Effect of Mass Transport on the Protein Adsorption in
a Miniaturized SPR Sensor; SpreetaTM
D. Yu1, S.-Y. Kim1, Y. Cho2, J. Y. Lee2,
H. J. Kim2, and J. W. Kim2
1 Department of Physics
Kangwon National University
2 Biomedlab Co.
• Effect of Mass Transport
Using the SPREETATM that is a SPR based sensor, we studied the effect of mass
transport on the adsorption of albumin to the gold surface. The mass transport
effect dominates the adsorption rate when the binding of albumin onto the gold
surface becomes more dominant than the diffusion of albumin near the surface.
• Expectation effect
Under completely transport-limited conditions initial binding rates can be
expected to increase in parallel with the albumin concentration and flow rate1/3.
1
Surface Plasmon Resonance

x
Protein solution
s
d  50 nm


mr
p
Metal
Surface plasmon wave (Ksp)
Evanescent wave (Kev)
z
Prism
x
Light (ω)
  800 nm
2D-detector
array
Reflectivity
 * angle
Resonance: Surface plasmon wave vector( K sp ) = Evanescent wave vector( K ev )
At resonance angle, incident light dramatically decreases.
Refractive index(ns ) from resonance angle: ns   s
 mr  p sin 2  *
, s 
 mr   p sin 2  *
2
Inner Structure of SpreetaTM
Gold wafer
28㎜
Gold Mirror Film
Thermistor
18.5㎜
LED
41㎜
Detector
SPREETATM sensor based on the SPR principle
3
Mass Transport(M.T.)
Mass transport effects occur when the
binding rate of analyte to the ligand is
higher than diffusion of analyte to the
surface. Flow rate is experimental
parameter that can be controlled to
minimize mass transport effects.
Compartment models
A compartment model for ligands binding to
receptors on spherical surface of radius a.
The space outside the sphere is divided into
an inner region a< r ≤ ri, where the ligand
concentration is C and outer region, r > ri,
where the ligand concentration equals the
bulk concentration C.
C
C
ri
a
4
Calculation of Mass transport coefficient(km)
_
VdC / dt  ka ARC  kd AB  k (C  C )
dB / dt  ka RC  kd B
V : denote the volume of inner
compartment.
A : the surface area of the cell.
R : the concentration of free
receptors on the cell surface.
C : free ligand concentration in
the inner compartment.
B : bound ligand concentration
on the cell surface.
C : bulk concentration.
At t=0, dC/dt=0 (initial condition)
_
dB / dt  k R C  kre B
e
f
_
lim dB / dt  k C/ A
R
1/ 3
C
 D v
km  k  1.82

A
 hL 
 dB / dt  ckm
2
(km  v )
1/ 3
5
Process of Experiment
Deionized Water(D.W)
0.1M NaOH + 1% Triton X-100
Calibration sensor
Washing sensor
PBS
D.W
Albumin Solution
Phosphate Buffered Saline(PBS)
Measurement of M.T.
Set a base line
Temperature Sensor
Teflon Tubing
Backing Plate
Teflon Connector Block
Flow Cell
Gold SPR Surface
6
Experiment Result
Relation between concentration and initial binding rate
Binding rate(B)
0.00090
0.00045
0.00000
0
55
Albumin concentration(g/ml)
110
Fixed flow rate(15㎕/min)and variable concentration(5, 25, 50, 100㎍/㎖)
The initial binding rate was clearly influenced by changes in the concentration.
7
Experiment Result
Response Unit data on flow rate
Relation between flow rate and initial binding rate
-3.2
Log(B)
Binding rate(B)
0.0006
0.0003
-4.0
0.0000
0
70
Flow rate(l/min)
140
0.5
1/3*Log(v)
Fixed concentration(25㎍/㎖) and variable flow rate(5, 15, 25, 125㎕/min)
The initial binding rate was clearly influenced by changes in the flow rate.
8
Discussion
The initial binding rate was found to be proportional to concentration and flow
rate1/3, which is in good accordance with theoretical expectations.
We also found the reaction was dependent on concentration and flow rate, which
provides further support for the mass transport limited model.
A benefit of the mass transport is that it may be used to determine the amount
concentration of analyte.
The investigation of the mass transport effect may help to understand the fluidics.
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