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A chiral organic field effect transistor with cyclodextrin modulated copper hexadecafluorophthalocyanine semiconductive layer as the sensing unit Yuwei Sun, Yong Wang, Yifan Wu, Xuepeng Wang, Xianggao Li, Shirong Wang, and Yin Xiao Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b01806 • Publication Date (Web): 26 Jun 2018 Downloaded from http://pubs.acs.org on July 3, 2018

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Analytical Chemistry

A chiral organic field effect transistor with cyclodextrin modulated

copper

hexadecafluorophthalocyanine

semiconductive layer as the sensing unit

Yuwei Sun1,2, Yong Wang*2,3, Yifan Wu1,2, Xuepeng Wang1,2, Xianggao Li1,2, Shirong Wang 1,2, Yin Xiao*1,2 1

School of Chemical Engineering and Technology, Tianjin Engineering Research Center

of Functional Fine Chemicals, Tianjin University, Tianjin 300072, China 2

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin

300072, China 3

Tianjin Key Laboratory of Molecular Optoelectronic Science, Department of Chemistry,

School of Science, Tianjin University, Tianjin 300072, China E-mail addresses: [email protected], [email protected]

ABSTRACT This work reported the construction of a chiral sensor based on organic field effect transistor (COFET) to probe the subtle change of weak interactions in the chiral discrimination process, with the ability to achieve fast, sensitive quantitative real-time chiral analysis for various racemic pairs, where a β-cyclodextrin (β-CD) sensitized copper hexadecafluorophthalocyanine (F16CuPc) semiconductive layer was employed as the sensing unit. Physical adsorptive assembling of β-CD on the semiconductive layer guarantees the impressive field-effect amplified chiral sensitivity. The enantiomer induced aggregation pattern diversification of the sensing layer resulted in enhanced or weakened surface-dipole interactions in various degree hence brought about the drain current fluctuation. A fast and real-time detection of the enantiomer pairs in aqueous solution at 10-9 M was achieved. This COFET afforded reliable ability for quantitative determination of the pure isomer content in enantiomer pairs and was further proved to have great potential for resolution of “real world” pharmaceutical drugs.

INTRODUCTION Chiral discrimination has become an area of considerable interests in chemistry and biological science as well as food, medical and modern pharmaceutical industry. Because different enantiomers have identical physical and chemical properties but often exhibit different biological, pharmacological, toxicological and metabolism activities in living systems. Various techniques have been developed for chiral recognition and separation such as capillary electrophoresis,1 chromatography2 and electrochemical methods.3 However, these methods are always off-line detection and suffer from long

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response time and cost ineffectiveness. Alternatively, organic field effect transistors (OFETs) can provide ideal sensing platform because of their rapid response, high sensitivity, on-line analysis, and potential applications in integrated microarray chips.4 By far, OFET sensors have been widely implemented for sensing of gases,5-6 pH,7 humidity,8 ions,9-10 glucose,11 amino acids,12 pressure,13 antibodies14 and DNA15-16 et al. However, there are limited works reporting chiral organic field effect transistors (COFETs) since the enantiomer discrimination is difficult to achieve via organic semiconductive materials in OFETs. As commonly accepted, chiral recognition is usually achieved by formation of host-guest complexes between enantiomers and supramolecular chiral selectors based on weak intermolecular interactions, such as hydrogen bonds, π-π interactions, dipolar interactions and inclusions. Regrettably, most of OFET sensors are ion sensitive field effect transistors (ISFETs), which has no significant advantages in chiral sensing because there is no or very few ion concentration changes in the resolution process. Construction of chiral sensing systems to afford fast and sensitive online chiral analysis will be a disruptive technology and yet is a great challenge. Most of the reported COFETs focus on modification of the gate as sensing units. For example, Torsi et al. reported a chiral sensor based on a water-gate-OFET (WGOFET) against volatile carvone,17 where self-assembled monolayer odorant binding proteins was employed as the sensing layer. Osaka et al. achieved chiral discrimination of alanine (Ala) based on a WGOFET with modification of gate electrode by homocysteine.18 Cu(II) was required in their sensing system because the chiral response was originated from the enantioselective formation of diastereomeric Cu-Ala complexes. Willner et al. imprinted enantiomers in TiO2 thin films on the gate surface of ion sensitive field effect transistor to achieve chiral sensing.19 Although gate modified OFETs can realize some chiral sensing processes, direct modification of the semiconductive layer could afford more directive sensing for the subtle change of weak interaction in chiral discrimination. Toris et al made the first attempt to develop a bilayer COFET sensor using two conjugated oligomers with L-phenylalanine amino acid and β-D-glucosidic substituents, which realized the distinction of citronellol and carvone enantiomers.20 Reed et al. developed a β-cyclodextrins (β-CDs) functionalized Si nanowire transistor to detect thyroxine enantiomers.21 However, limited works reporting versatile COFET sensors via direct usage of the decorated organic semiconductive layer as sensing unites by far because the modification approaches may ruin the electrical properties of the semiconductors. Hence, seeking appropriate semiconductive and chiral recognition materials for assembling the sensing units is the key point for construction of such COFET sensors. Herein, aiming at sensing the subtle change of weak interactions in the process of chiral discrimination,

we

constructed

an

effective

chiral

sensor

based

on

a

copper

hexadecafluorophthalocyanine (F16CuPc) OFET with β-CDs assembled on the exposed channel for fast and sensitive quantitative real-time chiral analysis. F16CuPc is a commonly used n-type semiconductive material with high chemical and environmental stability.22 The strong electron-withdrawing property of -F endows F16CuPc with ability to form hydrogen-bonding and induce polarization, which provides active sites for further modification. On a separate note, CDs are the second generation supermolecules with a hydrophobic cavity and a hydrophilic outside region, which could form ‘fit’ inclusion with diverse molecules to implement stereoselective interactions.23-24 The fabricated COFET sensor afforded good field effect response that enables direct discrimination of various racemic chemicals. The influence of analyte structure and β-CD concentration on the sensing process was investigated. Fast and real-time qualitative and quantitative detections of enantiomers in aqueous solution at nanomolar concentration were achieved. The chiral sensing ability of the COFET was further evaluated with a


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“real world” pharmaceutical compound ibuprofen.

EXPERIMENTAL SECTION Materials and Instrumentations All the chemicals were of analytical reagent grade unless stated otherwise. F16CuPc was synthesized according to our previously reported method.25 p-Sexiphenyl (p-6P) and all the chiral compounds

were

purchased

(R)-(+)-1,1'-bi-2-naphthol,

from

TCI

(Japan),

2-chloro-D-mandelic

including

acid,

(S)-(-)-1,1'-bi-2-naphthol,

2-chloro-L-mandelic

acid,

(1S,2S)-(-)-1,2-diphenylethylenediamine, (1R,2R)-(+)-1,2-diphenylethylenediamine, 1D-chiro-inositol, 1L-chiro-inositol, L-(+)-mandelic acid, D-(-)-mandelic acid, L-phenylalanine, D-phenylalanine, L-(-)-3-phenyllactic

acid,

D-(+)-3-phenyllactic

(S)-(+)-2-phenylpropionic

acid,

acid,

(R)-(-)-2-phenylpropionic

acid,

(S)-(-)-1,1,2-triphenyl-1,2-ethanediol,

(R)-(+)-1,1,2-triphenyl-1,2-ethanediol, L-tartaric acid, D-tartaric acid, R-ibuprofen and S-ibuprofen. The fetal bovine serum (FBS) was purchased from Thermo Fisher Scientific Inc (USA). The gold wire used for electrode was purchased from Zhongnuo Advanced Material (Beijing, China). β-CD was purchased from Heowns (Tianjin, China). Acetone, anhydrous ethanol, isopropanol was obtained from Rianlon corporation (Tianjin, China). The elemental composition of the film surface was detected by the PHI 5000 Versa Probe X-ray photoelectron spectroscopy (Japan). The surface morphology of the organic thin film was characterized by AFM 5500 (Agilent, USA) in tapping mode. The electrical characteristics of the OFETs were measured using two Keithley 2400 sources under ambient conditions at room temperature.

Fabrication of COFET and sensing procedure F16CuPc were purified twice by thermal gradient sublimation prior to processing. A top-contact/ bottom-gate F16CuPc OFET was fabricated. An N-doped silicon wafer was used as a gate electrode with 300 nm SiO2 layer on the top as dielectric layer. A p-6P film (3 nm) was deposited on the silicon wafers as induced layer which can lead to a smooth semiconductive layer and higher electron mobility, followed by deposition of a F16CuPc (25 nm) film. Then gold source and drain electrodes were patterned with different channel length (L, µm) and width (W, µm), which are W/L=6000/200 and W/L=6000/1000. Finally, β-CDs were assembled on the channel surface via physical adsorption. Experimentally, 3 µL water solution of β-CDs with concentration ranged from 5 to 20 mM was pipetted onto the transistor channel and air dried for 20 min. The surface was rinsed with alcohol and dried with N2 before electrical characteristic measurements. Stocked solutions of racemic analytes were prepared with deionized water or ethanol. All sample solutions were filtrated with a 0.45 µm syringe-type Millipore membrane and degassed before use. The analytes solution of 1 µL was pipetted on channel of the COFET sensor (W/L=6000/200) and left for 15 min. Then the electrical characteristics of the sensor were measured. In real-time test, sensor devices with channel of W/L=6000/1000 µm were used. After baseline established, solution of analytes (0.1 µL) was placed on channel to give the analytes final concentration of 1, 5, 10, 15, 20 nM, respectively.The time interval of each concentration dropping is about 30 s. The electrical response was measured under the condition of VG = VDS = 30 V.



RESULTES AND DISCUSSION Surface immobilization of β-CDs β-CDs were physically immobilized on the surface of conducting channel of the COFET to afford chiral discrimination abilities. The COFET sensor configuration was illustrated in Fig. 1(a). The morphology of β-CDs on F16CuPc was examined by AFM. As shown in Fig. 1(b), whisker-like crystals of F16CuPc presented approximately a “stand-up” arrangement on p-6P induced layer. The formation of highly ordered microstructure is ascribed to the weak epitaxial growth of F16CuPc induced by p-6P.26 After physical adsorption of β-CDs, the AFM (Fig. 1(c)) image showed different feature of sheet-like shape significantly which indicates the formation of β-CDs sensing layer on F16CuPc semiconductive layer. The contact angle of water with the F16CuPc and β-CD/F16CuPc device channel surface was determined as 94.42 ° and 43.90 ° respectively (Supporting Information, Fig. S1), which indicates the increased surface hydrophilicity due to the large number of hydroxyl groups on CD’s rim.

Figure 1. (a) Device configuration of the OFET-based sensor and the molecular structures of the F16CuPc and β-CDs. (b)(c) AFM images of channel surface without and with β-CDs.

Figure 2. The XPS fully scanned spectra of (a) F16CuPc OFET and core level spectra of (b) C 1s, (c) F 1s, (d) Cu2p3. The XPS fully scanned spectra of (e) β-CD/F16CuPc COFET and core level spectra of (f) C 1s, (g) F 1s, (h) O 1s.


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The wide energy survey and core level spectra of the channel surface were presented in Fig.2. For C1s spectrum of F16CuPc (Fig. 2(b)), two peaks with binding energies of 285.5 and 287.6 eV were distinguished. The former one is associated with C-C bonds and the later one is due to the C-F bonds, which are typical features of F16CuPc film.27 The Cu2p3 (Fig. 2(d)) spectrum of F16CuPc located on 936.0 eV representing the typical Cu-N bonds.28 After immobilization of β-CDs, the C1s spectrum was fitted into two main components with binding energies of 285.1 and 286.8 eV (Fig. 2(f)), which are assigned to C-C and C-OR. That is the typical feature of β-CDs.29 It can be seen that the binding energy of the C-C bond after the sensing layer assembly changed ~0.4 eV, which may be due to the fact that the chemical environment of C-C bond in the β-CD is not consistent with the C-C bond in the F16CuPc. The F1s spectrum of F16CuPc (Fig. 2(c)) located on 688.0 eV while that of β-CD/F16CuPc (Fig. 2(g)) located on 687.3 eV. This phenomenon may be owing to the inducing effect between the hydroxyl groups of β-CDs and the F16CuPc, resulting in an increase in the negative charge of F element and decreased binding energy of F.30 The O1s spectrum of β-CD/F16CuPc (Fig. 2(h)) was fitted into two peaks with binding energy of 531.8 and 533.0 eV, associated with the O-H and O-C bonds of β-CDs29. These results indicate that the β-CD has been successfully immobilized on the surface of semiconductive layer by physical adsorption. The elemental compositions of the channel surface were summarized in Table 1. The increased C% and O% while decreased N%, F% and Cu% for β-CD/F16CuPc also revealed the successful localization of β-CDs on F16CuPc.

Table 1．．Elemental compositions of channel surface of F16CuPc OFET and β-CD/F16CuPc COFET from XPS wide energy survey Sample F16CuPc β-CD/F16CuPc

C 53.45 68.74

N 13.36 0.60

Atomic percentage (%) O F 0.83 30.91 27.74 0.34

Cu 1.29 0.03

Chiral response of β-CD/F16CuPc COFET sensor As expected, both the F16CuPc OFET and β-CD/F16CuPc COFET displayed typical n-channel behaviors since F16CuPc is a n-type semiconductor. The representative IDS-VDS output and IDS-VG transfer characteristic curves were shown in Fig. S2. Interestingly, the device with β-CD functional layer exhibited higher drain current than that of F16CuPc device. This is related to the formation of hydrogen bonding (-O-H···F) between the hydroxyl group of CDs and F atoms in the periphery of F16CuPc, which is consistent with the XPS results. Owing to the strong electron-withdrawing nature of F atoms, the number of electrons (e-) as the charge carrier would increase due to the induced surface polarization leading to a higher drain current for the n-channel OFET sensors. To verify our speculation, OFET with CuPc as the semiconductive layer was fabricated and representative output curve was presented in Fig. S3. As expected, the current level of the CuPc OFET with and without CDs showed no significant difference since the absence of electron-withdrawing F atoms. The enantioselective response of β-CD/F16CuPc COFET sensor was evaluated with eight enantiomer pairs. The structures of these racemic compounds were shown in Fig. 3(a). The relative drain current changes ∆I/I0 = (I-I0)/I0 extracted from output curves at VG = 50 V for each pair of enantiomers are illustrated in Fig. 3(b), where I0 and I are the saturated drain current before and after addition of analytes. Based on ∆I/I0, all the analytes could be resolved effectively with the β-CD/F16CuPc COFET sensor revealing the versatility of the current COFET sensor. The molecular



structure of the analytes plays an important role in the chiral recognition process since the enantio-recognition occurs via host-guest formation with the β-CD cavity. A common feature of the analyte structures is the presence of aromatic rings. In the chiral discrimination process, these analytes could form complexes with β-CD through the penetration of aromatic rings into the CD hydrophobic cavity. In addition, their hydroxyl or amino group near to the chiral center could form hydrogen bonds with the CD secondary hydroxyl groups, which makes a positive contribution to the chiral recognition.31 The lower resolution for TE could be attributed to the steric hindrance due to its bulky structure.32 The influence of CD amount on sensing response of the COFET sensor was also investigated with 20 mM racemic analytes. The absolute value of drain current change differences (∆I/I0)D-(∆I/I0)L extracted from output curves at VG = 50 V for each pair of enantiomers are presented in Fig. 3(c) and (d). The concentration of β-CD solution for the absorption process was used to represent the amount of β-CD on the surface approximately. As shown in Fig. 3(c) and (d), most of the analytes were well resolved over a wide range of β-CD concentrations (5-20 mM). For Phe, PPA, CI, TE, the current change differences between pure isomers increased with the increase of β-CD concentration in the studied range, while an optimal β-CD concentration was observed for other analytes.

Figure 3. (a) Structures of the racemic compounds. (b) Sensing responses toward various enantiomers (CD concentration: 5 mM; red square: L-isomer of Phe, MA, PA, TA, CA and CI; S-isomer for PPA and TE; black square: D-isomer of Phe, MA, PA, TA, CA and CI; R-isomer for PPA and TE). Each data point is the average value along with standard error bar estimated over five replicates. (c) (d) Sensing responses at different CD concentration. Analytes concentration: 20 mM. Taking Phe as model analyte, the sensing mechanism was discussed. The drain current increased in the presence of Phe and higher current was observed for L-form than that of D-form (Fig. S4). It is well known that chiral resolution is achieved based on formation of complexes between CD and each enantiomer with different geometry and stabilization energy. Consequently, the configuration and arrangement of CD molecules on F16CuPc changed after inclusion occurred, which affected the induced surface-dipole interaction between CDs and F16CuPc hence resulted in drain current change. The


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different geometry of D- and L-complexes led to enhanced or weakened induced surface-dipole interactions in varying degree (Fig. 4), hence resulting in the ascendant or declined drain current. This could be supported by the different morphology of L-complex with needle-like crystalline and D-complex of smooth film without visible crystallization as shown in Fig. S5. This result demonstrates that the β-CD/F16CuPc unit could achieve signal extraction and amplification to the subtle change of weak interaction in the chiral discrimination process. Furthermore, F16CuPc OFET without CDs showed no such sensing response towards Phe (Fig. S6), confirming the effectiveness of the CD layers.

Figure 4. Schematic illustration of changed surface polarization due to D- and L-complexes with different molecular geometry.

Real-time sensing response The real-time sensing to the enantiomers was performed to further evaluate the chiral selective response of the β-CD/F16CuPc COFET sensor. To avoid ionic conduction, a device configuration with a channel width and length of 6000 and 1000 µm respectively was employed to confirming the analytes solution away from the source and drain electrodes. With a water droplet covering the channel, the COFET could work normally and show field effect (Fig. S7). After baseline establishment, the deionized water solution of enantiomers (0.1 µL) was placed on the channel to give the final analyte concentrations of 1, 5, 10, 15, 20 nM. The dependence of drain current on time for deionized water without enantiomers was also tested and the representative curve was presented in Fig. S8, which reflected the baseline natural attenuation. Fig. 5(a) showed the real-time sensing responses of the COFET to all the enantiomer pairs, in which the baseline current was deducted from the drain current to exclude the influence of baseline drift. The device showed a decrease in conductance when exposed to 1 nM analytes and the responses became more significant at higher analyte concentrations. Except for PA, all the enantiomer pairs could be well resolved at 10-9 M concentrations level according to the drain current, which confirmed the practical application of the as-prepared COFET sensor. For TE, due to its limited solubility in water, we used its ethanol solution for the tests. However, the sensor cannot afford normal response, which could be explained by the fact that the ethanol solution is prone to cross the source and drain electrodes because of its large surface tension.



Figure 5. (a) Real-time sensing responses to eight chiral enantiomers (CD concentration: 5 mM). (b) Real-time sensing responses to 20 nM D- and L-Phe and their mixtures (CD concentration: 5 mM). Calibrated response (∆I/gm) versus enantiomer concentration and Langmuir fitting for (c) L-Phe and (d) D-Phe. The error bar is obtained by the average of all data points except the current attenuation. The response of the COFET sensor to the enantiomer pairs with different compositions of isomers was examined using Phe as model analyte by fixing the total Phe concentration at 20 nM. After a stable baseline was established, solutions of Phe were injected. As shown in Fig. 5(b), a clear decrease of the measured current was observed at sample injection and the sensing response was significantly enhanced as the percentage of L-Phe increased, revealing a differential selective binding affinity of L-form and D-form on the CD layer. This indicates that the β-CD/F16CuPc COFET could be applied as a chiral sensor to quantify the enantiomeric compositions at nano-molar concentration. The surface titration of Phe was also estimated. After the baseline was established, L-Phe solutions with concentrations of 1, 5, 10, 15, and 20 nM were sequentially dropped onto the channel. The measured current change of device (∆I) was calibrated using ∆I/gm to obtain the surface potential change,21,33,34 which depended on the number of captured L-Phe molecules on the channel surface.21,34 As shown in Fig. 5(c), the calibration curve was fitted using the Langmuir isotherm model with 1:1 stoichiometry35,21,36 and the affinity constant (KL) for L-Phe is determined as (2.95±0.58)×108 M-1. Surface titration with D-Phe was performed in a similar manner and the affinity constant for D-Phe was obtained as (7.49±2.09)×107 M-1 (Fig. 5(d)). The higher affinity of L-form compared with D-form suggests that the surface capture of L-Phe was more favorable over D-Phe, which is consistent with the more obvious sensing response to L-form.


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The enantiorecognition ability of the current COFET was further evaluated with a“real world” pharmaceutical compound (ibuprofen, Ibu). Ibu is a drug used to treat minor pain, fever, and inflammation. It could be well resolved using the fabricated COFET with a lowest detection concentration (LDC) down to 1 nM as shown in Fig. 6(a). In addition, the sensing response showed composition dependence towards enantiomers mixture of Ibu with enhanced response as the percentage of S-Ibu increased (Fig. 6(b)). As shown in Fig. 6(c) and (d), the calibration curves for Ibu were fitted and the affinity constants for R-Ibu and S-Ibu is determined as (1.98±0.11)×106 and (6.52±0.62)×107 M-1, respectively. These results showed that the COFET could be applied in the sensitive quantitative resolution of “real world” pharmaceutical compounds. To further investigate the reliability of the COFET in the real-life sample matrix, the sensing response to Ibu in fetal bovine serum (FBS) was evaluated. The response of the COFET to FBS without Ibu was tested firstly and served as control (Fig. S9(a)), which only generated random and inconsequential signals when the FBS was dropped. Chiral resolution could be achieved as the concentration of Ibu in FBS is 20 nM (~ ng/mL) as shown in Fig. S9(b), which could satisfy the medically necessary (ng to µg/mL)37 and hence promise practical application of the COFET. The loss of sensitivity in FBS could be ascribed to the interferences induced by nonspecific binding of nontarget molecules in serum. The nonspecific binding could be reduced by employing specific polymer, such as Tween 20, to passivate the device36, and further investigation is in progress.

Figure 6. (a) Real-time sensing responses to Ibu (CD concentration: 5 mM). (b) Real-time sensing responses to 20 nM R- and S-Ibu and their mixtures (CD concentration: 5 mM). Calibrated response (∆I/gm) versus enantiomer concentration and Langmuir fitting for (c) R-Ibu and (d) S-Ibu. The error bar is obtained by the average of all data points except the current attenuation.



CONCLUSIONS In summary, we demonstrated an effective chiral sensor based on a COFET employing β-CD-modulated F16CuPc semiconductive layer as the sensing unit, which could probe the subtle change of weak interactions in enantiorecognition hence afford fast and sensitive chiral sensing of racemic compounds. Well-defined sensing results were achieved based on the induced polarization ascribed to the interaction of enantiomers with CD on the semiconductive layer. The various β-CD/enantiomer complexing geometries resulted in different induced surface polarizations hence led to enhanced or reduced drain current of the COFET. A real-time detection of the enantiomers in aqueous solution at 10-9 M was achieved. The devices showed composition dependence for their response towards enantiomers mixture of Phe as well as a pharmaceutical compound (ibuprofen), which demonstrated the ability and potentiality of the present COFET for on-line quantitative enantiomeric analysis for “real world” drug in complex systems.

SUPPORTING INFORMATION The contact angle of channel surface of F16CuPc OFET and β-CD/F16CuPc COFET to deionized water, representative output and transfer characteristic curves of F16CuPc OFET before and after the β-CDs assembled, representative output curves of CuPc OFET before and after the β-CDs assembled, sensing response of the β-CD/F16CuPc COFET to Phe, the surface morphology of channel, response of the F16CuPc OFET to Phe, the output curve of the β-CD/F16CuPc COFET with and without deionized water, the dependence of drain current of the β-CD/F16CuPc COFET on time with deionized water, and sensing responses of the of the β-CD/F16CuPc COFET to FBS without and with Ibu are given in the supplementary figures.

ACKONWLEDGEMENTS We acknowledge the financial support from the National Natural Science Foundation of China (No. 21575100, 21676188) and the Natural Science Foundation of Tianjin (16JCZDJC37100).

REFERENCES (1) Voeten, R. L. C.; Ventouri, I. K.; Haselberg, R.; Somsen, G. W. Anal. Chem. 2018, 90, 1464-1481.

(2) Yao, X. B.; Zheng, H.; Zhang, Y.; Ma, X. F.; Xiao, Y.; Wang, Y. Anal. Chem. 2016, 88, 4955-4964. (3) Dong, L.; Zhang, Y.; Duan, X.; Zhu, X.; Sun, H.; Xu, J. Anal. Chem. 2017, 89, 9695-9702. (4) Liao, C.; Yan, F. Polym. Rev. 2013, 53, 352-406. (5) (a) Nketia-Yawson, B.; Jung, A. R.; Noh, Y.; Ryu, G.-S.; Tabi, G. D.; Lee, K.-K.; Kim, B.; Noh, Y.-Y. ACS Appl. Mat. Interfaces 2017, 9, 7322-7330; (b) Kim, K. S.; Ahn, C. H.; Jung, S. H.; Cho, S. W.; Cho, H. K. ACS Appl. Mat. Interfaces 2018, 10, 10185-10193. (6) Dai, M.-Z.; Lin, Y.-L.; Lin, H.-C.; Zan, H.-W.; Chang, K.-T.; Meng, H.-F.; Liao, J.-W.; Tsai, M.-J.; Cheng,


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For TOC only



Figure 1. (a) Device configuration of the OFET-based sensor and the molecular structures of the F16CuPc and β-CDs. (b)(c) AFM images of channel surface without and with β-CDs. 170x106mm (299 x 299 DPI)


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Figure 2. The XPS fully scanned spectra of (a) F16CuPc OFET and core level spectra of (b) C 1s, (c) F 1s, (d) Cu2p3. The XPS fully scanned spectra of (e) β-CD/F16CuPc COFET and core level spectra of (f) C 1s, (g) F 1s, (h) O 1s. 170x74mm (300 x 300 DPI)



Figure 3. (a) Structures of the racemic compounds. (b) Sensing responses toward various enantiomers (CD concentration: 5 mM; red square: L-isomer of Phe, MA, PA, TA, CA and CI; S-isomer for PPA and TE; black square: D-isomer of Phe, MA, PA, TA, CA and CI; R-isomer for PPA and TE). Each data point is the average value along with standard error bar estimated over five replicates. (c) (d) Sensing responses at different CD concentration. Analytes concentration: 20 mM. 450x282mm (300 x 300 DPI)


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Figure 4. Schematic illustration of changed surface polarization due to D- and L-complexes with different molecular geometry. 113x72mm (300 x 300 DPI)



Figure 5. (a) Real-time sensing responses to eight chiral enantiomers (CD concentration: 5 mM). (b) Realtime sensing responses to 20 nM D- and L-Phe and their mixtures (CD concentration: 5 mM). Calibrated response (∆I/gm) versus enantiomer concentration and Langmuir fitting for (c) L-Phe and (d) D-Phe. The error bar is obtained by the average of all data points except the current attenuation. 170x119mm (300 x 300 DPI)


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Figure 6. (a) Real-time sensing responses to Ibu (CD concentration: 5 mM). (b) Real-time sensing responses to 20 nM R- and S-Ibu and their mixtures (CD concentration: 5 mM). Calibrated response (∆I/gm) versus enantiomer concentration and Langmuir fitting for (c) R-Ibu and (d) S-Ibu. The error bar is obtained by the average of all data points except the current attenuation. 170x126mm (300 x 300 DPI)


A Chiral Organic Field-Effect Transistor with a ... - ACS Publications

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