Smart Sense
Posted date : Jul 26, 2010

UCL researchers leverage SOI in a powerful, affordable sensor design.

Medical challenge

In pharmacology, medical diagnostics or security applications, sensors that detect micro-nano-objects like biomolecules, cancer markers or infectious agents need to be faster, smarter and more sensitive, but also more affordable.

Design challenge

There are many different approaches to integrated sensor-on-a-chip design, but basically they comprise:

  • a transducer, which is the “detector”  incorporating several electrodes used to transform a physicochemical property into a quantifiable electrical signal
  • the associated “read-out” electronics.

However, current nano-devices for detecting biomolecules are expensive to manufacture, difficult to integrate into standard CMOS, and cannot easily be “tuned” in a “smart sensor” scenario.

Cross-section of the ISIT showing a high concentration of carriers in the SOI body below the insulated electrodes (left) and the induction of a depleted region by the biomolecule target (right). (Courtesy: UC Louvain)

SOI solution

UCL researchers have patented an innovative, new bio-compatible Insulated Substrate Impedance Transducer (ISIT).

The ISIT combines a semiconductor transduction principle with a dielectric impedance measurement method derived from electrochemistry and telecommunications. As in sensors based on the Ion-Sensitive FET, the ISIT working principle involves the conductance change of a semiconductor in response to an extrinsic physicochemical stimulus.

But the ISIT is based on pairs of  aluminum micro-electrodes insulated from the SOI layer by a thin dielectric, and from the external medium by a thin alumina layer. This confers biochemical protection as well as high molecular coupling. Because the conductance change is sensed through an insulator, a modification of the ISIT intrinsic dielectric relaxation constant is induced.

The resulting field-effect modulation of channel conductance is accurately measured by dielectric impedance spectroscopy between the electrodes, which enables substantially more sophisticated signal analysis than current methods. Furthermore, the SOI solution enables the operation to be tuned using the back gate, thereby enabling multi-parameter measurements with improved quality, higher sensitivity and better detection limits.

The first ISIT demonstrators detected 530 base pair DNA targets in a concentration below 1nM. Another demonstration achieved the specific detection of less than 100 Stapphylococcus Aureus bacteria as can be found in a ml sample of infected blood.

Importantly, the ISITs are easy to manufacture on SOI, opening the door to a dynamic, intelligent measurement system-on-chip.

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