Scholarly article on topic 'Grafting Amino-acid Molecular Imprinted Polymer on Carbon Nanotube for Sensing'

Grafting Amino-acid Molecular Imprinted Polymer on Carbon Nanotube for Sensing Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — N. Farhanah. Ab. Halim, M. Noor. Ahmad, A.Y. Md. Shakaff, N. Deraman

Abstract Molecular imprinted polymer (MIP) is a good matrix that exhibit satisfactory recognition ability when integrated onto sensing transducer. We report on the preparation of such material by graft-polymerizing MIP on the surface of carbon nanotube (CNT) as using MIP as a probe material for chemical sensor fabrication. The MIP is characterized by Fourier transform infrared analysis and UV-Vis analysis. The batch binding analysis is carried out to analyze selective recognition of MIP towards serine (amino acid). SEM images showed the structure of MIP on CNT surface. The serine-imprinted polymer grafted on CNT possessed higher binding capacity for serine than non-imprinted polymer (NIP) grafted on CNT.

Academic research paper on topic "Grafting Amino-acid Molecular Imprinted Polymer on Carbon Nanotube for Sensing"

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Engineering

ELSEVIER Procedía Engineering 53 (2013) 64 - 70

www. el sevi er. com/1 ocate/procedi a

Malaysian Technical Universities Conference on Engineering & Technology 2012, MUCET 2012 Part 3 - Civil and Chemical Engineering

Grafting Amino-acid Molecular Imprinted Polymer on Carbon Nanotube

for Sensing

N. Farhanah. Ab. Halima*, M. Noor. Ahmada, A. Y. Md. Shakaff and N. Deramana

aCentre of Excellence for Advanced Sensor Technology (CEASTech), Pusat Pengajian Jejawi II, Taman Muhibah, University Malaysia Perlis, 02600 Arau, Perlis,Malaysia.

Abstract

Molecular imprinted polymer (MIP) is a good matrix that exhibit satisfactory recognition ability when integrated onto sensing transducer. We report on the preparation of such material by graft-polymerizing MIP on the surface of carbon nanotube (CNT) as using MIP as a probe material for chemical sensor fabrication. The MIP is characterized by Fourier transform infrared analysis and UV-Vis analysis. The batch binding analysis is carried out to analyze selective recognition of MIP towards serine (amino acid). SEM images showed the structure of MIP on CNT surface. The serine-imprinted polymer grafted on CNT possessed higher binding capacity for serine than non-imprinted polymer (NIP) grafted on CNT.

© 2013TheAuthors.Publishedby ElsevierLtd.

Selectionandpeer-reviewunderresponsibility oftheResearch Management & InnovationCentre, Universiti Malaysia Perlis

Keywords: Molecular imprinted polymer ; grafted carbon nanotube ; amino acid..

1. Introduction

Molecular imprinted is a technique to produce template-shape cavities in polymer matrices with memory of the template molecules to be used in molecular recognition. The molecular recognition on molecular imprinted polymer (MIP) matrices provides strong and specific binding between molecule and substrate. MIP are cross linked polymers that synthesized by the existing of template molecule that binds with functional monomer during the copolymerization of the functional monomer and cross linking agent. After the polymerization, the templates are removed by washing procedure and would leave cavities in the polymers. These cavities provide recognition sites for the template molecules which own the geometrical, affinity and binding properties of the template .Template molecules would rebind selectively in the cavities.

It has been reported that there are two types of interaction between the template and functional monomer. Those interactions are covalent bond and non-covalent bond. The interaction between the template and functional monomer is very important and it will determine the selectivity and sensitivity of MIPs. Since most of biological interactions in nature are conducted by non-covalent interaction, many researches have been carried out to imitate the processes [1]. In recent times, non-covalent becomes the most frequent used method for producing MIP because of easier to produce, shorter response time for rebinding of template and variety of functional monomers .

MIP has been established as a sensing material for sensor fabrication. A lot of research have been done with many kind of sensing transducers such as IDE (interdigitated electrode), FET (field effect transistor) and SAW (surface acoustic wave) sensors. Recently MIP have been used for carbon nanotube field effect transistor (CNT-FET), MIP are immobilized on the carbon nanotube surface and MIP-CNT is aligned between the source and drain of transistor. The fabrication of CNT-FET was an effort to develop a chemosensor based on CNT transistor using MIP as sensing material [2-11].

1877-7058 © © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of the Research Management & Innovation Centre, Universiti Malaysia Perlis doi:10.1016/j.proeng.2013.02.011

Currently, CNT-FET are widely used as biosensor and chemosensor due to its ability to directly translate the interaction with templates "target" on CNT-FET surface into readable signal. Furthermore using CNT-FET as sensing transducer could provide a device with a high selectivity and sensitivity, real-time response and label-free detection capabilities. A CNT-FET transducer will be able to optimize the MIP sensing because of high surface to volume ratio, these characteristic will improve accessibility to the target species and reduce mass transfer resistance, for fast sensor response[12]. The purpose of this studies is to immobilize MIP on the surface of CNT for amino acid detection. In order to produce a chemosensor on CNT-FET using MIP as sensing material.

2. Material and Method

Tween 20, dimethyl sulfoxide(DMSO), acetic acid, toluene, L-valine, L-Serine,3-chloropropyl trimethoxysilane, methacrylate acid(MAA), ethylene glycol dimethacrylate (EDGMA), sodium N,N-diethyldithiocarbamate trihydrate and Azobisisobutyronitrile(AIBN), were obtained from Aldrich. Single-walled CNT (product No: P2-SWNT) is obtained from Carbon Solutions Inc., Canada.

The method of MIP grafting on CNT is introduced by H.-Y. Lee et al [13]. CNT is first functionalized using Tween 20.Carbon nanotubes were dissolved in Tween 20:distilled water (1:9) mixture for 15 minutes. Then the hydroxyl-functionalized CNT obtained and are dissolved in 3-chloropropyltrimethoxysilane in toluene 10% (w/w) solution. Then, the reaction mixture is heated at 80°C for 4 hours. After the reaction the mixture is filtered. The solvent is removed and the remaining CNT is dried. The activated CNT is soaked in 0.29M ethanol solution of sodium N,N-diethyldithiocarbamate trihydrate. The mixture is stirred (700 rpm) for 18 hours at room temperature and then photoactive iniferter-CNT is formed (fig.1(c)).A 0.43045g (5mmol) of MAA, 0.11715g (1mmol) of serine, and 3.9644g (20mmol) of EDGMA were dissolved in 33ml dimethyl sulfoxide (DMSO). The activated CNT was soaked into the reaction mixture and the irradiated with a UV lamp at room temperature for 2 hours to cause radical copolymerization. MIP-immobilized CNT were collected by filtration, after photopolymerization process. Then MIP-immobilized CNT were stirred in DMSO/acetic acid (9:1, v/v) in order to extract serine and the remaining CNT were dried. Non-imprinted polymer (NIP) was prepared without serine.

The FT-IR spectra of grafted MIP and NIP (non-imprinted polymer) were measured using a FT-IR_spectrometer. The surface morphology analysis of CNT grafted MIP was done by scanning electron microscope. For rebinding experiment, it was monitored by UV-Vis spectrometer at wavelength 300nm. A 50mg of polymers (both for MIP and NIP) were incubated in 6ml of serine in acetic acid(24^g/ml is the initial concentration of serine) and 50mg MIP were incubated in 6ml of valine in acetic acid(24^g/ml is the initial concentration of valine). The samples are shook at 180rpm by orbital shaker. After incubation, the final concentration was checked using UV-VIS Spectrometer at wavelength 300nm. The amount of serine and valine bound to polymer, Q is calculated using equation:

Where V, w, Ci and Cf represent the volume of solution(ml), weight of polymer(mg), initial solution concentration (^g/ml) and final solution concentration (^g/ml) after a few hours of incubation. For imprinting factor (IF) value, the incubation

takes about 24hours, IF is calculated to find the most efficient imprinting effect using the equation:

¡p = ®M,P

Where QMIP and QNIP are the total binding amount of serine or valine for MIP and NIP, respectively.

? W /mI ) -

3. Result and Discussion

A typical imprinting procedure should have a type of template, functional monomer, a cross linker and an initiator.

The hydroxyl-functionalized CNT were dissolved in 3-chloropropyltrimethoxysilane in toluene 10% (w/w) solution.

Then, the reaction mixture was heated at 80»C for 4 hours.

•Methyl methacrylate acid(functional monomer), serine(template), and EDGMA(cross linker) were dissolved in dimethyl sulfoxide (DMSO).

Then M IP-grafted CNT were stirred in DMSO/acetic (9:1) acid solution In order to extract out valine from the activated CNT.

Fig.1. Schematic diagram for the immobilization of MIP on CNT surface. (a) CNT surface is functionalized with hydroxyl group. (b) 3-chloropropyl groups introduced on CNT surface by silane coupling.(c) photoactive inifereter is introduced (d) MIP are formed by photografting polymerization. (e) Template is removed by extraction.

For this study, the technique of photografting polymerization was used for the fabrication of MIPs. Firstly the carbon nanotube(CNT) was soaked in Tween 20(Figure 1(a)), the hydrocarbon chains in Tween 20 interact with carbon nanotube. Then, CNT functionalized with hydroxyl group was formed. The Tween 20 introduced hydroxyl on the surface of CNT because the hydroxyl groups are important for introduced 3-chloropropyl groups by silane coupling (Figure 1(b)). The method of immobilizing an inerferter on CNT surface is the key of photografting polymerization method. The photoactive layer was grafted to the CNT surface(Figure 1(c)). Photoactive means that it will undergo a chemical reaction with the existence of sunlight or ultra-violet light. A polymerized feature was capped with the iniferter, which is photoactive. Inerferter means initiator, transfer agent and terminator. Then, polymerization takes place via the active radical attached to the CNT (Figure 1(d)). The SEM images in Figure 2 shows that the surface of MIP grafted CNT's surface rougher then surface of pristine CNT.

(a) Pristine CNT Sf

(b) Serine-imprinted Polymer CNT *

Fig. 2.Scanning electron micrograph (SEM) of (a) pristine CNT (b) serine-imprinted polymer CNT

Fourier transforms infrared spectroscopy measures intensity over a narrow range of wavelengths at a time. The infrared spectrum of CNT grafted MIP (molecular imprinted polymer) are shown figure 3.

Fig. 3.FTIR spectrum of MIP showing rebinding and remove spectrum

The IR spectra of molecular imprinted polymer during rebinding indicates the stretching vibrations at 3454.15 cm-1 which correspond to -OH stretching vibrations, respectively shift a bit to 3440.82 cm-1 during the removal process, the spectral differences came about from the interaction between template and monomer to gave changeable peaks in the MIP spectrum. There are differences of absorbance between rebinding and removal process, the absorbance for -OH stretch in rebinding is 0.02812 and for removal is 0.062711.Since the absorbance of -OH stretch during removal is increased therefore more -OH radical are available and ready for hydrogen bonding with serine, the higher absorbance are observed. A broad peak that vibrated between 1718.14 cm-1(after exposing with Serine)and 1659.59 cm-1 (during removal) shows carbonyl (C=O) stretching band. The spectral differences arised from the interaction between template and monomer gave changeable peaks in the MIP spectrum .The absorbance increase from 0.026712(rebinding) to 0.038798(removal).The absorbance spectrum of rebinding process is much lower than the removal process due to the number of C=O radical that occupied during the hydrogen bonding process. The differences of the absorbance also shown that C=O molecules that exist in MIP reduced during the rebinding. Apart from that the number of C=O molecules that involved in hydrogen bonds interaction with the template (serine) would reduce the quantity of C=O radicals in MIP and thus reduce the absorbance. The spectrum of MIP shows that a few peaks at 1436.33 are indeed the region of strong -OH in-plane and at 952.37 are the expected -OH out-of-plane bending mode. Meanwhile, the absorbance during the rebinding of MIP with serine emit a low absorbance, it is because the number of -OH radical that involved in the interaction.

Fig. 4.FTIR spectrum of NIP showing rebinding and remove spectrum

Figure 4 shows the FTIR spectrum for NIP where C=O stretch found at 3411.69 cm-1 (rebinding) and 3398.39 cm-1 (removal) with the respective absorbance of 0.035990 to 0.043831. C=O radical play an important role as electrons acceptors during rebinding and removal process of serine and other templates. The existence of C=O stretching band is not sufficient to proof the availability ofhydrogen bonding interaction between -COOH of MIP. Other functional group's bands

such as -OH stretch and out of plane -OH must be found to confirm the existence of methacrylate acid. A broad peak of -OH stretch obtained at 3411.69 cm-1 (rebinding) and 3398.39 cm-1 (removal) with a small differences of absorbance from 0.035990 (rebinding) to 0.043831 (removal). The out-of-plane -OH bending of NIP appeared at 950.33cm-1 (rebinding) and 951.42 cm-1 (removal) with small difference absorbance value of 0.018293.

Fig. 5.Binding profile of serine and valine imprinted polymer and serine non-imprinted polymer on CNT

Figure 5 shows representative batch binding analysis of serine and valine to the serine-imprinted polymer. The data (Figure 5), showed binding amount of MIP and NIP are increased with increasing of serine concentration. Binding analysis was carried out by incubating 50mg of MIP and NIP in solutions of serine in acetic acid and valine in acetic acid. The adsorption time was 2 hours. The data (Figure 3) showed binding amount of MIP and NIP are increased. The binding amount is saturated at 24^g/ml. The saturation normally occurred when all binding sites are occupied with serine and it can no longer diffuse into the polymer. The binding amount of serine adsorbed by MIP shows higher capacity compare to NIP in the entire range of concentrations. The binding amount of valine adsorbed by MIP shows lower capacity because MIP prepared with serine as a template has cavity sites that compliment towards serine only. The binding amount of MIPs at 120 min were 8.435^g/ml for serine and 7.417^g/ml for valine, which was 1.13 times higher than for valine. The behavior occurred because MIP consist of complimentary interaction, shape, size and binding sites that similar to serine.

Fig. 6.Imprinting Factor (IF) of serine-imprinted polymer towards serine and valine.

The effectiveness of prepared polymer is further discussed using imprinting factor value. Figure 6 shows that the composition of serine-imprinted polymer has the IF value which is 9.01 for serine and 1.08 for valine. The lower value of valine IF means that valine is not bound well in MIP which is prepared serine as template. Sufficient binding sites will results higher binding amount,Q and lead to higher IF.

4. Conclusion

It is found that higher binding capacity of serine-imprinted polymer towards serine. The smaller results for binding amount of NIP proves that NIP has less ability for binding interaction with serine. Together with other analysis, FTIR spectrum and SEM images, shows that MIPs were successfully grafted on CNT surface. The MIP grafted CNT is suitable biosensor and chemo sensor fabrications.

5. Acknowledgement

This research was financially supported by FRGS(Fundamental Research Grant Scheme) from the Malaysian Ministry of Higher Education.

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