Chad K. Park's Blog

24, November 2010

IP placeholder – ultimate in waveguide resonance

Filed under: Uncategorized — chadkpark @ 9:37 pm

So, this post has been stewing around my mind for a long time. The cons are that I don’t trust several of the professors who would seek to take my idea as their own – likely patenting it and then giving me a rough time when I finally get everything together to make it happen. Pros of writing it are that (i) I get it off my chest and (ii) it may actually be a way of establishing the time of my idea(s).

I’d been told by someone (or I read it on the infallible web) that you can blog about an idea and it counts as establishing a timed proof of when that idea occurred. This is critical for intellectual property rights and comes up all the time in patent litigation. Of course, I don’t know for a fact that it’s true, and I worry that I’ll offend the professorial powers that be if they knew. On the other hand those same professors are known for telling me (and others) to “just put the protein in the instrument.” I also heard, “well, so-and-so got a paper on it.” Not exactly supporting the control experiments …. anyway.

On to the ideas. Bilayers (typically phospholipids) can be formed on two (native) surfaces. That is, bilayers as we understand them in contact with solid supports. First is clean silica. You can get bilayers to form on silicon wafers, but only if you let the native oxide remain and it’s clean. Dirty surfaces tend to get you messier stuff – not usually bilayers or at least incomplete things. The second native surface is mica. My Ph. D. was a whole lot about making bilayers on mica with a little bit about making some on silica. It turns out you can get bilayers to form on other surfaces, but you usually have to do some chemistry first. I spent time in Zyomyx making bilayers form on alkane thiol monolayers attached to gold surfaces. The thiols usually had to have a different end group to support the formation of bilayers. I did some work on tethering bilayers with reactive lipids and I have made bilayers form on polyethylenimine. This is all established in the scientific literature.

By ‘making bilayers’ I mean the two main ways of getting phospholipids to self-assemble on a surface such that it’s two layers thick with the tails in the middle. The first is with Langmuir-Blodgett deposition and the second is vesicle adsorption. I’ve done both.

So, when it comes to deciding on a surface for forming bilayers in a resonance spectrometer like the plasmon waveguide resonance spectrometer developed at U. of AZ, my idea is to use backsilvered mica as a disposable support. There are huge advantages. It’s atomically smooth so you should get much better resonances. The silvering doesn’t need any adlayer like chromium which is what makes coating glass surfaces tricky. You can use a drop of optical coupling (Cargille) liquid to bring the laser (or white light source) onto the surface from the prism. Actually, I would use a hemispherical glass instead of a prism. That way, once aligned, you don’t have to worry about refraction of the incident light. I mean we can calculate the deviation from Snell’s law, but why bother when you can build the surface correctly? That way the angle of incidence, established by the optical components, is actually the angle of incidence in the waveguide resonator and substrate.

The next big part is that there should be corroborative data for the waveguide resonance experiment. This works for all such spectrometers, Biacore’s, Aviv’s all the other guys making these things. I spent a lot of time with the surface forces apparatus and I had to do a lot of corroborative imaging on the same substrates to confirm that I had what I thought I had on my experimental surfaces. I propose to do this in situ. Ideally, I’d like an inverted fluorescent microscope with an AFM designed for liquids on top. The plasmon generating light comes in from the side. You can use the light microscope to look at formation of the bilayer as in black-lipid membranes. You can use the fluorescence to probe the lipid and proteins in the field of view. There’s a *huge* literature on fluorescence and quantifying lipid and protein properties. You can even fluorescently tag your ligand and have a corroborative binding curve that should match the resonance shifts in a typical plasmon waveguide resonance titration experiment. You can also use the plasmons themselves as a way of exciting the fluorophores and then the fluorescent microscope can monitor them. The AFM would ideally be the one from Asylum research which is designed for biological materials in aqueous environments and sits on top of an inverted microscope. The advantage is that you can further corroborate the thickness of your bilayer and possibly have a way of looking at the dispersal or even shape of the extramembranous protein domains. How fun would it be to see ligand binding induced dimerization occur in real time by AFM and fluorescence while simultaneously measuring the binding constant with shifts in the waveguided plasmons’ resonance shifts? It’d be difficult to get the orientation right with the AFM and fluorescence and waveguide resonance. You’d have to have a substrate that’s half silvered and you’d have to have the bilayer sitting on the substrate and then image through the spherical lens.

Finally, no moving parts. Oh my stars and garters. What a genius idea. Except Biacore did it first. For some reason Aviv chose to go with the whole sample stage moving which I think is ludicrous. I mean, at least raster the beam, not the sample, but no….. Well, I say bring in a cone of light at the angles at which you expect the resonance to occur and then read out the resulting image on a linear diode array or a camera like a CCD. Even better, you can use a white light source and separate the various wavelengths in the reflected beam. Since the resonance position depends on thickness and refractive index, having multiple wavelength data will let you differentiate thickness changes from RI changes. Turns out thickness is not a function of wavelength and refractive index is.

So that’s about it. I hope it doesn’t come to patent lawyers and litigation. But for better or worse I’ve established my claim to some extent; hijacking patenters beware. Now, I feel a little better about putting this idea into grant form so I can beg for money to actually *build* the thing.


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