Sensitive Evanescence-Field Waveguide Interferometer for Aqueous Nitro-Explosive Sensing

Abstract

The development of novel chemical nitro-explosive sensors with high sensitivity, low cost and a compact size is essential for homeland security, environmental protection and addressing military challenges. Polymeric optical waveguides based on refractive index sensing are widely used in biochemical detection due to their advantages of large-scale integration, low cost, high sensitivity and anti-electromagnetic interference. In this study, we designed and fabricated a polymer waveguide Mach–Zehnder interferometer (MZI) sensor to detect 2,4-dinitrotoluene (DNT) in water. One phase shifter of the MZI waveguide was functionalized by coating a thin cladding layer of polycarbonate with dipolar chromophores and used as the sensing arm; the other arm was coated with passive epoxy resin cladding and used as the reference arm. The phase difference between the two arms of the MZI was modulated using the refractive index (RI) change in the polycarbonate cladding when dipolar chromophores interacted with electro-deficient DNT. The theoretical sensitivity of the designed MZI can reach up to 24,696 nm/RIU. When used for explosive detection, our fabricated sensor had a maximum wavelength shift of 4.465 nm and good linear relation, with an R2 of 0.96 between the wavelength shift and a concentration ranging from 3.5 × 10−5 to 6.3 × 10−4 mol/L. The sensitivity of our device was 6821.6 nm/(mol/L). The design of an unbalanced MZI sensor, together with the sensing material, provides a new approach to using low-cost, compact and highly sensitive devices for in-field explosive detection.

Sensitive and Compact Evanescent-Waveguide Optical Detector for Sugar Sensing in Commercial Beverages

“…In this regard, the interchangeability of the light sources can be seen as one of the most valuable assets of our device, providing great versatility; as long as the working wavelength is in the detection window of the thin-film a-Si:H photodetector, light sources can be changed and the wavelength can be tuned according to the specific analyte under investigation. In addition to this, it should be noted that the developed system can be upgraded as an ultra-compact, integrated optical interferometer [44,45] by simply changing the geometry of the waveguide; a preliminary feasibility study in this direction has been recently published by our research group [46]. This may play an important role in the field of optical interferometry for biosensing, as it improves the compactness of the system, making it more suitable for in-field scenarios.…”