swomitra mohanty - Academia.edu (original) (raw)

Papers by swomitra mohanty

Annals of Nuclear Energy, Jun 1, 2021

Abstract We present a systematic and detailed approach to simulate the University of Utah TRIGA R... more Abstract We present a systematic and detailed approach to simulate the University of Utah TRIGA Reactor (UTR) in support of core criticality calculations to profile the entire reactor in detail. In performing this work, we utilized both a 3-D Cartesian SN deterministic code, PENTRAN, and a Monte Carlo code, MCNP6, to calculate complimentary, high accuracy 3-D transport derived neutron flux distributions at reactor full power. For deterministic models, our study shows that a 14-group CONTRIBUTON weighted multi-group cross-section library with up-scattering compared extremely well with continuous energy Monte Carlo results. We also modeled results to confirm the activity of an activated arsenic sample placed in the heavy water moderated thermal irradiation chamber of the UUTR (University of Utah TRIGA Reactor). A 138 pcm difference in the system eigenvalue for the full 3-D core PENTRAN discrete ordinates (SN) UUTR model utilizing 2 × 109 equations, in 14 energy groups, is compared to the reference case of a similar full core MCNP6 Monte Carlo calculation with continuous energy cross-sections. On average, deterministic and Monte Carlo core neutron group flux values differ by less than 1%, with some local maximum relative differences between 10% and 20% for the 3-D core flux distribution in some energy groups are observed. The differences of neutron fluxes from group 3/14 to group 10/14, with energies spanning from 1.11 eV to 13.8 MeV, are comparable to within 5% in the UUTR core active fuel region. For energy groups with energies greater than 13.8 MeV, MCNP6 is not able to resolve the flux distributions with reasonable statistical uncertainties due to the extremely low sampling probability for neutrons in those energies; orders of magnitude more histories would be required to do so. In contrast, the PENTRAN 3D SN calculation shows a very detailed flux distribution for energies larger than 13.8 MeV, highlighting the complimentary utility of applying both methods. Detailed approaches for the PENTRAN calculation, including energy group collapsing, homogenization of fuel + gap + cladding, and analysis are presented in the narrative.

Journal of environmental chemical engineering, Mar 1, 2016

Microfluidic reactors have gained considerable interest for photocatalytic degradation of contami... more Microfluidic reactors have gained considerable interest for photocatalytic degradation of contaminants in water. These systems have advantages such as large surface-area-to-volume ratio and high control of fluid flow, yet still suffer from drawbacks due to limited mass transport associated with laminar flow. The use

Abstract A multi-layer plastic/glass technology has been developed for microfluidic systems with ... more Abstract A multi-layer plastic/glass technology has been developed for microfluidic systems with integrated functionality. Hot embossing and heat staking of plastics, microstenciling of electrodes, and stereolithography (SLA) was combined with conventional MEMS ...

Journal of The Electrochemical Society, Dec 29, 2015

2019 AIChE Annual Meeting, Nov 11, 2019

IEEE Sensors Journal, Jun 15, 2021

Cost-effectively detecting benzene, a human carcinogen, at occupationally and atmospherically rel... more Cost-effectively detecting benzene, a human carcinogen, at occupationally and atmospherically relevant concentrations would benefit individuals at risk of exposure. This paper presents the development of a titania (TiO2) nanotube-based sensor array that has a high surface area, is highly sensitive, and operates at room temperature using simple, portable instrumentation. An n-type TiO2 nanotube was synthesized through electrochemical anodization in an electrolytic solution of ammonium fluoride-ethylene glycol and oxygen annealed at 500 °C for up to 8 hours. The nanotube sensor had a bandgap (Eg) of ~2.6 eV, and it was operated at a bias voltage of +1.5 V. The response of the sensor to benzene vapor was measured using an amperometric technique at room temperature, and when exposed to benzene, the sensor exhibited a decrease in current, as expected for an n-type metal oxide semiconductor. The sensor response was proportional to benzene concentration over a range of 100–400 ppb. A sensing mechanism based on Fermi level changes caused by band bending has been explained for this benzene sensor.

Journal of Materials Science & Technology, Jun 1, 2018

Titania nanotubular arrays (TNA) synthesized via electrochemical anodization is a stable and vers... more Titania nanotubular arrays (TNA) synthesized via electrochemical anodization is a stable and versatile material, widely studied for photocatalytic and sensing applications, whereas nano-sized gold particles are a known plasmonic material. Semiconductor-metal nanocomposites in isolated, embedded, or encapsulated form, when irradiated with proper light frequency can exhibit localized surface plasmon resonance (LSPR) effect. This effect can result in improved light adsorption and electrical properties of a material. In this study, we report the enhanced visible light photo-response of LSPR induced volatile organic biomarker vapor sensing at room temperature using a Au-embedded TNA electrochemical sensor. Two mechanisms are proposed. One based on classical physics (band theory), which explains operation under non-irradiated conditions. The second mechanism is based on the coupling of classical and quantum physics (molecular orbitals), and explains sensor operation under irradiated conditions.

This report provides a summary of the work performed under NIAC Phase I award NNX15AL86G entitled... more This report provides a summary of the work performed under NIAC Phase I award NNX15AL86G entitled "CubeSat with Nanostructured Sensing Instrumentation for Planetary Exploration". The objective of this research is to investigate the feasibility of an innovative, low cost, CubeSat based planetary mission concept for in situ "ground truth" analysis of small asteroids and comets. The project includes an instrument study and a mission/spacecraft design study. The instrument study concerns with the development of a new TiO 2 nanotube sensor with integrated compound semiconductor nanowires to determine surface composition element via neutron activated analysis (NAA). The mission/spacecraft design study concerns with the development of CubeSat based lander to small asteroids and comets. The Phase I study suggests that our concept is feasible and could provide significant benefit to NASA's future planetary missions. This research was carried out at the

Meeting abstracts, 2017

Benzene is one of the few known human carcinogens as identified by the International Agency for R... more Benzene is one of the few known human carcinogens as identified by the International Agency for Research on Cancer. It is a common indoor and outdoor pollutant, with sources ranging from cigarette smoke to traffic. Hence, there is an increasing need to detect low concentrations of benzene. Metal-oxide based nano-sensors, with their simple sensing mechanisms make for a good choice. Thin films based on titanium dioxide (TiO2) have previously been shown to respond to benzene (1), however these sensors are run at high temperatures (160-200°C), require a complex setup for operation, and have low surface area for sensing. This paper presents the development of TiO2 nanotube based sensor array (Figure 1) that has high surface area, is highly sensitive, and operates at room temperature using portable and simple instrumentation. TiO2 nanotubes were synthesized through anodization in electrolytic solution of ammonium fluoride (NH4F)-ethylene glycol (EG) and oxygen annealed for up to 500°C. The response of the synthesized hollow nanotubes was studied at room temperature for different concentrations of benzene vapor (100-500ppm). The response of the sensor coupons to benzene vapor was measured using an amperometric technique. The results showed an increase in current that was directly proportional to the concentration of benzene in the sample which indicates a quantitative nature of the sensor (Figure 2). The sensor was placed in a portable system which can be deployed to potential contamination sites for real-time monitoring applications. Results on sensing mechanism, stability of the sensor over time, sensor reusability, and detection limit will be presented. (1) Mabrook M., Hawkins P. (2001) Sensors and Actuators, B: Chemical 75, 197-202. Figure 1

Meeting abstracts, 2015

Analysis of volatile organic compounds (VOCs) from exhaled breath presents a potential non-invasi... more Analysis of volatile organic compounds (VOCs) from exhaled breath presents a potential non-invasive, label-free, and point-of-care (POC) medical diagnostic technique. Sensor detection of specific volatile organic biomarkers (VOBs) directly associated with a pulmonary or other disease presents itself as a facile method for early diagnosis. Tuberculosis (TB) is arguably one of the most devastating infectious diseases in the world today. A major contributing factor to such a large number of cases is due to inadequate diagnostic methods for TB. Research has shown that various strains of the mycobacteria produce distinct gaseous volatile biomarkers that can be used as a methodology for detecting and identifying the mycobacterium.1-2 Syhre and Chambers2 found that Mycobacterium tuberculosis and Mycobacterium bovis cultures give off four specific volatile organic compounds (methyl phenylacetate, methyl p-anisate, methyl nicotinate, and o-phenylanisole). In this work, we demonstrate the use of next generation titania nanotube arrays for the detection of TB VOB vapors. Functionalization of the nanotubular arrays is carried out in situ during electrochemical anodization to obtain next generation titania nanotube arrays.3 Preliminary studies (electrochemical and density functional theory) indicate Co(II) to have favorable binding affinity with TB VOBs. Amperometric testing results show that cobalt (II) functionalized TiO2 nanotubes are capable of detecting methyl nicotinate and methyl p-anisate when derived from chemical mimics dissolved in ethanol and delivered to the sensor by bubbling N2 gas. Results also show that the sensor response to ethanol and humidity alone is minimal as well as to other VOCs commonly found in human breath (e.g., acetone, ethanol, benzene, and phenol) when compared to exposure to biomarkers under the same testing conditions. The concentration of the VOB vapor reaching the sensor was estimated to be ~2 mM. Under conditions previously described, in situ functionalized titania nanotubes shows a greater sensor response (80~100 μA) with drastically faster response and recovery (a few to 10’s of seconds) compared to titania nanotube functionalized by ion exchange method (6~10 μA signal and 100’s of seconds response).4 The in situ functionalized synthesis approach not only demonstrates a higher and quicker sensor response than previous results, but also eliminates a synthesis step and ensures greater reproducibility. References: 1. Phillips, M.; Cataneo, R. N.; Condos, R.; Ring Erickson, G. A.; Greenberg, J.; La Bombardi, V.; Munawar, M. I.; Tietje, O., Volatile biomarkers of pulmonary tuberculosis in the breath. Tuberculosis 2007, 87 (1), 44-52. 2. Syhre, M.; Chambers, S. T., The scent of Mycobacterium tuberculosis. Tuberculosis 2008, 88 (4), 317-23. 3. Smith, Y. R.; Sarma, B.; Mohanty, S. K.; Misra, M., Formation of TiO2-WO3 Nanotubular Composite via Single-Step Anodization and its Application in Photoelectrochemical Hydrogen Generation. Electrochem. Comm. 2012, 19, 131-134. 4. Bhattacharyya, D.; Smith, Y. R.; Misra, M.; Mohanty, S. K., Electrochemical Detection of Methyl Nicotinate Biomarker Using Functionalized Anodized Titania Nanotube Arrays. Mater. Res. Express Accepted-In press.

Meeting abstracts, 2016

Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detect... more Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detection time, equipment portability, and performance. Detection of volatile organic compounds (VOCs) based disease biomarkers from the breath provides a potential solution to the aforementioned problems. One such tuberculosis (TB) biomarker identified from breath is methyl nicotinate. In this regard, development of smart sensor systems can provide an economically feasible solution and pave the way for rapid disease diagnostics. In this paper, we present the fabrication of a smart sensor developed by synthesis of self-organized TiO2 nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) magnetron sputtering. Site-specific interdigitated patterned growth of gold electrode was achieved using photolithography techniques. The gold interdigitated electrodes behave as the working electrode while platinum deposited on the back surface of the Si wafer acts as the back contact. Au on TiO2 presents a Schottky junction due to differences in their work function and can be overcome by light irradiation. On the other hand, an ultra-thin, inherent SiO2 layer on Si aids in tunneling electrons across the TiO2 – Si junction. Thus, Au/TiO2/SiO2/Si behaves as a Schottky tunneling diode junction that electronically couples a VOC oxidation catalyst (Au) to a photovoltaic absorber (Si). A sweep of the bias voltage (-5V to 5V) and associated sensor response at room temperature upon exposure to both air and biomarker vapors (~1000 ppm) was carried out. From the current-voltage plot (I-V), the operating voltage was chosen overcoming the negative differential resistance such that the sensor current response to the biomarker vapor would be maximized under forward bias condition. The sensor current when exposed to the biomarker vapor was higher than that in air. All sensor measurements were carried out under illuminated conditions. The variation in the output current of the sensor biased at the chosen operating voltage (~ 0.7V) at room temperature was observed for the range of 0.01 ppm to 1000 ppm biomarker concentration. The sensor demonstrated a strong response and the results suggest that the sensor is capable of detecting extremely small concentrations of the biomarker in the vapor phase. This smart sensor presents significant enhancement in sensor response over previously reported metal functionalized TiO2 nanotube array based sensing platform developed in our group for electrochemical detection of similar disease biomarkers.

Meeting abstracts, 2015

Current available state-of-art tuberculosis (TB) detection techniques face four challenges: cost,... more Current available state-of-art tuberculosis (TB) detection techniques face four challenges: cost, time of detection, equipment portability, and performance. For rapid, point-of-care (POC) detection, sensing of volatile organic compounds (VOCs) from the breath is important for early diagnosis of several pulmonary diseases such as TB. VOCs such as methyl nicotinate, methyl p-anisate, methyl phenylacetate, and o-phenylanisole have been identified as prominent TB breath biomarkers. Sensing of VOCs using solid-state TiO2 nanotube array sensors is a robust method to detect VOC vapors. Highly ordered titania nanotubular arrays (TNA) were synthesized through electrochemical anodization and functionalized with cobalt. Passing nitrogen gas through an ethanol biomarker solution was used to deliver the vapor of the individual biomarkers to the sensor. Detection of biomarkers was carried out in amperometric mode at optimized bias potentials determined from cyclic voltammetry studies. The sensor response towards the biomarkers was calculated by subtracting the base current (only N2/ethanol) from the peak current obtained (N2/ethanol + biomarker). Varying the concentration of the biomarker in solution was used to determine the sensitivity of the sensors. Further, the sensitivity was also examined through electrochemical sensing of all the four biomarkers mixed in solution. The selectivity of the sensor was investigated by operating the sensor at different potentials when exposed to the mixture of biomarker vapors. The results illustrate that titania nanotubular morphology and cobalt are necessary for volatile organic biomarker (VOB) detection. Also, the sensor exhibits good sensitivity and selectivity towards the four prominent TB biomarkers. Further, mechanisms have been proposed to describe the attachment of the biomarkers to Co-TNA and are supported by XPS characterization and band theory.

IEEE Sensors Journal, 2021

Rapid screening of tuberculosis by evaluation of associated volatile organic biomarkers in breath... more Rapid screening of tuberculosis by evaluation of associated volatile organic biomarkers in breath is a promising technology that is significantly faster and more convenient than traditional sputum culture tests. Methyl nicotinate (MN) and methyl p-anisate (MPA) have been isolated as potential biomarkers for mycobacterium tuberculosis and have been found in the breath of patients with active pulmonary tuberculosis. A novel approach to detection of these biomarkers in liquid droplets (e.g. from breath condensate) using inexpensive screen-printed electrodes is presented. Previous modelling studies suggest that these biomarkers complex with certain transition metals of particular valence state. This interaction can be exploited by mixing the biomarker sample into an electroactive solution (EAS) containing the functional metal ion and observing the change electrochemically. The study focuses on low biomarker concentrations, determined to be clinically relevant based on preliminary GC-MS studies of the levels found in patient breath. It was found that both the cyclic voltammogram and square wave voltammogram of copper(II) change significantly when as little as 0.1 mM MN is added to the solution, with analysis times of less than 2 min. Copper(II) exhibits three separate peaks during square wave voltammetry. The location and area of each peak are affected differently as the concentration of MN increases, suggesting a reaction with specific oxidation states of the metal. In this way, a “fingerprint” method can be used to identify biomarkers once their known interaction is established.

BMC Infectious Diseases, 2021

BackgroundThe World Health Organization (WHO) has endorsed the next-generation Xpert MTB/RIF Ultr... more BackgroundThe World Health Organization (WHO) has endorsed the next-generation Xpert MTB/RIF Ultra (Ultra) cartridge, and Uganda is currently transitioning from the older generation Xpert MTB/RIF (Xpert) cartridge to Ultra as the initial diagnostic test for pulmonary tuberculosis (TB). We assessed the diagnostic accuracy of Ultra for pulmonary TB among adults in Kampala, Uganda.MethodsWe sampled adults referred for Xpert testing at two hospitals and a health center over a 12-month period. We enrolled adults with positive Xpert and a random 1:1 sample with negative Xpert results. Expectorated sputum was collected for Ultra, and for solid and liquid culture testing for Xpert-negative patients. We measured sensitivity and specificity of Ultra overall and by HIV status, prior history of TB, and hospitalization, in reference to Xpert and culture results. We also assessed how classification of results in the new “trace” category affects Ultra accuracy.ResultsAmong 698 participants include...

ECS Meeting Abstracts, 2020

In this presentation two point-of-care electrochemical sensing platforms (gas and liquid phase) t... more In this presentation two point-of-care electrochemical sensing platforms (gas and liquid phase) to detect volatile organic compounds (VOCs) present in the breath of tuberculosis (TB) patients will be discussed. Rapid screening using patient breath is significantly faster, less expensive and more convenient than traditional sputum-based tests, and up to one third of adults and the majority of young children with TB are unable to produce sufficient sputum for traditional culture testing, making the development of non-sputum-based tests a priority in TB screening and diagnostics. Methyl nicotinate (MN) and methyl p-anisate (MPA) have been identified as specific biomarkers for TB in patient breath and culture by GC-MS [1], and are not found in readily in ambient air or the breath of healthy patients, making them good candidates for TB screening. Previous modelling studies [2] suggest that these biomarkers complex with certain transition metals (such as cobalt and copper) given a particu...

Annals of Nuclear Energy, Jun 1, 2021

Abstract We present a systematic and detailed approach to simulate the University of Utah TRIGA R... more Abstract We present a systematic and detailed approach to simulate the University of Utah TRIGA Reactor (UTR) in support of core criticality calculations to profile the entire reactor in detail. In performing this work, we utilized both a 3-D Cartesian SN deterministic code, PENTRAN, and a Monte Carlo code, MCNP6, to calculate complimentary, high accuracy 3-D transport derived neutron flux distributions at reactor full power. For deterministic models, our study shows that a 14-group CONTRIBUTON weighted multi-group cross-section library with up-scattering compared extremely well with continuous energy Monte Carlo results. We also modeled results to confirm the activity of an activated arsenic sample placed in the heavy water moderated thermal irradiation chamber of the UUTR (University of Utah TRIGA Reactor). A 138 pcm difference in the system eigenvalue for the full 3-D core PENTRAN discrete ordinates (SN) UUTR model utilizing 2 × 109 equations, in 14 energy groups, is compared to the reference case of a similar full core MCNP6 Monte Carlo calculation with continuous energy cross-sections. On average, deterministic and Monte Carlo core neutron group flux values differ by less than 1%, with some local maximum relative differences between 10% and 20% for the 3-D core flux distribution in some energy groups are observed. The differences of neutron fluxes from group 3/14 to group 10/14, with energies spanning from 1.11 eV to 13.8 MeV, are comparable to within 5% in the UUTR core active fuel region. For energy groups with energies greater than 13.8 MeV, MCNP6 is not able to resolve the flux distributions with reasonable statistical uncertainties due to the extremely low sampling probability for neutrons in those energies; orders of magnitude more histories would be required to do so. In contrast, the PENTRAN 3D SN calculation shows a very detailed flux distribution for energies larger than 13.8 MeV, highlighting the complimentary utility of applying both methods. Detailed approaches for the PENTRAN calculation, including energy group collapsing, homogenization of fuel + gap + cladding, and analysis are presented in the narrative.

Journal of environmental chemical engineering, Mar 1, 2016

Microfluidic reactors have gained considerable interest for photocatalytic degradation of contami... more Microfluidic reactors have gained considerable interest for photocatalytic degradation of contaminants in water. These systems have advantages such as large surface-area-to-volume ratio and high control of fluid flow, yet still suffer from drawbacks due to limited mass transport associated with laminar flow. The use

Abstract A multi-layer plastic/glass technology has been developed for microfluidic systems with ... more Abstract A multi-layer plastic/glass technology has been developed for microfluidic systems with integrated functionality. Hot embossing and heat staking of plastics, microstenciling of electrodes, and stereolithography (SLA) was combined with conventional MEMS ...

Journal of The Electrochemical Society, Dec 29, 2015

2019 AIChE Annual Meeting, Nov 11, 2019

IEEE Sensors Journal, Jun 15, 2021

Cost-effectively detecting benzene, a human carcinogen, at occupationally and atmospherically rel... more Cost-effectively detecting benzene, a human carcinogen, at occupationally and atmospherically relevant concentrations would benefit individuals at risk of exposure. This paper presents the development of a titania (TiO2) nanotube-based sensor array that has a high surface area, is highly sensitive, and operates at room temperature using simple, portable instrumentation. An n-type TiO2 nanotube was synthesized through electrochemical anodization in an electrolytic solution of ammonium fluoride-ethylene glycol and oxygen annealed at 500 °C for up to 8 hours. The nanotube sensor had a bandgap (Eg) of ~2.6 eV, and it was operated at a bias voltage of +1.5 V. The response of the sensor to benzene vapor was measured using an amperometric technique at room temperature, and when exposed to benzene, the sensor exhibited a decrease in current, as expected for an n-type metal oxide semiconductor. The sensor response was proportional to benzene concentration over a range of 100–400 ppb. A sensing mechanism based on Fermi level changes caused by band bending has been explained for this benzene sensor.

Journal of Materials Science & Technology, Jun 1, 2018

Titania nanotubular arrays (TNA) synthesized via electrochemical anodization is a stable and vers... more Titania nanotubular arrays (TNA) synthesized via electrochemical anodization is a stable and versatile material, widely studied for photocatalytic and sensing applications, whereas nano-sized gold particles are a known plasmonic material. Semiconductor-metal nanocomposites in isolated, embedded, or encapsulated form, when irradiated with proper light frequency can exhibit localized surface plasmon resonance (LSPR) effect. This effect can result in improved light adsorption and electrical properties of a material. In this study, we report the enhanced visible light photo-response of LSPR induced volatile organic biomarker vapor sensing at room temperature using a Au-embedded TNA electrochemical sensor. Two mechanisms are proposed. One based on classical physics (band theory), which explains operation under non-irradiated conditions. The second mechanism is based on the coupling of classical and quantum physics (molecular orbitals), and explains sensor operation under irradiated conditions.

This report provides a summary of the work performed under NIAC Phase I award NNX15AL86G entitled... more This report provides a summary of the work performed under NIAC Phase I award NNX15AL86G entitled "CubeSat with Nanostructured Sensing Instrumentation for Planetary Exploration". The objective of this research is to investigate the feasibility of an innovative, low cost, CubeSat based planetary mission concept for in situ "ground truth" analysis of small asteroids and comets. The project includes an instrument study and a mission/spacecraft design study. The instrument study concerns with the development of a new TiO 2 nanotube sensor with integrated compound semiconductor nanowires to determine surface composition element via neutron activated analysis (NAA). The mission/spacecraft design study concerns with the development of CubeSat based lander to small asteroids and comets. The Phase I study suggests that our concept is feasible and could provide significant benefit to NASA's future planetary missions. This research was carried out at the

Meeting abstracts, 2017

Benzene is one of the few known human carcinogens as identified by the International Agency for R... more Benzene is one of the few known human carcinogens as identified by the International Agency for Research on Cancer. It is a common indoor and outdoor pollutant, with sources ranging from cigarette smoke to traffic. Hence, there is an increasing need to detect low concentrations of benzene. Metal-oxide based nano-sensors, with their simple sensing mechanisms make for a good choice. Thin films based on titanium dioxide (TiO2) have previously been shown to respond to benzene (1), however these sensors are run at high temperatures (160-200°C), require a complex setup for operation, and have low surface area for sensing. This paper presents the development of TiO2 nanotube based sensor array (Figure 1) that has high surface area, is highly sensitive, and operates at room temperature using portable and simple instrumentation. TiO2 nanotubes were synthesized through anodization in electrolytic solution of ammonium fluoride (NH4F)-ethylene glycol (EG) and oxygen annealed for up to 500°C. The response of the synthesized hollow nanotubes was studied at room temperature for different concentrations of benzene vapor (100-500ppm). The response of the sensor coupons to benzene vapor was measured using an amperometric technique. The results showed an increase in current that was directly proportional to the concentration of benzene in the sample which indicates a quantitative nature of the sensor (Figure 2). The sensor was placed in a portable system which can be deployed to potential contamination sites for real-time monitoring applications. Results on sensing mechanism, stability of the sensor over time, sensor reusability, and detection limit will be presented. (1) Mabrook M., Hawkins P. (2001) Sensors and Actuators, B: Chemical 75, 197-202. Figure 1

Meeting abstracts, 2015

Analysis of volatile organic compounds (VOCs) from exhaled breath presents a potential non-invasi... more Analysis of volatile organic compounds (VOCs) from exhaled breath presents a potential non-invasive, label-free, and point-of-care (POC) medical diagnostic technique. Sensor detection of specific volatile organic biomarkers (VOBs) directly associated with a pulmonary or other disease presents itself as a facile method for early diagnosis. Tuberculosis (TB) is arguably one of the most devastating infectious diseases in the world today. A major contributing factor to such a large number of cases is due to inadequate diagnostic methods for TB. Research has shown that various strains of the mycobacteria produce distinct gaseous volatile biomarkers that can be used as a methodology for detecting and identifying the mycobacterium.1-2 Syhre and Chambers2 found that Mycobacterium tuberculosis and Mycobacterium bovis cultures give off four specific volatile organic compounds (methyl phenylacetate, methyl p-anisate, methyl nicotinate, and o-phenylanisole). In this work, we demonstrate the use of next generation titania nanotube arrays for the detection of TB VOB vapors. Functionalization of the nanotubular arrays is carried out in situ during electrochemical anodization to obtain next generation titania nanotube arrays.3 Preliminary studies (electrochemical and density functional theory) indicate Co(II) to have favorable binding affinity with TB VOBs. Amperometric testing results show that cobalt (II) functionalized TiO2 nanotubes are capable of detecting methyl nicotinate and methyl p-anisate when derived from chemical mimics dissolved in ethanol and delivered to the sensor by bubbling N2 gas. Results also show that the sensor response to ethanol and humidity alone is minimal as well as to other VOCs commonly found in human breath (e.g., acetone, ethanol, benzene, and phenol) when compared to exposure to biomarkers under the same testing conditions. The concentration of the VOB vapor reaching the sensor was estimated to be ~2 mM. Under conditions previously described, in situ functionalized titania nanotubes shows a greater sensor response (80~100 μA) with drastically faster response and recovery (a few to 10’s of seconds) compared to titania nanotube functionalized by ion exchange method (6~10 μA signal and 100’s of seconds response).4 The in situ functionalized synthesis approach not only demonstrates a higher and quicker sensor response than previous results, but also eliminates a synthesis step and ensures greater reproducibility. References: 1. Phillips, M.; Cataneo, R. N.; Condos, R.; Ring Erickson, G. A.; Greenberg, J.; La Bombardi, V.; Munawar, M. I.; Tietje, O., Volatile biomarkers of pulmonary tuberculosis in the breath. Tuberculosis 2007, 87 (1), 44-52. 2. Syhre, M.; Chambers, S. T., The scent of Mycobacterium tuberculosis. Tuberculosis 2008, 88 (4), 317-23. 3. Smith, Y. R.; Sarma, B.; Mohanty, S. K.; Misra, M., Formation of TiO2-WO3 Nanotubular Composite via Single-Step Anodization and its Application in Photoelectrochemical Hydrogen Generation. Electrochem. Comm. 2012, 19, 131-134. 4. Bhattacharyya, D.; Smith, Y. R.; Misra, M.; Mohanty, S. K., Electrochemical Detection of Methyl Nicotinate Biomarker Using Functionalized Anodized Titania Nanotube Arrays. Mater. Res. Express Accepted-In press.

Meeting abstracts, 2016

Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detect... more Rapid, point-of-care (POC) disease diagnostics presents several challenges including cost, detection time, equipment portability, and performance. Detection of volatile organic compounds (VOCs) based disease biomarkers from the breath provides a potential solution to the aforementioned problems. One such tuberculosis (TB) biomarker identified from breath is methyl nicotinate. In this regard, development of smart sensor systems can provide an economically feasible solution and pave the way for rapid disease diagnostics. In this paper, we present the fabrication of a smart sensor developed by synthesis of self-organized TiO2 nanotube arrays formed by anodization of thin Ti film deposited on Si wafers by direct current (D.C.) magnetron sputtering. Site-specific interdigitated patterned growth of gold electrode was achieved using photolithography techniques. The gold interdigitated electrodes behave as the working electrode while platinum deposited on the back surface of the Si wafer acts as the back contact. Au on TiO2 presents a Schottky junction due to differences in their work function and can be overcome by light irradiation. On the other hand, an ultra-thin, inherent SiO2 layer on Si aids in tunneling electrons across the TiO2 – Si junction. Thus, Au/TiO2/SiO2/Si behaves as a Schottky tunneling diode junction that electronically couples a VOC oxidation catalyst (Au) to a photovoltaic absorber (Si). A sweep of the bias voltage (-5V to 5V) and associated sensor response at room temperature upon exposure to both air and biomarker vapors (~1000 ppm) was carried out. From the current-voltage plot (I-V), the operating voltage was chosen overcoming the negative differential resistance such that the sensor current response to the biomarker vapor would be maximized under forward bias condition. The sensor current when exposed to the biomarker vapor was higher than that in air. All sensor measurements were carried out under illuminated conditions. The variation in the output current of the sensor biased at the chosen operating voltage (~ 0.7V) at room temperature was observed for the range of 0.01 ppm to 1000 ppm biomarker concentration. The sensor demonstrated a strong response and the results suggest that the sensor is capable of detecting extremely small concentrations of the biomarker in the vapor phase. This smart sensor presents significant enhancement in sensor response over previously reported metal functionalized TiO2 nanotube array based sensing platform developed in our group for electrochemical detection of similar disease biomarkers.

Meeting abstracts, 2015

Current available state-of-art tuberculosis (TB) detection techniques face four challenges: cost,... more Current available state-of-art tuberculosis (TB) detection techniques face four challenges: cost, time of detection, equipment portability, and performance. For rapid, point-of-care (POC) detection, sensing of volatile organic compounds (VOCs) from the breath is important for early diagnosis of several pulmonary diseases such as TB. VOCs such as methyl nicotinate, methyl p-anisate, methyl phenylacetate, and o-phenylanisole have been identified as prominent TB breath biomarkers. Sensing of VOCs using solid-state TiO2 nanotube array sensors is a robust method to detect VOC vapors. Highly ordered titania nanotubular arrays (TNA) were synthesized through electrochemical anodization and functionalized with cobalt. Passing nitrogen gas through an ethanol biomarker solution was used to deliver the vapor of the individual biomarkers to the sensor. Detection of biomarkers was carried out in amperometric mode at optimized bias potentials determined from cyclic voltammetry studies. The sensor response towards the biomarkers was calculated by subtracting the base current (only N2/ethanol) from the peak current obtained (N2/ethanol + biomarker). Varying the concentration of the biomarker in solution was used to determine the sensitivity of the sensors. Further, the sensitivity was also examined through electrochemical sensing of all the four biomarkers mixed in solution. The selectivity of the sensor was investigated by operating the sensor at different potentials when exposed to the mixture of biomarker vapors. The results illustrate that titania nanotubular morphology and cobalt are necessary for volatile organic biomarker (VOB) detection. Also, the sensor exhibits good sensitivity and selectivity towards the four prominent TB biomarkers. Further, mechanisms have been proposed to describe the attachment of the biomarkers to Co-TNA and are supported by XPS characterization and band theory.

IEEE Sensors Journal, 2021

Rapid screening of tuberculosis by evaluation of associated volatile organic biomarkers in breath... more Rapid screening of tuberculosis by evaluation of associated volatile organic biomarkers in breath is a promising technology that is significantly faster and more convenient than traditional sputum culture tests. Methyl nicotinate (MN) and methyl p-anisate (MPA) have been isolated as potential biomarkers for mycobacterium tuberculosis and have been found in the breath of patients with active pulmonary tuberculosis. A novel approach to detection of these biomarkers in liquid droplets (e.g. from breath condensate) using inexpensive screen-printed electrodes is presented. Previous modelling studies suggest that these biomarkers complex with certain transition metals of particular valence state. This interaction can be exploited by mixing the biomarker sample into an electroactive solution (EAS) containing the functional metal ion and observing the change electrochemically. The study focuses on low biomarker concentrations, determined to be clinically relevant based on preliminary GC-MS studies of the levels found in patient breath. It was found that both the cyclic voltammogram and square wave voltammogram of copper(II) change significantly when as little as 0.1 mM MN is added to the solution, with analysis times of less than 2 min. Copper(II) exhibits three separate peaks during square wave voltammetry. The location and area of each peak are affected differently as the concentration of MN increases, suggesting a reaction with specific oxidation states of the metal. In this way, a “fingerprint” method can be used to identify biomarkers once their known interaction is established.

BMC Infectious Diseases, 2021

BackgroundThe World Health Organization (WHO) has endorsed the next-generation Xpert MTB/RIF Ultr... more BackgroundThe World Health Organization (WHO) has endorsed the next-generation Xpert MTB/RIF Ultra (Ultra) cartridge, and Uganda is currently transitioning from the older generation Xpert MTB/RIF (Xpert) cartridge to Ultra as the initial diagnostic test for pulmonary tuberculosis (TB). We assessed the diagnostic accuracy of Ultra for pulmonary TB among adults in Kampala, Uganda.MethodsWe sampled adults referred for Xpert testing at two hospitals and a health center over a 12-month period. We enrolled adults with positive Xpert and a random 1:1 sample with negative Xpert results. Expectorated sputum was collected for Ultra, and for solid and liquid culture testing for Xpert-negative patients. We measured sensitivity and specificity of Ultra overall and by HIV status, prior history of TB, and hospitalization, in reference to Xpert and culture results. We also assessed how classification of results in the new “trace” category affects Ultra accuracy.ResultsAmong 698 participants include...

ECS Meeting Abstracts, 2020

In this presentation two point-of-care electrochemical sensing platforms (gas and liquid phase) t... more In this presentation two point-of-care electrochemical sensing platforms (gas and liquid phase) to detect volatile organic compounds (VOCs) present in the breath of tuberculosis (TB) patients will be discussed. Rapid screening using patient breath is significantly faster, less expensive and more convenient than traditional sputum-based tests, and up to one third of adults and the majority of young children with TB are unable to produce sufficient sputum for traditional culture testing, making the development of non-sputum-based tests a priority in TB screening and diagnostics. Methyl nicotinate (MN) and methyl p-anisate (MPA) have been identified as specific biomarkers for TB in patient breath and culture by GC-MS [1], and are not found in readily in ambient air or the breath of healthy patients, making them good candidates for TB screening. Previous modelling studies [2] suggest that these biomarkers complex with certain transition metals (such as cobalt and copper) given a particu...