Nano Overview Top-Down Approach PRASAD - Portland …web.pdx.edu/.../Lectures/Top-Down_Approach_to_Na… · · 2006-06-29The Top-Down Approach to Nanotechnology. BIOMEDICAL MICRODEVICES

BIOMEDICAL MICRODEVICES & BIOMEDICAL MICRODEVICES & NANO LABORATORYNANO LABORATORY

Shalini Prasad, Ph.D.Department of Electrical and Computer EngineeringBiomedical Micro devices and Nanotechnology Lab

Portland State University

BIOMEDICAL MICRODEVICES ANDNANOTECHNOLGY LAB

The Top-Down Approach to Nanotechnology


Theme

Micro/NanoSensors and

Devices

Carbon nanotubes

Lemay et. al. Nature, 412 (2001) 617

CdSe

ZnS

Quantum Dots

Yamaguchi et. al. Nature.Mat. 3, (2004) 337Porous Alumina

Belcher et. al. Science 303,(2004) 213Nanowires

Bio-electronic interfaces

1

2

3

1

2

3

( )( )

Chemical Sensing Platforms


Motivation

There is an immense need for sensors with broad based broad based detection capabilitydetection capability, rapid response timesrapid response times, automation automation capabilitycapability, and portabilityportability.Over the past 10 years, there has been growing interest in the use of nanomaterial as sensors in environmental, medical, toxicological, and defense applications.Nanomaterial improve the 3 R’s –reliability, reproducibility reliability, reproducibility and robustnessand robustness of the sensor due to improved surface area, increased functionality and amenability towards integration with existing sensor platforms.Development of nanomaterial based sensors can be achieved in “ off-clean room” environments


Micromachining and “Soft” Fabrication


Micromachining Materials


“Soft” Fabrication Materials


Bulk Micromachining


Surface Micromachining

Courtesy: Fatikow and Rembolt 1997


Mask Creation


Silicon Wafer Preparation


Thermal Silicon Oxide


Thermal Silicon Oxide Methods


Spin Casting Resist


Resist Types


Photolithography Process


Photoresist Types


UV-Exposure at 350-400 nm


Developing the UV Exposed Wafer


Etching Methods


Etching Profiles


Dry Chemical Etching: Reaction Mechanisms

Courtesy: M.Madou, Fundamentals of Microfabrication


Dry Chemical Etching: Loading effects- bull’s eye


Dry Chemical Etching: Ion energy vs. Pressure


Reactive Ion Etching


Physical Sputtering


Sputter Yield


Resist Stripping


Profilometry


Profilometry Graph


Energy, Vacuum and Directionality


“Soft” Lithography


PDMS Lithography (Silicone)


Micro contact Printing (μCP)


Micro Transfer Molding (μTM)


Micro molding in Capillaries (MIMIC)


“Smart” Polymers and Hydrogels


Microelectrode

Array

Technology

(MEA)


Si

A. PECVD Silicon Nitride Deposition4

Si

Si3N4

-B. E beam Platinum Deposition Pt

C. Photoresist Patterning

D. Platinum Etching

E. Photoresist Removal

Planar Microelectrode ArrayFabrication Sequence

S.Prasad, et. al. J.Biomed.Microdevices.5(2), (2003) 125


40 μm

Prototypes of Microelectrode Arrays that Function as Analysis Platforms

200 μm

2x2 platinum MEA with fibronectinpermeation layer used for cell morphological studies

3x3 platinum/titanium MEA used for environmental sensing applications.

5x5 microelectrode array comprising of platinum electrodes used for sensing and diagnostic applications.


Determination of Electrical Field Distribution on a Microelectrode Array

Electric field distribution on a 4x4 section of the microelectrode array in the absence of micro particles

Electric field distribution on a 4x4 section of the microelectrode array in the presence of micro particles 20 μm in diameter with a surface charge of -25mV

Min

MaxStrength (V/m)

Electrode

Min

MaxStrength (V/m)

ElectrodeParticle


Manipulation

Of

Micro particles


80 μm

20 μm

0V Peak to Peak

Optical micrograph of a section of the 10x10 microelectrode array comprising of platinum electrodes 80 μm in diameter with 200 μm center-to-center spacing. The geometry of the design allows positive dielectrophoretic traps to develop over the electrodes.

Initial random dispersion of 10 μm Polystyrene beads. The beads are functionalized (negatively charged to mimic the membrane of biological cells) in sodium dodecyl sulfate detergent-deionized water solution (SDS). The beads after several wash cycles are re-suspended in detergent free medium

Bead Assembly


1V peak to Peak 1.2 kHz

20 μm

80 μm

1V peak to Peak 1.2 kHz

Negative Dielectrophoresis- Bead Congregation away from electrode edges in regions of low electric fields

Polystyrene beads have lower polarizability as compared to the suspenion medium and get localized are regions of low electric field at the specified parameters

The concentration of the beads is 10000 beads/ml. Visualization magnification:8x

Visualization magnification: 2.5x

Equipment: Microzoom Optical Probe Station

Bead Assembly as a Cell Patterning Model


1.2V peak to Peak 3.8 kHz

20 μm

Positive Dielectrophoresis- Bead Congregation towards electrode edges in regions of high electric fields

Polystyrene beads have higher polarizability as compared to the suspension medium and get localized are regions of high electricfield at the specified parameters

Visualization magnification: 8x

Bead Assembly as a Cell Patterning Model


Separation and Positioning of Bio-particles

Neurons-Positive and Negative Dielectrophoresis

Neurons

Glial Cells

S.Prasad, M. Yang, X. Zhang, C. S. Ozkan and M. Ozkan, Journal of Biomedical Microdevices, 5(2)(2003) 125

(A) Random deposition of neurons on electrodes before the application of AC fields, (B) Patterned arraying of neurons on electrode edges on applying an AC field of 8Vpp at 4.6 MHz due to positive dielectrophoresis, (C) Movement of neurons away from electrodes due to negative dielectrophoresis

80 µm80 µm80 µm80 µm80 μm80 μm


Cell Sorting

Problem Statement:Problem Statement: Separate a specific cell type from a hybrid mix based on variations to dielectric properties, surface charge and size for a specific cell type.

Current Technological Limitations:Current Technological Limitations: Reproducibility, Speed of separation, volume of separation.

Solution:Solution: Integrate electric field effects in the micro scale to achievesorting

Goal:Goal: Separation with purity ~> 95%


Sorting Platforms

Planar, angular micro electrode array arrangement for generating point field effects

Process involving cell isolation and separation

A

20 μm

B

20 μm


Summary

Top down fabrication for micro and nanodevices using wet and dry micromachining techniques and nanomaterial integration.Silicon and soft lithography techniquesCombination of the two techniques are essential for device developmentMicro scale platforms base for both micro and nanodevicesApplications: Bead assembly, Cell sorting platforms, Drug testing platforms, Biochemical sensors

Documents

Nano Overview Top-Down Approach PRASAD - Portland …web.pdx.edu/.../Lectures/Top-Down_Approach_to_Na… · · 2006-06-29The Top-Down Approach to Nanotechnology. BIOMEDICAL MICRODEVICES