This document summarizes a study investigating how lipid composition affects the permeability of the drug Norfloxacin using microfluidic platforms and graphene-based sensing. Giant unilamellar vesicles composed of different lipids (DOPC, DOPE, DOPG) were exposed to Norfloxacin at pH 5 and pH 7. Permeability was highest for vesicles with high amounts of PE and lowest for DPhPC vesicles. The results demonstrate how lipid composition influences drug permeation. The researchers propose combining microfluidics with graphene field-effect transistor biosensors for high-throughput, label-free studies of membrane permeation, which could aid drug development efforts.

1. Drug permeability using microfluidics and graphene based sensing
S.Purushothaman, J. Cama, Ulrich. F. Keyser*
Cavendish Laboratory, Biological Soft Systems, J.J. Thompson Avenue, Cambridge CB30HE, UK.
ufk20@cam.ac.uk
Motivation
Antibiotic resistance is a growing concern
in medicine and raises the need to
develope new drugs that inhibit bacterial
infection. One of the major obstacles in
drug developement is the lack of
understanding of drug-lipid interactions
governing the passive entry of drugs into
the cell.
Challenges
(i) Presence of overwhelming variety of lipid
constituiting cellular membranes.
(ii) Lack of facile tools to understand lipid-drug
interactions
(a) Experimental setup used to
measure intensity in a vesicle due to
Norfloxacin permeation
Vesicle inlet Drug inlet
Outlet
t=0 t-tf
(b) & (c) Designs of the microfluidic
chip used for experiments 1
(b)
(c)
Lipids
Set-up
Analysis
The intensity differences at t=0 and t=tf can be related to the
permeability P = (R/3t)(ΔI2 - ΔI1 +1)
We investigated the effect of lipids
DOPE, DOPC and DOPG on the
permeability of Norfloxacin using label
free high throughput microfluidic
plarform.
Giant unilaemllar vesicles were used for the assay
Two pH conditions were tested.
- pH 5 at which Norfloxacin is neutral.
- pH7 at which Norfloxacin is charged.
(a) (b)
pH5 pH7
Schematic of the experiment
DOPC
DOPE
DOPG
Norfloxacin
O
O
HO
O O
N+
P
-O
O
O
Graphene
The vesicles are tracked using
MATLAB for radius, center and
average intensity
Lipid composition affects permeability of Norfloxacin at pH7
At pH 5 membrane is less
permeable for the observed time
scales
Results
DiscussionVesicles with high PE are more
permeable
At low PE the H-bonds in the headgroup increases lipid order
which decreases permeability.
At high PE curvature frustration dominates leading to more leaky
membranes.
DOPC vesicles are orders of magnitude more permeable
than DPhPC vesicles
Branched chain DPhPC has less free volume than DOPC.
DPhPC has very large area per
lipid molecule2,3
which
increases the permeation area
thereby slowing diffusion.
Graphene-FET
and Microfluidics
Graphene is an ideal material for the construction
of FET bio-sensors.
It is bio-compatible, transparent,versatile and selective.
It has extraordinary electrical sensing capabilties.
A combined microfluidic-electric setup can therefore provide
ultra-sensitive, high-throughput and label-free platform for
understanding membrane permeation.
pH 3
pH10
Vgs
Conductivity
pH sensing using G-FET
- Vesicles on graphene FET are stable.
- It can be therefore used for ion transport
across membranes
Conclusions
Lipid composition
affects drug permeation
Graphene bio-sensing is
showing great promise for
molecular detection.
The research will be continued
towards developement of G-FET
sensing for quantifying protein to
lipid ratios in the next coming
months.
- Norfloxacin is autofluroscent at 463nm.
- We observed the change in the intensity
inside the vesicle to quantify permeability.
pH5 pH7
DPhPC
??
1
1.Cama.J, Lab on a chip, 2014,14(13), 2303.
2.Merino,Langmuir, 2002,18, 3288-3292.
3.Nagle.J. F,Chem Phys Lipids, 2010,163(6), 630-637.
EPSRC- EP/K016636/1.