Molecular imprinted polymer
Encyclopedia
A Molecularly Imprinted Polymer (MIP), or plastic antibody
is a polymer
that is formed in the presence of a molecule that is extracted afterwards, thus leaving complementary cavities behind. These polymers show a certain chemical affinity
for the original molecule and can be used to fabricate sensors, catalysis or for separation methods. The functional mechanism is similar to antibodies or enzymes.
However, one of the greatest advantages of artificial receptors over naturally occurring ones is freedom of molecular design. Their frameworks are never restricted to proteins, and a variety of skeletons (e.g., carbon chains and fused aromatic rings) can be used. Thus, the stability, flexibility, and other properties are freely modulated according to need. Even functional groups that are not found in nature can be employed in these man-made compounds. Furthermore, when necessary, the activity to response towards outer stimuli (photo-irradiation, pH change, electric or magnetic field, and others) can be provided by using appropriate functional groups. The spectrum of functions is far wider than that of naturally occurring ones.
In a molecular imprinting processes, one need a 1) template, 2) functional monomer
3) crosslinker, 4) initiator
, 5) porogenic solvent and 6) extraction solvent. According to polymerization method and final polymer format one or some of the reagent can be avoided.
Over the recent years, interest in the technique of molecular imprinting has increased rapidly, both in the academic community and in the industry. Consequently, significant progress has been made in developing polymerization methods that produce adequate MIP formats with rather good binding properties expecting an enhancement in the performance or in order to suit the desirable final application, such as beads, films or nanoparticles. One of the key issues that have limited the performance of MIPs in practical applications so far is the lack of simple and robust methods to synthesize MIPs in the optimum formats required by the application.
Chronologically, the first polymerization method encountered for MIP was based on “bulk” or solution polymerization. This method is the most common technique used by groups working on imprinting especially due to its simplicity and versatility. It is used exclusively with organic solvents mainly with low dielectric constant and consists basically of mixing all the components (template, monomer, solvent and initiator) and subsequently polymerizing them. The resultant polymeric block then pulverized, freed from the template, crushed and sieved to obtain particles of irregular shape and size between 20 and 50 µm.
Depending on the target (template) type and the final application of the MIP, MIPs are appeared in different formats such as nano/micro spherical particles, nanowires and thin film or membranes. They are produced with different polymerization techniques like bulk
, precipitation
, emulsion
, suspension
, dispersion
, gelation, multi-step swelling polymerization. Most of investigators in the field of MIP are making MIP with heuristic techniques such as hierarchical imprinting method. The technique for the first time was used for making MIP by Sellergren et al for imprinting small target molecules. With the same concept, Nematollahzadeh et al developed a general technique, so-called polymerization packed bed, to obtain a hierarchically structured high capacity protein imprinted porous polymer beads by using silica porous particles for protein recognition and capture.
produces SupelMIP for Beta-agonists, Beta-blockers, pesticides and some drugs of abuse such as Amphetamine
.
Fast and cost-effective molecularly imprinted polymer technique has applications in many fields of chemistry, biology and engineering, particularly as an affinity material for sensors, detection of chemical, antimicrobial
, and dye, residues in food, adsorbents for solid phase extraction
, binding assays, artificial antibodies, chromatographic stationary phase, catalysis, drug development and screening, and by-product removal in chemical reaction.
Shortly after this work had appeared, molecular imprinting attracted wide interest from the scientific community as reflected in the 4000 original papers published in the field during for the period 1931-2009 (from Scifinder).
However, although interest in the technique is new, commonly the molecularly imprinted technique has been shown to be effective when targeting small molecules of molecular weight <1000. Therefore, in following subsection molecularly imprinted polymers are reviewed into two categories, for small and big templates.
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
that is formed in the presence of a molecule that is extracted afterwards, thus leaving complementary cavities behind. These polymers show a certain chemical affinity
Chemical affinity
In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds...
for the original molecule and can be used to fabricate sensors, catalysis or for separation methods. The functional mechanism is similar to antibodies or enzymes.
Molecular Imprinting technique (State of the art and perspectives)
Molecular imprinting is, in fact, making an artificial tiny lock for a specific molecule that serve as miniature key. Like plastic receptors the imprinted polymer grabs specific chemicals. Many basic biological processes, from sensing of odours to signalling between nerve and muscle cells, rely on such lock-and-key combinations. For decades, scientists trying to understand these interactions often play locksmith, searching for the right key to fit a particular receptor. Now, the elegance of molecular imprinting in nature has been spurring many scientists to build the locks themselves. They etch a material to create specific cavities which in size, shape and functional groups, fit the target molecule.However, one of the greatest advantages of artificial receptors over naturally occurring ones is freedom of molecular design. Their frameworks are never restricted to proteins, and a variety of skeletons (e.g., carbon chains and fused aromatic rings) can be used. Thus, the stability, flexibility, and other properties are freely modulated according to need. Even functional groups that are not found in nature can be employed in these man-made compounds. Furthermore, when necessary, the activity to response towards outer stimuli (photo-irradiation, pH change, electric or magnetic field, and others) can be provided by using appropriate functional groups. The spectrum of functions is far wider than that of naturally occurring ones.
In a molecular imprinting processes, one need a 1) template, 2) functional monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
3) crosslinker, 4) initiator
Initiator
An initiator can refer to:* A person that takes an initiative in making something happen.* Modulated neutron initiator, a neutron source used in some nuclear weapons...
, 5) porogenic solvent and 6) extraction solvent. According to polymerization method and final polymer format one or some of the reagent can be avoided.
Chronologically, the first polymerization method encountered for MIP was based on “bulk” or solution polymerization. This method is the most common technique used by groups working on imprinting especially due to its simplicity and versatility. It is used exclusively with organic solvents mainly with low dielectric constant and consists basically of mixing all the components (template, monomer, solvent and initiator) and subsequently polymerizing them. The resultant polymeric block then pulverized, freed from the template, crushed and sieved to obtain particles of irregular shape and size between 20 and 50 µm.
Depending on the target (template) type and the final application of the MIP, MIPs are appeared in different formats such as nano/micro spherical particles, nanowires and thin film or membranes. They are produced with different polymerization techniques like bulk
Bulk
-Industry:* Bulk cargo* Bulk liquids* Bulk mail* Bulk material handling* Bulk pack, packaged bulk materials/products* Bulk purchasing- Physics :*Bulk density*Bulk modulus...
, precipitation
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
, emulsion
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
, suspension
Suspension
Suspension may refer to:In science and engineering:*Suspension , in mathematics*Suspension , in mathematics*Suspension , mixture of two chemicals with the property that one does not rapidly settle out...
, dispersion
Dispersion
Dispersion may refer to:In physics:*The dependence of wave velocity on frequency or wavelength:**Dispersion , for light waves**Dispersion **Acoustic dispersion, for sound waves...
, gelation, multi-step swelling polymerization. Most of investigators in the field of MIP are making MIP with heuristic techniques such as hierarchical imprinting method. The technique for the first time was used for making MIP by Sellergren et al for imprinting small target molecules. With the same concept, Nematollahzadeh et al developed a general technique, so-called polymerization packed bed, to obtain a hierarchically structured high capacity protein imprinted porous polymer beads by using silica porous particles for protein recognition and capture.
Applications
Niche areas for application of MIPs are in sensors and separation. Despite the current good health of molecular imprinting in general one difficulty which appears to remain to this day is the commercialization of molecularly imprinted polymers. Even though no molecularly imprinted silica product has reached the market yet, at least several patents (123 patents, up to 2010, according to Scifinder data base), on molecular imprinting, were held by different groups. That some commercial interest existed is also confirmed by the fact that Sigma-AldrichSigma-Aldrich
Sigma-Aldrich Corporation , is a life science and high technology company with over 7,600 employees and operations in 40 countries. Its chemical and biochemical products and kits are used in scientific research, biotechnology, pharmaceutical development, the diagnosis of disease, and as key...
produces SupelMIP for Beta-agonists, Beta-blockers, pesticides and some drugs of abuse such as Amphetamine
Amphetamine
Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
.
Fast and cost-effective molecularly imprinted polymer technique has applications in many fields of chemistry, biology and engineering, particularly as an affinity material for sensors, detection of chemical, antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...
, and dye, residues in food, adsorbents for solid phase extraction
Solid phase extraction
Solid-phase extraction is a separation process by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties. Analytical laboratories use solid phase extraction to concentrate and purify...
, binding assays, artificial antibodies, chromatographic stationary phase, catalysis, drug development and screening, and by-product removal in chemical reaction.
History
In a paper published in 1931, Polyakov reported the effects of presence of different solvents (benzene, toluene and xylene) on the silica pore structure during drying a newly prepared silica. When H2SO4 was used as the polymerization initiator (acidifying agent), a positive correlation was found between surface areas, e.g. load capacities, and the molecular weights of the respective solvents. Later on, in 1949 Dickey reported the polymerization of sodium silicate in the presence of four different dyes (namely methyl, ethyl, n-propyl and n-butyl orange). The dyes were subsequently removed, and in rebinding experiments it was found that silica prepared in the presence of any of these "pattern molecules" would bind the pattern molecule in preference to the oth er three dyes. Shortly after this work had appeared, several research groups pursued the preparation of specific adsorbents using Dickey's method. Some commercial interest was al so shown by the fact that Merck patented a nicotine filter, consisting of nicotine imprinted silica, able to adsorb 10.7% more nicotine than non-imprinted silica. The material was intended for use in cigarettes, cigars and pipes filters.Shortly after this work had appeared, molecular imprinting attracted wide interest from the scientific community as reflected in the 4000 original papers published in the field during for the period 1931-2009 (from Scifinder).
However, although interest in the technique is new, commonly the molecularly imprinted technique has been shown to be effective when targeting small molecules of molecular weight <1000. Therefore, in following subsection molecularly imprinted polymers are reviewed into two categories, for small and big templates.