Phase sensitive diffraction sensor for high sensitivity refractive index measurement

Nityanand Kumawat, Manoj Varma, Sunil Kumar

Research output: Chapter in Book/Report/Conference proceedingConference contribution


In this study a diffraction based sensor has been developed for bio molecular sensing applications and performing assays in real time. A diffraction grating fabricated on a glass substrate produced diffraction patterns both in transmission and reflection when illuminated by a laser diode. We used zeroth order I(0,0) as reference and first order I(0,1) as signal channel and conducted ratiometric measurements that reduced noise by more than 50 times. The ratiometric approach resulted in a very simple instrumentation with very high sensitivity. In the past, we have shown refractive index measurements both for bulk and surface adsorption using the diffractive self-referencing approach. In the current work we extend the same concept to higher diffraction orders. We have considered order I(0,1) and I(1,1) and performed ratiometric measurements I(0,1)/I(1,1) to eliminate the common mode fluctuations. Since orders I(0,1) and I(1,1) behaved opposite to each other, the resulting ratio signal amplitude increased more than twice compared to our previous results. As a proof of concept we used different salt concentrations in DI water. Increased signal amplitude and improved fluid injection system resulted in more than 4 times improvement in detection limit, giving limit of detection 1.3×10-7 refractive index unit (RIU) compared to our previous results. The improved refractive index sensitivity will help significantly for high sensitivity label free bio sensing application in a very cost-effective and simple experimental set-up.

Original languageEnglish (US)
Title of host publicationOptical Diagnostics and Sensing XVIII
Subtitle of host publicationToward Point-of-Care Diagnostics
EditorsGerard L. Cote
ISBN (Electronic)9781510614871
StatePublished - 2018
EventOptical Diagnostics and Sensing XVIII: Toward Point-of-Care Diagnostics 2018 - San Francisco, United States
Duration: Jan 29 2018Jan 30 2018

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


OtherOptical Diagnostics and Sensing XVIII: Toward Point-of-Care Diagnostics 2018
Country/TerritoryUnited States
CitySan Francisco


  • Diffraction grating
  • Label-Free
  • Optical Biosensor
  • Ratiometric
  • Refractive Index
  • Self-Referencing

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Radiology Nuclear Medicine and imaging
  • Biomaterials


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