New Insights toward Efficient Charge-Separation Mechanism for High

Subscriber access provided by University of Newcastle, Australia

Article

New Insights towards Efficient Charge Separation Mechanism for High-Performances Photoelectrochemical Aptasensing: Enhanced Charge Carriers Lifetime via Coupling Ultrathin MoS2 Nanoplates with Nitrogen Doped Graphene Quantum Dots Ding Jiang, Xiaojiao Du, Lei Zhou, Henan Li, and Kun Wang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b04949 • Publication Date (Web): 24 Mar 2017 Downloaded from http://pubs.acs.org on March 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 33

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

New Insights towards Efficient Charge Separation Mechanism for High-Performances Photoelectrochemical Aptasensing: Enhanced Charge Carriers Lifetime via Coupling Ultrathin MoS2 Nanoplates with Nitrogen Doped Graphene Quantum Dots Ding Jiang,† Xiaojiao Du,‡ Lei Zhou,‡ Henan Li‡ and Kun Wang∗‡ †

School of Food and Biological Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China

‡

Key Laboratory of Modern Agriculture Equipment and Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013, P.R. China

∗ Corresponding author. Tel.: +86 511 88791800; fax: +86 511 88791708. E-mail address: [email protected]

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: Deeply understanding the internal mechanism of photoelectrohemical (PEC) process is conducive to fabricate high-performances PEC biosensors. In this work, we proposed a new insight towards efficient charge separation mechanism in high-performances PEC biosensors. Specifically, we disclosed that the lifetimes of photogenerated charge carriers of ultrathin MoS2 nanosheets could be prolonged by approximately millisecond timescales after a proper mole ratio of NGQDs were coupled, leading to the promoted charge separation, and giant photocurrent signal-magnify. Benefiting from the dramatic signal amplification and the introduction of acetamiprid aptamer, subfemtomolar level detection of acetamiprid is achieved, which makes our strategy among the most sensitive electronic approach for PEC-based monitoring of targets. This study was beneficial to further understand the charge separation mechanism in PEC biosensing, which paved the way for the development of more efficient PEC biosensors.


Page 2 of 33

Page 3 of 33

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 The establishment of ultrasensitive, cost-effective and highly selective biosensing platforms for identifying and quantifying a trace amount of target molecules has continuously been a core of pushing the boundary on analytical chemistry.1 Photoelectrochemical (PEC) biosensing represents a unique and dynamically developing methodology that offers an elegant route for sensitive biomolecular detection due to the smart combination of photoexcitation process with electrochemical bioanalysis, which has advantageously inherited the low cost, simple instrumentation, low background, high sensitivity and wide dynamic concentration response range.2-4 Traditionally, the range of sensitivity in PEC biosensing strongly relies on the separation of charge carriers.2 Further, construction of a heterojunction composite is widely used to promote its separation.5-8 For instance, Niu’s group designed a sensitive PEC sensor for the real-time evaluation of global antioxidant capacity by using ultrathin g-C3N4/TiO2 composites as photoelectrochemical elements, which could efficiently reducing the amount of recombination between electrons and holes.5 Zhao et al. fabricated a BiOI nanoflakes/TiO2 nanoparticles p-n heterojunction as the photoelectrode for sensitive assaying enzyme inhibition, which contributed to the spatial charge separation.6 In spite of the attention devoted to this charge separation, there are many fundamental aspects that are not fully clarified and require further studies. A detailed knowledge of the underlying mechanism of efficient charge separation in different compounds is necessary for both designing photoactive materials and maximizing the efficiency of the process.



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 basic theory of electron-hole pair recombination was put forth in 1952 by Hall and Shockley and Read, which has been extensively applied in mechanism exploration of photoelectronic fields.9,10 In the recent decades, the concept of carrier lifetime, which is time of survival for electrons and holes excited in materials, has come into being and been proved to play a crucial role in photocatalysis and photovoltaics areas.11-15 It was reported that carrier lifetime is positively related to charge carrier concentration, while the carrier concentration depends on the carrier recombination rate.16-18 In this regard, the longer the carrier lifetime were produced, the more efficient charge separation could be achieved. In light of the strategies for promoting the charge separation in PEC biosensors are mostly referenced from those explored in photovoltaics and photocatalysis, we envision that the carrier lifetime might have a great effect on charge separation in PEC process. However, this intrinsic property of carrier lifetime has seldom been explored for PEC biosensor fabrication. Therefore, it is imperative to fully understand the effect of carrier lifetime on charge separation process taking place in PEC biosensor. Owing to the large optical absorption coefficients and relative long photoexcited carrier lifetimes, ultrathin two-dimensional (2D) molybdenum disulfide (MoS2) is proved to be interesting materials for a variety of different low-cost photoactive fields.19,20 Meanwhile, 2D ultrathin MoS2 nanosheets were demonstrated to be able to spontaneously adsorb single-stranded DNA by the van der Waals force between nucleobases and the basal plane of MoS2 nanosheets, which make it advantageous in biosensing applications, especially in DNA aptasensing.21,22 So, it is feasible to


Page 4 of 33

Page 5 of 33

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


fabricate PEC aptasensor by the integration of unique photoelectric properties and the adsorption of single-stranded DNA. However, several experimental and theoretical studies demonstrated that non-radiative electron-hole recombination in ultrathin MoS2 nanoplates results in photoexcited carrier lifetimes in the few hundreds of picosecond range, which is detrimental to the PEC performances (photocurrent).19,23 Hence, there still remains considerable room to prolong photoexcited carrier lifetimes and improve the PEC performances of ultrathin MoS2 nanoplates. Nitrogen doped graphene quantum dots (NGQDs), has been attracting much attention in various optoelectronic applications due to their size-dependent and edge-sensitive photoluminescence properties.24-26 Moreover, in our previous study, we found that NGQDs was beneficial to the boost the charge transfer, and effectively restrains the recombination of photoinduced electron-hole pairs.26 However, all these study ignored the intrinsic property of NGQDs in carrier lifetime at internal mechanism level. Herein, we designed a high-performance photoactive materials based on NGQDs/ultrathin MoS2 nanosheets (NGQDs/MoS2), and then further explored the detailed mechanisms. It is demonstrated that the lifetimes of photogenerated charge carriers of ultrathin MoS2 nanosheets could be prolonged by approximately millisecond timescales after a proper mole ratio of NGQDs were coupled, leading to the promoted charge separation, and giant photocurrent signal-magnify. Moreover, a novel label-free PEC aptasensor based on the “signal-off” system has been constructed for the sensitive and selective detection of acetamiprid. This study not only offered an ingenious transducer for future uses in the



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 6 of 33

broad PEC analytical field but also further understanding the charge separation mechanism in PEC biosensing, which opens up the possibility for designing more efficient PEC biosensors. EXPERIMENTAL SECTION Materials and Reagents. Ammonium molybdate (NH4)6Mo7O24 · 4H2O, N-N’-dimethyl formamide (DMF), thiourea were obtained from Sinopharm Chemical Reagent

Co.,

Ltd.

Acetamiprid,

flusilazole,

dichlofenthion,

imidacloprid,

tribenuron-methyl, and prochloraz were purchased from Sigma-Aldrich. The NGQDs were prepared according to our previous study.26 The oligonucleotides used were synthesized and purified by Sangon Biological Engineering Technology & Co. Ltd. (Shanghai, China) with the following sequences: Acetamiprid aptamer: 5’-TGT AAT TTG TCT GCA GCG GTT CTT GAT CGC TGA CAC CAT ATT ATG AAG A-3’ All other chemicals employed were all of analytical grade and millipore water with a resistivity of 18.2 MΩ cm−1 was used throughout the study. Preparation of NGQDs modified MoS2 ultrathin nanosheets and pure MoS2 ultrathin nanosheets. NGQDs/MoS2 nanomaterials were synthesized by a facile hydrothermal process. Typically, 40 mg ammonium molybdate and 80 mg thiourea was dissolved in 25 ml DMF at room temperature. Then, a certain amount of NGQDs were added into above solution. After 30 min stirring, the mixtures were poured into a 50 ml Teflon-lined autoclave and subjected to heating at a temperature of 200 oC for 24 h, followed by natural cooling to room temperature. For comparison, pristine MoS2


Page 7 of 33

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


ultrathin nanosheets was prepared under the same process except for the addition of NGQDs. Preparation of the modified electrodes. Primarily, the ITO electrodes were placed in boiling 0.1 M NaOH solution for 30 min, and then were ultrasonically cleaned in water and alcohol for 30 min, respectively. 2 mg mL−1 NGQDs/MoS2 suspension was prepared by dispersing 1.0 mg of NGQDs/MoS2 in 1.0 mL of DMF with ultrasonic agitation for about 10 min. Then 20 µL of the as-prepared suspension was dropped on the electrode surface with a fixed area of 0.5 cm2 and dried in ambient air for 24 h. For comparison, MoS2 ultrathin nanosheets modified ITO, NGQDs modified ITO were obtained using a similar procedure. Design and fabrication of the aptasensor for acetamiprid assay. NGQDs/MoS2 modiﬁed ITO electrode was coated with 10 µL of aptamer at a desired concentration, and then dried at 37 oC for several hours to ensure the effective immobilization of aptamer on the electrode. After that, the electrode were washed by buffer solution to remove the excess nonadsorbed aptamer and dried at room temperature. Finally, the aptamer modiﬁed NGQDs/MoS2 photoanode has been successfully developed. For the PEC analysis, 20 µL acetamiprid solutions with different concentrations were casted on the PEC aptasensor and incubated at room temperature for some time. Finally, the resulting electrodes were rinsed with buffer solution and then applied in PEC detection. RESULTS AND DISCUSSION Materials Characterizations. The as-prepared NGQDs/MoS2 nanoscomposites



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 33

were comprehensively characterized by a number of spectroscopic and microscopic tools. Figure 1A presented the phase structures of the obtained samples examined by X-ray diffraction (XRD) analysis. As can be seen, all the samples displayed quite similar profiles and all the diffraction peaks could be indexed to hexagonal phase MoS2 structure (JCPDS card No. 65-7025). It should be noted that the (002) peak shifts from 14.0o to 10.2o, indicating that the interlayer spacing along c axis expands.27,28 However, no diffraction signal for NGQDs could be discerned in the present XRD pattern of the NGQDs/MoS2 nanoscomposites, which probably resulted from low amount NGQDs in the NGQDs/MoS2 nanoscomposites or high dispersion of NGQDs and the similar results could also be found in other systems.26 The morphology and microstructure of the NGQDs/MoS2 nanoscomposites were investigated by the field emission scanning electron microscope (SEM). As shown in Figure S1, the as-prepared NGQDs/MoS2 nanoscomposites were composed of numerous

nanosheets

with

several

hundred

nanometers.

Furthermore,

the

corresponding elemental mapping images of the NGQDs/MoS2 nanoscomposites (Figure 1B) revealed that the as-prepared samples were composed of N, Mo and S elements with uniform distribution of all the elements. TEM was applied to further explore the microstructure of the as-prepared samples. As can be seen in Figure 1C, it is obviously that the well-defined plate-like morphology of MoS2 had ripples and corrugations, revealing the ultrathin nature of the MoS2 nanoplate. After NGQDs hybridizing with ultrathin MoS2 nanoplates (Figure 1D), it can be seen clearly that several dark dots with diameters of about 3 nm were randomly dispersed on the


Page 9 of 33

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


ultrathin MoS2 nanoplates. The quantum dots on ultrathin MoS2 nanoplates were further investigated by high-resolution trans-mission electron microscopy (HRTEM). As shown in the inset of Figure 1D, the lattice spacing of 0.20 nm were observed, indicating the existence of NGQDs, which further confirmed that NGQDs have been coupled with the ultrathin MoS2 nanoplates in the nanoscale successfully.26 XPS spectra were employed to investigate the surface element composition and chemical nature of the NGQDs/MoS2. Figure 2A displayed the survey scan XPS spectrum, which suggested that the NGQDs/MoS2 samples contained C, N, O, Mo and S elements. The deconvoluted Mo 3d XPS spectrum in Figure 2B exhibited two characteristic peaks at 229.5 and 232.7 eV, which correspond to the Mo 3d5/2 and Mo 3d3/2 orbitals, respectively, suggesting a Mo (IV) characteristic in MoS2.28-30 As for the spectrum of S 2p (Figure 2C), the binding energies located at 162.3 and 163.5 eV are due to S 2p3/2 and 2p1/2, respectively, which could be indexed to Mo-S bonding in MoS2.29,30 The high-resolution XPS spectra of N 1s verify the successful doping of N in the nanocomposites. As demonstrated in Figure 2D, it could be deduced into four peaks centered at about 398.1 eV, 399.2 eV, 400.5 eV and 401.9 eV, which are assigned to pyridine N, pyrrolic N, graphitic N, and N-H, respectively.26 Furthermore, 0.56 wt % nitrogen was estimated to be present in the composites on the base of the XPS analysis, which are expected to improve the PEC performance. Raman spectrum is a powerful tool to characterize the crystalline of 2D materials. As shown in Figure S3, two remarkable peaks can be observed at 1365 cm-1 and 1585 cm-1, which corresponded to the D and G bands of NGQDs, respectively.26



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

Furthermore, the peaks at 375 cm-1 and 420 cm-1 could be attributed to the E12g and A1g vibrational modes of the MoS2, respectively.29 Interestingly, the Raman peaks located at 293 cm-1, and 345 cm-1 could be also detected, which might be assigned to the Mo-O bounds.30 The presence of the Mo-O bonds should be attributed to the good coupling between Mo and oxygen function groups of the NGQDs, which revealed NGQDs were doped into MoS2 rather than mechanically mixed. To examine the PEC performances of the as-synthesized NGQDs/MoS2 nanocomposites, a comparative trial has been applied. As shown in Figure 3A, the NGQDs modified ITO electrode displayed a weak photocurrent of 0.038 µA (curve a) at a potential of 0 V upon photoexcitation with light illumination. The pristine ultrathin MoS2 nanoplates exhibited a relatively high photocurrent of 0.527 µA (curve b), which might be attributed to the excellent PEC performances of ultrathin MoS2 nanoplates. After the introduction of NGQDs into the ultrathin MoS2 nanoplates, a significantly higher photocurrent could be observed, which was 2.15-fold compared to that of the synthesized ultrathin MoS2 nanoplates. The reason might be attributed to the introduction of NGQDs, which improve the photoinduced carriers separation efficiency and benefit to suppress recombination of the electron-holes, resulting the enhanced PEC performances.26 EIS measurements were carried out to further investigate the separation efficiency of the charge carriers and the charge transfer resistance.31 As shown in Figure 3B, the diameter of the arc radius on the EIS Nyquist plot of NGQDs/MoS2 is smaller than that of pristine ultrathin MoS2 nanoplates, indicating an effective separation of


Page 10 of 33

Page 11 of 33

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


photogenerated electron-hole pairs and rapid interfacial charge transfer to the electron donor or electron acceptor over NGQDs/MoS2.26,31 Interestingly, the resistances of the samples are 115.3 and 87.4 Ω for pristine ultrathin MoS2 nanoplates and NGQDs/MoS2, respectively, which demonstrated that the conductivity of ultrathin MoS2 nanoplates is increased greatly after coupling with NGQDs. The high conductivity can facilitate kinetic charge transfer and thus improve the PEC activity.26,31 Photoluminescence (PL) technique was employed to reveal the efficiency of charge carrier trapping and separation of the photoinduced electrons and holes. Figure 4A presented the steady-state PL spectra of the pure MoS2 nanoplates (curve a) and NGQDs/MoS2 samples (curve b) with an excitation wavelength of 480 nm. It is well-known that the PL intensity with higher value stands for higher recombination possibility of electron-hole pairs, while weaker intensity represents lower recombination probability of photoexcited charge carriers.31,32 Obviously, the pristine MoS2 samples and NGQDs/MoS2 nanocomposites exhibited two emission peaks centered at about 620 nm and 730 nm. The peak at 620 nm can be assigned to the direct-gap luminescence influenced by an interlayer coupling and spin-orbit coupling, while the peak located at 730 nm implied indirect-gap luminescence of ultrathin MoS2.33 Compared with pure ultrathin MoS2, the NGQDs/MoS2 nanocomposites displayed much lower PL intensity, which indicated that the modification of NGQDs could enable the effective separation of photo-generated charge carriers.32,33 To further understand the photophysical characteristics of photoexcited charge carriers,



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

ns-level time-resolved fluorescence decay spectra of pristine MoS2 nanoplates and NGQDs/MoS2 were recorded. As shown in Figure 4B, the fluorescence intensities of the four samples decayed exponentially. Notably, in contrast to pristine ultrathin MoS2 nanoplates, the NGQDs/MoS2 displayed slow decay kinetics. Furthermore, the lifetime of charge carriers in NGQDs/MoS2 materials was longer than that of ultrathin MoS2 nanoplates. It is believed that the increased lifetimes of the charge carriers are associated with the improved electron transport, which means a lower recombination rate of the electron-hole pairs.32,34 As we know, the interface and contact are very essential to the properties of 2D heterostructures. Herein, we have investigate the charge separation and charge carriers lifetime of mechanically mixed NGQDs/MoS2 to contrast with the direct grown NGQDs/MoS2 nanocomposites by using the steady-state PL spectra and time-resolved transient PL decay spectra. As shown in Figure. S3A, both mechanically mixed NGQDs/MoS2 and the direct grown NGQDs/MoS2 nanocomposites exhibited two emission peaks centered at about 620 and 730 nm with an excitation wavelength of 480 nm. For the direct grown NGQDs/MoS2 nanocomposites, the emission intensity was much lower than that of the mechanically mixed NGQDs/MoS2 samples, which means that direct grown NGQDs/MoS2 nanocomposites displayed the more efficient charge separation than the mechanically mixed NGQDs/MoS2 samples.32-34 The time-resolved transient PL spectra was employed to further study the mechanically mixed NGQDs/MoS2 samples and the direct grown NGQDs/MoS2 nanocomposites. As exhibited in Figure S3B, the lifetime of charge carriers in the direct grown


Page 12 of 33

Page 13 of 33

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


NGQDs/MoS2 nanocomposites (3.25 s) was much longer than that in the mechanically mixed NGQDs/MoS2

samples (1.84 s),

indicating a lower

recombination rate of the electron-hole pairs in the direct grown NGQDs/MoS2 nanocomposites.32 Feasibility and stepwise fabrication of photoelectrochemical aptasensor. Based on the intense and stable PEC signal, a “signal-off” PEC aptasensor was fabricated for acetamiprid assay, as illustrated in Scheme 1. Figure 5A displayed the photocurrent response

of

the

“signal-off”

PEC

aptasensor

fabrication

process.

Upon

photoexcitation with visible light, the NGQDs/MoS2 modified electrode (curve a) shown a high photocurrent of 1.14 µA owing to the efficient charge separation and the enhanced lifetime of the carriers. However, the photocurrent of the electrode sequentially modified by acetamiprid aptamer (curve c) was declined owing to the steric hindrance of aptamer.35,36 After the aptasensor having specific reaction with 10 pM acetamiprid, the photocurrent decreased to approximately 0.19 µA (curve d) because of the presence of acetamiprid resulting in the change of its aptamer structure, which further prevented the transfer of photogenerated electrons. The stepwise assembly process of the acetamiprid aptasensor was further investigated by EIS using [Fe(CN)6]3-/4- as a redox probe, as shown in Figure 5B. The NGQDs/MoS2 modified ITO electrode (curve a) displayed a electron-transfer resistance (Ret) of 87.4 Ω. With the aptamer (curve c) assembled on ITO-NGQDs/MoS2 electrode, the value of Ret is found to be drastically increased to 160.1 Ω. Such phenomenon might be attributed to the fact that aptamer molecules



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

carrying negative charges induce electrostatic repulsion between electrode surface and negatively charged redox species of [Fe(CN)6]3-/4-.35,37 In the presence of acetamiprid, the aptamer probe could have specific reaction with acetamiprid to form acetamiprid-aptamer complex, which further blocked electron transfer, resulting in the increased electron-transfer resistanc (233.5 Ω).38 All these results suggested the successful stepwise fabrication of the proposed aptasensor. Optimization of conditions for photoelectrochemical detection. To achieve a highly sensitive method with a low detection limit for acetamiprid detection, several experiment parameters including the amount of NGQDs in the nanocomposites, the concentration of aptamer and the incubation time of of acetamiprid with aptamer were optimized. As exhibited in Figure S4, the photocurrent response increased gradually with increasing the weight ratio of NGQDs from 1% to 5% and then slightly decreased as further elevation of the NGQDs, which might be attributed that the increasing NGQDs cover on the surface of ultrathin MoS2 nanosheets would limit the light absorption of MoS2. Therefore, NGQDs5%/MoS2 was selected for the construction of aptasensor in this work. Furthermore, as an acetamiprid recognition probe, the aptamer concentration and incubation time showed an obvious effect on the PEC response to acetamiprid. As displayed in Figure S5, with an increasing concentration of aptamer, the PEC response dramatically declined because it could capture more target analytes. While the aptamer concentration was further increased to more than 2 µM, the photocurrent intensity nearly reached a plateau. Thus, 2 µM of aptamer was employed as the optimal concentration in this work. Figure S6 presented


Page 14 of 33

Page 15 of 33

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 PEC behaviors of different incubation time between aptamer and acetamiprid. It is clearly that the photocurrent intensity of the as-prepared electrode gradually declined with the increasing of the interaction time from 0 min to 40 min and then reached a minimum value in 40 min. Thus, 40 min was chosen as the optimal reaction time to for fabricating the PEC aptasensor. Analytical performances of photoelectrochemical aptasensor. Under the optimal conditions, the as-prepared PEC aptasensor was employed to acetamiprid detection as stated above. Figure 6A depicts the photocurrent response of the aptasensor toward different concentrations of acetamiprid. It is obviously that the photocurrent intensity decreased obviously with the acetamiprid concentration increasing, meaning that more acetamiprid molecules are captured in the PEC process. Figure 6B outlined the relationship between the decrement of photocurrent ∆I ( ∆I = I0

−

I) and logarithm of

acetamiprid concentration, where I0 and I represented the photocurrent intensities of aptasensor in the absence and presence of acetamiprid, respectively. A linear range was determined from 0.05 pM to 1 nM with a detection limit of 16.7 fM at the signal-to-noise ratio of three. For comparison, the analytical characteristics of several acetamiprid biosensors are presented in Table S1. Apparently, our sensing device showed lower detection limit and wider linear range. Such a low detection limit can be satisfactory for the rapid determination of trace acetamiprid in environmental waters and acetamiprid residues in food. The selectivity of the as-prepared aptasensor has been investigated by testing the response of other common species, such as flusilazole, dichlofenthion, imidacloprid,



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 33

tribenuron-methyl, and prochloraz at the same concentration of 1 nM. As can be seen from Figure 7A, the relative response was evaluated from (I0

−

I) / I, where I0 and I

refer to the photocurrent intensity obtained before and after incubation with different pesticides, respectively. The results indicated that all these pesticides displayed negligible photocurrent response on the PEC aptasensor as compared with acetamiprid, revealing the high selectivity against interfering substances for acetamiprid detection. This could be attributed to the specific interaction of aptamer and target acetamiprid molecules.38,39 Since the stability is one of the important points for PEC sensor, it is necessary to investigate this feature of the presented sensor. Figure 7B shown the time-based photocurrent response of the as-prepared PEC aptasensor for 10 times under the optimization condition. There was no obvious change of photocurrent response with the light on, indicating that this PEC aptasensor exhibited very stable performances. Furthermore, the reproducibility of PEC aptasensor was also investigated by measuring

the

photocurrents

of

five

independently

prepared

aptamer-NGQDs/MoS2/ITO electrodes toward 10 pM acetamiprid. The relative standard deviation (RSD) value of 5.9% was obtained, suggesting the good reproducibility. When the aptasensor was not in use, the electrode was stored in dark conditions at 4 oC. The photocurrent response had no significant change after storage for two weeks, showing high stability and detection reliability. Analytical application in real samples. In order to demonstrate the feasibility of the acetamiprid aptasensor in practical analysis, it was employed to measure


Page 17 of 33

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


acetamiprid in tomato and cucumber. The extraction solutions were prepared according to our previous literature.38 100 g of samples were chopped in a conventional food processor for 15 min to obtain thoroughly mixed homogenates. The homogenates were centrifuged for 20 min at 1000 rpm to remove the solids, and then the supernatant was filtered through a 0.22 µm membrane. Subsequently, the liquid transferred into a 10 mL volumetric flask that was brought to volume with ethanol, and reserved for PEC assay. The recoveries were evaluated for the tomatoes and cucumber extraction solutions by standard addition method. As demonstrated in Table 1, the average recoveries range from 89.7% to 108.3% with relative standard deviations (RSD) lower than 6.2% based on triplicate experiments at each concentration, indicating that the proposed method was stable and could be applied to determine acetamiprid residues in food samples. The generality of this method. To further demonstrate the generality of this method, we have developed a novel sensitive and label-free PEC sensor to detect ochratoxin A (OTA), one of the most toxic and widespread naturally occurring mycotoxins, by using the NGQDs/MoS2 nanocomposites with the aids of OTA aptamer. Figure S7 displayed the photocurrent response and EIS results of the “signal-off” OTA PEC aptasensor fabrication process, which is similar to the results of acetamiprid PEC sensor. The as-prepared PEC aptasensor was then employed to OTA detection. As shown in Figure S8A, with the target OTA concentration increasing, the photocurrent intensity decreased gradually, indicating that more OTA molecules are captured on the electrode in the PEC process. A good linear relationship



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

between the the decrement of photocurrent and the concentration of OTA can be obtained in the range from 0.1 pM ~ 0.1 nM (Figure S8B). Notably, the limit of detection (LOD) was calculated to be 0.033 pM at the signal-to-noise ratio of 3. The achieved limit of detection was much lower than those published reports.40,41 In addition, the selectivity of this aptasensor was also evaluated by the comparison of the sensing results of fumonisin B1 (FB1), aflatoxins B1 (AFB1), ochratoxin B (OTB), and OTA (as seen in Figure S9). As expected, the photocurrent response signals to FB1, AFB1, and OTB were neglectable with a concentration of 1 pM, while an obvious increase in response was observed for OTA with the same concentration of. These results indicated the proposed biosensor was highly selective for OTA, which could be attributed to the specific recognition force of aptamer to OTA. All these results indicated the excellent performances of the PEC aptasensor, which makes our strategy among the most sensitive electronic approach for PEC-based monitoring of targets.

CONCLUSION In summary, a simple, ultrasensitive, and selective MoS2-based PEC aptasensing has been demonstrated and successfully used for acetamiprid assay. The results displayed the lifetimes of photogenerated charge carriers of ultrathin MoS2 nanosheets could be prolonged by approximately millisecond timescales after a proper mole ratio of NGQDs were coupled, leading to the promoted charge separation, and giant photocurrent signal-magnify. This work not only enriched the applications of


Page 18 of 33

Page 19 of 33

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


MoS2-based materials, but also provided a new thinking for further understanding the charge separation mechanism in PEC biosensing.

ASSOCIATED CONTENT Supporting Information SEM image of the as-prepared NGQDs/MoS2 nanocomposites. Effects of NGQDs contents, aptamer concentrations, and incubation time on the PEC performances of the as-fabricated PEC aptasensor. Comparison of methods for the determination of acetamiprid. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author Kun Wang*

Tel.: +86 511 88791800; fax: +86 511 88791708. E-mail address: [email protected]

Author Contributions The manuscript was written through the contributions of all the authors. All the authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The present work was supported by the National Natural Science Foundation of



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

China (Nos., 21375050, and 21505055), Key Laboratory of Modern Agriculture Equipment and Technology (No. NZ201109), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (No. PAPD-2014-37) and Qing Lan Project. REFERENCES (1) Du, X. J.; Jiang, D.; Hao, N.; Qian, J.; Dai, L. M.; Zhou, L.; Hu, J. P.; Wang, K. Anal. Chem. 2016, 88, 9622-9629. (2) Devadoss, A.; Sudhagar, P.; Terashima, C.; Nakata, K.; Fujishima, A. J. Photochem. Photobiol. C 2015, 24, 43-63. (3) Zhao, W.-W.; Xu, J.-J.; Chen, H.-Y. Chem. Soc. Rev. 2015, 44, 729-741. (4) Zhao, W.-W.; Xu, J.-J.; Chen, H.-Y. Chem. Rev. 2014, 114, 7421-7441. (5) Ma, W. G.; Han, D. X.; Zhou, M.; Sun, H.; Wang, L. N.; Dong, X. D.; Niu, L. Chem. Sci. 2014, 5, 3946-3951. (6) Zhao, W.-W.; Shu, S.; Ma, Z.-Y.; Wan, L.-N.; Xu, J.-J.; Chen, H.-Y. Anal. Chem. 2013, 85, 11686-11690. (7) Ma, W. G.; Wang, L. N.; Zhang, N.; Han, D. X.; Dong, X. D.; Niu, L. Anal. Chem. 2015, 87, 4844-4850. (8) Shen, Q. M.; Han, L.; Fan, G. C.; Zhang, J. R.; Jiang, L. P.; Zhu, J. J. Anal. Chem. 2015, 87, 4949-4956. (9) Hall, R. N. Phys. Rev. 1952, 87, 387. (10) Shockley, W.; Read, W. T. Phys. Rev. 1952, 87, 835-842. (11) Slavney, A. H.; Hu, T.; Lindenberg, A. M.; Karunadasa, H. I. J. Am. Chem. Soc.


Page 20 of 33

Page 21 of 33

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


2016, 138, 2138-2141. (12) Bi, Y.; Hutter, E. M.; Fang, Y. J.; Dong, Q. F.; Huang, J. S.; Savenije, T. J. J. Phys. Chem. Lett. 2016, 7, 923-928. (13) Zhang, F.; Tan, L. Z.; Liu, S.; Rappe, A. M. Nano Lett. 2015, 15, 7794-7800. (14) Jing, L. Q.; Zhou, J.; Durrant, J. R.; Tang, J. W.; Liu, D. N.; Fu, H. G. Energy Environ. Sci. 2012, 5, 6552-6558. (15) Xie, M. Z.; Fu, X. D.; Jing, L. Q.; Luan, P.; Feng, Y. J.; Fu, H. G. Adv. Energy Mater. 2014, 4, 1300995. (16) Baek, D. J. Korean Phys. Soc. 2015, 67, 1064-1070. (17) Pivrikas, A.; Neugebauer, H.; Sariciftci, N. S. IEEE J. Sel. Top. Quant. 2010, 16, 1746-1758. (18) Chang, Y.; Grein, C. H.; Zhao, J.; Becker, C. R.; Flatte, M. E.; Liao, P.-K.; Aqariden, F.; Sivananthan, S. Appl. Phys. Lett. 2008, 93, 192111. (19) Wang, H. N.; Zhang, C. J.; Rana, F. Nano Lett. 2015, 15, 8204-8210. (20) Liu, Q.; Li, X. L.; He, Q.; Khalil, A.; Liu, D. B.; Xiang, T.; Wu, X. J.; Song, L. Small 2015, 11, 5556-5564. (21) Zhu C. F.; Zeng, Z. Y.; Li, H.; Li, F.; Fan, C. H.; Zhang, H. J. Am. Chem. Soc. 2013, 135, 5998-6001. (22) Ge, J.; Ou, E.-C.; Yu, R.-Q.; Chu, X. J. Mater. Chem. B, 2014, 2, 625-628. (23) Shi, H. Y.; Yuan, R. S.; Bertolazzi, S.; Brivio, J.; Gao, B.; Kis, A.; Jena, D.; Xing, H. G.; Huang, L. B. ACS nano 2013, 7, 1072-1080. (24) Tang, L. B.; Ji, R. B.; Li, X. M.; Bai, G. X.; Liu, C. M.; Hao, J. H.; Lin, J. Y.;



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

Jiang, H. X.; Teng, S. K.; Yang, Z. B.; Lau, S. P. ACS nano 2014, 8, 6312-6320. (25) Yeh, T.-F.; Teng, C.-Y.; Chen, S.-J.; Teng, S. Adv. Mater. 2014, 26, 3297-3303. (26) Yin, Y. Y.; Liu, Q.; Jiang, D.; Du, X. J.; Qian, J.; Mao, H. P.; Wang, K. Carbon 2016, 96, 1157-1165. (27) Xing, J. H.; Liu, Y. H.; Wang, D. K.; Liang, S. J.; Wu, W. M.; Wu, L. J. Mater. Chem. A 2015, 3, 12631-12635. (28) Yu, X. Y.; Hu, H.; Wang, Y. W.; Chen, H. Y.; Lou, X. W. Angew. Chem. Int. Ed. 2015, 54, 7395-7398. (29) Long, H.; Trochimczyk, A. H.; Pham, T.; Tang, Z. R.; Shi, T.; Zettl, A.; Carraro, C.; Worsley, M. A.; Maboudian, R. Adv. Funct. Mater. 2016, 26, 5158-5165. (30) Xie, J. F.; Zhang, J. J.; Li, S.; Grote, F.; Zhang, X. D.; Zhang, H.; Wang, R. X.; Lei, Y.; Pan, B. C.; Xie, Y. J. Am. Chem. Soc. 2013, 135, 17881-17888. (31) Jiang, D.; Du, X. J.; Chen, D. Y.; Li, Y. Q.; Hao, N.; Qian, J.; Zhong, H.; You, T. Y.; Wang, K. Carbon 2016, 102, 10-17. (32) Xu, L.; Xia, J. X.; Wang, L. G.; Qian, J.; Li, H. M.; Wang, K.; Sun, K. Y.; He, M. Q. Chem. Eur. J. 2014, 20, 2244-2253. (33) Zhao, Z. Y.; Zhou, Y.; Wang, F.; Zhang, K. H.; Yu, S.; Cao, K. ACS Appl. Mater. Interfaces 2015, 7, 730-737. (34) Niu, P.; Zhang, L. L.; Liu, G.; Chen, H. M. Adv. Funct. Mater. 2012, 22, 4763-4770. (35) Zang, Y.; Lei, J. P.; Hao, Q.; Ju, H. X. ACS Appl. Mater. Interfaces 2014, 6, 15991-15997.


Page 22 of 33

Page 23 of 33

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


(36) Jiang, D.; Du, X. J.; Chen, D. Y.; Zhou. L.; Chen, W.; Li, Y. Q.; Hao, N.; Qian, J.; Liu, Q.; Wang, K. Biosens. Bioelectron. 2016, 83, 149-155. (37) Li, R. Z.; Liu, Y.; Cheng, L.; Yang, C. Z.; Zhang, J. D. Anal. Chem. 2014, 86, 9372-9375. (38) Jiang, D.; Du, X. J.; Liu, Q.; Zhou, L.; Dai, L. M.; Qian, J.; Wang, K. Analyst 2015, 140, 6404-6411. (39) Fei, A. R.; Liu, Q.; Huan, J.; Qian, J.; Dong, X. Y.; Qiu, B. J.; Mao, H. P.; Wang, K. Biosens. Bioelectron. 2015, 70, 122-129. (40) Jiang, L.; Qian, J.; Yang, X. W.; Yan, Y. T.; Liu, Q.; Wang, K.; Wang, K. Anal. Chim. Acta 2014, 806, 128-135. (41) Wang, C. Q.; Qian, J.; Wang, K.; Hua, M. J.; Liu, Q.; Hao, N.; You, T. Y.; Huang, X. Y. ACS Appl. Mater. Interfaces 2015, 7, 26865-26873.



A

B

b

Intensity / a.u.

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 24 of 33

Mo

a

S

N

PDF#65-7025 10

30

50

70

2θ / degree

C

D

20 nm

50 nm

Figure 1. (A) XRD patterns of JCPDS No. 65-7025, pristine ultrathin MoS2 nanosheets (curve a), and ultrathin NGQDs/MoS2 (curve b); (B) Elemental mapping of the as-prepared ultrathin NGQDs/MoS2; (C) TEM image of the as-prepared ultrathin MoS2 nanosheets; (D) TEM image of the as-prepared ultrathin NGQDs/MoS2. Inset: High-magnification TEM image of NGQDs in the nanocomposites.


0

O 1s

C 1s

Survey N 1s Mo 3p

S 2p Mo 3d

Intensity / a.u.

A

300

B

600

900

Mo 3d52

225

160

S 2p3/2

164

D Intensity / a.u.

S 2p1/2

168

Binding Energy / eV

230

235

240

Binding Energy / eV

S 2p

C

Mo 3d

Mo 3d3/2

Binding Energy / eV

Intensity / a.u.

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


Intensity / a.u.

Page 25 of 33

N 1s

Graphitic N

Pyrrolic N N-H

396

Pyridine N

400

404

Binding Energy / eV

Figure 2. (A) XPS survey spectra of ultrathin NGQDs/MoS2; The high-resolution XPS spectra of the (B) Mo 3d, (C) S 2p, (D) N 1s region of ultrathin NGQDs/MoS2.



1.2

A

B

c 100

0.9 0.6

b

Z'' / Ω

Photocurrent / µA

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 26 of 33

50

0.3 0.0

a Time / s

0

a 0

c 100

b

Z' / Ω

200

Figure 3. (A) Photocurrent responses of NGQDs/ITO (curve a), ultrathin MoS2/ITO (curve b) and NGQDs/MoS2/ITO (curve c); (B) EIS Nyquist plots of NGQDs/ITO (curve a), ultrathin MoS2/ITO (curve b) and NGQDs/MoS2/ITO (curve c).


Page 27 of 33

B Intensity / a.u.

A Intensity / a.u.

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


a

τa = 1.03 s

b

b 600

τb = 3.25 s

a

650

700

Wavelength / nm

750

0

10

20

30

Time / ns

Figure 4. (A) Steady-state PL spectra of the ultrathin MoS2 nanoplates (curve a) and NGQDs/MoS2 samples (curve b) with an excitation wavelength of 480 nm; (B) time-resolved transient PL decay for ultrathin MoS2 nanoplates (curve a) and NGQDs/MoS2 samples (curve b).



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

Scheme 1. Schematic illustration of PEC aptasensing of acetamiprid based on NGQDs/MoS2 nanocomposites.


Page 28 of 33

Page 29 of 33

1.2

A

a

150

B

0.9

100

0.6 0.3

Z'' / Ω

Photocurrent / µ A

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


b

c

50

c

b a

0

0.0

0

Time / s

100

200

Z' / Ω

300

Figure 5. PEC (A) and EIS (B) characterization of the “signal-off” switch system based

aptasensor

fabrication

aptamer-NGQDs/MoS2/ITO

(curve

process: b),

NGQDs/MoS2/ITO and

acetamiprid

aptamer-NGQDs/MoS2/ modified ITO (curve c).


(curve interact

a), with


0.5

A

0.4

B -0.2

a k

0.3 0.2 0.1

∆ I / µA

0.6

Photocurrent / µA

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 30 of 33

-0.3

-0.4

0.0

Time / s

-14

-12

-10

-8

log [C / M]

Figure 6. (A) Photocurrent response of the PEC aptasensor at different concentrations of acetamiprid: 0 (a), 0.05 pM (b), 0.1 pM (c), 0.5 pM (d), 1 pM (e), 5 pM (f), 10 pM (g), 50 pM (h), 100 pM (i), 500 pM (j) and 1 nM (k). (B) The corresponding linear calibration curve.


60

A

1.2

Photocurrent/ µA

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


Relative response / %

Page 31 of 33

40 20 0

B

0.8 0.4 0.0

l ol d os ary rid thion phen pri rif op mi carb orpy a o d a r r a t a o id lp chl ace chl im thy enta me p

0

100

200

300

400

500

Time/ s

Figure 7. (A) Selectivity of NGQDs/MoS2 nanocomposites based PEC aptasensor for acetamiprid detection over other interferences under the optimal conditions; (B) Stability of PEC aptasensor based on NGQDs/MoS2.



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 32 of 33

Table 1. Analysis of real samples with acetamiprid at different concentrations. Sample

Added (pM)

Detected (pM)

Recovery (%)

RSD (%) (n=3)

Tomato

0

-

-

-

50.0

45.2

90.4

3.7

100.0

105.9

105.9

6.2

150.0

138.6

92.4

4.8

0

-

-

-

50.0

45.9

91.8

4.3

100.0

89.7

89.7

5.4

150.0

162.5

108.3

6.1

Cucumber


Page 33 of 33

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


TOC


New Insights toward Efficient Charge-Separation Mechanism for High

Recommend Documents