Materials Science and Engineering C 45 (2014) 438–445
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Facile synthesis of nano silver ferrite (AgFeO2) modified with chitosan applied for biothiol separation Hani Nasser Abdelhamid a,b, Hui-Fen Wu a,c,d,e,f,⁎ a
Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan Department of Chemistry, Assuit University, Assuit 71515, Egypt School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung 800, Taiwan d Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan e Doctoral Degree Program of Marine Biotechnology, National Sun Yat-Sen University and Academia Sinica, Kaohsiung 804,Taiwan f Institute of Medical Science and Technology, National Sun Yat-Sen University b c
a r t i c l e
i n f o
Article history: Received 2 February 2014 Received in revised form 29 July 2014 Accepted 31 August 2014 Available online 6 September 2014 Keywords: AgFeO2 Chitosan Matrix assisted laser desorption/ionization Thiol separation
a b s t r a c t Silver iron oxide nanoparticles (AgFeO2 NPs) with narrow size distribution have been synthesized, characterized and was applied for biothiols separation. AgFeO2 and AgFeO2 modified chitosan (AgFeO2@CTS NPs) were synthesized using a hydrothermal method and then characterized by electron microscopy (transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX)), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different biological thiols (dithiothreitol, glutathione, thiabendazole, and sulfamethizole) were investigated and characterized using matrix assisted laser desorption/ionization mass spectrometry (MALDI–MS) and surface assisted laser desorption/ionization mass spectrometry (SALDI– MS). The new material displays dual functionality; 1) for separation and 2) can be served as the matrices for SALDI–MS. Data showed a clear background in the case of nanomaterials compared to conventional matrices (mefenamic acid and 2,5-dihydroxybenzoic acid (DHB) for MALDI–MS). © 2014 Elsevier B.V. All rights reserved.
1. Introduction Because of their numerous applications for catalysis, batteries, and transparent conductors; delafossite-type oxides (ABO2) have been investigated widely in efforts to design advanced materials with enhanced properties. Delafossites are named in honor of French mineralogist Gabriel Delafosse [1]. Delafossites are ternary oxides with the general formula of ABO2, which consists of alternating layers of A cations and edge-sharing BO2 octahedral oriented perpendicular to caxis. The A cations possess two-fold linear coordination with the oxygen atoms, which is often described as a “dumbbell” O–A–O arrangement. The delafossite structure can exist as two polytypes; hexagonal and rhombohedral [2,3]. Among various delafossites, AgFeO2 is attractive for scientific research and applications interests [4–6]. One of the important and attractive features of AgFeO2 is their super-magnetic properties [7]. Generally, colloidal iron oxide particles have been used intensively for biomedicine [8–14] and biotechnology [15,16]. Moreover, functionalization of
⁎ Corresponding author at: Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan. Tel.: +886 7 5252000 3955; fax: +886 7 525 3908. E-mail address: [email protected] (H.-F. Wu).
http://dx.doi.org/10.1016/j.msec.2014.08.071 0928-4931/© 2014 Elsevier B.V. All rights reserved.
Fe3O4 with Au and Ag has demonstrated vast potential in catalysis and biotechnological applications such as protein separation [17], cancer diagnosis [18], biosensors and bioactuators [19]. The prime reason is due to multifunctionality of these new composites. In recent years, the detection of thiols attracted numerous interests of the researcher because of the important roles that they play in biological systems [20–27]. The previous studies revealed that abnormal levels of thiols were related to a variety of diseases, such as liver damage, skin lesions, Alzheimer's and Parkinson's diseases, cardiovascular diseases, diabetes and HIV disease [28]. Thus, detection or separation for these compounds is essential in medicine. So far, the analytical tools that were used to detect thiols are capillary electrophoresis [29], highperformance liquid chromatography [30], mass spectrometry [31–33], and fluorescence [23,34–46]. These techniques show high sensitivity and selectivity. However, in most cases, these approaches require expensive and sophisticated instrumentation; long analysis times, require expensive chemical modification and has low applicability. Thus, they have their limited practical applications. Herein, we report the synthesis of silver ferrite composite (AgFeO2) by the hydrothermal method. AgFeO2 modified chitosan and their application for biothiol separation/detection using matrix (surface) assisted laser desorption/ionization mass spectrometry (M(S)ALDI–MS) are investigated. The new material does not only provide separation facilities,
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but it can serve also as a surface for surface assisted laser desorption/ionization mass spectrometry (SALDI–MS).
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3. Results and discussion 3.1. Characterization of AgFeO2@CTS
2. Materials and methods Fe2(SO4)3, AgNO3, mefenamic acid (MA), 2,5-dihydroxybenzoic acid (DHB), chitosan (low molecular weight; 50,000–190,000 g mol− 1, 75–85% deacetylation), dithiothreitol, glutathione, thiabendazole, and sulfathiazole, were purchased from Sigma-Aldrich (USA). All the chemicals used in this study are of analytical reagent grade. 2.1. Instrumentation X-ray diffraction (XRD) pattern of the composite was recorded using a Bruker AXS D8 Advance, German (operating at 40 KV and 45 mA) with Cu Ka (1.5406 Å) radiation. Scanning electron microscope (SEM, JOEL 6700 F, Japan) with energy dispersive spectrometer (EDS) working at 30 kV was used to examine the surface morphology and elemental composition of the powders. The MALDI–MS analysis was performed by employing positive ion modes on a time-of-flight (TOF) mass spectrometer (Microflex, Bruker Daltonics, Bremen, Germany) with a 1.25 m flight tube. Desorption/ionization was obtained by using a 337 nm nitrogen laser with a 3 ns pulse width. The accelerating potential in the source was maintained at + 20 kV. All MALDI–MS spectra were obtained at an average of 200 laser shots. The laser power was adjusted to slightly above the ionization threshold to obtain a good resolution and signal-to-noise ratios. The dried droplet method was used for all experiments. 2,5-dihydroxy benzoic and mefenamic acids were used as matrices for thiol study [47]. To check the reproducibility, all experimental results were repeated at least three times. 2.2. Experimental 2.2.1. Preparation of AgFeO2 The method of AgFeO2 preparation is based on co-precipitation/ hydrothermal of Fe2(SO4)3 and AgNO3 in the presence of glycerol. Schematic representations of all the steps were represented in Fig. 1A. Typically, 1 mmol of Fe2(SO4)3 and 1 mmol AgNO3 were mixed together in 30 mL deionized water with 3 mL glycerol. Then, 10% of NaOH was added with stirring for about 1 h. The precipitate was transferred to a Teflon autoclave and was heated at 180 °C for 24 h. The precipitate was cooled and separated using a magnet and washed several times by deionized water.
Silver ferrite (AgFeO 2 ) was prepared by co-precipitation/ hydrothermal method. Silver ferrite (AgFeO2) possesses the α-type delafossite structure with rhombohedral type stacking (3R-polytype), consisting of close packed double layers of FeO6 octahedra with monovalent Ag ions positioned between the layers. It is of considerable interest from a magnetic viewpoint because of the intrinsic frustration of bond antiferromagnetism in triangular lattices. AgFeO2 was prepared via modifications of the previous reports describing co-precipitation syntheses, using silver nitrate, iron (III) sulfate, and sodium hydroxide as reagents (Fig. 1A) [5,48,49]. The present methodology is simple and gives good quality of AgFeO2 according to the analytical tools that were used to characterize the synthesized material. The prepared materials were characterized by TEM, SEM, EDX, XRD, and FTIR. TEM images show silver ferrite consisting of aspherical nanoparticles (Fig. 2A). It shows almost no change after modification with chitosan (Fig. 2B). However, the SEM image (Fig. 2C) of AgFeO2 shows agglomeration of particles that may take place during the sample preparation. EDX analysis shows the ratio of Ag:Fe is 1:1 (Fig. 2D). The XRD pattern (Fig. 2E) of the powder clearly shows the formation of the nano silver ferrites. Stimulated XRD (green-dotted lines) reveals that the same phase of AgFeO2 has been prepared successfully. The sizes of the silver ferrite particles were calculated using the Scherer's formula and were found between 1 and 40 nm that agree with TEM image (Fig. 2A). Recently, the syntheses of silver delafossite oxides have been excellently reviewed by Poeppelmeier et al. [3]. There are many proposed methods such as coprecipitation of α-AgFeO2 using FeOOH and Ag2O in a boiling NaOH solution at 100 °C. The new approach shows good applicability to prepare AgFeO2 nanoparticles. Modification of AgFeO2 by chitosan was confirmed by FTIR (Fig. 2F). The spectrum (Fig. 2F) of pure chitosan shows an intensive peak at 1588 cm−1, corresponding to amide II band, while the peak at 1074, 3450 cm−1 could be due to the\C\O\C\vibration and O\H stretching, respectively [50]. The wideness of these peaks was decreased after capping the nanoparticles. For instance, peaks at 1074 and 3450 cm−1 become sharper due to the coordination with magnetic nanoparticles. We can conclude that AgFeO2 is well prepared using hydrothermals. However, other methods were proposed to prepare delafossites such as ion exchange [51–55]; the present approach is more simple and cheap. The major advantages of AgFeO2 nanoparticles possess high ferromagnetism, so it is an attractive subject [55–58]. 3.2. Application for thiol separation
2.2.2. Preparation of AgFeO2 modified chitosan (AgFeO2@CTS) About 0.5 g of the dried AgFeO2 was stirred in 25 mL chitosan (0.1 g in 1% acetic acid). The solution was kept for stirring for 5 h. The prepared material was separated and washed using deionized water with the help of external magnet. 2.2.3. Separation of thiols In order to investigate the separation applicability of the prepared materials (AgFeO2, and AgFeO2@CTS), different thiols (dithiothreitol, glutathione, thiabendazole, and sulfamethizole) were tested. Typically, 10 μL of the prepared materials (AgFeO2 and AgFeO2@CTS) were added to 1 mL of each thiol solution separately (1 × 10− 3 M). After 10 min, the magnetic nanoparticles were separated using external magnets and washed two times to removed unattached molecules. The separated materials were diluted with 10 μL deionized water. Then it was divided to three portions; first one (2 μL) was spotted directly to MALDI plate. Second and third portions (2 μL) were mixed with DHB and MA (2 μL, 50 mM), separately and then spotted in a MALDI plate. The spots were dried before the measurements. The overall procedures were represented in Fig. 1B.
The new materials are applied to separate biological thiols (biothiols) such as (dithiothreitol, glutathione, thiabendazole, and sulfamethizole). Separation of biothiols is paramount for medicine and biomedicine applications [20–27]. It can be used as biomarkers for a variety of diseases, such as liver damage, skin lesions, Alzheimer's, Parkinson's diseases, cardiovascular diseases, diabetes and HIV disease [28]. Thus, we investigate the applications of these materials in biothiol separation. The separation approach is based on the specific interactions between biothiols and silver via robust Ag\S bonds [59] and the noncovalent interaction with CTS on AgFeO2@CTS. Various biothiols such as dithiothreitol (154 gmol−1), glutathione (307 gmol−1), thiabendazole (201 gmol−1), and sulfamethizole (255 gmol− 1) were tested. Simply, into 1 mL of biothiol biomolecules, we added a small amount (10 μL) of magnetic nanoparticles (AgFeO2 & AgFeO2@CTS), then it was separated by external magnets (Fig. 1B). The separated materials are diluted and then spotted on the MALDI plates for detection using two different matrices (MA and DHB), and we also checked the applicability of using these nanomaterials to serve as matrices for SALDI–MS. Note that the conventional matrices (MA and DHB) are also assistant in elution that helps biothiols to detach from the
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A
NaOH, 10% Fe2(SO4)3 Glycerol AgNO3 Stirring
Chitosan
AgFeO2
AgFeO2
B
AgFeO2@Chitosan
Thiols
Separation using external Magnets
Fig. 1. (A) Schematic representation for the preparation of AgFeO2 and AgFeO2@CTS. (B) Schematic representation for thiol separation using magnetic nanoparticles.
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B
A
C
D
F 80
E
AgFeO2@Chitosan
Transmission%
70
60
50
40
30 4000
Chitosan 3500
3000
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2000
Wavenumber. cm
1500
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Fig. 2. Characterization of the prepared magnetic nanoparticles using TEM for (A) AgFeO2 and (B) AgFeO2@CTS, (C) SEM, (D) EDX, (E) XRD and (F) FTIR.
nanoparticle surfaces. MALDI and SALDI–MS of biothiols (dithiothreitol (Fig. 3), glutathione (Fig. 4), thiabendazole (Fig. 5), sulfamethizole (Fig. S1) and their mixture (Fig. S2) were reported for AgFeO2 and AgFeO2@CTS. Data show variation among the different molecules due to the selectivity and because they have different ionizability. Dithiothreitol (M.Wt 154 Da) shows high detectability in the case of bare AgFeO2 and for DHB and MA. The molecules cannot be detected in the case of AgFeO2@CTS as it formed hydrogen bonds with CTS and prevented separation/detection during MALDI measurement. In
contrast, AgFeO2 and AgFeO2@CTS display high ionization of GSH. All the other molecules can be detected for AgFeO2 and AgFeO2@CTS, except that thiabendazole was not detected for DHB. This is due to the matrix related peaks that submerge the analyte peaks. All results are summarized in Table S1. It is interesting to check the separation of the mixture of these compounds. Only bare AgFeO2 can separate DTT and thiabendazole, while the rest cannot be detected from the mixture. The prime reason may be due to the competition between these molecules that makes binding to the nanomaterials difficult.
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A
a
1. [DTT+H]+ 1
b
1
c
1
B a
1. [DTT+H]+ 1
b
c
1
Fig. 3. Separation of ditheitol using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
The present methods are fast, have good sensitivity and selectivity for biothiols, and do not require expensive chemical modification. They eliminate the needs for chemical modifications, and sophisticated instrumentations are convenient and low cost. So far, the analytical tools that were used to detect biothiols such as chromatography [29, 30], mass spectrometry [31–33], and fluorescence [23,34–46] are expensive, sophisticated, need modification of long analysis times, require expensive chemical modification and have low applicability. To our best knowledge, these new materials offer great potentials for
thiols and other molecule separation. It can also serve for analyte ionization due to its large surface area [60–64]. Recently, AgFeO2 was proposed for Surface Enhancement Raman Spectroscopy (SERS) [65]. 4. Conclusion A bimetallic delafossite structured material (AgFeO2) has been prepared and modified with chitosan, ‘AgFeO2@CTS’. It has been shown to be an effective nanoparticle for biothiol separation and surface
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A a 1. [GSH+H]+ 1 b
1 c 1
B a
1. [GSH+H]+ 1
b 1 c
1
Fig. 4. Separation of GSH using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
for surface assisted laser desorption/ionization mass spectrometry (SALDI–MS). SALDI–MS displays a clear background compared to the conventional MALDI–MS. We believe that these new materials have a promising application in the near future for biothiol separation and applications for SALDI–MS.
H.N.Abdelhamid ([email protected]) thanks Assuit university for the support to carry this work.
Acknowledgment
Appendix A. Supplementary data
The authors are particularly grateful to the Ministry of Science and Technology of Taiwan for the financial support.
Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.msec.2014.08.071.
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A
a
1. [Thiabendazole+H]+
b
1 c 1
B
a
1. [Thiabendazole+H]+ 1
b 1
c
1
Fig. 5. Separation of thiabendazole using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
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Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Facile synthesis of nano silver ferrite (AgFeO2) modified with chitosan applied for biothiol separation Hani Nasser Abdelhamid a,b, Hui-Fen Wu a,c,d,e,f,⁎ a
Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan Department of Chemistry, Assuit University, Assuit 71515, Egypt School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung 800, Taiwan d Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan e Doctoral Degree Program of Marine Biotechnology, National Sun Yat-Sen University and Academia Sinica, Kaohsiung 804,Taiwan f Institute of Medical Science and Technology, National Sun Yat-Sen University b c
a r t i c l e
i n f o
Article history: Received 2 February 2014 Received in revised form 29 July 2014 Accepted 31 August 2014 Available online 6 September 2014 Keywords: AgFeO2 Chitosan Matrix assisted laser desorption/ionization Thiol separation
a b s t r a c t Silver iron oxide nanoparticles (AgFeO2 NPs) with narrow size distribution have been synthesized, characterized and was applied for biothiols separation. AgFeO2 and AgFeO2 modified chitosan (AgFeO2@CTS NPs) were synthesized using a hydrothermal method and then characterized by electron microscopy (transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX)), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different biological thiols (dithiothreitol, glutathione, thiabendazole, and sulfamethizole) were investigated and characterized using matrix assisted laser desorption/ionization mass spectrometry (MALDI–MS) and surface assisted laser desorption/ionization mass spectrometry (SALDI– MS). The new material displays dual functionality; 1) for separation and 2) can be served as the matrices for SALDI–MS. Data showed a clear background in the case of nanomaterials compared to conventional matrices (mefenamic acid and 2,5-dihydroxybenzoic acid (DHB) for MALDI–MS). © 2014 Elsevier B.V. All rights reserved.
1. Introduction Because of their numerous applications for catalysis, batteries, and transparent conductors; delafossite-type oxides (ABO2) have been investigated widely in efforts to design advanced materials with enhanced properties. Delafossites are named in honor of French mineralogist Gabriel Delafosse [1]. Delafossites are ternary oxides with the general formula of ABO2, which consists of alternating layers of A cations and edge-sharing BO2 octahedral oriented perpendicular to caxis. The A cations possess two-fold linear coordination with the oxygen atoms, which is often described as a “dumbbell” O–A–O arrangement. The delafossite structure can exist as two polytypes; hexagonal and rhombohedral [2,3]. Among various delafossites, AgFeO2 is attractive for scientific research and applications interests [4–6]. One of the important and attractive features of AgFeO2 is their super-magnetic properties [7]. Generally, colloidal iron oxide particles have been used intensively for biomedicine [8–14] and biotechnology [15,16]. Moreover, functionalization of
⁎ Corresponding author at: Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan. Tel.: +886 7 5252000 3955; fax: +886 7 525 3908. E-mail address: [email protected] (H.-F. Wu).
http://dx.doi.org/10.1016/j.msec.2014.08.071 0928-4931/© 2014 Elsevier B.V. All rights reserved.
Fe3O4 with Au and Ag has demonstrated vast potential in catalysis and biotechnological applications such as protein separation [17], cancer diagnosis [18], biosensors and bioactuators [19]. The prime reason is due to multifunctionality of these new composites. In recent years, the detection of thiols attracted numerous interests of the researcher because of the important roles that they play in biological systems [20–27]. The previous studies revealed that abnormal levels of thiols were related to a variety of diseases, such as liver damage, skin lesions, Alzheimer's and Parkinson's diseases, cardiovascular diseases, diabetes and HIV disease [28]. Thus, detection or separation for these compounds is essential in medicine. So far, the analytical tools that were used to detect thiols are capillary electrophoresis [29], highperformance liquid chromatography [30], mass spectrometry [31–33], and fluorescence [23,34–46]. These techniques show high sensitivity and selectivity. However, in most cases, these approaches require expensive and sophisticated instrumentation; long analysis times, require expensive chemical modification and has low applicability. Thus, they have their limited practical applications. Herein, we report the synthesis of silver ferrite composite (AgFeO2) by the hydrothermal method. AgFeO2 modified chitosan and their application for biothiol separation/detection using matrix (surface) assisted laser desorption/ionization mass spectrometry (M(S)ALDI–MS) are investigated. The new material does not only provide separation facilities,
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but it can serve also as a surface for surface assisted laser desorption/ionization mass spectrometry (SALDI–MS).
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3. Results and discussion 3.1. Characterization of AgFeO2@CTS
2. Materials and methods Fe2(SO4)3, AgNO3, mefenamic acid (MA), 2,5-dihydroxybenzoic acid (DHB), chitosan (low molecular weight; 50,000–190,000 g mol− 1, 75–85% deacetylation), dithiothreitol, glutathione, thiabendazole, and sulfathiazole, were purchased from Sigma-Aldrich (USA). All the chemicals used in this study are of analytical reagent grade. 2.1. Instrumentation X-ray diffraction (XRD) pattern of the composite was recorded using a Bruker AXS D8 Advance, German (operating at 40 KV and 45 mA) with Cu Ka (1.5406 Å) radiation. Scanning electron microscope (SEM, JOEL 6700 F, Japan) with energy dispersive spectrometer (EDS) working at 30 kV was used to examine the surface morphology and elemental composition of the powders. The MALDI–MS analysis was performed by employing positive ion modes on a time-of-flight (TOF) mass spectrometer (Microflex, Bruker Daltonics, Bremen, Germany) with a 1.25 m flight tube. Desorption/ionization was obtained by using a 337 nm nitrogen laser with a 3 ns pulse width. The accelerating potential in the source was maintained at + 20 kV. All MALDI–MS spectra were obtained at an average of 200 laser shots. The laser power was adjusted to slightly above the ionization threshold to obtain a good resolution and signal-to-noise ratios. The dried droplet method was used for all experiments. 2,5-dihydroxy benzoic and mefenamic acids were used as matrices for thiol study [47]. To check the reproducibility, all experimental results were repeated at least three times. 2.2. Experimental 2.2.1. Preparation of AgFeO2 The method of AgFeO2 preparation is based on co-precipitation/ hydrothermal of Fe2(SO4)3 and AgNO3 in the presence of glycerol. Schematic representations of all the steps were represented in Fig. 1A. Typically, 1 mmol of Fe2(SO4)3 and 1 mmol AgNO3 were mixed together in 30 mL deionized water with 3 mL glycerol. Then, 10% of NaOH was added with stirring for about 1 h. The precipitate was transferred to a Teflon autoclave and was heated at 180 °C for 24 h. The precipitate was cooled and separated using a magnet and washed several times by deionized water.
Silver ferrite (AgFeO 2 ) was prepared by co-precipitation/ hydrothermal method. Silver ferrite (AgFeO2) possesses the α-type delafossite structure with rhombohedral type stacking (3R-polytype), consisting of close packed double layers of FeO6 octahedra with monovalent Ag ions positioned between the layers. It is of considerable interest from a magnetic viewpoint because of the intrinsic frustration of bond antiferromagnetism in triangular lattices. AgFeO2 was prepared via modifications of the previous reports describing co-precipitation syntheses, using silver nitrate, iron (III) sulfate, and sodium hydroxide as reagents (Fig. 1A) [5,48,49]. The present methodology is simple and gives good quality of AgFeO2 according to the analytical tools that were used to characterize the synthesized material. The prepared materials were characterized by TEM, SEM, EDX, XRD, and FTIR. TEM images show silver ferrite consisting of aspherical nanoparticles (Fig. 2A). It shows almost no change after modification with chitosan (Fig. 2B). However, the SEM image (Fig. 2C) of AgFeO2 shows agglomeration of particles that may take place during the sample preparation. EDX analysis shows the ratio of Ag:Fe is 1:1 (Fig. 2D). The XRD pattern (Fig. 2E) of the powder clearly shows the formation of the nano silver ferrites. Stimulated XRD (green-dotted lines) reveals that the same phase of AgFeO2 has been prepared successfully. The sizes of the silver ferrite particles were calculated using the Scherer's formula and were found between 1 and 40 nm that agree with TEM image (Fig. 2A). Recently, the syntheses of silver delafossite oxides have been excellently reviewed by Poeppelmeier et al. [3]. There are many proposed methods such as coprecipitation of α-AgFeO2 using FeOOH and Ag2O in a boiling NaOH solution at 100 °C. The new approach shows good applicability to prepare AgFeO2 nanoparticles. Modification of AgFeO2 by chitosan was confirmed by FTIR (Fig. 2F). The spectrum (Fig. 2F) of pure chitosan shows an intensive peak at 1588 cm−1, corresponding to amide II band, while the peak at 1074, 3450 cm−1 could be due to the\C\O\C\vibration and O\H stretching, respectively [50]. The wideness of these peaks was decreased after capping the nanoparticles. For instance, peaks at 1074 and 3450 cm−1 become sharper due to the coordination with magnetic nanoparticles. We can conclude that AgFeO2 is well prepared using hydrothermals. However, other methods were proposed to prepare delafossites such as ion exchange [51–55]; the present approach is more simple and cheap. The major advantages of AgFeO2 nanoparticles possess high ferromagnetism, so it is an attractive subject [55–58]. 3.2. Application for thiol separation
2.2.2. Preparation of AgFeO2 modified chitosan (AgFeO2@CTS) About 0.5 g of the dried AgFeO2 was stirred in 25 mL chitosan (0.1 g in 1% acetic acid). The solution was kept for stirring for 5 h. The prepared material was separated and washed using deionized water with the help of external magnet. 2.2.3. Separation of thiols In order to investigate the separation applicability of the prepared materials (AgFeO2, and AgFeO2@CTS), different thiols (dithiothreitol, glutathione, thiabendazole, and sulfamethizole) were tested. Typically, 10 μL of the prepared materials (AgFeO2 and AgFeO2@CTS) were added to 1 mL of each thiol solution separately (1 × 10− 3 M). After 10 min, the magnetic nanoparticles were separated using external magnets and washed two times to removed unattached molecules. The separated materials were diluted with 10 μL deionized water. Then it was divided to three portions; first one (2 μL) was spotted directly to MALDI plate. Second and third portions (2 μL) were mixed with DHB and MA (2 μL, 50 mM), separately and then spotted in a MALDI plate. The spots were dried before the measurements. The overall procedures were represented in Fig. 1B.
The new materials are applied to separate biological thiols (biothiols) such as (dithiothreitol, glutathione, thiabendazole, and sulfamethizole). Separation of biothiols is paramount for medicine and biomedicine applications [20–27]. It can be used as biomarkers for a variety of diseases, such as liver damage, skin lesions, Alzheimer's, Parkinson's diseases, cardiovascular diseases, diabetes and HIV disease [28]. Thus, we investigate the applications of these materials in biothiol separation. The separation approach is based on the specific interactions between biothiols and silver via robust Ag\S bonds [59] and the noncovalent interaction with CTS on AgFeO2@CTS. Various biothiols such as dithiothreitol (154 gmol−1), glutathione (307 gmol−1), thiabendazole (201 gmol−1), and sulfamethizole (255 gmol− 1) were tested. Simply, into 1 mL of biothiol biomolecules, we added a small amount (10 μL) of magnetic nanoparticles (AgFeO2 & AgFeO2@CTS), then it was separated by external magnets (Fig. 1B). The separated materials are diluted and then spotted on the MALDI plates for detection using two different matrices (MA and DHB), and we also checked the applicability of using these nanomaterials to serve as matrices for SALDI–MS. Note that the conventional matrices (MA and DHB) are also assistant in elution that helps biothiols to detach from the
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A
NaOH, 10% Fe2(SO4)3 Glycerol AgNO3 Stirring
Chitosan
AgFeO2
AgFeO2
B
AgFeO2@Chitosan
Thiols
Separation using external Magnets
Fig. 1. (A) Schematic representation for the preparation of AgFeO2 and AgFeO2@CTS. (B) Schematic representation for thiol separation using magnetic nanoparticles.
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B
A
C
D
F 80
E
AgFeO2@Chitosan
Transmission%
70
60
50
40
30 4000
Chitosan 3500
3000
2500
2000
Wavenumber. cm
1500
1000
500
-1
Fig. 2. Characterization of the prepared magnetic nanoparticles using TEM for (A) AgFeO2 and (B) AgFeO2@CTS, (C) SEM, (D) EDX, (E) XRD and (F) FTIR.
nanoparticle surfaces. MALDI and SALDI–MS of biothiols (dithiothreitol (Fig. 3), glutathione (Fig. 4), thiabendazole (Fig. 5), sulfamethizole (Fig. S1) and their mixture (Fig. S2) were reported for AgFeO2 and AgFeO2@CTS. Data show variation among the different molecules due to the selectivity and because they have different ionizability. Dithiothreitol (M.Wt 154 Da) shows high detectability in the case of bare AgFeO2 and for DHB and MA. The molecules cannot be detected in the case of AgFeO2@CTS as it formed hydrogen bonds with CTS and prevented separation/detection during MALDI measurement. In
contrast, AgFeO2 and AgFeO2@CTS display high ionization of GSH. All the other molecules can be detected for AgFeO2 and AgFeO2@CTS, except that thiabendazole was not detected for DHB. This is due to the matrix related peaks that submerge the analyte peaks. All results are summarized in Table S1. It is interesting to check the separation of the mixture of these compounds. Only bare AgFeO2 can separate DTT and thiabendazole, while the rest cannot be detected from the mixture. The prime reason may be due to the competition between these molecules that makes binding to the nanomaterials difficult.
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A
a
1. [DTT+H]+ 1
b
1
c
1
B a
1. [DTT+H]+ 1
b
c
1
Fig. 3. Separation of ditheitol using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
The present methods are fast, have good sensitivity and selectivity for biothiols, and do not require expensive chemical modification. They eliminate the needs for chemical modifications, and sophisticated instrumentations are convenient and low cost. So far, the analytical tools that were used to detect biothiols such as chromatography [29, 30], mass spectrometry [31–33], and fluorescence [23,34–46] are expensive, sophisticated, need modification of long analysis times, require expensive chemical modification and have low applicability. To our best knowledge, these new materials offer great potentials for
thiols and other molecule separation. It can also serve for analyte ionization due to its large surface area [60–64]. Recently, AgFeO2 was proposed for Surface Enhancement Raman Spectroscopy (SERS) [65]. 4. Conclusion A bimetallic delafossite structured material (AgFeO2) has been prepared and modified with chitosan, ‘AgFeO2@CTS’. It has been shown to be an effective nanoparticle for biothiol separation and surface
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A a 1. [GSH+H]+ 1 b
1 c 1
B a
1. [GSH+H]+ 1
b 1 c
1
Fig. 4. Separation of GSH using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
for surface assisted laser desorption/ionization mass spectrometry (SALDI–MS). SALDI–MS displays a clear background compared to the conventional MALDI–MS. We believe that these new materials have a promising application in the near future for biothiol separation and applications for SALDI–MS.
H.N.Abdelhamid ([email protected]) thanks Assuit university for the support to carry this work.
Acknowledgment
Appendix A. Supplementary data
The authors are particularly grateful to the Ministry of Science and Technology of Taiwan for the financial support.
Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.msec.2014.08.071.
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A
a
1. [Thiabendazole+H]+
b
1 c 1
B
a
1. [Thiabendazole+H]+ 1
b 1
c
1
Fig. 5. Separation of thiabendazole using (A) AgFeO2 and (B) AgFeO2@CTS by applying (a) DHB, (b) MA, and (c) SALDI–MS.
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