Researchers at the Technical University of Madrid's Laser Center (Madrid, Spain) say they have created chip-based label-free optical biosensors that combine semiconductor technology with photonics, optics, and biochemistry for improved biomedical diagnostic capability. "Our vision is to create a highly sensitive, label-free optical biosensing system that is fully compatible with semiconductor technology and can be fabricated and interrogated at wafer or disposable chip level," report Miguel Holgado, María-Fe Lagunas, and Rafael Casquel in a paper describing their approach published by the SPIE. "Our holistic approach combines biophotonic resonant or interferometric sensing cells and advanced micron and sub-micron spot size high-sensitivity optical interrogation technologies. This approach leads to a new generation of high-value biochips that are scalable at the wafer level without the need for complex coupling systems, thus offering an inexpensive solution for integration and packaging."
Planar photonic biosensors are generally more attractive than traditional biosensors because they integrate multiple compact devices on a single chip. But, although they use low cost mature semiconductor technology, they normally need complex optical coupling systems, such as inverted taper and grating couplers, which make the devices less cost effective. The Madrid researchers take a different approach to solve this problem.
The team uses a tightly focused beam to allow in situ measurement of micron and sub-micron size geometries. They previously demonstrated the capability to measure extremely small volumes of analytes (on the order of 0.1fL per hole). This system, they say, makes routine screening more cost effective and, because each wafer can integrate hundreds of sensing structures, it is also suitable for performing hundreds of measurements on one or multiple samples with high throughput and on-wafer monitoring. To determine the interactions with receptor biomolecules with more reliability and sensitivity, the system will be tremendously sensitive to refractive index variations: on the order of 10−6 or even 10−7 refractive index units (RIUs). This means that direct detection of picomolar or even lower concentrations is feasible. Both observation of the reflectivity profile and magnification of the biophotonic resonant or interferometric sensing cells will facilitate this sensitivity.
The researchers say their system is more cost effective and provides more capabilities than current options. "The system will be much more reliable, removing ambiguities during the sensing interrogation process and achieving higher throughput and productivity in comparison with other established analytical techniques," they report.
The paper, Label-free optical biosensor on a single chip at spie.org.