Breaking paradigms in biochemical sensing

By Jose Fernandez Villasenor

Originally posted on Freescale’s Medical by Design, The Embedded Beat blog

Early stage detection of potentially life-risking disease conditions, as well as easily accessible, low-cost detection devices for the general population, challenges our healthcare services. Why wait until you need a triple or quadruple coronary cardiac bypass surgery if you could easily detect at an early stage the genetic risk factors for diabetes, hypercholesterolemia, obesity or arterial hypertension? Early detection can lead to correction with appropriate medical treatment and changes to the patient’s lifestyle.

How the testing is done

The reality is these tests are not commonly screened in patients worldwide. Sometimes it is because the patient does not have regular visits to the doctor’s office and they wait until they have an annoying symptom. Other times it is because these tests are not available to the general population or doctors only screen when they are suspicious of a condition.

Think about a suspected pregnancy. Most women do home testing before confirmation of the pregnancy by their obstetrician and gynecologist (OB/GYN) doctor. They prefer to do a simple urine test (by the way, this does not confirm the pregnancy at all). These tests are low cost and available to everyone without the need of a prescription. The way these home tests work are simple. The protein, antigen or antibody you want to detect, in this case human chorionic gonadotropin (better known as hCG), reacts to the chemical in the testing strip and changes its color.  The problem is that this is a YES/NO test, whether you have the particle or you do not have it. However the amount or quantity of this particle is useful for the diagnosis as well, i.e. an abnormal high level of hCG could also mean other potentially serious pathologies like molar pregnancy (an abnormal form of pregnancy wherein a non-viable fertilized egg implants in the uterus and converts a normal pregnancy into an abnormal one which will fail to come to term), multiple pregnancy, whereas low levels  can indicate a possible miscarriage or blighted ovum or ectopic pregnancy.

Delivering both qualitative – and quantitative results

A new generation of sensors should be available to the general population for not only giving qualitative results but also quantitative results.

Freescale is working on a new generation of biochemical sensors that help to solve these issues. This technology is based on Ion Sensitive Field Effect Transistors (IsFETs). In these sensors, we show that by using Metal-Insulator-Metal (MIM) structures integrated in series to the gate of submicron Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices, highly-sensitive and ultra-low power consumption pH sensors can be obtained. One MIM capacitor enables external polarization of the MOSFET device while a second MIM capacitor is connected to a sensing plate whose surface is either a thick polyimide layer or the last metallization level. The electrochemical response of these surfaces to pH buffer solutions resembles that of ISFET devices whose pH sensitivity is dependent on the type of surface material being exposed.

The IsFETs are then used to create Immunological sensitive FETs ImFETs, which can be used to detect not only pH, but also to detect antigens and antibodies of specific pathogens that cause a wide array of infectious diseases that could be markers used to detect chronic degenerative diseases.

New needs in the world need to be solved with a new generation of medical sensors. This means breaking the paradigms of optical tests and moving to the electrochemical space, with more reliable sensors that can give you detailed results of the quantities of the specific particle you want to measure. Semiconductor companies should and must turn their eyes to this and enable the OEMs with new products of low cost and low power specifications.


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