Enantiomers of Single Chirality Nanotube as Chiral Recognition

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Enantiomers of Single Chirality Nanotube as Chiral Recognition Interface for Enhanced Electrochemical Chiral Analysis Chunling Pu, Yunxia Xu, Qi Liu, Anwei Zhu, and Guoyue Shi Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b05336 • Publication Date (Web): 15 Jan 2019 Downloaded from http://pubs.acs.org on January 19, 2019

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Analytical Chemistry

Enantiomers of Single Chirality Nanotube as Chiral Recognition Interface for Enhanced Electrochemical Chiral Analysis Chunling Pu, Yunxia Xu, Qi Liu, Anwei Zhu* and Guoyue Shi* School of Chemistry and Molecular Engineering, Shanghai Key Laboratory for Urban Ecological Processes and Eco-Restoration, East China Normal University, 500 Dongchuan Road, Shanghai 200241, P.R. China

E-mail adress: [email protected] Tel: +86-21-54340042; Fax: +86-21-54340042

1 ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT:

Although separation of single-walled carbon nanotubes (SWCNTs) according to their helicity and handedness has been attracting tremendous interest recently, exploration of the left- and right-handed SWCNT enantiomers (defined as M and P) to chiral sensing still remains in the early stage. Here we presented a new electrochemical sensor for chiral discrimination, which for the first time amplified the chiral selection on the electrode surface based on the left- or righthanded

semiconducting

SWCNT

enantiomers

with

(6,

5)-enriched

chirality.

The

enantioselectivity was demonstrated by different peak current response to analyte enantiomers, observed in differential pulse voltammogram (DPV). Chiral distinguishing might be a result of the formation of an efficient chiral nanospace originating from the high purity of single enantiomer of (6, 5) SWCNT. The obtained chiral electrodes were also applied to determine the enantiomeric excess (ee) of DOPA. There was a good linear relationship between DPV peak currents and % ee of ʟ-DOPA. This study is the first example showing how the structure of chiral SWCNTs influences electrochemical chiral recognition.


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INTRODUCTION Chirality is an intrinsic property of living world. The different enantiomers of one compound may show differences on the part of biochemical activity, transport mechanism and pathways of metabolism. Thus, chiral discrimination has attracted great interest in chemical and biological research. Although diversified methods for chiral recognition, including chromatography,1 circular dichroism,2,3 and capillary electrophoresis method,4 have been developed, a simple, low cost, and highly sensitive chiral discrimination approach is still highly demanded. Electrochemical chiral sensors have attracted much attention in recent years owing to their exceptional advantages such as simple operation, low cost, high sensitivity and many potential applications.5 However, the development of electrochemical chiral analysis is still limited by the design of new sensing interfaces with an effective chiral selection.6-13 Single-walled carbon nanotubes (SWCNTs) have attracted tremendous attention in various electrochemical analysis due to its size and defect effect.14,15 A SWCNT is a seamless hollow cylindrical tube formed by rolling up a single graphene sheet. Meanwhile, each SWCNT structure is indexed by two integers (n, m) that define the diameter and helicity of that tube’s roll-up vector on a graphene sheet.16-18 While (n, 0) and (n, n) SWCNTs named as zigzag and armchair, respectively, are achiral, all the other SWCNTs have chirality. Hence, each chiral SWCNT is either of the enantiomers defined as M and P.19,20 Recently, an electrochemical chiral sensor for 3,4-dihydroxyphenylalanine (DOPA) was reported based on chiral (6, 5) SWCNT.21 However, (6, 5) SWCNTs contain both left- and right-handed SWCNT enantiomers, and such enantiomixtures limited the formation of chiral space and then reduced the chiral recognition effect. Thus, the enantioselective discrimination was achieved only when (6, 5) SWCNTs were combined with square wave voltammetry and sulfuric acid, through extending the interaction



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time between the DOPA enantiomers and chiral SWCNTs. Although the structure control of SWCNTs is vital in electrochemical analysis and enantiomeric separation of single-chirality carbon nanotubes is possible, exploration of a single enantiomer of specific (n, m) SWCNT as electrochemical chiral interface to enantioselective recognition has never been reported. In this work, the enantiomers from (6, 5) single-chirality SWCNTs were separated using a mixed surfactant multi-column gel chromatography method. And then the enantioselectivity was imparted to a glass carbon electrode by modifying its surface with the left handed (M-(6, 5)) or right handed (P-(6, 5)) SWCNTs. Electrochemical chiral distinguish of analyte enantiomers can be achieved by differential pulse voltammetry (DPV), in which different magnitudes of peak currents were observed. Of particular interest, the chiral selectivity of the electrode interface for the analyte enantiomers depended on the handedness of single-chirality SWCNTs. Finally, the well-developed analytical performance of this electrochemical sensor established a direct, simple, and sensitive approach for the determination of enantiomeric excess (ee) in enantiomeric mixtures of DOPA.

EXPERIMENTAL SECTION Reagents and Materials CoMoCAT high purity SWCNTs (SG65i, 0.7-0.9 nm in diameter, (6,5) chirality), ascorbic acid (ʟ-AA, >99%), ᴅ-isoascorbic acid (ᴅ-AA, 98%), ʟ-3,4-dihydroxyphenylalanine (ʟ-DOPA, 99%), ᴅ-3,4-dihydroxyphenylalanine (ᴅ-DOPA, >95%), sodium cholate (SC, >98%), sodium deoxycholate (DOC, >97%), sodiumdodecyl sulfate (SDS, 99%) were purchased from SigmaAldrich. SWCNTs produced by high-pressure catalytic CO (HiPco) depocomposition were purchased from Carbon Nanotechnologies Inc. and were used as mixture containing both


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semiconducting- and metallic-SWCNTs with many chirality indices. Allyl dextran-based sizeexclusion gels (Sephacryl gel, S-200 HR) were obtained from GE Healthcare. Other reagents were of analytical grade. All aqueous solutions were prepared from doubly distilled water (18 MΩ cm).

Instrumentation and Apparatus UV-Vis-NIR

absorption

spectra

was

measured

on

a

PerkinElmer

Lambda

950

spectrophotometer. Circular dichroism (CD) spectra was recorded with a JASCO J-820 CD spectropolarimeter. X-ray photoelectric spectroscopy (XPS) was taken on a Kratos Axis Ultra DLD spectrometer with Al Kα source (1486.6 eV photons). Scanning electron microscope (SEM) images were taken using HITACHI S-4800 SEM. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were carried out on a CHI 660C electrochemical workstation in a traditional three-electrode cell containing Ag|AgCl reference electrode, Pt counter electrode, and glassy carbon electrode (GCE).

Dispersion of Raw (6, 5)-SWCNTs 100 mg of raw (6, 5)-SWCNTs were first dispersed in 100 mL of water containing 0.5% SC and 0.5% SDS using an ultrasonic homogenizer (SCIENTZ- IID, Ningbo Scientz Biotechnology Co., Ltd) equipped with a flat tip for 10h at output power of 30%. To remove the residue of catalytic metal particles, amorphous carbon, nanotube bundles and other impurities, the above solution was then centrifuged at 178000g for 30 min at 10°C in a SW 41 rotor (Optima L-80XP, Beckman Coulter, Inc). The upper 80% of the supernatant was finally collected for the following enantiomeric separation of SWCNT.



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Enantiomeric Separation of (6, 5) SWCNT To separate the enantiomers of (6, 5) SWCNTs, a gel column chromatography method was modified in which mixed surfactants and vertically connected gel columns strategies were combined.22,23 Medical plastic syringes (50 mL; 8 cm in length and 3.5 cm in inner diameter) were used as the columns and three columns packed with allyl dextran-based gel were connected vertically in series. Before each column was filled with 25 mL of allyl dextran-based gel, the outlet of column was plugged with cotton evenly. After the gel columns were equilibrated with an aqueous solution containing 0.5% SC and 0.5% SDS, 10 mL of the above SWCNT solution was added into the top column and the mixture solution containing 0.5% SC and 0.5% SDS was subsequently added to elute the unbound nanotubes. Finally, the stepwise elution was performed by using a mixed surfactant solution of 0.5% SC + 0.5% SDS + x% DOC. The values of x were optimized and determined as 0.0270 and 0.0320 for eluting the M-(6, 5) and P-(6, 5) enantiomers, respectively.

Purity of the Separated SWCNT Enantiomers Usually, the enantiomeric purity of chiral compounds can be determined by comparing the optical rotation to that of a reference pure enantiomer. But this method is difficult for SWCNTs due to absence of a reference pure SWCNT enantiomer. On the other hand, (6,5)-SWCNTs are optically

resolved

into

two

well-separated

bands

by

Weisman

through

gradient

ultracentrifugation and, therefore, are considered to have very high optical purity.24 Hence, based on the results reported by Weisman, the enantiomeric excess (ee) of (6,5)-SWCNTs were


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calculated by dividing the normalized CD intensity of M-/P-(6,5)-SWCNTs to that (CDnorm=36 mdeg) reported by Weisman, a method reported by Komatsu.19 CDnorm = (CDraw / LCD) / (AE22 / Labs) where CDraw, CDnorm and AE22 are the CD intensity (mdeg) before and after normalization, and the background-corrected absorbance in the E22 transition. LCD and Labs are the optical path length (cm) in measurement of CD and UV-vis-NIR, respectively.

Electrodeposition of M-(6, 5) or P-(6, 5) SWCNT Enantiomers onto GCE The separated SWCNT dispersions were first filtered to remove SC and DOC surfactants using a centrifugal filter tube with 100K membrane at 3000 × g. Next, the upper unfiltered SWCNT enantiomers were washed with 0.5% SDS solution. The same procedures were repeated several times. Then, approximately 0.75 mg of the enantiomers obtained were dispersed in 5 mL of aqueous solution containing 0.1 M NaCl and 0.5% SDS. After that, the electrodeposition was performed in SWCNT enantiomers dispersion in which NaCl and SDS were used as supporting electrolyte and dispersant, respectively. A repeated CV waveform from −1.0 to +1.0 V at a scan rate of 0.05 V/s for 15 cycles was applied to the GCE to obtain M-(6, 5) SWCNTs or P-(6, 5) SWCNTs modified GCE (referred to as SWCNT/GCE). Finally, the SWCNT/GCE was oxidative etched to remove SDS residues and introduce defects on SWCNT/GCE by applying a constant potential of +1.5 V for 120 s in 1 M NaOH, and was denoted as ox-SWCNT/GCE.

Electrochemical Chiral Recognition of Analyte Enantiomers Electrochemical chiral recognition of analyte enantiomers was investigated by differential pulse voltammetry (DPV). The as-prepared chiral electrodes were placed into 5 mL of 0.25 M



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H2SO4 containing DOPA enantiomers or 0.1 M PBS (pH=7.0) containing AA enantiomers. Then, DPVs were recorded from 0.4 to 0.8 V or −0.2 to 0.4 V with a step potential of 2 mV and an amplitude of 50 mV. Finally, the peak current ratio was calculated to evaluate the recognition efficiency.

RESULTS AND DISCUSSION Separation of (6, 5) SWCNT Enantiomers As a starting point for this work, M-(6, 5) and P-(6, 5) SWCNT enantiomers were separated from the CoMoCAT SWCNTs with (6, 5)-enriched chirality as described in the Experimental Section. Figure 1A shows the UV-vis-NIR spectra of the separated M-(6, 5) and P-(6, 5) SWCNT enantiomers. Both spectra were almost overlapped and showed a series of absorption peaks corresponding to the E11, E22, E33, and E44 transitions, indicating high enrichment of the M-(6, 5) and P-(6, 5) SWCNTs.23 The CD spectra (Figure 1B) of the separated M-(6, 5) and P-(6, 5) SWCNT enantiomers showed a mirrored symmetric relationship, which was clear evidence of the enantiomers.23 According to the method described in the Experimental Section, CDnorm were measured to be 23 mdeg for M-(6, 5) SWCNTs and −22 mdeg for P-(6, 5) SWCNTs, thus, the enantiomeric excess (ee) of M-(6, 5) SWCNTs and P-(6, 5) SWCNTs were calculated to be 64% ee and 61% ee, respectively, which were close to previous reports.19, 25


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0.30 A

0.20

E11

CD (mdeg)

M- (6,5) P- (6,5)

0.25 Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


E44

0.15

E33

E22

0.10 0.05 200

400

600

800 1000 1200

Wavelength (nm)

8 B E33 6 E22 M- (6,5) 4 2 0 -2 P- (6,5) -4 E44 -6 -8 200 300 400 500 600 700 800 Wavelength (nm)

Figure 1. (A) Optical absorption spectra and (B) CD spectra of the (red curve) M-(6, 5) SWCNTs and (blue curve) P-(6, 5) SWCNTs.

Fabrication and Characterization of M-(6, 5) or P-(6, 5) SWCNTs Modified GCE Since individual SWCNT was covered by SDS molecules as a negatively charged micelle, when a repeated CV waveform scanned from −1.0 to 1.0 V was applied to the GCE in M-(6, 5) SWCNTs or P-(6, 5) SWCNT dispersion, SWCNTs may be attracted to the surface of GCE through electrostatic interaction, during which SDS molecules were dissolved back into aqueous solution.26 The SEM images in Figure 2A,B show that SWCNTs modified GCE (SWCNT/GCE) has typical uniform arrangement of M-(6, 5) SWCNTs or P-(6, 5) SWCNT enantiomers on the surface of GCE. These SEM images confirmed that the CV electrodeposition was a suitable technology to prepare SWCNT/GCE. The observation of XPS peak for S2p (Figure 2E) indicated that SDS residues remained on the SWCNT/GCE.27 Hence, the redox peak attributed to the redox reaction between [Fe(CN)6]4− and [Fe(CN)6]3− was smaller at SWCNT/GCE than that at bare GCE owing to the electrostatic repulsion between the negatively charged SDS and Fe(CN)64−/3− couple (Figure 2F). Note that the CV curves for Fe(CN)64−/3− couple on either M-(6, 5) SWCNT/GCE or P-(6, 5) SWCNT/GCE were almost the same (data not shown). The 9 ACS Paragon Plus Environment


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Then, SWCNT/GCE was further oxidatively etched in 1 M NaOH solution to remove SDS residues and to introduce defects containing surface oxide groups for enhanced electrocatalysis, which was denoted as ox-SWCNT/GCE.26,28 After oxidative etching, the oxygen content increased from 5.99% to 10.54% with the sulfur content decreasing from 0.81% to ~0% (Figure 2E), indicating that the oxide groups increased and SDS residues were removed from SWCNTs surface. From the high-resolution C1s spectra of SWCNT/GCE and ox-SWCNT/GCE (Figure 2C,D), an obvious increase in the signals at 286-289 eV revealed an increase of C=O and O=C-O groups on SWCNTs.11 Thus, the redox peak currents significantly decreased and peak separation (∆Ep) increased after oxidative etching due to the increased electrostatic repulsion between Fe(CN)64−/3− couple and ox-SWCNTs (Figure 2F), which can also be confirmed by using Ru(NH3)63+/2+ couple (Supporting Information Figure S1). The above XPS and CV curves were almost the same on either ox-M-(6, 5) SWCNT/GCE or ox-P-(6, 5) SWCNT/GCE.


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279

282

285

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291

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279

282

285

288

291

294

8 6 4 2 0 -2 -4 -6

174 172 170 168 166 164

-0.2

0.0

0.2

0.4

0.6

Figure 2. SEM images of (A) M-(6,5) SWCNTs and (B) P-(6,5) SWCNTs deposited on GCE. Highresolution XPS spectra of C1s for (C) SWCNT/GCE and (D) ox-SWCNT/GCE. (E) High-resolution XPS spectra of S2p for (black curve) SWCNT/GCE and (red) ox-SWCNT/GCE. (F) Cyclic voltammogram obtained on the (a) bare GCE, (b) SWCNT/GCE, or (c) ox-SWCNT/GCE in 0.1 M KCl containing 5 mM Fe(CN)63−/4−.

Electrochemical Recognition of Enantiomeric Pairs As a model of electroactive enantiomeric pairs, the electrochemical response of ʟ- and ᴅDOPA was first studied by DPV. As shown in Figure 3A, the differences of DPV peaks for ʟand ᴅ-DOPA were too small to be distinguished on GCE which was modified with the mixtures 11 ACS Paragon Plus Environment


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containing both semiconducting- and metallic-SWCNTs with many chirality indices, and thus ʟand ᴅ-DOPA cannot be recognized with the above electrode. But a different result occurred using the left- or right-handed semiconducting SWCNT enantiomers with single chirality, the DPV peak current ratio of ʟ- and ᴅ-DOPA (Iʟ/Iᴅ) was 1.90 on P (6, 5)-SWCNT/GCE (Figure 3C). In contrast, the peak current ratio of ᴅ- and ʟ-DOPA (Iᴅ/Iʟ) was 2.05 with M-(6, 5) SWCNT/GCE (Figure 3D). The DPV peak current of one enantiomer was almost two times larger than the other one on P-(6, 5) SWCNT/GCE or M-(6, 5) SWCNT/GCE. So the difference in DPV peak currents had a potential to enable an accurate determination of the enantiomeric purity of DOPA. To the best of our knowledge, it is the first report about right- and left-handed semiconducting SWCNT enantiomers as electrode interface for electrochemical chirality sensing. 3.0

3.0

2.5 2.0

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3.0

2.0 2.0

1.5 1.0 0.5 0.4

1.0

0.5

0.6

0.7

0.8

0.0 0.4

Figure 3. DPVs of (A) racemic mixtures SWCNT/GCE, (B) raw chiral (6, 5)-SWCNT/GCE, (C) P-(6, 5) SWCNT/GCE or (D) M-(6, 5) SWCNT/GCE in 0.25 M H2SO4 containing 25 μM ʟDOPA or ᴅ-DOPA. 12 ACS Paragon Plus Environment

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We have optimized the SWCNTs electrodeposition process by changing the number of electrodeposition cycles and there was an obvious effect of the number of electrodeposition cycles on the peak current ratio of analyte enantiomers. The peak current ratio increased with increasing the number of electrodeposition cycles from 1 to 15, but then decreased after that (Figure S2), possibly because the thicker coating layer would not all be accessible for chiral selection. Therefore, the number of electrodeposition cycle was optimized to be 15 cycles.

Mechanism of Chiral Recognition To study the chiral recognition mechanism in this system, the influence of enantiomeric purity of single-chirality SWCNT on the peak current ratio of ʟ- and ᴅ-DOPA was first studied. As shown in Figure 3B, when raw chiral (6, 5) SWCNTs modified GCE was used, much smaller difference in DPV peak current was observed with Iʟ/Iᴅ being 1.20. In contrast, the separated P-(6, 5) SWCNT and M-(6, 5) SWCNT in this work amplified the Iʟ/Iᴅ and Iᴅ/Iʟ to be 1.90 and 2.05, respectively (Figure 3C,D). This result confirmed that the chiral recognition efficiency was lowered with the decrease of enantiomeric purity of single-chirality SWCNTs. Basically, chiral (6, 5) SWCNTs had a potential in discriminating the enantiomers of chiral molecules due to their intrinsic chirality and thus the obtained Iʟ/Iᴅ was larger than 1 (Figure 3B). However, chiral (6, 5) SWCNTs contained both left- and right-handed semiconducting SWCNT enantiomers, and such enantiomixtures may limit the formation of chiral space and then reduce the recognition effect of chiral SWCNTs. While the separated P-(6, 5) SWCNT and M-(6, 5) SWCNT with high enantiomeric purity may provide true single-structure SWCNTs and, thus, unlock their intrinsic chiral properties and improve the recognition effect.



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Another amazing finding of the enantiomers of (6, 5) SWCNTs was that P-(6, 5) SWCNT/GCE and M-(6, 5) SWCNT/GCE exhibited an opposite selectivity for the enantiomers of chiral molecules; i.e., P-(6, 5) SWCNT/GCE exhibited a higher selectivity for ʟ-DOPA, whereas M-(6, 5) SWCNT/GCE preferred ᴅ-DOPA. The chiral selectivity of the electrode interface for the DOPA enantiomers depended on the handedness of single-chirality SWCNTs. A similar result emerged if DOPA enantiomers were replaced by ascorbic acid (AA) which also undergo two-electron-two-proton oxidation but irreversibly. As shown in Figure S3, the current ratio (Iʟ/Iᴅ) was 2.15 at P-(6, 5)-SWCNTs modified GCE, while the selectivity was reversed at M-(6,5)-SWCNTs modified GCE with Iᴅ/Iʟ bing 2.35. These results suggested that the space formed on the P-(6, 5) SWCNT/GCE and M-(6, 5) SWCNT/GCE might be differently orientated. As shown in Figure 4, the chiral space formed by the left-handed M-(6, 5) SWCNTs on GCE may be more favorable for the right-handed molecules such as ᴅ-DOPA and ᴅ-AA to get close to the electrode, whereas the chiral space of the right handed P-(6, 5) SWCNT on GCE was easier for the left-handed molecules such as ʟ-DOPA and ʟ-AA to pass through. Compared with most electrochemical enantiorecognition which required the modification of electrodes with chiral molecular selectors,29-32 this is the first report to achieve electrochemical chiral distinguish by inherently chiral (6, 5) SWCNT enantiomers without further designing chiral molecular selectors on electrode interface.


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Figure 4. Schematic illustration showing the formation of chiral space on the the left handed (M-(6, 5)) or right handed (P-(6, 5)) SWCNTs modified GCE and the possible mechanism of electrochemical enantiorecognition.

Determination of Enantiomeric Excess of DOPA With the chiral sensing established, we decided to access its performance in the determination of enantiomeric excess (ee) in enantiomeric mixtrues of DOPA. On the other hand, the concentration of DOPA would affect the efficiency of chiral recognition. As shown in Figure S4, Iᴅ/Iʟ at M-(6,5) SWCNT/GCE gradually increased with the concentrations of DOPA enantiomers until 25 μM, but then decreased after that, possibly due to the limited chiral space on the electrode available for the chiral selection. Therefore, 25 μM DOPA racemic mixture with different % of ʟ-DOPA was chosen for the determination of ee of DOPA. As shown in Figure 5A, the peak current obtained by the P-(6, 5) SWCNT/GCE gradually increased with increasing ʟDOPA in the mixture and there was a good linear relationship between Ip and % ee of ʟ-DOPA (Figure 5B). It was exciting to find that the % of ʟ-DOPA measured by M-(6, 5) SWCNT/GCE coincided with the results by P-(6, 5) SWCNT/GCE, although the peak current decreased 15 ACS Paragon Plus Environment


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linearly with ʟ-DOPA% (Figure 5C,D). The above results implies that it is possible to determine % ee of ʟ-DOPA in mixture by the developed electrochemical chiral system, showing its potential in future practical applications. 3.5

2.4

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3.6 3.2 2.8 2.4 2.0 1.6

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Figure 5. DPVs of 25 μM DOPA racemic mixture solution with different ʟ-DOPA% (0%, 20%, 40%, 60%, 80%, and 100%, respectively) on (A) P-(6,5) SWCNT/GCE and (C) M-(6,5) SWCNT/GCE in 0.25 M H2SO4. (B, D) Linear relationship between peak current and ʟ-DOPA% in solution. Error bars represent standard error measurements (s.e.m.).

CONCLUSIONS In conclusion, we have developed a novel electrochemical sensor for chiral discrimination based on the left- or right-handed semiconducting SWCNT enantiomers with (6, 5)-enriched chirality. The enantiomers of single-chirality SWCNT modified on the GCE has not only demonstrated chiral distinguish ability but also amplified the difference of DPV peak currents to 16 ACS Paragon Plus Environment

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enable a determination of the enantiomeric excess of ʟ-DOPA. The present work has not only designed a new electrochemical sensing interface with an effective chiral selection but also established that the functionalized electrode are promising tools to study chiral molecules. What’s more, this work has provided a new thinking for the rational design of surface chemistry of SWCNTs in other electrochemical analysis.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: CVs of Ru(NH3)63+/2+, Effect of the number of electrodeposition cycles, DPVs of AA enantiomers, Effect of the concentration of DOPA enantiomers.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. Tel: +86-21-54340042. Fax: +86-21-54340042. *E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (Grants 21405048, 21675053, 21635003).



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Fukuhara,

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Inoue,

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Highly

Selective

Oligosaccharide

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Enantiomers of Single Chirality Nanotube as Chiral Recognition

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