Journal of Membrane Science 385– 386 (2011) 269– 276
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Journal of Membrane Science
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ibacron Blue F3GA functionalized poly(vinyl alcohol-co-ethylene) (PVA-co-PE)anofibrous membranes as high efficient affinity adsorption materials
ing Zhua, Jun Yangb, Gang Suna,∗
Fiber and Polymer Science, University of California, Davis, CA 95616, United StatesDepartment of Entomology, University of California, Davis, CA 95616, United States
r t i c l e i n f o
rticle history:eceived 26 July 2011eceived in revised form9 September 2011ccepted 1 October 2011vailable online 6 October 2011
a b s t r a c t
Poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibrous membranes with surface incorporated CibacronBlue F3GA (CB) were prepared for bio-separation and purification applications. PVA-co-PE nanofiberswere fabricated via melt extrusion of an immiscible blend of PVA-co-PE polymer with cellulose acetatebutyrate (CAB) as a sacrificial matrix and subsequent removal of CAB. PVA-co-PE nanofiber dispersionswere coated on a releasing surface to form nanofibrous membranes with fiber sizes ranging in 50–300 nm.Cibacron Blue F3GA (CB) was covalently immobilized onto the nanofiber surfaces and reached a maximum
eywords:anofibrous membraneibacron Blue F3GAffinity membranelbumin adsorption
amount of 220 mg/g on the nanofibers. The CB attached PVA-co-PE nanofibrous membranes could adsorblarge amount of bovine serum albumin (BSA) (105.5 mg/g nanofiber) at pH 5.0 while the non-specific BSAadsorption on the pristine PVA-co-PE nanofibrous membrane was negligible. The elution efficiency of BSAin 1 M NaSCN was 92.5%. After 10 adsorption–elution cycles, a slight decrease of BSA capture capacityon the membrane was observed. This work demonstrated the feasibility of using the CB functionalizedPVA-co-PE nanofibrous membranes in bio-separation and purification applications.
. Introduction
Recently, affinity membrane chromatography, as a promisinglternative technology to the traditional packed-bed column chro-atography, has attracted much attention. This is attributed to the
dvantages of the affinity membranes, such as low pressure drops,igh flow rates and no intraparticle diffusion, overcoming the basic
imitations of traditional column methods. Moreover, the surfacemmobilized affinity ligands allowed the membranes to become
ore efficient and specific in capturing target biomolecules [1–4].mong the variety of potential materials, nanofibrous membranesre ideal structures due to their intrinsically large surface areao volume ratio, highly porous structures, and proper mechani-al and chemical stability. So far, nature and synthetic polymersuch as cellulose [5,6], polysulphone [7], polyacrylonitrile [8] andhitosan/nylon-6 [9] were electrospun into nanofibers to preparehe desired affinity membranes.
As an effort to prepare affinity membrane materials with con-rolled properties, we explored using thermoplastic poly(vinyl
lcohol-co-ethylene) (PVA-co-PE) nanofibers as a basic material.VA-co-PE consists of both hydrophilic vinyl alcohol and hydropho-ic ethylene segments, possessing good mechanical strength,
thermal stability, chemical and biological resistance and neededbiocompatibility [10]. Moreover, the abundant hydroxyl groups onPVA-co-PE can be further utilized to immobilize affinity ligandsand biomolecules. Beside of these advantages, previous studieshave shown that the hydrophilic PVA-co-PE matrix existed excel-lent resistance to non-specific protein adsorption, which has beena major concern for the solid materials used in purification ofbiomolecules [11]. PVA-co-PE hollow-fiber and porous membraneshave been prepared as solid materials for enzyme immobilizationsand protein purifications [12–15]. We envision that PVA-co-PEnanofibrous membranes will possess higher surface areas andincreased surface affinity power, which could result in broad appli-cations in bio-separation, bio-purification and bio-detection.
Here, we will present the development of PVA-co-PE nanofi-brous membranes with dye-ligand functionalized surfaces asbio-separation and purification materials. The membranes can beemployed in bio-detectors as well, if specific surface modifica-tions are applied. PVA-co-PE nanofibers were prepared by a meltextrusion of immiscible blends of PVA-co-PE and cellulose acetatebutyrate (CAB) through a twin-screw extruder and subsequentremoval of CAB matrix [16]. The nanofibers were then made intomembrane structures by coating nanofiber dispersions on a releas-ing support with controlled thickness. Cibacron Blue F3GA (CB)
and bovine serum albumin (BSA) were employed as a ligand–ligatemodel. After covalent immobilization of the CB ligand, thesurface functionalized PVA-co-PE nanofibrous membranes (PVA-co-PE-CB) were characterized via scanning electron microscope
270 J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276
to PVA
(sto
2
2
tew4Ctup
2
vwccNedrdwwpoc
2
lStnop8witi
Scheme 1. CB immobilization on
SEM) and Attenuated Total Reflectance-Fourier Transform Infraredpectroscopy (ATR-FTIR). Then, the effects of initial protein concen-ration, pH, ionic strength and adsorption time on BSA adsorptionnto the PVA-co-PE-CB nanofibrous membranes were studied.
. Experimental
.1. Materials
Poly (vinyl alcohol-co-ethylene) (PVA-co-PE, ethylene con-ent 27%) and bovine serum albumin (BSA, 98% agarose gellectrophoresis, 66 kDa) were purchased from Sigma–Aldrich (Mil-aukee, USA). Cellulose acetate butyrate (CAB, butyryl content
4–48 wt %) was obtained from Acros Organics (Pittsburg, PA, USA).ibacron Blue F3GA (CB) was supplied by Polysciences (Warring-on, FL, USA). The other chemicals were purchased from Acros andsed as received. All water used was purified via a Millipore Milli-Qlus water purification system.
.2. PVA-co-PE nanofibrous membrane preparation
The PVA-co-PE nanofibers were prepared according to a pre-iously published procedure [16]. Briefly, PVA-co-PE was mixedith CAB, the sacrificial matrix, in a blend ratio of CAB/PVA-
o-PE = 80/20, which was gravimetrically fed into a Leistritzo-rotating twin-screw (18 mm) extruder (Model MIC 18/GL 30D,urnberg, Germany) at a feed rate of 12 g/min. The blends werextruded into composite fibers through a two strand (2 mm iniameter) rod die, hot-drawn by a take-up device with a drawingatio of 25 (the area of cross-section of the die to that of the extru-ates) and air cooled to room temperature. Then, the CAB matrixas removed via extraction of the CAB/PVA-co-PE composite fibersith acetone. To fabricate PVA-co-PE nanofibrous membrane, therepared nanofibers were made into suspensions and depositednto a polyester monofilament fabric as a releasing surface withontrolled thickness.
.3. Cibacron Blue F3GA immobilization
Cibacron Blue F3GA (CB) is a reactive dye that can be cova-ently attached to PVA-co-PE nanofibrous membranes according tocheme 1. 50 mg CB was dissolved in 50 mL water, and the dye solu-ion was heated to 60 ◦C, followed by addition of 30 mg of PVA-co-PEanofibrous membranes. After soaking for 15 min, certain amountf sodium chloride (NaCl) was added into the mixture. The tem-erature was maintained at 60 ◦C for 1 h, and then increased to0 ◦C for another 4 h. During the course, the pH of this solution
as adjusted to more alkaline by addition of 1 M sodium hydrox-
de (NaOH). The modified nanofibrous membranes were washedhoroughly by warm water until no CB molecule in the wash-ng solution was detected by measurement of UV–vis absorbance.
-co-PE nanofibrous membranes.
Residual CB solutions and the washing solutions were carefullycollected together and measured by a UV–vis spectrophotometer(Evolution 600, Thermo, USA) at 600 nm to determine the amountof CB that was not incorporated onto the nanofibers. A standardcalibration curve was established to calculate the concentrationsof the CB solutions. The CB loading on the nanofibrous membranewas determined by the difference of initial and final CB amounts insolutions.
2.4. Material characterization
Morphologies of nanofibers and membranes were observedby using a scanning electron microscopy (SEM) (XL 30-SFEG,FEI/Philips, USA) at 5 kV accelerating voltage on gold sputter coatedsamples. Attenuated Total Reflection-Fourier Transform Infrared(ATR-FTIR) spectra were measured from 4000 to 500 cm−1 at a res-olution of 4 cm−1 by a Nicolet 6700 spectrometer (Thermo FisherScientific, USA). A laser scanning confocal microscope (OlympusAmerica FV1000) with excitation at 480 nm and emission at 540 nmwas used to obtain the confocal fluorescent images of the nanofi-brous membranes.
2.5. BSA adsorption studies
Bovine serum albumin (BSA) adsorption capacities of the CBattached PVA-co-PE (PVA-co-PE-CB) nanofibrous membranes weremeasured under different concentrations, adsorption times, pHvalues and ionic strengths of the adsorption media. 0.1 M aceticacid–sodium acetate buffer was used to prepare the adsorptionmedia with pH varied from 4.0 to 6.0, while 0.1 M phosphatebuffer was used in the media with pH at 7.0. The ionic strengthwas adjusted by using NaCl solution from 0 to 1 M. The ini-tial BSA concentration was varied from 0.5 to 4.0 mg/mL. For atypical adsorption test, 30 mg of PVA-co-PE-CB nanofibrous mem-brane was placed into 20 mL BSA solution for certain time at30 ◦C, followed by extensive washing with distilled water. The BSAadsorption amount on the membranes was calculated by measur-ing the initial and final BSA concentrations of the adsorption media,and the BSA concentration was determined by a bicinchoninic acidassay using a Pierce BCATM Protein Assay Kit [17].
To study reusability of the PVA-co-PE-CB nanofibrous mem-brane, one piece (about 30 mg) of nanofibrous membrane with aknown amount of adsorbed BSA was immersed in 20 mL of 1 MNaSCN solution as an elution medium for 1 h at 30 ◦C. The amountof the eluted BSA was determined by measuring the concentrationof BSA in the elution via the bicinchoninic acid assay (BCA) men-tioned above. This BSA adsorption–elution process was repeated
ten times with the same nanofibrous membranes.
To test the quality of BSA eluted from PVA-co-PE-CB nanofi-brous membrane, a Waters 2795 HPLC system (Waters Co., Milford,MA) was used for the chromatographic studies. Chromatographic
J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276 271
120100806040200
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1mg/ml 0.1mg/ml
c
) NaCl
sup9gfl7vtuvv1
3
3
ibaro
Fig. 1. CB immobilizations on PVA-co-PE nanofibrous membrane: (a
eparation of proteins was achieved on a VYDAC MS C18 m300A, 5m column (150 mm × 1 mm i.d. HPLC mobile phase A and B wererepared by adding formic acid (0.1%, v/v) in Milli-Q water and5% acetonitrile and 5% Milli-Q water, respectively. The chromato-raphic separation was performed using a gradient at 0.2 mL/minow-rate (0–12 min, phase B from 5 to 70%, and 12–12.5 min, from0 to 5%, then hold on 5% until 15 min) and the sample injectionolume of the auto sampler was 5 �L. The HPLC system was coupledo a Waters LCT Electrospray-Time of Flight Mass Spectrometernder positive mode. The MS spectra was operated under capillaryoltage 3000 V, sample cone voltage 40 V, RF lens 600 V, extractionoltage 4 V, desolvation temperature 300 ◦C, Source temperature00 V, and microchannel plate detector (MCP) voltage 2300 V.
. Results and discussion
.1. CB immobilization on PVA-co-PE nanofibrous membrane
Cibacron Blue F3GA (CB) is a popular affinity dye ligand formmobilization and purification of protein molecules, and has
een covalently immobilized onto various solid materials, suchs beads [18], gels [19] and membranes [20], via nucleophiliceactions between CB triazinyl chloride and reactive sites (aminor hydroxyl groups) on the polymers. Similarly, CB immobilized
effect, (b) pH effect, and (c) time effect with two CB concentrations.
PVA-co-PE nanofibrous membranes were prepared via the nucle-ophilic reaction between the CB triazinyl chloride and abundanthydroxyl groups on the PVA-co-PE membrane surfaces.
During the immobilization of the affinity dye, the adsorptionof CB molecules onto the membrane surfaces is a physical pro-cess, and ionic strength of the solution has an impact. As Fig. 1(a)shows no CB adsorption on the membrane surfaces was observedin the absence of NaCl in the system. When the concentrationNaCl was raised in the solution, the amounts of CB adsorbed onthe membranes increased. The addition of NaCl, an electrolyte inthe solution, reduced the electric repulsion between the negativecharged CB molecules and the membrane surfaces. The CB immo-bilization reactions were further optimized by adjusting mediumpH values and reaction time. More alkaline condition should befavored by the nucleophilic reaction between hydroxyl and tri-azinyl chloride groups, as shown in Fig. 1(b). But, at pH 12, theharsh alkaline condition could damage some nanofibers, therefore,pH 11 was selected for further studies. In addition, the amountsof CB immobilized (CB loading) on the membranes were increasedinitially, and then reached saturation after 4 h, shown in Fig. 1(c).
Under an optimum condition (CB concentration: 1 mg/mL, NaClconcentration: 2.5 M, medium pH: 11, and reaction time: 4 h), PVA-co-PE nanofibrous membranes reached the CB loading of 220 mg/gnanofibers, which were then used in the following BSA adsorption
272 J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276
bran
stbmpb
3n
bPwfiwfPacot[tcb
3
mt
co-PE-CB nanofibrous membranes. Meanwhile, the blank resultfrom the pristine PVA-co-PE nanofibrous membrane (Fig. 4, left)suggested no non-specific protein adsorption on this membrane, amain requirement for solid matrices in biomolecular purifications.
Inte
nsity
(a) CB
(b) PV A-co-P E
(c) PV A-co-PE- CB1226 cm-1
1568 cm-1
Fig. 2. SEM images of (a) pristine PVA-co-PE nanofibrous mem
tudies. Moreover, the stability of immobilized CB molecules onhe membranes was studied by incubating PVA-co-PE-CB mem-ranes in various pH solutions (pH 3, 5, 7 and 9) for 1 week. No CBolecules were released from the membranes, further proved the
ermanent covalent bonding of the dye molecule onto the nanofi-rous membranes.
.2. Characterization of pristine and CB immobilized PVA-co-PEanofibrous membranes
The morphologies of the PVA-co-PE and PVA-co-PE-CB nanofi-rous membranes were observed via SEM. As shown in Fig. 2,VA-co-PE nanofibrous membranes were in non-woven structuresith large amount of fine pores and quite uniform nanofibers. Theber sizes ranged from 50 to 300 nm, and the average diameteras around 150 nm. Also, no significant morphological change was
ound after the CB immobilization, suggesting good stability ofVA-co-PE nanofibrous membranes against the surface function-lization. ATR-FTIR was used to observe the chemical structuralhanges. Fig. 3 shows two main adsorption peaks of CB moleculesn the membranes, 1568 cm−1 and 1248 cm−1, corresponding tohe aromatic ring and stretching vibrations of C–N, respectively21,22]. Compared with the pristine PVA-co-PE membrane, thewo characteristic adsorption peaks on PVA-co-PE-CB membranesonfirmed the presence of CB molecules on the nanofibrous mem-ranes.
.3. BSA adsorption on PVA-co-PE-CB nanofibrous membrane
Bovine serum albumin (BSA) has been widely used as a proteinodel since the BSA has a molecular weight range similar to pro-
eins and enzymes, and also it is less costly than other biological
e and (b) CB immobilized PVA-co-PE nanofibrous membrane.
agents. In addition, BSA and CB can form a ligand–ligate pairwhich is one of the most well-known research models for affinitychromatography [23]. The feasibility of BSA adsorption onto thePVA-co-PE-CB membranes was studied by using a fluorescein isoth-iocyanate (FITC) labeled BSA (FITC-BSA) which can be visualizedunder a confocal microscope. The evenly distributed appearance ofFITC-BSA could be seen in the image (Fig. 4, right), indicating thatBSA molecules were uniformly adsorbed onto the surface of PVA-
100015002000250030003500Wavenumber (cm-1 )
Fig. 3. ATR-FTIR spectra of (a) Cibacron Blue F3GA, (b) pristine PVA-co-PE nanofi-brous membrane, and (c) PVA-co-PE-CB nanofibrous membrane.
J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276 273
ig. 5. Effect of adsorption time on BSA adsorption capacity on PVA-co-PE-CBanofibrous membranes (pH: 5.0, T: 25 ◦C and initial BSA concentration: 2 mg/mL).
.4. BSA adsorption kinetics and isotherm
As seen in Fig. 5, the amount of adsorbed BSA on the PVA-co-PE-
B membranes increased significantly in first 60 min until reachingquilibrium at 105.5 mg/g nanofiber after 90 min, while the pris-ine membrane showed almost no adsorption to BSA. At a fixeddsorption time of 2 h (Fig. 6), the amount of BSA adsorption on the
432100
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Ads
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d B
SA
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ig. 6. Effect of BSA concentration on BSA adsorption capacity on PVA-co-PE-CBanofibrous membranes (pH: 5.0, T: 25 ◦C and adsorption time: 2 h).
-co-PE nanofibrous membrane and (right) PVA-co-PE-CB nanofibrous membrane.
PVA-co-PE-CB nanofibrous membranes increased with the increaseof the initial BSA concentration, and then reached the plateau valueat about 1.5 mg/mL of the initial BSA concentration. After this point,the BSA adsorption capacity on the membrane was 105.5 mg/gnanofibers, possibly the maximum accessible CB molecules on thenanofibrous membranes. Again, the non-specific binding of BSA tothe pristine nanofibrous membrane was below 4 mg/g nanofibers,which is consistent with the confocal microscope result from theFITC-BSA adsorption experiments. The negligible amount of non-specific BSA adsorption further indicated that the PVA-co-PE-CBnanofibrous membrane possesses the specific interactions andbindings with BSA molecules. Since ideal affinity membrane mate-rials should have minimum non-specific interactions with a targetabsorbent, the PVA-co-PE nanofibrous membrane seems a promis-ing medium for development of affinity membranes.
Since the adsorption of BSA on the PVA-co-PE-CB membranesis based on bimolecular interaction, Langmuir adsorption isothermcould be employed to study this process. Langmuir equation can beexpressed by Eq. (1):
1q
= Kd
qm × C+ 1
qm(1)
where qm is the maximum adsorption capacity (mg/g), Kd is thedissociation constant of the system (mg/mL), q is the adsorbed BSA
on nanofiber (mg/g) and C is the equilibrium BSA concentration(mg/mL).
From the Langmuir isotherm plot (Fig. 7), the maximum adsorp-tion capacity (qm) of BSA on the PVA-co-PE-CB membranes and the
2.22.01.81.61.41.21.00.80.60.40.2
0.009
0.010
0.011
0.012
0.013
0.014
0.015
0.016
1/q
(g n
anof
iber
/mg)
1/C (ml/mg)
Fig. 7. Linear representation of Langmuir equation of BSA with PVA-co-PE-CBnanofibrous membranes.
274 J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276
76540
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PVA- co-PEPVA- co-PE-CB
Fb
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ig. 8. Effect of pH on BSA adsorption capacity on PVA-co-PE-CB nanofibrous mem-ranes (Temp: 25 ◦C; adsorption time: 2 h; initial BSA concentration: 2 mg/mL).
angmuir constant (Kd) were obtained as 124.22 mg/g nanofibersnd 0.25 mg/mL, respectively. Zhang and co-workers [24] reportedhat CB attached chitosan microspheres could achieve a maximumSA adsorption capacity of 108.7 mg/g. Qu et al. [25] prepared mag-etic poly(methyl methacrylate) (PMMA) nanospheres carrying theB affinity ligand, and the maximum BSA adsorption capacity ofhe materials was 121.98 mg/g. Comparing with these results, theB functionalized PVA-co-PE nanofibrous membranes obviouslyxhibited even higher BSA adsorption capacities.
.5. Effect of pH
The pH of the BSA solution could affect its adsorption on theembranes, which was varied from 4.0 to 7.0 with different buffers.o significant difference of physical adsorption on the pristineanofibrous membrane was found in various pH media (Fig. 8). But
he maximum BSA adsorption capacity on the PVA-co-PE-CB mem-rane was observed at pH 5.0, while the amount of BSA adsorptionas drastically low at either higher or lower than that pH value. The
soelectric point of BSA is at pH 4.7, close to pH 5.0. Since proteins
Fig. 10. HPLC Chromatographic result of: (Sample 1) eluted BSA from
Fig. 9. Effect of ionic strength on BSA adsorption capacity on PVA-co-PE-CBnanofibrous membranes (pH: 5.0; T: 25 ◦C; adsorption time: 2 h; and initial BSAconcentration: 2 mg/mL).
have no net charge at their isoelectric points and thus have lowestsolubility in aqueous solution [26], enhancing more BSA moleculesmoving onto adsorbent surface. Also, since the BSA molecules arenegatively charged at pH above the isoelectric points, while the CBdye molecules also carry negative charges at higher pH, which willresult in lower BSA adsorption on the membranes, consistent withthe results shown in Fig. 8.
3.6. Effect of ionic strength
When the NaCl concentration increased from 0 to 1 M, a 65.4%reduction of BSA adsorption capacity was observed (Fig. 9) on themembrane, indicating an adverse effect of increased ion strength.These results are consistent with the results reported in otherliteratures [18,27]. The addition of more salt electrolyte may depro-
tonate the sulfonate groups of CB molecules, reducing interactionsbetween the CB dye ligands on the fiber surfaces and the proteinmolecules. Thus, increasing the ionic strength played a negativerole in the BSA adsorption on the membranes.
PVA-co-PE-CB nanofibrous membrane, (Sample 2) standard BSA.
J. Zhu et al. / Journal of Membrane Science 385– 386 (2011) 269– 276 275
trum
4
tictnNetriPo
sfotaFol[tgtwf
5
afiF
Fig. 11. (A) Mass spectrum and (B) reconstructed mass spec
. Elution and reusability
It has been reported that thiocyanate ion cannot only interrupthe electrostatic interactions but also decrease the hydrophobicnteractions between BSA and CB molecules by changing the BSAonformation [19]. Herein, NaSCN solution was selected as an elu-ion medium to remove BSA from the BSA adsorbed PVA-co-PE-CBanofibrous membranes. After the membrane was placed in 1 MaSCN solution for 60 min, above 92% of the adsorbed BSA wasluted off. Also, the BSA adsorption–elution cycles were appliedo the same membrane in order to study its reusability. After 10epeating cycles, only slight decrease of 4% in BSA adsorption capac-ty was observed, suggesting the durability and reusability of theVA-co-PE-CB nanofibrous membranes in BSA adsorption and des-rption.
In order to check if the eluted BSA is identical to the originaltandard, the eluted BSA was injected to a reverse phase high per-ormance liquid chromatography coupled to an electrospray Timef Flight mass spectrometer. As seen clearly in Fig. 10, the elu-ion time of the eluted BSA is identical to the standard BSA atround 8.6 min. The mass spectrum of the eluted BSA is shown inig. 11A. The electrospray mass spectrometer generates a groupf characteristic multi-charge ions for the protein. In Fig. 11A, weabeled the multi-charge ions from [M+55H]55+ (m/z 1211.8) toM+41H]41+ (m/z 1625.5). Using the software, we reconstructedhe mass spectrum (Fig. 11B) of the eluted BSA to show the sin-le charge molecular ion, which can provide the information ofhe molecular weight. The calculated molecular weight is 66,535,hich further confirmed the purity of adsorbed BSA after elution
rom PVA-co-PE-CB nanofibrous membrane.
. Conclusion
PVA-co-PE nanofibers were fabricated via a novel process,nd PVA-co-PE nanofibrous membranes were prepared with thebers in sizes ranging from 50 to 300 nm. After Cibacron Blue3GA, a general affinity dye ligand, was covalently immobilized
of eluted BSA from PVA-co-PE-CB nanofibrous membranes.
onto the surfaces of the nanofibrous membranes, the modifiedmembrane showed specific adsorption to BSA. The immobilizeddye ligand on the membrane reached 220 mg/g nanofibers. Theresult of BSA adsorption experiments showed that the CB attachedPVA-co-PE nanofibrous membranes achieved a high BSA capturecapacity (105.46 mg/g nanofiber) at pH 5.0 while the non-specificBSA adsorption of the pristine PVA-co-PE nanofiber was negligi-ble. The elution test was performed by using 1 M NaSCN as anelution medium, and the elution efficiency was 92.5%. After 10adsorption–elution cycles, only a slight decrease of BSA capturecapacity was observed on the PVA-co-PE-CB membrane. This workdemonstrated the potential of the PVA-co-PE nanofibrous mem-branes as affinity materials for biomolecular purifications.
Acknowledgements
This research is financially supported by Defense ThreatReduction Agency (HDTRA1-08-1-0005). J. Zhu is grateful to aJastro-Shields Graduate Student Research Fellowship Award at Uni-versity of California, Davis.
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