Abstract
The progressive scaling in semiconductor technology allows for advanced miniaturization of intelligent systems like implantable biosensors for low-molecular weight analytes. A most relevant application would be the monitoring of glucose in diabetic patients, since no commercial solution is available yet for the continuous and drift-free monitoring of blood sugar levels. We report on a biosensor chip that operates via the binding competition of glucose and dextran to concanavalin A. The sensor is prepared as a fully embedded micro-electromechanical system and operates at GHz frequencies. Glucose concentrations derive from the assay viscosity as determined by the deflection of a 50 nm TiN actuator beam excited by quasi-electrostatic attraction. The GHz detection scheme does not rely on the resonant oscillation of the actuator and safely operates in fluidic environments. This property favorably combines with additional characteristics-(i) measurement times of less than a second, (ii) usage of biocompatible TiN for bio-milieu exposed parts, and (iii) small volume of less than 1 mm3-to qualify the sensor chip as key component in a continuous glucose monitor for the interstitial tissue.
Highlights
Microelectronics is increasingly recognized as a unique technology platform for biomedical devices due to its functional performance on the meso- and nanoscale, at the dimensions of which most physiological processes are operative
We report on a biosensor chip that operates via the binding competition of glucose and dextran to concanavalin A
All commercially available sensors operate by enzymatic principles, where glucose is converted to gluconic acid and H2O2 and the detection of the latter is performed electrochemically
Summary
Microelectronics is increasingly recognized as a unique technology platform for biomedical devices due to its functional performance on the meso- and nanoscale, at the dimensions of which most physiological processes are operative. The technique has reached the highest degree of maturity among all biosensors in form of teststripes.5 It operates reliably, only outside the body, since the growth of body tissue on an implant affects the influx of reactants and typically causes a drift of cg(t) transients. An interesting alternative is offered by GHz frequencies The latter became accessible to the dominating CMOS (complementary metaloxide-semiconductor) technology since the late 1990s in accordance with Dennard’s scaling rules or—from a more general perspective—Moore’s law, when first MOSFETs in the GHz range were introduced.. The drift of solved ions is small in this frequency range since ionic mobilities in water (on the order of 10À8 m2 VÀ1 sÀ1 1⁄4 10 nm GHz VÀ1 (Ref. 18)) allow. It will be shown that the fundamental problem of mechanical biosensors to operate in fluid environments is conveniently solved by the approach
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