5 years ago



40 potentiometry,

40 potentiometry, amperometry and conductometry are very popular. They are easy to miniaturize and are (relatively) cheap. Piezo-electric systems react quickly and are conceptually simple: with the capturing of the target molecule by the bioreceptor, the resonance frequency of the biosensor is changed according to the amount of captured molecules. Piezo-electric systems are considered as very sensitive systems. Advances in the field of nanotechnology allow the miniaturization of optical components, such as optical waveguides, light sources, and detector systems. As a consequence, optical transducer systems gain importance in biosensor design (Ligler, 2009). A very sensitive technology for the monitoring of the biomolecular interactions is based on the principle of ‘surface plasmon resonance’ (SPR). Lab-on-a-chip technology An important trend in biosensor technology is the integration of the aforementioned biosensor concepts into miniaturized analytical devices or ‘labon-a-chip’ systems. This term refers to the implementation, miniaturization and the automation of laboratory operations on a portable microchip, typically in the range of millimetre to centimetres. In these chips, small amounts of liquids (µL or nL) are transported, mixed, and separated at the microscale. These microscale operations allow the development of fast and sensitive diagnostic assays in medical as well as in food diagnostics. The way the elementary fluid manipulations are executed on the chip, differentiates ‘lab-on-a-chip’ systems in two groups, namely continuous flow (figure 2A) and digital or droplet based (figure 2B) systems. In continuous flow systems, fluid is pumped through the micro- or nanochannels by external or internal micropumps. With the aid of microvalves and –mixers, fluids are mixed to initiate the reaction or improve the binding of the target to the bioreceptor. In some applications, transport is achieved by means of electrokinetics, eliminating the need for moving parts such as valves. In digital or droplet based systems, liquids are not transported as continuous flows but as individual droplets in a microchannel or even on a two dimensional surface by means of the electrowetting-on-dielectric principle. Both systems have their specific advantages and disadvantages but depending on the application one of both systems is recommended. The main advantage of lab-on-a-chip technology

is the degree of miniaturization, resulting in a strong improvement in analytical performance, cost reduction and high-throughput sampling. This makes lab-ona-chip a very attractive technology to substitute/complement conventional analytical techniques used in food diagnostics. (A) (B) Figure 2. Typical examples of the two different lab-on-a-chip systems. Figure A represents a continuous system where fluid is pumped continuously through the microchannels and Figure (B) represents a digital system where droplets are transported on a matrix of individual electrodes. Nanoparticles in biosensors Materials with nanoscale dimensions (

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