Detection of various Thrombin concentrations using etched fiber Bragg gratings functionalized with DNA aptamer

The response of etched fiber Bragg grating (EFBG) functionalized with 29-mer DNA aptamer to the different concentrations of Thrombin protein has been investigated. Etched FBGs are an efficient technology for detection of refractive index, and have been demonstrated also for biosensors applications. EFBGs have a simpler manufacturing approach comparing to other methodologies and are based on a low-cost device; their fabrication can be achieved by simple chemical etching, without requiring fusion splicing. During the test we assessed its feasibility for small variations of thrombin concentrations (10μg/ml, 20μg/ml, 40μg/ml and 80μg/ml). In particular, we performed experiments of chemical etching with hydrofluoric acid, which progressively depletes the fiber cladding exposing the core to the outer medium. Additionally, unstriped not etched FBGs were also used as a control for temperature pattern compensation. Before functionalization, EFBG was calibrated with different sucrose and ethanol solutions that validated the sensitivity to refractive index change. EFBG was further silanized with 3-Aminopropyl-triethoxysilane (APTES) in order to immobilize Thrombin binding aptamer on the silica surface of the fiber. The change of Bragg wavelength when functionalized EFBG is exposed to different concentrations of Thrombin using Micron Optics Hyperion si255-x55 sensing system was demonstrated. A small yet detectable sensitivity (several tens of nanomolars) even between small protein variations allows hypothesizing a future use of this kind of functionalized fiber for biosensor development.