Multiple superimposed interface pattern porous microstructure multi layer biosensing method
A preferred embodiment biosensor is a multi-layer micro-porous thin film structure. Pores in a top layer of the micro-porous thin film structure are sized to accept a first molecule of interest. Pores in a second layer of the micro-porous thin film structure are smaller than the pores in the top layer and are sized to accept a second molecule of interest that is smaller than the first molecule of interest. The pores in the second layer are too small to accept the first molecule of interest. The pores in the top layer and the pores in the second layer are sized and arranged such that light reflected from the multi-layer micro-porous thin film structure produces multiple superimposed interference patterns that can be resolved. In preferred embodiments, the multi-layer micro-porous thin film structure is a porous silicon thin film multi-layer structure formed on a silicon substrate, such as a silicon wafer. Specific and nonspecific binding can be detected with biosensors of the invention. The position of peaks in the Fourier transform of the reflection spectrum and the shift in peak amplitudes can be used to determine the presence and quantity of targeted biological molecules of interest.
1. A method for biosensing, the method comprising:
exposing a biological analyte to a multi-layer micro-porous thin film structure that has a top layer with larger pores than a second layer, the pores being sized to produce multiple superimposed interference patterns that can be resolved in the reflectivity spectrum;
exposing the multi-layer micro-porous thin film structure to light to produce a reflectivity spectrum;
sensing the reflectivity spectrum to obtain reflectivity data;
extracting optical parameters from the reflectivity data;
determining, from the optical parameters, whether at least one biomolecule of interest is present in said biological analyte, wherein said extracting comprises fitting the interference spectrum to a double layer interference model, and wherein the double layer interference model comprises computing optical interference spectra from a model of reflectance R of light given by:
R =(ρ a 2 +ρ b 2 +ρ c 2 )+2 ρ a ρ b cos(2δ 1 )+2 ρ b ρ c cos(2δ 2 )+2ρ a ρ c cos [2(δ 1 +δ 2 )] (Eq 2)
where δ i represents the phase relationship of layer i:
δ
i
=
N
π
n
i
L
i
λ
n i represents the refractive index of layer i with thickness L i , N is a constant related to a configuration of a light source and detector respectively used in said steps of sensing and detecting, the terms ρ a , ρ b , and ρ c in eq. 2 represent the index contrast at each of the interfaces a, b, or c (top surface a, transition from top layer to second layer, and bottom of second layer):
ρ
a
=
n
air
-
n
1
n
air
+
n
1
,
ρ
b
=
n
1
-
n
2
n
1
+
n
2
,
ρ
c
=
n
2
-
n
Si
n
2
+
n
Si
where n air , n 1 , n 2 , and n Si represent the refractive index of air (or of a solution), layer 1 , layer 2 , and material used to form the thin film, respectively, the quantities n 1 and n 2 represent the total refractive index of the layer and everything it contains.
2. The method of claim 1 , wherein the phase relationship δ i is extracted.
3. The method of claim 1 , further comprising computing a fast Fourier transform of the optical interference spectra to deconvolve its interference pattern into components consisting of a top layer component, a second layer component and a top plus second layer component.
4. The method of claim 1 , wherein the multi-layer micro-porous thin film consists of the top layer, the second layer and bulk silicon.
5. The method of claim 4 , wherein the the top layer and second layer are thermally oxidized.