Photoelectrochemical Bioanalysis Platform of Gold Nanoparticles

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Photoelectrochemical Bioanalysis Platform of Gold Nanoparticles Equipped Perovskite Bi4NbO8Cl Yi-Fan Ruan, Nan Zhang, Yuan-Cheng Zhu, Wei-Wei Zhao, Jing-Juan Xu, and Hong-Yuan Chen Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b05153 • Publication Date (Web): 26 Jun 2017 Downloaded from http://pubs.acs.org on June 26, 2017

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Analytical Chemistry

Photoelectrochemical Bioanalysis Platform of Gold Nanoparticles Equipped Perovskite Bi4NbO8Cl Yi-Fan Ruan,† Nan Zhang,† Yuan-Cheng Zhu,† Wei-Wei Zhao,*,†,‡Jing-Juan Xu*,† and Hong-Yuan Chen†

†

State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of

Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China ‡

Department of Materials Science and Engineering, Stanford University, Stanford, California 94305,

United States

* E-mail: [email protected]; [email protected]

Fax: +86-25-89684862; Tel: +86-25-89684862

* E-mail: [email protected]; Fax: +86-25-89687294; Tel: +86-25-89687294

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Abstract: We have developed sensitive photoelectrochemical (PEC) detection of cysteine using the gold nanoparticles (Au NPs) equipped perovskite Bi4NbO8Cl heterostructure. The Bi4NbO8Cl was prepared by a solid-state reaction, and the Au NPs/Bi4NbO8Cl electrode was made through electrostatic layer-by-layer self-assembly technique. The Au NPs/Bi4NbO8Cl electrode provided much enhanced photocurrent with great increase compared to the bare Bi4NbO8Cl electrode and allow for the plasmon-enhanced PEC detection of cysteine with good performance. It demonstrated rapid response, high stability, wide linear detection range and certain selectivity, implying its great promise in its application. Therefore, the Au NPs/Bi4NbO8Cl heterostructure has provided a promising platform for the development of PEC bioanalysis. More generally, these findings offered an insight into the exploitation of perovskite materials for PEC bioanalytical purposes.

Keywords: Photoelectrochemical; Bioanalysis; Perovskite; Gold Nanoparticles; Cysteine


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Photoelectrochemical (PEC) bioanalysis is a rapidly developing method to probing bioaffinity interactions and biocatalytic transformations.1−7 Because it uses two separated energy forms for sensor excitation and detection, it could reduce undesired noises arising from the background and thus possesses higher sensitivity towards novel PEC bioanalytical platforms.8−10 In principle, the typical PEC bioanalysis necessitates the specific recognition events that intimately associated with the photoelectrodes. So the construction of such electrodes is undoubtedly one of the key factors in the total PEC bioanalysis development. Proper photoactive materials could offer many advantages, including ideal biomolecule interfacing, fast responsibility and exciton generation, as well as enhanced signal intensity and stability. For example, various quantum dots (QDs)11−13 and TiO2-based materials14 have been largely used due to their unique features and functions. Recently, some promise materials such as graphene and graphitic carbon nitride have also been exploited in the field.15,16 Significantly, due to the excellent electronic and optical characteristics of Au nanoparticles (NPs) that supporting localized surface plasmon resonance (LSPR),17 increasing effort has been devoted to integrating Au NPs as efficient light-harvesting enhancers with different photoactive species to exploit the innovative photoelectrodes for advanced PEC bioanalysis. With enhanced absorption in the visible region due to LSPR and a large enhancement of the electromagnetic field at the interface of plasmonic nanostructures, the presence of Au NPs could increase the rate of electron−hole formation and promote the separation of photogenerated charge carriers near the semiconductors. Besides, their good stability, biocompatibility, and catalytic performance also make them interesting for the construction of semiconductors-based hybrids for bioanalysis utilization.18 For instance, Au NPs/3D iron oxide nanopyramid islands19 and Au NPs/TiO2 nanotubes20 has been used for specific purposes. More recently, Au nanocrystal decorated specific crystal facets BiVO4 photoanode has also been developed.21 In spite of these progresses, the study in this direction is still in its inception phase and yet leaves much to be desired. The development of novel photoelectrodes is thus expected.22,23 Perovskite materials, a large family of versatile species, have ignited tremendous interests and been envisioned to fuel the future development of next-generation photocatalysis, photovoltaics, ACS Paragon Plus Environment

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photodetection and etc.24−27 However, they are seldom exploited in the field of PEC bioanalysis, which may be due to the relatively short development time of this technique. Among different perovskites, Bi4NbO8Cl, a single layer Sillen-Aurivillius perovskite historically discovered by J. F. Ackerman in 1986,28 has recently been used as an efficient O2-evolving photocatalyst and achieved overall water splitting under visible light irradiation for the first time.29 Inspired by this work and aforementioned plasmonic schemes, of our particular interest is the possibility to synergize the features of Bi4NbO8Cl with Au NPs towards the PEC bioanalytical application, the success of which would introduce a large variety of perovskite materials and their based plasmonic hybrids for advanced PEC bioanalysis development. On the other hand, as an essential sulfur-containing amino acid, cysteine plays a fundamental role as building block for many proteins and enzymes and in many biological processes.30 This critical amino acid helps to fold and maintain a stable structure of protein, contributes towards enzymatic reactions and detoxification processes, as well as takes part in numerous posttranslational modifications.31 Deficiency of cysteine leads to many diseases, such as slowed growth, depigmentation of hair, loss of muscle and fat, skin lesions, edema, lethargy, and liver damage.32,33 Alzheimer’s disease and acquired immune deficiency syndrome (AIDS) were also found to be accompanied by a deficiency of cysteine.34,35 Previous techniques for cysteine detection mainly include liquid chromatography,36 UV– visible absorption spectroscopy,37 spectrofluorimetry,38 circular dichroism spectroscopy,39 mass spectrometry,40 and electrochemical techniques.41,42 Among all the these methods, electrochemical technique possesses its advantages of simple instrument and low cost. However, it also suffers from the interruption of other electric active compound at high overpotential for oxidation of cysteine. Obviously, facile, sensitive and low-cost cysteine detection is still desirable. In this work, we report the PEC bioanalysis of cysteine by the Au NPs equipped perovskite oxychloride Bi4NbO8Cl. Specifically, we fabricated the Au NPs/Bi4NbO8Cl hybrid to take advantage of Au NPs as light harvesting antennas and plasmon exciter, and the characteristics of Bi4NbO8Cl. In contrast to the pure Bi4NbO8Cl, the heterostructure demonstrated the excellent PEC activity, exhibiting ACS Paragon Plus Environment

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enhanced photocurrent intensity by the resonant surface plasmon excitation generated on plasmonic Au NPs through the light harvesting and conversion. Subsequently, we applied this heterostructure for the PEC bioanalysis of cysteine, and the plasmon-enhanced biomolecular detection was achieved with good performance. It demonstrated rapid response, high stability, wide linear detection range and certain selectivity, implying its great promise in the application of PEC biosensors. These findings provided an insight into the development of perovskite materials for PEC bioanalytical uses and a new method for cysteine detection.

Experimental Section Reagents and Apparatus. All chemical reagents were supplied from Sigma-Aldrich, Alfa Aesar, Sunshine, Nanjing Chemical Reagent Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd, and were used without further purification. Bi2O3 was purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China), BiOCl was purchased from Alfa Aesar (Shanghai, China) and Nb2O5 was purchased from Aladdin (Shanghai, China). HAuCl4 was purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. (Shanghai, China). Poly diallyldimethylammonium chloride (PDDA; 20%, w/w in water, MW = 200000−350000) and bovine serum albumin (BSA) was purchased from Sigma-Aldrich (St. Louis, MO). L-cysteine, trisodium citrate dehydrate, Glucose, L-histidine, L-lysine and lactic acid were purchased from Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). L-Glutathione reduced (GSH) was purchased from Sunshine (Nanjing, China). Phosphate buffer solution (PBS, pH 7.4) was prepared from Na2HPO4·12H2O (Nanjing Chemical Reagent Co., Ltd., 99.0%) and NaH2PO4 (Nanjing Chemical Reagent Co., Ltd., 99.0%). Ultrapure water (18.2 MΩ·cm resistivity at 25 °C, Millier Q) was used in all experiments. SEM (scanning electron microscopy) and EDX (energy-dispersive X-ray) images were recorded by a Hitachi S4800 scanning electron microscope (Hitachi Co., Japan). TEM (transmission electron microscope) was performed with a JEM-2100 microscope (JEOL, Japan). XPS (X-ray photoelectron spectroscopy) was obtained from PHI 5000 VersaProbe (UlVAC-PHI Co., Japan). The UV-vis absorption spectra and ACS Paragon Plus Environment

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UV−vis diffuse reflectance spectra were obtained on a Shimadzu UV-3600 UV-vis-NIR spectrophotometer (Shimadzu Co., Japan). XRD (X-Ray Diffraction) spectra were characterized by powder X-ray diffraction (XRD, X'TRA, Cu Kα; ARL Co., Switzerland). Synthesis of Bi4NbO8Cl. Perovskite Bi4NbO8Cl (particle size of ∼200 nm to 500 nm) was prepared by a solid-state reaction. Stoichiometric quantities of Bi2O3 (99.0%), BiOCl (98%) and Nb2O5 (99.9%) powders were weighed, grinded in agate mortar, mixed and eventually heated in an evacuated silica tube at 1173 K for 20 h according to literature method.23 Synthesis of Au NPs. The Au NPs are synthesized with following steps: 0.863 mL of 1.0% HAuCl4·4H2O (mass fraction, 0.024 mol L−1) was primarily added into 94.138 mL boiling water, and then immediately following 5.0 mL 1.0% trisodium citrate dihydrate (mass fraction, 0.034 mol L−1) added into the boiled reaction solution, keep the solution boiling for 30 minutes and cool down to room temperature. And the diameters of synthetic Au NPs are around 15 to 20 nm. Electrodes Fabrication. The ITO (indium tin oxide) slices (type N-STN-S1−10, China Southern Glass Holding Co., Ltd.) were used as the working electrode. To prepare each perovskite Bi4NbO8Cl modified ITO, the perovskite Bi4NbO8Cl suspension was prepared by mixture of Bi4NbO8Cl (100 mg) and ultrapure water (1000 µL), coated on ITO substrate, and then dried at 40 °C. The working area of the electrode is a circular region in 0.5 cm in diameter. Au NPs/Bi4NbO8Cl electrode was made through electrostatic layer-by-layer self-assembly technique with PDDA solution (pH = 8.0) and the prepared Au NPs solution for both one layer. The electrode was then calcinated under 450 °C in nitrogen condition. Electrochemical & PEC measurements. The electrochemical testings were measured using an electrochemical analyzer (CHI-660c). The electrochemical cell consisted of (Au NPs-)perovskite Bi4NbO8Cl/ITO electrode, a counter electrode (Pt wire), an Ag/AgCl reference electrode (with KCl in the saturated solubility), and different electrolyte solutions. PEC measurements were performed with a homemade PEC system. With anodic i-t mode of electrochemical workstation, all photocurrent measurements are under nitrogen protecting condition with 0 V bias voltage. A 5 W LED lamp with ACS Paragon Plus Environment

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multichromatic emitting from 380 nm to 760 nm was used as irradiation source to produce the white light in front of the electrode. A 500 W Xenon lamp with prism gratings for monochromatic light in different wavelengths was used to occupy the photocurrent intensity curve. All photocurrent values used for numerical analysis are measured after quiet time for 1 minute. The achromatic light (white light) irradiation was provided to system every 10 seconds and last another 10 seconds (no irradiation from beginning of photocurrent generation test).

Results and Discussion

Figure 1. (A) SEM image of Bi4NbO8Cl, Inset: the TEM image of the Au NPs. (B) SEM image of Au NPs/Bi4NbO8Cl. (C) XPS spectrum of Au NPs/Bi4NbO8Cl. (D) Normalized UV-vis absorption spectrum of Au NPs (blue line) and UV−vis diffuse reflectance spectrum of Bi4NbO8Cl (black line) and Au NPs/Bi4NbO8Cl (red line).

Structural and Optical Properties. The perovskite Bi4NbO8Cl was initially solid-state-prepared using stoichiometric quantities of Bi2O3, BiOCl and Nb2O5 powders weighed, mixed, and heated in an evacuated silica tube at 1173 K for 20 h. Then the Bi4NbO8Cl suspension was coated onto ITO substrate ACS Paragon Plus Environment

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as transparent back contact and dried at 313 K for 1 h. Au NPs were fabricated and then integrated with the Bi4NbO8Cl film via the positively charged polyelectrolyte poly (diallyldimethylammonium chloride) (PDDA, pH = 8). After the thus-obtained Au NPs/Bi4NbO8Cl nanostructure was calcined in nitrogen, the as-fabricated samples were allowed for respective measurements to reveal their structural properties. As shown in Figure 1A of the SEM image, pure Bi4NbO8Cl was with particle size about 200 nm to 500 nm and exhibited a relatively roughness that could offer an excellent microenvironment for following adsorption. Besides, XRD pattern of synthetic Bi4NbO8Cl was also determined with the result shown in Figure S1. Figure 1 inset demonstrated the TEM image of the used Au NPs, which were spherical particles with the size of ca. 15 nm. After the modification, as shown in Figure 1B, the smooth particle surface of bulk Bi4NbO8Cl was coated with many spherical Au NPs particles, as highlighted with the red circles. As shown in Figure S2, the corresponding EDX spectroscopy was also acquired, the result of which demonstrated the presence of Au element. We further verified this successful modification by XPS with the results shown in Figure 1C. The Au 4f peak which was attributed to the metallic gold was observed, indicating the successful immobilization of Au NPs on the Bi4NbO8Cl film. Incidentally, the XPS spectra of bare Bi4NbO8Cl and bare Au NPs on the substrate were also recorded as shown in Figure S3. The optical properties of the samples were also followed by the spectra characterizations, and Figure 1D of the normalized spectrum manifested the change of the optical properties before and after the Au NPs modification. Clearly, as depicted, bare Bi4NbO8Cl exhibited no absorption over 520 nm, whereas plasmon absorption of the Au NPs can be seen with the maximum peak just at 520 nm. Such coincidence might indicate the good coupling effect and thus the possible extension of the absorption onset of the Bi4NbO8Cl. As expected, the absorption edge moved to over 600 nm as the red line, which was obviously due to the presence of Au NPs. Note that the UV−vis absorption spectrum was acquired in solution, whereas the solid UV−vis diffuse reflection spectra were measured using powder samples that scraped off from the electrode substrates. So, the result shown as red line in Figure 1D was


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corresponding to the mixture of the scraped modified sample, which should essentially be inferior to the original sample with Au NPs all on the external surface of Bi4NbO8Cl.

Figure 2. (A) Photocurrents generated from Bi4NbO8Cl (black line), Au NPs/PDDA/perovskite Bi4NbO8Cl (blue line), and Au NPs/Bi4NbO8Cl (red line). (B) Photocurrent action spectra of Bi4NbO8Cl (black line) and Au NPs/Bi4NbO8Cl (red line) with increased incident wavelengths. The spectra were the photocurrent intensity curve was occupied under illumination of the Xenon lamp with prism gratings for monochromatic light in different wavelengths. All photocurrent measurements are performed using 0.1 mol L−1 PBS (phosphate buffered saline) containing 1.0% sodium citrate (mass fraction, 0.034 mol L−1) under nitrogen and with 0 V bias.

Electrochemical and PEC Properties. Electrochemical characterization of cyclic voltammogram (CV) was performed with the results and corresponding discussion shown with Figure S4-S6. Briefly, the bare Au NPs/ITO, the as-fabricated Bi4NbO8Cl/ITO and Au NPs/Bi4NbO8Cl/ITO electrodes were studied, and the results indicated the successful Au NPs modification and its presence didn’t affect the property of Bi4NbO8Cl. The PEC properties were further investigated by acquiring the transient photocurrent responses of the samples upon the intermittent visible light irradiation. All the photocurrent values used for numerical analysis are measured after quiet time for 1 minute, and the irradiation was applied every 10 seconds and last another 10 seconds. As shown in Figure 2A, bare Bi4NbO8Cl (black line) only generated relatively weak photocurrent response, after the PDDA self-assembly process for Au NPs adsorption (blue line), no obvious variation in photocurrent intensity was observed, which was due to the presence of PDDA layer that inhibited the charge transfer process. Especially, with the light switching on and off, both the photocurrent signs (black and blue lines) ACS Paragon Plus Environment

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changed slowly. This was due to the presence of shallow and deep surface states on both the samples. Specifically, upon light irradiation, the photoexcited conduction band (CB) electrons will firstly filled into the shallow traps that lying close to the CB, and then be released constantly from these shallow surface states and retrapped into the deep ones. During such trapping-releasing-retrapping process, only a part of the CB electrons could transfer to the ITO electrode, exhibiting the slowly increasing signals. Similarly, the slow decay of the photocurrent to zero was due to the charge-carrier release from the surface traps.43−45 However, the slow response disappeared and the signals responded promptly following the onset/offset of the light irradiation after PDDA removal (red line). This phenomenon demonstrated that the presence of Au NPs on the Bi4NbO8Cl could diminish the trapping of the surface states and facilitate the fast charge separation and transfer and thereby the photocurrent generation. However, with the illumination turned on, an initial spike in photocurrent (photocharging) emerged, which was then quickly decayed to the stable level within 1.0 second. This phenomenon implied the fast separations of photogenerated electron-hole pairs at the electrode surface, i.e., the electrons “sink” toward the ITO electrode while the holes “move” to the electrode–solution interface, and the rapid decay of the signal indicated that a great amount of the electrons/holes were accumulated at the interface, rather than immediately communicated with the electrolyte. With the illumination turned off, a similar but slight transient behaviour of the cathodic photocurrent (photodischarging) appeared which should be attributed to the recombination of the charge carriers at the electrode surface.46 Significantly, comparing with the bare Bi4NbO8Cl, the Au NPs modified one enabled an obvious growth of the photocurrent intensity. The photocurrent action spectra of Bi4NbO8Cl and Au NPs/Bi4NbO8Cl were then performed. As shown in Figure 2B, the photocurrent intensity of Au NPs/Bi4NbO8Cl (red line) exhibited significant increase as compared to bare Bi4NbO8Cl (black line). More importantly, the photoresponse of bare Bi4NbO8Cl ceased at around 500 nm, whereas the Au NPs/Bi4NbO8Cl had obvious photoresponse in a wide range to near 700 nm. Such phenomenon was obviously caused by the presence of Au NPs. In detail, such photocurrent enhancement should be ascribed to the following possible reasons: (1) when Au NPs are ACS Paragon Plus Environment

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equipped with Bi4NbO8Cl, a Schottky barrier could be formed in the interfacial region of Au NPs and Bi4NbO8Cl. The presence of the Schottky barrier is favorable for the separation of electrons and holes and prevents the recombination of electron–hole pairs. The internal electric field existing in hetero-junctions between Bi4NbO8Cl and Au NPs could induce faster carrier migration, thus enhancing the PEC performance. (2) The Au NPs could increase the visible light absorption due to the strong surface plasmon resonance (SPR) of Au NPs. (3) With good carrier transport property, the presence of Au NPs could improve the conductivity of the electrode.47 Analytical Performances. The developed system was then applied for the PEC cysteine biodetection. As shown in Figure 3A, for the detection of 0.1 mol L−1 cysteine, the Au NPs/Bi4NbO8Cl (red line) exhibited greater signal response as compared to the bare Bi4NbO8Cl (black line). The enhancement of the Au NPs/Bi4NbO8Cl heterostructure can be explained in the Scheme 1. Following irradiation, both the Bi4NbO8Cl and Au NPs can be simultaneously excited, and the cysteine served as the electron donor to the photogenerated holes and was oxidized to glutathione disulfide. Specifically, electrons are photoexcited from the occupied valence band (VB) to the empty conduction band (CB) of the Bi4NbO8Cl, while the “hot electrons” (near the Fermi level) in Au NPs are excited to surface plasmon states. Then, the hot electrons would transfer from Au NPs to the CB of Bi4NbO8Cl due to the suitable band alignment and then transfer to the external circuit to generate photocurrent, leaving the photogenerated holes produced on the VB of Bi4NbO8Cl and the “hot holes” over Au NPs are rapidly quenched by cysteine molecules. As aforementioned, the presence of Au NPs on the Bi4NbO8Cl could diminish the trapping of the surface states and facilitate the fast charge separation and transfer. In this way, these in situ photoinduced holes from Bi4NbO8Cl and Au NPs would concurrently oxidize the cysteine biomolecules, allowing the photo-oxidation reactions to take place not only on the surface of Bi4NbO8Cl but also on the Au NPs, and thus resulting in greatly enhanced reaction speed and PEC performances of the Au NPs/Bi4NbO8Cl heterostructure. To evaluate the operation stability of the prepared Au NPs/Bi4NbO8Cl electrode, time-based photocurrent response was tested for detecting 200 µmol L−1 cysteine. As shown in Figure 3B, the photocurrent responses were recorded as the repeated ACS Paragon Plus Environment

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irradiation turned on and off for several cycles and the electrode displayed reproducible responses without any noticeable decrease during this period. The result indicated the high photophysical stability of the electrode for the intended application.

Figure 3. (A) Photoresponses of ITO electrode (blue line), Bi4NbO8Cl (black line) and Au NPs/Bi4NbO8Cl (red line) for detection of 0.1 mol L−1 cysteine. (B) Stability of the Au NPs/Bi4NbO8Cl in the detection of 200 µmol L−1 cysteine.

Scheme 1. Schematic illustration of the mechanism for the charge separation and transfer in the Au NPs/Bi4NbO8Cl system under visible light illumination.


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Effect of different cysteine concentrations on the differential photocurrent responses against the modified and unmodified electrodes were then investigated with the results shown in Figure 4A and B, respectively. We further compared the progressive photocurrent responses of the two electrodes, and the specific working dependence and the corresponding linearity regions were depicted in Figure 4C and D. The detection limits of Bi4NbO8Cl and Au NPs/Bi4NbO8Cl electrodes were 10−4 mol L−1 and 10−5 mol L−1, respectively, with the corresponding linearity regions of 5×10−4 mol L−1 − 5×10−3 mol L−1 and 1×10−4 mol L−1 − 5×10−3 mol L−1, respectively. Obviously, the Au NPs/Bi4NbO8Cl electrode possessed a higher sensitivity and fast responses with a wider linearity region against cysteine detection. Given the concentrations of cysteine in human serum varies from 165.1 to 335.3 µmol L−1,48−50 these results indicated the potential suitability of the developed system for cysteine detection in biological samples. Incidentally, using the developed electrode, we also conducted the PEC detection of GSH, with the results and corresponding discussion as shown with Figure S7 and S8.

Figure 4. Photocurrents generated from (A) Bi4NbO8Cl and (B) Au NPs/Bi4NbO8Cl in 0.1 mol L−1 PBS with variable cysteine concentrations. (C) The specific working dependences and (D) The corresponding linearity regions.


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The selectivity is critical in the bioanalysis application. Therefore, the influences of different biological species (GSH, glucose, L-histidine, L-lysine, lactic acid, sodium citrate and BSA in the electrolyte of 0.1 mol L−1 PBS) on the photocurrent responses of the Au NPs/Bi4NbO8Cl electrode were studied. Especially, since the normal concentrations of cysteine in human serum is 165.1 − 335.3 µmol L−1, which is nearly 10 times higher than the 14 ± 7 µmol L−1 level of GSH,48−50 the interfering GSH was set at the high level of 50 µmol L−1 in this selectivity test. The concentrations of other interfering species were provided with the Figure 5. As shown, compared with the results of pure 0.1 mol L−1 PBS solution and mixture sample containing the cysteine and all interfering species, it could be find that these biomolecules had negligible influence on the cysteine detection. The difference in responses between the cysteine and GSH as well as other species could be reasonably attributed to their different electron-donating ability.51 The precision and reproducibility of this PEC bioassay was evaluated by relative standard deviation (RSD). Analysed from the experimental results, the RSD of 2.1% was obtained by measuring the same 200 µmol L−1 sample with at least four electrodes prepared independently at the identical experimental conditions, respectively. Besides, after several repeated measurements, no significant difference of photocurrent response could be observed as compared to the result obtained, indicating the stable readout for signal collection.

Figure 5. Photocurrent interference ratio of the Au NPs/Bi4NbO8Cl electrode in 0.1 mol L−1 PBS (pH = 7.4) containing 200 µmol L−1 cysteine, various species (GSH, glucose, L-histidine, L-lysine, lactic acid, sodium citrate, BSA), pure PBS and mixture added in 200 µmol L−1 cysteine at 0 V (vs. Ag/AgCl) under illumination. The concentrations of GSH was 50 µmol L−1, the sodium citrate was 0.034 mol L−1 (1.0% with mass fraction), BSA was 10−4 mol L−1 and other


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biomolecules were 0.01 mol L−1.

Conclusions In summary, we successfully developed a PEC biosensor for the cysteine detection using the Au NPs equipped perovskite Bi4NbO8Cl heterostructure. The Bi4NbO8Cl was prepared by a solid-state reaction, and the Au NPs/Bi4NbO8Cl electrode was made through electrostatic layer-by-layer self-assembly technique. It was found that the presencen of the Au NPs could diminish the trapping of the surface states and facilitate the fast charge separation and transfer, and significantly, enable a obvious growth of the photocurrent intensity as compared to the bare Bi4NbO8Cl. Due to their synergy effect, the as-fabricated Au NPs/Bi4NbO8Cl electrode possessed a higher sensitivity and fast responses with a wider linearity region against cysteine detection. These results suggested that the Au NPs/Bi4NbO8Cl heterostructure can be a competitive candidate in the development of PEC bioanalysis. And it is believed that our work could inspire new avenues for developing advanced schemes for perovskites utilization toward PEC bioanalytical purposes. Further studies and developments of various perovskite-based hybrids may allow for more opportunities for the advanced PEC bioanalysis with fast response, enhanced sensitivity, and long-term stability.

Author Information Corresponding Authors * E-mail: [email protected]; [email protected] * E-mail: [email protected] Notes The authors declare no competing financial interest.


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Acknowledgment We thank the National Natural Science Foundation of China (Grant Nos. 21327902, 21305063, and 21675080) for support. This work was also supported by a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. Associated Content Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.analchem.xxxxx. XRD spectra of synthetic source Bi2O3, BiOCl, Nb2O5, prepared Bi4NbO8Cl and standard spectrum of Bi4NbO8Cl, XPS spectra of Bi4NbO8Cl and Au modified ITO electrode, EDX spectroscopy of Au NPs/ Bi4NbO8Cl/ITO electrode, CV curves and PEC GSH detection based on Au NPs/Bi4NbO8Cl electrodes and the corresponding discussion. References (1) Zhao, W. W.; Xu, J. J.; Chen, H. Y. Chem. Rev. 2014, 114, 7421-7441 (2) Zhao, W. W.; Xu, J. J.; Chen, H. Y. Chem. Soc. Rev. 2015, 44, 729-741. (3) Freeman, R.; Girsh, J.; Willner, I. ACS Appl. Mater. Interfaces 2013, 5, 2815−2834. (4) Tanne, J.; Schäfer, D.; Khalid, W.; Parak, W.; Lisdat, F. Anal. Chem. 2011, 83, 7778-7785. (5) Zhao, W. W.; Xu, J. J.; Chen, H. Y. TrAC, Trends Anal. Chem. 2016, 82, 307-315. (6) Zhao, W. W.; Xu, J. J.; Chen, H. Y. Biosens. Bioelectron. 2016, 92, 294304. (7) Li, Z. Z.; Xin, Y. M.; Zhang, Z. H. Anal. Chem. 2015, 87, 10491-10497. (8) Zhan, W. W.; Kuang, Q.; Zhou, J. Z.; Kong, X. J.; Xie, Z. X.; Zheng, L. S. J. Am. Chem. Soc. 2013, 135, 1926-1933.


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