Shalini Prasad, Ph.D. Department of Electrical and Computer Engineering Biomedical Micro devices and Nanotechnology Lab Portland State University

Transcription

1 The Top-Down Approach to Nanotechnology Shalini Prasad, Ph.D. Department of Electrical and Computer Engineering Biomedical Micro devices and Nanotechnology Lab Portland State University BIOMEDICAL MICRODEVICES AND NANOTECHNOLGY LAB

2 Theme () Chemical Sensing Platforms Micro/Nano Sensors and Devices Lemay et. al. Nature, 412 (2001) 617 Carbon nanotubes Yamaguchi et. al. Nature.Mat. 3, (2004) Porous 337 Alumina CdSe ZnS Quantum Dots Belcher et. al. Science 303,(2004) 213 Nanowires Bio-electronic interfaces

3 Motivation There is an immense need for sensors with broad based detection capability, rapid response times, automation capability, and portability. 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 and 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

4 Micromachining and Soft Fabrication

5 Micromachining Materials

6 Soft Fabrication Materials

7 Bulk Micromachining

8 Surface Micromachining Courtesy: Fatikow and Rembolt 1997

9 Mask Creation

10 Silicon Wafer Preparation

11 Thermal Silicon Oxide

12 Thermal Silicon Oxide Methods

13 Spin Casting Resist

14 Resist Types

15 Photolithography Process

16 Photoresist Types

17 UV-Exposure at nm

18 Developing the UV Exposed Wafer

19 Etching Methods

20 Etching Profiles

21 Dry Chemical Etching: Reaction Mechanisms Courtesy: M.Madou, Fundamentals of Microfabrication

22 Dry Chemical Etching: Loading effects- bull s eye

23 Dry Chemical Etching: Ion energy vs. Pressure

24 Reactive Ion Etching

25 Physical Sputtering

26 Sputter Yield

27 Resist Stripping

28 Profilometry

29 Profilometry Graph

30 Energy, Vacuum and Directionality

31 Soft Lithography

32 PDMS Lithography (Silicone)

33 Micro contact Printing (μcp)

34 Micro Transfer Molding (μtm)

35 Micro molding in Capillaries (MIMIC)

36 Smart Polymers and Hydrogels

37 Microelectrode Array (MEA) Technology

38 Planar Microelectrode Array Fabrication Sequence A. PECVD Silicon Nitride Deposition Si 3 N 4 4 D. Platinum Etching Si B. E- beam Platinum Deposition Pt E. Photoresist Removal C. Photoresist Patterning S.Prasad, et. al. J.Biomed.Microdevices.5(2), (2003) 125

39 Prototypes of Microelectrode Arrays that Function as Analysis Platforms 40 μm 2x2 platinum MEA with fibronectin permeation layer used for cell morphological studies 3x3 platinum/titanium MEA used for environmental sensing applications. 200 μm 5x5 microelectrode array comprising of platinum electrodes used for sensing and diagnostic applications.

40 Determination of Electrical Field Distribution on a Microelectrode Array Electrode Strength (V/m) Max Particle Electrode Strength (V/m) Max Electric field distribution on a 4x4 section of the microelectrode array in the absence of micro particles Min 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

41 Manipulation Of Micro particles

42 Bead Assembly 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. 0V Peak to Peak 80 μm 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 detergentdeionized water solution (SDS). The beads after several wash cycles are re-suspended in detergent free medium 20 μm

43 Bead Assembly as a Cell Patterning Model Negative Dielectrophoresis- Bead Congregation away from electrode edges in regions of low electric fields 1V peak to Peak 1.2 khz Polystyrene beads have lower polarizability as compared to the suspenion medium and get localized are regions of low electric field at the specified parameters Visualization magnification: 2.5x 1V peak to Peak 1.2 khz 80 μm The concentration of the beads is beads/ml. Visualization magnification:8x Equipment: Microzoom Optical Probe Station 20 μm

44 Bead Assembly as a Cell Patterning Model Positive Dielectrophoresis- Bead Congregation towards electrode edges in regions of high electric fields 1.2V peak to Peak 3.8 khz 20 μm Polystyrene beads have higher polarizability as compared to the suspension medium and get localized are regions of high electric field at the specified parameters Visualization magnification: 8x

45 Separation and Positioning of Bio-particles Neurons-Positive and Negative Dielectrophoresis 80 µm Glial Cells Neurons 80 μm 80 μm (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 S.Prasad, M. Yang, X. Zhang, C. S. Ozkan and M. Ozkan, Journal of Biomedical Microdevices, 5(2)(2003) 125

46 Cell Sorting 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. Goal: Separation with purity ~> 95% Current Technological Limitations: Reproducibility, Speed of separation, volume of separation. Solution: Integrate electric field effects in the micro scale to achieve sorting

47 Sorting Platforms A Planar, angular micro electrode array arrangement for generating point field effects 20 μm B Process involving cell isolation and separation 20 μm

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