Bismuth-containing semiconductors for photoelectrochemical sensing and biosensing

Coordination Chemistry Reviews 393 (2019) 9–20

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Coordination Chemistry Reviews journal homepage: www.elsevier.com/locate/ccr

Review

Bismuth-containing semiconductors for photoelectrochemical sensing and biosensing Si-Yuan Yu a,b,c,1, Ling Zhang c,1, Li-Bang Zhu c,1, Yuan Gao a,c,1, Gao-Chao Fan b,1, De-Man Han a,⇑, Guangxu Chen d,⇑, Wei-Wei Zhao c,⇑ a

Department of Chemistry, Taizhou University, Jiaojiang 318000, China Shandong Key Laboratory of Biochemical Analysis, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China d Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, United States b c

a r t i c l e

i n f o

Article history: Received 13 March 2019 Accepted 7 May 2019 Available online 15 May 2019 Keywords: Bismuth Semiconductor Photoelectrochemical Sensing Biosensing Review

a b s t r a c t Photoelectrochemical (PEC) sensing and biosensing have received much attention owing to their great potential for future biomolecular detection. The use of an appropriate photoelectrode is essential for PEC sensing and biosensing. Among the numerous semiconductors, many Bi-based ones are of great interest due to their high visible-light-responsivity, easy fabrication and good biocompatibility. Currently, the impetus for advanced Bi-based PEC sensing and biosensing has grown rapidly, as demonstrated by increased scholarly reports. This review introduces the state-of-the-art type and properties of Bi-based photoelectrodes, as well as their analytical applications toward various biomolecules, gas biomolecules and metal ions etc. The future prospects in this area will also be discussed based on our own opinions. Ó 2019 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

4.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PEC sensing and biosensing based on Bi-containing compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Binary oxides and sulfides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Multi-component oxides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Bismuth oxyhalides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Solid solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PEC sensing and biosensing based on Bi-containing composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Heterojunctions between two Bi-containing semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Heterojunctions between Bi-containing semiconductors with other semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Heterojunctions between Bi-containing semiconductors and carbon-based materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Heterojunctions between Bi-containing semiconductors and noble metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. Heterojunctions between Bi-containing semiconductors and Bi metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions and perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

⇑ Corresponding authors. 1

E-mail addresses: [email protected] (D.-M. Han), [email protected] (G. Chen), [email protected] (W.-W. Zhao). These authors contributed equally to this work.

https://doi.org/10.1016/j.ccr.2019.05.008 0010-8545/Ó 2019 Elsevier B.V. All rights reserved.

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1. Introduction Photoelectrochemical (PEC) sensing and biosensing have been drawing growing attention for their desirable properties and promising potential for biomolecular detection [1–25]. Originating from the synergy between photoelectrochemistry and electrochemical (bio)sensing, such a methodology is low-cost, with simple instrumentation and possesses potentially higher sensitivity with a low background compared to electrochemical (bio)sensing because of its totally different energy forms for the input and output signals. As compared to electrochemiluminescent (ECL) and fluorescent (bio)sensing, the PEC approach is cheap and easy to manufacture with benchtop techniques and also is very suitable for miniaturization and portable applications. From the very beginning, substantial efforts have been committed to its extensive investigation and considerable progress has been accomplished. Today, numerous configurations for PEC sensing and biosensing have been proposed toward different analytes of interest [1–4,7,1 3,14,16,18–20,24]. Essentially, the emphasis of these works generally lies on the use of new photoelectrodes, the selection of specific biorecognition elements addressing the corresponding targets or the development of analytical formats with innovative signaling mechanisms. Among them, semiconductive species with superior characteristics are of vital importance for the success of PEC sensing and biosensing. The extensively involved materials, e.g. various Cd chalcogenide quantum dots (QDs) and TiO2-based materials, often suffer from serious problems like relatively low PEC efficiency, toxicity issues or susceptibility to photobleaching [26– 35]. More advanced photoactive semiconductors with suitable properties remain to be sought and implemented in PEC sensing and biosensing. Bismuth (Bi), a non-toxic post-transition metal and one of the pnictogens with atomic number 83, generally forms trivalent and pentavalent compounds. With unique physicochemical properties, Bi-containing semiconductors feature easy-synthesis, low-cost, environmental compatibility, high-stability and excellent visiblelight-activities. Especially, many Bi3+-based semiconductors, with proper conduction band (CB) and valence band (VB) positions, possess excellent visible-light-responsivity due to the hybridized VBs of O 2p and Bi 6s2 orbitals, while the empty 6s orbital of the Bi5+ ion also endows Bi5+-based semiconductors with a similar property. With diverse nanostructures, e.g. nanoparticles (NPs), nanorods (NRs), nanowires (NWs), nanotubes (NTs), nanobelts (NBs), nanosheets (NSs) or nanoflakes (NFs), the family of Bi-based semiconductors has thus drawn much research attention in various fields, e.g. photocatalysis and solar cells, and their synthesis, structure control and property manipulation have been comprehensively exploited [36–59]. In the field of PEC sensing and biosensing, their fascinating properties also make the application of Bi-based semiconductors very promising. The appeal of Bibased PEC sensing and biosensing relies on the extraordinary properties of Bi-based semiconductors, including excellent PEC responsivity, good photostability and minimal toxicity. The manifold Bibased semiconductors also enable the development of various PEC sensing and biosensing protocols with specific purposes. Additionally, the unique biomimetic properties of some Bi-based semiconductors may provide special opportunities for advanced PEC sensing and biosensing applications. Nevertheless, while many reviews have summarized specific topics in the area of PEC sensing and biosensing [5,6,8– 12,15,17,22,23], no effort has yet been devoted to a survey of this frontier. Focusing on the basics and also state-of-the-art applications, this work will cover the most recent advances in Bicontaining semiconductor-based PEC sensing and biosensing [26,29,34,60–123], aiming to offer the interested readers an intro-

duction to this booming area. Note, this work is not intended to cover the detailed preparation and morphological development of Bi-containing semiconductors, but rather to highlight the employment of Bi-based semiconductors in the research activities of PEC sensing and biosensing. Moreover, the important advancements that stimulate further research have been highlighted through using illustrative examples in this field. Such innovative developments are precious for the future advancement of Bibased PEC sensing and biosensing. Section 2 of this paper mainly presents the types of Bi-containing compounds and some PEC sensing and biosensing applications. Section 3 summarizes the PEC sensing and biosensing applications on the basis of various Bi-containing composites. Conclusions remarks are included in Section 4. 2. PEC sensing and biosensing based on Bi-containing compounds Bi-based compounds can mainly be sorted as binary oxides (Bi2O3) and sulfides (Bi2S3), multi-component oxides (e.g. BiVO4) and oxyhalides (e.g. BiOI). Fig. 1 shows the flat band-edge positions of some Bi-based semiconductors. According to the equation Eg [eV] = 1240/k [nm], one can obtain the minimum light wavelength (kmin) to activate electrons from the VB to the CB. Some compounds (e.g. Bi2S3 and BiOI) are thus well visibly responsive, some (e.g. BiOBr and Bi2WO6) are weakly responsive, while some (such as BiOF, BiOCl and BiPO4) are not responsive. Incidentally, as well known, the limited absorption ability and the fast charge carrier combination of a single compound would restrict their practical application; these Bi-based compounds are commonly used in heterostructures for better PEC sensing and biosensing. In this section, along with the classification of these Bi-containing compound families, we will simultaneously introduce their PEC sensing and biosensing applications toward various biomolecules, gas biomolecules and metal ions etc. 2.1. Binary oxides and sulfides Bi2O3, one of the most industrially important compounds of bismuth, has multiple morphs, e.g. alpha (monoclinic), beta (tetragonal), gamma (body-centered cubic), delta (face-centered cubic) and omega (triclinic) phases, and its band gap varies from 2.1 to 2.85 eV. Particularly, a-, b- and c-Bi2O3 are the most common phases with band gaps of 2.85, 2.58 and 2.68 eV, respectively. At room temperature, the Bi2O3 exists as the a-phase with a monoclinic crystal structure and exhibits p-type electronic conductivity (with positive holes as the major charge carriers). With an indirect band gap of around 2.1 eV, Bi2O3 could be excited by light irradiation which has greater energy than the band gap energy. However, the photo to electric conversion efficiency of pure Bi2O3 is relatively low. Improvements (e.g. doping by metal ions and heterostructure construction) are usually needed for its better application. Bi2S3, a chemical compound of Bi and S, occurs in nature as the mineral bismuthinite and it is used as a starting material to produce many other Bi compounds. Bi2S3 is a layered n-type semiconductor with an orthorhombic crystal structure. Depending on its size, shape, dimensionality and morphology, Bi2S3 has a small and adjustable band gap from around 1.3 to 1.7 eV, absorbing visible light of longer wavelengths. Bi2S3 of various morphologies can be prepared by different methods, such as hydrothermal synthesis and a chemical precipitation method using specific Bi and S sources. Because of its stability, non-toxicity, cost-effectiveness, as well as good optoelectronic properties, it has obtained considerable attention in the field of PEC sensing and biosensing.

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Fig. 1. Flat band-edge positions of some Bi-based semiconductors, both in a normal hydrogen electrode (NHE) and an absolute vacuum energy system (AVS) scale. [38]. Reprinted with permission from Elsevier.

Fig. 2. (A) The preparation procedure of Co3O4-Au. (B) The mechanism of a B2S3 and Co3O4-Au polyhedral-based PEC sensor [60]. Reprinted with permission from American Chemical Society.

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For example, Ai and co-workers fabricated Bi2S3 NRs via a facile hydrothermal method using Bi(NO3)3 and Na2S. The as-fabricated Bi2S3 NRs have good morphology, high crystallinity, and an excellent absorption property. On the basis of an indium tin oxide (ITO) electrode, the assembled Bi2S3 NRs exhibited strong wavelength-dependent photocurrents. Using the in situ production of ascorbic acid (AA) by catalysis of alkaline phosphatase (ALP), a novel signal-on PEC immunoassay was realized for the determination of subgroup J of avian leukosis virus (ALVs-J) [73]. Recently, as shown in Fig. 2, Chen and coworkers reported the room temperature preparation of Bi2S3 NPs by facile chemical precipitation method. Based on a Bi2S3 NPs photoelectrode, they then synthesized a zeolitic imidazolate framework and the as-derived Co3O4 NPs were further decorated with Au NPs. As a multifunctional signal amplifier and peroxidase mimetic, the Co3O4-Au NPs can bring about the photobleaching of Bi2S3 for its competition toward AA and irradiation light, as well as the production of a catalytic precipitate. While caspase-3 exists, the peptide sequence can be specifically recognized and cleaved, resulting in the photocurrent recovery for the sensitive PEC assay of caspase-3 activity [60]. 2.2. Multi-component oxides Bi-containing mixed oxides have drawn comprehensive attention recently for their potentially excellent properties under visible light irradiation. Due to the numerous stoichiometries and modified structures of Bi-containing mixed oxides (e.g. numerous doped ones), this section introduces some representative examples. Bismuth vanadate (BiVO4) majorly exists as monoclinic (clinobisvanite) or tetragonal (dreyerite) phases. In the monoclinic phase, BiVO4 is an n-type photoactive semiconductor with a small band gap of ca. 2.3–2.4 eV. It thus could absorb a substantial portion of the visible spectrum and show brilliant PEC activity under visible light. BiVO4 has been demonstrated to be promising material for photocatalysis and a photoanode for water-splitting applications [124]. In the field of PEC sensing and biosensing, it has also been attracting increasing attention. Mascaro et al. have prepared a BiVO4 photoanode via heat treatment of Bi(NO3)3 and NH4VO3, applying it toward the PEC sensing of nitrite anions (NO2 ). Upon visible-light-illumination, the NO2 anion can reduce the photoexcited holes efficiently and the increment of photocurrent response was proportional to the NO2 concentration in the solution [85]. Recently, Yu et al. reported the hydrothermal synthesis of BiVO4 microrods, where were then deposited onto an FTO electrode for the PEC sensing of H2O2 at a zero working potential. Similarly, H2O2, as an electron donor, could efficiently scavenge the holes generated from BiVO4 to increase the photocurrent signal [78]. Bismuth phosphate (BiPO4) is a low-cost, non-toxic n-type semiconductor with high chemical stability. Nevertheless, due to its wide band gaps, around 3.8–4.6 eV, BiPO4 can only utilize UV light which has less than 5% solar energy, limiting the use of visible light. Therefore, to realize its absorption of visible light, hybridizing BiPO4 with small band-gap semiconductors will be a feasible approach for its further practical application. In the area of PEC sensing and biosensing, as will be discussed later, its application involved the coupling with many other narrow band-gap semiconductors. Bismuth ferrite (BiFeO3) is a promising multiferroic material for many fields, including magnetoresistance, non-volatile logic and memory devices. BiFeO3 is not a naturally occurring mineral and can be commonly obtained by solid state synthesis, sol-gel chemistry and hydrothermal synthesis. Additionally, depending on its narrow band gap (2.18 eV), BiFeO3 is perhaps the most popular visible-light responsive p-type semiconductor with a rhombohedral distorted perovskite structure. In the field of PEC sensing, as

demonstrated in Fig. 3, using BiFeO3 nanostructures as photoactive materials, Lu et al. employed mesoporous silica nanoparticles (MSNs) as a signal amplifier with target–controlled-releasing glucose backfilled to fabricate a PEC platform for the detection of the carcinoembryonic antigen (CEA) [91]. Copper bismuth oxide (CuBi2O4) is a typical spinel-type compound which shares the common formula AB2O4 (A is a divalent metal cation and B is a trivalent metal cation). CuBi2O4 is a ptype semiconductor with many desirable physicochemical features, such as photostability. Especially, its narrow band gap of about 1.5–1.8 eV allows it to well absorb visible light and to utilize a significant part of the light energy. Due to its unique feature, CuBi2O4 has been extensively applied as a visible-lightresponsive photocatalyst and also as photocathode for solar water splitting. In PEC sensing and biosensing, Tang et al. employed hemin as an electron acceptor for the photocathode of p-CuBi2O4 NRs and thus a cathodic PEC immunoassay was developed for alpha-fetoprotein (AFP) sensing [92]. Recently, Zhuang et al. proposed a similar utilization of a p-CuBi2O4 NR-based PEC sensor for probing telomerase activity by magnet control [89]. The Aurivillius structure of oxides with the general formula (Bi2O2)(An 1BnO3n+1) (where A is a large 12 coordinate cation, e.g. Ca, Sr, Ba, Pb, Bi, Na or K, and B is a small 6 coordinate cation, e.g. Ti, Nb, Ta, Mo, W or Fe) has layered structures of perovskite slabs of metal oxides sandwiched between (Bi2O2)2+ layers along the c axis [125]. For example, as one of the simplest members (n = 1), the n-type Bi tungstate (Bi2WO6) semiconductor has a narrow band gap (2.6–2.8 eV) and wide spectrum light response. Its perovskite layered structure is composed of [WO4]2 layers sandwiched between [Bi2O2]2+ layers, which is advantageous for the formation of electron-hole pairs and the generation of internal electric fields among the slabs. Bi2WO6 has found broad application in environmental sciences [126,127]. The Mo-homologous Aurivillius phase Bi molybdate (Bi2MoO6) is another n-type semiconductor with a layered structure containing perovskite-like slabs of MoO6 sandwiched between (Bi2O2)2+ layers. It has good visible light responsivity due to its narrow band gap of around 2.7 eV. As a member of the Aurivillius family with different chemical compositions, Bi titanates (BixTiyOz), solid inorganic compounds of Bi, Ti and O, include a very large family, such as Bi2Ti2O7, Bi2Ti4O11, Bi4Ti3O12, Bi12TiO20 and Bi20TiO32. The BixTiyOz family have a small band gap of around 2.65 eV and are proven to have higher visible-light-response abilities than TiO2. BixTiyOz compounds have demonstrated their numerous applications. For example, due to its low dielectric losses, high dielectric constant and low temperature coefficient of capacitance, Bi2Ti2O7 attracts much attention as a capacitor material. Bi4Ti3O12 is a strong candidate for lead-free piezoelectric transducers, photo catalysis, ferroelectric materials and electrocatalysts. With the general formula ABiO3, bismuthate, consisting of a monovalent metal and the BiO3 anion with the Bi ion in its +5 oxidation state (e.g. LiBiO3, NaBiO3, KBiO3 and AgBiO3 etc), also has high visible light responsivities. The band gaps of LiBiO3, NaBiO3, KBiO3 and AgBiO3 are 1.8, 2.6, 2.1 and 2.5 eV, respectively. These materials and some other compounds, such as Bi subcarbonate, Bi niobate, Bi tantalite and Bi silicate, may also have practical potential. 2.3. Bismuth oxyhalides As typical main group V-VI-VII semiconductor materials, bismuth oxyhalide compounds (BiOX with X = F, Cl, Br, I) are interesting owing to their chemical stability, low toxicity, structural novelty and high activity upon illumination. Specifically, BiOF has no visible-light-responsibility because of its band gap of 3.6 eV, while BiOCl, BiOBr and BiOI have band gaps of 3.3, 2.7 and

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Fig. 3. Schematic illustration of BiFeO3-based photoactive materials for the PEC detection of CEA coupled with the target-responsive release of glucose from multifunctional MSNs [91]. Reprinted with permission from the Royal Society of Chemistry.

2.4. Solid solution

Fig. 4. Schematic illustration for the principle of PEC determination of an OP compound using AChE–BiOI NFs/ITO [112]. Reprinted with permission from Elsevier.

1.8 eV, respectively. Obviously, the narrower band gaps of BiOBr and BiOI enable their excellent visible light activities. In the field of PEC sensing and biosensing, many recent advances has been made in the implementation of BiOX for innovative applications. As shown in Fig. 4, Gong et al. presented the fabrication of BiOI NF arrays as a cathodic photoelectrode and then the immobilization of enzyme of acetylcholinesterase (AChE) yielded a porous network for enzymatic biosensing. In such a system, the AChE catalytic hydrolysis of ATCl can produce acetate and thiocholine, which would scavenge the photogenerated holes and facilitate charge separation. However, the presence of organophosphate pesticides (OPs) would poison AChE and impair the photocurrent signal. On the basis of this effect of OPs, they could be detected sensitively and selectively [112]. Recently, Zhang et al. reported an innovative dual-enhanced photocathodic aptasensors for detection of thrombin and Pb2+ ions, accompanied by the synergistic effect of the target-controlled release of Au NPs and the redox moiety G quadruplex/hemin or ferrocene (Fc) [102].

A solid solution is a unique solid phase that contains compatible components. Two or more crystalline phases form a homogeneous crystalline structure with components hybridized at the atomic scale. The change of the components may result in a change of the structure and properties of solid solutions and thus enable the tuning of the photo absorption properties. Bi2O3 can form many solid solutions with many (rare earth) metal oxides, displaying various structures and properties, depending on the kind and amount of the dopants. Due to their identical properties to each another and similar size to the Bi3+ ion, rare earth metal cations (e.g. La3+, Y3+, Lu3+ and Er3+) have been the most widely studied dopants for Bi2O3-based solid solutions. These elements can also dope multi-component oxides to form multi-component oxide solid solutions (e.g. Bi0.5La0.5VO4 and BiYWO6). Alternatively, replacing the partial sites of other metal atoms is also an effective strategy to regulate semiconductor properties. For example, Mo6+ or W6+ ions could be doped into the partial sites of V5+ ions; Moand W-doped BiVO4 have been reported to have a change in crystal symmetry and enhanced charge carrier concentration. Han, Zhang et al. have reported the use of such a Mo-doped BiVO4 for PEC sensing of the antioxidant capacity in food [84] and aptasensing of streptomycin [80]. Fig. 5 shows the characterization of the used BiMo0.015V0.985O4 in the report of Han and coworkers [84]. In addition, due to the similar crystal structures of bismuth oxyhalides, solid solutions can be obtained between them with tuned band structures. BiOX solid solutions (BiOClxBr1-x, BiOClxI1-x and BiOBrxI1-x) with tunable band gaps and better absorption properties than the individual ones (BiOCl, BiOBr and BiOI) have been reported [46]. Recently, Zhao, Zeng et al have reported the I doping of BiOCl for PEC sensing of chlorpyrifos [101]. 3. PEC sensing and biosensing based on Bi-containing composites Although many Bi-containing compounds possess excellent visible-light-responsivities, heterostructures composed of different functional components are being regarded as favorable candidates and could synergy different advantages of the pure ones to enhance the properties, e.g. improved charge separation and suppressed charge recombination. In the area of PEC sensing and biosensing, much attention has been paid to developing Bi-

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Fig. 5. (a) The HETEM image, (b) HAADF-STEM image, elemental mapping images of (c) Bi, (d) Mo, (e) V and (f) O, (g) EDX spectrum and (h) the survey XPS spectrum of BiMo0.015V0.985O4 [84]. Reprinted with permission from the Royal Society of Chemistry.

3.1. Heterojunctions between two Bi-containing semiconductors

Fig. 6. (a) Sandwich immunorecognition and ALP catalyzed AA formation, and (b) PECCC RCA on Bi2S3/Bi2WO6 photoelectrode [61]. Reprinted with permission from American Chemical Society.

containing composites that are rich in heterojunctions. In this section, we summarize the intensively involved strategies, which include the construction of various p-p, p-n, Z-scheme, semiconductor/conductor heterojunctions.

As aforementioned, in spite of the inherent issue of rapid recombination of photogenerated excitons, some Bi-containing compounds, such as Bi2S3 (1.3–1.7 eV) and BiOI (1.7–1.9 eV), have relatively small band gaps and high visible-light-responsivities, and thus can act as good visible-light sensitizers for heterojunction construction. For example, Niu and co-workers recently studied the tailoring of heterostructured Bi2S3/Bi2MoO6 NBs for PEC biosensing of gallic acid at the drug level. In this work, c-Bi2MoO6 NSs were directed to accommodate Bi2S3 species via a hydrothermal reaction. The resultant Bi2S3/Bi2MoO6 NBs have excellent light-harvesting capability and the generated holes can efficiently react with the antioxidants in the solution [64]. Wang et al. proposed an interesting PEC biosensor for sulfate-reducing bacteria (SRB) detection based on bioetching the prepared Bi2S3/BiOCl heterojunction. In this work, BiOCl was bio-etched to generate a Bi2S3/BiOCl p–n heterostructure when the bacterial metabolite (H2S) existed, bringing about a significant signal improvement [97]. Very recently, Cao’s group used the Bi2S3/Bi2Sn2O7 heterojunction to induce the chemical redox cycling amplification (RCA) for an enhanced PEC immunoassay. The elegant bridging of the enzymatic catalysis of ascorbic acid (AA) with photoexcited hole-induced RCA permitted the sensitive split-type assay of myoglobin (Myo) [63]. Later, as shown in Fig. 6, using a Bi2S3/Bi2WO6 electrode, they further proposed PECchemical-chemical redox cycling as a strengthened signal amplification strategy [61]. With BiOI as a sensitizer, Xu et al. prepared the BiOI/BiPO4 heterojunction for the PEC sensing of catechol. In

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such a system, upon injection of catechol, the VB holes could oxidize catechol into small molecules, promoting the charge carrier separation and resulting in the improved photocurrent [99]. Using a similar BiOBr/BiPO4 heterojunction, they also reported the sensitive PEC sensing of 4-chlorophenol (4-CP) [100]. 3.2. Heterojunctions between Bi-containing semiconductors with other semiconductors In addition to heterojunctions composed of two Bi-based semiconductors, Bi-based semiconductors have also been coupled with many other inorganic semiconductors (e.g. ZnO, TiO2, CdS, Ag2S, NiO and g-C3N4) and organic semiconductors (e.g. molecularly imprinted polymers, thiophenyl-3-boronic acid and polyoxometalates) to form various heterojunctions. For example, Zhao et al. deposited BiOI NFs onto TiO2 NPs to form a BiOI NFs/TiO2 NPs heterostructured photoelectrode for general PEC enzymatic analysis, based on which the AChE antibody was employed as a biorecognition element through the connection of protein A. In this work, the enzyme could maintain its optimal state when in the absence of an inhibitor; otherwise, the extent of enzyme inhibition could be correlated directly with the inhibitor concentration [34]. Later, to facilitate the directional electron transfer, they prepared BiOI NFs on TiO2 NTs arrays, which was integrated with a unique bioanalysis protocol for addressing vascular endothelial growth factor (VEGF). Because of the desirable performance of the BiOI NFs/TiO2 NTs arrays, the study could sensitively realize VEGF detection [111]. Integrating BiVO4 NPs with TiO2 nanospheres, Liu et al. recently demonstrated the sensitive PEC aptasensing of 17b-estradiol. The TiO2 nanospheres featured modest biocompatibility and a high surface area to enhance the loading of biomolecules, greatly improving the sensitivity of the aptasensor [81]. Using a ZnO NRs/BiOI NFs p–n heterojunction, Pei et al. reported the development of a PEC biosensor using a G-quadruplex/Pb2+ complex. In the presence of Pb2+ ions, the photocurrent showed an obvious quenching, resulting from the formation of the hemin-containing G-quadruplex/Pb2+ complex [120]. Using ZnO nanoflowers, Yan et al. recently fabricated the ZnO/Bi2S3 heterojunction and applied it for PEC biosensing of squamous cell carcinoma antigen (SCCA). In this system, reduced graphene oxide (rGO) was utilized as labels to trigger the chemiluminescence resonance energy transfer for signaling [66]. Based on the BiOBr/Ag2S composite, Fan et al. reported the label-free PEC immunoassay of insulin [105]. For the previous conventional type-II heterojunction, both the CB and VB of semiconductor A are higher than those of semiconductor B. Therefore, upon light stimulation, the CB electrons of A will migrate to the CB of B, while the VB holes of B will transfer to the VB of A. Different from the type-II heterojunctions that separate the excitons through band alignment, the Z-scheme ones have a different and efficient ‘‘Z” -like transfer route for charge carriers. Zhao and Zeng recently prepared the direct Z-scheme BiOI/ CdS nanohybrid for PE Cu2+ ion detection via the selective replacement reaction between the ions and CdS. In such a scheme, the photogenerated CB electrons of BiOI will migrate to the VB of CdS to contribute to the photocurrent generation, whereas the presence of Cu2+ ions will lead to exciton recombination and hence a photocurrent decrement [117]. As shown in Fig. 7, Liang and coworkers recently coupled BiOI NFs with a NiO nanofilm to construct a p-p composite and studied its application for cathodic PEC oxidase biosensing, which found that H2O2 had a stronger influence than dissolved O2. This interesting phenomenon was caused by a unique dual-catalysis process. Specifically, the effect of the natural oxidase was succeeded by that of the peroxidase mimetic. The oxygen vacancies around the Bi cations could cause

Fig. 7. Proposed mechanism for the peroxidase-like activity of BiOI toward in situ generated H2O2 in GOx-based PEC glucose bioanalysis [96]. Reprinted with permission from American Chemical Society.

Fig. 8. (A) Schematic diagram for the formation of the BiFeO3/g-C3N4 heterojunction and (B) The schematic drawing illustrating the as-fabricated PEC AMP aptasensor based on the BiFeO3/g-C3N4 heterojunction [86]. Reprinted with permission from Elsevier.

the formation of Bi(+3 x) species to start the H2O2 reduction reaction. This work is envisioned to offer a new BiOI-based photoelectrode for future PEC sensing and biosensing development [96]. Besides binary ones, many ternary composites have also been investigated. By further incorporating Ag2S NPs, Li et al. then reported the TiO2/BiVO4/Ag2S-based PEC aptasensing of ochratoxin A (OTA) [76]. Indeed, for both binary and ternary composites, the charge separation along the junctions is improved and the transfer direction of excitons locked because of the Schottky barrier and the inner electric field. Using WO3 to replace TiO2, Li et al. further reported the use of WO3/BiVO4/Ag2S formation for competitive

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PEC detection of aflatoxin B1 (AFB1) [77]. Recently, Wu and colleagues reported a PEC immunosensor for CEA detection with a CdS NWs/WO3@BiOI composite [29]. Based on the formation of the Mn:CdSe/CdS/Bi2WO6 heterojunction, Zhang et al. then reported the PEC immunoassay of amyloid beta (Ab) [26]. Graphite-like carbon nitride (g-C3N4) has a band gap of ca. 2.7 eV, absorption of visible light, environmentally benignity, as well as thermal and photochemical stability due to the high extent of polymerization and p-conjugated structure. In spite of its advantages, drawbacks including low absorption of visible light, high exciton recombination rate, low conductivity and small specific surface area still limit its practical applications. To improve its feasibility for application, g-C3N4 has been combined with various Bicontaining semiconductors for innovative PEC sensing and biosensing. For example, Li et al. proposed the PEC sensing of ciprofloxacin, tetracycline and bisphenol A on the basis of BiOCl/g-C3N4 [107], BiOBr/g-C3N4 [98] and BiOI/g-C3N4 [116], respectively. As shown in Fig. 8, Wang et al. developed the p-n BiFeO3/g-C3N4 composite and applied it for on-off-on PEC aptasensing of ampicillin (AMP). In the presence of targets, the holes can easily oxidize the AMP molecules in the AMP/aptamer complex and the recombination rate of the charge carriers are suppressed [86]. Moreover, as a large family of functional species, organic semiconductors also have great potential for coupling with Bi-based semiconductors, the composites of which have recently been studied. Benefiting from the specific bonding between boric acid and sialic acid on the surface of subgroup J of avian leukosis virus (ALVs-J), Ai et al. developed a tungsten-doped Bi2S3/poly (thiophenyl-3-boronic acid) hybrid with boronic acids, used as probing receptors for PEC sensing of ALVs-J [122]. Employing a molecularly imprinted polymer (MIP) as the photoactive substrate and recognition element, Gong et al. put forward two novel PEC sensing platforms for the detection of 2,4-dichlorophenoxyacetic acid and perfluorooctanoic acid, based on the smart combination of BiOI NFs and AgI/BiOI with MIP, respectively [109,121]. In addition, Xu et al. fabricated a BiVO4/polyoxometalate (POM) photoanode for NO2 detection. With the incorporation of the POM, electron-hole recombination in BiVO4 could be retarded [74]. In the presence of organic semiconductors, owing to the appropriate energy level cascade between the Bi-based semiconductors and organic semiconductors, charge separation could be effectively facilitated. Some organic semiconductors could play two roles, the photoactive substrate and the recognition element, in one PEC sensing platform, exhibiting a great application prospect in this field. 3.3. Heterojunctions between Bi-containing semiconductors and carbon-based materials Carbon materials are considered as outstanding electron capture agents due to their superior conductivity and they have been widely coupled with Bi-containing semiconductors for PEC sensing and biosensing. Graphene, constituted of single-layer 2D graphite, has obtained much interest owing to its superior properties, such as excellent electronic mobility at room temperature. Upon light irradiation, the photoinduced electrons of graphene-coupled semiconductors can rapidly transfer to the graphene surface, thus suppressing the charge carriers’ recombination. Recently, a Bi-containing semiconductor/graphene composite has attracted intensive attention in PEC sensing and biosensing. For example, using BiPO4/reduced graphene oxide (rGO), Wang et al. reported a novel PEC sensor for innovative detection of chlorpyrifos. With the addition of chlorpyrifos, the formed Bi–chlorpyrifos complex on the BiPO4 NPs cause enhanced steric hindrance and consequently resulted in a distinct photocurrent decrement [95]. Based on this work, they fur-

ther improved the photoelectrode by developing BiPO4/N-doped graphene hydrogel, and the enhanced photocurrent was attributed to the fact that the porous structure of 3D graphene could be beneficial for the anchoring of BiPO4 NRs and the N atoms could improve the conductivity of graphene and suppress the recombination of the electrons and holes [90]. As demonstrated in Fig. 9, Zhang and co-workers prepared BiOI/graphene nanocomposites by directly mixing BiOI and graphene suspensions under vigorous stirring. The resultant BiOI/graphene was then applied as a photoactive material for the cathodic ‘‘signal-off” PEC aptasensing of oxytetracycline (OTC). When OTC was captured by the aptamer, a decreased photocurrent can be recorded due to the enhanced steric hindrance [108]. Later, they prepared Bi2S3 NRs/graphene and applied it for PEC aptasensing of sulfadimethoxine (SDM). With specific recognition between the aptamer and SDM, the photocurrent response of the aptasensor was changed due to the oxidization of the SDM molecules by the photogenerated holes of the Bi2S3 NRs [67]. Recently, they further prepared Mo-BiVO4/graphene for the PEC aptasensing of streptomycin. In the presence of the target, the aptasensor exhibited an enhanced photocurrent due to the reduction of photoinduced holes by the streptomycin molecules after specific binding [80]. Using BiVO4/rGO, Lu et al. reported an enzymatic oxydate-triggered self-illuminated PEC immunoassay using a digital multimeter [82]. Very recently, Lee and coworkers proposed the hydrothermal fabrication of BiOCl/graphene and its application for non-enzymatic PEC glucose sensing [104]. Using BiFeO3/rGO and a target-triggered hybridization chain reaction (HCR), Tang et al. reported magnetic controlled amplified PEC sensing toward prostate-specific antigen (PSA) [87]. As shown, commonly used graphene is usually obtained by reducing graphene oxides; note, the as-obtained graphene sometimes exhibits a semiconductor property [128]. Wang et al. developed p-n BiOBr/N-doped graphene composites and used them as a visiblelight-driven PEC sensing platform [119]. In their later report on N-doped graphene QDs/Bi2WO6 for PEC sensing of pentachlorophenol (PCP), N-doped graphene QDs acted as good electron transfer agents to reduce the charge carrier recombination for good electrical conductivity [94]. Especially, the Z-scheme I-BiOCl/N-doped graphene QDs heterojunction has also been reported by Zhao et al. for PEC detection of chlorpyrifos. In this heterojunction, the doped I could decrease the BiOCl band gap, the N-doped graphene QDs could enhance light harvesting and prolong the lifetime of the generated electrons, and the resultant Z-scheme heterojunction could improve the spatial separation of the interfacial charges [101]. In addition to the binary heterojunction, they also fabricated a BiOCl/BiVO4/N-doped carbon QDs ternary heterojunction for PEC sensing of dopamine [118]. Incidentally, since carbon materials can usually strongly absorb light, they might shield against light absorption for the composite; modifying a certain amount of carbon materials is required for improvement of the sensing performance.

3.4. Heterojunctions between Bi-containing semiconductors and noble metals Noble metals, with a strong electron trapping ability and excellent conductivity, can serve as electron traps to accelerate the separation and transportation of charge carriers. Generally, there are two possibilities: in one case, the photoexcited electrons from the semiconductor will transfer to the noble metals; in the other case, when nanostructured noble metals are coupled with a wide band gap semiconductor that is not responsive to visible light, the surface plasmon resonance (SPR)-induced hot electrons of the noble metal will transfer to the semiconductor. Recently, nanostructured noble metals, especially Au NPs, have been frequently

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Fig. 9. Schematic illustration of a cathodic ‘‘signal-off” PEC aptasensor-based on BiOI/graphene nanocomposites [108]. Reprinted with permission from the American Chemical Society.

Fig. 10. Schematic illustration of PEC sensing for PSA by coupling with ‘Z-Scheme’ double photosystems and the 3D DNA Walker Amplification Strategy: (A) PSA-induced release of DNA walker; (B) DNA walker-triggered walking reaction on hairpin DNA1-functionalized AuNPs@BiVO4 with the aid of CdS QD-labelled hairpin DNA2; and (C) The photogenerated electron transfer between BiVO4 photosystem II (PS II) and CdS QD photosystem I (PS I) in the artificial ‘Z-Scheme’ system [75]. Reprinted with permission from the American Chemical Society.

coupled with Bi-containing semiconductors for PEC sensing and biosensing. Manna et al. reported the Au NPs/Bi2S3 NRs heterojunction, which displays a red-shifted light absorption. Enhanced charge carrier separation over the heterojunctions were confirmed to be in favor of improving the photocatalytic activity [129]. On the basis of a similar Au NPs/Bi2S3 NRs heterojunction, Ai et al. reported a series of PEC biosensors, addressing various targets of interest. In these reports, anchoring Au NPs on Bi2S3 caused a decrease of the photocurrent [68–72]. In another report by Zhang et al., immobilization of Au NPs on Bi2S3 NRs also caused a decrease of the photocurrent [62]. Recently, Liu, Hu et al. reported using Au NPs/Bi2S3 to fabricate a single light-addressable label-free PEC sensor for the high-throughput multiplex detection of tumor biomarkers. However, in this work, modification of Au NPs onto Bi2S3 caused an increased photocurrent, which was assigned to the good conductivity of the Au NPs [65]. The above contradictory phenomena maybe due to the different loading amount and spatial distribution of the Au NPs against Bi2S3. Some other heterojunctions, e.g. Au

NPs/BiVO4, Au NPs/BiOX and Au NPs/CuBi2O4, have also been reported. For example, Zhang et al. sputtered Au NPs on nanoporous BiVO4 for PEC aptasensing of thrombin. In such a system, the presence of Au NPs on BiVO4 brought about a photocurrent increment because of the high conductivity of the Au NPs accelerated the electron transfer [79]. A similar phenomenon was also observed by Tang et al [83]. As shown in Fig. 10, Tang et al. further induced the formation of a sandwiched BiVO4/Au NPs/CdS composite to form a Z-Scheme for a PEC immunoassay application. In this system, the excited electrons are transfered from the BiVO4 CB to the CdS VB via the electron mediator of Au NPs between them, thus resulting in the enhanced photocurrent response [75]. As for Au NPs/BiOX heterojunctions, Ai et al. used the Au NPs/BiOI photoelectrode for PEC biosensing of a DNA MTase activity assay [110]. Wang, Zhang et al. exploited the employment of Au NPs/BiOI for PEC capture and inactivation of pathogenic bacteria [113]. Using the Au NPs/BiOCl composite, Xia, Zhang et al. demonstrated the PEC sensing of 4-chlorophenol [106]. Very recently, Yu et al. proposed the liposome-mediated in situ formation of the AgI/Ag/BiOI

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Z-scheme heterojunction on a foamed nickel electrode for signalon PEC bioanalysis. Based on the presence of metallic Ag as the electronic mediator, the AgI/Ag/BiOI Z-scheme heterojunction was formed in situ to distinctly enhance the cathodic photocurrent signals [123]. With hemin as the assistant, Tang et al. recently proposed the use of Au NPs/CuBi2O4 for split-type cathodic PEC immunosensing of alpha-fetoprotein (AFP) [92]. Interestingly, on the basis of g-C3N4/Bi2MoO6, Tang et al. recently explored the localized surface plasmon resonance (LSPR) effect of Au NPs for plasmonic PEC aptasensing of CEA. In this work, upon visible light illumination, the attachment of Au NPs onto g-C3N4/Bi2MoO6 caused a prominent photocurrent enhancement, which was due to the synergistic effect of plasmon resonance energy transfer and a hot electron injection mechanism [88]. 3.5. Heterojunctions between Bi-containing semiconductors and Bi metal Bismuth, a non-toxic and cheap semi-metal, has a Fermi surface with a high anisotropy, long carrier mean free path and narrow band gap. Similar to noble metals, Bi has been used as one of the alternatives to be deposited on semiconductors, and it is found that metallic Bi coupling could improve the charge carrier separation in the semiconductors and thus improve the performance of the system [130,131]. For instance, Xu, Xia et al. recently demonstrated the use of Bi/BiOI [115] and Bi/BiOBr [114] composites for the PEC monitoring of phenol and ciprofloxacin, respectively. In these reports, the photo-induced electrons of the CB of BiOI or BiOBr can transfer to Bi via the Schottky barrier, while metallic Bi, as an electron sink, can facilitate the transfer of interfacial electrons, thus enhancing the photocurrent. Note, Bi also possesses an interesting SPR property and can be used as an alternative in the generation of the SPR effect. Dong et al. reported a Bi/Bi2O2CO3 composite with enhanced photocatalytic activity, which was ascribed to the SPR effect of Bi, and the Bi metal in Bi2O2CO3 can prolong the exciton lifetime [132]. Such a phenomenon would also have great potential for the PEC sensing and biosensing. Incidentally, the application of Bi-modified composites should be careful since Bi metal is unstable under atmospheric conditions and can be readily oxidized into Bi2O3. 4. Conclusions and perspectives Due to their unique physicochemical properties, Bi-containing semiconductors have attracted increasing attention in the field of PEC sensing and biosensing. In this review, we have presented the advancement in this field, offering a summary of the Bicontaining semiconductors and their current applications. Especially, we emphasized on the state-of-the-art studies toward the use of various Bi-containing compounds and composites. Significantly, the development of Bi-containing composites that are rich in heterojunctions has already allowed high-performance PEC sensing and biosensing. However, compared to Cd chalcogenide QDs- or TiO2-based ones, both the photoelectrode design and the development of Bi-containing semiconductor-based PEC sensing and biosensing are still in their early stages. Further effort is still needed to advance Bi-based semiconductors for PEC sensing and biosensing. Currently, from our perspective, there are some trends for further investigation among which are: (1) Development of new Bibased photoactive materials. New Bi-based photoactive materials and their composites with good visible-light-responsibility, biocompatibility and high stability would be advantageous for utilization as PEC platforms. For instance, Dai et al. exploited the innovative Bi@N,O-codoped-carbon core shell nanostructure and

the photo-excited electrons could transfer from the Bi core to the shell, resulting in the inhibition of the electron-hole recombination and giving an enhanced photocurrent [93]. By photocatalytic reduction of Bi3+ ions on the surface of TiO2 NTAs, Xu, Wu et al. have developed a Bi/TiO2 composite for PEC sensing of glucose [133]. Compared to BiOX, Bi-rich BiOX (BixOyXz; X = Cl, Br and I) has higher stabilization and different band structures, which might be suitable for specific PEC sensing and biosensing [37]. In addition, Au, Pt, Pd, Rh and Ag could also modify the Bi-based semiconductors. An ideal combination with conductive polymers (especially photoactive ones) also presents a promising direction [134]. To date, less effort has been devoted to these aspects. (2) Appropriate engineering of nanostructured Bi-containing semiconductors. Nanostructures with unique shapes could reduce the charge-carrier diffusion distance and improve the interfacial redox reactions, leading to enhanced photocurrent generation. Incorporation of a co-catalyst or a charge-selective layer can open a different route to ingenious photoelectrode construction. For example, a polyoxometalate (POM), as an efficient electron acceptor dopant in semiconductor composite materials, has been used to strengthen BiVO4 for PEC NO2 detection [74]. Special attention should be paid to the charge-transfer process in rationally designed biomolecule/nanostructured Bi-containing semiconductors and their novel applications in PEC sensing and biosensing. (3) Utilization of the biomimetic properties of some Bicontaining semiconductors. For example, BiOI exhibits a superior peroxides-like catalytic property which has been used for enhanced cathodic PEC enzymatic biosensing [96]. Manipulation of exposed facets may contribute to the better performance [132]. (4) Construction of new sensing and biosensing platforms. Ideal integration of Bi-based photoelectrodes and specific recognition probes would open new directions for applications. For example, integration of functional molecularly imprinted polymer (MIP) and Bi-containing semiconductors has already broadened the range of applications [103,109,121]. There is great space for developing new sensing and biosensing systems toward different analytes in both fundamental research and practical applications. In all, Bi-containing semiconductor-based PEC sensing and biosensing is an on-going research field with both potential and challenges. With its prompt development, we envision its bigger significance in the future. Acknowledgments We thank the National Natural Science Foundation of China (Grant Nos. 21575097 and 21675080) and the Natural Science Fundation of Jiangsu Province (Grant BK20170073) for support. References [1] Y.C. Zhu, L. Zhang, N. Zhang, W.W. Zhao, Y.Y. Liang, J.J. Xu, H.Y. Chen, Curr. Opin. Electrochem. 10 (2018) 120–125. [2] W.W. Zhao, J.J. Xu, H.Y. Chen, Anal. Chem. 90 (2018) 615–627. [3] W.W. Tu, Z. Wang, Z. Dai, TrAC, Trends Anal. Chem. 105 (2018) 470–483. [4] R. Gill, M. Zayats, I. Willner, Angew. Chem. Int. Ed. 47 (2008) 7602–7625. [5] H. Pang, Y. Zang, J. Fan, J. Yun, H.G. Xue, Chem. Eur. J. 24 (2018) 14010–14027. [6] I. Ibrahim, N.L. Hong, R.M. Zawawi, A.A. Tajudin, H.N. Yun, G. Hang, N.M. Huang, J. Mater. Chem. B 6 (2018) 4551–4568. [7] W.W. Zhao, J.J. Xu, H.Y. Chen, Biosens. Bioelectron. 92 (2017) 294–304. [8] N. Zhang, L. Zhang, Y.F. Ruan, W.W. Zhao, J.J. Xu, H.Y. Chen, Biosens. Bioelectron. 94 (2017) 207–218. [9] Z. Yang, J. Lei, H. Ju, Biosens. Bioelectron. 96 (2017) 8–16. [10] W.W. Zhao, J. Wang, Y.C. Zhu, J.J. Xu, H.Y. Chen, Acta Phys. Chim. Sin. 87 (2017) 9520–9531. [11] J. Shu, D.P. Tang, Chem. Asian J. 12 (2017) 2780–2789. [12] W.W. Zhao, X.D. Yu, J.J. Xu, H.Y. Chen, Nanoscale 8 (2016) 17407–17414. [13] W.W. Zhao, J.J. Xu, H.Y. Chen, TrAC, Trends Anal. Chem. 82 (2016) 307–315. [14] W.W. Zhao, J.J. Xu, H.Y. Chen, Analyst 141 (2016) 4262–4271. [15] H. Zhou, J. Liu, S. Zhang, TrAC, Trends Anal. Chem. 67 (2015) 56–73. [16] W.W. Zhao, J.J. Xu, H.Y. Chen, Chem. Soc. Rev. 44 (2015) 729–741.

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Si-Yuan Yu obtained his B.S. degree from Wuhan Institute of Technology at 2017. He is currently pursuing his MSc with Profs. De-Man Han and Wei-Wei Zhao at Nanjing University (NJU). His research focuses on developing new photoactive materials for PEC sensing and biosensing.

Ling Zhang obtained her B.S. and M.S. degree from Huaibei Normal University (2003) and Zhejiang University (2006), respectively. She is currently pursuing her Ph.D. with Profs. Yan-Yu Liang and Wei-Wei Zhao at NJU. Construction of new nanomaterial/biomolecule architectures and their applications for new PEC bioanalysis are among her main research interests.

Li-Bang Zhu received his B.S. and M.S. degree from Shandong Agricultural University in 2015 and 2018, respectively. He is currently a Ph.D. candidate under the supervision of Prof. Wei-Wei Zhao at NJU. The main objects of his research are advanced bioanalysis and biosensor development.

Yuan Gao obtained her B.S. degree from Taizhou University at 2016. She is currently pursuing her MSc with Profs. De-Man Han and Wei-Wei Zhao at Nanjing University (NJU). Her research is about new sensing strategies for PEC sensing and biosensing.

Gao-Chao Fan received his Ph.D. degree in Analytical Chemistry from NJU, China, in 2015. He then worked as a postdoctoral fellow in the State Key Laboratory of Analytical Chemistry for Life Science at NJU. He is currently an associate professor at the College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology. His research interests concentrate on synthesizing photoelectric functional nanomaterials and developing biosensors.

De-Man Han obtained his Ph.D. degree in Analytical Chemistry from Nankai University, China, in 2007. He is currently a professor at the college of Pharmaceutical and Materials Engineering, Taizhou University. His research interests concentrate on synthesizing photoelectric functional materials and developing biosensors.

Guangxu Chen obtained his Ph.D. degree in Inorganic Chemistry from Xiamen University in 2014. He then worked as a postdoc fellow in Xiamen University for one year and then moved to the department of Material Science & Engineering of Stanford University as a postdoc scholar. His research interests include the control and synthesis of well-defined nanomaterials for their advanced catalysis and analysis applications.

Wei-Wei Zhao obtained his Ph.D. from NJU in 2012 and now serves as an associate professor at the Department of Chemistry of NJU. His research is focused on biomolecular and single-cell detection via various advanced electrochemical techniques.