Tapered optical fiber sensor using near-infrared fluorophores to assay hybridization

We present an all-fiber hybridization assay sensor that relies on the evanescent field excitation of fluorescence from surface-bound fluorophores. The evanescent field is made accessible through the use of a long, adiabatically tapered single-mode fiber probe. A laser diode with a 785-nm wavelength is used in a pulsed mode of operation to excite fluorescence in the tapered region of a fiber probe using the near-infrared fluorophore IRD 41. We have used various chemical treatments to prepare the tapered fiber surface for chemical, as well as physical, binding of fluorophores. We have carried out real-time hybridization tests for IRD 41-labeled oligonucleotide, at various probe concentrations, binding to complementary oligonucleotide cross-linked to the tapered fiber surface. The biospecificity of our sensor is confirmed through hybridization tests with a control oligonucleotide. Short oligonucleotides (20-mer) bound to the fiber surface have been used to detect near-IR dye-labeled complementary sequences at subnanomolar levels. Sandwich assays with Helicobacter pylori total RNA were conducted to examine the capability of the biosensor for detecting bacterial cells using rRNA as the target. The results indicate that this fluorosensor is capable of detecting H. pylori in a sandwich assay at picomolar concentrations.