This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021 Mater. Chem. Front.

Cite this: DOI: 10.1039/d1qm00926e

Poly(3,4-ethylenedioxythiophene) bearingfluoro-containing phenylboronic acid for specificrecognition of glucose†

Wenji Bao,‡a Wenfeng Hai, ‡*a Layue Bao,a Fan Yang,a Yushuang Liu,*a

Tatsuro Goda b and Jinghai Liu *a

In this study, we synthesized a new monomer, namely, 3,4-ethylenedioxythiophene bearing a fluoro-

containing phenylboronic acid (EDOT–FPBA) for enzyme-free glucose sensing at physiological conditions.

The EDOT–FPBA monomer is electropolymerized on a glassy carbon electrode (poly(EDOT–FPBA)/GCE)

at a constant voltage. The electrochemical polymerization was optimized to obtain a low impedance film

interface and then characterized by scanning electron microscopy, atomic force microscopy, water

contact angle measurements, and electrochemical impedance spectroscopy. The specific interaction and

pH dependence between poly(EDOT–FPBA)/GCE and glucose are detected by electrochemical

impedance spectroscopy in a detection range from 0.05 to 25 mM with a detection limit of 0.05 mM at pH

7.0. The poly(EDOT–FPBA) exhibits 6 times higher sensitivity under physiological pH conditions in comparison

with phenylboronic acid and 3-pyridylboronic acid conjugated poly(3,4-ethylenedioxythiophene), due to the

introduction of an electron-withdrawing F substituent into the benzene ring of phenylboronic acid (PBA)

reducing the pKa value of PBA. The sensitivity and the dynamic range cover all levels of blood glucose in the

serum of patients with diabetes. Furthermore, with advantages of high sensitivity and wide detection range,

reusability, stability, and mass productivity, poly(EDOT–FPBA) as a glucose sensor has great potential for

enzyme-free glucose continuous monitoring applications.

1. Introduction

Diabetes is a common chronic non-communicable disease,which has become a serious worldwide public healthconcern.1 Because continuous monitoring of blood glucose isthe key to better control of blood glucose concentration in thetreatment of diabetes, we urgently need new electrode materialsand sensor designs to meet this requirement. In recent years,the application of conducting polymers in this field has beenincreasing, among which poly(3,4-ethylenedioxythiophene)(PEDOT) and its derivatives have attracted more and moreattention.2,3 PEDOT is a typical thiophene conducting polymer,which has good conductivity, environmental stability in thedoping state, low redox potential, good film-forming property,

flexibility, and other characteristics.4,5 Besides, PEDOT can beeasily functionalized to achieve specific excitation, detection,and sensing and has great potential applications in bio-electronics and biosensing.6,7 Because the 3 and 4 positionsof 3,4-ethylenedioxythiophene (EDOT) are both replaced byalkoxyl groups, the alkoxyl substituents reduce the oxidationpotential of thiophene monomers and polymers, making iteasier to electropolymerize and more stable in redox (dopingand de-doping) cycles.8 A series of progresses in the perceptionof the current of the cerebral cortex and the skin has beenmade, owing to the nature of its good conductivity, non-toxicity,softness, large surface area, and the low impedance at tissue/electrode interfaces,9,10 however, PEDOT does not have specificrecognition functions. It is necessary to impart specificrecognition elements to PEDOT in advance for biosensingapplications. Two approaches have been explored to introducespecific recognition elements to PEDOT. Physical adsorptionthrough mechanical mixing and doping imparts specificrecognition elements into PEDOT. However, the doped smallmolecules can easily be de-doped during operation. EDOTfunctionalization through chemical synthesis has the advantagesof precise modulation of a versatile functional unit at themolecular scale and adjustable modification density.11,12 EDOT

a Inner Mongolia Key Laboratory of Carbon Nanomaterials, Nano Innovation

Institute (NII), College of Chemistry and Chemical Engineering, Inner Mongolia

Minzu University, Tongliao 028000, China. E-mail: hai_wenfeng@163.com,

yushuangliu1989@163.com, jhliu2008@sinano.ac.cnb Department of Biomedical Engineering, Faculty of Science and Engineering,

Toyo University, 2100 Kujirai, Kawagoe, 350-8585 Saitama, Japan

† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1qm00926e‡ These authors contributed equally to this paper.

Received 25th June 2021,Accepted 22nd August 2021

DOI: 10.1039/d1qm00926e

rsc.li/frontiers-materials

MATERIALS CHEMISTRYFRONTIERS

RESEARCH ARTICLE

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

.

View Article OnlineView Journal

Mater. Chem. Front. This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021

derivatives carrying target-capturing elements have beendeveloped to detect influenza virus,13 DNA,14 protein,15 sialicacid,16 and glucose.17

Glucose oxidase (GOD) catalyzes the oxidation of beta-D-glucose to gluconic acid with simultaneous production ofhydrogen peroxide. GOD is the most commonly used glucoserecognition element and is widely used in various glucosesensors.2,18 Three generations of GOD-based biosensors havebeen proposed, where the first generation is based on themeasurement of hydrogen peroxide formation and oxygenconsumption, the second one uses additional media to transferelectrons from the enzyme active site to the electrode, and thethird one is the direct electron transfer strategy between GODand electrode without medium.19 Recently, GOD has beencombined with nanomaterials to increase the electron transferrate, such as noble metal and transition metal nanoparticles,20

nanostructured metal oxides or metal sulfides,21,22 conductivepolymers,23 carbon nanotubes24 and graphene.25 Althoughenzymatic glucose sensors commonly provide a high selectivityand quantification platform, these approaches suffer fromdifficulties in long-term use and storage caused by denaturingof the protein GOD.19 This fact has become a driving force forresearch on non-enzymatic synthetic glucose sensors as analternative strategy for enzymatic glucose sensors.

The non-enzymatic glucose sensing approaches can beclassified into the artificial (GOD-free) electrochemical oxidationof glucose, and synthetic ligands with glucose, e.g., a-cyclodextrin(a-CD) and phenylboronic acid (PBA) derivatives.26 The PBAmolecule can reversibly form boronic esters with hydroxyl groupsof glucose.27,28 And, the effective coordination binding ofPBA with polyol compounds (such as glucose) requires the sp3

hybridization of boron (B) atoms (tetrahedral anion, –B(OH)3�),

which can only be achieved at a high pH value close to the originalpKa (about 8–9) of PBA.29–31 As a result, a limited proportion of sp3

hybridized PBA can bind effectively with glucose at pH 7.0.Therefore, PBA has poor sensitivity to glucose under physiologicalpH conditions, which limits its use in sensors under physiologicalpH conditions.

Here, we design a new monomer, namely 3,4-ethylene-dioxythiophene, bearing a fluoro-containing phenylboronic acid(EDOT–FPBA). The electron-withdrawing F substituent into the

benzene ring of phenylboronic acid (PBA) reduces the pKa valueof PBA, endowing the poly(EDOT–FPBA) more sensitivity for glucoseunder physiological pH conditions. The optimum electrochemicalpolymerization conditions, including solvent, time, and tempera-ture, were explored to obtain a low impedance film interface forglassy carbon electrodes (poly(EDOT–FPBA)/GCE). Compared topoly(EDOT–PBA) and poly(EDOT–PyBA), poly (EDOT–FPBA) has ahigher sensitivity to glucose at pH 7.0, even in the presence ofgalactose, mannose, dopamine, urea, Na+, and K+, and alarge detection range from 0.05 to 25 mM (R2 = 0.9826) with aLOD of 0.05 mM. Practically, the poly(EDOT–FPBA) with highsensitivity and wide detection range has successfully been utilizedin glucose continuous detection in human serum samples,demonstrating the future potential for enzyme-free glucosemonitoring applications.

2. Results and discussion2.1. Monomer synthesis and optimization ofelectropolymerization conditions

In this study, we developed a new monomer, namely EDOTpossessing a fluorine (F) containing PBA moiety (EDOT–FPBA),and carried out electrochemical polymerization on a glassycarbon electrode (GCE) in the presence of tetrabutylammoniumperchloride into poly(EDOT–FPBA) for glucose detection undera physiological pH environment. F was introduced into thebenzene ring of PBA as an electron-withdrawing group, intendingto lower the pKa of PBA (Fig. 1). The EDOT–FPBA was successfullysynthesized and examined by 1H-NMR and high-resolution ESI-MS (Fig. S1 and S2, ESI†). The oxidation current of EDOT–FPBAgradually reached equilibrium and the capacitance of poly(EDOT–FPBA)/GCE increased when a constant voltage of 1.5 V (versus Ag/AgCl reference electrode) was applied to the GCE workingelectrode for 10 seconds in a dichloromethane solutioncontaining 10 mM EDOT–FPBA and 100 mM ammoniumperchlorate (Fig. S3a, ESI†). Meanwhile, the impedance of poly-(EDOT–FPBA)/GCE increased in contrast to the bare GCE andPEDOT/GCE (Fig. S3b, ESI†), indicating that poly(EDOT–FPBA) issuccessfully electropolymerized on a GCE. The optimal electro-polymerization conditions were determined using EIS Nyquist

Fig. 1 Scheme for the synthetic route of an EDOT derivative possessing a 3-fluorophenylboronic acid group (EDOT–FPBA) and electrochemicalpolymerization of EDOT–FPBA into poly(EDOT–FPBA) on a glassy carbon electrode (GCE) for glucose detection.

Research Article Materials Chemistry Frontiers

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021 Mater. Chem. Front.

curves with the lowest charge transfer resistance (Rct) at variousmonomer solvents (Fig. 2a), electropolymerization time (Fig. 2b),and temperature (Fig. 2c) for poly(EDOT–FPBA)/GCE. The Rct inthe corresponding Randales equivalent circuit and modelingindicates EDOT–FPBA should undergo electropolymerization witha monomer solvent of dichloromethane (CH2Cl2) at 25 1C for 10 sunder a constant voltage of 1.5 V (Fig. 2d).

2.2. Characterization of poly(EDOT–FPBA) films

The surface morphology of poly(EDOT–FPBA) films on a planarAu electrode was investigated by scanning electronic micro-scopy (SEM) and atomic force microscopy (AFM). The monomersolvents have significant effects on the morphology, where asmooth superimposed sheet-like surface with a cavity forms inCH2Cl2 containing 100 mM butylammonium perchlorate(Fig. 3a), relative to a rough cavity surface in an aqueoussolution containing 100 mM sodium perchlorate (Fig. 3b) anda uniform dense surface in acetonitrile solution with 100 mMbutylammonium perchlorate (Fig. 3c). AFM analysis furtherreveals the surface profile of poly(EDOT–FPBA) films and thecorresponding height variations. Various concave–convexcavities of about 100 nm, 80 nm, and 80 nm depth were formedwith a film thickness of 0.46 mm, 0.25 mm, and 0.062 mmprepared in CH2Cl2 (Fig. 3d and g), H2O (Fig. 3e and h),and CH3CN (Fig. 3f and i) respectively. The XPS analysisdemonstrates the existence of F, B, and N elements in

poly(EDOT–FPBA) films, in comparison to only C, O, and S inPEDOT films (Fig. S4, ESI†), with 2.95 at% F, 6.00 at% B, and5.52% N (Table S1, ESI†).

2.3. Selectivity and pH dependence of poly(EDOT–FPBA) forglucose recognition

We then examined the selectivity and pH dependence ofpoly(EDOT–FPBA)/GCE for glucose recognition by an electro-chemical impendence spectroscopy (EIS) method at pH 7.0 inPBS buffer containing a redox couple of 5 mM potassiumferricyanide/potassium ferrocyanide (K3Fe(CN)6/K4Fe(CN)6).The charge transfer resistance change (DRct) of poly(EDOT–FPBA)/GCE denotes the specific interaction towards glucose,galactose, mannose, dopamine, uric acid, Na+ and K+ (5 mM).As shown in Fig. 4a, the response of DRct was significantlyincreased to 53.8 O cm2 after the addition of glucose in PBSbuffer, 12 times larger than the one for galactose, 14 times formannose, 8 times for dopamine, 8 times for urea, 22 times forNa+ and 10 times for K+, indicating the specific recognizationtowards glucose. In contrast to bare GCE and PEDOT/GCE, thespecific glucose recognition originates from the functionalFPBA unit conjugated to a PEDOT side chain (Fig. 4a insert).Fig. 5 shows the possible structure of the bis-boronate ester ofglucose with poly(EDOT–FPBA). The work of Shinkai et al.shows that glucose can form a bis-boronate complex withboronic acid derivatives.32 In D-glucose the 2- and 4-hydroxyl

Fig. 2 Optimization of the electropolymerization conditions of poly(EDOT–FPBA)/GCE examined using EIS Nyquist curves in PBS buffer containing5 mM potassium ferricyanide/potassium ferrocyanide (K3Fe(CN)6/K4Fe(CN)6) redox pairs. Electropolymerization at a constant voltage of 1.5 V underdifferent (a) solvents, (b) times and (c) temperatures. (d) Charge transfer resistance (Rct) for the poly(EDOT–FPBA)/GCE at different conditions. Inset:corresponding equivalent circuit and modeling. The data are shown as the mean � SD (n = 3).

Materials Chemistry Frontiers Research Article

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

Mater. Chem. Front. This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021

groups adopt the same configuration, with both binding toboronate, while, in D-mannose and D-galactose, the hydroxylgroups adopt the opposing configurations, which would lead to

spatial distortions and prevent the formation of D-mannose andD-galactose bis-boronate complexes.32,33 Thus, the impact ofthose non-glucose sugars on glucose detection was minimal.

Fig. 3 Morphology of poly(EDOT–FPBA) electropolymerized on a planar Au electrode. SEM images for the monomer solvents of (a) CH2Cl2, (b) H2O,and (c) CH3CN. (d–f) AFM scanning profile and (g–i) height profile.

Fig. 4 Selectivity and pH dependence of poly(EDOT–FPBA) for glucose recognition in PBS buffer (7.0) containing a redox couple of 5 mM K3Fe(CN)6/K4Fe(CN)6. (a) The charge transfer resistance changes of poly(EDOT–FPBA)/GCE after the addition of 5 mM glucose, galactose, mannose, dopamine,urea, Na+, and K+. Inset: glucose (5 mM) for the GCE with or without PEDOT deposited as the control. (b) pH dependence of the normalized EIS signal(DRct/R

0ct) for poly(EDOT–FPBA)/GCE (red curve), poly(EDOT–PBA)/GCE (blue curve), and poly(EDOT–PyBA)/GCE (green curve) at 5 mM glucose in PBS

buffer. The data are shown as the mean � SD (n = 3).

Research Article Materials Chemistry Frontiers

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021 Mater. Chem. Front.

The pH-dependent glucose-binding ability of poly(EDOT–FPBA) was studied by the normalized EIS modeling signal(DRct/R

0ct) for the poly(EDOT–FPBA)/GCE, poly(EDOT–PBA)/

GCE, and poly(EDOT–PyBA). As for the addition of 5 mM

glucose at pH 5.0–8.0, the DRct/R0ct of poly(EDOT–FPBA) at pH

7.0 is 6 times larger than that of poly(EDOT–PBA), together withalmost no signal response for poly(EDOT–PyBA) (Fig. 4b). Theseresults indicate the electron-withdrawing substituent F at thebenzene ring of poly(EDOT–FPBA) reducing the electrondensity on the boron atom and then the pKa of PBA,26 meaningthat poly(EDOT–FPBA) can be used for glucose sensing underphysiological pH conditions. In comparison, the introductionof electron-denoting N increases the pKa of PBA leading topoly(EDOT–PyBA) showing no more interaction with glucose atpH 5.0–8.0.

2.4. Electrochemical glucose sensing using poly(EDOT–FPBA)/GCE

We further evaluated the sensitivity of poly(EDOT–FPBA)/GCEfor glucose sensing under the EIS method in PBS buffercontaining a 5 mM redox couple of 5 mM K3Fe(CN)6/K4Fe(CN)6

at pH 7.0. The Nyquist curves in Fig. 5a show that theimpedance of poly(EDOT–FPBA)/GCE gradually becomes15 times larger with the increasing addition of glucose from0.05 mM to 25 mM. With the Randles equivalent circuit formodeling and quantitative analysis in Fig. 5b, the DRct of

Fig. 5 The possible structure of a bis-boronate complex of glucose withpoly(EDOT–FPBA).

Fig. 6 Poly(EDOT–FPBA)/GCE for the detection of glucose using an EIS method in PBS (pH 7.0) containing a redox couple of 5 mM K3Fe(CN)6/K4Fe(CN)6. (a) Nyquist curves for glucose concentrations from 0.05 to 25 mM. (b) Linear relations of DRct and lg[Glucose concentration], R2 = 0.9826.The data are shown as the mean � SD (n = 3). Inset: Randles equivalent circuit and modeling. (c) EIS Nyquist curves showing continuous monitoring ofglucose in three repeated cycles at 0 and 5.0 mM glucose concentration. (d) Corresponding DRct signal after storing for 2, 5, 12, and 36 hours.

Materials Chemistry Frontiers Research Article

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

Mater. Chem. Front. This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021

poly(EDOT–FPBA)/GCE presents a linear relation with thelog10[glucose concentration] in the linear range of 0.05 to25 mM (R2 = 0.9826). And, the limit of detection (LOD) is0.05 mM. We also compared the sensing performances in thechemical environment (pH), selectivity, and linear rangewith that from literature based on PBA derivatives as glucoserecognition elements (Table S2, ESI†). The dynamic range ofour system covers not only the normal human serum glucoselevel of 3.3–6.1 mM,34 but can also be used to measure bloodglucose in diabetic patients. As we know, the diagnostic criteriafor type 2 diabetes are that a random blood glucose level ishigher than 11.1 mM,35 and the detection ranges reported inmost literature reports are out of this range. In addition, ourelectrode material does not contain heavy metals, and there isno risk of leaking toxic compounds.

Then, we examined the reproducibility of poly(EDOT–FPBA)/GCE for continuous glucose monitoring over three repeatedcycles at 0 and 5 mM. As shown in Fig. 6a, these EIS signalsfrom glucose recognition match very well and are reproduciblein the subsequent three cycles for 5 mM glucose concentration,indicating the capability of the poly(EDOT–FPBA)/GCE platformfor reusable and continuous monitoring. The stability forcontinuous glucose monitoring was also investigated, wherepoly(EDOT–FPBA)/GCE presents a stable DRct signal for almost36 hours in the subsequent 15 cycles, with only a little declinein DRct signal after the first 5 hours.

2.5. Blood glucose detection by poly(EDOT–FPBA)/GCE

To evaluate the practical application of poly(EDOT–FPBA)electrochemical glucose sensors in blood glucose detection,we analyzed the glucose concentrations in human serumsamples. The Nyquist curves in Fig. S5 (ESI†) show the increaseof Rct as the glucose concentration rises from 2.5 mM to10 mM. Through the linear relationship established for thepoly(EDOT–FPBA)/GCE glucose sensor, the recovery of thespiked glucose (2.5 mM, 5.0 mM, 10 mM) ranges from 96 to103.2%, calculated based on the results of three repeated testsin 100-fold diluted human serum samples (Table 1). Theseresults strongly support the future application of poly(EDOT–FPBA) as an enzyme-free electrochemical sensor for humanblood glucose monitoring. In the future, we will try to introducean antifouling-PEDOT to sense whole blood glucose levelswithout dilution.36

3. Conclusion

A glucose sensing functional unit, fluoro-containing phenyl-boronic acid (FPBA), grafted poly(3,4-ethylenedioxythiophene)

was developed for enzyme-free glucose sensing at physiologicalpH conditions. The optimum electropolymerized poly(EDOT–FPBA)/GCE exhibits high sensitivity, a wide linear range, andreproducible stability using an EIS method for glucose detection.Furthermore, the successful application demonstration forhuman blood glucose detection suggests its future healthcareapplication in daily continuous blood glucose monitoring. Thiswork provides a new approach for the design of a biocompatiblePEDOT-based enzyme-free electrochemical sensor for bloodglucose monitoring at physiological pH conditions.

4. Materials and methods4.1 Materials

3,4-Dimethoxythiophene, 4-carboxy-3-fluorobenzeneboronic acid,4-(4,6-dimethoxy-1,3,5-triazine-2-yl)–4-methylmorpholinium chloride(DMT–MM), 3-chloro-1,2-propanediol, tetrabutylammonium per-chlorate, and dopamine hydrochloride were purchased from Energychemical (Shanghai, China). Glucose, mannose, galactose, and uricacid were purchased from Adamas Reagent, (Shanghai, China).Dulbecco’s phosphate-buffered saline (DPBS) was purchased fromSolarbio life sciences (Beijing Solarbio Science & Technology Co.Beijing, China). All reagents were of analytical grade and usedwithout further purification.

4.2 Instrumentations1H NMR spectra were collected on a Bruker NMR spectrometer(500 MHz Bruker Corporation, Karlsruhe, Germany). 1H spectrawere recorded in D2O. High-resolution mass spectrometry wasrecorded on a Waters xevo G2-S spectrometer (Waters Corporation,Milford Massachusetts, USA). Electro-polymerization of EDOTderivatives and electrochemical measurements were performed usinga multi-channel potentiostat (VMP3, Bio-Logic Science Instruments,France) via EC-Lab software version 11.10 (bio-logic, France). Thesurface morphology of electrodeposited films was examined byscanning electron microscopy (SEM) (S-4800, Hitachi, Japan) andatomic force microscopy (AFM) (Asylum Research MFP-3D OriginAFM, Oxford Instruments, UK) respectively. The AFM probe wasusing a silicon cantilever with a tip radius of 7 nm (Asylum ResearchProbes, 6310 Hollister Ave. Santa Barbara, CA 93117). X-ray photo-electron spectroscopy (XPS) (ESCALAB Xi+, Thermo Fisher Scientific,USA) was used to measure the elemental compositions.

4.3 Synthesis of EDOT–FPBA

The synthesis procedures of amine-functionalized 3,4-ethylene-dioxythiophene (EDOT–NH2) was described in previous work.13

EDOT–NH2 (0.70 g, 4.45 mmol), 4-carboxy-3-fluorobenzene-boronic acid (0.83 g, 4.45 mmol), and DMT-MM (1.35 g,4.90 mmol) were dissolved in methanol (50 ml) and placed ina 100 ml eggplant flask and the mixture was continuouslystirred for 1.5 h at 30 1C. After removing methanol, the residuewas purified by column chromatography using silica gel(200–400 mesh) and eluting with dichloromethane/methanol (15/1, v/v), to give a white solid product of (4-(((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methyl)carbamoyl)-3-fluorophenyl)boronic

Table 1 Detection of glucose in human serum using poly(EDOT–FPBA)/GCE

Test no. Added (mM) Found (mM) Recovery (%)

1 2.5 2.58 103.22 5.0 4.82 963 10.0 9.73 97.3

Research Article Materials Chemistry Frontiers

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021 Mater. Chem. Front.

acid (EDOT–FPBA) (yield 68.6%). 1H NMR (500 MHz, D2O) d 7.35(t, J = 7.5 Hz, 1H), 7.35 (t, J = 7.5 Hz, 1H), 7.22 (d, J = 7.6 Hz, 1H),7.22 (d, J = 7.6 Hz, 1H), 7.11 (d, J = 12.7 Hz, 1H), 7.11 (d, J =12.7 Hz, 1H), 6.24 (s, 2H), 6.24 (s, 2H), 4.25–4.16 (m, 1H),4.08 (dd, J = 11.9, 2.1 Hz, 1H), 3.85 (dd, J = 12.0, 6.7 Hz, 1H),3.49 (d, J = 5.7 Hz, 2H), 3.16 (s, 2H). Theoretical m/zfor C14H14BFNO5S+ (M + H+) at 338.07, experimentally foundat 338.26.

4.4 Preparation of poly(EDOT–FPBA) films

A glassy carbon electrode (GCE) of 3 mm in diameter (SansheIndustrial Co. Shanghai, China) was used as a workingelectrode. Before electropolymerization of the film, bare GCEswere polished using 0.05 mm alumina slurries then washed withultrapure water. To find the optimized electropolymerizationconditions, we prepared poly(EDOT–FPBA) films at differentconditions. First we chose different solvents to dissolve theEDOT–FPBA monomer, (i) 10 mM EDOT–FPBA monomer and100 mM tetrabutylammonium perchlorate in dichloromethane,and in (ii) acetonitrile, and (iii) 10 mM EDOT–FPBA monomerand 100 mM sodium perchlorate in water. Then, take 1 ml ofthe mixed solution in a glass cell, and then introduce the threeelectrodes (a glassy carbon working electrode, a platinum platecounter electrode, and an Ag/AgCl electrode) which connectedto the potentiostat in the cell. The electropolymerization wasperformed at a constant potential of 1.5 V (vs. Ag/AgCl) for10 seconds at room temperature. Second, we chose differentelectropolymerization times. 10 mM EDOT–FPBA monomerand 100 mM tetrabutylammonium perchlorate were electro-polymerized in dichloromethane at room temperature for 10,20, and 30 seconds at 1.5 V (vs. Ag/AgCl) constant potential.Third, we chose different electropolymerization temperatures.10 mM EDOT–FPBA monomer and 100 mM tetrabutyl-ammonium perchlorate were electropolymerized in dichloro-methane at 0 1C and 25 1C for 10 seconds, at 1.5 V (vs. Ag/AgCl)constant potential.

4.5 General characterization

EIS measurements were performed in a solution of 5 mMK3Fe(CN)6/K4Fe(CN)6 + 1 � DPBS, under an AC amplitude of50 mV superimposed on a DC bias of +0.2 V and a frequencyrange of 0.1 Hz to 10 kHz. Three electrodes consisting ofa polythiophene deposited working electrode, an Ag/AgCl(in 3.3 M KCl) reference electrode, and a platinum plate counterelectrode were used. The surface observations of the electrodepos-ited films were performed by SEM at an accelerating potential of5.0 kV and a working distance of 8 mm. The polythiophenederivative films were prepared on a flat gold-sputtered siliconelectrode by an electrodeposition process and treated with a Ptcoater for 30 s before SEM observations. The micro-and nano-structures of the polythiophene films were studied by the tappingmode imaging technique AFM with the following parameters:setpoint: 668 mV, drive amplitude: 33.5 mV, integral gain: 5.47.The samples were prepared by electrodeposition of polymers onto agold electrode. An XPS spectrometer equipped with a Al Ka

radiation source (1486.6 eV) was used. The takeoff angle of thephotoelectron analyzer was 901.

4.6 Glucose sensing in PBS

Glucose in the range from 0.05 to 25 mM in 1 � DPBS (pH 7.0)was measured by EIS in the presence of 5 mM K3Fe(CN)6/K4Fe(CN)6 at room temperature. A multi-channel potentiostatwith a three electrodes cell was used. The glassy carbonelectrode deposited by polythiophene was used as the workingelectrode, a platinum plate as the counter electrode, and Ag/AgCl (in 3.3 M KCl) as the reference electrode. Rct is determinedby fitting the Randles equivalent circuit to the Nyquist diagram.The mean and standard deviation were obtained from threeindependent tests.

4.7 Glucose detection in serum samples

Blood samples were provided by the Affiliated Hospital of InnerMongolia University with the approval of the school ethicscommittee. Blood samples were pretreated before use. Thesamples were centrifuged at 5000 rpm for 20 minutes, thenfiltered with a 0.22 membrane, and the supernatant was usedfor the subsequent tests. In the EIS recovery test, the collectedserum samples were diluted 100 times using PBS buffer, andthen glucose was added to obtain the final concentration. Therecoveries were calculated from three concentrations of glucosespiked human serum samples.

Conflicts of interest

There are no conflicts to declare.

References

1 R. Williams, S. Karuranga, B. Malanda, P. Saeedi, A. Basit,S. Besancon, C. Bommer, A. Esteghamati, K. Ogurtsova,P. Zhang and S. Colagiuri, Global and regional estimatesand projections of diabetes-related health expenditure:Results from the International Diabetes Federation Dia-betes Atlas, 9th edn, Diabetes Res. Clin. Pract., 2020,162, 108072.

2 E. Sehit and Z. Altintas, Significance of nanomaterials inelectrochemical glucose sensors: An updated review (2016-2020), Biosens. Bioelectron., 2020, 159, 112165.

3 M. Wei, Y. Qiao, H. Zhao, J. Liang, T. Li, Y. Luo, S. Lu, X. Shi,W. Lu and X. Sun, Electrochemical non-enzymatic glucosesensors: recent progress and perspectives, Chem. Commun.,2020, 56, 14553–14569.

4 M. J. Donahue, A. Sanchez-Sanchez, S. Inal, J. Qu,R. M. Owens, D. Mecerreyes, G. G. Malliaras andD. C. Martin, Tailoring PEDOT properties for applicationsin bioelectronics, Mater. Sci. Eng., R, 2020, 140, 100546.

5 D. Mantione, I. Del Agua, A. Sanchez-Sanchez andD. Mecerreyes, Poly(3,4-ethylenedioxythiophene) (PEDOT)Derivatives: Innovative Conductive Polymers for Bioelectro-nics, Polymers, 2017, 9, 354.

Materials Chemistry Frontiers Research Article

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

Mater. Chem. Front. This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021

6 Y. Hui, C. Bian, S. H. Xia, J. H. Tong and J. F. Wang,Synthesis and electrochemical sensing application ofpoly(3,4-ethylenedioxythiophene)-based materials: A review,Anal. Chim. Acta, 2018, 1022, 1–19.

7 M. N. Gueye, A. Carella, J. Faure-Vincent, R. Demadrille andJ. P. Simonato, Progress in understanding structure andtransport properties of PEDOT-based materials: A criticalreview, Prog. Mater. Sci., 2020, 108, 100616.

8 H. C. Ko, S.-a. Park and H. Lee, Characteristics of dual-typeelectrochromic device based on poly(3-tetradecylthiophene)and poly(3,4-ethylenedioxythiophene), Synth. Met., 2004,143, 31–35.

9 K. Parashar, D. Prajapati, R. McIntyre and B. Kandasubramanian,Advancements in Biological Neural Interfaces Using ConductingPolymers: A Review, J. Ind. Eng. Chem., 2020, 59, 9707–9718.

10 T. Araki, L. M. Bongartz, T. Kaiju, A. Takemoto, S. Tsuruta,T. Uemura and T. Sekitani, Flexible neural interfaces forbrain implants-the pursuit of thinness and high density,Flexible Printed Electron., 2020, 5, 043002.

11 R. Balint, N. J. Cassidy and S. H. Cartmell, Conductivepolymers: Towards a smart biomaterial for tissue engineer-ing, Acta Biomater., 2014, 10, 2341–2353.

12 T. Jarosz, A. Stolarczyk and C. Glosz, Recent Advances in theElectrochemical Synthesis of Copolymers Bearing pi-Conjugated Systems and Methods for the Identification oftheir Structure, Curr. Org. Chem., 2020, 24, 339–353.

13 W. F. Hai, T. Goda, H. Takeuchi, S. Yamaoka, Y. Horiguchi,A. Matsumoto and Y. Miyahara, Specific recognition ofhuman influenza virus with PEDOT bearing salic acid-terminated trisaccharides, ACS Appl. Mater. Interfaces,2017, 9, 14162–14170.

14 T. Galan, B. Prieto-Simon, M. Alvira, R. Eritja, G. Gotz,P. Bauerle and J. Samitier, Label-free electrochemical DNAsensor using ‘‘click’’-functionalized PEDOT electrodes, Bio-sens. Bioelectron., 2015, 74, 751–756.

15 T. Goda, M. Toya, A. Matsumoto and Y. Miyahara, Poly(3,4-ethylenedioxythiophene) Bearing PhosphorylcholineGroups for Metal-Free, Antibody-Free, and Low-ImpedanceBiosensors Specific for C-Reactive Protein, ACS Appl. Mater.Interfaces, 2015, 7, 27440–27448.

16 W. F. Hai, S. H. Pu, X. Wang, L. M. Bao, N. Han, L. M. Duan,J. H. Liu, T. Goda and W. M. Wu, Poly(3,4-ethylenedioxythiophene) Bearing Pyridylboronic Acid Group forSpecific Recognition of Sialic Acid, Langmuir, 2020, 36, 546–553.

17 P.-C. Huang, M.-Y. Shen, H.-h. Yu, S.-C. Wei and S.-C. Luo,Surface Engineering of Phenylboronic Acid-FunctionalizedPoly(3,4-ethylenedioxythiophene) for Fast Responsive andSensitive Glucose Monitoring, ACS Appl. Bio Mater., 2018, 1,160–167.

18 D. W. Hwang, S. Lee, M. Seo and T. D. Chung, Recentadvances in electrochemical non-enzymatic glucose sensors- A review, Anal. Chim. Acta, 2018, 1033, 1–34.

19 E. Witkowska Nery, M. Kundys, P. S. Jelen and M. Jonsson-Niedziolka, Electrochemical Glucose Sensing: IsThere Still Room for Improvement?, Anal. Chem., 2016, 88,11271–11282.

20 L. Fang, B. Liu, L. Liu, Y. Li, K. Huang and Q. Zhang, Directelectrochemistry of glucose oxidase immobilized on Aunanoparticles-functionalized 3D hierarchically ZnO nanos-tructures and its application to bioelectrochemical glucosesensor, Sens. Actuators, B, 2016, 222, 1096–1102.

21 Y. Song, M. Xu, C. Gong, Y. Shen, L. Wang, Y. Xie andL. Wang, Ratiometric electrochemical glucose biosensorbased on GOD/AuNPs/Cu-BTC MOFs/macroporouscarbon integrated electrode, Sens. Actuators, B, 2018, 257,792–799.

22 J.-M. Jeong, M. Yang, D. S. Kim, T. J. Lee, B. G. Choi andD. H. Kim, High performance electrochemical glucosesensor based on three-dimensional MoS2/graphene aerogel,J. Colloid Interface Sci., 2017, 506, 379–385.

23 H. Al-Sagur, S. Komathi, M. A. Khan, A. G. Gurek andA. Hassan, A novel glucose sensor using lutetium phthalo-cyanine as redox mediator in reduced graphene oxide con-ducting polymer multifunctional hydrogel, Biosens.Bioelectron., 2017, 92, 638–645.

24 F. N. Comba, M. R. Romero, F. S. Garay and A. M. Baruzzi,Mucin and carbon nanotube-based biosensor for detectionof glucose in human plasma, Anal. Biochem., 2018, 550,34–40.

25 Z. Pu, R. Wang, J. Wu, H. Yu, K. Xu and D. Li, A flexibleelectrochemical glucose sensor with composite nanostruc-tured surface of the working electrode, Sens. Actuators, B,2016, 230, 801–809.

26 A. Matsumoto, H. Matsumoto, Y. Maeda and Y. Miyahara,Simple and robust strategy for potentiometric detection ofglucose using fluorinated phenylboronic acid self-assembled monolayer, Biochim. Biophys. Acta, Gen. Subj.,1830, 2013, 4359–4364.

27 A. Matsumoto and Y. Miyahara, ‘Borono-lectin’ based engi-neering as a versatile platform for biomedical applications,Sci. Technol. Adv. Mater., 2018, 19, 18–30.

28 W. Zhai, X. Sun, T. D. James and J. S. Fossey, Boronic Acid-Based Carbohydrate Sensing, Chem. – Asian J., 2015, 10,1836–1848.

29 X. Sun and T. D. James, Glucose Sensing in SupramolecularChemistry, Chem. Rev., 2015, 115, 8001–8037.

30 R. Nishiyabu, Y. Kubo, T. D. James and J. S. Fossey, Boronicacid building blocks: tools for sensing and separation,Chem. Commun., 2011, 47, 1106–1123.

31 Y. J. Zhang, Y. Guan and S. Q. Zhou, Synthesis and volumephase transitions of glucose-sensitive microgels, Biomacro-molecules, 2006, 7, 3196–3201.

32 Y. Shiomi, M. Saisho, K. Tsukagoshi and S. Shinkai, Specificcomplexation of glucose with a diphenylmethane-3,3 0-diboronic acid derivative: correlation between the absoluteconfiguration of mono- and di-saccharides and the circulardichroic activity of the complex, J. Chem. Soc., Perkin Trans.1, 1993, 2111–2117.

33 M. Takeuchi, T. Mizuno, S. Shinkai, S. Shirakami andT. Itoh, Chirality sensing of saccharides using a boronicacid-appended chiral ferrocene derivative, Tetrahedron:Asymmetry, 2000, 11, 3311–3322.

Research Article Materials Chemistry Frontiers

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online

This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2021 Mater. Chem. Front.

34 P. J. Martins, M. Haas and S. Obici, Central nervous systemdelivery of the antipsychotic olanzapine induces hepaticinsulin resistance, Diabetes, 2010, 59, 2418–2425.

35 F. de Vegt, J. M. Dekker, H. G. Ruhe, C. D. A. Stehouwer, G. Nijpels,L. M. Bouter and R. J. Heine, Hyperglycaemia is associated with

all-cause and cardiovascular mortality in the Hoorn population:the Hoorn Study, Diabetologia, 1999, 42, 926–931.

36 T. Goda and Y. Miyahara, Electrodeposition of ZwitterionicPEDOT Films for Conducting and Antifouling Surfaces,Langmuir, 2019, 35, 1126–1133.

Materials Chemistry Frontiers Research Article

Publ

ishe

d on

23

Aug

ust 2

021.

Dow

nloa

ded

by T

OY

O U

NIV

ER

SIT

Y o

n 9/

15/2

021

2:50

:10

AM

. View Article Online