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
