Fabrication of Noncoplanar Molecule Aggregates with Inherent Porous

Subscriber access provided by JAMES COOK UNIVERSITY LIBRARY

Article

Fabrication of Non-coplanar Molecule Aggregates with Inherent Porous Structures for Electrochemiluminescence Signal Amplification Xiaocen Zhao, Wenjuan Zhou, and Chao Lu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b02921 • Publication Date (Web): 25 Aug 2017 Downloaded from http://pubs.acs.org on August 26, 2017

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 22

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

Fabrication of Non-coplanar Molecule Aggregates with Inherent Porous Structures for Electrochemiluminescence Signal Amplification

Xiaocen Zhao, † Wenjuan Zhou, ‡ and Chao Lu*, †

†

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical

Technology, Beijing 100029, China ‡

Department of Chemistry, Capital Normal University, Beijing 100048, China

*E-mail: [email protected]

1

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

ABSTRACT: A simple and time-saving strategy was developed for the amplification of electrochemiluminescence (ECL) by dropping the non-coplanar tetraphenylethylene (TPE) solution on the surface of gold electrode. The self-assembled TPE aggregates exhibited inherent porous structures, endowing them with high specific surface area and oxygen adsorption capability. Therefore, the fabricated porous structures could lead to a 50-fold increase in the ECL signal of luminol in neutral aqueous solution, in comparison to that on the bare electrode. In contrast, the aggregates of the two typical coplanar polycyclic aromatic hydrocarbons (PAHs), perylene and pyrene, gave a weaker ECL enhancement, owing to their disc-like molecular structure and densely packed layers under aggregated conditions. The proposed ECL system has been successfully applied for the detection of hydrogen peroxide (H2O2) in the linear range of 0.25−1000 μM with a detection limit (S/N = 3) of 0.1 μM. Our findings provide inspiration for revealing the role of inherent molecular structure in the aggregate configuration, and open attractive perspectives for the usage of non-coplanar molecules in analytical applications.

2


Page 2 of 22

Page 3 of 22

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


INTRODUCTION Luminol-based electrochemiluminescence (ECL) provides a valuable advantage that can be used specially in aqueous medium with high luminous efficiency, sufficient reagent source, and broad applications.1-4 More recently, advances in luminol-based ECL platform have been widely used for chemo- and biosensing.5-10 Typically, the luminol-based ECL is developed to detect the analyst which has catalytic or quenching effect on the ECL reaction of luminol (e.g., metal ions).5,6 Based on the enhancement of luminol ECL from H2O2, a series of oxidoreductases and their substrates can be sensitively detected through monitoring the generation

of

H2O2.7-8

In

addition,

some

derivatives

of

luminol,

such

as

N-(aminobutyl)-N-(ethylisoluminol) (ABEI), have been used as biological molecular markers for immunoassay.9,10 For a long time, stronger ECL intensity of luminol was usually generated in alkaline condition, limiting its extensive applications under physiological conditions.11 Typically, the surface area of working electrode has a direct influence on the concentration of luminophors and co-reactants in the diffusion layer near the surface of working electrode, leading to the fluctuation of ECL intensity.12,13 Various nanomaterials including carbon nanohorns and metal nanoparticles (e.g., silver nanoparticle, gold nanoparticle, and flower-like Au@BSA nanoparticles),14-19 have been used to enhance the ECL intensity of luminol in neutral solution through increasing the available area of the electrode surface. However, modification of nanomaterials on the surface of working electrode always requires complicated, time-consuming assembly procedure, and stringent conditions.20 Therefore, the development of a facile and convenient strategy for amplifying the ECL signal in neutral medium is a crucial need to expand the analytical applications of the luminol-based ECL platform. Self-assembly of organic molecules on solid surfaces might induce the formation of three-dimensional (3D) porous frameworks with high specific surface area.21-23 Several 3



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

approaches for the self-assembled films with nanostructure, such as introduction of non-coplanar units into the molecule backbone or incorporation of the non-coplanar complexes into planar construction, have been used to achieve a highly porous structure with permanent porosity and special functions (e.g., high gas-adsorption selectivity).24-28 Tetraphenylethylene (TPE), a typical non-coplanar molecule, owns four highly twisted phenyl rings in the molecule backbone, enabling to form a multi propeller-shape molecular structure in solid state.29 More recently, a TPE-based small molecule with unique 3D configuration has been prepared for the construction of non-fullerene organic solar cells.28 In comparison with the coplanar structure, the 3D molecule configuration exhibits more incompact and amorphous aggregation in solid state. In this work, a non-coplanar TPE molecule was dispensed on the surface of gold electrode to fabricate a novel porous aggregate film. The obtained porous film could greatly amplify ECL signals of luminol in neutral medium, while the coplanar PAHs, perylene- and pyrene-modified gold electrodes in the control experiment exhibited a weaker ECL signal. Figure 1 and Figure S1 in the Supporting Information show the schematic diagram of amplified ECL based on the non-coplanar TPE aggregates and the coplanar structural aggregates, respectively. The morphologies of TPE, pyrene, and perylene aggregates were characterized by Transmission electron microscopy (TEM) and scanning electron microscope (SEM) techniques. In addition, the cyclic voltammetry (CV) and ECL properties on the PAH-modified electrode demonstrated that the porous TPE aggregate film could enrich more O2 and O2•− during ECL reaction in comparison to the disc-like pyrene and perylene aggregates on the surface of gold electrode. In view of the highly amplified ECL based on TPE-modified gold electrode and the stability and reproducibility of the amplified ECL signal, the ECL system was applied for detecting H2O2. To the best of our knowledge, non-coplanar structural aggregates as an efficient ECL signal amplifier have never been reported. Our work not only introduces non-coplanar molecules in the ECL field, but also provides a new 4


Page 4 of 22

Page 5 of 22

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


perspective of the nanostructure in self-assembled molecular aggregates for expanding their applications.

Figure 1. Schematic diagram of amplified ECL based on the non-coplanar TPE aggregates.

EXPERIMENTAL SECTION Chemicals and Materials. Analytical grade reagents used in this experiment, including Na2HPO4, NaH2PO4, NaOH, ethanol, H2SO4 and tetrahydrofuran (THF), were purchased from Beijing Chemical Reagent Company (Beijing, China). Luminol was obtained from J&K scientific Ltd. (Beijing, China). 0.01 M stock solution of luminol was prepared by dissolving luminol in 0.1 M NaOH solution. And in order to assure the stability of luminol solution, it is better to use it after about two weeks. TPE was supplied by Tokyo Chemical Industry (TCI, Japan). Perylene was supplied by Adamas Reagent Co. Ltd. (Shanghai, China). Pyrene was supplied by Shanghai Macklin Biochemical Co. Ltd. (Shanghai, China). Both nitrogen (N2) and oxygen (O2) used were high-purity of 99.999 %. The 0.1 M phosphate buffer solution (PBS, pH = 7.5) was prepared by mixing the stock solutions of 0.1 M Na2HPO4 and 0.1 M NaH2PO4. In this work, all reagents were used without further purification, and water was prepared by purifying with a Milli Q purification system (Millipore, Barnstead, CA, USA). Apparatus. TEM photographs were obtained by using a Hitachi HT7700 TEM (Japan). 5



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

Samples for TEM observations were prepared by depositing the drop of THF solution of PAHs on the top of ultrathin carbon film. The surface state of the PAH-modified gold electrodes was characterized by using SEM (Hitachi S-4700, Japan). Electrochemical measurements were performed with a CHI 660E electrochemical analyzer (CHI, USA), and the ECL signal was recorded by a BPCL luminescence analyzer (Institute of Biophysics, Chinese Academy of Science, Beijing, China) The voltage of the photomultiplier tube (PMT) was maintained at -900 V. ECL spectra of various PAH-modified electrode were obtained by collecting the ECL signals of a series of filters (400, 425, 440, 460, 490, 535, 555, 575, and 620 nm) under CV conditions. All measurements were carried out at room temperature. Fabrication of PAH-Modified Electrode. Firstly, the gold electrode was polished sequentially with 0.3 µm and 0.05 µm alumina slurry. Then it was washed with deionized water thoroughly, and sonicated in ethanol and deionized water, orderly. The cleaned electrode was rinsed electrochemically in 0.5 M H2SO4 solution under the CV potential from -0.2 V to 1.5 V at the scan rate of 100 mV/s until observing a stable redox wave of H 2SO4. The gold electrode was washed again by deionized water, and dried by blowing dry N2 gas. To guarantee the equivalent coverage of the electrode, the same molar quantity of TPE, pyrene, and perylene was used for the electrode modification. In detail, 2.5 µL THF solution of TPE, pyrene, and perylene with the same molar concentration (30 mM) was dropped on the surface of the pretreated gold electrode, respectively, and dried at room temperature. According to the chemical formulas of PAHs, the percent carbon values for the TPE-, pyrene-, and perylene-modified electrodes were calculated to be 94.0 %, 95.0 %, and 95.2 %, respectively. Electrochemical and ECL Experiments. All electrochemical experiments were carried out with a conventional three-electrode system, including the modified gold electrode (3 mm diameter) as the working electrode, a saturated Ag/AgCl electrode as the reference electrode, and a platinum electrode as the counter electrode, respectively. The ECL reactions occurred in 0.1 M PBS (pH = 7.5) containing 100 µM luminol, and the potential range was set from -0.5 6


Page 6 of 22

Page 7 of 22

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


V to 0.6 V at the scan rate of 100 mV/s. The O2 saturated atmosphere was achieved by bubbling O2 into the working electrolyte for 20 minutes. Similarly, the N2 saturated atmosphere was obtained in the same way.

RESULTS AND DISCUSSION PAH Aggregate Configuration. The 3D structures of typical non-coplanar molecule (i.e., TPE) and coplanar molecules (i.e., pyrene and perylene) were shown in Figure S2 in the Supporting Information, whose energy was minimized in a CS Chem3D Pro program by the MM2 method. TPE showed a non-coplanar molecular configuration. The intramolecular rotation of TPE would be restricted to form highly twisted structure in the solid state.28,30 In contrast, the aromatic rings of both pyrene and perylene are all on the same plane, exhibiting a disc-like structure. This rigid planar configuration makes them easy to form densely packed layers because of strong π‒π stacking interactions between molecules under aggregated conditions.31 Self-assembled PAH aggregates were formed by dropping THF solution of PAHs on the surface of gold electrode. All the PAH-modified electrodes showed homogeneous fluorescence emission under UV irradiation (Figure S3 in the Supporting Information), indicating that the electrodes were uniformly covered with PAHs. The morphology of TPE, pyrene, and perylene aggregates was characterized by TEM. It was observed that the TPE aggregates revealed apparent porous structures with wrinkles and protuberances (Figure 2A, 2B), while pyrene and perylene aggregates always existed in the form of flat and smooth layer (Figure 2C, 2D). The surface states of the PAH-modified gold electrodes were demonstrated by using SEM (Figure S4 in the Supporting Information). It can be seen that the pyrene- and perylene-modified gold electrode showed the same smooth surface morphology composing of few protuberances. The film of TPE aggregates on the gold electrode displayed extremely rough morphology with abundant protuberances. These results 7



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

were consistent with the observation from TEM images. It is concluded that the irregular porous structure by self-assembly of non-coplanar TPE molecules was formed on the surface of gold electrode, which would provide higher specific surface area than the film of coplanar molecular aggregates.

Figure 2. TEM images of (A, B) TPE aggregates; (C) pyrene aggregates; and (D) perylene aggregates.

ECL Signal Amplification on the PAH-Modified Electrodes. With respect to the difference in the structure of the aggregates formed by non-coplanar and coplanar molecules, we investigated the influence of these PAH-modified gold electrodes on ECL intensity. The cyclic ECL curves of luminol in PBS solution (pH = 7.5) on the TPE-modified gold electrode and a bare electrode at the optimal scan rate (Figure S5 in the Supporting Information) in the potential range from -0.5 V to 0.6 V were shown in Figure 3A. The ECL peak on TPE-modified gold electrode at ~ 0.60 V was amplified approximately 50-fold higher than that on the bare gold electrode. In comparison, the ECL intensity on coplanar structural molecules (perylene and pyrene) modified gold electrode were ~ 20 times higher than that on 8


Page 8 of 22

Page 9 of 22

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


the bare electrode. The ECL spectra on the PAH-modified gold electrodes were measured by using a series of optical filters. As shown in Figure 3B and Figure S6 in the Supporting Information, the maximum emission of the ECL was located at the peak of 440 nm, corresponding to the emission of 3-aminophthalate (AP2−*), which indicated that the ECL emission was originated from the electrochemical oxidation of luminol on the PAH-modified gold electrodes.32 These results indicated that the PAH aggregates were all capable of catalyzing the ECL reaction of luminol on the surface of gold electrode. In comparison with pyrene and perylene aggregates, the TPE aggregates exhibited more porous-like structure with abundant wrinkles and protuberances, as mentioned before. Thus, the highest ECL signal amplification from TPE aggregate among the PAH-modified gold electrodes could be attributed to its high specific surface area of the porous structure on the gold electrode.

Figure 3. (A) Cyclic ECL curves on the PAH-modified gold electrodes and a bare gold electrode. Inset: the cyclic ECL curves on a bare gold electrode; (B) ECL spectrum of luminol obtained on the TPE-modified gold electrode.

PAH-Modified Electrode Facilitated the Electro-oxidization of Luminol. In general, the ECL reaction of luminol and O2 on gold electrode is sensitive to the properties of electrode surface.33,34 The CV responses on a bare gold electrode and the PAH-modified gold electrodes 9



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 10 of 22

were measured, respectively. An irreversible oxidation peak caused by the electro-oxidization of luminol anions to luminol radicals (L•–) at ~ 0.5 V was observed in the CV curves of the PAH-modified gold electrodes under air atmosphere, which could be hardly observed in the absence of luminol and O2 and on a bare gold electrode (Figures S7 and S8 in the Supporting Information). And yet, owing to relative poor electrical conductivity of PAHs, the integral CV current could not be improved after modification of PAH aggregates on the gold electrode surfaces in neutral PBS (pH = 7.5) containing 100 µM luminol under air atmosphere. It could be concluded that the enhanced ECL of the system was ascribed to the catalytic effect from the PAH aggregates on the surface of gold electrode, rather than the change in the electrical conductivity.35 This is because the ECL intensity and the conductivity of electrode do not always have positive correlation, and the determining factor is attributed to the concentration of electrochemically active molecules in the diffusion layer. When the electrochemically active molecules still keep their accumulated state onto the surface of electrode, the ECL intensity could be enhanced even though the PAH layers had relative poor electrical conductivity.36,37 In the ECL reaction, OOH– could be produced at negative potentials when the initial scan direction was negative, and further oxidized to O2•− on the reverse scan.38 Hydrophobic micro-environment at the vicinity of the gold electrode is known to be capable of stabilizing and accumulating superoxide anion radicals (O2•−), and preventing gold electrode from being fouled by electrochemical polymerization of luminol during the ECL reaction.39 High hydrophobicity of the surface of working electrode also can improve O2 supply on the electrode.40 The PAH layer with a hydrophobic surface contributed to the stability of the reactive intermediates in the ECL system. On the other hand, the PAH layer exhibited a tendency to absorb gases.41-43 As a result, more O2•− and O2 would be accumulated and stabilized on the surfaces of the PAH-modified gold electrodes. Accordingly, the ECL intensity of luminol could be enhanced with the enrichment of more reactants onto the surface 10


Page 11 of 22

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


of the PAH-modified working electrodes. ECL Enhancement Mechanism of Non-coplanar Structural Aggregates. To verify the capacity of the immobilized PAH aggregates to accumulate O2 or O2•− in the ECL system, we explored the influence of the lower limiting potential on the ECL intensity on the PAH-modified gold electrodes (Figure 4A and Figure S9 in the Supporting Information). It was found that the ECL signal of luminol on the TPE-modified gold electrode increased with the decrease of lower limiting potential, which reached a maximum at about -0.5 V, corresponding to the reduction of O2 and formation of O2•− later in the diffusion layer. Then, as the limiting potential continued to drop, the ECL signal was gradually declined because of further reduction of dissolve O2 in the electrolyte. The same tendency was observed on pyrene- and perylene-modified gold electrode. These results demonstrated that content of O2•− was a decisive factor for the dominant ECL reaction mechanism, and O2•− was confirmed to be accumulated on the PAH-modified electrode surface. Figure 4B showed the cyclic ECL curves of luminol on the TPE-modified gold electrode with initial positive/negative scan direction. Even though the ECL signal in a circle of potential window under CV was no obvious change under different scan direction, there is almost no ECL emission produced during the negative potential scan from 0.6 V to -0.5 V, and the ECL peak of luminol was generated from -0.5 V to 0.6 V later. This result was also consistent with the observation in the previous literature,38 further indicating that the ECL signal at ~ 0.60 V was mainly independent on the O2•− produced at the negative potential. The ECL intensities and CV curves on TPE-modified gold electrode under saturated air, O2, and N2 atmosphere were further investigated. As shown in Figure 4C, the ECL intensity significantly increased under saturated O2 atmosphere compared with that under saturated air atmosphere, while it decreased sharply by bubbling N2 into the working electrolyte for 20 minutes. These results indicated that the dissolved O2 had a key role in the ECL pathways; high levels of dissolved O2 in the electrolyte could contribute to obtaining the efficient ECL 11



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 12 of 22

signals. The corresponding CV curves in these different atmospheres were shown in Figure 4D. It was appeared that the current intensity under negative potential could also be raised by increasing the O2 content in the electrolyte. In conclusions, more OOH– could be produced at higher O2 levels under negative potential, resulting in brighter ECL emission. The ECL mechanism of luminol in the proposed system can be concluded in Scheme S1 in the Supporting Information, in which the concentration of O2•− and L•− in the diffusion layer near the surface of working electrode were the key factors towards the ECL intensity of luminol.

Figure 4. (A) Effect of lower limiting potential on the ECL intensity of luminol on the TPE-modified gold electrode; (B) Cyclic ECL curves of luminol on the TPE-modified gold electrode with initial positive scan direction (blue line) and negative scan direction (red line); (C) ECL intensity and (D) Cyclic voltammograms of the TPE-modified gold electrode in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol under saturated air, O2, and N2 atmosphere, respectively. Scan rate: 100 mV/s.

TPE aggregates on the surface of gold electrode exhibited a porous structure, which could enrich more O2 and O2•− during ECL reaction. However, pyrene and perylene aggregates showed a disc-like conformation on the surface of gold electrode, impairing their ability of 12


Page 13 of 22

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


enriching O2 and O2•−. As shown in Figure 5A and Figure S10A in the Supporting Information, the ECL intensity from the TPE-modified gold electrode in O2-saturated electrolyte was about 9-fold higher than that in air-saturated atmosphere, while the ECL intensity ratio of the perylene- and pyrene-modified gold electrode in air-saturated and O2-saturated atmosphere was only about 1:6. These results suggested the great advantage of using non-coplanar structural TPE aggregates instead of planar pyrene and perylene aggregates for enriching O2 and O2•− on the surface of working electrode, thus producing the most intense ECL emission. According to the above study, the maximum of ECL signal obtained on the PAH-modified gold electrode was obtained when the lower limiting potential was set at about -0.5 V, which corresponding to the reduction of O2 and formation of O2•− later. To further confirm the superiority of non-coplanar structural TPE aggregates for enriching O2 and O2•−, the ECL responses of luminol obtained on bare gold electrode and the PAH-modified gold electrodes by constant cathodic potential electrolysis at -0.5 V for 25 s within a potential window from 0 to 0.6 V were shown in Figure 5B and Figures S10B-S10D in the Supporting Information. It can be observed that the ECL signals of luminiol on the PAH-modified gold electrodes were apparently amplified after pre-electrolysis at -0.5 V for 25 s, however, only weak ECL signals were produced without pre-electrolysis. In comparison, the great difference in the ECL responses of luminol wasn’t observed on bare gold electrode, indicating that the O2 and O2•− indeed can be accumulated by PAH aggregates on the surface of working electrode. Furthermore, it is a remarkable fact that as for these PAH-modified gold electrodes, the most intense ECL emission of luminol after pre-electrolysis was obtained on the TPE-modified gold electrode. This result is consistent with the above deduction that TPE aggregate films were capable of stabilizing and accumulating more O2•− and O2 on the surface of working electrode.

13



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 14 of 22

Figure 5. (A) ECL intensity obtained on the TPE-modified gold electrode and perylene-modified gold electrode in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol under saturated air and O2 atmosphere, respectively. Scan rate: 100 mV/s; (B) ECL responses of luminol obtained on the TPE-modified gold electrode before and after constant cathodic potential electrolysis at -0.5 V for 25 s in the voltage range from 0 to 0.6 V; (C) Calibration curves of H2O2 (μM) obtained on the TPE-modified gold electrode. Inset: the calibration curves for H2O2 in the range of 0.25−25 μM; (D) The ECL signals obtained on different TPE-modified gold electrodes in 0.1 M PBS solution (pH = 7.5) containing 100 μM luminol in presence of 1 μM, 10 μM, 100 μM, and 1000 μM H2O2, respectively.

Stability and Reproducibility of the Amplified ECL. As shown in Figure S11 in the Supporting Information, the ECL signals obtained on the three parallel PAH-modified electrodes exhibited acceptable reproducibility. In addition, the stability of the ECL from the PAH-modified electrodes was estimated by recording consecutive ECL signals from -0.5 V to 0.6V for 20 cycles on the TPE-, pyrene-, and perylene-modified gold electrode, respectively (Figure S12 in the Supporting Information). The relative standard deviation (RSD) of ECL signals of luminol on TPE-modified gold electrode was calculated to be 5.25 %, and that on the pyrene- and perylene-modified gold electrodes were 4.45 % and 5.29 %, respectively. According to previous literatures, the luminol ECL system generally requires H2O2 as a 14


Page 15 of 22

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


co-reactant to amplify its ECL signal.44,45 We have compared the stabilization of ECL signals from the proposed system and the most commonly used luminol-H2O2 system. Consecutive ECL signals were obtained on the bare gold electrode in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol in presence of 100 µM H2O2 (Figure S13 in the Supporting Information). It was observed that the ECL signals on the bare gold electrode were greatly decreased with an increase of the potential scanning cycle, indicating unstable electrochemical reaction of ECL on the bare gold electrode.39 In comparison, the ECL on the PAH-modified electrodes had good stability and reproducibility, showing great potential for the construction of high-sensitive electrochemical sensing platforms. Detection of H2O2 Based on TPE-Modified Gold Electrode. To verify the feasible use of the TPE-modified gold electrode for chemo- and biosensing application, the detection of H2O2 was performed in this work. As shown in Figure 5C, the ECL intensity increased linearly with the concentration of H2O2 in the range of 0.25–1000 μM, and the limit of detection (LOD) was 0.1 μM (S/N = 3). In addition, we investigated the reproducibility of the analytical figures of merit for different electrodes prepared by the same way. As shown in Figure 5D, the error level of each concentration of H2O2 was acceptable from different electrodes.

CONCLUSIONS In conclusion, a simple and facile strategy based on non-coplanar structural aggregates was developed to amplify the ECL signal of luminol in neutral condition. Non-coplanar molecule can self-assemble into porous structures under aggregate conditions, providing high specific surface area of the working electrode. The ECL of luminol could be enhanced greatly on the TPE-modified electrode. In contrast, the aggregates of the two typical coplanar PAHs, perylene and pyrene, gave a weaker enhancement in the ECL signal of luminol because of their densely packed layers. The hydrophobic microenvironment and porous nanostructures of 15



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 16 of 22

the TPE aggregate films were capable of stabilizing and accumulating O2•− and O2 on the surface of working electrode, thus displaying excellent catalytic effect on the ECL reaction of luminol. High stability and good reproducibility make the TPE aggregates as a potential amplified ECL system for chemo- and biosensing application, and exhibit a desirable analysis of H2O2 with the LOD of 0.1 μM. This success not only revealed the role of inherent molecular configuration in the aggregate structure, but also set a precedent for future use of non-coplanar molecules in ECL platform.

ASSOCIATED CONTENT Supporting Information Schematic diagram of weakly amplified ECL based on the coplanar structural aggregates; 3D chemical structures of pyrene, perylene and TPE; the photographs of a bare gold electrode and the PAH-modified gold electrode under UV irradiation; SEM images of the PAH-modified gold electrode; cyclic voltammograms of the TPE-modified gold electrode at various scan rates (a) 10, (b) 20, (c) 40, (d) 60, (e) 80, (f) 100 mV/s; inset: plots of peak current vs scan rate; ECL spectra of luminol on the pyrene- and perylene-modified gold electrode; cyclic voltammograms of the PAH-modified gold electrodes in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol under air atmosphere and without luminol under saturated N2 atmosphere; cyclic voltammogram of a bare gold electrode in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol under air atmosphere; effect of lower limiting potential on the ECL intensity of luminol on the pyrene- and perylene-modified gold electrode; ECL intensity from the pyrene-modified gold electrode under saturated air and O2 atmosphere, respectively; ECL responses of luminol obtained on the bare gold electrode, pyrene- and perylene-modified gold electrode after and before constant cathodic potential electrolysis at -0.5 V for 25 s in the voltage range from 0 to 0.6 V; consecutive ECL signals obtained on the PAH-modified gold electrodes; consecutive ECL signals obtained on the bare gold electrode in 0.1 M PBS solution (pH = 7.5) with 100 µM luminol in presence of 100 µM H2O2; ECL mechanism of 16


Page 17 of 22

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


luminol in the proposed system. The Supporting Information is available free of charge on the ACS Publications website.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Tel./Fax: +86 10 64411957. ORCID Chao Lu: 0000-0002-7841-7477 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by National Basic Research Program of China (973 Program, 2014CB932103), the National Natural Science Foundation of China (21375006, 21656001, 21521005 and 21575010), and Innovation and Promotion Project of Beijing University of Chemical Technology.

REFERENCES (1) Shu, J. N.; Wang, W.; Cui, H. Chem. Commun. 2015, 51, 11366–11369. (2) Hu, L. Z.; Xu, G. B. Chem. Soc. Rev. 2010, 39, 3275–3304. (3) Zhang, H. L.; Cui, H. Nanoscale 2014, 6, 2563–2566. (4) Yang, H. Y.; Wang, H. J.; Xiong, C. Y.; Liu, Y. T.; Yuan, R.; Chai, Y. Q. Electrochim. Acta 2016, 213, 512–519. (5) Richter, M. M. Chem. Rev. 2004, 104, 3003–3036. 17



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 18 of 22

(6) Jiang, X. Y.; Wang, H. J.; Wang, H. J.; Yuan, R.; Chai, Y. Q. Anal. Chem. 2016, 88, 9243–9250. (7) Wang, J.-X.; Zhuo, Y.; Zhou, Y.; Wang, H.-J.; Yuan, R.; Chai, Y.-Q. ACS Appl. Mater. Interfaces 2016, 8, 12968–12975. (8) Zhang, L.; Wang, Y. Z.; Tian, Q. Q.; Liu, Y.; Li, J. H. Biosens. Bioelectron. 2017, 89, 1013–1019. (9) Li, L. L.; Chen, Y.; Zhu, J.-J. Anal. Chem. 2017, 89, 358–371. (10) Tian, D. Y.; Duan, C. F.; Wang, W.; Cui, H. Biosens. Bioelectron. 2010, 25, 2290–2295. (11) Miao, W. J. Chem. Rev. 2008, 108, 2506–2553. (12) Fähnrich, K. A.; Pravda, M.; Guilbault, G. G. Talanta 2001, 54, 531–559. (13) Zhang, A. M.; Xiang, H. K.; Zhang, X.; Guo, W. W.; Yuan, E. H.; Huang, C. S.; Jia, N. Q. Biosens. Bioelectron. 2016, 75, 206–212. (14) Xu, G. F.; Zhang, S. P.; Zhang, Q. R.; Gong, L. S.; Dai, H.; Lin, Y. Y. Sens. Actuators, B 2016, 222, 707–713. (15) Wang, C.-M.; Cui, H. Luminescence 2007, 22, 35–45. (16) Xu, S. J.; Liu, Y.; Wang, T. H.; Li, J. H. Anal. Chem. 2010, 82, 9566–9572. (17) Zhang, H.-R.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2013, 85, 5321–5325. (18) Zhang, H.-R.; Wu, M.-S.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2014, 86, 3834–3840. (19) Zhang, A. M.; Huang, C. S.; Shi, H. Y.; Guo, W. W.; Zhang, X.; Xiang, H. K.; Jia, T.; Miao, F.; Jia, N. Q. Sens. Actuators, B 2017, 238, 24–31. (20) Li, G. X.; Yu, X. X.; Liu, D. Q.; Liu, X. Y.; Li, F.; Cui, H. Anal. Chem. 2015, 87,

18


Page 19 of 22

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


10976–10981. (21) Bajpe, S. R.; Kirschhock, C. E. A.; Aerts, A.; Breynaert, E.; Absillis, G.; Parac-Vogt, T. N.; Giebeler, L.; Martens, J. A. Chem. Eur. J. 2010, 16, 3926–3932. (22) Thomas-Gipson, J.; Beobide, G.; Castillo, O.; Cepeda, J.; Luque, A.; Pérez-Yáñez, S.; Aguayo, A. T.; Román, P. CrystEngComm 2011, 13, 3301–3305. (23) Otero, R.; Gallego, J. M.; de Parga, A. L. V.; Martín, N.; Miranda, R. Adv. Mater. 2011, 23, 5148–5176. (24) Thomas-Gipson, J.; Beobide, G.; Castillo, O.; Fröba, M.; Hoffmann, F.; Luque, A.; Pérez-Yáñez, S.; Román, P. Cryst. Growth Des. 2014, 14, 4019–4029. (25) Chen, Q.; Liu, D. -P.; Luo, M.; Feng, L. -J.; Zhao, Y. -C.; Han, B. -H. Small 2014, 10, 308–315. (26) Zhou, D.; Cheng, Q. -Y.; Cui, Y.; Wang, T.; Li, X. X.; Han, B. -H. Carbon 2014, 66, 592–598. (27) Lin, Y. Z.; Wang, Y. F.; Wang, J. Y.; Hou, J. H.; Li, Y. F.; Zhu, D. B.; Zhan, X. W. Adv. Mater. 2014, 26, 5137–5142. (28) Liu, Y. H.; Mu, C.; Jiang, K.; Zhao, J. B.; Li, Y. K.; Zhang, L.; Li, Z. K.; Lai, J. Y. L.; Hu, H. W.; Ma, T. X.; Hu, R. R.; Yu, D. M.; Huang, X. H.; Tang, B. Z.; Yan, H. Adv. Mater. 2015, 27, 1015–1020. (29) Pogodin, S.; Assadi, N.; Agranat, I. Struct. Chem. 2013, 24, 1747–1757. (30) Wang, Z. M.; Nie, H.; Yu, Z. Q.; Qin, A. J.; Zhao, Z. J.; Tang, B. Z. J. Mater. Chem. C 2015, 3, 9103–9111.

19



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 20 of 22

(31) Hong, Y. N.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev. 2011, 40, 5361–5388. (32) Dong, Y.-P.; Gao, T.-T.; Zhou, Y.; Zhu, J.-J. Anal. Chem. 2014, 86, 11373–11379. (33) Zhang, L.; Niu, W. X.; Gao, W. Y.; Majeed, S.; Liu, Z. Y.; Zhao, J. M.; Anjum, S.; Xu, G. B. Chem. Commun. 2013, 49, 8836–8838. (34) Zhang, L.; Niu, W. X.; Gao, W. Y.; Qi, L. M.; Lai, J. P.; Zhao, J. M.; Xu, G. B. ACS Nano. 2014, 8, 5953–5958. (35) Dai, H.; Yang, C. P.; Tong, Y. J.; Xu, G. F.; Ma, X. L.; Lin, Y. Y.; Chen, G. N. Chem. Commun. 2012, 48, 3055–3057. (36) Chikhaliwala, P.; Chandra, S. J. Organomet. Chem. 2016, 821, 78–90. (37) Liu, X. Q.; Niu, W. X.; Li, H. J.; Han, S.; Hu, L. Z.; Xu, G. B. Electrochem. Commun. 2008, 10, 1250–1253. (38) Cui, H.; Xu, Y.; Zhang, Z.-F. Anal. Chem. 2004, 76, 4002–4010. (39) Rong, J. F.; Chi, Y. W.; Zhang, Y. J.; Chen, L. C.; Chen, G. N. Electrochem. Commun. 2010, 12, 270–273. (40) Tada, S.; Privatananupunt, P.; Iwasaki, T.; Kikuchi, R. J. Electrochem. Energy 2017, 14, 020903. (41) Gross, S.; Bertram, A. K. J. Phys. Chem. A 2008, 112, 3104–3113. (42) Shiraiwa, M.; Garland, R. M.; Pöschl, U. Atmos. Chem. Phys. 2009, 9, 9571–9586. (43) Chu, S. N.; Sands, S.; Tomasik, M. R.; Lee, P. S.; McNeill, V. F. J. Am. Chem. Soc. 2010, 132, 15968–15975. (44) Xu, S. J.; Liu, Y.; Wang, T. H.; Li, J. H. Anal. Chem. 2011, 83, 3817–3823.

20


Page 21 of 22

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


(45) Gu, W. L.; Deng, X.; Gu, X. X.; Jia, X. F.; Lou, B. H.; Zhang, X. W.; Li, J.; Wang, E. K. Anal. Chem. 2015, 87, 1876–1881.

21



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

For TOC only

22


Page 22 of 22

Fabrication of Noncoplanar Molecule Aggregates with Inherent Porous

Recommend Documents