A MEMS viscometric sensor for continuous glucose monitoring

Abstract

We present a MEMS sensor aiming to enable continuous monitoring of glucose levels in diabetes patients. The device features a magnetically-driven vibrating microcantilever, which is situated in a microchamber and separated from the environment by a semi-permeable membrane. Glucose sensing is based on affinity binding principles using a solution of dextran concanavalin-A (Con A) as the sensing fluid. The glucose concentration is determined by detecting viscosity changes induced by the binding of glucose to Con A through the measurement of the cantilever's vibration parameters. The device is capable of measuring physiologically relevant glucose concentrations from 0 to 25 mM with a resolution better than 0.025 mM and a phase sensitivity better than 0.4 • mM −1. The response of the sensor to glucose concentration changes has a time constant down to 4.27 min, and can be further improved with optimized device designs.

Fabrication and Testing of an Osmotic Pressure Sensor for Glucose Sensing Application

“…Nevertheless, the response time of the present work is much higher when compared to a value of 1.5 min reported in [10,11]. The response time is much smaller in those glucose affinity sensors [10,11,35], because the time needed for the glucose molecule to associate/dissociate with the polymer is smaller. The response time is high for the glucose sensor in [26], even though it involves chemical binding, due to the expansion or contraction time required for the hydrogel.…”

“…In the case of the glucose affinity smart hydrogel, glucose solute molecules permeate through membrane [10,11,26], where in the present work, the solvent molecules flow through the semi-permeable membrane. Moreover, the present work is related to the volume change inside the cavity with respect to the change in glucose concentrations, which finally brings a deflection in the Si membrane, and like in [10][11][12]26,35], neither any chemical reactions nor any mechanical excitation's are involved, so that the lifetime of the device is improved. The sensing mechanism employed in the present work is very simple compared to the other glucose sensing devices, as the variations in the glucose concentration levels are directly measured in terms of voltage, with the help of a simple Wheatstone bridge and a battery.…”

“…The sensing mechanism employed in the present work is very simple compared to the other glucose sensing devices, as the variations in the glucose concentration levels are directly measured in terms of voltage, with the help of a simple Wheatstone bridge and a battery. In the case of the capacitance change reported in [11,35], an external circuit is employed to convert the changes into a voltage. Another sensing mechanism is optical in nature, and the one required to detect the deflection in the cantilever beam corresponds to glucose concentrations [12]; such a method is not suitable for implantation purposes, and it is unstable in a mobile environment.…”

A viscosity-dependent affinity sensor for continuous monitoring of glucose in biological fluids

“…Affinity sensing is more tolerant to biofouling that only increases the time for the system to stabilize, and is also insensitive to electroactive interferences. For these reasons, investigation on affinity binding sensors has been undertaken using various technologies, such as fluorescence (Ballerstadt et al, 2004(Ballerstadt et al, , 2006(Ballerstadt et al, , 2007Ballerstadt and Schultz, 2000) or viscosity-based (Beyer et al, 2001;Diem et al, 2004;Huang et al, 2009;Kuenzi et al, 2011;Zhao et al, 2007) principle. Recently, hydrogel-based sensors have emerged as promising tools for affinity sensing (Tierney et al, 2009a(Tierney et al, , 2009b.…”

Frequency Response of Nanoelectromechanical Cantilevers Operating in Fluid

“…As the applications of cantilever-based nano-systems [1] expand to include chemical sensing [2], medical instrumentation [3], data storage [4], atomic-force microscopy [5], and nano-fabrication [6] the need for sophisticated actuation and control will also increase. [7] This requires determination of the frequency response of the system, which will be heavily influenced by the damping.…”