Fiber optic based surface plasmon aptasensor

In this research, we aimed to develop a cost-effective surface plasmon resonance (SPR) probe for the label-free detection of human Immunoglobulin E (hIgE). This target protein plays an important role in many allergic reactions in the human body. To the best of our knowledge, this is the first research project where a SPR probe is combined with the aptamer-technology. SPR is probably the best known method for online detection of biological binding reactions. In the search for more convenient SPR-sensors, we have replaced the prism based systems by a fiber optic design. In the setup, replaceable and interchangeable sensing probes can be affixed onto the end of a bifurcated optical fiber. The fiber probe is attached to a computer-controlled robot. Aptamers are nucleic acids which have the potential to bind to specific target molecules. These selective oligonucleotides are produced through a selection process based on systematic evolution of ligands by the exponential enrichment (SELEX). Their most pronounced advantages over antibodies are stability to biodegradation and low production cost. We utilized this high stability of the DNA aptamers to develop reusable biosensors. The gold surface of the sensor is coated with a mixture of mercapto poly-ethylene glycol and different length mercapto alcohol chains. On this layer, streptavidin is immobilized by 1-Ethyl-3-[3-dimethyl aminopropyl]carbodiimide hydrochloride. Finally, biotinylated aptamers are attached. Our results illustrate that this surface design prevents non-specific binding and is very stable, which is important for regeneration. The sensors have an average detection limit of 2 nM for hIgE. The detection range depends on the amount of aptamers immobilized on the sensor surface. We are able to regenerate the aptasensors for more than 25 measurements. No wavelength shift was visible when the same experiment was repeated with hIgG. In the near future we will repeat these experiments in real blood serum samples.status: publishe