Filter-free optofluidic micropipette devices for fluorescence sensing

We demonstrate a novel optofluidic micropipette device for filter-free fluorescence-based biosensing. The optofluidic micropipette tube composed of a glass capillary microtube and a polymer-based structure designed to load analyte solution using a regular micropipette and serves as an optical waveguide. Ray-tracing simulations suggest that the excitation light can be effectively guided along the glass capillary with a small amount of leakage through the scattering at the solution-air interface. Fluorescence emission of the analyte propagates in the radial direction of the glass capillary which can be efficiently captured by a smartphone camera through a miniaturized objective lens. Fluorescence intensity and spectra were characterized using Rhodamine 6G (R6G) with various concentrations. The emission was collected via a microscope with 5X magnification and a smartphone camera. Both experimental and simulation results suggest that the excitation rays are efficiently coupled into the glass micropipette tube for fluorescence excitation. The fluorescence emissions from the analyte will either pass along the glass tube or propagate in the radial direction collected by the detector. A limited amount of excitation leakage scattered from the liquid-air interface showed a minimal effect on fluorescence detection. We demonstrated the platform that combines the optofluidic micropipette and smartphone camera to detect steroid hormone.