Biomolecule-Free, Selective Detection of o-Diphenol and Its

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Biomolecule-free, selective detection of o-diphenol and its deriva-tives with WS2/TiO2-based photoelectrochemical platform Weiguang Ma, Lingnan Wang, Nan Zhang, Dongxue Han, XianDui Dong, and Li Niu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b00315 • Publication Date (Web): 06 Apr 2015 Downloaded from http://pubs.acs.org on April 14, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

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

Page 1 of 8

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

Analytical Chemistry

Biomolecule-free, selective detection of o-diphenol and its derivatives with WS2/TiO2-based photoelectrochemical platform Weiguang Ma †,‡, Lingnan Wang †,‡, Nan Zhang †,‡, Dongxue Han* †, Xiandui Dong † and Li Niu* † †State Key Laboratory of Electroanalytical Chemistry, c/o Engineering Laboratory for Modern Analytical Techniques, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, Jilin, China， ‡University of Chinese Academy of Sciences, Beijing 100039, China ABSTRACT: Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. Firstly, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid and catechin were also detected by employing this proposed photoelectrochemical sensor; Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: i) chelate effect of adjacent double oxygen atoms in the o-diphenol with Ti (IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make photo-generated electron and hole easily separated, and results in great improvement of sensitivity. By employing such photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient and cost effective advantages, as well as low detection limit (e.g. 0.32 µmol·L-1 for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields.

INTRODUCTION Photoelectrochemical sensor presents the advantages of both optical and electrochemical strategies such as easy-to-operate, rapidly response, low cost etc., which have been widely attracted for the interesting of researchers1-4. The mechanism of photoelectrochemical sensor is based on reductive property of photoelectron or oxidative capacity of photo-generated hole. Based on this principle, in recent years we have reported two photoelectrochemical platforms, which were designed and applied to assay antioxidant capacity in our group5,6. In these platforms, the photo-generated hole can simultaneously oxidize all the antioxidants and thus achieve the determination of global antioxidant capacity in the analyte systems. Yet, it is still a great challenge for photoelectrochemical sensors to discriminate individual species without any auxiliary. In order to achieve the accurate selection of photoelectrochemical sensors, certain of biomolecules, such as DNA7-10, cells11,12, enzyme3, antibody13,14 etc., were always introduced as ancillary means. Although it presents excellent selectivity with the help of these biological guides, the complex design process, harsh storage conditions and expensive cost substantially limit its practical applications. Therefore, it is of great significance to implement selective detections with biomolecule-free photoelectrochemical sensors. O-diphenol and its derivatives, which exist in a wide range of foods, show strong antioxidant capacity15,16 and make great sense to human health. According to previous reports, these molecules as well as their derivative species were conventionally detected via optical17-21, electrochemical22-25 and chroma-

tographic approaches26-28. Yet, the results of optical way were often overestimated due to the interference of coexisted sugars29. Upon the electrochemical method, for example, the modified electrodes were popularly used, however they always tend to be fouled and the stability and durability are difficult to be assured. In addition, the expensive instrument and complex operation are still the biggest restriction for chromatographic analysis. In the present work, we developed a novel biomolecule-free photoelectrochemical platform for accurate discrimination of o-diphenol and its derivatives. It is well known that the performance of photoelectrochemical sensing is largely determined by the optoelectronic materials. TiO2 with poison-free, stability and high electronic mobility was widely used to be photocatalyst in hydrogen evolution, environmental purification and solar cell etc30. Yet, the wide bandgap of TiO2 limited their application, since it does not absorb visible light. As a member of transition-metal dichalcogenide (TMD), layered tungsten sulphide (WS2) exhibits excellent physical, electronic and optical prosperities (wide bandgap), which was therefore applied in solid state lubricants31, hydrogen evolution32, solar cells33, field-effect transistors (FETs)34 and biosensors35,36 Herein, thin layer tungsten sulphide/titanium dioxide (WS2/TiO2) nanocomposites were synthesized via a simple method and employed as optoelectronic materials in a novel photoelectrochemical platform. Such a biomolecule-free photoelectrochemical sensor demonstrated a series of advantages, such as rapid response, anti-fouling and high sensitivity in determination of o-diphenol and its derivatives. Meanwhile, the possible mechanism upon excellent selectivity and sensi-

ACS Paragon Plus Environment


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

tivity of this photoelectrochemical platform have been proposed and elaborately explored.

EXPERIMENTAL SECTION Chemical reagents. Titanium(IV) oxysulfate solution (15 wt. % in dilute sulfuric acid), Tungsten(IV) sulfide (powder, 2 µm, 99%), Caffeic acid (CA), Catechin hydrate (CT), Glucose and Sodium cholate hydrate were received from SigmaAldrich. Titanium trichloride, Zinc acetate dehydrate, Catechol (CC), Resorcinol (RC) and Hydroquinone (HQ) were obtained from Alfa. Dopamine hydrochloride (DA), Uric acid, L-proline, L-glycine, L-histidine, Ascorbic acid, L- tyrosine and L-threonine were purchased from Shanghai Ding Guo Biotechnology Co., Ltd. Dopamine hydrochloride Injection was got from Shanghai Harvest Pharmaceutical Co., Ltd. The human urine samples were obtained from volunteers in our lab, which were diluted 10 times with a 0.1 mol·L-1 PBS (pH 7.4) before assayed. Other reagents were used as received without purification. The PBS buffer was made from sodium phosphate (0.1 mol·L-1 NaH2PO4/ Na2HPO4, 81:19 (molar ratio)) and sodium chloride dissolved in deionized water at the final concentrations of 10 mmol·L-1 (pH: 7.4). Characterization. Transmission electron microscope (TEM) and high-resolution transmission electron microscope operating (HRTEM) images were obtained by a TECNAI G2 highresolution transmission electron microscope operating at 200 kV. Scanning electron microscope (SEM) images were recorded with a XL30 environmental scanning electron microscope (ESEM, Philips Electron Optics) with finite element model and 20 kV accelerating voltage. X-ray photoelectron spectroscopy (XPS) was recorded on an ESCALAB-MKⅡ250 photoelectron spectrometer with Al Kα X-ray radiation as the X-ray source for excitation. The UV-visible diffused reflectance spectra (DRS) were performed on the dry-pressed disk samples using a Hitachi U-3900 spectrophotometer equipped with an integrating sphere assembly, where BaSO4 was employed as the reference sample. All electrochemical experiments were performed with a CHI660A Electrochemical Workstation(CHI) using a conventional three-electrode system, comprising modified ITO as the working electrode, a platinum wire as the auxiliary electrode and a Ag/AgCl (3 mol·L-1 KCl) as reference electrode. All potentials were reported versus Ag/AgCl reference electrode at room temperature. The PBS solution was applied as supporting electrolyte and bubbled with N2 for 15min before each experiment. LED light (365nm, 420 nm, 470nm, 545nm, 645nm, 750nm. Beijing Perfectlight Technology) was used as light source of the photoelectrochemical platform. Peristaltic pump was purchased from longerpump (BT100-2J). Electrochemical impedance spectroscopy (EIS) measurements were performed on a Solartron 1255 B Frequency Response Analyzer (Solartron Inc.UK) in 0.1 mol·L-1 Na2SO4 with the irradiation of visible light. Preparation of WS2/TiO2 nanoparticles. The obtained thin layer WS2 solution was referenced by Ronan37 with some modifications. Typically, 0.5 g bulk WS2 and 0.075 g sodium cholate were dispersed in 50 mL deionized water with ultrasonic for 30 min by a probe sonicating (562.5 W). After 24 h settlement, the upper suspension was collected and centrifuged at 1500 r·min-1 for 90 min. Then the obtained transparent thin layer WS2 solution was collected and prepared for further use. The WS2/TiO2 composites were synthesized by using a hydro-

Page 2 of 8

thermal procedure. Typically, 0.75 mL titanium (IV) oxysulfate was added into 20 mL thin layer WS2 solution with constant stirring for 30 min. The mixed solution was then put into an autoclave and heated at 120 °C for 5 h. When cooled to room temperature, the reaction solution was centrifuged at 8000 r·min-1 for 10 min. Then, the separated precipitates were washed with water and ethanol for three times, dried at 70 °C, and calcined in nitrogen at 350 °C for 2 h with a heating rate of 2 K min-1. Finally, the obtained composites were treated with a cleaning process involving three cycles of centrifugation/ washing/ re-dispersion in water and dried at 70 °C in air. For the control experiment, the synthesis of pristine TiO2 was similar to that of WS2/TiO2, just without addition of thin layer WS2. Moreover, ultrathin graphitic carbon nitride (utg-C3N4) /ZnS and utg-C3N4/TiO2 composites were also fabricated for comparisons. utg-C3N4/ZnS was obtained with the following steps: 25 mg utg-C3N4 was mixed with 55.044 mg zinc acetate dehydrate in 50 ml DMF solvent, and then the mixed solution was heated to 180 °C and maintained for 12 h. The product was subjected to repeated washing with ethanol by centrifugation, and then with water. The final utg-C3N4/ZnS powder was obtained after drying the product at 55 °C. The utg-C3N4/TiO2 composites were got according to our previous method5. The process of assay with photoelectrochemical sensor. ITO electrode was first cleaned with NaOH (1 mol·L1 ) and H2O2 (30 %), washed with acetone and twice-distilled water, and dried at room temperature. Then 100 µL of the WS2/TiO2 suspension (1 mg·mL-1) was cast onto the ITO and dried at room temperature to obtain a WS2/TiO2-modified ITO electrode. Similarly, the utg-C3N4/TiO2, utg-C3N4/ZnS, WS2 and TiO2 modified ITO electrode were prepared. As shown in Figure S1, the process of detection is as following: After the modified ITO electrode was fastened on the photoelectrochemical flow cell, 5 ml PBS solution is injected the photoelectrochemical cell through Peristaltic pump (BT100-2J) at 2r·min-1, then turn on the light source (On 10s, off 30s, three times) and collected the blank data; Followed by 2 ml sample is injected the photoelectrochemical cell, other steps is similar with PBS solution. Note that 5ml PBS solution should be injected to wash the photoelectrochemical cell when change the

Figure 1. SEM image of bulk WS2 (a), TEM image of thin layer WS2 sheets (b), WS2/TiO2 nanocomposites (c) and HRTEM image of WS2/TiO2 nanocomposites (d). Inset: selected area electron diffraction of (d).


Page 3 of 8

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


Figure 2. The photocurrent responses of CC, HQ and RC on WS2/TiO2 (a), TiO2 (b) and WS2 (c) modified ITO electrode in 0.1 mol·L-1 pH 7.4 PBS with an applied potential of 0.0 V at light wavelength of 420 nm.

different sample. In order to effectively decrease the interference from colored sample solution 5, visible light irradiation from the backside of the working electrode was then performed (an illumination power on the work electrode of 73.89 mW·cm-2). Each sample was detected for three times and the average value was collected and recorded. The photocurrent engage principle in the detection of o-diphenol and its derivatives should follow such a rule: I = Ismpale – Iblank (Ismpale, the photocurrent with sample; Iblank, the photocurrent without analyte).

RESULTS AND DISCUSSION Characterization of WS2/TiO2 nanocomposites. WS2 is known for the layered structure with strong covalent bonding within each layer and weak Van der Waals forces among different WS2 sheets37. Therefore it is easily exfoliated with ultrasonic method into thin layer WS2 sheets. Figure 1a presents the SEM image of classic bulk WS2 material with the appearance of overlapping of several sheets. As shown in Figure 1b, TEM image displays that the obtained thin layer WS2 sheets material is only a few hundred nanometers in length, which seems much smaller than the bulk WS2 (Figure 1a). However, the thin layer structure endows WS2 higher specific surface area, which can greatly enhance the loading capacity of TiO2 nanoparticles. Figure 1c shows the typical TEM image of WS2/TiO2 sample at low magnification, which clearly displays a very uniform distribution of TiO2 nanoparticles throughout the thin layer of WS2 sheets. The diameters of the TiO2

Figure 3. Interference of detection of RC (a) and HQ (b) on WS2/TiO2-based photoelectrochemical platform in 0.1 µmol·L-1 pH 7.4 PBS with an applied potential of 0.0 V at light wavelength of 420 nm.

nanoparticles are calculated to be ca. 5 nm. Selected area electron diffraction (SAED) pattern of WS2/TiO2 reveals that the crystal lattice fringes observed in insert of Figure 1d originate from anatase TiO2, which presents high photocatalytic capacity38. XPS measurements were performed to probe the chemical composition of WS2/TiO2. As shown in Figure S2a, the exhibitions of W4f, S2p, Ti2p and O1s confirm the successful synthesis of WS2/TiO2 composites. DRS of TiO2 and WS2/TiO2 have been recorded in Figure S2b. As is seen clearly that compared to the pristine TiO2, the introducing of thin layer WS2 sheets induces the increased light absorption intensity to a large extent in visible light regions39,40. Therefore, compared with bare TiO2 material, WS2/TiO2 composites demonstrates preferable photoelectrochemical properties and show promising feasibility towards visible light utilization. Selective detection with WS2/TiO2 nanocomposites. CC was firstly chosen as a model for study due to its simple molecular structure and advisable photoelectrocatalytic behavior on the WS2/TiO2 based photoelectrochemical platform. As shown in Figure 2a (black), the WS2/TiO2-based photoelectrochemical platform shows a low photocurrent response

Figure 4. Effects of excitation wavelength (a) and applied potential (b) on photocurrent response of WS2/TiO2-modified ITO electrode in 0.1 µmol·L-1 pH 7.4 PBS containing 50 µmol·L-1 CC. Inset: enlarge image of (a) at short wavelength.



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

Page 4 of 8

Figure 5. Photocurrent responses of different concentration of CA (a), CC (b), CT (c) and DA (d) on WS2/TiO2-modified ITO electrode in 0.1 µmol·L-1 pH 7.4 PBS with an applied potential of 0.0 V at light wavelength of 420 nm. Inset: linear calibration curve.

(142.5 nA) in the analyte free PBS solution under 420 nm irradiation. After addition of 110 µmol·L-1 CC, the photocurrent dramati-cally increases to 1010.0 nA, which indicates an efficient performance of CC on such a photoelectrochemical platform. Yet, when 110 µmol·L-1 HQ was introduced into this system under the same condition, only a faint increase of photocurrent was observed (208.3 nA, Figure 2a, red). However, the photocurrent sharply increases to 1030.5 nA after adding the same concentration of CC again. Similar phenomenon was observed towards RC (shown in Figure 2a, blue). Thanks to the significant difference of the photocurrent responses to these isomers, such a WS2/TiO2-based photoelectrochemical platform should be applied as an efficient strategy for directly discriminate O-diphenol from meta and para structures. Meanwhile, the photocurrent responses of CC, HQ and RC on the photoelectrochemical platform designed by pristine TiO2 or WS2 were also investigated. It is revealed that on both of the two pristine materials based photoelectrochemical platform, these three isomers showed ambiguous distinctions (Figure 2b, c), which indicated that WS2/TiO2 nanocomposites devote remarkable performances for discrimination of CC from RC and HQ. In order to deeply study the selectivity of the WS2/TiO2based photoelectrochemical platform, different concentration of RC and HQ were performed and investigated. As shown in Figure 3a, while even 5.50 mmol·L-1 of RC was added, only a little increase of the photocurrent is observed. Yet, when CC(110 µmol·L-1) was added to the system again, the photocurrent sharply increases, which indicated that even 50 times of RC could not interfere with the detection of CC. Upon interference of para isomer, the results showed that five times of HQ (550 µmol·L-1) could not interfere with the detection of CC (Figure 3b). Condition Optimization. The wavelength of irradiation and working potential were optimized for the WS2/TiO2-based photoelectrochemical platform. As shown in Figure 4a, with the applied potential at 0.0V, upon addition of 50 µmol·L-1

CC, the photocurrent increment decreases as the exciting wavelength increases from 365 to 750 nm. The highest photocurrent was observed under 365 nm irradiation due to the strong light absorption of both WS2 and TiO2 materials (Figure S2b)39,40. Based on this consideration, irradiation at 365nm has been particularly investitaged upon different applied potentials for photocatalysis of the three phenols on TiO2 and WS2/TiO2 composite (shown in Figure S3). Although the photocurrent responses at this wavelenth demonstrate preferable sensitivity, it will trigger new problems of serious interference due to coexisting species during actural sample examinations (eg. Glucose and ascorbic acid, Figure S4), which should be avoidable at weaker wavelenth irradiation. Meanwhile, in the UV region, the photo-generated holes of TiO2 show strong oxidative capability, which can oxidize the S2- in the thin WS2 sheets and subsequently lead to the photocorrosion of WS241. Therefore, 420 nm was chosen for detection of o-diphenol and its derivatives, which could simultaneously ensure the excellent sensitivity and stability of this photoelectrochemical sensor. Moreover, the working potential should be another key factor for photoelectrochemical sensor42. First, the influence of applied potential without light irradiation was evaluated on the bare ITO and WS2/TiO2 modified ITO electrode (Figure S5). The faint current (close to zero) was observed on both electrodes at all the applied potential, which indicate that the applied potential almost has no impact on the black current. Then, under 420nm irradiation, upon addition of 50 µmol·L-1 CC, the photocurrent increment sharply increases as the applied potential increased from -0.1 V to 0.0 V and trends to arrive at a maximum at 0.0 V, while from 0.0 V to 0.15 V almost no distinct change was found. As the applied potential improved to 0.2 V, the photocurrent is observed to increase again (Figure 4b). Yet, the photocurrent at 0.0 V was 66.1% of that at 0.2 V, which shows adequate sensitivity for the photoelectrochemical detection of CC. to be convenient to design two electrode system for photoelectrochemical antioxidant instrument, the details of design two electrode photoelectrochemical system will be systematic elaborated in our future work. 0.0 V


Page 5 of 8

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


was chosen for the photoelectrochemical sensing of the odiphenol and its derivatives in the following experiments. Detection of o-phenols and its derivatives. Under optimized conditions, the relationship between photocurrent and concentrations of four kinds of o-phenols and its derivatives, caffeic acid (CA), catechol (CC), catechin hydrate (CT) and dopamine (DA) are investigated and the results are shown in Figure 5. It reveals that the photocurrent vs. time curve of WS2/TiO2-based photoelectrochemical platform clearly illustrates the rapid response to these four species at the applied potential of 0.0 V. The linear concentration ranges are calculated to be 19.96~291.26 and 566.04~2000.00 µmol·L-1 for CA, 2.49~24.63 and 61.12~235.84 µmol·L-1 for CC, 12.47~193.10 and 370.37~1000.00 µmol·L-1 for CT, 0.99~48.78 and 72.29~333.33 µmol·L-1 for DA, respectively. Their relative standard deviation (RSD, %) are 3.1 %, 5.6 %, 4.6 % and 3.8 % respectively. The detection limit are estimated to be 6.65 µmol·L-1, 0.72 µmol·L-1, 4.21 µmol·L-1 and 0.32 µmol·L-1, respectively. Obviously, the proposed WS2/TiO2based photoelectrochemical platform shows promised application in the monitoring of o-diphenol and its derivatives with advantages of wide concentration range, desirable detection limit and prompt detection time. Stability and interference. Since the stability is the key point for sensor, the operation stability as well as the longterm stability of such photochemical sensor has been studied. Commonly, poisoning of the photocatalyst from the production of analyte5 and the photocorrosion of optoelectronic materials41 are the two main factors that affect the stability of photoelectrohemical sensors. In our system, a particularly designed flow cell was employed, which can successfully avoid the fouling of the electrode. In addition, WS2/TiO2 was selected as the appreciated optoelectronic material in this work and no photocorrosion was found even for a long duration photocurrent monitoring. As shown in Figure S6, the photocurrent of DA keeps 98.11% of the initial value even after more than 2000 s scanning, which indicated that the present sensor demonstrates excellent operation stability. It is also studied that, even after keeping for one month in desiccator under room temperature without light, such a photoelectrochemical sensor could still remain at least 91.3% of the initial detection signals, which indicated that this photoelectrochemical platform can be reused with advisable stability and reproducibility. Moreover, some kinds of possible interference species commonly found in the detection solution containing 110 µmol·L-1 DA have been investigated. 1000 times of Na+, K+, Ca2+, Mg2+, Zn2+, Ni2+, Cl-, NO3-, ClO4-, CO32-, SO42-, PO43-, 500 times of L-proline, L-glycine, L-histidine, ethanol, methanol, L-threonine, fructose, glucose, 100 times of uric acid, 50 times of L- tyrosine and 20 times of ascorbic acid were investigated. The test results disclosed that these species at proposed concentrations did not lead to distinct interference with the detection of DA on this WS2/TiO2-based photoelectrochemical platform (shown in Figure S7). Table 1. Results of Analysis of DA in Real Samples Sample

Added (µmol·L-1)

Found (µmol·L-1)

Recovery (%)

RSD (%) (n=3)

Urine 1

1.50

1.535

102.3

3.6

Urine 2

1.50

1.486

99.1

4.5

Urine 3

1.50

1.578

105.2

4.3

Figure 6. The CV of 0.5 mmol·L-1 HQ, CC and RC on the glassy carbon electrode in 0.1 µmol·L-1 pH 7.4 PBS (a), The photocurrent of CC, HQ and RC on utg-C3N4/TiO2 (b) and utg-C3N4/ZnS (c) modified ITO electrode in 0.1 µmol·L-1 pH 7.4 PBS with an applied potential of 0.0 V at light wavelength of 420 nm, EIS plot of TiO2 and WS2/TiO2-modified ITO electrode in 0.1 mol·L-1 Na2SO4 with an excitation light of 420 nm (d).

Detection of practical sample. Due to the role of catecholamines of o-diphenol derivatives in neurochemistry, their qualitative and quantitative assays are of clinical and biochemical importance43,44. Many neurological diseases, such as Pakinson’s disease, Huntington’s disease, Tourette syndrome and Psychosis etc. are considered to connect with the abnormal level of dopamine (DA)45. Here, two brands of clinical drugs DA hydrochloride Injections and three human urine samples were detected with WS2/TiO2-based photoelectrochemical platform. The test results of DA hydrochloride Injections are 0.0532, and 0.0536 mol·L-1, which are well agreed with the brand marked concentration (0.0527mol·L-1). Concerned to the human urine samples, the corresponding DA detection results are shown in Table 1. The average recoveries ranged was considered from 99.1 % to 105.2%. The performance of practical investigations shows excellent applications of the present photoelectrochemical platform for the detection of DA. Discussion of the mechanism. A kind of molecules with proper redox property will be reduced with photoelectrons or oxidized by the photo-generated holes in a photoelectrochemical platform. Conventionally, the photo-generated holes will react with species with lower redox potential in priority. However, it is very hard to discriminate the analyte with similar redox potentials via the photoelectrochemical sensor without any assistant. As shown in Figure 6a, the redox potential of HQ is 0.074 mV, which is lower than that of CC (0.171 mV). Normally, HQ should be first oxidized by the holes. However, an abnormal circumstance was observed that CC reacted in priority, which is presented in Figure 2a. Such an interesting phenomenon is so amazing, which attract us to investigate the corresponding mechanism in advance. As mentioned above according to Figure 2c, all CC, RC and HQ present low photocurrents on the pristine WS2 photocatalyst, and it is hard to discriminate CC from HQ and RC. Yet, although the low photocurrents of CC, HQ and RC were observed on the TiO2 based photoelectrochemical platform, CC still shows stronger photocurrent than that of HQ and RC (Figure 2b). In order to better elaborate this phenomenon, three optoelectronic materi-



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

als modified electrodes were irradiated at the 365 nm. Similar strong photocurrent and excellent selectivity were obtained upon TiO2 and WS2/TiO2 modified electrode (Figure S8). This discloses that TiO2 component plays the significant role in selective determination of CC. Recent research showed that both oxygen atoms of the CC species will bind with the Ti (IV) surface site to form a chelate structure with a five/sixatom ring, which can be excited by the visible light46-49. This principle should also present in the WS2/TiO2-based photoelectrochemical platform. In order to verify the above surmise, control experiments were performed, in which the other two photocatalysts utg-C3N4/TiO2 and utg-C3N4/ZnS were synthesized. As is expected, CC presents much higher photocurrent than that of HQ and RC on the utg-C3N4/TiO2 modified ITO electrode due to the TiO2 component (Figure 6b). Yet, the results exhibit that the three isomers show similar photocurrent on the utg-C3N4/ZnS modified ITO electrode (Figure 6c). It is concluded that such a chelate binding of Ti and adjacent O in the o-diphenol should be the key factor for the selective detection of CC. Herein, the proposed mechanism is illustrated in Scheme 1 and explained as the following: both oxygen atoms of the CC molecule bind with the Ti (IV) surface site and form a chelate structure with a five/six-atom ring, which can be easily excited by the visible light. The generated electron will inject into the ITO electrode and produce photocurrent. Meanwhile, since plenty of chelate structures formed on the surface of TiO2, it will lead to high concentration of CC near the WS2, and the holes produced by WS2 can conveniently oxidize CC molecule. The refilled holes of WS2 can be exited again and therefore enlarge the photocurrent. The proper conduction band formed in WS2/TiO2 nanocomposites efficiently enhance the electron transfer from TiO2 to ITO electrode50, which can not only decrease the recombination rate between electron and hole, but also improve the sensitivity of the WS2/TiO2-based photoelectrochemical platform. This conclusion can be further confirmed by the results of EIS. As shown in Figure 6d, the charge-transfer resistance of WS2/TiO2 is calculated to be 1430 Ω·cm2 under visible light irradiation, which is much smaller than that of TiO2 (4981 Ω·cm2). This smaller arc radius implies a much higher efficiency of

Page 6 of 8

charge transfer. Since the formation of chelate structures with the Ti atoms, o-diphenol and its derivatives who have the similar molecular structure, should comply with the same mechanism with CC on the WS2/TiO2 based photoelectrochemical platform.

CONCLUSION In this work a novel photoelectrochemical platform based on WS2/TiO2 composite as optoelectronic materials has been designed for selective detection of o-diphenol and its derivatives without auxiliary of biomolecule or labelled materials. Such a photoelectrochemical sensor can be directly applied for discriminate o-diphenol sutructured species with remarkable advantages of high sensitivity, fast response, longtime stability, low cost and convenient operation. The excellent selectivity and high sensitivity should be attributed to two aspects: i) the chelate effect of adjacent two oxygen atoms of the o-diphenol with Ti (IV) surface site is considered as the key point for preferential recognition of ortho isomers. ii) The proper band level between WS2 and TiO2 is capable to make photogenerated electron and hole easily separated, which will result in great improvement in photocurrent. The combination of WS2 and TiO2 demonstrates more sensitivity than the individual pristine material. By employing this WS2/TiO2 based photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been performed for DA detection. Such a direct analytical technique without assistant of any biomolecules holds great promise to be applied in a lot of fields and will finally contribute to environment and human health.

ASSOCIATED CONTENT Supporting Information Additional information including the photograph detection instrument of photoelectrochemical platform, results of XPS spectra, DSR spectra, the stability and interference of the WS2/TiO2-based photoelectrochemical platform, the effect of potential to TiO2 and WS2/TiO2 modified electrode with and without light, the three phenols photocurrent on the TiO2 and WS2/TiO2 modified electrode with 365 nm irradiation and the interference of glucose and ascorbic acid on TiO2 modified ITO electrode with an applied potential of 0.0 V under 365 nm irradiation. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Fax: +86-4 31-85262800; Tel: +86-431-852 62425 [email protected], [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT The authors are most grateful to the NSFC, China (No.21225524, No.21205112, No.21475122, No.211175130, No.21127006, No.21127007 and No.21127010), the Department of Science and Techniques of Jilin Province (No.20120308, No.201215091 and SYHZ0006) and Chinese Academy of Sciences (YZ201354, YZ201355) for their financial support.

Scheme 1. The mechanism of WS2/TiO2-based photoelectrochemical platform for selective detection of o-diphenol and its derivatives.

REFERENCES (1) Zhao, W.-W.; Xu, J.-J.; Chen, H.-Y. Chem. Soc. Rev. 2014. 44, 729-741.


Page 7 of 8

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


(2) Zen, J. M.; Chung, H. H.; Yang, H. H.; Chiu, M. H.; Sue, J. W. Anal. Chem. 2003, 75, 7020-7025. (3) Yildiz, H. B.; Freeman, R.; Gill, R.; Willner, I. Anal. Chem. 2008, 80, 2811-2816. (4) Zhao, W.-W.; Ma, Z.-Y.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2013, 85, 8503-8506. (5) Ma, W.; Han, D.; Zhou, M.; Sun, H.; Wang, L.; Dong, X.; Niu, L. Chem. Sci. 2014, 5, 3946-3951. (6) Wang, L.; Ma, W.; Gan, S.; Han, D.; Zhang, Q.; Niu, L. Anal. Chem. 2014, 86, 10171-10178. (7) Liang, M.; Guo, L.-H. Environ. Sci. Technol. 2007, 41, 658664. (8) Li, J.; Tu, W.; Li, H.; Han, M.; Lan, Y.; Dai, Z.; Bao, J. Anal. Chem. 2014, 86, 1306-1312. (9) Wang, W.; Hao, Q.; Wang, W.; Bao, L.; Lei, J.; Wang, Q.; Ju, H. Nanoscale 2014, 6, 2710-2717. (10) Zhao, W.-W.; Xu, J.-J.; Chen, H.-Y. Chem. Rev. 2014, 114, 7421-7441. (11) Qian, Z.; Bai, H.-J.; Wang, G.-L.; Xu, J.-J.; Chen, H.-Y. Biosens. Bioelectron. 2010, 25, 2045-2050. (12) Zhao, X.; Zhou, S.; Jiang, L.-P.; Hou, W.; Shen, Q.; Zhu, J.-J. Chem.-Eur. J. 2012, 18, 4974-4981. (13) Zhao, W.-W.; Dong, X.-Y.; Wang, J.; Kong, F.-Y.; Xu, J.-J.; Chen, H.-Y. Chem. Commun. 2012, 48, 5253-5255. (14) Zhao, W.-W.; Ma, Z.-Y.; Yu, P.-P.; Dong, X.-Y.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2012, 84, 917-923. (15) Kilmartin, P. A.; Zou, H. L.; Waterhouse, A. L. J. Agr. Food Chem. 2001, 49, 1957-1965. (16) Bendini, A.; Cerretani, L.; Pizzolante, L.; Toschi, T. G.; Guzzo, F.; Ceoldo, S.; Marconi, A. M.; Andreetta, F.; Levi, M. Eur. Food Res. Technol. 2006, 223, 102-109. (17) Yuan, J.; Guo, W.; Wang, E. Anal. Chem. 2008, 80, 11411145. (18) Liu, X.; Jiang, H.; Lei, J.; Ju, H. Anal. Chem. 2007, 79, 80558060. (19) Alkasir, R. S. J.; Ornatska, M.; Andreescu, S. Anal. Chem. 2012, 84, 9729-9737. (20) Yuan, J.; Gaponik, N.; Eychmueller, A. Anal. Chem. 2012, 84, 5047-5052. (21) Wang, H.-F.; Wu, Y.-Y.; Yan, X.-P. Anal. Chem. 2013, 85, 1920-1925. (22) Nadifiyine, S.; Haddam, M.; Mandli, J.; Chadel, S.; Blanchard, C. C.; Marty, J. L.; Amine, A. Anal. Lett. 2013, 46, 27052726. (23) Wang, B.; Zheng, J.; He, Y.; Sheng, Q. Sensor Actuat. B-chem 2013, 186, 417-422. (24) Lakshmi, D.; Bossi, A.; Whitcombe, M. J.; Chianella, I.; Fowler, S. A.; Subrahmanyam, S.; Piletska, E. V.; Piletsky, S. A. Anal. Chem. 2009, 81, 3576-3584. (25) Prathap, M. U. A.; Satpati, B.; Srivastava, R. Sensor Actuat. B-chem 2013, 186, 67-77. (26) Zhang, S.; Liu, H.; Wu, X.; Xu, X.; Wu, Y. J capill electrophor microchip technol 2002, 7, 15-18. (27) Mateos, R.; Espartero, J. L.; Trujillo, M.; Rios, J. J.; LeonCamacho, M.; Alcudia, F.; Cert, A. J. Agr. Food Chem. 2001, 49, 2185-2192. (28) Khokhar, S.; Magnusdottir, S. G. M. J. Agr. Food Chem. 2002, 50, 565-570. (29) Prior, R. L.; Wu, X. L.; Schaich, K. J. Agr. Food Chem. 2005, 53, 4290-4302. (30) Chen, X.; Mao, S. S. Chem. Rev. 2007, 107, 2891-2959. (31) Rapoport, L.; Bilik, Y.; Feldman, Y.; Homyonfer, M.; Cohen, S. R.; Tenne, R. Nature 1997, 387, 791-793. (32) Voiry, D.; Yamaguchi, H.; Li, J.; Silva, R.; Alves, D. C. B.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Nat. Mater. 2013, 12, 850-855. (33) Shanmugam, M.; Durcan, C. A.; Jacobs-Gedrim, R.; Yu, B. Nano Energy 2013, 2, 419-424. (34) Georgiou, T.; Jalil, R.; Belle, B. D.; Britnell, L.; Gorbachev, R. V.; Morozov, S. V.; Kim, Y.-J.; Gholinia, A.; Haigh, S. J.; Makarovsky, O.; Eaves, L.; Ponomarenko, L. A.; Geim, A. K.;

Novoselov, K. S.; Mishchenko, A. Nat. Nanotechnol. 2013, 8, 100103. (35) Xi, Q.; Zhou, D.-M.; Kan, Y.-Y.; Ge, J.; Wu, Z.-K.; Yu, R.Q.; Jiang, J.-H. Anal. Chem. 2014, 86, 1361-1365. (36) Yuan, Y.; Li, R.; Liu, Z. Anal. Chem. 2014, 86, 3610-3615. (37) Smith, R. J.; King, P. J.; Lotya, M.; Wirtz, C.; Khan, U.; De, S.; O'Neill, A.; Duesberg, G. S.; Grunlan, J. C.; Moriarty, G.; Chen, J.; Wang, J.; Minett, A. I.; Nicolosi, V.; Coleman, J. N. Adv. Mater. 2011, 23, 3944-3948. (38) Ma, W.; Han, D.; Zhang, N.; Li, F.; Wu, T.; Dong, X.; Niu, L. Analyst 2013, 138, 2335-2342. (39) Jing, D.; Guo, L. Catal. Commun. 2007, 8, 795-799. (40) Ho, W. K.; Yu, J. C.; Lin, J.; Yu, J. G.; Li, P. S. Langmuir 2004, 20, 5865-5869. (41) Fujii, H.; Ohtaki, M.; Eguchi, K.; Arai, H. J. Mol. Catal. Achem. 1998, 129, 61-68. (42) Ma, W.; Han, D.; Gan, S.; Zhang, N.; Liu, S.; Wu, T.; Zhang, Q.; Dong, X.; Niu, L. Chem. Commun. 2013, 49, 7842-7844. (43) Jentsch, J. D.; Redmond, D. E.; Elsworth, J. D.; Taylor, J. R.; Youngren, K. D.; Roth, R. H. Science 1997, 277, 953-955. (44) Schwarting, R. K. W.; Huston, J. P. Prog. Neurobiol. 1996, 49, 215-266. (45) Farjami, E.; Campos, R.; Nielsen, J. S.; Gothelf, K. V.; Kjems, J.; Ferapontova, E. E. Anal. Chem. 2013, 85, 121-128. (46) Liu, L.-M.; Li, S.-C.; Cheng, H.; Diebold, U.; Selloni, A. J. Am. Chem. Soc. 2011, 133, 7816-7823. (47) Liu, Y.; Dadap, J. I.; Zimdars, D.; Eisenthal, K. B. J. Phys. Chem. B 1999, 103, 2480-2486. (48) Rego, L. G. C.; Batista, V. S. J. Am. Chem. Soc. 2003, 125, 7989-7997. (49) Dimitrijevic, N. M.; Saponjic, Z. V.; Rabatic, B. M.; Rajh, T. J. Am. Chem. Soc. 2005, 127, 1344-1345. (50) Weiss, J.; Thomalla, M.; Tributsch, H. J. Photochem. Photobiol. A 2013, 255, 36-40.



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

Page 8 of 8

Table of Contents

A biomolecule-free photoelectrochemical platform based on WS2/TiO2 nanocomposite was designed for selective detection of o-diphenol and its derivatives, which demonstrates excellent stability, reproducibility, remarkably convenient and cost effective advantages, as well as low detection limit.


Biomolecule-Free, Selective Detection of o-Diphenol and Its

Recommend Documents