Correction to: Magnetic-core@dual-functional-shell nanocomposites with peroxidase mimicking properties for use in colorimetric and electrochemical sensing of hydrogen peroxide
- 237 Downloads
A self-sacrificing catalytic method is described for the preparation of magnetic core/dual-functional-shell nanocomposites composed of magnetite, gold and Prussian blue (type Fe3O4@Au-PB). Two reaction pathways are integrated. The first involves chemical dissolution of Fe3O4 (the self-sacrificing step) by acid to release ferrous ions which then reacts with hexacyanoferrate(IV) to generate PB in the proximity of the magntic nanoparticles (MNPs). The second involves the reduction of tetrachloroaurate by hydroxylamine to generate gold under the catalytic effect of the MNPs. At the end, the MNP@Au-PB nanocomposite is formed. This method exploits both the chemical reactivity and catalytic effect of the MNPs in a single step. The multi-function material was applied (a) in an optical assay for H2O2; (b) in an amperometric assay for H2O2; (c) in an enzymatic choline assay using immobilized choline oxidase. The limit of electrochemical detection of H2O2 (at a potential as low as 50 mV) is 1.1 μM which is comparable or better than most analogous methods. The sensors display superior performance compared to the use of conventional core@single-shell (MNP@Au-PB) nanomaterials.
KeywordsMagnetic nanoparticles Core@shell nanocomposites Self-sacrifice Peroxidase-mimetic Electrochemical catalysis Colorimetry Sensor H2O2 Glucose Choline oxidase
Magnetic nanocomposites, integrating unique magnetic properties/functions and desired functions from other components, have drawn increasing attractions and have been applied in various fields [1, 2, 3, 4, 5]. Plenty of preparation methods have been developed to meet various requirements. Due to abundant surface properties of magnetic materials, it is readily to introduce/modify other components onto the surface of magnetic core and form functional shell(s) [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]. The exposed shell makes itself sensitive and reactive to the surroundings, thus realizes applications such as sensing [6, 7, 10, 11, 16], adsorption [12, 13], catalysis [14, 15], therapy , and so on. On the other hand, the shell cooperates with the magnetic core, even generates synergistic effect [9, 12, 13]. Currently, the construction of single (functional) layer of shell is well established [6, 7, 8, 9, 10]. On the other hand, multiple layers of shells have to be elaborated for multiple extraneous functions [22, 23, 24, 25]. The introduction of multiple shells, however, makes the preparation complicated and time consuming. It also brings about other deficiencies such as the unstable linking between layers and the spatial separation of magnetic core from the outer shell. Therefore, methods that can introduce layer of shell with multiple components/functions should flourish the branches of magnetic nanocomposites and lead to new applications.
Owning to the abundant properties of ferrous elements and their compounds, plenty of strategies have been developed for the modification of outer layers (shells) to magnetic nanomaterials, mainly including physical and chemical ways [1, 3, 4, 5]. Recently, a sacrificing method was also explored with characteristics of supplying reactants of shell from the sacrificing of magnetic nanomaterials themselves through chemical/electrochemical ways [7, 9, 10]. Briefly, ferrous components in magnetic nanomaterials release ferrous ions in acidic solution, followed by the formation of new shell via the reaction between the released ferrous ions with other co-existing reactants. For example, recently our group developed a new electrochemical method to converse magnetic nanoparticles (MNPs) to Prussian blue (PB) . By applying a high-potential on the gold electrode, water can be split into gaseous oxygen and hydrogen ions, which reacted with MNPs (Fe3O4) to release ferrous ions. Then in a low-potential process, ferrous ions reacted with co-existing Fe(CN)64− ions to form PB. The sacrificing methods presented unique proximity effect, namely, confining the reactions occurred on the surface of magnetic nanomaterials. Moreover, the formed shell shares same ferrous components with magnetic nanomaterials, gifting high stability of the core@shell structure. However, current researches exploited the sacrificing method for the generation of sole-component shell, leaving the methods for the preparation of multiple-component shell rarely exploited [7, 9, 10]. Furthermore, the shell generated from the sacrificing method is PB analogues. As well known, PB analogues are with high catalysis ability and even the peroxidase-like activity, however, the lack of chemical groups on the surface inhibits further functionalization , so complicated procedures are required to introduce other species onto PB surface [27, 28, 29]. This significantly limits potential of applications. Therefore, by integrating the unique advantages of sacrificing method with other properties/functions of magnetic nanomaterials, it remains vast space and impetus to exploit new method to extend the modification/functionalization of magnetic nanomaterials to fulfill diversified requirements of applications.
Materials and apparatus
Fe3O4 MNPs were purchased from Aladdin Bio-Chem Technology Co., LTD (Shanghai, China, www.aladdin-e.com). Hydrogen peroxide (H2O2, 30%), sulfuric acid (H2SO4, assay NLT 98.0%), hydrochloric acid (HCl, assay NLT 36.0%), potassium ferricyanide (K3Fe(CN)6), potassium ferrocyanide (K4Fe(CN)6), ferrous sulfate (FeSO4), hydroxylamine hydrochloride (NH2OH·HCl), chloroauric acid (HAuCl4) and sodium citrate (Na3C6H5O7) were purchased from Shanghai Chemical Reagent Co. (Shanghai, China, www.reagent.com.cn). ChOx and choline chloride were purchased from Sigma-Aldrich (St. Louis, MO, USA, www.sigmaaldrich.com). N-(Sulfopropyl)-3,3′,5,5-tetramethylbenzidine, sodium salt (TMB-PS), L-Cysteine, L-Aspartic acid, L-Glycine and L-Proline were purchased from Sangon Biotech. (Shanghai, China, www.sangon.com). Phosphate buffer (0.1 M, pH = 6.0, 0.1 M K2HPO4/KH2PO4 + 0.1 M K2SO4) was adopted for sensing. All chemicals were of analytical grade or better quality. Milli-Q (Millipore, ≥18 MΩ cm) ultra-pure water was used throughout. All experiments were conducted at room temperature (25 °C).
All electrochemical experiments were conducted on a CHI660E electrochemical workstation (CH Instrument Co., China, www.chinstr.com) with a conventional three-electrode electrolytic cell. The Au electrode with 2.0-mm diameter served as the working electrode, a KCl-saturated calomel electrode (SCE) as the reference electrode, and a carbon rod as the counter electrode. All potentials reported here are cited versus SCE. The FT-IR spectrophotometry, SEM images, TEM images and UV-vis spectrophotometry were collected in a JASCO-4100 Fourier transform infrared spectrometer (Nicolet Instrument Co., Madison, www.thermofisher.com), SU-8010 (Hitachi, Japan, www.hitachi.com) scanning electronic microscope, JEOL JEM-1200EX transmission electron microscope (Hitachi, Japan, www.hitachi.com) and Agilent 8453 UV-vis spectrophotometer (Agilent, USA, www.agilent.com), respectively.
Preparation of MNP@Au-PB, MNP@PB and PB
For the typical preparation of MNP@Au-PB, 4 μL of HCl (1 M), 50 μL of HAuCl4 (1 mM), 50 μL of NH2OH·HCl (0.1 M) and 50 μL of K4Fe(CN)6 (10 mM) were added to 150 μL of MNPs suspension (0.5 mg mL−1) in sequence. After 10 min, the yielded black-blue suspension was washed with dilute hydrochloric acid (pH = 6.0) for three times assisted by magnetic separation and was finally dispersed in 0.1 M phosphate buffer (pH = 6.0).
The preparation of MNP@PB was similar to that for the MNP@Au-PB except the addition of NaAuCl4 and NH2OH·HCl. For the preparation of PB thin film, a typical electrochemical deposition method was adopted according to literature .
Electrochemical detection of H2O2
Firstly, 2 μL of MNP@Au-PB suspension was dropped on the surface of Au electrode. By placing a magnet under the electrode, the MNP@Au-PB composites were anchored on the electrode for further characterization and detection. The characterization of the presence of PB and Au was conducted using CV in a mixture solution containing 0.1 M H2SO4 and 0.1 M K2SO4 and a solution of 0.05 M H2SO4, respectively. Potentiostatic measurements at −0.05 V were adopted for the electrochemical detection of H2O2 in 0.1 M phosphate buffer (pH 6.0). Briefly, H2O2 stock solutions of different concentrations were successively added to the stirred phosphate buffer, and the differences between currents before and after each addition of H2O2 were adopted as response signals.
Optical detection of H2O2
Firstly, 30 μL of TMB (10 mM) and 30 μL of H2O2 of different concentrations were added into 30 μL of MNP@Au-PB suspensions and kept for 10 min at room temperature for reaction, followed by the addition of 10 μL of 6 M H2SO4 to stop the reaction. Second, the suspension was magnetically separated and 60 μL of the supernatant was used for quantification in UV-vis measurements at 460 nm. For the specificity evaluation, H2O2 was replaced by ascorbic acid, L-cysteine, L-aspartic acid, L-proline, L-glycine and urea, respectively.
Optical detection of glucose in wine samples
The white grape wine, J.J.Muller wine (Jerry Moselle, Germany), was bought from a local supermarket (Hangzhou, China). For glucose assay, the calibration plot was obtained first. The detection procedures are similar to that for H2O2 except that the addition of 30 μL of H2O2 was replaced by the addition of the mixture of 15 μL of 0.6 mg·mL−1 glucose oxidase and 15 μL of glucose of different concentrations (n = 3). For the detection of glucose in wine samples, the procedures were the same to the assay of glucose except replacing the addition of 15 μL glucose solutions by 15 μL of wine samples (n = 3).
Immobilization of ChOx
MNP@Au-PB suspensions were diluted 10-fold with 0.1 M phosphate buffer (pH = 6.0, 50 μL), which were then mixed with 50 μL of ChOx (1 mg mL−1) and kept at 4 °C for 1 h. Afterwards, the mixtures were magnetically separated and washed with 0.1 M phosphate buffer (pH = 6.0, 50 μL) for three times, and the supernatants were collected for the quantification using UV-vis spectroscopy at 280 nm. The mixtures of 50 μL of 0.1 M phosphate buffer (pH = 6.0) and 50 μL of ChOx (1 mg mL−1) were adopted as the control and treated similarly, followed by the quantification of ChOx in supernatants using the same method. The immobilization rate was calculated as the rate of the absorbance of ChOx in the MNP@Au-PB case to that of the control. For comparison, the immobilization rates of ChOx in MNPs, MNP@PB and MNP@Au cases were also obtained using the same method.
Results and discussion
Characterization of MNP@Au-PB
We inspected the preparation of the MNP@Au-PB nanocomposites through digital imaging, as shown in Table S1 (please see detailed description in ESM). Because the preparation involved a series of precursors, we thus mixed some precursors to investigate the mechanism. The mixture of NaAuCl4 and NH2OH (sample 2) presented colorless, because NH2OH was not able to reduce NaAuCl4 solely . In contrast, the presence of MNPs led to the production of MNP@Au (sample 3) . The reason was that the reduction of NaAuCl4 by NH2OH was catalyzed by the nucleating effect from MNPs . The mixing of MNPs, HCl and K4Fe(CN)6 (sample 4) led to rapid appearance of plenty of blue PB products, as illustrated as the Path 1 in Scheme 1. The mixture of NaAuCl4, NH2OH, K4Fe(CN)6 and HCl (sample 6) slowly turned to light blue due to the formation of PB-like KFex[Au(CN)2]y compounds . Finally, the mixture of MNPs, NaAuCl4, NH2OH, K4Fe(CN)6 and HCl (sample 7) rapidly showed blue-light-green color, indicating the co-existing of PB and PB-like KFex[Au(CN)2]y compounds. The PB-like KFex[Au(CN)2]y were generated in solution while Au-PB was on the surface of MNPs (proximity effect). Hence, one can readily purify the MNP@Au-PB nanocomposites by magnetic separation (sample 9). In a magnetic field, MNP@Au-PB nanocomposites were rapidly collected leaving the supernatant totally clear, indicating the MNPs core and the magnetic property were well retained even after the self-sacrificing. It should guarantee the magnetic operability for applications.
Electrochemical detection of H2O2
Based on the high catalysis ability of MNP@Au-PB, we further used the modified electrodes for the electrochemical detection of H2O2 by potentiostatic method at −0.05 V in 0.1 M phosphate buffer (pH 6.0). As shown in Fig. 3b, the current increases along with the addition of H2O2 and stabilizes within 5 s. The sensor exhibits a sensitivity of 0.738 μA cm-2 μM-1, a linear detection range (LDR) from 4.0 μM to 22.12 mM and a limit of detection (LOD) of 1.1 μM (S/N = 3). Compared with some H2O2 sensors reported (Table S2), performance of the sensor is comparable to or better than most of analogues. The high performance should be the contribution of strong catalysis ability of PB and the synergetic effect from Au.
Colorimetric detection of H2O2
Reversibility and selectivity
During the catalysis process, PB played a role mimic to HRP. Briefly, PB catalyzed the reduction of H2O2 and turned themselves to the oxidative form. While the co-existing TMB turned the oxidative form of PB to reductive one that was capable to catalyze H2O2 again. Therefore, the catalysis ability of MNP@Au-PB was reversible. Moreover, the reusability of the nanocomposites was examined. Briefly, after one detection, the nanocomposites were collected using magnet and then used for another round of detection. After five rounds of detections, the responses (n = 3) were still (95 ± 1) % of the initials. This should prove the nanocomposites are capable for repeated detections.
To investigate the selectivity of MNP@Au-PB-based sensor, some interferences, including ascorbic acid, urea, L-Cysteine, L-Aspartic acid, L-Glycine and L-Proline, were chosen for comparison. The results are shown in Fig. S2. Briefly, the intensity of the absorption peak at 460 nm of 500 μM H2O2 was compared with the those of ultrapure water (control experiment), 1 mM ascorbic acid, 1 mM urea, 1 mM L-Cysteine, 1 mM L-Aspartic acid, 1 mM L-Glycine and 1 mM L-Proline. All above interferences exhibited responses lower than 6.0% of that of H2O2, indicating good selectivity. Because a key procedure of the colorimetric detection is the oxidation of TMB to its oxide, general interferences lack of oxidation ability have minor influence on the detection.
Detection of glucose in wine samples
The feasibility of the sensor for real application was examined by applying for the detection of glucose in wine. Glucose was catalyzed by glucose oxidase to generate H2O2, which then was detected using the sensor. The value of adsorption peak at 460 nm were collected for quantification. Firstly, we obtained the calibration plot for the detection of glucose in 0.1 M phosphate buffer (pH 6.0). As shown in Fig. S3, the linear detection range was from 10.0 μM to 500.0 μM. Then the white grape wine, whose glucose content is 28.58 mM as determined by a standard high performance liquid chromatography method , was diluted for the real sample detection. The concentration detected by the sensor was 29.89 ± 2.9 mM. The relative standard deviation is 104.6%. Above results should prove that the sensor is feasible for real sample detection.
Immobilization of ChOx
For a state-of-concept application, we further examined and compared the biosensing abilities of MNPs, MNP@PB and MNP@Au-PB to choline using the colorimetric method. After the modification of ChOx on above three matrices, TMB and choline were added to trigger the catalysis cascade. Namely, ChOx catalyzed choline to generate H2O2, which was catalyzed by peroxidase-like PB to make TMB turn to its oxide (blue in color). Finally, the supernatants after the magnetic separation were collected for UV-vis spectroscopy measurements at 650 nm, as shown in Fig. 5b. Clearly, the efficiency of the enzyme catalysis cascade should be determined by the amount of ChOx and the catalysis ability of the peroxidase-like analogues. As the control, the ChOx solution itself can not finish the catalysis cascade in the absence of PB, thus gave no absorption peak. Similarly, although the MNP/ChOx have good ChOx immobilized and MNPs themselves play a little role as peroxidase, the absence of PB led to very small absorption peak. In contrast, although MNP@PB/ChOx had less ChOx than MNP@ChOx, the strong catalysis ability of PB shell gifted a complete enzyme catalysis cascade, giving a strong peak. Imaginably, the MNP@Au-PB contributed the strongest adsorption peak, which is 1.62 fold of that of MNP@PB, due to the increased ChOx immobilization. Again, this result highlights the superiority of the dual-function shell and promising prospect of MNP@Au-PB for biosensing applications.
In summary, a self-sacrificing-catalyzing method has been developed to prepare MNP@Au-PB core@dual-functional-shell nanocomposites. The nanocomposites exhibit inherent magnetic property from the core for magnetic operations, and integrate the peroxidase-like catalysis ability of PB and enhanced conductivity from Au, exhibiting sensing performances comparable with or better than most of analogues. Furthermore, the incorporation of Au also gifts the nanocomposites with the superiority to immobilize ChOx for biosensing. The MNP@Au-PB should be promising in catalysis and sensing/biosensing fields, and the self-sacrificing-catalyzing method might open new avenue for preparation of multi-functional nanocomposites. However, because PB is inherently susceptive to alkali, so alkaline solutions should be avoided. Moreover, appropriate block of the surface of the nanocomposites should be conducted to avoid interferences prior to the application in complex samples. Therefore, further efforts are needed to make the nanocomposites more robust.
This work was supported by National Natural Science Foundation of China (Grants 21505120, 21775137), and the State Key Laboratory of Chemo/Biosensing and Chemometrics.
Compliance with ethical standards
The author(s) declare that they have no competing interests.
- 7.Zhang Q, Li L, Qiao Z, Lei C, Fu Y, Xie Q, Yao S, Li Y, Ying Y (2017) Electrochemical conversion of Fe3O4 magnetic nanoparticles to electroactive Prussian blue analogues for self-sacrificial label biosensing of avian influenza virus H5N1. Anal Chem 89(22):12145–12151. https://doi.org/10.1021/acs.analchem.7b02784 CrossRefPubMedGoogle Scholar
- 8.Bordage Al, Moulin R, Fonda E, Fornasieri G, RiviÃre E, Bleuzen A (2018) Evidence of the Core–Shell Structure of (Photo)magnetic CoFe Prussian Blue Analogue Nanoparticles and Peculiar Behavior of the Surface Species Journal of the American Chemical Society 140 (32):10332–10343. doi: https://doi.org/10.1021/jacs.8b06147 CrossRefGoogle Scholar
- 11.Ma Y, Xu G, Wei F, Cen Y, Xu X, Shi M, Cheng X, Chai Y, Sohail M, Hu Q (2018) One-pot synthesis of a magnetic, Ratiometric fluorescent Nanoprobe by encapsulating Fe3O4 magnetic nanoparticles and dual-emissive rhodamine B modified carbon dots in metal–organic framework for enhanced HClO sensing. ACS Appl Mater Interfaces 10 (24):20801–20805. doi: https://doi.org/10.1021/acsami.8b05643 CrossRefGoogle Scholar
- 13.Chen Y, Xiong Z, Peng L, Gan Y, Zhao Y, Shen J, Qian J, Zhang L, Zhang W (2015) Facile preparation of Core–Shell magnetic metal–organic framework nanoparticles for the selective capture of Phosphopeptides. ACS Appl Mater Interfaces 7 (30):16338–16347. doi: https://doi.org/10.1021/acsami.5b03335 CrossRefGoogle Scholar
- 15.Chen L, Li H, Zhan W, Cao Z, Chen J, Jiang Q, Jiang Y, Xie Z, Kuang Q, Zheng L (2016) Controlled encapsulation of flower-like Rh–Ni alloys with MOFs via tunable template Dealloying for enhanced selective hydrogenation of alkyne. ACS Appl Mater Interfaces 8 (45):31059–31066. doi: https://doi.org/10.1021/acsami.6b11567 CrossRefGoogle Scholar
- 18.Bagheri H, Afkhami A, Sabertehrani M, Khoshsafar H (2012) Preparation and characterization of magnetic nanocomposite of Schiff base/silica/magnetite as a preconcentration phase for the trace determination of heavy metal ions in water, food and biological samples using atomic absorption spectrometry. Talanta 97:87–95. https://doi.org/10.1016/j.talanta.2012.03.066 CrossRefGoogle Scholar
- 20.Bagheri H, Yamini Y, Safari M, Asiabi H, Karimi M, Heydari A (2016) Simultaneous determination of pyrethroids residues in fruit and vegetable samples via supercritical fluid extraction coupled with magnetic solid phase extraction followed by HPLC-UV. J Supercrit Fluids 107:571–580. https://doi.org/10.1007/s12161-015-0264-x CrossRefGoogle Scholar
- 21.Bagheri H, Pajooheshpour N, Afkhami A, Khoshsafar H (2016) Fabrication of a novel electrochemical sensing platform based on a core–shell nano-structured/molecularly imprinted polymer for sensitive and selective determination of ephedrine. RSC Adv 6(56):51135–51145. https://doi.org/10.1039/C6RA09488K CrossRefGoogle Scholar
- 22.Yin PT, Pongkulapa T, Cho H-Y, Han J, Pasquale NJ, Rabie H, Kim J-H, Choi J-W, Lee K-B (2018) Overcoming Chemoresistance in Cancer via combined MicroRNA therapeutics with anticancer drugs using multifunctional magnetic Core–Shell nanoparticles. ACS Appl Mater Interfaces 10 (32):26954–26963. doi: https://doi.org/10.1021/acsami.8b09086 CrossRefGoogle Scholar
- 24.Moorthy MS, Subramanian B, Panchanathan M, Mondal S, Kim H, Lee KD, Oh J (2017) Fucoidan-coated core-shell magnetic mesoporous silica nanoparticles for chemotherapy and magnetic hyperthermia-based thermal therapy applications. New J Chem 41(24):15334–15346. https://doi.org/10.1039/c7nj03211k CrossRefGoogle Scholar
- 26.Sun L, Li Q, Hou M, Gao Y, Yang R, Zhang L, Xu Z, Kang Y, Xue P (2018) Light-activatable Chlorin e6 (Ce6)-imbedded erythrocyte membrane vesicles camouflaged Prussian blue nanoparticles for synergistic photothermal and photodynamic therapies of cancer. Biomater Sci 6(11):2881–2895. https://doi.org/10.1039/C8BM00812D CrossRefPubMedGoogle Scholar
- 27.Wang T, Fu Y, Chai L, Chao L, Bu L, Meng Y, Chen C, Ma M, Xie Q, Yao S (2014) Filling carbon nanotubes with Prussian blue nanoparticles of high peroxidase- like catalytic activity for colorimetric Chemoand biosensing. Chem Eur J 20(9):2623–2630. https://doi.org/10.1002/chem.201304035 CrossRefPubMedGoogle Scholar
- 28.Wang T, Fu Y, Bu L, Qin C, Meng Y, Chen C, Ma M, Xie Q, Yao S (2012) Facile synthesis of Prussian blue-filled multiwalled carbon nanotubes nanocomposites: exploring filling/electrochemistry/mass-transfer in Nanochannels and cooperative biosensing mode. J Phys Chem C 116(39):20908–20917. https://doi.org/10.1021/jp306492a CrossRefGoogle Scholar
- 29.Farka Z, Čunderlová V, Horáčková V, Pastucha M, Mikušová Z, Hlaváček A, Skládal P (2018) Prussian blue nanoparticles as a catalytic label in a Sandwich Nanozyme-linked immunosorbent assay. Anal Chem 90 (3):2348–2354. doi: https://doi.org/10.1021/acs.analchem.7b04883
- 34.Deng C, Li M, Xie Q, Liu M, Tan Y, Xu X, Yao S (2006) New glucose biosensor based on a poly(o-phenylendiamine)/glucose oxidase-glutaraldehyde/Prussian blue/au electrode with QCM monitoring of various electrode-surface modifications. Anal Chim Acta 557(1):85–94. https://doi.org/10.1016/j.aca.2005.10.009CrossRefGoogle Scholar
- 37.C. Carvalho CL, B. Silva AT, Luz RAS, Castro GMB, da Luz Lima C, Mastelaro VR, da Silva RR, Oliveira ON, CantanhÃªde W (2018) Development of Co3[Co(CN)6]2/Fe3O4 Bifunctional Nanocomposite for Clinical Sensor Applications. ACS Appl Nano Mater: https://doi.org/10.1021/acsanm.1028b01106. doi: https://doi.org/10.1021/acsanm.8b01106