Silica Gel Coated Spherical Micro resonator for Ultra-High Sensitivity Detection of Ammonia Gas Concentration in Air

A silica gel coated microsphere resonator is proposed and experimentally demonstrated for measurements of ammonia (NH3) concentration in air with ultra-high sensitivity. The optical properties of the porous silica gel layer change when it is exposed to low (parts per million (ppm)) and even ultra-low (parts per billion (ppb)) concentrations of ammonia vapor, leading to a spectral shift of the WGM resonances in the transmission spectrum of the fiber taper. The experimentally demonstrated sensitivity of the proposed sensor to ammonia is estimated as 34.46 pm/ppm in the low ammonia concentrations range from 4 ppm to 30 ppm using an optical spectrum analyser (OSA), and as 800 pm/ppm in the ultra-low range of ammonia concentrations from 2.5 ppb to 12 ppb using the frequency detuning method, resulting in the lowest detection limit (by two orders of magnitude) reported to date equal to 0.16 ppb of ammonia in air. In addition, the sensor exhibits excellent selectivity to ammonia and very fast response and recovery times measured at 1.5 and 3.6 seconds, respectively. Other attractive features of the proposed sensor are its compact nature, simplicity of fabrication

Silica Gel Coated Spherical Micro resonator for Ultra-High Sensitivity Detection of Ammonia Gas Concentration in Air

A silica gel coated microsphere resonator is proposed and experimentally demonstrated for measurements of ammonia (NH3) concentration in air with ultra-high sensitivity. The optical properties of the porous silica gel layer change when it is exposed to low (parts per million (ppm)) and even ultra-low (parts per billion (ppb)) concentrations of ammonia vapor, leading to a spectral shift of the WGM resonances in the transmission spectrum of the fiber taper. The experimentally demonstrated sensitivity of the proposed sensor to ammonia is estimated as 34.46 pm/ppm in the low ammonia concentrations range from 4 ppm to 30 ppm using an optical spectrum analyser (OSA), and as 800 pm/ppm in the ultra-low range of ammonia concentrations from 2.5 ppb to 12 ppb using the frequency detuning method, resulting in the lowest detection limit (by two orders of magnitude) reported to date equal to 0.16 ppb of ammonia in air. In addition, the sensor exhibits excellent selectivity to ammonia and very fast response and recovery times measured at 1.5 and 3.6 seconds, respectively. Other attractive features of the proposed sensor are its compact nature, simplicity of fabrication

Whispering-Gallery Mode Microsphere Resonators for Applications in Environmental Sensing

Humidity, temperature and volatile organic compounds (VOCs), particularly ammonia, are key environmental conditions that have a major impact on human comfort, well-being and productivity, as well as on agriculture, food processing and storage, electronic manufacturing and many other industries. This results in the urgent need for the development of sensing technologies allowing rapid detection and accurate measurement of these environmental parameters. Over the past decades many electrical as well as optical sensors have been proposed and demonstrated for environmental applications. However, challenge always exists for these sensors in terms of sensitivity, selectivity, detection limit, speed of response and robustness, where researchers and engineers are still working continuously on improving the performance of these sensors. Whispering gallery mode (WGM) optical micro-resonators have been shown to be able of detecting minute changes in their environment. This has made them a well-established platform for highly sensitive physical, chemical and biological sensors. Silica micro-resonators with high quality factors and low absorption loss can be fabricated easily at the tip of an optical fiber, and the WGMs in such resonators can be excited by evanescent light coupling using tapered fibers. The aim of this PhD thesis is the development of novel ultra-high sensitivity sensors based on silica micro-spheres functionalized with specific coatings with a particular focus on measurement of water vapor and ammonia concentration in air. A numerical simulation model has been analysed based on perturbation theory to facilitate deep understanding of WGMs in coated micro-sphere resonators and the results of the simulations have been validated by experimental studies. Relationship between key design parameters of the sensor such as microsphere size, thickness of the coating layer, tapered fiber waist diameter, its Q factor and sensitivity has been investigated and established. A novel high sensitivity relative humidity (RH) sensor based on an agarose-coated spherical micro-resonator has been proposed and experimentally demonstrated. The sensor’s spectrum shows a wavelength shift of approximately 518 pm corresponding to a relative humidity change of 40% RH. Detailed experimental investigation of the influence of the agarose coating thickness on the sensor’s humidity response has been carried out and correlated with the analytical model results. Sensor’s performance in very low humidity environments ( A novel ultra-sensitive ammonia sensor has been proposed and developed by coating a porous silica gel on a microsphere acting as the sensing head. The sensor offers high resolution and the lowest reported to date detection limit of 0.16 ppb with response and recovery times of 1.5 s and 3.6 s respectively. Finally, a novel approach to simultaneous measurement of ammonia vapors and humidity in air with high resolution has been proposed and demonstrated experimentally. In the proposed two-parameter sensor WGMs are exited at the same time in an array of two micro-spheres coated with different polymers, namely, silica gel and agarose hydrogel, coupled to a single adiabatic fiber taper. The method can be further expanded to achieve sensing of multiple chemical and biological quantities utilizing various coatings and possibly increasing the number of sensors within the array, thus reducing the cost of sensors interrogation

Performance of Eudragit Coated Whispering Gallery Mode Resonator-Based Immunosensors

Whispering gallery mode resonators (WGMR) are an efficient tool for the realization of optical biosensors. A high Q factor preservation is a crucial requirement for good biosensor performances. In this work we present an Eudragit®L100 coated microspherical WGMR as an efficient immunosensor. The developed resonator was morphologically characterized using fluorescence microscopy. The functionalization process was tuned to preserve the high Q factor of the resonator. The protein binding assay was optically characterized in terms of specificity in buffer solution

Performance of Eudragit Coated Whispering Gallery Mode Resonator-Based Immunosensors

Whispering gallery mode resonators (WGMR) are an efficient tool for the realization of optical biosensors. A high Q factor preservation is a crucial requirement for good biosensor performances. In this work we present an Eudragit®L100 coated microspherical WGMR as an efficient immunosensor. The developed resonator was morphologically characterized using fluorescence microscopy. The functionalization process was tuned to preserve the high Q factor of the resonator. The protein binding assay was optically characterized in terms of specificity in buffer solution