Graphene-based biosensor platform for the development of an artificial nose

The sense of smell is the oldest, most versatile and as some biologists claim, the most important one for living creatures. It is understandable that mimicking this sense by building an arti cial nose would be highly useful in an abundance of applications. For instance it could be used in food industry, cosmetic production, environmental monitoring and medical diagnostics, where the detection of volatile biomolecules plays an important role. However, the sense of smell in humans and animals still outperforms any analytical device. As the sensitivity and selectivity of the biological olfactory system is by far not reached yet, new approaches to build a stable and miniaturised biosensor as an arti cial nose are needed.This study is an attempt to improve and miniaturise a biosensor used for the detection of odorants. A reduced graphene oxide eld-eect transistor (rGO-FET) functionalised with odorant-binding proteins is used as a biosensor. Due to its unique electrical properties and easy handling procedure, reduced graphene oxide is utilized as the transducer. To reduce the complexity of the biological olfactory system, odorant-binding proteins (OBP) are chosen as a biorecognition element. They are very stable and can bind selectively to odorants. This sensor platform consisting of an rGO-FET functionalised with odorant-binding proteins can be used to detect binding events of odorants in real-time. To test the sensor properties and gain more insights in the function of an odorant binding protein, the binding properties of the wild type of the OBPs of a moth are compared to an engineered mutant of this protein. The mutant shifts its anity from pheromones to plant volatiles. Therefore, the binding of a plant volatile and a pheromone to these two proteins are investigated. With the here presented sensor the detection of odorants is possible. However, a shift in the anity of the mutant OBPs could not be detected. This biosensor oers an approach to the easy and safe construction of an electrical smell sensing device. As the described biosensor could be modi ed easily for future investigations using dierent biomolecules immobilised on the sensor as a biorecognition element, the current study may serve as a basis for further steps towards the development of an arti cial nose.7

Induction by low Na(+) or Cl(−) of cocaine sensitive carrier-mediated efflux of amines from cells transfected with the cloned human catecholamine transporters

1. COS-7 cells transfected with the cDNA of the human dopamine transporter (DAT cells) or the human noradrenaline transporter (NAT cells) were loaded with [(3)H]-dopamine or [(3)H]-noradrenaline and superfused with buffers of different ionic composition. 2. In DAT cells lowering the Na(+) concentration to 0, 5 or 10 mM caused an increase in (3)H-efflux. Cocaine (10 μM) or mazindol (0.3 μM) blocked the efflux at low Na(+), but not at 0 Na(+). Lowering the Cl(−) concentration to 0, 5 or 10 mM resulted in an increased efflux, which was blocked by cocaine or mazindol. Desipramine (0.1 μM) was without effect in all the conditions tested. 3. In NAT cells, lowering the Na(+) concentration to 0, 5 or 10 mM caused an increase in (3)H-efflux, which was blocked by cocaine or mazindol. Desipramine produced a partial block, its action being stronger at 5 or 10 mM Na(+) than at 0 mM Na(+). Efflux induced by 0, 5 or 10 mM Cl(−) was completely blocked by all three uptake inhibitors. 4. In cross-loading experiments, 5 mM Na(+)- or 0 Cl(−)-induced efflux was much lower from [(3)H]-noradrenaline-loaded DAT, than NAT cells and was sensitive to mazindol, but not to desipramine. Efflux from [(3)H]-dopamine-loaded NAT cells elicited by 5 mM Na(+) or 0 Cl(−) was blocked by mazindol, as well as by desipramine. 5. Thus, cloned catecholamine transporters display carrier-mediated efflux of amines if challenged by lowering the extracellular Na(+) or Cl(−), whilst retaining their pharmacological profile. The transporters differ with regard to the ion dependence of the blockade of reverse transport by uptake inhibitors