Dopamine (DA) analysis is complicated by the interference from other electrochemically active endogenous compounds present in the brain, including DA precursors and metabolites and other neurotransmitters (NT). Here we report a simple, sensitive and selective optical fiber biosensor for the detection of DA in the presence of other NT. It is composed of a 57-mer dopamine-binding aptamer (DBA) as recognition element and nonadiabatic tapered optical fiber (NATOF) as probe. Upon the addition of DA, the conformation of DBA would change from a random coil structure to a rigid tertiary structure like a pocket. The conformational change of DBA lead to the refractive index (RI) change around the tapered fiber surface. Specific recognition of DA by the aptamer allowed a selective optical detection of DA within the physiologically relevant 500 nM to 10 μM range. Some common interferents such as epinephrine (EP) and ascorbic acid (AA) showed no or just a little interference in the determination of DA.
Real-time observation of intracellular process of signal transduction is very useful for biomedical and pharmaceutical applications as well as for basic research work of cell biology. For feasible and reagentless observation of intracellular alterations in real time, we examined the use of a nonadiabatic tapered optical fiber (NATOF) biosensor for monitoring of intracellular signal transduction that was mainly translocation of protein kinase C via refractive index change in PC12 cells adhered on tapered fiber sensor without any indicator reagent. PC12 cells were stimulated with KCl . Our results suggest that complex intracellular reactions could be real-time monitored and characterized by NATOF biosensor.
A single-mode nonadiabatic tapered optical fiber (NATOF) biosensor based on ssDNA aptamer for detection of potassium ion (K<sup>+</sup>) was developed. Upon binding to K+, the G-rich single-stranded DNA can fold into the G-quadruplex structure, thus allowing the formation of G-quadruplex complex after incubation with K<sup>+</sup> which is led to changing in refractive index (RI). Under optimum conditions, the wavelength shift was proportional to the concentration of K<sup>+</sup> in the range of 10 ×10<sup>-4</sup> to 2×10<sup>-2</sup> mM. A detection limit of 4.5×10<sup>-4</sup> was achieved. Moreover, this method was able to detect K<sup>+</sup> with high selectivity in the presence of Na<sup>+</sup> ion of biological fluids.