A fiber-tip label-free biological sensing platform: a practical approach toward in-vivo sensing

Abstract

The platform presented here was devised to address the unmet need for real time label-free in vivo sensing by bringing together a refractive index transduction mechanism based on Whispering Gallery Modes (WGM) in dye doped microspheres and Microstructured Optical Fibers. In addition to providing remote excitation and collection of the WGM signal, the fiber provides significant practical advantages such as an easy manipulation of the microresonator and the use of this sensor in a dip sensing architecture, alleviating the need for a complex microfluidic interface. Here, we present the first demonstration of the use of this approach for biological sensing and evaluate its limitation in a sensing configuration deprived of liquid flow which is most likely to occur in an in vivo setting. We also demonstrate the ability of this sensing platform to be operated above its lasing threshold, enabling enhanced device performance.

Figure 1.

(A) schematic of the optical setup; (B,C) bright field and fluorescence images of a 20 µm diameter dye doped polystyrene microsphere positioned onto the tip of a suspended core silica fiber respectively (Ø_core = 4 µm, Ø_hole = 17 µm).

Figure 2.

(A,B) WGM spectra below and above the lasing threshold respectively; (C) resonance amplitude as function of the pump power.

Figure 3.

(A) Wavelength shift of the WGM of a Ø = 20 µm polystyrene dye doped microsphere for increasing number of deposited polyelectrolyte layers; (B) Cumulative and individual layer thickness calculated after the deposition of each polyelectrolyte layer.

Figure 4.

Binding kinetic for neutravidin on a Ø = 20 µm biotin functionalized sphere with sphere operated (A) below and (B) above the lasing threshold.