scientific

2. • In the past few years, molecular imprinting has been considered as a promising method which allows the
creation of synthetic receptors, namely MOLECULARLY IMPRINTED POLYMERS (MIPS)
consisting of highly cross-linked porous-rich polymers with recognition properties comparable to the
biological antibody−antigen systems.
• As such, they operate by a “lock and key” mechanism to selectively bind the molecule with which they
were templated during production.
• Molecular imprinting allows the creation of artificial recognition sites in synthetic polymers, these sites are
tailor-made in situ by co-polymerization of functional monomers and cross-linkers around the template
molecules. The print molecules are subsequently extracted from the polymer, leaving accessible
complementary binding sites in the polymeric network to a target molecule.

4. • And since Molecularly imprinted polymers, MIPs, are best described as synthetic analogues to the natural,
biological antibody−antigen systems. They potentially offer THE SPECIFICITY AND SELECTIVITY of
the biological receptors with the explicit advantages of durability with respect to environmental conditions
and low cost.
• For example, Natural receptors typically require storage and application at temperatures in the range
of the human body temperature, while MIPs, based on a polymer host :
• can usually be stored indefinitely,
• as a rule do not require special environmental storage conditions,
• and can be applied over a much wider temperature range.
• So they’re capable of withstanding much harsher conditions such as high temperature, pressure,
extreme pH, and organic solvents compared to proteins and nucleic acids.

5. • An ADDITIONAL ADVANTAGE of the synthetic receptors is near universality,
especially with regard to small molecules. MIPs can be produced for almost any target
molecule, which contrasts with the biological systems where the target must match an
available antibody or an antibody must be specifically produced for that target.
• Nevertheless, molecular imprinting technology still needs TO OVERCOME SOME
WEAKNESS, such as template leakage, poor accessibility of the binding sites, low
binding capacity and non-specific binding.

6. • We specifically focus on the application of these polymers as SENSORS.
• In these applications, the polymers are paired with a reporting system, which may
be electrical, electrochemical, optical, or gravimetric. The presence of the targeted
molecule effects a change in the reporting agent, and a calibrated quantity of the
target is recorded.
• The standard definition of sensor as contained in the Oxford dictionaries is
adopted: “A device which detects or measures a physical property and records,
indicates, or otherwise responds to it”.

7. • MIP-based potentiometric sensors are a promising and useful
technology for detection of environmental contaminants, hazardous
substances and bio analytes due to their low cost, ease of operation,
excellent selectivity and high stability. The past few decades have
witnessed remarkable achievements in MIP-based potentiometric
sensors.

9. Table of content:
Particle size, shape
Chemical properties
Adsorption capacity
Binding isotherm models

10. 1. SEM
2. TEM
3. Laser particle size
analyzer
• The high magnification, high-
resolution imaging of Scanning
Electron Microscopy (SEM) analysis
supports the determination of the
number, size, and morphology of
small particles.
• Transmission Electron Microscopy
(TEM) provides much higher
resolution than is possible with light-
based imaging techniques. TEM is the
preferred method to directly measure
nanoparticle size, grain size, size
distribution, and morphology.
• Laser diffraction particle size
analyzers are used to measure
the sizes of particles in a
material. Particle size is calculated by
measuring the angle of light scattered
by the particles as they pass through
a laser beam.
Particle size, shape

12. • FTIR offers quantitative and qualitative analysis for organic and inorganic samples.
• Fourier Transform Infrared Spectroscopy (FTIR) identifies chemical bonds in a molecule by producing an infrared absorption
spectrum. The spectra produce a profile of the sample, a distinctive molecular fingerprint that can be used to screen and scan
samples for many different components. FTIR is an effective analytical instrument for detecting functional groups and characterizing
covalent bonding information.
1. FT-IR (Fourier Transform Infrared Spectroscopy)
• Solid-state 13C nuclear magnetic resonance (NMR) is a spectroscopic method that yields results sensitive to the local atomic
environment and which has been used in studies of carbon materials of diverse types. In the 13C NMR spectra of these materials,
contributions due to aromatic and aliphatic groups are readily separated based on the 13C isotropic chemical shifts, which fall
typically between 0 and 90 ppm for aliphatic and in the range 110–160 ppm for aromatic groups.
2. Solid state NMR (13C )
• Elemental analysis, also known as carbon hydrogen nitrogen sulfur (CHNS) analysis, is a destructive method of choice for fibers
with organic backbones. It can determine the percentage of carbon, hydrogen, nitrogen, and sulfur by combustion of nanofibers and
subsequent analysis of the gases produced
3. Elemental analysis (H,C,N)
• X-ray diffraction (XRD) characterization is a powerful nondestructive technique for characterizing crystalline materials.
• It provides information on crystal structure, phase, preferred crystal orientation (texture), and other structural parameters, such as
average grain size, crystallinity, strain, and crystal defects
4. X-ray diffraction (XRD)
Chemical properties

14. • MIPs are much like other porous adsorbents in which physisorption occurs through interaction
with surface functional groups. Since isotherm models have been developed to account for
adsorbate binding with materials of both heterogeneous and homogeneous binding sites, these
models can be applied to MIPs.
• Adsorption isotherm models have already been used to characterize interactions between analytes
and MIP surfaces to enhance understanding of the adsorption chemistry.
• Models that are applied to MIPs include Langmuir (LI), Freundlich (FI), and
Langmuir−Freundlich (L-FI) isotherms. Although the Brunauer, Emmett, and Teller (BET)
isotherm model has not been previously used to characterize MIPs, its ability to model multilayer
formation warrants investigation of its Suitability.
Adsorption capacity isotherm models

15. • A key element of the isotherm models is the idea that polymer surfaces can be classified based on
two types of recognition, homogeneous and heterogeneous, which influence the choice of the
isotherm model.
• In a HOMOGENEOUS POLYMER, the binding sites have the same energy, which suggests
consistent distribution and orientation of functionalities for the accessible sites on the polymer
surface. In such a system, the affinity of the analyte for the surface is independent of concentration.
• In a HETEROGENEOUS POLYMER, the binding sites available can have a range of energies
leading to significant differences in binding affinities depending on the concentration of the analyte.
Adsorption capacity isotherm models

16. • The adsorption models are classified into TWO GROUPS:
• (i) models of discrete distribution for the homogeneous surface and
• (ii) models of continuous distribution that take into consideration the surface heterogeneity.
• The LI and bi-LI are the most common discrete models where LI describes only one type of
binding site and bi-LI two.
• The BET isotherm model is an extension of the LI model, incorporating the possibility of the
formation of multilayers of adsorbate on the sorbent surface.
• The FI and L-FI are the most common continuous distribution models.
Adsorption capacity isotherm models

17. • Langmuir isotherm
• Brunauer, Emmett, and Teller
(BET)
Discrete
Distribution Models
• The hybrid L-FI model
• Freundlich isotherm
Continuous
Distribution Models.
Adsorption isotherm models

18. Discrete Distribution Models
• In 1916, Irving Langmuir introduced a new adsorption isotherm model to describe the adsorption
behavior of gaseous molecules onto a solid surface at a constant temperature; the eponymous
Langmuir isotherm is the most widely used model for adsorption studies.
• LI assumes that
1. all surface binding sites are the same,
2. adsorption cannot occur beyond monolayer coverage,
3. and each binding site can be occupied by only one molecule.
• The LI model has been used to characterize MIP adsorption based on these assumptions.
The Langmuir equation illustrates the assumed relationship between the amount of bound (B) analyte and the
free analyte in the system (Ce) at equilibrium:
where N is the binding site density and K is the adsorption constant (a measure of the adsorbate affinity).

19. • In 1938, Brunauer, Emmett, and Teller proposed a multilayer adsorption model, giving their
names to the common abbreviation BET.
• In this model, gas−solid adsorption begins with formation of an incomplete monolayer (n = 1)
to which additional molecules are adsorbed through intermolecular interactions to form layers
(n = 2 → ∞).
• BET assumes the following:
(i) there is no interaction between the solute molecules,
(ii)the adsorbent surface is homogenous, and
(iii)adsorption can occur in multilayers as the adsorbed molecules provide adsorption sites,
WHICH IS A KEY FEATURE OF THE MODEL.
Discrete Distribution Models

20. Discrete Distribution Models
• The general form of the BET isotherm is shown in
• For the gas−solid adsorption,
• x is the ratio of the partial pressure of the adsorbate to saturation vapor pressure of the system (x =
P/Psat)
• c = KS/KL where KS is the equilibrium adsorption constant for the first layer and KL is the equilibrium
adsorption constant for all upper layers (related to intermolecular interactions between adsorbed solute
molecules)
• n is the number of adsorbed layers.
• q is the amount (moles or mass) of analyte adsorbed relative to the mass of sorbent.
• qm is the amount adsorbed corresponding to formation of a complete monolayer.

21. Discrete Distribution Models
• This is the general form of the BET isotherm model can be simplified
and rearranged to the linear form which estimates the adsorption
capacity for the monolayer (qm) and the relative adsorption
equilibrium constants (as c) can be calculated from the slope and the
intercept using the linear regression of data for q and x.

22. Continuous Distribution Models.
• In 1906, Freundlich presented a model of the relationship between the amount of gas adsorbed
per unit mass of adsorbent and pressure at a constant temperature.
• The FI is the most familiar continuous distribution isotherm model providing a descriptor of the
surface binding site energy heterogeneity, which can be more useful than the LI model as most
solid surfaces, including MIPs tend to be heterogeneous.
• The FI assumes a power function relationship between B and Ce where B and Ce are the
concentrations of bound and the free analyte respectively.
• The pre-exponential constant a is the product of the total number of binding sites (Nt) and average binding
affinity (Kο), m is the heterogeneity index and is constrained to values between 0 and 1.
• Systemswithmcloserto1aremorehomogeneous.
.

23. Continuous Distribution Models.
• This equation can be linearized to give this:

24. Continuous Distribution Models.
• In 1948, Sips described the hybrid L-FI model, which gives the Langmuir binding parameters along with the
heterogeneity index, m, as found in the FI.
• This means that the LFI isotherm can be applied to homogeneous and heterogeneous MIPs.
• In the L-FI model, a relationship between the concentration of a bound analyte (B) and the free analyte
concentration in the solution (Ce) is described by:
• where Nt represents the total number of binding sites,
• a is related to the affinity constant,
• Kο = a1/m, and m is the heterogeneity index

25. Binding isotherm models used to characterize binding sites
in imprinted polymers
1. Batch binding
studies
2. Frontal
chromatographic
analysis
3. Radioligand
binding studies
4. Calorimetry

26. • The simplest possible experiment to characterize the properties of an imprinted material involves
incubating a known mass of material (MMIP, in g), with a known quantity of analyte (nanalyte, in mol) in
a known volume of solvent (V, in L or mL).
• Once equilibrium has been reached (minutes, or hours, depending on the nature of the material), some
will have bound to the material and some remains free in solution. The material is separated from the
solution by filtration or the supernatant can be carefully removed and the free concentration F
remaining in solution is measured. The incubation time for most assays is the time required for 90% of the
template to bind.
• The equilibrium free concentration of template F, is determined using a calibration curve of the
molecule versus UV–vis absorption, fluorescence, room temperature phosphorescence or radioactivity,
while the equilibrium bound template concentration B, is calculated by simple subtracting free from total.
1. Batch binding studies

28. • Frontal analysis has been applied to elucidate template–imprinted polymer interactions and
to estimate the adsorption energies and saturation capacities in the binding of templates to MIPs.
• In this technique, a solution containing a known concentration of the template to be studied is
continuously applied to a molecularly imprinted chromatographic column.
As the template binds to the imprinted polymer, the polymer becomes saturated and once the bound
concentration of template reaches equilibrium with the concentration in the mobile phase over the whole
of the column no more template can bind, and the template begins to elute from the column, the
concentration in the eluent soon becoming the same as in the mobile phase which continues to be fed on to
the column. So, the amount of template eluting from the column gradually increases, forming a
characteristic breakthrough curve.
• The measured parameter is the breakthrough time, t breakthrough which is the interval from the point
at which the mobile phase is changed, to the time when the analyte appears in the eluent.
2. Frontal chromatographic analysis

29. • A variation on the batch binding assay is where, rather than incubating
polymer and analyte in the assay solvent, a mixture of polymer, analyte
and radio labelled probe are incubated in the assay solvent. When the
radio labelled probe is simply an isotopic variant of the analyte, it may be
assumed that the probe binding directly reflects the analyte binding.
3. Radioligand binding studies

30. • When the target analyte (or a competitor) binds to an imprinted
binding site, there is expected to be a change in enthalpy H.
• If the binding process is thermodynamically favorable then the change
in Gibbs free energy, G for the process must be negative, where G
is related to the changes in enthalpy and entropy, S :
:
4. Calorimetry

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33. THANK YOU