Sonia SheikhOctober 12, 2014

The Role of Water in the Antifouling Properties of Ultrathin Organic Adlayers: Experimental & Computational Evidence

9th Annual Conference on the Physics, Chemistry & Biology of WaterPamporovo, Bulgaria

Gilbert LingPoster Award Presentation

The Ubiquitous Problem of Fouling

Undesirable adsorption/accumulation of species (proteins, cells,organisms) on artificial surfaces from surrounding environment

Some examples of fouling in everyday life:

Food processing, water purification systems Marine equipment Biotechnology: biomedical/surgical equipment &

implants; biosensors (non-specific adsorption)2

Biomedical & Bioanalytical Concerns

3

(B) Biosensor applications: Non-specific adsorption

(A) In vivo biomaterial applications: Foreign body reaction

Synthetic Implant

BloodForeign body giant cell

Fibrous capsule

Adsorbed proteinImplant

Indistinguishable signal False positives False negatives

Biological sample:

Target analyte

Matrix interferents

Biosensing Platform

Specific binding (target analyte)&

Non-specific adsorption (interferents)

Surface Passivation: Surface Chemistry

Surface modifiers are short organic molecules designed tospontaneously attach to substrates and form ultrathin adlayers

Blaszykowski, C.; Sheikh, S.; Thompson, M. Chem. Soc. Rev. 2012, 41, 5599 4

Antifouling adlayer

Surface modifiers

Surface Modifiers for Customized Surfaces

5

Anchoring function

Head function

Backbone

Substrate Quartz (piezoelectric), gold (electrical/optical), plastics (flexible), ...

Trichlorosilyl (Cl3Si), thiol (SH), ...

Any (chemically compatible) organic group

Alkyl: (CH2)n

Oligoethylene glycol (OEG): (OCH2CH2)n

Perfluoroalkyl: (CF2)n

Peptides: (NHCHRCO)n

Functionalizable for subsequent biomolecule immobilization

Linkers for biosensors

Examples of Surface Modifiers

O

OF

FSi

F

Cl

ClCl

OO

O

O

OF

FSi

F

Cl

ClCl

O

OSiCl

ClCl

F

F

F

F

F

TTTA

OEG-TTTA

PFP-TTTA Si O O

O

ClCl

ClF

FF

SiO

O

ClCl

ClF

FF

SiClCl

Cl

Si OO

ClCl

Cl

OTS

MEG-OMe

OTS-TFA

MEG-TFA

TFE

PFP

6

Transducer & Detection: EMPAS Technology

ElectroMagnetic Piezoelectric Acoustic Sensor (EMPAS) is ananalytical flow-through device able to detect on-surface biomolecularinteractions in a real-time and label-free manner

Remotely triggers acoustic resonance within thin, electrode-free quartzdiscs using an external electromagnetic field generated by a coil

Thompson, M.; Ballantyne, S. M.; Cheran, L.-E.; Stevenson, A. C.; Lowe, C. R. Analyst 2003, 128, 1048

Electromagnetic field

Secondary electric field

AC-powered copper coil

Quartz disc

Thickness: 83 m

7

Resonant Frequency Shift

Biosensors:biorecognition & non-

specific adsorption (NSA)

Biomaterial Coatings:antifouling behaviour

Biomolecule adsorption / interaction=

Change in resonant frequency

F

Sampleinjection

8

Motivation, Objectives & Strategy

Bioanalytical:Biosensors

Biomedical:Biomaterials

Design & synthesis of new trichlorosilane surface modifiers Prepare & characterize organosilane adlayers on quartz Evaluate the antifouling (& biorecognition) properties of the

resulting molecular assemblies with the EMPAS

Couple surface chemistry with EMPAS technology to developorganic coatings able to minimize fouling occurring uponexposure to biological fluids (e.g. blood serum & plasma)

9

UnimolecularAntifouling Adlayers

10

Fouling of Bare Quartz by Serum

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

0 500 1000 1500 2000

Time (s)

944.410

944.420

944.430

944.440

944.450

944.460

F

r

e

q

u

e

n

c

y

(

M

H

z

)

34 kHz

Full serum injection

11

Systematic Structural Modification

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

1/1 (v/v) H2O/MeOHroom temp., overnight

--------------------------------------------------

quartz quartz quartz quartz quartz

12

MEG family Alkyl family

Antifouling Behaviour Against Serum

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

Through the use of structurally simple surface modifiers, thefrequency shift due to the adsorption of goat serum wassubstantially reduced from 31 kHz for bare quartz to below3 kHz for MEG-OH coatings

13

Adlayer Characterization: CAM & XPS

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

16

90

30 MEG-OH

MEG-TFA

Cleaned quartz

14

Comparing EMPAS Profiles

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

MEG-OH coating profile: comparatively limited

initial drop gradual and extensive

rinse-off reversible adsorption

Bare quartz profile: sharp initial drop gradual decrease no rinse-off irreversible adsorption

15

Bare quartzFr

e

q

u

e

n

c

y

(

M

H

z

)

MEG-OH coating

F

r

e

q

u

e

n

c

y

(

M

H

z

)

Surface Hydration? EMPAS Experiments

Sheikh, S.; Yang, D. Y.; Blaszykowski, C.; Thompson, M. Chem. Commun. 2012, 48, 1305

A overnight soaking in 1/1 (v/v) H2O/MeOH B no treatment(15% RSD, N = 6) (8% RSD, N = 5)

16

F

r

e

q

u

e

n

c

y

(

M

H

z

)

Water, Surface Hydration & Antifouling

Antifouling properties linked to (the state of) surface hydration

Water is crucial

17

Neutron Reflectometry

18

Si, SLDSi = 2.07 x 10-6 -2

Transitional water

Silane adlayer

Bulk water (D2O/H2O), SLDB = 3.54 x 10-6 -2

d1

1-B

SiO2-1

L

a

y

e

r

1

SiO2, SLDSiO2 = 3.48 x 10-6 -2Si-SiO2

dSiO2

SLD1

Contrast variation Match the SLD of bulk

water to SiO2 substrate Enhance scattering

contrast of Layer 1

Data fitting: adjustment of

d = thickness

= interfacial roughness

SLD = scattering length density

Pawlowska, N. M.; Fritzsche, H.; Blaszykowski, C.; Sheikh, S.; Mansoor, V.; Thompson, M. Langmuir 2014, 30, 1199

Stratified model to study surface hydration

Probing Surface Hydration with NR (1/2)

19

NR: Experimental Overview

NRReflectivity Data

Modelling+

Data Fitting

Sample

SLD Profile

WATER

20

SLD profiles

SiO2 Layer 1Bulkwater

MEG-OH vs. OTS-OH hydration

Layer 1 not well defined for MEG-OH compared to OTS-OH (as seen by the sharpness of the peaks)

Ability to absorb water?

MEG-OH: SLD value near the SiO2interface close to that of bulk water suggesting water absorption

OTS-OH: SLD value near the SiO2interface deviates from that of bulk water suggesting water does not absorb

Water organization?

MEG-OH: long-range (~40) & less structured (higher SLD)

OTS-OH: shorter-range (~20) & more structured (lower SLD)

Probing Surface Hydration with NR (2/2)

21Pawlowska, N. M.; Fritzsche, H.; Blaszykowski, C.; Sheikh, S.; Mansoor, V.; Thompson, M. Langmuir 2014, 30, 1199

OTS-OHMEG-OH

|F| < 3 kHz

|F| ~ 22 kHz

Two Distinct Hydration Patterns

22not to scale

Computational approach to investigate the molecular-level structuration of water within and atop variousantifouling adlayers (MEG versus alkyl family)

23

Molecular Dynamics Simulation

MD Simulations: Models

The atom colour code is as follows: yellow (silicon), turquoise (carbon), red (oxygen), and white (hydrogen) 24

Solvated simulation cell:

~23,000 atoms

Surface functionalizationof -quartz with residue

Quartz slab:1.97 x 1.97 x 0.90 nm

Full 5 x 5 coverage

Radial Distribution Function (RDF)

Hydration innermost film Hydration top film

The RDF describes the probability of finding water moleculesorganized at a certain distance from a reference

Seen as distinct peaks with proportional magnitude

25Sheikh, S.; Blaszykowski, C.; Nolan, R.; Thompson, D.; Thompson, M. J. Colloid Interface Sci. 2015, 437, 197

Water Dynamicity: MEG-OH System (1/2)

MD simulations with the MEG-OH system revealed:

multiple molecules of water absorb simultaneously around the internal ether atoms of oxygen (A, C, D)

full assortment of possible H-bonding interactions of water with the internal ether or/and distal hydroxyl moieties

Water dynamicity refers to the lability & mobility of water moleculeswithin and atop an adlayer

26Sheikh, S.; Blaszykowski, C.; Nolan, R.; Thompson, D.; Thompson, M. J. Colloid Interface Sci. 2015, 437, 197

Water Dynamicity: MEG-OH System (2/2)

9 ns

1 ns

27 ns

1 ns

Water clustering

Water residency time within the adlayer well into the ns regime

As we move closer to the top of the adlayer, then away from it: interfacial water is more

labile & mobile bulk water diffuses freely

27Sheikh, S.; Blaszykowski, C.; Nolan, R.; Thompson, D.; Thompson, M. J. Colloid Interface Sci. 2015, 437, 197

Antifouling & Surface Hydration:Basic Requirements

Limited dynamicity

for hydration waterMolecular-level

water structuration

Tightly-bound hydration water

Adlayer internal & interfacial

hydrophilicity

28Sheikh, S.; Blaszykowski, C.; Nolan, R.; Thompson, D.; Thompson, M. J. Colloid Interface Sci. 2015, 437, 197

Summary & Conclusions

Water via surface hydration (and its state) plays a key role insurface antifouling/protein repellency

Molecular-level mechanism rationalized in terms of a set ofbasic requirements: internal & interfacial hydrophilicity, waterstructuration, hydration strength, water dynamicity (lability &mobility)

The antifouling mechanism postulated for such ultrathinstructures concurs with that generally invoked in the literature,and accounts for the uniqueness of the MEG-OH nanogelsurface chemistry

29

Acknowledgments

Supervisor: Professor M. Thompson

Collaborators: Drs. C. Blaszykowski and D. Thompson, Ms. N. Pawlowska

Current and former members of the Bioanalytical Research Group

Funding: Ontario Graduate Scholarship (OGS) Program, IrelandCanadaDobbin Scholarship, Department of Chemistry and the University of Toronto

Organizing Committee of the 9th Annual Conference on the Physics,Chemistry & Biology of Water

30

Thank You for Your Attention

31