High Performance Electrochemical Biosensor for

Waste and Biomass Valorization https://doi.org/10.1007/s12649-018-0505-5

ORIGINAL PAPER

High Performance Electrochemical Biosensor for Bisphenol A Using Screen Printed Electrodes Modified with Multiwalled Carbon Nanotubes Functionalized with Silver-Doped Zinc Oxide Kwanele Kunene1 · Myalowenkosi Sabela1 · Suvardhan Kanchi1 · Krishna Bisetty1 Received: 11 May 2018 / Accepted: 30 October 2018 © Springer Nature B.V. 2018

Abstract This study reports on a novel electrochemical biosensor for the detection of Bisphenol A (BPA) using a carbon-screen printed electrode modified with multiwalled carbon nanotubes that are functionalized with silver doped zinc oxide nanoparticles (Ag-ZnONPs) on which laccase enzyme was immobilized. The nanocomposite was characterized in stages by UV–visible, Fourier Transform Infrared Spectroscopy, scanning and transmission electron microscopes. The synthesized hybrid AgZnONPs were spherical in shape with an average size of ~ 20 nm. The surface of Lac/Ag–ZnO/MWCNTs/C-SPE was also characterized using electrochemical methods. The presence of laccase on the surface of the nanocomposite-modified electrode reduced the charge transfer resistance of the redox couple and thereby improved the sensitivity towards the oxidation of Bisphenol A. The catalytic activity was further evaulated with 80 µM solution by cyclic voltammetry. Under optimum conditions, the biosensor displayed outstanding performance for BPA with a linear range 0.5–2.99 µM (R2 > 0.9943) and a limit of detection (LOD) of 6.0 nM. Furthermore, this proposed lacasse biosensor is more selective and stable with a high reproducible response factor (RSD of 0.86%), and was able to adequately quantify BPA in plastic bottle samples. In the light of our results, the biosensor showed promising and trustworthy analytical performance that is ideal for routine sensing applications for BPA in plastic bottles.

* Suvardhan Kanchi [email protected] Myalowenkosi Sabela [email protected] Krishna Bisetty [email protected] 1

Department of Chemistry, Durban University of Technology, P.O Box 1334, 4000 Durban, South Africa

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Waste and Biomass Valorization

Graphical abstract

Keywords Bisphenol A · Screen printed electrode · Electrochemical biosensor · Laccase reductase

Statement of Novelty

Introduction

This manuscript deals with the development of smart electrochemical signaling platform amplified with a silver-doped ZnO on screen printed electrodes for the detection of a Bisphenol A. The present work is the first on its own for the determination of Bisphenol A using laccase based nanocomposite on carbon-screen printed electrode by using portable 910 MINI PSTAT. Cyclic voltammetry and differential pulse voltammetry techniques were performed to better understand the redox mechanism of BPA and to test the performance of the developed electrochemical biosensor. The comparison of the results obtained from bare and modified C-SPE revealed the sensitivity of the developed sensor (6.0 nM). Furthermore, the modified electrochemical sensor was successfully employed to detect BPA in plastic bottles offering tantalizing prospects on the future of analytical sensing devices.

Bisphenols are essential organic chemicals that are commonly used as intermediates in the production of flame retardants and polycarbonate plastics [1–3]. These compounds are used in the production of food and beverage wrapping, as well as adhesives and paper coverings [4, 5]. Specifically, Bisphenol A (BPA) have received considerable attention based on their endocrine-disrupting activities due to its structural similarity to natural hormones with possible toxic impact on the environment [6]. Their concentrations have been reported to be around 0.15 µM in biological, food and water samples [7]. Therefore, it is crucial to establish a simple, sensitive method to detect the presence of BPA in biological and food samples. Previous reports reveal that a number of commonly used traditional techniques such as capillary electrophoresis, spectrophotometry, gas chromatography (GC) and liquid chromatography (LC) have been used for the determination of BPA [8, 9]. Although these advanced techniques can be costly, but they do deliver low limit of detection (LODs) and their samples require complicated pre-treatment procedures, which calls for skilled operators [9, 10]. Therefore this has

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prompted greater efforts for the development of analytical techniques that are sensitive, selective and effective for the detection of BPA with the focus on electrochemical sensors [11–16]. The biosensors using screen-printed electrode (SPE) appears to be the ideal choice because they are fast, portable, selective and suitable for mass production. Their applications for detection of organic molecules have been an expanding area of research for the past two decades, with most applications of carbon based SPE in the literature [17, 18]. Many modifiers such as nanoparticles (NPs) [19], carbon black paste [20], and graphene [21] have been reported for the fabrication of electrochemical biosensors. The fabrication of electrodes with nanomaterials such as zinc oxide nanoparticles (ZnONPs) [22], gold nanoparticles (AuNPs) [23], or hydroxyapatite nanoparticles [24], can increase the sensitivity of a biosensor while they can also be used to fabricate enzyme-based biosensors. The enzyme laccase (polyphenoloxidase; EC 1.10.3.2) which is a blue multi-copperoxidase family is well know for it ability to oxidize a variety of organic substrates, and to reduce molecular oxygen to water [25]. Enzymes such as tyrosinase [26], peroxidase and laccase [27], have been used for the development of the electrochemical biosensors. Furthermore, amperometric biosensors modified with bismuth and bismuth oxide for detection of phenolic compounds has been studied by several authors [28, 29]. The use of such materials to electroanalysis have widen the possibilities for the novel construction of electrochemical biosensors for phenolic compounds, resulting in various types of sensors available in the market. In the present study carbon-screen printed electrodes (C-SPEs) were modified with MWCNTs functionalized with silver doped zinc oxide nanoparticles (Ag-ZnONPs). The novel nanomaterial composite was further combined with laccase in order to improve it selectivity. The exceptional properties of Ag-ZnONPs result in the enhanced electrochemical performance and to the best of our knowledge, the electrochemical sensing devices for the detection of BPA using this modifier has not been reported. Accordingly, in this study optimization of variables included investigating the pH, deposition time and the scan rate at room temperature followed by quantifying BPA in commercially available plastic water bottles.

Materials and Methods Materials Sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, Bisphenol A (BPA), zinc gluconate, silver nitrate, sodium acetate, catechol, 4-aminophenol, 2-nitrophenol, lacasse reductase (20 Units/mg)

from Trametes Versicolor (CAS No.: 80498-15-3), phenol, 4,4-sulfonyldiphenol and MWCNTs with dimension: O.D. × L 7–12 nm × 0.5–10 µm (CAS No.: 308,068-56-6) were purchased from Sigma Aldrich (Durban, SA). Sulphuric acid, ethanol, ammonia solution, acetone (absolute, 99.9%), glutaraldehyde were supplied by Capital Lab Supplies (Durban, SA). A 0.5 mM working solution of BPA was prepared to dissolve adequate amount of a solid compound in 99% ethanol as a solvent. All reagents were of analytical grade and no purification was made to them before use.

Instrumentation A portable USB-powered mini potentiostat called 910 PSTAT [Metrohm, Durban, South Africa (SA)] which is controlled with the PSTAT software was used for electrochemical measurements. The three-electrodes configuration on the ceramic substrate was made of a silver reference electrode, carbon based working electrode and a carbon auxiliary electrode. Morphological analysis of the composite was examined by Scanning Electron Microscope (SEM) model EVO HD15, equipped with a LaB6 emitter and coupled with energy dispersive X-ray (EDX, OXFORD instruments). Transmittance Electron Microscopy (TEM) model JEM 2100 equipped with a L aB6 emitter (MAXOXFORD instruments) was used to study the nanocomposite coated on the surface of C-SPE. UV–Visible spectra were recorded in the wavelength ranging from 300 to 600 nm with VARIAN Cary 50 spectrophotometer. An FTIR spectrum was recorded in the wavelength between 4000 cm−1 and 400 cm−1 using Perkin-Elmer, Midrand, South Africa.

Methods Synthesis of Ag‑ZnONPs/ZnONPs The Ag-ZnONPs and ZnONPs were prepared according to the previous report with slight modification [30]. Briefly, a solution of 100 mM zinc gluconate and 1.0 mM silver nitrate was prepared in deionized water by dissolving approximately 3.40 g and 0.040 g respectively. Thereafter, 25% of ammonia solution was added drop-wise until a white precipitation was formed, then a few more drops were added further until the clear solution was observed. Into this solution, 1.25 mL of 0.1 M acetate buffer was added drop-wise while stirring until a white precipitate was formed. The resulting precipitate was washed with 100 mL deionised water, followed by 10 mL acetone and then centrifuged. Finally, the residue was oven dried overnight at 75 °C. For the synthesis of pure ZnONPs, a similar procedure was followed with the exclusion of silver salt, therefore the yield was much smaller.

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Preparation and Fabrication of Lac/Ag‑ZnONPs/MWCNTs/ C‑SPE In the first step, a homogenous paste was achieved by mixing 2.0 mg of MWCNTs, 2.5 mg of Ag-ZnONPs or ZnONPs with 2 mL of DMF:H 2O (1:1) as a dispersion medium of the mixture and sonicated for 3 h [31]. The presence of 50% of water in the solution allows for C-SPEs modification due to its compatibility with the ink. It is important to note that pure DMF dispersion solution of MWCNTs is not suitable to modify most of the plastic substrates because of the conductive inks on C-SPEs. Consequently, 5.0 µL of the resulted 1:1 mixture was deposited on the working electrode surface and dried at 20 °C for 3.0 min, then Ag-ZnONPs/MWCNTs was produced. The use of high temperatures can damage the SPE completely [32]. In the second step, solution of Laccase was prepared by adding 3 mg of Lac into 1 mL of 0.1 M phosphate buffer, pH 6.5. Thereafter, the biosensor Lac/Ag-ZnONPs/ MWCNTs was prepared by drop casting of 10 µL Lac on Ag-ZnONPs/MWCNTs and allowed to dry at 4 °C for 3 h. After drying, the electrode was covered with 5 µL of glutaraldehyde and left to dry at room temperature for 10 min in order to avoid enzyme leakage. The fabrication of biosensor was illustrated in Scheme 1.


Sample Preparation The mineral water bottles were collected from a local disposal site (Durban, South Africa). These samples were pre-cleaned by ultrasonication in acetone, followed by successive rinsing with alcohol, doubly distilled water and finaly dried at ambient temperature overnight. Bisphenol A was extracted from mineral water bottles using the method reported by Ntsendwana et al. with minor modifications [33]. Briefly, the samples were cut manually to an average size of 0.3 cm, and thereafter approximately 1.0 g was mixed with 25 mL of deionized water into a round bottom flask. The flask was then fitted with a condenser placed for 48 h into an oil bath heated to 70 ± 3 °C. After cooling to room temperature, the condenser was washed with about 15 mL of deionized water into the same flask. Thereafter, the sample was filtrated, through a 0.45 µm filter paper. Finally, the collected filtrate was made up to 50 mL and stored at 4.0 °C for further studies.

Electrochemical Measurements of BPA with Lac/ Ag‑ZnONPs/MWCNTs/C‑SPE Voltammetric measurements were carried out with a portable USB-powered 910 PSTAT mini potentiostat. The modified circular area of Lac/Ag-ZnONPs/MWCNTs/C-SPE was used as a working electrode. All measurements were carried out at room temperature in a 10 mL electrochemical cell. Into the electrochemical cell, 9.0 mL of 0.1 M phosphate

Scheme 1 A schematic representation of the electrochemical biosensor for the detection of oxidation of BPA using Lac/Ag-ZnONPs/MWCNTs/ C-SPE

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buffer (PB) solution with pH 6.0 and 10 µL of 0.5 mM BPA were added and thereafter cyclic voltammetry (CV) and differential pulse voltammetric (DPV) measurements were carried out in the potential range of 0.0 to 1.0 V vs. Ag/AgCl reference electrode at a scan rate of 0.08 V s−1 and scan rate of 0.1 V s−1 respectively.

Results and Discussion Choice of Materials Electrochemical sensors, were the electrodes of which MWCNTs modified by nanoparticles (NPs) acts as an enhancer of electron transfer reaction that is taking place between analytes and base of electrode surface, i.e. MWCNTs [17, 34]. This combination of MWCNTs with NPs improves the mechanical strength of the hybrid material and electrical conductivity. Amongst the semiconductor nanostructured materials, zinc oxide (ZnO) has been commonly used in optoelectronic industry and other many applications [35]. This is due to its diverse properties, both chemically and physically. However, the ZnO is an n-type semiconductor, thus its use as a single electrode modifier is limiting factor in the electrochemical biosensors development. This property leads to low operating speed and fast recombination of the generated electron-hall pairs and therefore direct

Fig. 1 a UV–Visible absorption spectra. b FTIR spectra of (i) ZnONPs Ag-ZnONPs (C:C2–C4) morphology of bare C-SPE, AgZnONPs/C-SPE and Ag-ZnONPs/MWCNTs/C-SPE obtained by

electron transfer is challenge [36]. This has led to the use of several doping agents like aluminuim [37], copper [38], strontium [39], cobalt [40], and silver [41] ions doped into ZnONPs for sensors. Amongst them, silver is a potential candidate for various optical and photocatalytic applications due to its shallow acceptor level into ZnO. Furthermore, doping ZnO with Ag also improve the surface charge distribution, reasonable conduction band formation during photoreaction [42]. The optical band gap of Ag-ZnONPs was found to be 3.07 eV which is much less than 3.23 eV of pure ZnONPs as can be seen in Fig. 1a. Therefore, in this study MWCNTs integrated with Ag-ZnONPs was used as a high performance electrochemical biosensor for the detection of BPA.

Characterization of Ag‑ZnONPs Hybrid and Modified Electrodes The UV–visible spectrum of ZnONPs dispersed in ethanol depicted in Fig. 1a shows an absorption peak at 352 nm which is equivalent to 3.237 eV (see curve i), in agreement with the literature [30]. On the other hand, the Ag-ZnONPs spectrum (shown in curve ii) indicates a broader absorption peak at 357 nm (3.229 eV) with a red shift and low particle size as observed by Karami and Fakoori [43]. However, the band gap of ZnONPs decreased from 3.237 eV to 3.229 eV when doped with Ag. This was due to the p-type

scanning electron microscope and with corresponding Transmission electron microscope images (C:C4–C5) showing C-SPE modification

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conductivity of nanoparticles (NPs) and in accordance with those reported by Reddy et al. [44]. The band gap of the Ag-ZnONPs decreases due to the downwards shifts of the conduction band. The FTIR spectra of the synthesized ZnONPs and AgZnONPs were shown in Fig. 1b. Chithra et al. observed similar spectra for ZnONPs and Ag-ZnONPs exhibiting absorbance in the infrared region at 516 and 506 cm−1 are due to ZnONPs [45]. The characteristic absorption peaks at 3382 cm−1 corresponds to –OH stretching vibrations of water [30, 44], the band at 2869 cm−1 represents –CH stretching vibrations of alkanes [46], while the sharper peak observed at 1582 cm−1 represents –C=O stretching vibration [46]. The CH3 vibration was observed at 1423 and 1387 cm−1. The C–H in-plane vibration was noticed at 1105 and 1091 cm−1. With the addition of Ag, there is a minor shift towards lower frequencies, due to the partial substitution of the A g+ ion at the ZnO lattice [46]. The absence of Ag–O absorption bands below at 400 cm−1 suggests that there was no chemical bonding between Ag–O and Ag–ZnO NPs [47, 48]. Fig. C1 represents the SEM morphology of the bare C-SPE (see C2), Ag-ZnO NPsMWCNTs/C-SPE (see C3) and Lac/Ag-ZnO NPs/MWCNTs/C-SPE (see C4). The SEM images clearly illustrate the roughness of the coating increases from the bare C-SPE to Lac/Ag-ZnONPs/ MWCNTs/C-SPE, confirming an increase in the surface area of the electrode with each modification. The morphology of Ag-ZnONPs and MWCNTs functionalized with Ag-ZnONPs were characterized by using transmission electron microscope (TEM). The obtained results confirmed the presence of Ag-ZnONPs on the MWCNTs surfaces. The morphology is shown in Fig. C1–C3 obtained from SEM confirms the coating of Ag-ZnONPs on the bare C-SPE. Results indicated that the synthesized hybrid Ag-ZnONPs were spherical in shape and ~ 20 nm in average size. The Fig. C1–C6 shows the hollow inner tube of MWCNTs functionalized with Ag-ZnONPs which corresponds to the Fig. C1–C4 obtained from SEM. The π–π non-covalent interaction that exist between MWCNTs and the Ag-ZnONPs is relatively strong because of the hydrophobic surface which support the formation of Ag-ZnONPs/ MWCNTs nanocomposite. Cyclic voltammetry (CV) was used to characterize the unmodified and modified electrodes in the presence of BPA. Figure 2a shows cyclic voltammograms of 0.5 mM BPA measured in 0.1 M PB with several elelctrodes, namely: C-SPE, Ag-ZnONPs/MWCNTs/C-SPE and Lac/AgZnONPs/MWCNTs/C-SPE. Cyclic voltammograms of bare electrode C-SPE show a low oxidation peak at 30.12 µA as expected, followed by Ag-ZnONPs/MWCNTs/C-SPE and Lac/Ag-ZnONPs/MWCNTs/C-SPE showed the highest oxidation peak current, this signifies an increased sensitivity. Low oxidation peak currents that are not well-defined were

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observed with C-SPE. However, a well-defined oxidation peak was observed when Ag-ZnONPs/MWCNTs/C-SPE and Lac/Ag-ZnONPs/MWCNTs/C-SPE were introduced and the oxidation peak current increased significantly. This is due to the large surface and electrochemical conductivity of MWCNTs and the catalytic activity of laccase. The strong adsorption effects of Ag-ZnO/MWCNTs/C-SPE and Lac/Ag-ZnO/MWCNTs/C-SPE results in the high oxidation current compared to the bare C-SPE.

Optimization of Analytical Parameters for Lac/ Ag‑ZnONPs/MWCNTs/C‑SPE In order to fabricate a biosensor, laccase (Lac) was immobilized on the modified carbon screen-printed electrode (C-SPE) with Ag-ZnONPs/MWCNTs. The fully fabricated biosensor electrode was represented as Lac/Ag-ZnONPs/ MWCNTs/C-SPE. Numerous parameters such as enzyme loading, pH, scan rate and deposition time were investigated to optimize the analytical performances of the biosensor. The effects on the amount of the enzyme that was immobilized onto the surface of the electrode was investigated by changing concentration from 1.0 to 7.0 mg mL−1. The enzyme was prepared in 0.1 M PB at pH 6.5 and the corresponding electrochemical response was then monitored as shown in Fig. 2b. The current increases until its reach the maximum value of 3.0 mg mL−1, then the current decreases significantly as the laccase increases. This is due to an increase in the film thickness and resulted in slow electron transfer due to interfacial electron transfer resistance [49]. Therefore, 3.0 mg mL−1 of laccase was immobilized onto the surface of the working electrode for the entire experiments and covered by glutaraldehyde as a cross linker. The pH dependence of the Lac/Ag-ZnONPs/MWCNTs/ C-SPE was investigated between pH 3.0 and 10.0 in 0.1 M PB in the presence of 0.5 mM BPA. In Fig. 2c, the peak current at 0.65 V increases from 11.15 µA to 61.31 µA with the increase of pH from 3.0 to 6.0. Therefore, pH 6.0 was used for the entire experiments to obtain maximum sensitivity. These results correlate well with the optimum pH which is acidic for free laccase, and thus confirming that the laccase activity was not altered during the immobilization step [27, 50]. The effects of deposition time were investigated in 0.5 mM BPA. Figure 2D shows that the oxidation current increases gradually with the deposition time up to 25 s. The longer deposition time, the more BPA that is adsorbed onto the electrode surface. Beyond 25 s, the BPA oxidation peak current decreases due to the saturation of electrode surface with BPA. Therefore, deposition time of 25 s was employed for the entire experiments. The relationship between the peak current and scan rate gives the valuable information that involves


Fig. 2 a Cyclic voltammograms of 0.5 mM BPA in 0.1 M PBS (pH 6.0) at different modified electrodes and C-SPE. b Effects of enzyme loading on the electrode. c Effect of pH on the oxidation of 0.5 mM BPA in 0.1 M PB solution. d Effect of deposition time on the biosen-

sor response in the presence of 0.5 mM BPA in 0.1 M PBS at pH 6.0. e Effects of scan rate from 0.01 to 0.08 V s−1 (f). The relationship between scan rate and current on BPA

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electrochemical mechanism. Hence, the effects of scan rate on the oxidation of BPA was studied using 0.5 mM BPA in PB at pH 6.0, by monitoring the oxidation peak current. Figure 2e shows the cyclic voltammograms of 0.5 mM BPA at Lac/Ag-ZnONPs/MWCNTs/C-SPE with different scan rates ranging from 0.01 to 0.08 V s−1, the oxidation peak current increases with the increase of scan rate. The peak current of BPA increases linearly with the increase in the scan rate from 0.01 to 0.10 V s −1 as shown in Fig. 2e. The linear relationship at the scan rate 0.01 to 0.08 V s−1 confirms the adsorption of BPA onto the electrode surface. The linear relationship between a scan rate and oxidation peak current is confirmed by the regression equation y = 67.345x + 0.41321 with R2 = 0.9980 (Fig. 2f), which does not include scan rates, 0.09 and 0.1 V s−1, as they were considered as outliers and therefore scan rate of 0.08 V s−1 was chosen as the optimum parameter. This indicates that the oxidation of BPA on the surface of the


modified C-SPE is an adsorption-controlled process and the electron transfer process. Literature reveals that the oxidation reaction of BPA involved two electron transfer (n), therefore the number of protons that are involved in the reaction is two. The electrooxidation of BPA at Lac/ Ag-ZnONPs/MWCNTs/C-SPE is a two-electron and twoproton process [51]. The possible reaction mechanisms for oxidation of BPA on the surface of the electrode is shown in Scheme 2. In Fig. 3b different organic solvents namely acetone, acetic acid, ethanol, deionised water and dimethylformamide (DMF) were adopted for effectiveness in removing the analyte while retaining the nanocomposite modified surface. Among these solvents, acetone was the best solvent to rinse the electrode based on the current response which increases from 5.32 µA to 26.67 µA in comparison to deionised water.

Scheme 2 Electrochemical oxidation reaction mechanism of BPA at Lac/Ag-ZnONPs/ MWCNTs/C-SPE

Fig. 3 a Biosensor response on BPA in 0.1 M PBS, pH 6.0, 3 mg/mL laccase. Insect: linear range of BPA response in the biosensor (b) Effect of rinsing solvents on current signal between the runs of one modification

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Electrochemical Behavior of BPA at Lac/Ag‑ZnONPs/ MWCNTs/C‑SPE

Reproducibility and Stability of Lac/Ag‑ZnONPs/ MWCNTs/C‑SPE

The current signal was investigated as a function of BPA concentration. In this study, the electrochemical responses of the electrode were measured as a function of the amount of BPA solutions (0.5, 0.99, 1.49, 1.99, 2.49, 2.99 µM) in 0.1 M PB at pH 6.0. Figure 3a shows that the peak current of BPA increases with increase in concentration, however at higher concentrations from 3.49 µM, the current decreases, due to the formation of higher amounts of phenoxy radicals, and thus limits surface area on the electrode. This also confirms that the oxidation reaction is not limited by diffusion alone. The oxidation peak current increases with the increase of BPA concentration up to 2.99 µM due to the increased electroactive species in a BPA solution.

The reproducibility of Lac/Ag-ZnONPs/MWCNTs/C-SPE was evaluated using same nanocomposites, but with different SPE’s (carbon, platinum and gold) on the same day under the optimized parameters with 0.36 mM BPA (n = 6). A similar behaviour was observed, but platinum and gold display lower currents. The Au-SPE had an outlier in the third measurement hence, the run was eliminated based on the Q test. Overall relative standard deviation (%RSD) is in the order of Au-SPE > C-SPE > Pt-SPE, but the C-SPE with 0.86% RSD hence it was chosen as the preferred electrode as it showed a much better current response in contrast to Au-SPE. The stability of the Lac/Ag-ZnONPs/MWCNTs/C-SPE was evaluated for ten consecutive days using DPV (Fig. 4). After using the Lac/Ag-ZnONPs/MWCNTs/C-SPE for the determination of BPA on the first day, it was stored in

Calibration Figure 3a shows a calibration plot constructed from DPV response, with the biosensor showing a linear concentration range from 0.5 µM to 2.99 µM with R2 = 0.9943. This linear behaviour has been observed in the literature for the electroanalytical behaviour of BPA [8]. The LOD has been calculated as (3 × SDblank)/slope was 6.0 nM (n = 3). The LOD obtained was then compared to other methods that have been reported in the literature, as shown in Table 1. On comparing the methods presented in Table 1, differential pulse voltammetry shows lower LOD in contrast to amperometric methods. However, the current method is much more cost effective as it uses Lac/Ag-ZnO NPs/MWCNTs in contrast to GR/Au-TYR-CS elelctrode.

Fig. 4 Stability of the Lac/Ag-ZnONPs/MWCNTs/C-SPE in PBS of pH 6.0, scan rate 0.08 V s−1 tested using 0.5 mM BPA solution Table 1 Literature review for quantification of BPA in plastic bottle extract

Biosensor

Method

Linear range (µM)

Detection limits (nM)

References

GR/Au-TYR-CS/GCE Lac/CB/SPE TYR/TiO2/MWCNTs/PDDA/Nafion/GE TYR/AuNPs/SPCE TYR/NiNPs/SPCE TYR/Fe3O4/SPCE Lac/Ag-ZnO NPs/MWCNTs/C-SPE

DPV Amp Amp Amp Amp Amp DPV

0.0025–3.0 0.5–50 0.28–45.05 0.042–36 0.91–48 0.027–40 0.5–2.99

1.0 200.0 66.0 10.0 7.1 8.3 6.0

[19] [27] [26] [52] [52] [52] This work

Amp amperometric; Au gold; AuNPs gold nanoparticles; Ag-ZnO NPs silver doped zinc oxide; CS chitosin; CB carbon black; C-SP carbon screen printed electrode; DPV differential pulse voltammetry; Fe3O4 iron oxide; GR graphene;GE graphite electrode; GCE glassy carbon electrode; SPCE screen printed graphite carbon electrode; NiNPs nickel nanoparticles; Lac lacasse; MWCNTs multiwalled carbon nanotubes; PDDA polycationic polymer poly(diallyldi-methylammonium chloride); TYRtyrosinase; TiO2 titinum dioxide

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Conclusions

Table 2 Recovery studies of spiked plastic bottles Sample

BPA concentration added (µM)

BPA concentration found (µM)

Recovery (%)

Sample I Sample I Sample I Sample II Sample II Sample II

10 20 30 10 20 30

11.2 19.0 31.0 9.0 18.3 28.7

89.3 105.3 96.8 111.1 109.3 104.5

the refrigerator set at 4 °C without rinsing for second-day use. This process was repeated for ten consecutive days. The experimental results show that there is a very small variation in the peak currents (28.98%) at the end of the 10th day with % RSD of 0.234. The obtained results suggested that the electrochemical biosensor may be used for multiple analysis although it was designed for a single disposable electrode to make the method more economical.

Interferences and Practical Application The interference of foreign species on the detection of BPA was evaluated by using 100-higer concentration of metal ions ( Cu2+, Fe3+, Bi3+, Cd2+ and K +) and other phenolic compounds (catechol, 4-aminophenol, 2-nitrophenol, phenol and 4,4-sulfonyldiphenol). The analytical data from this study reveals that 15.5% variation in the peak current was observed, indicating that there were insignificant interference and thus better selectivity of Lac/Ag-ZnONPs/MWCNTs/C-SPE for the detection of BPA in real samples. In order to evaluate the performance of Lac/AgZnONPs/MWCNTs/C-SPE in practical analytical applications, BPA was quantified in the mineral water bottles. The sample was processed for further studies and named as sample-I and II prior to the DPV analysis. The analysis was performed with optimized parameters using Lac/AgZnONPs/MWCNT/C-SPE in PB solution (pH 6.0) with a scan rate 0.08 V s−1 for the detection of BPA. There was no distinguishable peak of BPA that was found due to its low concentration of BPA in real samples and therefore, samples were spiked with a known concentration of BPA standard. Three different concentrations of BPA were used for each sample, the obtained results are shown in Table 2. The recovery was between 89.3% and 111.1%, with the relative standard deviation (RSD) of 6% for three consecutive measurements of the same sample.

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In this work, a versatile electrochemical biosensor based approach for the detection of BPA using a Lac/Ag-ZnONPs/ MWCNTs/C-SPE is presented. The results from our study demonstrate the improved performance of the electrochemical biosensor in terms of better repeatability, reproducibility and stability. Moreover, the lower detection limits of 6.0 nM, the wider linear range of 0.5–2.99 µM reaffirms the higher sensitivity of this approach demonstrates the promising electrochemical biosensor for the determination of BPA in real samples. After electrode modification and characterization, the BPA oxidation peak current was enhanced significantly. Therefore, we envision that this method has great potential applicable to the food and beverage industries. Acknowledgements The authors gratefully acknowledge the financial assistance from the National Research Foundation (NRF) of South Africa and Durban University of Technology.

Compliance with Ethical Standards Conflict of interest All authors declare that there is no conflict of interest related to the manuscript for submission.

References 1. Peng, X., Tian, Y., Liu, S., Jia, X.: Degradation of TBBPA and BPA from aqueous solution using organo-montmorillonite supported nanoscale zero-valent iron. Chem. Eng. J. 309, 717–724 (2017) 2. Apetrei, C., Alessio, P., Constantino, C.J.L., de Saja, J.A., Rodriguez-Mendez, M.L., Pavinatto, F.J., Fernandes, E.G.R., Zucolotto, V., Oliveira Jr., O.N.: Biomimetic biosensor based on lipidic layers containing tyrosinase and lutetium bisphthalocyanine for the detection of antioxidants. Biosens. Bioelectron. 26, 2513–2519 (2011) 3. Mantilla, S.V., Manrique, A.M., Gauthier-Maradei, P.: Methodology for extraction of phenolic compounds of bio-oil from agricultural biomass wastes. Waste and Biomass Valorization. 6, 371–383 (2015) 4. Juhel, G., Bayen, S., Goh, C., Lee, W.K., Kelly, B.C.: Use of a suite of biomarkers to assess the effects of carbamazepine, bisphenol A, atrazine, and their mixtures on green mussels, Perna viridis. Environ. Toxicol. Chem. 36, 429–441 (2017) 5. Louizi, M., Massardier, V., Taha, M., Ayoub, A., Vernhet, L.: New routes of valorization of recycled and bio-sourced polyamides with a low toxicity process. Waste Biomass Valorization 4, 47–54 (2013) 6. Nadal, A., Fuentes, E., Ripoll, C., Villar-Pazos, S., CastellanoMuñoz, M., Soriano, S., Martinez-Pinna, J., Quesada, I., AlonsoMagdalena, P.: Extranuclear-initiated estrogenic actions of endocrine disrupting chemicals: Is there toxicology beyond paracelsus? J. Steroid Biochem. Mol. Biol. 176, 16–22 (2018) 7. Portaccio, M., Di Tuoro, D., Arduini, F., Lepore, M., Mita, D., Diano, N., Mita, L., Moscone, D.: A thionine-modified carbon paste amperometric biosensor for catechol and bisphenol A determination. Biosens. Bioelectron. 25, 2003–2008 (2010)

Waste and Biomass Valorization 8. Li, H., Wang, W., Lv, Q., Xi, G., Bai, H., Zhang, Q.: Disposable paper-based electrochemical sensor based on stacked gold nanoparticles supported carbon nanotubes for the determination of bisphenol A. Electrochem. Commun. 68, 104–107 (2016) 9. Ma, Y., Liu, J., Li, H.: Diamond-based electrochemical aptasensor realizing a femtomolar detection limit of bisphenol A. Biosens. Bioelectron. 92, 21–25 (2017) 10. Mayorga-Martinez, C.C., Guix, M., Madrid, R.E., Merkoçi, A.: Bimetallic nanowires as electrocatalysts for nonenzymatic realtime impedancimetric detection of glucose. Chem. Commun. 48, 1686–1688 (2012) 11. Lu, L., Zhang, L., Zhang, X., Huan, S., Shen, G., Yu, R.: A novel tyrosinase biosensor based on hydroxyapatite–chitosan nanocomposite for the detection of phenolic compounds. Anal. Chim. Acta 665, 146–151 (2010) 12. Deiminiat, B., Rounaghi, G.H., Arbab-Zavar, M.H., Razavipanah, I.: A novel electrochemical aptasensor based on f-MWCNTs/ AuNPs nanocomposite for label-free detection of bisphenol A. Sens. Actuator B 242, 158–166 (2017) 13. Zhang, J., Xu, X., Chen, L.: An ultrasensitive electrochemical bisphenol A sensor based on hierarchical Ce-metal-organic framework modified with cetyltrimethylammonium bromide. Sens. Actuators B 261, 425–433 (2018) 14. Hsine, Z., Bizid, S., Zahou, I., Ben Haj Hassen, L., Nasri, H., Mlika, R.: A highly sensitive impedimetric sensor based on iron (III) porphyrin and thermally reduced graphene oxide for detection of Bisphenol A. Synth. Met. 244, 27–35 (2018) 15. Abnous, K., Danesh, N.M., Ramezani, M., Alibolandi, M., Taghdisi, S.M.: A novel electrochemical sensor for bisphenol A detection based on nontarget-induced extension of aptamer length and formation of a physical barrier. Biosensors Bioelectron. 119, 204–208 (2018) 16. Wang, Z., Yan, R., Liao, S., Miao, Y., Zhang, B., Wang, F., Yang, H.: In situ reduced silver nanoparticles embedded molecularly imprinted reusable sensor for selective and sensitive SERS detection of Bisphenol A. Appl. Surf. Sci. 457, 323–331 (2018) 17. Barsan, M.M., Ghica, M.E., Brett, C.M.A.: Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: a review. Anal. Chim. Acta 881, 1–23 (2015) 18. Shan, D., Zhu, M., Han, E., Xue, H., Cosnier, S.: Calcium carbonate nanoparticles: a host matrix for the construction of highly sensitive amperometric phenol biosensor. Biosens. Bioelectron. 23, 648–654 (2007) 19. Pan, D., Gu, Y., Lan, H., Sun, Y., Gao, H.: Functional graphenegold nano-composite fabricated electrochemical biosensor for direct and rapid detection of bisphenol A. Anal. Chim. Acta 853, 297–302 (2015) 20. Arduini, F., Giorgio, F.D., Amine, A., Cataldo, F., Moscone, D., Palleschi, G.: Electroanalytical characterization of carbon black nanomaterial paste electrode: development of highly sensitive tyrosinase biosensor for catechol detection. Anal. Lett. 43, 1688– 1702 (2010) 21. Su, B., Shao, H., Li, N., Chen, X., Cai, Z., Chen, X.: A sensitive bisphenol A voltammetric sensor relying on AuPd nanoparticles/ graphene composites modified glassy carbon electrode. Talanta 166, 126–132 (2017) 22. Balgobind, K., Kanchi, S., Sharma, D., Bisetty, K., Sabela, M.I.: Hybrid of ZnONPs/MWCNTs for electrochemical detection of aspartame in food and beverage samples. J. Electroanal. Chem. 774, 51–57 (2016) 23. Santana, E.R., de Lima, C.A., Piovesan, J.V., Spinelli, A.: An original ferroferric oxide and gold nanoparticles-modified glassy carbon electrode for the determination of bisphenol A. Sens. Actuator B 240, 487–496 (2017) 24. Huang, Y., Tang, C., Liu, J., Cheng, J., Si, Z., Li, T., Yang, M.: Signal amplification strategy for electrochemical immunosensing

25.

26.

27.

28. 29.

30.

31.

32.

33.

34. 35.

36.

37.

38. 39.

40.

based on a molybdophosphate induced enhanced redox current on the surface of hydroxyapatite nanoparticles. Microchim. Acta 184, 855–861 (2017) Rodríguez-Delgado, M.M., Alemán-Nava, G.S., RodríguezDelgado, J.M., Dieck-Assad, G., Martínez-Chapa, S.O., Barceló, D., Parra, R.: Laccase-based biosensors for detection of phenolic compounds. TrAC Trends Anal. Chem. 74, 21–45 (2015) Kochana, J., Wapiennik, K., Kozak, J., Knihnicki, P., Pollap, A., Woźniakiewicz, M., Nowak, J., Kościelniak, P.: Tyrosinase-based biosensor for determination of bisphenol A in a flow-batch system. Talanta 144, 163–170 (2015) Portaccio, M., Di Tuoro, D., Arduini, F., Moscone, D., Cammarota, M., Mita, D., Lepore, M.: Laccase biosensor based on screen-printed electrode modified with thionine–carbon black nanocomposite, for Bisphenol A detection. Electrochim. Acta 109, 340–347 (2013) Merkoçi, A., Anik, U., Çevik, S., Çubukçu, M., Guix, M.: Bismuth film combined with screen-printed electrode as biosensing platform for phenol detection. Electroanalysis 22, 1429–1436 (2010) Shan, D., Zhang, J., Xue, H.-G., Zhang, Y.-C., Cosnier, S., Ding, S.-N.: Polycrystalline bismuth oxide films for development of amperometric biosensor for phenolic compounds. Biosens. Bioelectron. 24, 3671–3676 (2009) Siva Vijayakumar, T., Karthikeyeni, S., Vasanth, S., Ganesh, A., Bupesh, G., Ramesh, R., Manimegalai, M., Subramanian, P.: Synthesis of silver-doped zinc oxide nanocomposite by pulse mode ultrasonication and its characterization studies. J. Nanosci. 2013, 1–7 (2013) Fanjul-Bolado, P., Hernández-Santos, D., Lamas-Ardisana, P.J., Martín-Pernía, A., Costa-García, A.: Electrochemical characterization of screen-printed and conventional carbon paste electrodes. Electrochim. Acta 53, 3635–3642 (2008) Fanjul-Bolado, P., Queipo, P., Lamas-Ardisana, P.J., Costa-García, A.: Manufacture and evaluation of carbon nanotube modified screen-printed electrodes as electrochemical tools. Talanta 74, 427–433 (2007) Ntsendwana, B., Mamba, B., Sampath, S., Arotiba, O.: Electrochemical detection of bisphenol A using graphene-modified glassy carbon electrode. Int. J. Electrochem. Sci. 7, 3501–3512 (2012) Chen, A., Chatterjee, S.: Nanomaterials based electrochemical sensors for biomedical applications. Chem. Soc. Rev. 42, 5425– 5438 (2013) Pignotti, E., Farré, M., Barceló, D., Dinelli, E.: Occurrence and distribution of six selected endocrine disrupting compounds in surface-and groundwaters of the Romagna area (North Italy). Environ. Sci. Pollut. Res. Int. 24, 21153–21167 (2017) Schulz, P., Kelly, L.L., Winget, P., Li, H., Kim, H., Ndione, P.F., Sigdel, A.K., Berry, J.J., Graham, S., Brédas, J.-L., Kahn, A., Monti, O.L.A.: Tailoring electron-transfer barriers for zinc oxide/C60 fullerene interfaces. Adv. Funct. Mater. 24, 7381–7389 (2014) Zhao, X., Shen, H., Zhang, Y., Li, X., Zhao, X., Tai, M., Li, J., Li, J., Li, X., Lin, H.: Aluminum-doped zinc oxide as highly stable electron collection layer for perovskite solar cells. ACS Appl. Mater. Interfaces. 8, 7826–7833 (2016) Gurunathan, B., Ravi, A.: Biodiesel production from waste cooking oil using copper doped zinc oxide nanocomposite as heterogeneous catalyst. Bioresour. Technol. 188, 124–127 (2015) Yousefi, R., Jamali-Sheini, F., Cheraghizade, M., Khosravi-Gandomani, S., Sáaedi, A., Huang, N.M., Basirun, W.J., Azarang, M.: Enhanced visible-light photocatalytic activity of strontiumdoped zinc oxide nanoparticles. Mater. Sci. Semicond. Process. 32, 152–159 (2015) Oves, M., Arshad, M., Khan, M.S., Ahmed, A.S., Azam, A., Ismail, I.M.: Anti-microbial activity of cobalt doped zinc oxide

13

41.

42.

43. 44. 45.

46. 47.

Waste and Biomass Valorization nanoparticles: targeting water borne bacteria. J Saudi Chem Soc 19, 581–588 (2015) Lupan, O., Cretu, V., Postica, V., Ahmadi, M., Cuenya, B.R., Chow, L., Tiginyanu, I., Viana, B., Pauporté, T., Adelung, R.: Silver-doped zinc oxide single nanowire multifunctional nanosensor with a significant enhancement in response. Sens. Actuator B 223, 893–903 (2016) Kim, K., Lee, D.-H., Lee, S.Y., Jang, G.-E., Kim, J.-S.: Effect of Ag/Al co-doping method on optically p-type ZnO nanowires synthesized by hot-walled pulsed laser deposition. Nanoscale Res. Lett. 7, 273 (2012) Karami, H., Fakoori, E.: Sythesis and characterization of ZnO nanorods based on a new gel pyrolysis method. J Nanomater. 2011, 1–11 (2011) Reddy, S., Reddy, V., Reddy, K., Kumari, P.: Synthesis, structural, optical properties and antibacterial activity of co-doped (Ag, Co) ZnO nanoparticles. Res. J. Mater. Sci. 1, 11–20 (2013) Chithra, M.J., Sathya, M., Pushpanathan, K.: Effect of pH on crystal size and photoluminescence property of ZnO nanoparticles prepared by chemical precipitation method. Acta Metall. Sin. (Engl. Lett.). 28, 394–404 (2015) Hosseini, S., Sarsari, I.A., Kameli, P., Salamati, H.: Effect of Ag doping on structural, optical, and photocatalytic properties of ZnO nanoparticles. J. Alloys Compd. 640, 408–415 (2015) Waterhouse, G.I., Bowmaker, G.A., Metson, J.B.: The thermal decomposition of silver (I, III) oxide: a combined XRD, FT-IR

13

48.

49.

50.

51.

52.

and Raman spectroscopic study. Phys. Chem. Chem. Phys. 3, 3838–3845 (2001) Yıldırım, ÖA., Unalan, H.E., Durucan, C.: Highly efficient room temperature synthesis of silver-doped zinc oxide (ZnO:Ag) nanoparticles: structural, optical, and photocatalytic properties. J. Am. Ceram. Soc. 96, 766–773 (2013) Yin, H., Zhou, Y., Xu, J., Ai, S., Cui, L., Zhu, L.: Amperometric biosensor based on tyrosinase immobilized onto multiwalled carbon nanotubes-cobalt phthalocyanine-silk fibroin film and its application to determine bisphenol A. Anal. Chim. Acta 659, 144–150 (2010) Jaafar, A., Musa, A., Lee Yook, H., Nadarajah, K., Hamidah, S.: An optical biosensor based on immobilization of laccase and MBTH in stacked films for the detection of catechol. Sensors 7, 2238–2250 (2007) Xu, Y., Lei, W., Zhang, Y., Fan, H., Hao, Q., Gao, S.: Bamboo fungus-derived porous nitrogen-doped carbon for the fast, sensitive determination of bisphenol A. J. Electrochem. Soc. 164, B3043–B3048 (2017) Alkasir, R.S., Ganesana, M., Won, Y.-H., Stanciu, L., Andreescu, S.: Enzyme functionalized nanoparticles for electrochemical biosensors: a comparative study with applications for the detection of bisphenol A. Biosens. Bioelectron. 26, 43–49 (2010)