ELECTRICAL POROUS SILICON ELECTRICAL POROUS SILICON MICROARRAY FOR MICROARRAY FOR

DNA HYBRIDIZATION DETECTIONDNA HYBRIDIZATION DETECTION

M. Archer*, D. Persaud**, K. D Hirschman**, M. Christophersen*M. Archer*, D. Persaud**, K. D Hirschman**, M. Christophersen*and P. M Fauchet*and P. M Fauchet*

*Center for Future Health and Departments of Biomedical Engineering *Center for Future Health and Departments of Biomedical Engineering and Electrical and Computer Engineering, University of Rochester, and Electrical and Computer Engineering, University of Rochester,

Rochester, NYRochester, NY

**Departments of Microelectronic Engineering and Materials Science & **Departments of Microelectronic Engineering and Materials Science & Engineering, Rochester Institute of Technology, Rochester, NYEngineering, Rochester Institute of Technology, Rochester, NY

Acknowledged support by the Infotonics Technology Center (ITC)Acknowledged support by the Infotonics Technology Center (ITC)

OUTLINEOUTLINE

Motivation Background Sensing Element Device Integration Electrical Characteristics Conclusions

MOTIVATION – “Lab-on-a-Chip”MOTIVATION – “Lab-on-a-Chip”

Porous Silicon (PSi) is an excellent sensor material Large surface area to volume ratio Electrical properties sensitive to surface charge Effective medium host

PSi-based sensors Sensitive to chemical infiltration Label-free detection of DNA hybridization in real time Reduction to micro-scale dimensions

Electrically addressable PSi biosensor microarrays Compatible with silicon process technology Potential integration with microelectronics &

microfluidics

POROUS SILICONPOROUS SILICON

Chemical oxidation:H2O2 treatment for 24hrs • hydrophylic internal surface• electrical isolation of pores

• Smooth and straight pore walls

• Large internal surface area

(100) p-type

~ 100µm(vertical scale) +

-

Electrochemical EtchingMacroporous layer (1-2µm pores)

DNA HYBRIDIZATIONDNA HYBRIDIZATION

A T

G C

• DNA has specific recognition properties

•Becomes a charged molecule in its bound form

Archer and Fauchet. Phys. Stat. Sol. (a), 198, 2003.

• Induced change can be detected electrically

NaCl buffer solution

Electrical contact

10 mmPSi membrane

SENSOR RESPONSESENSOR RESPONSE

0.60

0.70

0.80

0.90

1.00

1.10

0 10 20 30 40 50 60 70 80 90 100 110

No

rmal

ized

Cap

acit

ance

(a.

u)

0 10 20 30 40 50 60 70 80 90 100 Time (min)

ProbecDNA

1.1

1

0.9

0.8

0.7

0.6

LCR 100KHz, 90mV p-p

G

C

Equivalent Circuit

LabViewTM

DEVICE INTEGRATION CHALLENGESDEVICE INTEGRATION CHALLENGES

P-type Silicon

PSi sensor membrane

Shunt Conductance

SensorCross-talk

• Shunt conductance decreases capacitance signal

• Sensors must have electrical isolation

INTEGRATED SENSORSINTEGRATED SENSORS

Individual Sensing ElementIndividual Sensing Element

Active sensing region

P-type substrate

n+ guard ring

Sensor “Macroarray”

p-type Silicon

SiO2

Si3N4

n+ Guard Ring

Aluminum

LTO

PSi

KOH Etch Backside Opening

Porous sensing membrane

n+ guard ring isolation

Electrodes

PROCESS FLOWPROCESS FLOW

SEM X-SECTIONSSEM X-SECTIONS

100µm

10µm

Angled CleavePSi Membrane

0 5 10 15 20 25 30 35 40 45

1.2

1

0.8

0.6

0.4

0.2

0Nor

mal

ized

Cap

acita

nce

(a.u

)

Time (min)

ELECTRICAL CHARACTERISTICSELECTRICAL CHARACTERISTICS

C

pDNA ncDNA

ELECTRICAL CHARACTERISTICS ELECTRICAL CHARACTERISTICS (continued)(continued)

0 5 10 15 20 25 30 35 40 45

1.2

1

0.8

0.6

0.4

0.2

0

pDNA

cDNA

C ~ 40 %

ncDNA

Time (min)

Discrimination between binding & non-binding DNAN

orm

aliz

ed C

apac

itanc

e (a

.u)

MICROSCALE INTEGRATIONMICROSCALE INTEGRATION

550µm

550µm

4 X 4 Microarray4 X 4 MicroarrayOptical Micrographs

CONCLUSIONSCONCLUSIONS

PSi-based biosensors exhibit an electrical response to DNA hybridization

Sensor arrays have been fabricated

A unique electrical isolation scheme has been developed

Future work in system integration