Micro Cantilever Bio Detection

8/14/2019 Micro Cantilever Bio Detection

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Microcantilever-based BiodetectionAlan, Ben, Sylvester


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Principle of Microcantilevers

The key elements in the detection of a mass arethe vibrational frequency and the deflection of thecantilever*

Deflection*Proportional to mass contentResonance frequency*

R =(k/m) 1/2

K = spring constantM= mass

*Sandeep Kumar Vashist (2007) Review of Microcantilevers for Sensing ApplicationsJournal of Nanotechnology 3: 1-15.


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Readout Method

There are several methods available toobserve the deflection and resonancefrequency of the microcantilever*Optical*Piezoelectric*

Piezoresistive*

*Sandeep Kumar Vashist (2007) Review of Microcantilevers for Sensing Applications Journal of Nanotechnology 3: 1-15.


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Optical

Optical method requires the use of a lowpower laser beam*

If microcantilever does not deflect, then nobiomolecules have been absorbed*Laser beam hits a specific position on theposition sensitive detector (PSD)*Major weakness-high cost*

*Karolyn M. Hansen, Hai-Feng Ji, Guanghua Wu, Ram Datar, Richard Cote, Arunava Majumdar, and Thomas Thundat(2001) Cantilever-Based Optical Deflection Assay for Discrimination of DNA Single-Nucleotide Mismatches. Analytical

Chemistry 73 (7): 1567-1571


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Piezoresistive

These sensors measure the strain inducedresistance change*When the biomolecules are absorbed bythe material there is a volumetric changein the sensing material*Volumetric change is measured byresistance change in cantilever*Advantages-Low cost*

*Viral detection using an embedded piezoresistive microcantilever sensor. Sensors and Actuators A: Physical 107 (3), 219-224


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Piezoelectric

These sensors detect the change in theresonance frequency of microcantilever only*Use microactuator to drive the plate intoresonance*Microsensor to the determine thefrequency of the plate*

*S. Zurn, M. Hsieh, G. Smith, D. Markus, M. Zang, G. Hughes,Y. Nam, M. Arik and D. Polla (2001) Fabrication and structuralcharacterization of a resonant frequency PZT microcantilever. Institute of Physics Publishing 10: 252-263


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Applications

Microcantilevers may beused to detect thepresence against

viruses, or evencancerous cells**Mass detection of Vaccina virus particle*Cancer monitoring**

*Amit K. Gupta, Pradeep R. Nair, Demir Akin, Michael R. Ladisch, SteveBroyles, Muhammad A. Alam, and Rashid Bashir (2006) Anomalousresonance in a nanomechanical biosensor. PNAS 103 (36): 13362-13367

**Mauro Ferrari (2005) Cancer Nanotechnology: Opportunities andChallenges. Nature Publishing Group 5, 161-171

Figure 1*

Figure 2**


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Simulation (Mode Analysis)

f 0=194,532Hz f 1=194,483Hz

S Morshed and B.C. Prorok (2007) Tailoring beam mechanics towards enhancing detection of hazardous biological species.Experiment Mechanics 47:405-415


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Design and optimization

Tailoring geometry to improve resonance frequency and shiftfrequency

K

m

Increase the spring constant

Reduce the effective mass at the fee end


f / m= k 1/2 m-3/2 f=2 k 1/2 m-1/2


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f= 41Hz

f= 49Hz

f= 69Hz

f= 36Hz

f= 31Hz

Conclusion: Increase the clamping width;

Reduce the width in free end



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f =

506Hz

Another advantage is the relativelyuniform stress distributions

We can put more piezoresistors on

Disadvantage: Not enough room at the tip for capturing bioparticles!S Morshed and B.C. Prorok (2007) Tailoring beam mechanics towards enhancing detection of hazardous biological species.

Experiment Mechanics 47:405-415


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Final StructureTrapezoid-like cantilever

f= 150Hz

Further improve thefrequency shift, how?

Higher frequency mode!



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Higher frequency mode

Element Model Solid187 6163 Elements overall

Material properties Youngs modulus Density Poisson Ratio

Value 100 GPa 2850 kg/m 3 0.24



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Higher frequency mode

Mode 1 Mode 2

f= 150Hz f= 300Hz


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Higher frequency modeMode 5

f= 200 Hz

1 2 3 4 55 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

3 5 0

4 0 0

Order

F r e q u e n c

y S h i f t ( H z )

Conclusion: Mode 2 has double shift frequency, and its amplitude is bigenough for piezoresistors to sense.


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Sensitivity Analysis

The mass of the applied particle is 0.285pg; while the frequency shift is 300Hz(using cantilever shape G and operating atthe second mode)

The sensitivity:S = 300Hz/0.285pg=1.0510 18 s -1kg -1


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Fabrication:Phase One

o The unaltered SOIwafer

o Ion implantation to formpiezoresistive element(Boron, dose ~10 14/cm 2)

o Deposition of photoresist on upper silicon layer (~1m)

Phase one of the fabrication process

Photoresist


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Fabrication:Phase Two

o Photolithography todefine tip andelectrode

o Wet etching toeliminate unexposedphotoresist

o Further etching toremove exposedphotoresist

Phase two


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Fabrication:Phase Three

o E-beam deposition of titanium (~5 nm)

o E-beam deposition of Au (~150 nm)

o Wet etching of remaining photoresist

Phase three


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Fabrication:Phase Four

o DRIE to definecantilever

o Bulk DRIE to

eliminate Sisubstrate

o Wet etching for removal of SiO 2 tofree cantilever

Phase four


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Fabrication:Phase Five

o Biosensitive filmselectively bindsto gold, allowingcantilever dipping

Cell selectively bindingto biosensitive layer*

*Images can be found in: Lan, S., Veiseh, M. and Zhang, M. Surface modification of silicon and gold-patterned silicon

surfaces for improved biocompatibility and cell patterning selectivity. Biosensors and Bioelectronics , 2005, 20(9), 1697-1708

Cells cultivated on gold withsilicon substrate after

biosensitive treatment*


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Fabrication:Phase Six

o Piezoelectricactuator stamped

on base of cantilever

The final product: a MEMSbiosensor


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Summary

Portable device with convenient readoutand external actuation.Optimized geometry and frequencysensitivityEasy fabrication using SOI wafer


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Questions?

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Micro Cantilever Bio Detection