Highly selective fluorescent chemosensor for Zn2+ derived from inorganic-organic hybrid magnetic core/shell Fe3O4@SiO2 nanoparticles.

6.1 MB·English

by  Wang, Yujiao

Wangetal.NanoscaleResearchLetters2012,7:86
http://www.nanoscalereslett.com/content/7/1/86
NANO EXPRESS Open Access
Highly selective fluorescent chemosensor for
2+
Zn derived from inorganic-organic hybrid
magnetic core/shell Fe O @SiO nanoparticles
3 4 2
Yujiao Wang, Xiaohong Peng, Jinmin Shi, Xiaoliang Tang, Jie Jiang and Weisheng Liu*
Abstract
Magnetic nanoparticles with attractive optical properties have been proposed for applications in such areas as
separation and magnetic resonance imaging. In this paper, a simple and novel fluorescent sensor of Zn2+ was
designed with 3,5-di-tert-butyl-2-hydroxybenzaldehyde [DTH] covalently grafted onto the surface of magnetic core/
shell Fe O @SiO nanoparticles [NPs] (DTH-Fe O @SiO NPs) using the silanol hydrolysis approach. The DTH-
3 4 2 3 4 2
Fe O @SiO inorganic-organic hybrid material was characterized by transmission electron microscopy, dynamic
3 4 2
light scattering, X-ray power diffraction, diffuse reflectance infrared Fourier transform, UV-visible absorption and
emission spectrometry. The compound DTH exhibited fluorescence response towards Zn2+ and Mg2+ ions, but the
DTH-Fe O @SiO NPs only effectively recognized Zn2+ ion by significant fluorescent enhancement in the presence
3 4 2
of various ions, which is due to the restriction of the N-C rotation of DTH-Fe O @SiO NPs and the formation of
3 4 2
the rigid plane with conjugation when the DTH-Fe O @SiO is coordinated with Zn2+. Moreover, this DTH-
3 4 2
Fe O @SiO fluorescent chemosensor also displayed superparamagnetic properties, and thus, it can be recycled by
3 4 2
magnetic attraction.
Background equipment. Hence, for convenience in future in vivo
Zinc is the second abundant transition metal ion in the applications, various fluorescent probes based on small
human body, which plays a vital role in various biologi- molecules have been designed. They were fairly efficient
cal processes, such as gene expression [1], apoptosis [2], as reported [12-22]; however, the small molecules would
enzyme regulation [3], and neurotransmission [4,5]. It is be toxic [23], and it is impossible to recover or remove
also believed that the Zn2+ homeostasis may have some them from organisms [24]. The limitation of recover-
bearing on the pathology of Alzheimer’s disease and ability blocked the practical applications of small mole-
other neurological problems [6-8]. Therefore, there is an cular fluorescent probes. To resolve this challenge, the
urgency to develop approaches to detect Zn2+ in vivo. inorganic supports incorporated with small molecular
Besides, techniques for the separation and removal of fluorescent probes were applied for the improvement on
metal ions and additives in the detection process are recoverability.
very important to prevent poisoning in environmental Various mesoscopic or nanoscopic materials can be
and biological fields. Conventional analytical methods acted as the inorganic supports in the design of fluores-
including atomic absorption spectrophotometry [9], cent probes, including magnetic nanoparticles, nano-
inductively coupled plasma atomic emission spectrome- tubes, mesoporous silica, metal nanoparticles, and TiO
2
try [10], and electrochemical method [11] can hardly be [25-34]. Among all these inorganic materials, magnetic
applied for Zn2+ ion detection in biological systems due silica core/shell nanoparticles have advantages over
to their complicated pretreatment steps and expensive other competitors for biological and environmental
applications [35-41]. Firstly, they could be simply sepa-
rated or recovered via external magnetic field. Besides,
*Correspondence:[email protected]
KeyLaboratoryofNonferrousMetalsChemistryandResourcesUtilizationof with magnetic silica core/shell nanoparticles as delivery,
GansuProvinceandStateKeyLaboratoryofAppliedOrganicChemistry, their low toxicity and biocompatibility also had advan-
CollegeofChemistryandChemicalEngineering,LanzhouUniversity,
Lanzhou,730000,People’sRepublicofChina tages for the design of biological fluorescent probes.
©2012Wangetal;licenseeSpringer.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttribution
License(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,
providedtheoriginalworkisproperlycited.
Wangetal.NanoscaleResearchLetters2012,7:86 Page2of13
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Furthermore, the silica shell around magnetic core has Thermal gravimetric analysis [TGA] (P.E. Diamond
large surface area, and it can be grafted by fluorescent TG/DTA/SPAECTRUN ONE thermal analyzer, Perki-
probes. Therefore, to develop nontoxic, biocompatible, nElmer Inc., Waltham, MA, USA), dynamic light scat-
and recoverable fluorimetric Zn2+ sensors, introducing tering (BI-200SM, Brookhaven Instruments Corporation,
the magnetic silica nanoparticles with small molecular Holtsville, NY, USA), transmission electron microscopy
fluorescent probes incorporated is very necessary and [TEM] (Tecnai G2 F30, 300 kV, FEI Company, OR,
highly desirable. USA), and energy-dispersive X-ray spectrometer [EDX]
In this work, we designed and synthesized a magnetic were used to characterize the materials. X-ray diffraction
recoverable fluorescence Zn2+ sensor based on 3,5-di- [XRD] pattern of the synthesized products was recorded
tert-butyl-2-hydroxybenzaldehyde [DTH] covalently with a Rigaku D/MAX 2400 X-ray diffractometer
grafted onto Fe O @SiO nanoparticles [NPs] (DTH- (Tokyo, Japan) using Cu Ka radiation (l = 0.154056 Å).
3 4 2
Fe O @SiO ) to provide highly selective fluorescence The scan range (2θ) was from 10° to 80°. Solid-state
3 4 2
changes and efficient magnetic recoverability (Figure 1). infrared [IR] using diffuse-reflectance infrared Fourier
This Zn2+-selective fluorescent switch of the immobi- transform [DRIFT] spectroscopy was performed in the
lized chemosensors displayed excellent reversibility, 400- to 4,000-cm-1 region using a Bruker Vertex 70v
combined with its superparamagnetic property, enabling (Bremen, Germany) and IR-grade KBr (Sigma-Aldrich
the recovery of material and repeated uses for Zn2+ Corporation, St. Louis, MO, USA) as the internal stan-
sensing. dard. 1H NMR and 13C NMR spectra were measured on
a Bruker DRX 400 spectrometer in a CDCl solution
3
Experimental details with TMS as the internal standard. Chemical shift mul-
Materials and methods tiplicities are reported as s = singlet, t = triplet, q =
All reagents are purchased commercially. Besides, etha- quartet, and m = multiplet. Mass spectra were recorded
nol was used after purification by standard methods. on a Bruker Daltonics esquire6000 mass spectrometer.
Other chemicals were used as received without further UV absorption spectra were recorded on a Varian Cary
purification. 100 spectrophotometer (Palo Alto, CA, USA) using
Figure1SynthesesofDTH-APTESandDTH-Fe O @SiO .
3 4 2
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quartz cells of 1.0-cm path length. Fluorescence mea- One hundred milligrams of dried Fe O @SiO NPs
3 4 2
surements were made on a Hitachi F-4500 spectrophot- and 356 mg (0.81 mmol) of DTH-APTES were sus-
ometer (Tokyo, Japan) and a Shimadzu RF-540 pended in 10 mL of anhydrous ethanol. The mixture
spectrofluorophotometer (Chorley, UK) equipped with was refluxed for 8 h at 80°C under N to obtain DTH-
2
quartz cuvettes of 1.0-cm path length with a xenon Fe O @SiO . The nanoparticles were collected by cen-
3 4 2
lamp as the excitation source. An excitation and emis- trifugation and repeatedly washed with anhydrous etha-
sion slit of 10.0 nm was used for the measurements in nol thoroughly. Unreacted organic molecules were
the solution state. All spectrophotometric titrations were removed completely and monitored by the fluorescence
performed with a suspension of the sample dispersed in of the upper liquid. Then, the DTH-Fe O @SiO NPs
3 4 2
ethanol. were finally dried under vacuum over night. About
Synthesis of Fe3O4@SiO2 NPs 2.81% DTH-APTES in the precursors was finally grafted
Fe O @SiO NPs were synthesized according to the on the NPs, and the rest could be recycled if no hydro-
3 4 2
study of Nigam et al. [42]. The process can be briefly lysis occurred.
described in the following two steps: (1) FeCl and
2
FeCl (molar ratio, 1:2) were added to a concentrated Results and discussion
3
solution of base (25% ammonium hydroxide) under N . Characterization of DTH-Fe O @SiO
2 3 4 2
The solution was mechanically stirred for 1 h at 20°C The TEM image (Figure 2A) of DTH-Fe O @SiO
3 4 2
and then heated at 70°C for 1 h. The mixture was then reveals that iron oxide NPs have entrapped in the silica
stirred for 30 min at 90°C upon addition of citric acid shell successfully, in which the core/shell structures are
(0.5 g/ml). After cooling the reaction mixture to room in a narrow size distribution of 60 to 70 nm [46,47], and
temperature, the magnetite NPs were obtained by per- the diameter of the magnetic core is about 10 nm. The
manent magnet, and then it was rinsed with deionized weight ratio of iron vs. silicon was measured to be
water to remove excess citric acid and other nonmag- 2.63:38.94 by EDX. Hence, according to TGA, each
netic particles thoroughly. (2) Then, the magnetite NPs magnetic NP has about 6,000 DTH-APTES molecules
were further coated with a thin silica layer via a modi- grafted (see Additional file 1). More importantly, the
fied Stöber method [43] to obtain stable Fe O @SiO . right size of magnetic core/shell NPs smaller than 100
3 4 2
Tetraethyl orthosilicate was hydrolyzed with magnetic nm is an advantage for their good dispersibility. In addi-
NPs as seeds in an ethanol/water mixture. The resulting tion, an inert silica coating on the surface of magnetite
silica-coated magnetite NPs with an average diameter of nanoparticles prevents their aggregation in liquid [48].
60 to 70 nm were used. Hence, such a good performance on the dispersibility
Synthesis of DTH-Fe3O4@SiO2 NPs can improve their chemical stability and provide better
As shown in Figure 1, the synthetic procedure for 2,4- protection against toxicity.
di-tert-butyl-6-((3-(triethoxysilyl)propylimino)methyl) In addition, dynamic light scattering [DLS] was per-
phenol [DTH-APTES] followed the method previously formed to further reveal the colloidal stability of NPs.
described in the literatures [44,45]. DTH (234 mg, 1 According to DLS results (Figure 2B), DTH-Fe O @-
3 4
mmol) and (3-aminopropyl) triethoxysilane [APTES] SiO presents good stabilization and a narrow size dis-
2
(221 mg, 1 mmol) were mixed in dry ethanol (15 mL) at tribution with peak centered at 147 nm, confirming its
room temperature. Then, the solution was refluxed for 3 good stabilization in ethanol. In a common sense, the
h under N . After that, the solvent was evaporated, and diameter achieved by DLS is mostly higher than the one
2
the crude product was further purified by flash column observed in TEM since the size of NPs identified by
chromatography (silica gel, ethyl acetate/petroleum DLS includes the grafted molecules’ steric hindering and
ether 1:2) to produce 371 mg (84.9%) of DTH-APTES the hydrodynamic radius of first few solvent layers
as yellow oil. ESI-MS: m/z 438.5 (M + H+). 1H NMR: [49-51]. Besides, according to the calculated size of
(400 MHz, CDCl ): δ (ppm) 0.69 (t, 2H, CH Si); 1.22 (t, DTH-APTES which covalently grafted on the surface of
3 2
9H, CH ); 1.30 (s, 9H, C(CH ) ); 1.43 (s, 9H, C(CH ) ); Fe O @SiO , the grafted molecules’ steric hindering
3 3 3 3 3 3 4 2
1.82 (m, 2H, CH ); 3.58 (t, 2H, NCH ); 3.82 (q, 6H, could increase the diameter by about 2.72 nm.
2 2
SiOCH ); 7.07, 7.36 (d, 2H, Ar); 8.34 (s, 1H, HC = N). Figure 3 shows the XRD powder diffraction patterns
2
13C NMR (100 MHz, CDCl ): 7.92 (CH Si); 18.30 (CH ); of two NPs for the identification of Fe O in core/shell
3 2 3 3 4
24.38, 29.40, 29.70, 31.50 (CH ); 34.11 (C), 35.01 (C); NPs. XRD patterns of the synthesized Fe O @SiO (a)
3 3 4 2
58.41 (CH ); 62.08 (CH ); 117.83, 125.69, 126.66, 136.65, and DTH-Fe O @SiO (b) display relative diffraction
2 2 3 4 2
139.75, 158.27 (Ar); 165.80 (C = N). FT-IR (KBr pellet) peaks in the 2θ region of 10° to 80°. We could find that
(cm-1): 1,637 (ν ), 1,275-1,252 (ν ), 1,596-1,342 XRD patterns show very low intensities for the peaks
C = N C-O
(ν ), 1,106-1,085 (ν ). attributed to the Fe O cores, due to the coating of
C = C Si-O 3 4
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Figure2TEMimage(A)andtheparticlesizehistogramfromDLS(B)ofDTH-Fe O @SiO .
3 4 2
amorphous silica shell, which deduced the efficient con- magnetite core (Figure S1 in Additional file 1) [52]. The
tent of Fe O cores and then affected the peak intensi- six characteristic diffraction peaks in Figure 3 can be
3 4
ties. However, the diffraction peaks of DTH- indexed to (220), (311), (400), (422), (511), and (440),
Fe O @SiO still maintain the same position as the which well agree with the database of magnetite in the
3 4 2
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Figure3XRDpatternsofFe O @SiO (a)andDTH-Fe O @SiO (b).
3 4 2 3 4 2
Joint Committee on Powder Diffraction Standards The successful conjugation of DTH onto the surface
[JCPDS] (JCPDS card: 19-629) file [42,46,53,54]. Also, of the Fe O @SiO NPs can be confirmed by DRIFT
3 4 2
the broad XRD peak at a low diffraction angle of 20° to (Figure 4). The bands at 3,400 to 3,500 cm-1 and 1,000
30° corresponds to the amorphous-state SiO shells sur- to 1,250 cm-1 are due to -OH stretching on silanol [55].
2
rounding the Fe O NPs [53]. It indicates that not all the silanol on Fe O @SiO NPs
3 4 3 4 2
Figure4DRIFTspectraofFe O @SiO (a)andDTH-Fe O @SiO (b).
3 4 2 3 4 2
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have been covalently modified. The band at 1,630 cm-1 Oe at 300 K. The result was consistent with the conclu-
represents the bending mode of -OH vibrations [56]. sion that magnetic Fe O NPs smaller than 30 nm are
3 4
DTH-Fe O @SiO (see Figure 1) has additional peaks at usually superparamagnetic at room temperature [47].
3 4 2
2,918 and 2,850 cm-1 that correspond to the -CH vibra- The saturation magnetization value for synthesized
tion of aliphatic and aromatic groups [28,57,58]. The DTH-Fe O @SiO is about 3.96 emu/g. The saturation
3 4 2
bands at 1,473 and 1,463 cm-1 of DTH-Fe O @SiO are magnetization value for Fe O @SiO support was mea-
3 4 2 3 4 2
probably due to the bending vibrations of -CH , which suredto be 4.24emu/g. Considering the grafting rate of
3
come from the DTH part [59]. According to the spectra 7.64% (according to TGA, Figure S2 and Table S1 in
of Fe O @SiO and DTH-Fe O @SiO , the bands which Additionalfile1),thedifferenceofsaturationmagnetiza-
3 4 2 3 4 2
appear as broad and strong and are centered at 1,102 tion values between DTH-Fe O @SiO and its support
3 4 2
(ν ) and 800 cm-1 can be attributed to the siloxane (-Si- could be due to the decreased weight ratio of magnetic
as
O-Si-) [60]. These results support the presence of the support after grafting. More importantly, from the hys-
organic DTH-APTES in the magnetic material DTH- teresisloopsofFe O @SiO NPsandtheDTH-Fe O @-
3 4 2 3 4
Fe O @SiO . SiO NPs, it can be found that both exhibited
3 4 2 2
The UV-visible [UV-Vis] spectra of DTH-APTES (1.0 superparamagnetic properties for no remanence was
× 10-5 M), Fe O @SiO (0.3 g/L), and DTH-Fe O @- observed when the applied magnetic field was removed.
3 4 2 3 4
SiO (0.3 g/L) can provide further evidence on the graft- These phenomena were due to the fact that the magne-
2
ing of DTH onto the surface of the Fe O @SiO NPs titecoreissmallerthan30nmincore/shellNPs(Figure
3 4 2
(Figure 5). Compared to Fe O @SiO (b), a new absorp- 2A). As a result of this superparamagnetic property,
3 4 2
tion band centered at about 330 nm of DTH-Fe O @- DTH-Fe O @SiO hada reversal magnetic responsivity.
3 4 3 4 2
SiO can be attributed to the typical electronic It could be easily separated from dispersion after only 5
2
transition of an aromatic ring and -C = N- conjugate minusingamagnet(Figure6,inset)andthenredispersed
system in a Schiff base molecule [29]. This result can by mild agitation when the magnet was removed. The
also imply the successful immobilization of DTH- reversal magnetic responsivity of DTH-Fe O @SiO
3 4 2
APTES onto the magnetic core/shell NPs. wouldbeakeyfactorwhenevaluatingtheirrecoverability
The superparamagnetic property of the magnetic NPs [61]. The magnetic separation capability of DTH-
plays a vital role for its biological application. Figure 6 Fe O @SiO NPsandthereversibilityofthecombination
3 4 2
shows the magnetizationcurves ofthe Fe O @SiO and betweenDTH-Fe O @SiO and Zn2+couldalsoprovide
3 4 2 3 4 2
DTH-Fe O @SiO whichwereinvestigatedwithavibrat- asimpleandefficientroutetoseparateZn2+ratherthan
3 4 2
ingsample magnetometer tuned from -15,000 to 15,000 throughfiltrationapproach(seeFigure6inset).
Figure5UV-VisspectraofDTH-APTES(a),Fe O @SiO (b),andDTH-Fe O @SiO (c).
3 4 2 3 4 2
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Figure6MagnetizationcurvesoftheFe O @SiO (a)andDTH-Fe O @SiO (b).InsetshowsthatDTH-Fe O @SiO wasdispersedtoan
3 4 2 3 4 2 3 4 2
externalmagnetinethanol.
Fluorescence response of DTH-Fe O @SiO rigid plane with conjugation is formed and the fluores-
3 4 2
To verify its fluorescence response towards various cence enhanced, which consists of our previous work
metal ions, we investigated fluorescence properties of [62]. The emission spectra of DTH-Fe O @SiO , which
3 4 2
DTH-Fe O @SiO NPs (0.3 g/L, containing 5.2 × 10-5 is excited at 397 nm, exhibit the emission maximum at
3 4 2
M DTH-APTES according to TGA in Figure S2 and 452 nm with a low quantum yield (F = 0.0042) at room
Table S1 in Additional file 1) towards various metal ions temperature in ethanol. Upon the addition of excess Zn2
Ag+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Hg2+, K+, Mg2+, +, the fluorescence intensity of DTH-Fe O @SiO
3 4 2
Mn2+, Na+, Ni2+, and Zn2+ in ethanol solution (all as increased by more than 25-fold, the emission maximum
perchlorates, 1.0 × 10-4 M). As shown in Figure 7A, shifts from 452 to 470 nm, and the quantum yield (F =
DTH-Fe O @SiO NPs exhibited significant ‘off-on’ 0.11) results in a 26-fold increase.
3 4 2
changes in fluorescence emission only for Zn2+, but not As illustrated in Figure 8A, the fluorescence emission
for the others. It is noted that Cd2+ with a d10 electron of DTH-Fe O @SiO (0.3 g/L) increases gradually when
3 4 2
configuration, which often exhibited coordination prop- adding various concentrations (0 to 30 μM) of Zn2+ in
erties similar to Zn2+ [19], do not influence the fluores- ethanol, indicating that Zn2+ is quantitatively bound to
cence intensity of DTH-Fe O @SiO NPs significantly. the Schiff base moiety attached to the NPs. Fluorescence
3 4 2
As a comparison, DTH (1.0 × 10-5 M) exhibited fluores- titration experiment suggests that the association con-
cence response towards both Zn2+ and Mg2+ ions (1.0 × stant (Kd) for Zn2+ binding to DTH-Fe3O4@SiO2 is cal-
10-4 M) in the same solution, which is not as selective culated to be 51.08 M-2 (log K = 1.71; Figure 8A). Job’s
as DTH-Fe O @SiO for Zn2+ detection (Figure 7B). plot suggested a 1:2 binding ratio for Zn2+ with DTH-
3 4 2
Compared to the single aldehyde DTH, the origin of APTES (Figure 8B).
selectivity for DTH-Fe O @SiO may come from its The competition experiments indicated that the pre-
3 4 2
Schiff base structure, which prefers to coordinate with sence of most metal ions, especially Na+, K+, Ca2+, and
Zn2+ under the interference of Mg2+. Mg2+,whichareabundantinthebiological environment,
The remarkable increase of fluorescence intensity can hadanegligibleeffectonZn2+sensing(Figure9A).Since
be explained as follows: DTH-Fe O @SiO is poorly Cr3+, Cu2+, Fe3+, and Hg2+ also appeared to bind DTH-
3 4 2
fluorescent due to the rotation of the N-C bond of Fe O @SiO sensors(FigureS3inAdditionalfile1),they
3 4 2
DTH-APTES part. When stably chelated with Zn2+, the quenchedthefluorescenceoftheZn2+-DTH-Fe O @SiO ,
3 4 2
N-C rotation of DTH-APTES part is restricted and the owingtoanelectronorenergytransferbetweenthemetal
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Figure7FluorescenceresponseofDTH-Fe O @SiO (A)andDTH(B)tovariouscations.Excitationwavelengthwas397nm.Spectrawere
3 4 2
recordedevery25minafteraddingZn2+.
cation and fluorophore known as the fluorescence Figure 10A depicts the UV-Vis spectra of DTH-
quenchingmechanism[63-66].Thefluorescenceenhance- APTES (10 μM), DTH-APTES (10 μM) + Zn2+ (100
mentthatoccurreduponexposuretoZn2+wasfullyrever- μM), DTH-Fe O @SiO (0.3 g/L), and DTH-Fe O @-
3 4 2 3 4
sibleastheadditionofEDTA(2.5×10-4M;Figure9Band SiO (0.3 g/L) + Zn2+ (100 μM). It can be seen that the
2
inset)restoredtheemissionband.Combinedwithitsmag- absorbance peaks at around 390 nm are formed when
netic property, the results above implied that DTH- Zn2+ is added in both DTH-APTES and DTH-Fe O @-
3 4
Fe O @SiO wasconsiderablyapplicabletosomefieldas SiO systems. The absorption spectra of DTH-Fe O @-
3 4 2 2 3 4
anewinorganic-organichybridsensorfortheZn2+ion. SiO (0.3 g/L) in the presence of various concentrations
2
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Figure8FluorescencetitrationsandJob’splot.(A)FluorescencetitrationsofDTH-FeO @SiO withZn2+.(B)Job’splotofDTH-APTESwith
3 4 2
Zn2+.Spectrawererecordedevery25minafteraddingZn2+.
of Zn2+ (0 to 240 μM) were investigated in ethanol at Conclusions
room temperature, as shown in Figure 10B. When Zn2+ In summary, we have successfully designed and synthe-
was added gradually, the absorbance of DTH-Fe O @- sizedfunctionalizedmagneticcore/shellFe O @SiO NPs
3 4 3 4 2
SiO at 390 nm gradually increases, which indicated that (DTH-Fe O @SiO NPs)whichcouldactasanewtypeof
2 3 4 2
DTH-Fe O @SiO NPs coordinated with Zn2+ gradually. fluorescent chemosensor for efficient sensing and
3 4 2
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Figure9CompetitionofDTH-Fe O @SiO towardscationsandreversibilityofDTH-Fe O @SiO towardsZn2+.(A)Fluorescentemission
3 4 2 3 4 2
changesofDTH-FeO@SiO (0.3g/L)uponadditionof1,blank;2,Zn2+;3,Na+;4,Na++Zn2+;5,K+;6,K++Zn2+;7,Ca2+;8,Ca2++Zn2+;9,
3 4 2
Mg2+;and10,Mg2++Zn2+(eachmetalionis100μM)inethanolatroomtemperature.(B)FluorescencespectraofDTH-FeO@SiO (0.3g/L)in
3 4 2
(a)without,(b)withZn2+(1.0×10-4M),and(c)aftertreatmentwithEDTA(2.5×10-4M)in(b)solution.Theinsetpictureshowsthephotograph
ofDTH-FeO@SiO withZn2+bytreatmentofEDTA(2.5×10-4M)undera365-nmUVlight.
3 4 2
separation of Zn2+ in ethanol. The inorganic-organic separationcapabilityofFe O @SiO NPsandthereversi-
3 4 2
hybrid fluorescent chemosensor DTH-Fe O @SiO was bilityofthecombinationbetweenDTH-Fe O @SiO and
3 4 2 3 4 2
able to recognize and adsorb Zn2+ with a selective and Zn2+ would also provide a simple route to separate Zn2+
sensitive fluorescence responseinethanol.The magnetic fromtheenvironment(Figure6,inset).