted to investigate the use of novel 2D materials for applications in chemical sensors.