In2S3 photoanode

Journal Pre-proof A self-powered photoelectrochemical cathodic aptasensor for the detection of 17βestradiol based on FeOOH/In2S3 photoanode Yuewen Li, Lei Liu, Jinhui Feng, Xiang Ren, Yong Zhang, Tao Yan, Xuejing Liu, Qin Wei PII:

S0956-5663(20)30086-5

DOI:

https://doi.org/10.1016/j.bios.2020.112089

Reference:

BIOS 112089

To appear in:

Biosensors and Bioelectronics

Received Date: 6 October 2019 Revised Date:

7 February 2020

Accepted Date: 9 February 2020

Please cite this article as: Li, Y., Liu, L., Feng, J., Ren, X., Zhang, Y., Yan, T., Liu, X., Wei, Q., A self-powered photoelectrochemical cathodic aptasensor for the detection of 17β-estradiol based on FeOOH/In2S3 photoanode, Biosensors and Bioelectronics (2020), doi: https://doi.org/10.1016/ j.bios.2020.112089. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Credit Author Statement Yuewen Li: Conceptualization, data curation, writing original draft. Lei Liu: methodology, data curation, review & editing. Jinhui Feng: Methodology. Xiang Ren: Formal analysis. Yong Zhang: Funding acquisition, project administration. Tao Yan: Methodology, review & editing. Xuejing Liu: Formal analysis. Qin Wei: Funding acquisition, Formal analysis

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A self-powered photoelectrochemical cathodic aptasensor for the

2

detection of 17β-estradiol based on FeOOH/In2S3 photoanode

3

Yuewen Lia, Lei Liub, Jinhui Fengb, Xiang Renb, Yong Zhangb, Tao Yana,

4

Xuejing Liub*, Qin Weib*

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a

6

P.R. China

7

b

8

Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan

9

250022, China.

School of Water Conservancy and Environment, University of Jinan, Jinan 250022,

Key Laboratory of Interfacial Reaction & Sensing Analysis in Universities of

10 11 12 13 14 15 16 17

*: Corresponding author: Qin Wei

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Email address: [email protected]

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Tel: 053-82767872

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1 / 24

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Abstract

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In this work, a novel self-powered photoelectrochemical (PEC) aptasensor

24

integrated photoanode and photocathode for the accurate and selective detection of

25

17β-estradiol (E2) was proposed for the first time. FeOOH/In2S3 heterojunction was

26

built initially and used as a substitute for platinum (Pt) counter electrode. The

27

matched band gap edge of FeOOH and In2S3 facilitated the transfer of photo-generate

28

electrons to photoanode, while the holes left in the valence band of photocathode

29

(CuInS2) can be attracted by the electrons flowed from the photoanode, which

30

reduced the recombination of electron-hole pairs and promote the cathodic

31

photocurrent. Under optimal conditions, the constructed cathodic aptasensor of E2

32

presented linear scope in 10 fg/mL-1 µg/mL with detection limit of 3.65 fg/mL.

33

Besides, the cathodic aptasensor exhibited admiring selectivity, stability and

34

reproducibility. This work verified that the cathodic photocurrent response can be

35

regulated by the corresponding photoanode which provided a new design thought for

36

PEC aptasensor on the basis of p-type semiconductor.

37

Key words: photoelectrochemical; self-power; FeOOH/In2S3; cathodic aptasensor;

38

photoanode

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2 / 24

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1 Introduction

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17β-estradiol (E2) with strong estrogenic activity was a kind of endogenous

42

estrogen, which has a positive significance for human and animals in terms of their

43

development and sexual maturity. However, due to the drug abuse in livestock growth

44

promotion and human drug therapy (Cantiello et al. 2008; Notelovitz et al. 2000;

45

Torres et al. 2018), large amounts of E2 has been discharged into the environment.

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According to the research, E2 residues in environment could enrich in the human body

47

through food chain and cause the decrease or overexcitement of estrogenic activity,

48

hence increase the incidence rate of endocrine dysfunction, breast cancer and male

49

infertility (Gatel et al. 2019; Pu et al. 2019; Singh et al. 2019). Many international

50

organizations have paid attention to this environmental micropollutant. The

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Environmental Protection Agency (EPA) limits the maximum content of E2 to

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1.47 pM while the European Union (EU) sets limits of 0.4–0.9 ng/kg. Thus, the

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development of accurate and sensitive methods for analysis of E2 has a profound

54

meaning. So far, there are many integrated and mature methods towards E2 detection

55

with low detection limit that have been extensive applied, such as gas

56

chromatography-mass spectrometry (GC-MS) (Zhang and Zuo 2005), liquid

57

chromatography-mass spectrometry (LC-MS) (Kumar et al. 2012), enzyme-linked

58

immunosorbent assay (ELISA) (Ahirwar et al. 2019; Huang and Sedlak 2001),

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fluorescence method that utilizes competitive binding between specific targets and

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complementary strand (Zhang et al. 2018a), electrochemical method that based on

61

conducting polymer poly(3,4-ethylenedioxylthiophene) (Olowu et al. 2010). 3 / 24

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Nevertheless, technical complexity, time-consuming process and poor large

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instrument application are some main shackles of their further development (Wang et

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al. 2018).

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As an emerging technique that developed from electrochemical technology,

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photoelectrochemical (PEC) sensing, which excels in easy miniaturization and

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operation, separation of input optical signal and output electrical signal, low

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background signal, accurate recognition and quick response, now has become the

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darling of sensing fields (Feng et al. 2019; Feng et al. 2018a; Xu et al. 2018b). Typical

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PEC system usually composes of a reference electrode, a platinum (Pt) counter

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electrode and a working electrode that modified with photoactive material. When the

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electrodes are exposed to the light sources and contacted with electrolyte, the

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potential difference between electrode and electrolyte urges the carriers to move in a

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particular direction and generates photocurrent. When the analyte exists in the sample,

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signal alteration will be triggered through recognition unit and achieve the detection

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(Wu et al. 2016). The previous studies mostly focus on improving the properties of

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working electrode, however, the performance of counter electrode could influence the

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carriers transport indirectly as well, which has drawn little comments.

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Substrate materials with high photoelectric activity are noteworthy in PEC

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sensing. According to the majority carriers, the semiconductors are usually classified

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into two types: n-type and p-type (Zang et al. 2018). P-type semiconductors use holes

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as majority carriers, the electrons in conduction band are prone to transfer to the

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electrolyte and generate cathodic current. Metal oxides (NiO, CuO) and Cu-based 4 / 24

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chalcogenides (CuBi2O4, CuInS2) are some most common and popular p-type

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substrate materials with brilliant photoelectric properties. Among them, CuInS2 is a

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promising ternary semiconductor with a large optical absorption coefficient (α>105

87

cm−1) and high stability (Xu et al. 2018a). The narrow band (1.5 eV-1.9 eV) and

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variable morphology (nanoflower, quantum dot, nanosheet etc.) assign values to delve

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the application of CuInS2 in photocatalysis (Luo et al. 2018), solar cell (Yue et al.

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2018) and energy conversion fields (Lewerenz et al. 1986). Besides, the employment

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of p-type semiconductors for working electrode could avoid oxidation to analyte

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which caused by photo-generate holes and diminish the influence of reducing agent

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(Dai et al. 2017). Nevertheless, p-type semiconductors suffer the rapid recombination

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of carriers and insufficient photocurrent response which limit its application in

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photochemical analysis.

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As for n-type semiconductor, the electrode works in an opposite way (He et al.

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1999; Zhao et al. 2014). The electrons in conduction band serve as carriers and flow

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to the electrode while the holes are left in valence band. As the one of most stable iron

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oxy-compound that composing of environmentally friendly and earth-plentiful

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elements (Zhang et al. 2018b; Zhou et al. 2017), iron oxyhydroxide (FeOOH) has

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wide application prospect in PEC water splitting, energy storage and photocatalytic

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degradation fields (Chemelewski et al. 2014; Chen et al. 2016; Liu et al. 2018; Zhong

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et al. 2018). FeOOH with relatively narrow band gap (1.9-2.6 eV) (Zhou et al. 2017)

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is beneficial for light absorption, which makes it one potential photoactive

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semiconductor, however, FeOOH suffers weak charge carrier mobility and poor 5 / 24

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photoelectric conversion efficiency. Indium sulfide (In2S3), as monosulfide material

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with narrow band gap of 2.0-2.3 eV (Xing et al. 2008), has already been reported to

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achieve the performance as good as cadmium sulfide (CdS) and become a candidate

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for toxic CdS in many fields (Feng et al. 2018b; Gao et al. 2015) owing to its splendid

110

capacity

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Heterojunction built between FeOOH and In2S3 facilitates photo-induced electrons to

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transfer along the adjacent matching conduction gap and flow to the photoanode,

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which promotes the separation rate of electron-hole pairs and lifts the photocurrent

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response. The brand new designs that make full use of the advantages of n-type

115

semiconductor and p-type semiconductors are desperately need.

of

photoconductivity,

stability,

and

minor

secondary

pollution.

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In this paper, a self-power PEC aptasensor for detection of E2 that used

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photoanode (FeOOH/In2S3) and photocathode (CuInS2) simultaneously to promote the

118

generated cathodic photocurrent was explored. Under light illumination, the

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photo-induced electrons of photoanode transmitted to photocathode and attracted the

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holes on photocathode. The preponderance of this design realized in controllable

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promotion of cathodic photocurrent through regulating the substrate material modified

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on photoanode. In detail, as presented in Scheme 1, the FeOOH/In2S3 heterojunction

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with matched band gap position was employed as counter electrode. For photocathode,

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flower ball-like CuInS2 with large specific surface area which boosted its exposure to

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visible light was employed. Besides, large specific surface area of CuInS2 increased

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the basal area to fix aptamer, which could capture target E2 accurately, hence altered

127

the photocurrent response and achieved the detection. The experiments also verified 6 / 24

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that the aptasensor could operate without additional electron acceptor or external

129

potential, which was to say, self-powered.

130 131

Scheme 1 Self-powered photoelectrochemical cathodic aptasensor for the detection of E2

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2 Experimental section

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2.1 Reagents and Apparatus

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All reagents and apparatus mentioned in this paper were stated elaborately in

135

Supplementary Information. All reagents were used originally without further

136

treatment. Tris(hydroxymethyl)aminomethane (Tris-HCl) (0.1 M) with the pH value

137

of 7.4 was always employed as electrolyte buffer.

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2.2 Synthesis of In2S3

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A mature method was applied to synthesize In2S3 nanoparticles (Yang et al.

140

2013). In brief, 0.3 g of indium nitrate hydrate (In(NO3)3 4.5 H2O) was added into 80

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mL of deionized water and stirred to dissolve. Afterwards, 0.12 g of thioacetamide

142

(TAA) as sulfur source was dissolved in above solution and stirred for 30 min. The

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final mixed solution was transferred to 100 mL Teflon-lined autoclave and the

144

reaction was carried out at 120 °C for 12 h. The obtained orange-yellow product was 7 / 24

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recovered by centrifugal separation with mass ethanol, followed by drying in vacuum

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drying oven to get final nanomaterial.

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2.3 Synthesis of 3D flower-like FeOOH

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The 3D flower-like FeOOH was prepared according the previous report with

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little modification (Feng et al. 2019). 2.3 g of ferric sulfate hydrate (FeSO4 7H2O) and

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0.6 g of urea were ultrasonic dissolved in a 500 mL three necked flask containing 80

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mL of deionized water and 20 mL of ethyl alcohol. Then the flask was refluxed in oil

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bath at 90 °C for 6 h. After cooling to room temperature, the product was collected

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and washed with deionized water and ethanol for three times, respectively. Finally,

154

drying process was arranged.

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2.4 Synthesis of flower-ball like CuInS2

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0.12 g of cuprous chloride (CuCl2), 0.27 g of indium (III) chloride hydrate

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(InCl3), and 0.37 g of thiourea were introduced into 40 mL of ethanol and stirred to

158

dissolve, which was employed as Cu, In, S sources, respectively. The mixture reacted

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in tightly sealed Teflon-lined autoclave at 200 °C for 24 h. The obtained black

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precipitate was collected and washed with deionized water and ethanol for several

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times before drying in vacuum drying oven (Fan et al. 2016).

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2.5 Design of PEC aptasensor for E2 detection

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The aptasensor was constructed on 0.8 cm 2.5 cm ITO (indium-tin-oxide)

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slides. Before the formal establishment of the aptasensor, the ITO slides were cleaned

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in acetone, ethanol, and deionized water for 30 min successively, then dried in drying

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box. 8 / 24

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Firstly, for photoanode, 20 µL of FeOOH homogeneous suspension (4 mg/mL)

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was dropped onto ITO slides and dried at room temperature. Afterwards, 20 µL of

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In2S3 solution (8 mg/mL) was modified on photoanode and dried to form

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ITO/FeOOH/In2S3 electrode.

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Secondly, for cathodic aptasensor, 20 µL of CuInS2 (8 mg/mL) solution was

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dropped on ITO slides and dried in the air. The ITO slides were calcined in muffle

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furnace at 170 °C for 2 h, then cooled to room temperature to obtain ITO/CuInS2

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electrode. The electrode was then modified with 6 µL of 0.5% chitosan solution which

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contained 1% acetic acid and half dried in the air, then the electrodes were rinsed with

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deionized water (DI). Following, the cross-link reaction between amino groups of

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chitosan and aldehyde groups of glutaraldehyde was initiated by incubating the

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electrode with 6 µL of glutaraldehyde solution (2.5%). After being incubated for 1 h,

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the electrode was washed with DI and further incubated with 6 µL of amino-modified

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aptamer solution (2 µM) for 4 h in 4 °C refrigerator. Next, the electrode was washed

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to wipe off the aptamers that didn’t covalently immobilize on the electrode. 4 µL of

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6-Mercapto-1-hexanol (MCH) was added to impede non-specific binding and rinsed.

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Finally, 6 µL of E2 with different concentrations were introduced and incubated for 2

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h then washed with DI. The electrodes were stored at 4 °C until applied to detection.

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2.6 PEC Measurement and Performance

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The PEC

experiments

were

conducted

in

a three-electrode system:

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ITO/FeOOH/In2S3 photoanode as counter electrode instead of traditional Pt electrode,

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ITO/CuInS2 photocathode as working electrode and Ag/AgCl as reference electrode. 9 / 24

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The PEC performance was measured under 450 nm Xe lamp in 0.1 M Tris-HCl (pH

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7.4). The irradiation source illuminated on both photoanode and photocathode and the

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photocurrent-time plot was recorded under intermittent light (on/off every 20 s). The

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bias voltage was set to be 0 V.

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3 Results and Discussion

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3.1 Characterization of synthesized materials

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The structural morphology of as-prepared FeOOH was examined by scanning

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electron microscopy (SEM) attached with transmission electron microscope (TEM).

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As displayed in Fig. 1A, the self-assembled FeOOH appeared to be a definite shape of

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daisy composed of crowded nanorods. The diameter of the flower was measured to be

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3 µm which indicated a relatively large surface for light illumination. The TEM image

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in the inset of Fig. 1A verified the flower-like microstructure likewise of FeOOH. Fig.

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1B demonstrated the TEM image of In2S3 which exhibited irregular micro-flake

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shapes and most of them aggregated together. The electron diffraction (ED) pattern in

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Fig. 1C for a single In2S3 contained distinct concentric diffraction rings that can be

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attributed to (311), (400), (440) facts. The SEM image and energy dispersive

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spectroscopy (EDS) patterns of CuInS2 were depicted in Fig S1. The obtained CuInS2

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structure was flower-ball like nanosphere composed of nanosheets with certain

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thickness. The thickness of nanosheets building on naosphere was ~80 nm. The rough

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surface of CuInS2 guaranteed a large surface for aptamer immobilization. Fig S1D

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displayed the EDS pattern of CuInS2 which confirmed the successful formation of

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CuInS2 without any impurities. 10 / 24

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The crystalline phase of FeOOH, In2S3 and CuInS2 were analyzed by X-ray

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diffraction (XRD) and the results were shown in Fig. 1D. The significant diffraction

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peaks at 2θ of 21.22°, 33.24°, 34.70°, 36.65°, 39.98°, 41.19°, 54.21°, 59.02°, 61.38°,

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63.97C, 60.06° (curve a) indexed to the orthorhombic crystal phase of FeOOH

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(JCPDS no. 29-0713). The typical and sharp diffraction patterns of as-prepared

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CuInS2 at 2θ around 27.87°, 32.09°, 46.23°, 55.08°, 74.88° were speculated from

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(112), (004), (204), (312), (332) planes of tetragonal phase (JCPDS no.0159). The

218

characteristic diffraction peaks located at 2θ=27.53°, 33.39°, 43.78°, 47.91°, 56.82°

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corresponded to the (311), (400), (511), (440), (622) planes of In2S3, respectively,

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which was in accord with ED patterns. The synthesized semiconductor all had high

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purity without any impurity peaks and remarkable crystallinity.

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The fourier transform infrared spectrometer (FTIR) spectra was employed to

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analyze chemical bond and functional group of FeOOH in the range of 400-4000 cm-1

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and presented in Fig.1E. The stretching vibration of -OH was located at 3200 cm-1,

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while the bands at 890, 795 cm-1 were characteristic modes of Fe-OH functional

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group. The last two bands at 610 and 466 cm-1 were assigned to Fe-O bond. The peak

227

around 1641 cm-1 was ascribed to the water molecule absorbed on the material or

228

potassium bromide surface.

229

The UV-vis diffuse reflectance (DRS) spectra of FeOOH and FeOOH/In2S3 was

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exhibited in Fig. 1F. The absorption edge of FeOOH was at about 588 nm and after

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the modification of In2S3, the light absorption edge extended to 625 nm. Then, further

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than these, the band gap energy (Eg) together with conduction band edges of FeOOH 11 / 24

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and In2S3 were studied through reflectance spectroscopy and linear sweep

234

voltammetry (LSV) measurement, which were displayed in Fig. S2. The results

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showed that the Eg of FeOOH and In2S3 was computed to be 2.2 eV and 2.1 eV

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respectively. The FeOOH had the conduction band edge at 0.44 V and the conduction

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band potential of In2S3 was -0.63 V vs Ag/AgCl (saturated KCl). The conduction band

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edge of In2S3 was more negative than FeOOH which implied that there was a

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potential gradient to trigger the movement of excited electrons from conduction band

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of In2S3 to the conduction band of FeOOH and then transferred to the electrode,

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which increased the cathodic photocurrent indirectly.

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Fig.1 (A)SEM image of daisy-like FeOOH; inset of A was TEM image of FeOOH; (B) TEM

244 245

image of In2S3; (C) ED patterns of In2S3; (D) XRD patterns of FeOOH (a), CuInS2 (b), In2S3 (c); (E) FTIR spectra of FeOOH; (F) DRS spectra of FeOOH and FeOOH/In2S3

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3.2 Photoelectrochemical properties of photoanode

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For the proposed self-powered photoelectrochemical photoanode-assisted

248

cathodic aptasensor, whose photoanode and photocathode were both exposed to the

249

intermittent visible incident light irradiation, substrate materials with charming and

250

brilliant photo-electricity activity were indispensable. Fig. 2A illustrated the 12 / 24

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photo-induced current characterization of photoanodes with different modified layers

252

(Pt electrode as counter electrode). FeOOH and In2S3 electrode alone exhibited the

253

signal of 4 µA and 24 µA respectively (curve a and b) while the PEC response of

254

FeOOH/In2S3 combined electrode (curve c) appeared to be 1.36 times higher than

255

simply sum PEC photocurrent response intensity of FeOOH and In2S3 which

256

benefited from their matching cascade band-edge levels. Fig. 2B presented the

257

photo-generated current of cathodic system using FeOOH/In2S3 electrode as

258

photoanode and CuInS2 electrode as working electrode. The photocurrent intensity of

259

cathodic system increased with the promotion of anodic photocurrent. What a flash of

260

insight was that more holes on photocathode could be collected using FeOOH/In2S3

261

photoanode (curve d) when light shined on the substrate materials compared with Pt

262

electrode (curve c). The detailed mechanism was displayed in Scheme 2. Besides,

263

under continuous illumination of visible light, the photocurrent appeared to decline to

264

some extent which may be because that there was no extra electron acceptor or donor

265

but the dissolved oxygen was constantly consumed.

266

The optimal photocurrent response that the three-electrode system could furnish

267

has also been explored and stated in Supporting Information. Among these, the bias

268

potential had a noticeable impact on the supplied photocurrent (-0.1 V~0.1 V). The

269

results showed that the strongest photocurrent response was appeared at the bias

270

potential of 0 V (Fig. S3D). Furthermore, the higher the external electrical bias was,

271

the weaker the photocurrent was. One possible explanation was that larger anodic bias

272

would push the photo-induced electrons move towards the electrode rather than the 13 / 24

273

electrolyte which decreased the cathodic photocurrent. At the same time, cathodic bias,

274

which impeded electron delivery from counter electrode to working electrode,

275

consequently weakened the incidences of holes collection and decreased the cathodic

276

photocurrent. Above all, 0 V was set to be the bias potential. The designed cathodic

277

photoelectrochemical apsesor could work as self-powered mode.

278 279 280 281 282 283

Fig. 2 (A) Photoelectrochemical characterization of photoanode with different modified layer: (a) ITO/FeOOH, (b) ITO/In2S3, (c) ITO/FeOOH/In2S3 (Pt electrode as counter electrode); (B) Photocurrent response of photocathode (ITO/CuInS2) in different situation: (a) FeOOH as counter electrode, (b) Pt as counter electrode, (c) In2S3 as counter electrode, (d) FeOOH/In2S3 as counter electrode, conducted in 10 mL of 0.1 M Tris-HCl solution (pH=7.4)

284 285 286

Scheme 2 Electron transfer mechanism of photoanode and photocathode co-exist system

3.3 Photocurrent and EIS characterization of cathodic aptasensor

287

The photocurrent characterization was applied to verify the cathodic sensing

288

progress (Fig. 3A). The photocurrent of aptasensor significantly increased in virtue of

289

the modification of CuInS2. After modifying with chitosan, glutaraldehyde, aptamer

290

and MCH layer by layer, the PEC signal was decreased gradually and continuously 14 / 24

291

due to their comparative bad electrical conductivity. Then, the photocathode was

292

incubated with E2, a sharp decrease of cathodic current was emerged which originated

293

from the steric hindrance of E2.

294

Electrochemical impedance spectroscopy (EIS) was another powerful way to

295

supervise the interface layer of electrode in the construction process. The EIS test was

296

carried out in electrolyte solution containing 0.1 mol/L KCl and 2.5 mmol/L

297

Fe(CN)63-/4-. Every impedance spectrum consisted of a semicircle at higher

298

frequencies represented electron-transfer limited process and a linear part at lower

299

frequencies suggested the diffusion limited process. Commonly, the electron-transfer

300

resistance (Ret) could be judged and evaluated by the diameter of semicircle. As

301

shown in Fig. 3B, Ret value of bare ITO slide was quite small (curve a). After the

302

addition of CuInS2 miroflowers, the Ret increased slightly. When chitosan,

303

glutaraldehyde, aptamer and MCH were modified onto the electrode successively, the

304

semicircle diameters of their Nyquist plots were larger constantly due to the increased

305

obstruction of electron transfer. Finally, Ret reached the maximum when the electrode

306

was incubated with E2, which proved that the specific recognition has occurred

307

between aptamer and E2, hence increased the steric hindrance.

308 309 310

Fig. 3 (A) Photocurrent response (conducted in 10 mL of 0.1 M Tris-HCl solution (pH=7.4)) and (B) Nyquist diagrams (conducted in the electrolyte solution containing 0.1 mol/L KCl and 2.5 15 / 24

311 312

mmol/L Fe(CN)63-/4-) of (a) ITO, (b) ITO/CuInS2, (c) ITO/CuInS2/chitosan, (d) ITO/CuInS2/chitosan/glutaraldehyde, (e) ITO/CuInS2/chitosan/ glutaraldehyde/aptamer, (f)

313 314

ITO/CuInS2/chitosan/glutaraldehyde/aptamer/MCH, (g) ITO/CuInS2/chitosan/glutaraldehyde/ aptamer/MCH/E2 standard sample (1 ng/mL),

315

3.5 Cathodic aptasensor performance for detecting 17β-estradiol

316

The cathodic aptasensor was performed under the optimal conditions and

317

evaluated by monitoring the photocurrent under intermittent light. As displayed in Fig.

318

4A, the photocurrent reduced significantly with increased E2 concentration due to the

319

formation of aptamer-E2 complex which impeded the electron transfer. Further

320

calculation and analysis were presented in Fig. 4B, logarithmic function was selected

321

to operate with E2 concentration and employed as abscissa. After a series of

322

computations, there was a good linear relation between I and E2 concentration in the

323

range of 10 fg/mL-1 µg/mL, and the regression equation was I=-1.2+0.31lgc (ng/mL)

324

with the correlation coefficient of 0.994, c represented the concentration of E2. The

325

limitation of detection (LOD, S/N=3) was deduced to be 3.65 fg/mL. The detection

326

result proved that the prepared aptasensor had excellent property and even performed

327

better than those of many reported sensors (Fig. S1), which contributed to the

328

cooperation of photoanode and photocathode.

16 / 24

329 330 331 332

Fig. 4 (A) Photocurrent and (B) calibration curve of cathodic aptasensor at different E2 concentration (10 fg/mL-1 µg/mL); (C) stability and (D) reproducibility of constructed PEC aptasensor (E2=1 ng/mL). Error bars were estimated from three replicate measurements.

333

3.6 Reproducibility, stability and selectivity of the PEC aptasensor

334

Stability was evaluated through looping over on-and-off switch light for 15 times

335

in 620 s. The concentration of E2 was 1 ng/mL and the bias voltage always maintained

336

at 0 V. As presented in Fig. 4C, there was no significant change in the intensity of

337

photocurrent under the constant and continuous light irradiation which indicated the

338

splendid stability of aptasensor.

339

Reproducibility was one valid tool to inspect the precision of the self-powered

340

PEC aptasensor. In this system, the reproducibility was assessed with relative standard

341

deviation (RSD) of six electrodes incubated in parallel (The concentration of E2 was 1

342

ng/mL) and the results were displayed in Fig. 4D. The relative standard deviation

343

(RSD) was assessed to be 0.8%.

344

Selectivity was an indispensable property for sensors to adapt to complex water

345

samples. In order to verify the specific capture of E2, other estrogens such as

346

diethylstilbestrol (DES), estriol (E3), progesterone (P4) was introduced in the test 17 / 24

347

(Nameghi et al. 2019). Besides, other pollutants such as humic acids and salt, that

348

exist in the actual water body were taken into consideration as well (Liu et al. 2019a;

349

Liu et al. 2019b; Ma et al. 2017). As shown in Fig. S4, the aptasensor only responded

350

to E2 and the interferents had no obvious influence on the detection which indicated

351

that the aptasensor was almost unaffected by the interferents coexist in the sample

352

owed to the specific recognition region between aptamer and E2.

353

3.7 Practical application in real sample

354

For practical application, the self-powered cathodic aptasensor was incubated

355

with tap water and lake water respectively. Standard addition method was chosen to

356

evaluate the practicability and applicability of constructed aptasensor. The results

357

were displayed in Table S2, the recoveries were in the range of 96.4%-100.9% while

358

the relative standard deviations (RSD) were 1.44%-6.81%. Above all, the as-prepared

359

aptasensor showed well-pleasing practicality and feasibility.

360

4 Conclusion

361

In conclusion, we successfully prepared

an impressive, self-powered

362

photoelectrochemical cathodic aptasensor for E2 detection. This was the first time that

363

FeOOH/In2S3 heterojunction, which could expand the light adsorption range and

364

promote photocurrent response, was formed and employed as photoanode. The

365

photo-generated electrons of photoanode flowed along the external circuit, attracted

366

the photo-induced holes of photocathode (CuInS2), which expedited carriers transfer

367

rate and elevated cathodic current response. After modifying with aptamer, E2 could

368

be specifically captured on photocathode and realized the detection. The constructed 18 / 24

369

aptasensor showed wide linear range of 10 fg/mL-1 µg/mL while the detection limit

370

was 3.65 fg/mL. Furthermore, the as-prepared aptasensor exhibited favorable stability

371

and satisfying specificity. All these results suggested that the self-powered

372

photoelectrochemical cathodic aptasensor has strong potential for application and

373

deserved further investigating.

374

19 / 24

375

Acknowledgments

376

This work was supported by the National Key Scientific Instrument and

377

Equipment Development Projects of China (No. 21627809, 21505051), and the

378

National Natural Science Foundation of China (No. 21575050), and QW thanks the

379

Special Foundation for Taishan Scholar Professorship of Shandong Province (No.

380

ts20130937) and UJN.

381

20 / 24

382

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Highlights A novel self-powered photoelectrochemical (PEC) cathodic aptasensor for the detection of 17β-estradiol (E2) was constructed.

FeOOH/In2S3 heterojunction was built for the first time and employed as photoanode.

The electrons generated on photoanode flowed to photocathode (CuInS2) and accelerated the transfer of photo-generated holes on photocathode.

The aptasensor exhibited the low detection limit of 3.65 fg mL-1.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: