nanotechnology in bio medical applications

M. MeyyappanNASA Ames Research Center

Moffett Field, CA 94035

email: [email protected]: http://www.ipt.arc.nasa.gov

Nanometer• One billionth (10-9) of a meter• Hydrogen atom 0.04 nm• Proteins ~ 1-20 nm• Feature size of computer chips 90 nm

(in 2005)• Diameter of human hair ~ 10 µm

Nanotechnology is the creation of USEFUL/FUNCTIONAL materials, devices and systems (of any useful size) through control/manipulation of matter on the nanometer length scale and exploitation of novel phenomena and properties which arise because of the nanometer length scale:

• Physical• Chemical• Electrical• Mechanical• Optical• Magnetic••

Research and technology development aimed to understand and control matter at dimensions of approximately 1 - 100 nanometer – the nanoscale

Ability to understand, create, and use structures, devices and systems that have fundamentally new properties and functions because of their nanoscale structure

Ability to image, measure, model, and manipulate matter on the nanoscale to exploit those properties and functions

Ability to integrate those properties and functions into systems spanning from nano- to macro-scopic scales Corral of Fe Atoms – D.

Eigler

Nanoarea Electron Diffraction of DW Carbon

Nanotube – Zuo, et.al

What Is Nanotechnology?What Is Nanotechnology?

Source: Clayton Teague, NNI

(Definition from the NNI)

• Examples- Carbon Nanotubes- Proteins, DNA- Single electron transistors

• Not just size reduction but phenomena intrinsic to nanoscale- Size confinement- Dominance of interfacial phenomena- Quantum mechanics

• New behavior at nanoscale is not necessarily predictable from what we know at macroscales.

AFM Image of DNA

• Quantum size effects result in unique mechanical, electronic, photonic, and magnetic properties of nanoscale materials

• Chemical reactivity of nanoscale materials greatly different from more macroscopic form, e.g., gold

• Vastly increased surface area per unit mass, e.g., upwards of 1000 m2 per gram

• New chemical forms of common chemical elements, e.g., fullerenes, nanotubes of carbon, titanium oxide, zinc oxide, other layered compounds

Unique Properties of Nanoscale MaterialsUnique Properties of Nanoscale Materials


• Atoms and molecules are generally less than a nm and we study them in chemistry. Condensed matter physics deals with solidswith infinite array of bound atoms. Nanoscience deals with thein-between meso-world

• Quantum chemistry does not apply (although fundamental lawshold) and the systems are not large enough for classical laws of physics

• Size-dependent properties

• Surface to volume ratio- A 3 nm iron particle has 50% atoms on the surface- A 10 nm particle 20% on the surface- A 30 nm particle only 5% on the surface

MORE IN SECTION II

• Many existing technologies already depend on nanoscale materialsand processes

- photography, catalysts are “old” examples- developed empirically decades ago

• In existing technologies using nanomaterials/processes, role ofnanoscale phenomena not understood until recently; serendipitousdiscoveries

- with understanding comes opportunities for improvement

• Ability to design more complex systems in the future is ahead- designer material that is hard and strong but low weight- self-healing materials

• Recently, there has been an explosion of research on the nanoscale behavior- Nanostructures through sub-micron self

assembly creating entities from “bottom-up” instead of “top-down”

- Characterization and applications- Highly sophisticated computer simulations to

enhance understanding as well as create ‘designer materials’

• 1959 Feynman Lecture “There is Plenty of Room at the Bottom” provided the vision of exciting new discoveries if one could fabricate materials/devices at the atomic/molecular scale.

• Emergence of instruments in the 1980s; STM, AFM providing the “eyes”, “fingers” for nanoscale manipulation, measurement…

STM

Image of Highly Oriented Pyrolitic Graphite

• Cluster- A collection of units (atoms or reactive molecules) of up to

about 50 units• Colloids

- A stable liquid phase containing particles in the 1-1000 nm range. A colloid particle is one such 1-1000 nm particle.

• Nanoparticle- A solid particle in the 1-100 nm range that could be

noncrystalline, an aggregate of crystallites or a single crystallite

• Nanocrystal- A solid particle that is a single crystal in the nanometer range

Source: Nanoscale Materials in Chemistry, Ed. K.J. Klabunde, Wiley, 2001

• Spherical iron nanocrystals

• J. Phys. Chem. 1996, Vol. 100, p. 12142

For example, 5 cubic centimeters – about 1.7 cm per For example, 5 cubic centimeters – about 1.7 cm per side – of material divided 24 times will produce 1 side – of material divided 24 times will produce 1 nanometer cubes and spread in a single layer could nanometer cubes and spread in a single layer could cover a football fieldcover a football field

Repeat 24 times

Nanoscale = High Ratio of Surface Area to Vol.Nanoscale = High Ratio of Surface Area to Vol.


• In materials where strong chemical bonding is present, delocalization of valence electrons can be extensive. The extent of delocalization can vary with the size of the system.

• Structure also changes with size.

• The above two changes can lead to different physical and chemicalproperties, depending on size

- Optical properties- Bandgap- Melting point- Specific heat- Surface reactivity--

• Even when such nanoparticles are consolidated into macroscale solids, new properties of bulk materials are possible.

- Example: enhanced plasticity

• For semiconductors such as ZnO, CdS, and Si, the bandgap changes with size

- Bandgap is the energy needed to promote an electron from the valence band to the conduction band

- When the bandgaps lie in the visible spectrum, a change in bandgap with size means a change in color

• For magnetic materials such as Fe, Co, Ni, Fe3O4, etc., magnetic properties are size dependent

- The ‘coercive force’ (or magnetic memory) needed to reverse an internal magnetic field within the particle is size dependent

- The strength of a particle’s internal magnetic field can be size dependent

• In a classical sense, color is caused by the partial absorption of light by electrons in matter, resulting in the visibility of the complementary part of the light

• On most smooth metal surfaces, light is totally reflected by the high density of electrons no color, just a mirror-like appearance.

• Small particles absorb, leading to some color. This is a size dependent property.Example: Gold, which readily forms nanoparticles but not easily oxidized, exhibits different colors depending on particle size.

- Gold colloids have been used to color glasses since early days of glass making. Ruby-glass contains finely dispersed gold-colloids.

- Silver and copper also give attractive colors

• C = ∆Q/m∆T; the amount of heat ∆Q required to raise the temperature by ∆T of a sample of mass m

• J/kg ·K or cal/g ·K; 1 calorie is the heat needed to raise the temp. of 1 g of water by 1 degree.

• Specific heat of polycrystalline materials given by Dulong-Petit law - C of solids at room temp. (in J/kg ·k) differ widely from one to

another; but the molar values (in J/moles ·k) are nearly the same, approaching 26 J/mol ·K; Cv = 3 Rg/M where M is molecular weight

• Cv of nanocrystalline materials are higher than their bulk counterparts. Example:

- Pd: 48% from 25 to 37 J/mol.K at 250 K for 6 nm crystalline- Cu: 8.3% from 24 to 26 J/mol.K at 250 K for 8 nm- Ru: 22% from 23 to 28 J/mol.K at 250 K for 6 nm

The melting point of gold particles decreases dramatically as the particle size gets below 5 nm

Source: Nanoscale Materials in Chemistry, Wiley, 2001

• Start from an energy balance; assume the change in internal energy(∆U) and change in entropy per unit mass during melting areindependent of temperature

2To /Lr∆ = Deviation of melting point from the bulk valueTo = Bulk melting point = Surface tension coefficient for a liquid-solid interface = Particle densityr = Particle radiusL = Latent heat of fusion

• Lowering of the melting point is proportional to 1/r

• can be as large as couple of hundred degrees when the particle size gets below 10 nm!

• Most of the time, the surface tension coefficient is unknown;by measuring the melting point as a function of radius, can beestimated.

• Note: For nanoparticles embedded in a matrix, melting point may be lower or higher, depending on the strength of the interaction between the particle and matrix.

• For metals, conductivity is based on their band structure. If the conduction band is only partially occupied by electrons, they can

move in all directions without resistance (provided there is a perfect metallic crystal lattice). They are not scattered by the regular building blocks, due to the wave character of the electrons.

e

4omevv = electron speedo = dielectric constant in vacuum

, mean time between collisions, is /v

• For Cu, v = 1.6 x 106 m/s at room temp.; = 43 nm, = 2.7 x 10-14s

• Scattering mechanisms(1) By lattice defects (foreign atoms, vacancies, interstitial

positions, grain boundaries, dislocations, stacking disorders)(2) Scattering at thermal vibration of the lattice (phonons)

• Item (1) is more or less independent of temperature while item #2 is independent of lattice defects, but dependent on temperature.

• Electric current collective motion of electrons; in a bulk metal, Ohm’s law: V = RI

• Band structure begins to change when metal particles become small. Discrete energy levels begin to dominate, and Ohm’s law is no longer valid.

• If a bulk metal is made thinner and thinner, until the electrons can move only in two dimensions (instead of 3), then it is “2D quantum confinement.”

• Next level is ‘quantum wire

• Ultimately ‘quantum dot’

Source: Nanoscale Materials in Chemistry, Wiley, 2001

• Adsorption is like absorption except the adsorbed material is held near the surface rather than inside

• In bulk solids, all molecules are surrounded by and bound to neighboring atoms and the forces are in balance. Surface atoms are bound only on one side, leaving unbalanced atomic and molecular forces on the surface. These forces attract gases and molecules Van der Waals force, physical adsorption or physisorption

• At high temperatures, unbalanced surface forces may be satisfied by electron sharing or valence bonding with gas atoms chemical adsorption or

chemisorption- Basis for heterogeneous catalysis (key to production of fertilizers,

pharmaceuticals, synthetic fibers, solvents, surfactants, gasoline, other fuels, automobile catalytic converters…)

- High specific surface area (area per unit mass)

• Frequently encountered powders:- Cement, fertilizer, face powder, table salt, sugar, detergents, coffee

creamer, baking soda…

• Some products in which powder incorporation is not obvious- Paint, tooth paste, lipstick, mascara, chewing gum, magnetic recording

media, slick magazine covers, floor coverings, automobile tires…

• For most applications, there is an optimum particle size- Taste of peanut butter is affected by particle size- Extremely fine amorphous silica is added to control the ketchup flow- Medical tablets dissolve in our system at a rate controlled by particle size- Pigment size controls the saturation and brilliance of paints- Effectiveness of odor removers is controlled by the surface area of

adsorbents.

From: Analytical methods in Fine Particle Technology, Webb and Orr

• Adding certain inorganic clays to rubber dramatically improves the lifetime and wear-characteristics of tires.

Why ?

The nanoscale clay particles bind to the ends of the polymer molecules - which you can think of as molecular strings - and prevent them from unraveling.

CNT is a tubular form of carbon with diameter as small as 1 nm. Length: few nm to microns.

CNT is configurationally equivalent to a single or mutliple two dimensional graphene sheet(s) rolled into a tube (single wall vs. multiwalled).

CNT exhibits extraordinary mechanical properties: Young’s modulus over 1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa.

CNT can be metallic or semiconducting, depending on (m-n)/3 is an integer (metallic)or not (semiconductor).

See textbook onCarbon Nanotubes:

Science and Applications,

M. Meyyappan, CRC Press, 2004.

• The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture

• Young’s modulus of over 1 TPa vs 70 GPa for Aluminum, 700 GPa for C-fiber

- strength to weight ratio 500 time > for Al; similar improvements over steel and titanium; one order of magnitude improvement over graphite/epoxy

• Maximum strain 10%; much higher than any material

• Thermal conductivity ~ 3000 W/mK in the axial direction with small values in the radial direction

See http://www.ipt.arc.nasa.gov/gallery.html for videos of bending, compression, etc., of CNTs

• Electrical conductivity higher than copper

• Can be metallic or semiconducting depending on chirality- ‘tunable’ bandgap- electronic properties can be tailored through application of external

magnetic field, application of mechanical deformation…

• Very high current carrying capacity(107 - 109 A/cm2)

• Excellent field emitter; high aspect ratio and small tip radius of curvature are ideal for field emission

• Other chemical groups can be attached to the tip or sidewall (called ‘functionalization’)

Sensors, Bio, NEMS

• CNT based microscopy: AFM, STM…

• Nanotube sensors: bio, chemical…

• Molecular gears, motors, actuators

• Batteries (Li storage), Fuel Cells, H2 storage

• Nanoscale reactors, ion channels

• Biomedical- Nanoelectrodes for implantation- Lab on a chip - DNA sequencing through AFM imaging- Artificial muscles- Vision chip for macular degeneration,

retinal cell transplantation

Electronics

• CNT quantum wire interconnects

• Diodes and transistors for computing

• Data Storage

• Capacitors

• Field emitters for instrumentation

• Flat panel displays

Challenges Challenges

• Control of diameter, chirality• Doping, contacts• Novel architectures (not CMOS based!)• Development of inexpensive manufacturing

processes

• Controlled growth• Functionalization with

probe molecules, robustness• Integration, signal processing• Fabrication techniques

SWNT

MWNTTower

Close view of MWNT Tower

MWNT StructuresCourtesy: Alan Cassell

• Certain applications such as nanoelectrodes, biosensors wouldideally require individual, freestanding, vertical (as opposed totowers or spaghetti-like) nanostructures

• The high electric field within the sheath near the substrate in a plasmareactor helps to grow such vertical structures

• dc, rf, microwave, inductiveplasmas (with a biased substrate)have been used in PECVD ofsuch nanostructures

Cassell et al., Nanotechnology, 15 (1), 2004

Biosensor

• High specificity• Direct, fast

response• High sensitivity• Single molecule

and cell signal capture and detection

3+

2+

e

3+

2+

Ru bPy 3

2

• Probe molecules for a given target can be attached to CNT tips for biosensor development

• Electrochemical approach: requires nanoelectrode development using PECVD grown vertical nanotubes

• The signal can be amplified with metal ion mediator oxidation catalyzed by Guanine.

Courtesy: Jun Li

• CNT tips are at the scale close to molecules

• Dramatically reduced background noise

Traditional Macro- or Micro- Electrode

NanoelectrodeArray

Nanoscale electrodes create a dramatic improvement in signal detection over traditional electrodes

Electrode

• Scale difference between macro-/micro- electrodes and molecules is tremendous

• Background noise on electrode surface is therefore significant

• Significant amount of target molecules required

• Multiple electrodes results in magnified signal and desired redundance for statistical reliability.

• Can be combined with other electrocatalytic mechanism for magnified signals.

Nano-Electrode

Insulator

Source: Jun Li

Functionalization of DNA

CO2H

NC

N

CH3

N

CH3

H

Cl-

O

CH3

HN

H2N ATGCCTTCCy3

ATGCCTTCCy3

CH3

H

Cl-

TACGGAAGGGGGGGGGGCy5

N

O

O

HO

SO3Na

CH3

C

O

NH

C

N

CH3

N

O

O

O N

O

O

SO3Na

O

HN ATGCC TTCCy3TACGGAAGGGGGGGGGGCy5

+

EDC

+

Sulfo-NHS

DNA probe

Target DNA

Cy3 image

Cy5 image C. Nguyen et al, NanoLett., 2002, Vol. 2, p. 1079.

Electrochemical Detectionof DNA Hybridization

- by AC Voltammetry

1st, 2nd, and 3rd scan in AC voltammetry 1st – 2nd scan: mainly DNA signal2nd – 3rd scan: Background

1st

2nd and 3rd

#1-#2

#2-#3

Lower CNT Density Lower Detection Limit J. Li, H.T. Ng, A. Cassell, W. Fan, H. Chen, J. Koehne, J. Han, M. Meyyappan, NanoLetters, 2003, Vol. 3, p. 597.

30 dies on a 4” Si wafer

200 m300 m

Potential applications:(1) Lab-on-a-chip applications(2) Early cancer detection(3) Infectious disease detection(4) Environmental monitoring(5) Pathogen detection

Target Molecule

1. Chen, G.Y., Thundat, T. Wachter, E. A., Warmack, R. A., “Adsorption-induced surface stress and its effects on resonance frequency of microcantilevers,” J. Appl. Phys 77, pp. 3618-3622 (1995).

2. Ratierri, R. et al., “Sensing of biological substances based on the bending of microfabricated cantilevers,” Sensors and Actuators B 61, 213-217 (1999).

3. Fritz, J. et al. “Translating Biomolecular Recognition into Nanomechanics,” Science 288, 316-318 (2000).

4. Wu, G. et al. “Origin of nanomechanical cantilever motion generated from biomolecular interactions,” PNAS 98(4), 1560-1564 (2001).

Courtesy: Prof. A. Majumdar, U.C. Berkeley

Thiolated ssDNA

5’-HS ATCCGCATTACGTCAATC

TAGGCGTAATGCAGTTAG-5’(Complementary Strand)

AuSelf-Assembly of ssDNA

PB = Sodium Phosphate Buffer Solution

-----

---+

++ +

+ ++

Wu, G. et al. “Origin of nanomechanical cantilever motion generated from biomolecular interactions,” PNAS 98(4), 1560-1564 (2001). Courtesy: Prof. A. Majumdar, U.C. Berkeley

Probe ssDNA Target ssDNA

Wu, G. et al. “Origin of nanomechanical cantilever motion generated from biomolecular interactions,” PNAS 98(4), 1560-1564 (2001).


Time [min]

0 60 120 180 240

Def

lect

ion

, h

[n

m]

-40

-20

0

20

40

60

80

Injections

[HSA] = 1 mg/ml[fPSA]

6 ng/ml

60 ng/ml

No PSA Ab ([fPSA] = 60 g/ml)

HP only ([HP] = 1 mg/ml)

No PSA

Time [min]

0 60 120 180 240 300

Def

lect

ion

, h

[n

m]

-50

0

50

100

150

200

[BSA] = 1 mg/ml

Injections

60 g/ml

6 g/ml

60 ng/ml

6 ng/ml

No fPSANo PSA Ab

([fPSA] = 60 g/ml)

[fPSA]

SiNx

AuDTSSP

Rabbit Anti-Human PSA

Glass

Analyte

SiNx

AuDTSSP

Rabbit Anti-Human PSA

Glass

Analyte

PSA

Wu, G. et al., “Bioassay of Prostate Specific Antigen (PSA) Using Microcantilevers,”

Nature Biotechnology (Sept., 2001)

HSA: Human Serum Albumin

HP: Human Plasminogen

fPSA: free PSA

cPSA: complex PSA


DNA SequencingUsing Nanopores

Goal: Very rapid gene sequencing

(~2nm diameter)

- Nanopore in membrane

- DNA in buffer

- Voltage clamp

- Measure current

G. Church, D. Branton, J. Golovchenko , HarvardD. Deamer , UC Santa Cruz

-hemolysin pore

Axial View Side View

(very first, natural pore)

Open nanopore

DNA translocation event

• When there is no DNA translocation, there is a background ionic current

• When DNA goes through the pore, there is a drop in the background signal

• The goal is to correlate the extent and duration of the drop in the signal to the individual

nucleotides

Source: Viktor Stolc

After a decade of using protein pores, efforts are underway in many groups to develop synthetic pores (such as in Si3N4)

• Interaction with single nuclotides

- ~20 nucleotides in HL simultaneously

• Slower translocation

- 1-5 s /nucleotide in HL

• Resistance to extreme conditions

- Temperature

- pH

- Voltage

• - hemolysin is toxic and hard to work with

Source: Viktor Stolc

• Voltage-clamp amplifier designed to measure pA level currents

• Fast (up to 1GHz) data acquisition• Software for automatic blocking event detection

and recording

AgC

l

AgC

l

Voltage ClampAmplifier

nanopore chip

KClKCl

Data Acquisition

Spontaneous Blocking Events with Smaller NASA Pores

10

0 p

A

0.5 s

+200 mV

GGA A A A

G

C CTT

Present Future

A AG G G G

C C

• Tree-like polymers, branching out from a central core and subdividing into hierarchical branching units

- Not more that 15 nm in size, Mol. Wt very high- Very dense surface surrounding a relatively

hollow core (vs. the linear structure in traditional polymers)

• Dendrimers consist of series of chemical shells built on a small core molecule

- Surface may consist of acids or amines means to attach functional groups control/modify properties

- Each shell is called a generation (G0, G1, G2….)- Branch density increases with each generation- Contains cavities and channels can be used to trap guest molecules for

various applications.

Courtesy of: http://www.uea.ac.uk/cap/wmcc/anc.htm

• Desired features of effective drug delivery- Targeted delivery, controlled release (either timed or in response to an external

signal)

• Desirable characteristics of dendrimers- Uniform size - Water Solubility- Modifiable surface functionality - Availability of internal cavity- Control of molecular weight - Control of the surface and internal structure

• Number of different drugs can be encapsulated in dendrimers and injected into the body for delivery

- Incorporating sensors would allow release of drugs where needed

• Gene Therapy- Current problem is getting enough genes into enough cells to make a difference.

Using viruses for this triggers immune reactions. Dendrimers provide an alternative without triggering immune response

• Cancer Therapy

• Antimicrobial and Antiviral Agents

• Dissolution kinetics may be the rate limiting step in the absorption process for many drugs

- Decreasing the particle size increases surface area and the dissolution kinetics.

• Liposomes are normally used as carrier for hydrophilic drugs. Typical difficulties: physical instability, low activity, drug leakage

- Alternative: water-soluble polymer based nanoparticles. These are more site-specific and exhibit better controlled-release characteristics.

- To overcome toxicity issues, solid lipid nanospheres as carrier systems have been reported*. This is a lipid that is solidified and stabilized by a surfactant.

Advantages: physical stabilityDisadvantage: low drug loading (25%)

* S.A. Wissing et al., Adv. Drug. Del. Rev. 56, p. 1257 (2004).

• Synthetic “droplets” containing anything from a single electron to thousands of atoms but behave like a single huge atom.

• Size: nanometers to microns

• These are nanocrystals with extraordinary optical properties- The light emitted can be tuned to desired wavelength by

altering the particle size- QDs absorb light and quickly re-emit but in a different color- Colors from blue to IR

• Common QDs: CdS, CdSe, PbS, PbSe, PbTd, CuCl…

• Manufacturing- Wet chemistry- Template synthesis (zeolites, alumina template)

®

Energy levels

Absorption

Radiationless decay

Fluorescence

Val

ence

B

and

Band gap

Small Molecules

Qdots Semiconductors

Con

duct

ion B

and

Source: Bala Manian, Quantum Dot Corp.

®

Size Dependent Absorbance and Emission

00.20.40.60.8

11.21.41.61.8

2

350 450 550 650

Wavelength (nm)

(A

U)

2.2 nm CdSe

5.0 nm CdSe

Eg ~ 1/L2

L L


Quantum dots change color with size because additional energy is required to “confine” the semiconductor

excitation to a smaller volume.

Ordinary light excites all color quantum dots.

(Any light source “bluer” than the dot of interest works.)


Material band-gap determines the emission range; particle size tunes the emission within the range

Nanocrystal quantum yields are as high as 80%

Narrow, symmetric emission spectra minimize overlap of adjacent colors

350 400 450 500 550 600 650 700 750

Emission Wavelength (nm)Excitation: ZnSe @ 290 nm, others 365 nm

No

rmali

zed

In

ten

sit

yZnSe CdSe CdTe


• LEDs, solar cells, solid state lighting

• Biomedical- Bioindicators- Lateral flow assays- DNA/gene identification, gene chips- Cancer diagnostics

• Biological Labeling Agent

• Broad output spectrum • Sharper spectrum• Fades quickly ~ 100 ps • 5-40 ns• Unstable • Stable output over time• One dye excited at a time • Multicolor imaging, multiple

dyes excited simultaneously