Label-free cocaine aptasensor based on a long-period fiber grating.

In this Letter, we combined a promising bioreceptor, a cocaine aptamer MN6, with an ultrasensitive optical platform long-period fiber grating (LPFG) to create a new cocaine biosensor. The cocaine induces a conformational rearrangement of the aptamer which changes the refractive index around the LPFG producing a measurable shift of the transmission spectrum. We were able to track subtle interaction between the receptor and cocaine molecules over a concentration range of 25 to 100 µM. The presented biosensor does not require labeling or signal enhancement, resulting in a simple user-friendly device.

Easily fabricated, robust fiber-optic probe for weak fluorescence detection: modeling and initial experimental evaluation.

Detection of fluorescence from a low quantum yield fluorophore is challenging for a fiber-optic probe, especially when an inexpensive and robust construction is desired. We propose a conceptually straightforward theoretical model to optimize the factors affecting the fluorescence-capture capability of a bifurcated/coaxial fiber-optic probe. Experimentally we verify that such a probe, if optimized, can detect the fluorescence of a polymer fluorophore with a low quantum yield of 0.0065.

Recapturing lost evanescent power by tuning end face total internal reflection capable tunneling modes at a roughened fiber end face.

We reveal that the overall evanescent wave (EW) power captured by an unclad multimode fiber employed in a sensing configuration is determined by the tunneling modes, not the guided modes. While enormous in strength, most of this power is inaccessible using traditional EW power enhancers. However, we found that by roughening the fiber end face, this supposedly lost power can be recaptured and thus can boost the detectable power level significantly. Intensive mode mixing events across various mode categories are proposed to interpret the observed phenomenon.