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)

OUTLINE  Motivation  Background  Sensing Element  Device Integration  Electrical Characteristics  Conclusions

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 SILICON Chemical oxidation: H 2 O 2 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 Etching Macroporous layer (1-2µm pores)

DNA 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, Induced change can be detected electrically NaCl buffer solution

Electrical contact 10 mm PSi membrane SENSOR RESPONSE Normalized Capacitance (a.u) Time (min) Probe cDNA LCR  100KHz, 90mV p-p G C Equivalent Circuit LabView TM

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

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

p-type Silicon SiO 2 Si 3 N 4 n + Guard Ring Aluminum LTO PSi KOH Etch Backside Opening Porous sensing membrane n+ guard ring isolation Electrodes PROCESS FLOW

SEM X-SECTIONS 100 µ m 10 µ m Angled CleavePSi Membrane

Normalized Capacitance (a.u) Time (min) ELECTRICAL CHARACTERISTICS CC pDNA ncDNA

ELECTRICAL CHARACTERISTICS (continued) pDNA cDNA  C ~ 40 % ncDNA Time (min) Discrimination between binding & non-binding DNA Normalized Capacitance (a.u)

MICROSCALE INTEGRATION 550µm 4 X 4 Microarray Optical Micrographs

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