Detecting cancer antigens with nano holes

According to recent research by US scientists, nanometer-sized recesses on ultrathin gold films built on glass substrates can be used in biochemical sensors.

This new technique does not require the marking of biological molecules as current exploration methods, conducted by measuring the change of surface plasmon resonance (SPR) peaks in light spectrum. Infrared light transmits through holes.

It can be used to sense the selection of carcinogenic antigens in small amounts to picogam (10-12g) when the gold and glass surfaces are altered by biological molecules (These results are moderate). Published in Applied Physics Letters 90 073901, 2007 ).

The tendency to use nanoparticles of precious metals is increasing in nano-optical sensors.These nanoparticles have high optical scattering properties and the ability to absorb near-visible and infrared wavelengths due to local surface plasmon resonance effects (localized SPR). The surface plasmon resonance is a classical effect in which the electromagnetic field of light drives the collective vibrations of free electrons in the nanoparticles to resonate. This effect can occur when a plane-polarized light wave hits a metal film under full-reflection conditions.

Recent researchers have shown that nanoscale niches in thin films (thin in optical properties) have a local surface plasmon resonance effect (LSPR). When these holes are randomly distributed, the LSPR effect of the cavities creates a resonant peak in the absorption spectrum. And the position of this peak can vary depending on the environment around the niches - an effect that can be exploited to design sensors based on the SPR effect that can be used to detect different molecules. around niches.

Jerome Schultz and colleagues at the University of California, Riverside (USA) have successfully built that sensor. To create nano holes on glass substrates, the team initially created nanoparticles of polystyrene spheres randomly distributed on the glass surface. Next, use gold to cover these spherical particles, and eventually remove the polystyrene spheres. These cavities have a diameter of about 60 nm on the surface of a thin film of gold 20 nm ( see Figure 1 ).

Fig. 1. Electron micrograph of cavities. (Photo: Nanotechweb)

Schultz and colleagues measured the absorption spectrum of the device and found that it had a resonant peak at 600 nm. To show that this plate can be used as a biological sensor without cell marking, the researchers attached antibodies to the 19-9 antigen (CA 19-9) on the surface in the form of solutions. contains CA 19-9 on the surface of the device, then measures the absorption spectrum again. As a result, the resonant peak peaks towards the 10 nm long wave (red shift).

The researchers also identified a small amount of antigens of only 1 pg that could be detected. They also confirmed that the device could be made to detect a selection of different carcinogenic antigens by functionalizing the glass surface with the previous antibodies.

Figure 2. CA125 Antigen.

"This technology allows us to detect and quantify probiotics without marking cells or biological molecules," Schultz explains. "Many other techniques require marking with fluorescence," he said. or enzymer or other secondary biology . but our technique is only needed with a bio-recognition molecule, such as an antibody, that can have specific affinities with biological preparations learn".

The team is conducting studies to deposit a variety of biomarkers onto a substrate. These results have just been published in the prestigious Applied Physics Letters .

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