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Biosensors

This video shows how photonic nanostructures are made into biosensors.
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Having made the grating using lithography techniques as described previously, we will now turn this grating into a biosensor. The first step is to activate the surface. Think about it – the grading is made of chemically-inert materials, such as glass and Silicon, while the sensing process uses the same organic chemistry reactions that happen inside your body. So there’s a clear mismatch. We need to build up the interface so that eventually we can bond organic antibodies to the surface and use them to help us detect the biomarkers that indicate certain diseases. We insert the sample into a solution, which will activate the surface. So it becomes ready to be functionalized.
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This is a process that we do in a special cabinet overnight, so it can really have time to activate the surface. And next morning, we then take it out. The next stage, which is to attach the antibodies to this activated surface, happens inside a microfluidic channel. And here you see Casper mounting the sample in a microfluidic circuit – so first there’s a base, and now we apply the fluidic circuit, and he secures it using screws. Then he attaches small pipes so we can pump the liquid in and out of the circuits.
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Then he prepares antibodies and biomarker solutions ready for Shrishty in the characterization lab.
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So here Shrishty receives the sample and takes it to be characterized. She does this inside a darkroom because we’re using light, so we don’t want outside interference. First Shrishty mounts the pipes and the fluidics together. And you see, there is a computer controlled pump, which allows us to control the flow very precisely. And then she takes the measurement. And here’s the actual measurement. Now you see two resonance curves. These are the actual grating resonances. We can see pixel number on the bottom, this actually reflects wavelength. And you can see there is a particular wavelength where the response is strongest, where there’s the peak of the curve, and this is what we’re tracking.
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And we’re having two channels there – one channel is a reference, that’s a control. The other channel, that’s channel two, is the actual measurement channel. And then we will simply subtract one from the other. And that allows us to take out any background noise, any background interference. Now please pay attention to channel two on the right. As we insert the solution with the biomarkers we want to detect, you will see a slight shift of this curve to the left. And there it is – you can see there’s a slight shift to the left, and this is exactly the measurement information that we’re looking for.
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Now we’re doing this again, zooming in, because it’s really exciting to watch this small change, which is what it’s all about. And again, you can see how the curve slightly shifts to the left. So this small resonance shift is then converted into concentration, and the result can tell the clinician whether the patient has a particular disease – for example, whether they’re at risk of heart disease, or whether they have an infection of some kind.

Having looked at how photonic nanostructures are manufactured, this video shows how they are converted into biosensors.

The biosensors developed at the University of York combine the diffraction and Bragg mirror effects described previously. With an appropriate design, the light can be made to go back and forth within the structure many times. This back-and-forth oscillation is described as a resonance and, because the light goes back and forth along the surface in this case, we call it a ‘surface resonance’. When we shine white light onto the grating, only the resonant wavelength is reflected: the particular wavelength which equals the grating period (λ=g).

By attaching specific antibodies to the surface of the photonic nanostructure, we can make it sensitive to different biomarkers. For example, we might want it to detect biomarkers for infection. When the biomarker we want to detect binds to the antibody on the photonic nanostructure, the peak of the resonance shifts. By measuring this shift, we can detect not only the presence of the biomarker we are interested in, but also its concentration.

Biosensors use a similar principle to that already being used in biomedical laboratories by researchers studying the interactions between protein biomarkers or developing new drugs. However, the photonic nanostructure sensors allow some major advantages. The sensor can be incorporated into a handheld instrument that can be used in a GP practice or even at home, and it only requires a single drop of blood. One of the main applications will be testing for infections (viral or a bacterial), so that healthcare professionals can administer the most appropriate treatment.

The handheld instrument has already demonstrated that it can reach the required level of performance, but it needs to be tested in clinical trials before becoming commercially available.

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Frontier Physics, Future Technologies

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