Biomedical Engineering Reference
In-Depth Information
2 lm and imaging bundles with a diameter of 500 lm are available. In the fiber-
optic chemosensing system, the optical sensing element is typically composed of a
reagent phase immobilized at the fiber tip by either physical entrapment or
chemical binding.
This reagent phase usually contains a chemical indicator that experiences some
change in optical properties, such as intensity change, spectrum change, lifetime
change, and wavelength shift in fluorescence upon interaction with analyte gases
or vapors. The responses depend upon the nature of the organic vapor and the
strength of its interaction with different polymer systems used.
Advantage:
• Excessive sensitivity.
• Identifications of individual compounds in mixtures.
• Capabilities of finding multiparameter.
Disadvantages:
• Connected electronics and software are very complex.
• Connected electronics and software also leading to increased cost.
• The sensors have quite a short lifetime (due to photobleaching).
• Complex sensor-array systems.
• Low portability due to delicate optics and electrical components.
Application:
• Fire detector.
• Simple gases detect such as O
2
,CO
2
,CH
4
, HCL, and HF.
• Detection of pathogens.
• Medical diagnosis based on protein or cell concentration.
• Real-time detection of DNA hybridization.
6.10 QCM/QMB
QCM is an advanced type of microbalance mass sensor. The transducer for the
QCM sensor is mass-sensitive and very similar to the SAW sensor. Only distinct
between SAW and QCM is that the sensor employment. SAW uses a surface
acoustic wave sensor while QCM uses a BAW sensor. The device (electro-
acoustic) based on the Piezo-electrical properties of quartz material has been
implemented in sensors.
QCM oscillation frequency decreases while the mass is bound on the crystal
surface, therefore it is identified as very sensitive mass measuring device. QCM
sensing mechanism is based on the shift in the quartz crystal (QC) resonant fre-
quency due to the adsorption of gas molecules onto the sensing films. QC which is
equipped with metal electrodes (e.g., gold) is the basic material of the QCM
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