1. Outline Background & Motivation
Fabrication of Porous Silicon structures
Etching pores in silicon
Optical properties of porous silicon – changing refractive index
Forming the resonant cavity structure
Porous Silicon as a sensor
Applications to biomolecule sensing
Avidin & biotin interaction
Tir-IBD & Intimin-ECD interaction

2. Porous silicon
There are different kinds of pores are present depending on their sizes; pores used for in this work ~ 100nm in diameter

3. Porous silicon fabrication
Many variables: electrolyte (HF) concentration, current density, silicon doping type & density, temperature

4. Changing refractive index of Si
Bruggeman effective medium approximation:
Material in the pores changes the spectral response
(Percentage of the void space in the material)

5. Alternating the current amplitude during etching:

6. Bragg structure:
Alternating porosities = complex optical structures
Form Bragg mirrors: periodic stack of layers with two different porosities
Higher the porosity contrast, higher the reflection, higher the quality factor (Q) of the cavity. But the pores should be big enough so that materials can go through!!

7. Pores should be small enough that the sensitivity doesn’t drop

8. Using the pores for sensing

9. Experiment1: Testing the flow in the pores
60nm latex spheres can penetrate into the pores that are nm

10. Experiment 2 : Avidin & biotin interaction
The structure first oxidized  blue shift due to conversion of Si to SiO2
APTES silanized  red shift
Sulfo-NHS-LC-LC-Biotin probe molecule in PBS was immobilized  red shift
no shift occurred with buffer that has no biotin
Streptavidin in PBS (1 mg/mL)  red shift
no shift occurred on the sample with no Biotin
They calibrate their sensitivity with their simulations; they claim

11. Experiment 3 : Tir-IBD & Intimin-ECD interaction
E. Coli
Surface oxidized
Tir was immobilized in the pores using APTES & Glutaraldehyde coupling chemistry
Sensor surface was blocked with glycine methyl ester against non-specific binding
Washing steps are done with HEPES buffer
After 1h incubation with Intimin, samples were washed with HEPES for 1-2 hours  this is the key to cleaning the nonspecific trapping of molecules in the pores
Experiments done with real cell lysate (supernatants)

13. For testing selectivity:
Lysate of BL21 E.Coli, expressing Intimin
Lysate of JM109 E.Coli, NOT expressing Intimin
Tir immobilized
No Tir

14. Thanks…