Optical biosensing transducer based on silicon waveguide structure coated with polyelectrolyte nano layers (original) (raw)

2003, Bioengineered and Bioinspired Systems

An optical biosensor based on attenuation of the light intensity during multiple reflections in a planar waveguide has been developed for water pollution monitoring. The planar waveguide consists of a 190 nm thick silicon nitride (Si 3 N 4) core layer sandwiched between 1.5 µm thick silicon dioxide (SiO 2) cladding layers. Composite polyelectrolyte selfassembled membranes containing Cyclotetrachromotropylene (CTCT) as an organic indicator and enzymes, such as Urease or Acetylcholine Esterase (AChE) were deposited on top of silicon nitride core layer within a 4 x 6 mm sensing window. Experimental studies on the light propagation through the planar waveguide show the advantages of this method over conventional UV-visible absorption spectroscopy. It was found that the planar waveguide sensitivity is higher by several orders of magnitude than that for the UV-visible absorption spectroscopy. The respective enzyme reactions as well as their inhibition by heavy metal ions were studied by monitoring the light intensity in the planar waveguide. Cadmium (Cd 2+) and lead (Pb 2+) ions were registered in very low concentrations down to 1 ppb with the planar waveguide transducer. The enzymes used were inhibited differently by the above pollutants, which is promising for the development of enzyme sensor arrays.

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