BIOMEMS Class I. Introduction: From MEMS to BIOMEMS/ Definitions Winter 2011. Dr. Marc Madou. Aequorea victoria. Content. From MEMS to BIOMEMS BIOMEMS and analytical chemistry Definition of sensors Sensitivity Cross-sensitivity and crosstalk
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Class I. Introduction: From MEMS to BIOMEMS/
Dr. Marc Madou
‘Miniaturization engineering’ is a more appropriate name than MEMS (NEMS), but the name MEMS (NEMS) is more popular. It involves a good understanding of scaling laws, different manufacturing methods and materials.Initially it involved mostly Si and mechanical sensors (e.g., pressure, acceleration, etc). Miniaturization engineering or MEMS applied to biotechnology is called BIOMEMS. In BIOMEMS the number of materials involved is much larger, modularity is often a must (not integration as in ICs !), costs often need to be less than what’s possible with Si and batch processes are not always the answer ( continuous manufacturing need !).
BIOMEMS may often be seen as a type of analytical technique used in many research areas :
Analytical techniques which are also used in many industrial areas :
Forensic science (e.g. O.J.’s DNA)
Clinical diagnostics (e.g.glucose in blood)
Product development (e.g. new drug)
Quality control (e.g.pH of swimming pool)
Both instruments and sensors (see next viewgraph for definition) are used in BIOMEMS both will be discussed in this course- the distinction between the two is rather vague (e.g. size, complexity, parts of an instrument might be called a sensor, etc.)
Effector (magnetic, chemical, physical,
Data storage and processing
A sensor detects information input, Iin, and then transduces or converts it to a more convenient form, Iout i.e Iout = F(Iin). So sensitivity is the amount of change in a sensor’s output in response to a change at a sensor’s input over the sensor’s entire range. NOT THE SAME AS LOWER LIMIT OF DETECTION!
Very often sensitivity approximates a constant; that is, the output is a linear function of the input
Sensitivity may mathematically be expressed as
Sensitivity 35,000 Ohms/K @ 4.2 K
Noise is normally measured "peak-to-peak": i.e., the distance from the top of one such small peak to the bottom of the next, is measured vertically. Sometimes, noise is averaged over a specified period of time. The practical significance of noise is the factor which limits detector sensitivity. A practical limit for this is a 2 x signal-to-noise ratio.
The electronic nose
The sensitivity of certain gas sensors to different gases depends on the choice of catalytic sensor material and the operating temperature. By combining several different gas sensors into a sensor array, complex gas mixtures can be analysed. Although the selectivity of the sensors is limited, qualitative and quantitative gas analysis can be performed using pattern-recognition techniques. The combination of multiple gas sensors and signal analysis using pattern-recognition techniques is the concept behind the electronic nose and tongue. These instruments have been successfully used in a number of applications, e.g., the quality estimation of ground meat, the identification of different paper qualities, the classification of grains with respect to microbial quality, and the screening of irradiated tomatoes.
Piezoelectric ceramics display hysteretic behavior. Suppose we start at zero applied voltage, gradually increase the voltage to some finite value,and then decrease the voltage back to zero. If we plot the extension of the ceramic as a function of the applied voltage, the descending curve does not retrace the ascending curve - it follows a different path.