Quenching effect of exciton energy transfer from CdS:Mn to Au nanoparticles: A highly efficient photoelectrochemical strategy for microRNA-21 detection

Sensors and Actuators B 254 (2018) 159–165

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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Quenching effect of exciton energy transfer from CdS:Mn to Au nanoparticles: A highly efficient photoelectrochemical strategy for microRNA-21 detection Bing Wang a,b , Yu-Xiang Dong a,b , Yu-Ling Wang a,b , Jun-Tao Cao a,b,∗ , Shu-Hui Ma c , Yan-Ming Liu a,b,∗ a

College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, China Institute for Conservation and Utilization of Agro-bioresources in Dabie Mountains, Xinyang Normal University, Xinyang 464000, China c Xinyang Central Hospital, Xinyang 464000, China b

a r t i c l e

i n f o

Article history: Received 22 May 2017 Received in revised form 4 July 2017 Accepted 12 July 2017 Available online 14 July 2017 Keywords: Energy transfer CdS:Mn AuNPs Photoelectrochemical biosensor microRNA-21

a b s t r a c t A novel and simple photoelectrochemical (PEC) biosensing method for microRNA-21 (miRNA-21) detection is reported based on energy transfer (ET) between CdS:Mn doped structure (CdS:Mn) and Au nanoparticles (AuNPs). In this protocol, TiO2 -CdS:Mn hybrid structure was used as a sensing platform for hairpin DNA immobilization. In the absence of miRNA-21, the immobilized DNA was in the hairpin form. In this state, the photocurrent of the electrode was greatly depressed, due to the effective ET effect produced by short interparticle distance between CdS:Mn and AuNPs. In the presence of miRNA-21, the hairpin DNA hybridized with miRNA-21 and changed into a more rigid, rodlike double helix, which forced the AuNPs away from the electrode surface, leading to obvious recover of photocurrent because of the vanished damping effect. Integrating the fine PEC performance of TiO2 -CdS:Mn hybrid structure with the significant ET effect between CdS:Mn and AuNPs, the sensitive detection of miRNA-21 was realized in a linear range of 1.0 fM to 10.0 pM with a low detection limit of 0.5 fM. This method might be aussichtsreich for the detection of miRNAs and other biomarkers. © 2017 Published by Elsevier B.V.

1. Introduction Photoelectrochemical (PEC), emerged as a newly promising method for the detection of biomarkers, with features such as high sensitivity, low price, simple equipment, and easy miniaturization [1–5]. Moreover, it owns potentially high sensitivity because of the totally separated and different energy forms of the excitation source and detection signal, resulting in the reduced background signals. Hence, PEC holds great promise for the applications in bioassay [6–10]. Since the demand for sensitive detection of biomarkers, it is vital to seek effective and sensitive method to evidently enlarge photoelectric transformation efficiency of the sensor. For this purpose, integrating of the large band gap semiconductors with narrow band gap semiconductive materials to fabricate sensitized structure has provided an effective approach to increase PEC signal [11–13]. Highly ordered TiO2 nanotube arrays

∗ Corresponding authors at: College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, China. E-mail addresses: [email protected] (J.-T. Cao), [email protected] (Y.-M. Liu). http://dx.doi.org/10.1016/j.snb.2017.07.078 0925-4005/© 2017 Published by Elsevier B.V.

(NTs) as an excellent substrate material, with inherent features such as chemical and physical stability, high surface area, photoelectric activity, biocompatibility etc. [14], have been widely used to construct PEC sensing platform [15–18]. However, TiO2 can only absorb the UV-light (<387 nm) due to the wide energy band gap (∼3.2 eV), causing the insufficient employment of optical energy. The band gap of CdS (∼2.4 eV) could match with the suitable absorption range of medium wavelength light (<520 nm). Mn2+ is usually drew into CdS to bring CdS:Mn doping structure (CdS:Mn) to significantly inhibit the electron-hole recombination, because the doped Mn2+ ion could create a new band gap in the midst of CdS [19–22]. Consequently, coupling TiO2 with narrow band gap semiconductors to form sensitized structure should be a very useful avenue to promote the electron transfer, depresses electron-hole recombination and improve the photoelectric conversion efficiency. Gold nanoparticles (AuNPs) with beneficial physical properties have been extensively studied and utilized in bioassay [23–25]. In a PEC system, due to certain spectral overlap, the luminescence resulted from the photoexcitation of the CdS QDs would induce the surface plasmon resonance of the proximal AuNPs, and in turn adjust the exciton states in the CdS QDs through the energy transfer

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(ET) effect, causing the obvious photocurrent reduction [26–28]. So, is there a similar ET effect between CdS:Mn and AuNPs? Herein, we developed a PEC biosensing platform for highly sensitive detection of microRNA-21 (miRNA-21) based on the structure of CdS:Mn sensitized TiO2 NTs (TiO2 -CdS:Mn) and AuNPs. There is a novel ET between CdS:Mn and AuNPs produced signal quenching effect for PEC detection. The detailed fabrication process of the biosensor was investigated. The prepared biosensor was successfully applied for the determination of miRNA-21 in real samples. 2. Experimental 2.1. Chemicals Hydrofluoric acid (HF), glacial acetic acid, methanol and ethanol were bought from Tianjin Yongda Chemical Reagent Co., Ltd. (China). Cadmium nitrate (Cd(NO3 )2 ·4H2 O), manganese acetate (Mn(Ac)2 ·4H2 O) and sodium sulfide (Na2 S·9H2 O) were purchased from Shanghai Aladdin Reagent Inc. (China). Sodium borohydride (NaBH4 ) was from Tianjin BASF Chemical Co., Ltd. (China). HAuCl4 ·4H2 O was from Shanghai Chemical Reagent Co., (China). AuNPs were prepared by NaBH4 reduction of HAuCl4 in aqueous solution [29]. Ascorbic acid (AA), chitosan powder (CS) and glutaraldyhyde (GLD) (50% aqueous solution) were from Sinopharm Chemical Reagent Co., Ltd. (China). Dipotassium hydrogen phosphate (K2 HPO4 ·3H2 O), monosodium phosphate (NaH2 PO4 ·2H2 O) and muriate of potash (KCl) were from Tianjin Kaitong Chemical Reagent Co., Ltd. (China). All other reagents were of analytical grade and used as received. All aqueous solutions were prepared using ultrapure water (Kangning water treatment solution provider, China). PBS was prepared with K2 HPO4 ·3H2 O, NaH2 PO4 ·2H2 O and KCl, being employed for washing buffer solution and detecting bottom liquid which contained 0.1 M AA. The oligonucleotides used in this work were from Shanghai Sangon Biotech Co., Ltd. (China) with the following sequences: hairpin DNA, 5 -NH2 -TTT TTT CGC AC TAG CTT ATC AGA TCA ACA TCA GTC TGA TAA GCT A-SH-3 ; target miRNA-21, UAG CUU AUC AGA CUG AUG UUG A. 2.2. Apparatus PEC experiments were carried out using a homemade photoelectrochemical system, containing a CHI660E electrochemical

workstation (Shanghai Chenhua Apparatus Corporation, China) and a PEAC 200A PEC reaction instrument (Tianjin Aidahengsheng Science-Technology Development Co., Ltd., China) with a three-electrode system: a modified TiO2 NTs electrode with a geometric area of 0.25 cm2 as the working electrode, a Pt wire as the counter electrode, and a saturated Ag/AgCl electrode as the reference electrode. Ultraviolet-visible (UV-vis) absorption spectra and fluorescence spectrum were recorded by an UVmini-1240 UV–vis spectrophotometer and the Hitachi F-7000 spectrofluorophotometer (Shimadzu, Kyoto, Japan), respectively. Scanning electron microscopy (SEM) images were got employing a S-4800 (Hitachi, Tokyo, Japan). Transmission electron microscopy (TEM) images were acquired utilizing a Tecnai G2 F20 TEM system (FEI Co., USA). 2.3. Fabrication of TiO2 -CdS:Mn electrode TiO2 NTs were prepared by the anodic oxidation method according to the literature with minor revision [30]. The modification lies in that the time of anodic oxidation was changed to 50 min. Next, the TiO2 -CdS:Mn electrode was equipped by the successive ionic layer adsorption and reaction (SILAR) technique with appropriate modifications [31]. Specific for, a prepared TiO2 NTs was immersed in the methanol solution including 0.1 M Cd(NO3 )2 and 0.08 M Mn(Ac)2 for 2 min, and then dipped into 0.1 M Na2 S ethanol/water mixture (1:1, v/v) for another 2 min, subsequently the film was carefully washed with absolute methanol. This progress was conducted six times, and the TiO2 -CdS:Mn electrode was accomplished. 2.4. Preparation of the biosensor The detailed procedure was described in Scheme 1. First of all, the TiO2 -CdS:Mn electrode was treated with 20 ␮L of 2% acetic acid solution containing 0.1 mg/mL CS and dried at 60 ◦ C. Then 20 ␮L of 2.5% GLD was covered onto the electrode surface and remained for 1 h at room temperature. Next, 20 ␮L of 0.5 ␮M hairpin DNA was dropped on the electrode and allowed to incubate at 37 ◦ C for 1 h. For target detection, the electrode was incubated with 20 ␮L of different concentrations of target miRNA at 37 ◦ C for 1 h. Subsequently the electrode was covered with 20 ␮L of AuNPs at 4 ◦ C in a humid atmosphere overnight. After each fabrication step, 0.1 M PBS was

Scheme 1. Schematic illustration of the equipment of PEC biosensor for miRNA-21 detection.

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Fig. 1. SEM images of the as-prepared (A) TiO2 NTs, (B) TiO2 -CdS:Mn; (C) and (D) corresponding EDX spectrums; (E) Photocurrent intensities of (a) TiO2 NTs, (b) modified with CdS and (c) modified with CdS:Mn; (F) UV−vis spectrum of Au NPs (curve a) and fluorescence spectrum of CdS:Mn (curve b), insert: TEM image of AuNPs.

utilized to rinse the modified electrode. Eventually, the resulting electrode was introduced into the photocurrent test. PEC detection was performed in PBS (pH 7.4, 0.1 M) including 0.1 M AA, and used the white light with a spectral range from 400 to 700 nm as excitation light.

that the obtained TiO2 NTs is pure. From Fig. 1D, it can be seen that only Ti, O, Cd, S and Mn elements existed, implying that CdS:Mn was successfully assembled on the TiO2 NTs.

3. Results and discussion

3.2. PEC behavior of TiO2 -CdS:Mn electrode

3.1. Characterization of TiO2 NTs and TiO2 -CdS:Mn

The wide band gap of TiO2 (∼3.2 eV) leads to the poor utilization of light energy which presented a low photoelectric response (curve a in Fig. 1E). The band gap of CdS (∼2.4 eV) corresponds to the optimal absorption range of medium wavelength light, in that way, combining of TiO2 with CdS can adequately use the energy of exciting light and significantly enhance the photocurrent intensity (curve b in Fig. 1E). In addition, the doped Mn2+ in CdS could evidently promote charge separation and depress the electron-hole recombination, hence, the photocurrent intensity of TiO2 -CdS:Mn obviously enhances (curve c in Fig. 1E). Accordingly, the TiO2 -CdS:Mn electrode was selected as the desired substrate in this work.

SEM was utilized to characterize the surface topographies of TiO2 and TiO2 -CdS:Mn. Fig. 1A and B exhibit the typical SEM images of the surfaces of TiO2 NTs and TiO2 -CdS:Mn, respectively. As shown in Fig. 1A, highly ordered TiO2 NTs with an average diameter of about 60 nm have been well fabricated on the titanium sheet. From Fig. 1B, after depositing CdS:Mn in situ, a great deal of small particles were distributed on the TiO2 NTs with the size range of 5–10 nm. For further investigating the situation of CdS:Mn coating on the TiO2 NTs, the corresponding EDX spectra were obtained. As demonstrated by Fig. 1C, only Ti and O elements existed, indicating

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Fig. 2. Effects of (A) coating time and (B) coating number of CdS:Mn on photocurrent responses of the TiO2 -CdS:Mn electrode; (C) effect of incubation time of miRNA-21 on photocurrent change of PEC biosensor.

3.3. Characterization of AuNPs The curve a in Fig. 1F displays the typical UV–vis absorption spectrum of the AuNPs with the maximum absorption peak at ca. 520 nm, and the insert in Fig. 1F demonstrates that the AuNPs have a quasi-spherical structure with a diameter of about 5 nm. Moreover, the curve b in Fig. 1F depicts the fluorescence spectrum of CdS:Mn, it could be observed a symmetrical excitonic emission peak centered at ca. 524 nm. Significantly, the fluorescence spectrum of the CdS:Mn has a large spectral overlap with the absorption of the Au NPs, which would be beneficial to induce the highly effective ET. 3.4. Optimization of experimental conditions The photocurrent intensity could be affected by the depositing amount of CdS:Mn on TiO2 electrode and the incubation time of miRNA-21. To optimize the loading amount of CdS:Mn on the TiO2 electrode, the different treatment time and cycles were investigated. As shown in Fig. 2A and B, the modification with two minutes in each step (A) and six SILAR cycles of CdS:Mn (B) could be used to fabricate the TiO2 -CdS:Mn electrode. The PEC response of incubation time of miRNA-21 with the electrode was depicted in Fig. 2C and the maximum value of photocurrent intensity was obtained after 60 min in the existence of 10 pM miRNA-21, therefore, 60 min was served as the incubation time for the miRNA-21 in this experiment. 3.5. PEC behaviors of the biosensor The assembly process of the biosensor was monitored by photocurrent changes, as shown in Fig. 3. The TiO2 NTs electrode displays a small photocurrent intensity (curve a), because TiO2 could only absorb UV light so that the photoelectric conversion efficiency is low. After deposition of CdS:Mn, the photocurrent intensity (curve b) has a sharp rise compared with that of the

Fig. 3. Photocurrent intensities of (a) bare TiO2 NTs electrode, (b) modified with CdS:Mn, (c) coated by CS, (d) after incubation with hairpin DNA, (e) after modified with AuNPs, (f) after being incubated with 10.0 pM miRNA-21 and then with fixed AuNPs.

TiO2 NTs electrode, revealing that CdS:Mn could promote charge separation and depress the electron-hole recombination. As compared to the CdS:Mn modified electrode, the immobilization of CS (curve c) and hairpin DNA (curve d) have caused gradually degressive photocurrent intensities, due to poor conductivity and steric hindrance, respectively. Moreover, the modification of AuNPs produces an evidently weak photocurrent response (curve e), the remarkable decline indicates the strong quenching effect of the AuNPs against the CdS:Mn, as shown in Scheme 2. Since after incubation of miRNA-21 and then with fixed AuNPs, the photocurrent response (curve f) rises again, confirming the successful hybridization of hairpin DNA and miRNA-21 which forced AuNPs away from

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Fig. 4. (A) Photocurrent response and (B) calibration curve of the biosensor for detection of miRNA-21. The error bars showed the standard deviation of three replicate determinations.

Scheme 2. Energy transfer mechanism of the operating PEC system in AA electrolyte.

CdS:Mn. Accordingly, photocurrent characterization proved that the proposed bioassay is successfully constituted. 3.6. Analytical performance To explore the relationship between the photocurrent response and the concentration of miRNA-21, a series of miRNA-21 concentrations were tested. The results recorded in Fig. 4A show that the photocurrent response of the biosensor enhances gradually with increase of the concentration of miRNA-21. The photocurrent response is proportional to the logarithm of miRNA-21 concentration ranged from 1.0 fM to 10.0 pM, as displayed in Fig. 4B. The regression equation is I = − 216.07 − 10.19 log C with the correlation coefficient of 0.9940. Furthermore, the limit of detection was experimentally found as 0.5 fM. Additionally, the stability of the biosensing platform was estimated (see Fig. 5), indicating stable readout for signal collection. The storage stability of the biosen-

Fig. 5. The stability of DNA/GLD/CS/CdS:Mn modified TiO2 NTs electrode.

sor was also tested before the 10.0 pM miRNA-21 capturing. The experimental results showed that there is no apparent change in PEC signal for the detection of miRNA-21 within 2 weeks of storage at 4 ◦ C.

3.7. Application in the human serum To estimate the applicability of this proposed approach, the recovery was determined by the standard addition method in two human serum samples from Xinyang Central Hospital, the serum samples were directly measured for determination of miRNA-21 without any dilution. As listed in Table 1, the recovery of miRNA21 in serum samples ranged from 90% to 103.3%, the RSDs are no more than 6.3%, indicating that the proposed approach has good potential for the analysis of miRNA-21 in real samples.

Table 1 Recovery of miRNA-21 in human serum samples. Serum samples

Found (pmol L−1 )

Added (pmol L−1 )

Total found (pmol L−1 )

Recovery (%)

RSD (%) (n = 3)

Normal person

0.013

patient

0.88

0.001 0.01 0.1 0.01 0.1 1.0

0.014 0.023 0.109 0.889 0.978 1.913

100 100 96 90 98 103.3

6.3 3.0 2.1 3.3 2.3 5.5

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4. Conclusion In summary, a sensitive PEC biosensing platform was developed for miRNA-21 detection based on the effective ET effect between CdS:Mn and AuNPs. As matrix of the PEC sensor, TiO2 -CdS:Mn hybrid structure could greatly improve the photocurrent response. As signal quenching elements, AuNPs could greatly influence the photocurrent intensity by combination of ET from CdS:Mn to AuNPs with conformation change of the hairpin DNA after hybridization with miRNA-21. Benefiting from the excellent PEC performance of the TiO2 -CdS:Mn hybrid structure and the strong quenching effect of AuNPs, the well-designed RNA assay achieves highly sensitive detection of miRNA-21. With advantages such as high sensitivity, simple operation, high stability, the method was successfully applied for the determination of miRNA-21 in real samples. This strategy could be easily extended to detect other biomarkers and provide promising potentials in the application of bioanalysis. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant 21675136, 21375114, 21405129), Plan for Scientific Innovation Talent of Henan Province (2017JR0016), Funding Scheme for the Young Backbone Teachers of Higher Education Institutions in Henan Province (2016GGJS-097), Major Projects of Science and Technology of Henan (141100310600), University Graduate Students Research Innovation Fund of Xinyang Normal University (2016KYJJ37), and Nanhu Young Scholar Supporting Program of XYNU. References [1] W.W. Zhao, J.J. Xu, H.Y. Chen, Photoelectrochemical bioanalysis: the state of the art, Chem. Soc. Rev. 44 (2015) 729–741. [2] Y. Zang, J.P. Lei, Q. Hao, H.X. Ju, CdS/MoS2 heterojunction-based photoelectrochemical DNA biosensor via enhanced chemiluminescence excitation, Biosens. Bioelectron. 77 (2016) 557–564. [3] Y.L. Li, S.P. Zhang, H. Dai, Z.S. Hong, Y.Y. Lin, An enzyme-free photoelectrochemical sensing of concanavalin A based on graphene-supported TiO2 mesocrystal, Sens. Actuators B 232 (2016) 226–233. [4] W.W. Zhao, J.J. Xu, H.Y. Chen, Photoelectrochemical enzymatic biosensors, Biosens. Bioelectron. 92 (2017) 294–304. [5] N. Zhang, L. Zhang, Y.F. Ruan, W.W. Zhao, J.J. Xu, H.Y. Chen, Quantum-dots-based photoelectrochemical bioanalysis highlighted with recent examples, Biosens. Bioelectron. 94 (2017) 207–218. [6] Y.X. Dong, J.T. Cao, Y.M. Liu, S.H. Ma, A novel immunosensing platform for highly sensitive prostate specific antigen detection based on dual-quenching of photocurrent from CdSe sensitized TiO2 electrode by gold nanoparticles decorated polydopamine nanospheres, Biosens. Bioelectron. 91 (2017) 246–252. [7] Q.M. Shen, L. Han, G.C. Fan, E.S. Abdel-Halim, L.P. Jiang, J.J. Zhu, Highly sensitive photoelectrochemical assay for DNA methyltransferase activity and inhibitor screening by exciton energy transfer coupled with enzyme cleavage biosensing strategy, Biosens. Bioelectron. 64 (2015) 449–455. [8] M. Zhao, G.C. Fan, J.J. Chen, J.J. Shi, J.J. Zhu, Highly sensitive and selective photoelectrochemical biosensor for Hg2+ detection based on dual signal amplification by exciton energy transfer coupled with sensitization effect, Anal. Chem. 87 (2015) 12340–12347. [9] H.B. Li, Y.F. Qiao, J. Li, H.L. Fang, D.H. Fan, W. Wang, A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles, Biosens. Bioelectron. 77 (2016) 378–384. [10] H.S. Yin, B. Sun, Y.L. Zhou, M. Wang, Z.N. Xu, Z.L. Fu, S.Y. Ai, A new strategy for methylated DNA detection based on photoelectrochemical immunosensor using Bi2 S3 nanorods, methyl bonding domain protein and anti-his tag antibody, Biosens. Bioelectron. 51 (2014) 103–108. [11] Q.Y. Wang, J.L. Qiao, J. Zhou, S.M. Gao, Fabrication of CuInSe2 quantum dots sensitized TiO2 nanotube arrays for enhancing visible light photoelectrochemical performance, Electrochim. Acta 167 (2015) 470–475. [12] G.C. Fan, L. Han, H. Zhu, J.R. Zhang, J.J. Zhu, Ultrasensitive photoelectrochemical immunoassay for matrix metalloproteinase-2 detection based on CdS:Mn/CdTe cosensitized TiO2 nanotubes and signal amplification of SiO2 @Ab2 conjugates, Anal. Chem. 86 (2014) 12398–12405. [13] Z. Li, L.B. Yu, Y.B. Liu, S.Q. Sun, CdS/CdSe quantum dots co-sensitized TiO2 nanowire/nanotube solar cells with enhanced efficiency, Electrochim. Acta 129 (2014) 379–388.

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Biographies Bing Wang is a graduate student at Xinyang Normal University. Her current researches include photoelectrochemical sensors and biosensors. Yu-Xiang Dong is a graduate student at Xinyang Normal University. His current researches include photoelectrochemical sensors and biosensors. Yu-Ling Wang is a graduate student at Xinyang Normal University. Her current researches include electrochemiluminescence sensors and biosensors. Jun-Tao Cao received his PhD in 2013 from Nanjing University. He now works in Xinyang Normal University. His research interests include preparation of functional nanomaterials, and fabrication of electrochemical, photoelectrochemical and electrochemiluminescent sensors and biosensors.

B. Wang et al. / Sensors and Actuators B 254 (2018) 159–165 Shu-Hui Ma is a technologist-in-charge in clinical laboratory. She now works in the Xinyang Central Hospital. Yan-Ming Liu began his academic career in 1988 at college of chemistry and chemical engineering, Xinyang Normal University. He received his PhD degree from college of chemistry and molecular science at Wuhan University in China in 2002.

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Since 2002, he has been a full professor of chemistry at Xinyang Normal University. His research interests focus on the bioanalysis based on preparation of functional nanomaterials, as well as their applications in chemiluminescence, electrochemiluminescence combined with capillary electrophoresis, and fabrication of electrochemical and electrochemiluminescent biosensors.