Laura InnesLaura InnesGraduate Students: Eric Kalman, Matt PowellGraduate Students: Eric Kalman, Matt Powell

Prof. Zuzanna SiwyProf. Zuzanna Siwy

Department of Physics and AstronomyDepartment of Physics and AstronomyUniversity of California, IrvineUniversity of California, Irvine

Looking at Single Molecules Looking at Single Molecules with Nanoporeswith Nanopores

Why are Nanopores Interesting?Why are Nanopores Interesting?

Biological channels are the basis of many physiological processes e.g. heart and muscle function and ‘wiring’ information from the brain to all the cells.

Nanopores are the basis for biosensors detecting single molecules

http://www1.engr.ucsb.edu/~saleh/Research/Saleh_Omar_Thesis.pdf

http://en.wikipedia.org/wiki/Cell_membrane

Making NanoporesMaking Nanopores

Creation of single nanopores starts at the GSI accelerator center in Darmstadt, Germany

Irradiated with a single ion of Au or U, at 2 GeV (15% c)

Deposition of energy from the swift, heavy ion creates a damage track in polymer

Chemical etching – ‘developing’ of the track created by single heavy ions

EquipmentEquipment

Conductivity Cell Faraday Cage

Etching CurrentEtching Current

1000 mV

pA

pA

Gold Replica of a Single NanoporeGold Replica of a Single Nanopore

Scopece et al. Nanotechnology 17 (2006) 3951.

Formulas

Dd

LR

4

minmin/ 13.22 etchingtnmD

R – ionic resistance of a nanopore - specific conductivity of electrolyteL – membrane thickness

D

d

Why a Conical Pore?Why a Conical Pore?

L L

d d

D

Icone >> Icylinder

DdL

Rcone4

2

4

d

LRcylinder <<

Graph of Voltage Profile inside a NanoporeGraph of Voltage Profile inside a Nanopore

x x

x

V

Structure of DendrimersStructure of Dendrimers

~3 nm

http://www.fda.gov/NANOTECHNOLOGY/powerpoint_conversions/chbsa-nanotech-presentation06-05_files/images/image4.png

H+

H+

Basic Physical Chemistry Basic Physical Chemistry of a Charged Particle in a Solutionof a Charged Particle in a Solution

ƒ F

ΔV - potential difference between two electrodes

l - distance apart

ƒ - frictional force

u - mobility of the ion

ze - charge

s - drift speed

l

VE

l

VzeF

uEs

af 6

Ff

a

zeu

6

When

2 a

I

U

1.0 M KCl1.0 M KCl

Dendrimer

Detecting DendrimersDetecting Dendrimers

current

time

Dendrimers at Various pH’sDendrimers at Various pH’s

pH 6 pH 8

pH 7 pH 10

l

VzeF

pH 10pH 10

- 1000 mV

KCl + dendrimers

KCl without dendrimers

pH 6pH 6

-1000 mV

-1000 mV

no dendrimers

pH 8pH 8

-200 mV

-800 mV

pH 8pH 8

Occasional openings

Blockage of the pore

-1000 mV

pH 8pH 8

pH 7pH 7

-300 mV

-1000 mV

pH 7pH 7

pH 7.5pH 7.5

-1000 mV

Close up of -1000 mV

pH 7.5pH 7.5

Lower VoltagesLower Voltages

1. Force of Friction

2. Entropy

ƒ F

There is a Voltage Threshold for the There is a Voltage Threshold for the Dendrimers to Enter a NanoporeDendrimers to Enter a Nanopore

-100 mV

-1000 mV

Future StudiesFuture Studies

current

time

• Continue to study the behavior of single molecules and nanopores

• Hopefully create an electromechanical valve

-700 mV

Is It a Single Dendrimer?Is It a Single Dendrimer?

- 900 mv

pH 6pH 6

-900 mV

pH 8pH 8