MEMS Biosensor

Biological sensors Diagnostic biochip Impedance biosensors Lab-on-a-Chip MEMS biosensor Nanobiosensors for nano- and microfluidics NEMS-based biosensors... 

Potentiometric MEMS biosensors (poten-tiometry) are based on potential measurement of an electrode in a solution. This potential is measured in an equilibrium state. In other words, current flow should not exist during the measurement. According to the Nemst equation, the potential is proportional to the logarithm of the concentration of the electroactive species. 

Voltammetric MEMS biosensors (voltammetry) are based on measuring the current-voltage relationship in an electrochemical cell consisting of electrodes in a solution. After a potential is applied to the sensor, current. 

Conductometric MEMS biosensors (conductometry) are based on measuring conductance between two electrodes in a solution. Conductance is measured by applying a small quantity of AC potential to block a polarization. The existence of ionic elements is measured as an increase in conductance. 

Theory of Electrochemical MEMS Biosensors Potentiometric MEMS Biosensors Potentiometric MEMS biosensors are a direct analytical application of the Nemst equation through measurement of the potential of nonpolarized electrodes when current is zero. A reference electrode is necessary to investigate potential changes due to biochemical reactions. Without a stable reference electrode, reliability of the biosensor cannot be achieved [3]. 

Among MEMS biosensors based on potentiometric methods, a microcalorimeter is a good example. A microcalorimeter is a kind of a self-generation sensor in which the heat of a biochemical reaction is detected. Generally, an output voltage is a function of the concentration of the substance to be measured. It is based on thermocouples. Thermocouples are two-lead elements that measure the temperamre difference between the ends of the wires. They are based... 

Conductometric MEMS Biosensors Electrolytic conductance is a non-faradaic process that can give useful chemical information. Electrolytic conductance originates from the transport of anions to the anode and cations to the cathode. In order to complete the current path, electrons are transferred at the electrode surface to and from the ions. The conductance of an electrol3Te is measured in a conductance cell consisting of two identical nonpolarizable electrodes. To prevent polarization, an AC potential is applied to these electrodes and the AC current is measured [8]. 

Among voltammetric MEMS biosensors, a piezoresistive microcantilever is a good example. The general configuration of a piezoresistive microcantDever sensor is shown in Fig. 4. The stress caused by biochemical reactions is concentrated on the surface of the microcantUever. Piezoresistors are usually placed on the microcantilever to the rim, where the stress is maximal. When the microcantilever is bent due to biochemical reaction, the resistivity of the microcantilever is changed. And by measuring the change, the concentration of the biochemical is detected [7]. 

Examples of Optical MEMS Biosensors Integrated Mach-Zehnder Interferometer... 

Besides MEMS-based electrochemical and optical biosensors, there are other types of MEMS biosensors acoustic wave, nanomaterial-based, and magnetic microbiosensors. 

When a biological substance reacts with a sensing layer which is coated on the piezoelectric substrate, the resonant frequency of the MEMS biosensor is changed. The frequency shift is related to the mass change of the biologically sensitive membrane. 

Nanomaterial-Based MEMS Biosensors Introduction A nanomaterial-based MEMS biosensor utilizes nanostractured materials as sensing media as well as a transducer. This is a unique characteristic compared to the other types of MEMS biosensors mentioned up to now. The nanomaterials have good electrical properties and high sensitivity for biological substances. Eurther-more, they are transducers as well as sensing media. This enables direct detection of biological substances without any labels. Nanomaterial-based MEMS biosensors are used for the detection of DNA, RNA, proteins, ions, small molecules, cells, and even the pH values [19]. 

MEMS biosensor based on the unique properties of nanowire enables highly sensitive and selective detection because nanowire as an electrode has a high surface-to-volume ratio for adsorption. When a chemically functionalized nanowire is immersed in an analyte solution, analytes react to biological active materials. As results of the reaction, electrical properties of the nanowire such as resonant frequency, conductivity, and resistance are changed [20, 21]. Schematic and SEM images of a MEMS-based nanowire biosensor are shown in Eig. 9. 

NEMS-based biosensors Impedance biosensors Nanobiosensors for nano- and microfluidics Biological sensors Lab-on-a-Chip Diagnostic biochip MEMS biosensor... 

Voltammetric MEMS biosensors (voltammetry) are based on measuring the current-voltage relationship in an electrochemical cell consisting of electrodes in a solution. After a potential is applied to the sensor, current, which is proportional to the concentration of the electroactive species of interest, is measured. Amperometry is a special case when potential is maintained so as to be constant with time. 

Among MEMS biosensors based on potentiometric methods, a microcalorimeter is a good example. A microcalo-... 

Voltammetric MEMS Biosensors Voltammetric MEMS biosensors measure the current flow at an electrode which is a function of the potential applied to the electrode. Voltammetric measurement gives the current-potential curve or voltammogram. These curves can be used for qualitative, quantitative, thermodynamic and kinetic studies. In contrast to potentiometry, voltammetry gives a linear current response as a function of the concentration, which is a notable advantage [6]. 

Conductometric MEMS Biosensors Electrolytic conductance is a non-faradaic process that can give useful chemical information. Electrolytic conductance originates from the transport of anions to the anode and cations to the cathode. In order to complete the current path. 

MEMS Biosensors Based on Nanoparticles Nanoparticles are often utilized as an analyte recognition element in MEMS biosensors. Nanoparticles have a quite large sensing area mainly due to their extremely small size. This enhances the reaction possibility of biomolecules. Furthermore, sensitivity of the biosensor can be increased when metal nanoparticles are positioned between two metal electrodes. When the analyte conjugated with metal nanoparticle is captured between two electrodes, the electric field intensity is amplified. Gold, silver, metal oxide and magnetic nanoparticles are widely used for detection... 

The piezoelectric biosensor is a class of micro electromechanical systems (MEMS) based on the principle of measurement of changes in oscillating crystal resonance frequency due to bioreceptor and analyte interactions. In piezoelectric MEMS biosensors, the transducer is made of piezoelectric material (hke quartz) and the biosensing material is then coated on the piezoelectric material, which vibrates at the natural frequency. Piezoelectric materials have no center of symmetry and produce an electric signal when stressed mechanically (i.e., by applying some pressure on them). A crystal oscillates at a certain... 

Ortiz, R, et al., 2008. A hybrid microfluidic system for cancer diagnosis based on MEMS biosensors. In 2008 IEEE Biomedical Circuits and Systems Conference, pp. 337-340. Available at http //ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm arnumber=4696943. 

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