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

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

Porous silicon

Porous silicon fabrication

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

Changing refractive index of Si

Material in the pores changes the spectral response

(Percentage of the void space in the material)

Bruggeman effective medium approximation:

Alternating the current amplitude during etching:

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!!

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

Using the pores for sensing

Experiment1: Testing the flow in the pores

60nm latex spheres can penetrate into the pores that are 100-120nm

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

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)

For testing selectivity:

Tir immobilized

No Tir

Lysate of BL21 E.Coli, expressing Intimin

Lysate of JM109 E.Coli, NOT expressing Intimin

Thanks…