A team of researchers from the Netherlands has developed chip-based fiber optic sensors with integrated laser systems to allow finding low levels of a cancer protein biomarker in a urine sample. Such fiber sensing technology is considered to offer more sensitivity than previous techniques, resulting in noninvasive, inexpensive fiber sensing ways to identify molecules that are responsible for the presence or progression of a disease.
To be more precise, such a fiber optic sensor enables researchers to make label-free detection of S100A4 that is regarded as a protein connected with human tumor development at clinically relevant levels. According to the team, fiber sensing technology promotes faster and more sensitive findings of tumor biomarkers, which favor faster treatment and better results.
The principle of fiber sensor operation is based on “the detection of specific molecules by illuminating the sample with an on-chip microdisk laser system, made with aluminum oxide”. Thus, it is possible to use aluminum oxide doped with ytterbium ions to manufacture a fiber laser that emits in a wavelength outside the laser beam light absorption band of water, while still allowing the accurate finding of biomarkers. Herewith, the frequency or color of the laser beam changes in a detectable way when there is its interaction with the biomarker under consideration.
The laser pump light equipped with the fiber optic sensor performs lasing in a micron into the resonator. Herein, fiber probes are held on the resonator surface capturing the required analytes. Then the laser beam in the ring goes through the fluid, and the attachment of required analytes shows the frequency shifting of laser system emission. Finally, it is possible to accurately measure this shift allowing the detection of minute amounts of analytes flowing over the fiber sensor in a “specific” way.
Despite the fact that fiber optic sensors that monitor laser frequency shifts are not novel, they are often regarded as not easily installed on small, disposable photonic chips, while aluminum oxide can be easily manufactured monolithically on-chip, herewith, it is compatible with conventional electronic manufacture procedures. Such fiber lasers enlarge their opportunities due to unprecedented sensitivity because of much narrower laser beam linewidth than the resonances of passive ring resonators. When other noise sources are overcome, this fiber sensing will enable the finding of minute frequency shifts from biomarkers at very low concentrations.
The developed fiber optic sensor has been already tested in complex liquids such as urine resulting in the detection of S100A4 at concentrations as low as 300 picomolar. Nowadays it is planned to integrate all the relevant optical sources and signal generation components onto the chip to make the fiber sensor even simpler to operate.
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