A ZnO-coated optical fiber sensor for detecting a volatile organic compound biomarker for diabetes has been recently demonstrated in a study published in Sensors. The researchers used a coreless silica fiber (CSF) coupled with single-mode fiber (SMF) at both ends to synthesize the SMF-CSF-SMF structure.
Multimode interference generates increased light interaction at the interface between the fiber and sensing medium in the CSF area of the sensor system, increasing sensitivity. The CSF length is numerically optimized to achieve the best coupling efficiency at the output. Surface functionalization can be accomplished through the hydrothermal development of ZnO nanorods on the CSF at low temperatures.
Volatile Organic Compounds as Biomarkers
Volatile organic compounds are generally present in the air as gases under specific pressure and temperature conditions. Factories, paints, personal care items, wax, fuels, and household products release volatile organic compounds into the atmosphere. Even at very low concentrations, they can harm human health.
Volatile organic compounds are released from exhaled breath when carried by body fluids to the excretory organs. Volatile organic compounds concentrations in the exhaled breath have been linked to several chronic diseases and can be used as reliable biomarkers. Acetone and isopropanol have received considerable attention as potential biomarkers for lung cancer and type 1 diabetes.
Limitations of Current Volatile Organic Compounds Detection Techniques
Several uses for sensing volatile organic compounds have sparked a lot of interest in their study, monitoring, and detection. Spectrophotometry, gas chromatography, and high-performance liquid chromatography are used to precisely identify volatile organic compounds. These traditional techniques typically take a long time, are costly, and require highly skilled workers. Gas-sensing devices must be affordable and portable for this reason.
Potential of Optical Fiber Sensors in Volatile Organic Compounds Detection
Optical fiber sensors can be used for volatile organic compounds detection owing to the advantages of being lightweight, less susceptible to electrical disturbances, and can perform remote sensing.
Low levels of ppm to ppb quantities of volatile organic compounds are found in breath. These chemicals can be found using a sensor made of optical fibers.
The coreless silica fiber (CSF) is used in the multimode fiber (MMF) region to enhance the interaction of light with the surroundings. This CSF section serves as a sensor's detecting zone to achieve the highest level of sensitivity. SMS fiber-based optical fiber sensors can be made quickly, which is appealing for practical applications.
Surface Functionalization Mechanism of Optical Fiber to Improve Volatile Organic Compounds Detection
The surface functionalization method at the optical fiber’s sensing region has recently received attention for increasing the sensing sensitivity and selectivity for volatile organic compounds detection. Zinc oxide (ZnO) is a good contender with several noteworthy benefits, including excellent stability, a broad band gap, and biocompatibility.
ZnO has a wide range of uses in optoelectronics, nano-sensing, and energy harvesting owing to these benefits. According to reports, ZnO-coated optical fiber sensors exhibit great sensitivity and selectivity for ethanol and ammonium gas.
Development of ZnO Nanorods Coated Optical Fiber Sensor for Volatile Organic Compounds Detection
Swargiary et al. synthesized ZnO nanorods-coated optical fiber sensor to detect volatile organic compounds biomarkers in breath using hydrothermally produced ZnO nanorods coated on the surface of the SMS optical fiber sensor.
Isopropanol (IPA) vapor is one of the biomarkers for non-invasive diabetes diagnosis; it was chosen as this study's volatile organic compounds marker. The vaporization of IPA solutions in deionized (DI) water produced IPA vapors with various concentrations ranging from 20% to 100%.
The IPA solution concentrations evaporated inside the chamber at ambient temperature throughout the studies. Numerical modeling was used to optimize the sensor's length to increase the device's sensitivity. With manufacturing optimization and sensor characterization, the development of ZnO nanorods onto the fiber was investigated.
This study successfully produced and applied a ZnO nanorod coated on an SMS optical fiber structure to detect volatile organic compounds biomarkers. The optical simulation demonstrated that a sensor length of 9.5 cm with a 0.05 volume fraction of ZnO at about 958-980 nm wavelength could be obtained to achieve the highest coupling efficiency of the sensing region.
Hydrothermally produced ZnO nanorods were functionalized on 9.4 cm-long SMS sensors to attain the highest level of sensitivity. The light interaction at the sensor region was improved by the ability of ZnO nanorods to absorb IPA vapor. The intensity spectra of the manufactured optical fiber sensors were captured using an optical spectrometer. The manufactured optical fiber sensor was tested with IPA vapor at varied concentrations, including 20%, 40%, 60%, 80%, and 100%.
Peak wavelengths and IPA vapor concentrations were linearly correlated. The data showed a blue shift in the 915–920 nm band. The optical fiber sensor demonstrated the capability of detecting IPA at various concentrations with a sensitivity of 0.053 nm/% IPA vapor.
As a result, the manufactured fiber sensor shows promise for further detecting IPA, one of the volatile organic compounds biomarkers for diabetes. By covering gold nanoparticles with ZnO nanorods and tapering multimode fibers, surface functionalization can be used to increase the optical fiber sensor's sensitivity and selectivity.
Swargiary, K., Metem, P., Kulatumyotin, C., Thaneerat, S., Ajchareeyasoontorn, N., Jitpratak, P., Bora, T., Mohammed, W. S., Dutta, J., & Viphavakit, C. (2022). ZnO Nanorods Coated Single-Mode–Multimode–Single-Mode Optical Fiber Sensor for VOC Biomarker Detection. Sensors, 22(16), 6273. https://www.mdpi.com/1424-8220/22/16/6273/htm