Sensor Detects Individual Particles in Blood Sample
19 Dec 2012
A new nanoparticle sensor was developed to detect particles in blood samples including low concentrations of proteins and nucleic acids.
The sensor comprises a thin silicon membrane. It is perforated with hundreds of small holes arranged in a regular pattern. The structure is called a photonic crystal. One of the properties of the crystal is that it amplifies parts of the light spectrum.
When looking for particles in blood samples, the photonic crystal is illuminated from behind. In this way, the intensity of light in the membrane is intensified. The crystal is impervious to light: all light is reflected and nothing gets through. Viewed from behind, therefore, the crystal looks like the dark night sky. However, each particle that is captured becomes trapped in a hole in the membrane and allows some light to leak through– giving it the appearance of a star in the sky.
Sintef (Trondheim, Norway) began the joint project with Stanford University (Stanford, CA, USA) and the University of Oslo (UiO; Norway). The aim was to build a sensor that could improve sensitivity a million fold, making it possible to detect individual particles in blood, including proteins at extremely low concentrations, as well as DNA and ribonucleic acid molecules (RNA). The result is a new nanoparticle sensor developed in MiNaLab in Oslo.
Currently, medical laboratories measure proteins to detect imbalances in the body that occur when an infection is present. The new sensor can take these analyses much further. The chemists are trying to attach receptors to the wall of each of the perforations in the membrane (biofunctionalization). When blood is pumped through, the receptors trap very specific molecules, depending on what the scientists are looking for. Because the sensor/membrane has many perforations, they can specify a wide range of different proteins. It will thereby be possible to detect illnesses such as prostate and ovarian cancer in their very early stages.
Work on the biosensors faces two challenges. The first is to make the sensors sufficiently sensitive. The second is to ensure that they measure what they are supposed to measure. The sensors must be able to differentiate between two particles, and select only those particles that have been specified. The Sintef scientists have improved their sensor''s sensitivity a million fold compared with ordinary sensors. They can now measure particles down to 20 nanometers.
"Many proteins relevant to diagnosis are in this size range, but many others are even smaller. We can currently detect individual molecules of the larger proteins. We can also detect smaller protein molecules, but not individually, i.e., we need more protein molecules before we can detect them with our sensor. However, the aim is to perfect the sensor''s architecture so that in the long term we will also be able to detect individual molecules of even the smallest proteins," said Michal Mielnik at Sintef ICT.