Perspective on Thin Film Waveguides for on-Chip Mid-Infrared Spectroscopy of Liquid Biochemical Analytes

Fiber-interfaced hollow-core light cage: a platform for on-fiber-integrated waveguides

Here, we demonstrate the realization of hollow-core light cages (LCs) on commercial step-index fibers using 3D nanoprinting, resulting in fully fiber-integrated devices. Two different light cage geometries with record-high aspect ratio strands and unique sidewise access to the core have been implemented, exhibiting excellent optical and mechanical properties. These achievements are based on the use of 3D nanoprinting to fabricate light cages and stabilize them with customized support elements. Overall, this approach results in novel, to the best of our knowledge, fiber-interfaced hollow-core devices that combine several advantages in a lab-on-a-fiber platform that is particularly useful for diffusion-related applications in environmental sciences, nanosciences, and quantum technologies.

On-chip mid-infrared optical sensing with GeSbSe waveguides and resonators

We fabricated single mode Ge₂₈Sb₁₂Se₆₀ waveguides and resonators using e-beam lithography and achieved a propagation loss of 3.88 dB/cm at 3.66 µm. We compared BCl₃ and CHF₃ etch chemistries and determined CHF₃ produced 1.5 dB/cm higher propagation losses at 3.6 µm due to C-H bond absorption. We use fabricated waveguides to detect an aromatic aldehyde dissolved in a non-polar solvent with a limit of detection of 1.09 µmol/mL. We then reduce this detection limit to 0.25 µmol/mL using the enhancement produced by a chalcogenide ring resonator.

Surface Functionalization with Polymer Membrane or SEIRA Interface to Improve the Sensitivity of Chalcogenide-Based Infrared Sensors Dedicated to the Detection of Organic Molecules

Priority substances likely to pollute water can be characterized by mid-infrared spectroscopy based on their specific absorption spectral signature. In this work, the detection of volatile aromatic molecules in the aqueous phase by evanescent-wave spectroscopy has been optimized to improve the detection efficiency of future in situ optical sensors based on chalcogenide waveguides. To this end, a hydrophobic polymer was deposited on the surface of a zinc selenide prism using drop and spin-coating methods. To ensure that the water absorption bands will be properly attenuated for the selenide waveguides, two polymers were selected and compared: polyisobutylene and ethylene/propylene copolymer coating. The system was tested with benzene, toluene, and ortho-, meta-, and para-xylenes at concentrations ranging from 10 ppb to 40 ppm, and the measured detection limit was determined to be equal to 250 ppb under these analytical conditions using ATR-FTIR. The polyisobutylene membrane is promising for pollutant detection in real waters due to the reproducibility of its deposition on selenide materials, the ease of regeneration, the short response time, and the low ppb detection limit, which could be achieved with the infrared photonic microsensor based on chalcogenide materials. To improve the sensitivity of future infrared microsensors, the use of metallic nanostructures on the surface of chalcogenide waveguides appears to be a relevant way, thanks to the plasmon resonance phenomena. Thus, in addition to preliminary surface-enhanced infrared absorption tests using these materials and a functionalization via a self-assembled monolayer of 4-nitrothiophenol, heterostructures combining gold nanoparticles/chalcogenide waveguides have been successfully fabricated with the aim of proposing a SEIRA microsensor device.

Advanced Waveguide Based LOC Biosensors: A Minireview

This mini review features contemporary advances in mid-infrared (MIR) thin-film waveguide technology and on-chip photonics, promoting high-performance biosensing platforms. Supported by recent developments in MIR thin-film waveguides, it is expected that label-free assimilated MIR sensing platforms will soon supplement the current sensing technologies for biomedical diagnostics. The state-of-the-art shows that various types of waveguide material can be utilized for waveguide spectroscopic measurements in MIR. However, there are challenges to integrating these waveguide platforms with microfluidic/Lab-on-a-Chip (LOC) devices, due to poor light-material interactions. Graphene and its analogs have found many applications in microfluidic-based LOC devices, to address to this issue. Graphene-based materials possess a high conductivity, a large surface-to-volume ratio, a smaller and tunable bandgap, and allow easier sample loading; which is essential for acquiring precise electrochemical information. This work discusses advanced waveguide materials, their advantages, and disease diagnostics with MIR thin-film based waveguides. The incorporation of graphene into waveguides improves the light-graphene interaction, and photonic devices greatly benefit from graphene's strong field-controlled optical response.

Infrared Spectroscopy in Aqueous Solutions: Capabilities and Challenges

Fourier-transform infrared (FTIR) spectroscopy provides rapid, reliable, quantitative, and qualitative analysis of samples in different aggregation states, i.e., gases, thin films, solids, liquids, etc. However, when analyzing aqueous solutions, particular issues associated with the rather pronounced IR absorption characteristics of water appear to interfere with the solute determination. In this review, Fourier-transform infrared spectroscopic techniques and their analytical capabilities for analyzing aqueous solutions are reviewed, and highlight examples are discussed.

Infrared spectroscopic monitoring of solid-state processes

We put a spotlight on IR spectroscopic investigations in materials science by providing a critical insight into the state of the art, covering both fundamental aspects, examples of its utilisation, and current challenges and perspectives focusing on the solid state.

High sensitivity infrared spectroscopy with a diamond waveguide on aluminium nitride

Mid-infrared waveguide spectroscopy promises highly sensitive detection and characterization of organic molecules. Different material combinations for waveguides and cladding have been demonstrated with promising results, each with its own strengths and weaknesses in terms of sensitivity, transmission window and robustness. In this article we present a 5 μm thick diamond planar waveguide on aluminium nitride cladding, using a new fabrication and polishing method. Diamond has a very wide transmission window in the infrared, and its hardness and high chemical stability allows for chemistries and cleaning protocols that may damage other materials. With an aluminium nitride cladding the waveguide has a useable range between 1000 and 1900 cm^-1, which we demonstrate using a tunable quantum cascade laser (QCL). This is a large improvement over silicon dioxide cladding. Compared to previously demonstrated free-standing diamond waveguides, the robustness of the sensor is greatly improved, which allows for a thinner diamond layer and increased sensitivity. The new waveguide was used in a QCL-based optical setup to detect acetone in deuterium oxide and isopropyl alcohol in water. The measurements showed higher sensitivity and lower noise level than previous demonstrations of mid-infrared diamond waveguides, resulting in a two orders of magnitude lower detectable concentration.

Toward Chalcogenide Platform Infrared Sensor Dedicated to the In Situ Detection of Aromatic Hydrocarbons in Natural Waters via an Attenuated Total Reflection Spectroscopy Study

The objective of this study is to demonstrate the successful functionalization of the surface of a chalcogenide infrared waveguide with the ultimate goal of developing an infrared micro-sensor device. First, a polyisobutylene coating was selected by testing its physico-chemical compatibility with a Ge-Sb-Se selenide surface. To simulate the chalcogenide platform infrared sensor, the detection of benzene, toluene, and ortho-, meta- and para-xylenes was efficaciously performed using a polyisobutylene layer spin-coated on 1 and 2.5 µm co-sputtered selenide films of Ge₂₈Sb₁₂Se₆₀ composition deposited on a zinc selenide prism used for attenuated total reflection spectroscopy. The thickness of the polymer coating was optimized by attenuated total reflection spectroscopy to achieve the highest possible attenuation of water absorption while maintaining the diffusion rate of the pollutant through the polymer film compatible with the targeted in situ analysis. Then, natural water, i.e., groundwater, wastewater, and seawater, was sampled for detection measurement by means of attenuated total reflection spectroscopy. This study is a valuable contribution concerning the functionalization by a hydrophobic polymer compatible with a chalcogenide optical sensor designed to operate in the mid-infrared spectral range to detect in situ organic molecules in natural water.

Fourier Transform Infrared Spectroscopy in Oral Cancer Diagnosis

Oral cancer is one of the most common cancers worldwide. Despite easy access to the oral cavity and significant advances in treatment, the morbidity and mortality rates for oral cancer patients are still very high, mainly due to late-stage diagnosis when treatment is less successful. Oral cancer has also been found to be the most expensive cancer to treat in the United States. Early diagnosis of oral cancer can significantly improve patient survival rate and reduce medical costs. There is an urgent unmet need for an accurate and sensitive molecular-based diagnostic tool for early oral cancer detection. Fourier transform infrared spectroscopy has gained increasing attention in cancer research due to its ability to elucidate qualitative and quantitative information of biochemical content and molecular-level structural changes in complex biological systems. The diagnosis of a disease is based on biochemical changes underlying the disease pathology rather than morphological changes of the tissue. It is a versatile method that can work with tissues, cells, or body fluids. In this review article, we aim to summarize the studies of infrared spectroscopy in oral cancer research and detection. It provides early evidence to support the potential application of infrared spectroscopy as a diagnostic tool for oral potentially malignant and malignant lesions. The challenges and opportunities in clinical translation are also discussed.