P.ghosh Protein Adsorption Lecture

NPTEL Chemical Engineering Interfacial Engineering Module 8: Lecture 1

Joint Initiative of IITs and IISc Funded by MHRD 1/20

Biointerfaces

&

Adsorption of Proteins at Soild Surfaces

Dr. Pallab Ghosh

Associate Professor

Department of Chemical Engineering

IIT Guwahati, Guwahati–781039

India



Table of Contents

Section/Subsection Page No. 8.1.1 Introduction 3

8.1.2 Adsorption of proteins at solid surfaces 4–18

8.1.2.1 Proteins 4

8.1.2.2 Adsorption 7

8.1.2.3 Driving force for protein adsorption 14

Exercise 19

Suggested reading 20



8.1.1 Introduction

Life sciences deal directly or indirectly with biological systems. Living systems

are heterogeneous, made up largely of proteins, polysaccharides and self-

assembled amphiphilic molecules, all contained in aqueous medium.

Many processes controlling life occur at the interfaces. For example, the

biological membrane itself is a self-assembled structure of phospholipids and

glycoproteins. Glycoproteins on the cell wall participate in cellular aggregation

and growth. Proteins of the reticuloendothelial system are involved in

phagocytosis.

Aggregation of protein molecules is responsible for the malfunction of the

cellular processes. For example, conformational diseases such as BSE,

CreutzfeldtJacob and Alzheimer’s seem to be related to the aggregation of

prion-like or amyloid proteins.

Biological systems are often brought into contact with surfaces of synthetic

materials, e.g., biomineralization, cardiovascular and other implants,

hemodialysis, teeth and dental restoratives, voice prostheses, contact lenses, drug

targeting, controlled release systems, biocatalysis, unit operations in food

processing, and many other small and large scale applications. Fig. 8.1.1 shows a

stem cell adhered to a solid surface (an application of medical prosthesis and

biocompatibility).

Fig. 8.1.1 Stem cell from from bone marrow adhered to a solid surface.

Certain components of biological fluids tend to become accommodated at the

surface. The adsorption at the surface may induce structural rearrangements in the

biomolecules with a concomitant change in their biological functioning.



The ubiquitous examples of biocolloidal materials are cytoplasm, blood and other

biofluids. These colloids have varied size and shape. The spherical shape is found

in vesicles, liposomes, some bacterial cells and globular proteins. Ellipsoidal

particles are found among proteins and bacterial cells. Long cylinders are

observed for collagen and double stranded DNA. Disc shapes are observed in

erythrocytes. The biological cells such as leucocytes and fibroblasts are readily

deformable and may adopt a shape that is appropriate for the environment. The

shape of biological membranes is lamellar. The photographs shown in Fig. 8.1.2

depict some of these shapes.

(a) (b)

(c) (d)

Fig. 8.1.2 (a) Erythrocytes from human blood, (b) staphylococcus aureus, (c) trehalose particles, and (d) tobaco mosaic virus.

8.1.2 Adsorption of proteins at solid surfaces

8.1.2.1 Proteins

Proteins are very important constituents of biological systems. All chemical

reactions that sustain life are catalyzed by enzymes, which are proteins. Some

proteins play a vital role in the transport processes ranging from electron transfer

to carrying oxygen, hormones and other substances. Membrane proteins control



the passage of ions and metabolites across the membranes which separate

biological cells and cell organelles from their surroundings. The immunoproteins

defend the organism against foreign invaders. In muscles, proteins take care of

converting chemical energy into mechanical work. The elasticity and structure of

connective tissues and bones is also provided by proteins.

Proteins are heteropolymers of ~20 different amino acids linked together in one

or more polypeptide chains. These amino acids are glycine, alanine, valine,

leucine, isoleucine, proline, 4-hydroxy proline, serine, threonine, aspartic acid,

glutamic acid, asparagine, glutamine, lysine, arginine, histidine, phenylaline,

tyrosine, tryptophan, cysteine and methionine. A number of amino acids along the

polypeptide chain contain a cationic or an anionic group. The various amino acid

side groups differ greatly in polarity so that the protein is amphiphilic.

The sequence of the amino acids in the polypeptide chain determines the folded

spatial architecture. The three-dimensional structure is the net result of the

interactions between segments within the protein molecule, and also between

segments of the protein and the environment (which is often aqueous).

Protein molecules, which are highly solvated and flexible, result in a disordered

coil-like structure. This class of proteins whose main roles are nutritional (e.g.,

glutelins in wheat grains and caseins in milk).

Protein molecules that have a very regular structure (e.g., helices and pleated

sheets) are known as fibrous proteins. Collagen, keratin and myosin belong to

this category. These proteins are usually insoluble in water. They are mainly

found in muscle and connective tissues.

The greatest proportion of the protein species contains different structural

elements, i.e., -helices, -pleated sheets, and parts that are unordered, which are

folded together into a compact dense globule. These are known as globular

proteins. These proteins constitute only a small fraction of the total protein mass

present on earth. In an aqueous environment, the non-polar amino acid residues

are mainly located in the interior whereas the polar residues are are primarily

found at the periphery of the molecule.



The globular proteins fulfill specific functions such as biocatalysis and

immunoreactions. An almost countless number of different kinds of globular

proteins exist, each kind having its own specific biological function related to its

own characteristic structure.

The general structure of the amino acids occuring in proteins is

H2N*CHRCOOH (except for proline and 4-hydroxy proline). The asterisk at

the -C atom indicates the asymmetry around this atom. Amino acids are

assembled in polypeptide chains by polycondensation.

The polypeptide backbone is composed of repeating units that consist of three

atoms and varying side-groups, R, as shown in Fig. 8.1.3.

(a) (b)

Fig. 8.1.3 (a) Polypeptide unit, and (b) geometry of the peptide backbone (the peptide bond is shaded).

Due to mesomery, the peptide unit is stabilized by a resonance energy of 8090

kJ/mol. The mesomeric structure has several consequences.

1. The peptide unit has a large dipole moment.

2. There is no rotational freedom around the peptide bond. Therefore, the

atoms depicted below have a strong tendency to be located in one plane.

The cis and trans configurations are depicted in Fig. 8.1.4.

Fig. 8.1.4 The cis and trans configurations in the peptide structure.



3. The trans configuration is the most stable structure because of the least

steric hindrance between the R-groups that are linked to the C-atoms. In

other words, the trans configuration has a larger rotational freedom around

the and bonds.

4. The C N bond (the peptide bond) is 10% shorter than normal. The

C O bond is longer than that in aldehydes and ketones. The C C

bonds have normal lengths.

In the polypeptide chain, each of the amino acid residues has a number of

distinguishable stable conformations in the backbone (due to rotations around the

and bonds) as well as in the side group R, which generally contains a number

of single covalent bonds.

It has been inferred that within the polypeptide backbone, each peptide unit may

attain about four conformations and for the side group R, an average of six

conformations is estimated. Thus, the number of conformations for a polypeptide

consisting of 100 amino acids adds up to 10100. It leads to a large conformational

entropy, lnk , where k is the Boltzmann's constant and represents the number

of distinguishable conformations.

In a globular protein molecule, however, the polypeptide adopts a specific, rather

fixed, structure. Such a compact inflexible architecture is stable only if

interactions within the protein molecule and between the protein and its

environment compensate for the loss of conformational entropy.

8.1.2.2 Adsorption

Among the various biopolymers, proteins are most surface active. Protein

adsorption is common in many scientific applications. In the prebiotic stage of the

genesis of terrestrial life, accumulation of proteins at soil–water interfaces may

have played an essential role. The microbial life in the soil is influenced by

adsorption of extracellular enzymes to the soil. Pancreatic lipases and

phospholipases control the digestion of alimentary fats in the duodenum. These

fats are soluble in water and they are present as emulsified globules. Intravascular



thrombosis is an interfacial process in which adsorption of proteins at the blood

vessel wall enhances the adhesion of blood platelets.

Biofouling is a common phenomenon in many biotechnological and biomedical

systems. A layer of organic material forms (including bacteria or other biological

cells) on the surface. Protein adsorption is the initial event in the fouling of

cardiovascular implants, teeth and dental restoratives, artificial kidney

membranes, contact lenses, catheters and blood bags. Similar processes occur at

pipelines, heat exchangers and separation membranes in food processing

equipment, marine environment and desalination units.

In some applications, proteins are adsorbed on purpose, e.g., immobilized

enzymes in biosensors and bioreactors, immunoglobulins in immunoassays, drugs

in drug targeting and controlled release systems, and as stabilizers of dispersions

in various applications.

Protein purification systems such as displacement, hydrophobic and ion-exchange

chromatographies require well-controlled adsorption and desorption.

When a protein molecule adsorbs from solution at an interface, it changes its

environment, which is often accompanied by structural rearrangements. This

implies a change in biological functioning as well. Therefore, optimization of the

adsorbent–protein interaction is necessary to preserve the biological activity after

adsorption and prevent adverse effects, e.g., biofouling.

The interaction between proteins and surfaces is mainly governed by the factors

such as: (i) changes in the hydration of the adsorbent surface and the protein

molecule, (ii) Coulomb interaction between the protein and the adsorbent, which

results in a redistribution of charged groups, and (iii) structure rearrangements in

the adsorbing protein molecules. The contribution of each of these interactions to

the overall adsorption process depends on the nature of the system.

Structural rearrangements do not contribute significantly to the adsorption

process for the proteins which have a strong internal coherence (‘hard’ proteins).

These proteins adsorb on hydrophobic surfaces, but they adsorb on hydrophilic

surfaces only if they are electrostatically attracted. Proteins of much lower

structural stability (‘soft’ proteins) adsorb even under the seemingly unfavorable



conditions of a hydrophilic, electrostatically-repelling surface. With these

proteins, a large driving force for adsorption results from the structural

rearrangements.

The various steps of adsorption and desorption of a protein molecule on a solid

surface are shown in Fig. 8.1.5.

Fig. 8.1.5 Protein adsorption process.

The steps are: (1) transport towards the surface, (2) deposition at the surface, (3)

relaxation of the adsorbed molecule, (4) detachment from the surface, and (5)

transport away from the surface. These processes are indicated by the

corresponding numbers in the figure. The asterisks indicate the degree of

relaxation of the adsorbed molecule. The possible restructuring of the desorbed

protein molecule has been shown by the dotted lines.

Let us consider a simple model for protein transport and adsorption. For the

transport of protein molecules towards the adsorbent surface driven by a

concentration gradient, the flux can be expressed as,

m b sJ k c c (8.1.1)

where bc and sc are the protein concentrations in the bulk solution and at the

surface, respectively, and mk is a transport coefficient that depends on the

hydrodynamic conditions.

Deposition of protein at the surface of the adsorbent can be considered as a first-

order process. The rate is given by,

eqd sr k c c (8.1.2)



where eqc is the concentration in bulk solution corresponding to the equilibrium

value for the adsorbed amount.

When r J , from Eqs. (8.1.1) and (8.1.2) we obtain,

eqm b ds

m d

k c k cc

k k

(8.1.3)

Substituting sc from Eq. (8.1.3) into Eq. (8.1.1) or (8.1.2) we get,

eq

1 1b

m d

c cr

k k

(8.1.4)

If the concentration of protein on the surface is mol/m2, then its build-up with

time can be expressed as,

eq

1 1b

m d

c cd

dt k k

(8.1.5)

The quantity eqc can be determined from the adsorption isotherm. An explicit

expression for d dt can be obtained employing this isotherm. The value of

d dt reflects the interaction of the protein molecules with the surface.

Protein adsorption isotherms depict the amount of protein adsorbed versus

the protein concentration in the solution eqc (as in the case of adsorption of

surfactants discussed in Lecture 4.1).

The equilibrium adsorption experiments for the determination of versus eqc

profiles are as follows (Arai and Norde, 1990). Protein solutions (prepared in

buffer media) of different concentrations are added to the dispersions of the

adsorbent material in the same buffer solutions in polycarbonate tubes. The tubes

are gently rotated for about one day (which is sufficient in most cases for

attaining equilibrium). The solution is filtered and centrifuged, and the protein

concentration in the filtrate is determined by liquid chromatography. The amount

of protein adsorbed is calculated from the mass balance.



The adsorption isotherms for negatively charged bovine serum albumin (BSA) on

negatively charged hydrophilic surfaces of hematite and silica are shown in Fig.

8.1.6.

Fig. 8.1.6 Adsorption isotherms for bovine serum albumin on hematite and silica at 295 K and pH = 7 (Norde and Anusiem, 1992) (adapted by permission from

Elsevier Ltd., © 1992).

We have discussed before that the driving force for the adsorption of the BSA

molecules under these conditions probably stems from structural rearrangements

leading to higher conformational entropy in the molecule. The initial parts of the

isotherms indicate that the affinity between BSA and the adsorbent surfaces is not

very high.

Once the protein molecule has attached to the surface, it relaxes towards its

equilibrium structure, which is different from its native structure in the solution.

Structural relaxation implies optimization of protein–surface interaction, and it

normally involves a certain amount of spreading of the protein molecule on the

surface of the adsorbent developing a larger number of protein–surface contacts.

As a consequence, the adsorbed layer becomes structurally heterogeneous, i.e.,

the molecules which arrived at an early stage of the adsorption process find

sufficient area available for spreading whereas this is not the case for the

molecules which arrive when the surface is already partially covered with protein.

The hysteresis in protein adsorption–desorption curves is often significant. The

eqc profiles for adsorption and desorption rarely coincide. The difference

between adsorption and desorption remains even when the observation time is



extended to several days and is therefore much longer than the relaxation time of

the protein at the surface.

The occurrence of such hysteresis indicates that at a given protein concentration

two metastable states exist: one on the adsorption isotherm and the other on the

desorption isotherm. They are separated by a free energy barrier that prevents

transition from one state to the other.

Since adsorption and desorption represent two metastable states, it is likely that a

physical change takes place in the system between adsorption and desorption.

Because the proteins do not easily desorb from the surface upon dilution, it is

virtually impossible to study the desorbed molecules. However, it is possible to

exchange adsorbed proteins with other surface active compounds. From such

exchange studies, it has been found that permanent structural changes indeed take

place (Chan and Brash, 1981).

Example 8.1.1: Consider the interaction of a biopolymer as depicted in Fig. 8.1.7.

Fig. 8.1.7 Interaction of a biopolymer with solid surface.

Derive the expression for its net rate of adsorption by taking surface coverage into

consideration.

Solution: The forward flux of the adsorbate molecules for attachment on the surface is

given by,

1d sf

dk c

dt

(i)

where is the fraction of the surface area of the sorbent that is occupied, and

max , where max is the adsorbed amount when the surface is saturated with the



adsorbate. This definition of strictly holds for molecules whose conformations do not

change when they adsorb (e.g., rigid molecules). Proteins may show adsorption-induced

change in conformation. The relation between and is more intricate than this. The

backward flux due to detachment is given by,

'd

b

dk

dt

(ii)

where 'dk is the detachment rate constant. As the surface coverage increases, the

backward flux increases. Eventually a steady state is attained when

0f bd dt d dt , which implies that,

'eq1d dk c k (iii)

where eqc is the equilibrium concentration of solute corresponding to the equilibrium

value of . The net adsorption rate is given by,

eq 1d sd

k c cdt

(iv)

Now, we have,

m b sd

k c cdt

(v)

where mk is a transport rate constant that depends on the hydrodynamic conditions and

the diffusion coefficient. From Eq. (v), we get,

s bm

d dtc c

k

(vi)

Substituting sc from Eq. (vi) into Eq. (iv) and simplifying, we get,

eq1 11

b

d m

c cd

dtk k



8.1.2.3 Driving force for protein adsorption

The tendency of proteins to accumulate at solid–liquid interfaces is determined

not only by properties of the protein molecules and the sorbent surface, but also

by the nature of the solvent, the presence of other solutes, pH, ionic strength and

temperature.

At constant temperature and pressure, adsorption proceeds spontaneously if the

Gibbs free energy of the system decreases, i.e., 0G H T S where H is

enthalpy and S is entropy of the system. A large affinity for adsorption is marked

by a large negative value of G .

One way to analyze the overall adsorption process is to establish how various

interactions contribute to G . Such a thermodynamic approach can be successful

if the system is well characterized.

Generally, both the protein molecule and the sorbent surface are electrically

charged. In an aqueous medium, charged sorbents and proteins are surrounded by

coions and counterions, together accounting for the so-called countercharge that

neutralizes the surface charge. A fraction of the countercharge may be bound to

the sorbent surface and/or the protein molecule, and the other part is diffusely

distributed in the solution. The surface charge and the countercharge together

form the electrostatic double layer.

The Gibbs free energy is related to the surface charge density and surface

potential by the following equation.

EDL0

G d (8.1.6)

where and are the variable surface potential and surface charge density,

respectively, during the charging process.

The knowledge of is required to solve Eq. (8.1.6), which can be obtained

from the models for the electrostatic double layer. Various models for the bare

sorbent surface, dissolved protein molecule and protein-covered surface are

available in the literature (Baszkin and Norde, 2000).



An interesting feature of the double layer in protein adsorption is that the Debye

length 1 is considerably smaller than the thickness of the adsorbed protein

layer. For example, in a solution of 100 mol/m3 ionic strength, the Debye length

is ~1 nm whereas, the thickness of the adsorbed protein layer in which the

molecules retain a compact conformation is at least a few nanometers. Hence,

such a compact protein layer shields the protein–sorbent contact region from

electrostatic interaction with the solution so that the net charge density in that

contact region is essentially zero.

The quantity, EDLG , is not very sensitive to the charge densities of the protein

and the sorbent. Its value is usually in the range of ~10–15RT per mole of

adsorbed protein. Its sign and value depend on the charge distributions and the

dielectric constants of the electrostatic double layers before and after adsorption,

respectively.

The transfer of ions from the aqueous solution into the nonaqueous protein–

sorbent environment is chemically unfavorable. In other words, the chemical

effect of ion incorporation opposes the overall adsorption process. This is why

maximum protein adsorption affinity is reached when the charge density on the

protein just matches that on the sorbent surface so that no additional ions have to

be incorporated.

In liquid water at low to moderate temperatures (< 350 K), the water molecules

are strongly bonded, causing strong internal coherence. Polar groups interact

favorably with water molecules by electrostatic forces (including hydrogen

bonding). These interactions overcompensate the strong cohesion between the

water molecules, which renders the polar components soluble in water.

The non-polar groups, which do not offer the possibility for such favorable

interactions with water, are expelled from an aqueous environment. This

mechanism is the basis for the hydrophobic interaction (Chandler, 2005). If the

surfaces of the protein molecule and the sorbent are polar, their hydration is

favorable. In that case, it is probable that some water of hydration is retained



between the sorbent surface and the adsorbed protein molecule. However, if one

of the surfaces is non-polar, dehydration would be a driving force for adsorption.

The non-polar residues of a globular protein in water tend to be buried in the

interior of the molecule. The surfaces of protein which water can access may still

constitute a large non-polar portion (e.g., 40%). For water soluble non-

aggregating proteins, the non-polar residues are more or less evenly distributed

over the exterior of the molecules. The presence of pronounced non-polar

portions may lead to protein aggregation.

Apart from the polarity of the outer shell, the overall polarity of the protein could

be relevant for its adsorption behavior. The overall polarity influences the protein

structural stability and, hence, the extent of structural perturbation upon

adsorption, which affects adsorption.

A fair estimate of the contribution from hydration effect on the Gibbs free energy

change, HydG , may be inferred from partitioning components in water–

nonaqueous two phase systems. In this manner, it has been estimated that at room

temperature, dehydration of non-polar surfaces involves a lowering of the Gibbs

energy of ~10–20 mJ/m2. For a protein of molar mass 15000 Da that adsorbs to

~1 mg/m2, HydG ranges between –60 and –120RT per mole of the adsorbed

protein.

London–van der Waals attractive interaction results from the attraction between

the electron clouds that are in close proximity. For a sphere interacting with a

planar surface, the contribution from dispersion forces to the Gibbs free energy of

adsorption, vdWG is given by,

vdW ln6 2 2HA a a h

Gh h a h a

(8.1.7)

where HA is Hamaker’s constant (see Lecture 1 of Module 3) for the interaction

between the flat sorbent surface and the spherical protein molecule across the

aqueous medium, a is the radius of sphere and h is the distance of closest

approach between the sphere and the surface.



In the aqueous media, 0HA , therefore, vdW 0G , which implies attraction.

The Hamaker constant for interaction across water is 21~ 6.6 10 J for globular

proteins. The value of vdWG varies proportionally with the dimensions of the

protein molecule. It drops-off hyperbolically with increasing distance between the

protein and the sorbent surface.

For a globular protein molecule of 3 nm radius and located at 0.15 nm separation

from the surface, the value of vdWG amounts to about –2RT per mole at a

synthetic polymer surface, and about –6RT at a metal surface.

The three-dimensional structure of a globular protein molecule is marginally

stable. Therefore, interaction with a sorbent surface may induce changes in that

structure. However, as compared to flexible polymers, the conformational

changes in adsorbing protein molecules are usually small. The thickness of a

monolayer of adsorbed protein can be determined by ellipsometry, light

scattering, viscometry, scanning probe microscopy and surface force techniques.

It has been found that this thickness is comparable to the dimensions of the native

protein molecule.

Structural rearrangements do not lead to unfolding into a loose, highly hydrated

“loop-and-tail” structure. After adsorption, one side of the protein molecule faces

the sorbent material. As a consequence, the intramolecular hydrophobic

interaction becomes less important as a structure stabilizing factor, i.e., the non-

polar parts of the protein that are buried in the interior of the dissolved molecule

may become exposed to the solvent surface without making contact with water.

Hydrophobic interactions between the amino acid residues support the formation

of -helices and -sheets. Hence, a reduction of these interactions tends to

destabilize such secondary mixtures. A reduction of the -helix and/or -sheet

can occur if the peptide units released from the helices and sheets can form

hydrogen bonds with the sorbent surface. Then a decrease in ordered structure

would result in an increased conformational entropy of the protein, and hence an

increased adsorption affinity.



The contribution from increased conformational entropy to a negative value for

StrucG may amount to ~10RT per mole of protein. However, adsorption at a

non-polar, non-hydrogen bonding surface may stimulate intramolecular peptide–

peptide hydrogen bonding, resulting in increased order in the protein’s structure.

The morphology of the sorbent surface also plays an important role in protein

adsorption. Many surfaces are not completely smooth and rigid. At natural

surfaces, such as those of biological membranes and bacterial cell walls, natural

polymers such as proteins and/or polysaccharides are often present. When these

surface polymers extend into the surrounding medium with some flexibility, the

surface will respond dynamically to adsorb protein. It would be possible to

optimize contact by conforming to the adsorbing protein molecule. On the other

hand, squeezing the surface polymers between the sorbent and the adsorbed

protein layer would cause steric repulsion because of increased osmotic pressure

and decreased conformational entropy.

Grafting or preadsorbing water-soluble oligomers or polymers has been used to

tune protein adsorption. Polyethylene oxide has been proved to be successful in

producing protein-repelling surfaces. The protein resistance is determined by the

length of the PEO chains and their density at the sorbent surface. The relative

short chains of PEO consisting of units of ~10 nm length do not severely hamper

protein adsorption, but they prevent intimate contact between the protein and the

underlying sorbent surface. As a consequence, less structural perturbation occurs

so that the adsorbed molecules retain more biological activity. Longer PEO

chains more effectively repel proteins.



Exercise

Exercise 8.1.1: Draw the versus t curve for protein adsorption on solid surface.

Explain the limiting parts of this profile. Under what condition will the protein flux

towards the surface equal the rate of adsorption?

Exercise 8.1.2: Fit a suitable semi-empirical adsorption isotherm to the experimental

data given in Fig. 8.1.6 for the adsorption of bovine serum albumin on hematite and

silica.

Exercise 8.1.3: For a globular protein molecule of 5 nm diameter, and located at 0.2 nm

separation from the surface, compute the dispersion force contribution to the Gibbs free

energy change due to adsorption. Take Hamaker constant = 216.5 10 J .

Exercise 8.1.4: Answer the following questions clearly.

i. Explain the salient features of biological interfaces. Give five applications

where biological interfaces are important.

ii. Explain how the protein molecules undergo structural arrangement in aqueous

solutions to minimize the free energy.

iii. What are globular proteins?

iv. What factors are important for adsorption of proteins on solid surfaces?

v. Illustrate the various steps of adsorption and desorption of proteins at solid

surfaces.

vi. Explain how the amount of protein adsorbed on a solid surface depends on the

equilibrium concentration of the protein in the solution.



Suggested reading

Textbooks

P. Ghosh, Colloid and Interface Science, PHI Learning, New Delhi, 2009,

Chapter 10.

W. Norde, Colloids and Interfaces in Life Sciences, Marcel Dekker, New York,

2003, Chapters 13–15.

Reference books

A. Baszkin and W. Norde, Physical Chemistry of Biological Interfaces, Marcel

Dekker, New York, 2000, Chapter 4.

Journal articles

B. M. C. Chan and J. L. Brash, J. Colloid Interface Sci., 84, 263 (1981).

D. Chandler, Nature, 437, 640 (2005).

T. Arai and W. Norde, Colloids Surf., 51, 1 (1990).

W. Norde and A. C. I. Anusiem, Colloids Surf., 66, 73 (1992).

P.ghosh Protein Adsorption Lecture

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Transcript of P.ghosh Protein Adsorption Lecture