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Gold Nanoparticles Decorated Hematite Photoelectrode for Sensitive and Selective Photoelectrochemical Aptasensing of Lysozyme Zhenzhen Li, Changjiang Su, Dan Wu, and Zhonghai Zhang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b04015 • Publication Date (Web): 06 Dec 2017 Downloaded from http://pubs.acs.org on December 7, 2017
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Analytical Chemistry
Gold Nanoparticles Decorated Hematite Photoelectrode for Sensitive and Selective Photoelectrochemical Aptasensing of Lysozyme Zhenzhen Li, Changjiang Su, Dan Wu, Zhonghai Zhang* School of Chemistry and Molecular Engineering, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China. ABSTRACT: Photoelectrochemical aptasensor (PECAS) is a new and promising detection platform with both high sensitivity and good selectivity. Exploration of new photoelectrode materials and establishment of effective charge transfer channel between photoelectrode and aptamer are the main challenges in this field. In this work, an efficient PECAS based on Au nanoparticles (NPs) decorated Fe2O3 nanorod photoelectrode is rationally designed, fabricated, and exhibited excellent sensitivity and selectivity for detection of lysozyme (Lys) with an ultralow detection limit of 3 pM and wide detection range from 10 pM to 100 nM. The Au NPs not only act as anchor to establish an efficient charge transfer channel between the photoelectrode and the aptamer, but also help to enhance the PEC performance through adjusting the carrier density of Fe2O3. The rationally designed photoelectrode opens up a distinctive avenue for promoting the PECAS to be a versatile analysis method.
Photoelectrochemical (PEC) analysis is a rapidly developing and promising detection platform with versatile detection ranges from ions, molecules, peptides, proteins, even to living cells.1,2 The PEC analysis is proposed to integrate light exciting and photocurrent recording in the same device, and such unique signal transducing modality significantly reduces the background noise, which guarantees high sensitivity.3,4 Beside sensitivity, the selectivity is also vital for its practical applications, and in PEC analysis, the selectivity is implemented through coupling molecular recognition units, such as enzymes, antibodies, and aptamers, into the photoelectrodes.5-8 Among them, aptamer, artificial synthesized single-stranded nucleic acid molecule with shorter than 100 nucleotides, distinguishes itself due to its following advantages: (1) in vitro synthesis through a systematic evolution of ligands by exponential enrichment (SELEX) process, (2) rationally designed spatial structures, (3) extremely high affinity and specific binding selectivity to targets, (4) good stability against biodegradation, and (5) nontoxicity for combination of any molecular targets,9-11 which promotes a new and important detection platform in PEC analysis of PEC aptasensor (PECAS). Recently, Zhao et al, have reviewed the latest research progress about PECAS,12 and some special and important works have been further mentioned here: Willner et al, have first proposed a CdS based PECAS for cocaine detection;13 based on functionalized graphene-CdSe nanoparticles, Zhang and co-authors have
proposed a PECAS for thrombin detection;14 an in-situ generated strategy has been developed by Dai for successfully detection of Hg2+ and Ag+;15,16 very recently, the twodimensional MoS2-graphene composites have been introduced by Wang and his co-authors to fabricate PECAS for acetamiprid detection with subfemtomolar level;17 our group have also contributed to design new PECASs with Au nanoparticle functionalized self-doped TiO2 nanotube and nanoporous BiVO4 for detection of kanamycin and thrombin respectively.18,19 As the photoactive species and substrate for aptamers anchoring, photoelectrodes are crucial for detection performance of PECAS. A series of efficient optoelectronic materials, such as TiO2, CdS, g-C3N4, BiVO4, Bi4NbO8Cl, have been employed for assembling of PECASs.20-25 Surprisingly, as an important and promising visible light responsive semiconductor of hematite, αFe2O3, with merits of suitable energy band gap for light harvesting, good biocompatibility and chemical stability, and low cost, widely investigated in PEC water splitting and photocatalytic applications,26,27 has rarely been employed for PEC detection,28,29 and only one paper about hematite-based PECAS has been reported.30 In our opinion, two main intrinsic drawbacks limit the application of hematite in PEC aptasensing: (1) poor electron mobility and short hole diffusion length result in the high electron-hole recombination rate;31 (2) lacking of proper binding between hematite and aptamer to establish an efficient charge transfer channel. To address these concerns,
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many efforts have been made to improve the PEC performance of hematite-based photoelectrode, such as nanostructure design, metal ion doping, and noble metal decoration.32-35 In this work, the hematite is rationally designed with one-dimensional nanorod structure to reduce the transfer distance of excited charges, with high crystallinity through annealing at high temperature for further facilitating electron transfer, and with decoration of gold nanoparticles (Au NPs) to inhibit the recombination of photo-generated electrons and holes, furthermore, the Au NPs act as an “anchor” to bind the aptamer through the Au–S bond between the Au NPs and premodified mercapto group on aptamer (HS-aptamer) and thus an efficient charge transfer channel has been established. Herein, Au NPs decorated hematite-based PECAS is proposed with lysozyme (Lys) as target model. Lys is a kind of alkaline protease with 129 amino acids stabilized by four cysteine disulfide bonds. The Lys is called “body’s own antibiotic” with natural protection function against pathogens, which plays essential roles in the innate immune system, and the concentration level of Lys can be used as a biological indicator of disease diagnosis and treatment, especially for the diagnosis and treatment of atherosclerotic cardiovascular diseases.36 The coupling of aptamer and Au/Fe2O3 not only efficiently accelerate the electron migration but also implement selective detection, finally, a promising PECAS with high sensitivity, good selectivity, reproducibility, and stability can be expected for practical applications. EXPERIMENTAL SECTION Chemicals and Materials All reagents are of analytical grade and used as received without any further purification. The fluorine doped Tin Oxide (FTO) glass was supplied by Zhuhai Kaivo Optoelectronic Technology Co., Ltd. Iron (III) chloride (FeCl3), urea, chloroauric acid (HAuCl4), potassium chloride (KCl), disodium hydrogen phosphate (Na2HPO4), potassium dihydrogen phosphate (KH2PO4), 6-mercapto-1hexanol (MCH), bovine serum albumin (BSA), trypsin from bovin pancreas (Trypsin), L-phenylalanine (L-Phe), L-proline (L-Pro), L-histidine (L-His), Lys from egg white were supplied by Macklin Inc, Shanghai, China. Thiol terminated Lys binding DNA aptamer (5’-HS-(CH2)6-ATC AGG GCT AAA GAG TGC AGA GTT ACT TAG-3’) was obtained from Sangon Biotech, Shanghai, China. All aqueous solutions were prepared using ultrapure deionized water with a resistivity of 18.2 MΩ cm. Preparation of Au/Fe2O3 photoelectrode The substrates of FTO glass (1 cm × 4 cm) were firstly cleaned in acetone, ethanol, and deionized water for 20 min respectively. The preparation of Fe2O3 was followed the previously reported method.37 Typically, 0.1 M FeCl3 and 0.15 M urea were dissolved to 12 mL aqueous solution, and then transferred into a Teflon-lined stainless auto-
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clave (25 mL) with a piece of cleaned FTO glass immersed into the solution. The autoclave was sealed and maintained at 100 °C for 4 h. As the autoclave cooling down naturally, the FTO glass covered with FeOOH was taken out, washed with ultrapure water, and dried at 60 °C. The FeOOH was converted to Fe2O3 with annealing in air at 550 °C for 3 h, 650 °C for 10 min, and 750 °C for 10 min. Finally, the Au NPs were decorated on the Fe2O3 with a photocatalytic reduction method with dipping the Fe2O3 into 1 mM of HAuCl4 solution (pH = 6.5) under simulated solar light irradiation (100 mW cm-2) for 30 min. Fabrication of PECAS Thiolated aptamer was first activated at 95 °C for 10 min and gradually cooled to room temperature for 30 min. Then, the Au/Fe2O3 was incubated with the aptamer in buffer with optimized concentration of 2 μM at 4 °C overnight. The aptamer can be tightly combined on the Au NPs surface though unique Au-S bond. The aptamer/Au/Fe2O3 was thoroughly rinsing with deionized water to remove unbinding aptamers, and dried in air. Next, the aptamer/Au/Fe2O3 was further immersed in 1 mM MCH for 1 h to occupy all possible binding sites on Au NPs, and was washed, dried, and stored at 4 °C for further sensing applications. Material Characterizations The micro-morphologies of photoelectrodes were characterized by scanning electron microscopy (SEM, Hitachi S4800) and transmission electron microscopy (TEM, JEOL JEM 2100). The crystalline structure of the electrodes was analyzed by X-ray diffraction (XRD) on a Bruker D8 Discover diffractometer using Cu Kα radiation (1.540 598 Å). Chemical compositions and status were analyzed by X-ray photoelectron spectroscopy (XPS) on an Axis Ultra instrument (Kratos Analytical) under ultrahigh vacuum (
