Biomedical Engineering Reference
In-Depth Information
Table 1
Comparison of features of both possible sensors
Optical
Electrochemical
Format
Size
10 9 40 mm
10 9 8mm
Number of parameters
Up to 500
Up to 16
Cost
*1 €
*1 €
Principle
TIRF
Single-electron redox cycling
necessary: (i) thermal oxidation of the base layer, (ii) vapor deposition for gold and
iridium metallization, (iii) photolithography, (iv) lift-off processing for metal
structuring, (v) plasma-enhanced chemical vapor deposition of silicon nitride as an
insulating layer, (vi) photolithography, and (vii) dry etching for the structuring of
silicon nitride. However, for the fabrication silicon wafers of 6- or 8-inches are
used. Hence, in the case of the 8-inch wafer about 400 electrochemical chips can
be fabricated at once thus maintaining a small production price (Table
1
).
The choice of which sensor is more suitable for a certain application is quite
difficult to answer. In general, both transducing types are well known and are used
in many applications. Nevertheless, because of the above-mentioned features the
choice of sensor is more dependent on price, number of parameters etc. than on
performance itself.
2.4 Read-Out and Processing Unit
Besides the cartridge in which many steps are integrated a read-out and processing
unit has to be used. The features to be delivered by this base station include:
• all circuitry necessary for pump and valve control;
• the hardware for the chosen read-out;
• a user-friendly interface for displaying results;
• patient identification via a barcode scanner;
• and in special cases: temperature control.
In general, the base station has to deliver all compounds for performing the
assay completely automatically with a high focus on user-friendliness and ease of
production to allow low-cost serial production.
