Ultrasensitive tantalum oxide nano-coated long-period gratings for detection of various biological targets

• Published in: Biosensors & bioelectronics 2019-05, Vol.133, p.8-15
• Main Authors: Piestrzyńska, Monika, Dominik, Magdalena, Kosiel, Kamil, Janczuk-Richter, Marta, Szot-Karpińska, Katarzyna, Brzozowska, Ewa, Shao, Liyang, Niedziółka-Jonsson, Joanna, Bock, Wojtek J., Śmietana, Mateusz
• Format: Article
• Language: English
• Subjects: adhesins; Atomic layer deposition; avidin; Bacteria detection; bacteriophages; biosensors; biotin; Escherichia coli; films (materials); Label-free biosensing; Long-period grating; Optical fiber sensor; Protein detection; refractive index; Tantalum oxide
• ISSN: 0956-5663; 1873-4235
• DOI: 10.1016/j.bios.2019.03.006

In this work we discussed a label-free biosensing application of long-period gratings (LPGs) optimized in refractive index (RI) sensitivity by deposition of thin tantalum oxide (TaOx) overlays. Comparing to other thin film and materials already applied for maximizing the RI sensitivity, TaOx offers good chemical and mechanical stability during its surface functionalization and other biosensing experiments. It was shown theoretically and experimentally that when RI of the overlay is as high as 2 in IR spectral range, for obtaining LPGs ultrasensitive to RI, the overlay's thickness must be determined with subnanometer precision. In this experiment the TaOx overlays were deposited using Atomic Layer Deposition method that allowed for achieving overlays with exceptionally well-defined thickness and optical properties. The TaOx nano-coated LPGs show RI sensitivity determined for a single resonance exceeding 11,500 nm/RIU in RI range nD= 1.335–1.345 RIU, as expected for label-free biosensing applications. Capability for detection of various in size biological targets, i.e., proteins (avidin) and bacteria (Escherichia coli), with TaOx-coated LPGs was verified using biotin and bacteriophage adhesin as recognition elements, respectively. It has been shown that functionalization process, as well as type of recognition elements and target analyte must be taken into consideration when the LPG sensitivity is optimized. In this work optimized approach made possible detection of small in size biological targets such as proteins with sensitivity reaching 10.21 nm/log(ng/ml). •Long-period grating (LPG) has been coated with tantalum oxide nano-coating.•Optimized refractive index sensitivity for a single resonance exceeds 11,500 nm/RIU.•Determination of the coating thickness at sub-nanometer level is crucial.•The LPGs were applied for detection of bacteria and proteins.•At LPG optimization one must consider functionalization process and the target.