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ELECTRICAL POROUS SILICON MICROARRAY FOR DNA HYBRIDIZATION DETECTION

ELECTRICAL POROUS SILICON MICROARRAY FOR DNA HYBRIDIZATION DETECTION. M. Archer*, D. Persaud**, K. D Hirschman**, M. Christophersen* and P. M Fauchet*

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ELECTRICAL POROUS SILICON MICROARRAY FOR DNA HYBRIDIZATION DETECTION

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  1. ELECTRICAL POROUS SILICON MICROARRAY FOR DNA HYBRIDIZATION DETECTION M. Archer*, D. Persaud**, K. D Hirschman**, M. Christophersen* and P. M Fauchet* *Center for Future Health and Departments of Biomedical Engineering and Electrical and Computer Engineering, University of Rochester, Rochester, NY **Departments of Microelectronic Engineering and Materials Science & Engineering, Rochester Institute of Technology, Rochester, NY Acknowledged support by the Infotonics Technology Center (ITC)

  2. OUTLINE • Motivation • Background • Sensing Element • Device Integration • Electrical Characteristics • Conclusions

  3. 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

  4. POROUS SILICON Macroporous layer (1-2µm pores) Electrochemical Etching - ~ 100µm (vertical scale) (100) p-type + • Chemical oxidation: • H2O2 treatment for 24hrs • hydrophylic internal surface • electrical isolation of pores • Smooth and straight pore walls • Large internal surface area

  5. DNA HYBRIDIZATION C T A • DNA has specific recognition properties G • Becomes a charged molecule in its bound form NaCl buffer solution • Induced change can be detected electrically Archer and Fauchet. Phys. Stat. Sol. (a), 198, 2003.

  6. SENSOR RESPONSE LCR 10 mm 1.1 1 0.9 0.8 0.7 0.6 1.10 Equivalent Circuit 1.00 G Normalized Capacitance (a.u) cDNA 0.90 Probe 0.80 0.70 C 0.60 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 110 Time (min)  PSi membrane LabViewTM 100KHz, 90mV p-p Electrical contact

  7. DEVICE INTEGRATION CHALLENGES Sensor Cross-talk Shunt Conductance PSi sensor membrane P-type Silicon • Shunt conductance decreases capacitance signal • Sensors must have electrical isolation

  8. INTEGRATED SENSORS Individual Sensing Element Sensor “Macroarray” Active sensing region n+ guard ring P-type substrate

  9. PROCESS FLOW p-type Silicon SiO2 Si3N4 n+ Guard Ring Porous sensing membrane Aluminum Electrodes LTO PSi n+ guard ring isolation KOH Etch Backside Opening

  10. SEM X-SECTIONS 100µm PSi Membrane Angled Cleave 10µm

  11. ELECTRICAL CHARACTERISTICS 1.2 1 0.8 0.6 0.4 0.2 0 0 5 10 15 20 25 30 35 40 45 DC Normalized Capacitance (a.u) ncDNA pDNA Time (min)

  12. ELECTRICAL CHARACTERISTICS (continued) Discrimination between binding & non-binding DNA 1.2 1 0.8 0.6 0.4 0.2 0 cDNA DC ~ 40 % ncDNA Normalized Capacitance (a.u) pDNA 0 5 10 15 20 25 30 35 40 45 Time (min)

  13. MICROSCALE INTEGRATION Optical Micrographs 4 X 4 Microarray 550µm 550µm

  14. CONCLUSIONS • 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

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