@article {46183, title = {Fiber optic Fabry-Perot interferometer sensor: an efficient and fast approach for ammonia gas sensing}, journal = {Journal of the Optical Society of America B-Optical Physics}, volume = {36}, year = {2019}, month = {MAR }, pages = {684-689}, type = {Article}, abstract = {

In this work, we propose and demonstrate a Fabry-Perot-interferometer-based polydimethylsiloxane (PDMS) and poly(methyl methacrylate) (PMMA)-composite-coated optical sensor for ammonia and volatile organic compounds (VOCs) detection at room temperature. The principle of sensing is based on change in the cavity length of the FP cavity in the presence of varied concentrations of gases, which results in changes in the total reflectance due to the shift in wavelength of an interference pattern. The sensing composite material was coated on a single-mode optical fiber by using a simple dip-coating technique and explored it for sensing. The ammonia and VOCs measurements were performed for concentrations ranging from 5 to 500 ppm. The corresponding sensitivity and limit of detection of the developed sensor for ammonia gas detection was observed of the order of around 4.16 pm/ppm and 4.8 ppm, respectively. The response and recovery times of the sensor were found to be of the order of 50 s and 10 s, respectively, for the ammonia gas. This sensor provides a simple, cost-effective, highly sensitive, and repeatable approach to measure ammonia gas and other VOCs at room temperature and could fulfill the demands of industrial applications. (C) 2019 Optical Society of America

}, issn = {0740-3224}, doi = {10.1364/JOSAB.36.000684}, author = {Kanawade, Rajesh and Kumar, Ajay and Pawar, Dnyandeo and Late, Dattatray and Mondal, Samir and Sinha, Ravindra K.} } @conference {48195, title = {Skin mimicking solid optical tissue phantom fulfillment and its characterization}, booktitle = {Photonics in Dermatology and Plastic Surgery 2022}, year = {2022}, publisher = {SPIE}, organization = {SPIE}, address = {1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98227-0010 USA}, abstract = {

Skin mimicking optical tissue phantoms are widely used in diagnostics systems for characterization, optimization, routine calibration and validation. In general, solid phantoms are more preferred in comparison to liquid phantoms. Therefore, our aim is to prepare and characterize the solid tissue phantoms having skin equivalent optical properties. In this work, we have used epoxy resin and hardener as a base material and titanium oxide (TiO2) nanoparticles and ink as a scatterer and absorber media, respectively. The total transmission (Tt), collimated transmission (Tc), and diffuse reflectance (Rd) spectra of the developed phantoms were measured with an integrating sphere installed in UV-VIS spectrometer within the wavelength range 400-700 nm. To characterize the optical properties such as absorption (mu(a)), reduced scattering (mu(s){\textquoteright}), and anisotropy factor (g) of the developed tissue phantoms, the numerical model based on Inverse Adding Doubling (IAD) has been used. With various concentrations of absorber and scatterer, a calibration curve was prepared. The calculated experimental optical properties from IAD matched with the predicted intrinsic optical properties of the skin. Thus, the preliminary results suggest that the recipe used in this study may be used as an alternative approach to developing skin mimicking solid optical phantom for diagnostics system applications.

}, keywords = {Absorption, anisotropy factor, scattering, skin mimicking, solid tissue phantom}, isbn = {978-1-5106-4740-4; 978-1-5106-4739-8}, doi = {10.1117/12.2609577}, author = {Kumar, Ajay and Hinge, Sarika and Dixit, Hemant and Kanawade, Rajesh and Kulkarni, Gauri}, editor = {Choi, B and Zeng, H} } @article {48814, title = {Response of cardiac pulse parameters in humans at various inclinations via 360{\textdegree} rotating platform for simulated microgravity perspective}, journal = {NPJ Microgravity}, volume = {9}, year = {2023}, month = {JUL}, pages = {54}, type = {Article}, abstract = {

On the Earth, the human body is designed and adapted to function under uniform gravitational acceleration. However, exposure to microgravity or weightlessness as experienced by astronauts in space causes significant alterations in the functioning of the human cardiovascular system. Due to limitations in using real microgravity platforms, researchers opted for various ground-based microgravity analogs including head-down tilt (HDT) at fixed inclination. However, in the present study, an investigation of response of various cardiac parameters and their circulatory adaptation in 18 healthy male subjects was undertaken by using an indigenously developed 360 \& DEG; rotating platform. Cardiac pulse was recorded from 0 \& DEG; to 360 \& DEG; in steps of 30 \& DEG; inclination using piezoelectric pulse sensor (MLT1010) and associated cardiac parameters were analyzed. The results showed significant changes in the pulse shape while an interesting oscillating pattern was observed in associated cardiac parameters when rotated from 0 \& DEG; to 360 \& DEG;. The response of cardiac parameters became normal after returning to supine posture indicating the ability of the cardiovascular system to reversibly adapt to the postural changes. The observed changes in cardiac parameters at an inclination of 270 \& DEG;, in particular, were found to be comparable with spaceflight studies. Based on the obtained results and the proposed extended version of fluid redistribution mechanism, we herewith hypothesize that the rotation of a subject to head down tilt inclination (270 \& DEG;) along with other inclinations could represent a better microgravity analog for understanding the cumulative cardiac response of astronauts in space, particularly for short duration space missions.

}, doi = {10.1038/s41526-023-00301-3}, author = {Jagtap, Sagar and Kumar, Ajay and Mahale, Bhoopesh and Dixit, Jyotsana and Kalange, Ashok E. and Kanawade, Rajesh and Gangal, Shashikala and Vidyasagar, Pandit} } @article {49433, title = {Fabrication and evaluation of a spatially resolved fiber-optic probe for diffuse reflectance measurement for noninvasive diabetic foot ulcer diagnosis perspective}, journal = {Optical Engineering}, volume = {63}, year = {2024}, month = {APR }, pages = {044103}, type = {Article}, abstract = {

Timely diagnosis and monitoring of wound progression or healing are key to improving the long-term outcome of diabetic foot ulcers (DFU). Diffuse reflectance spectroscopy (DRS) has the potential to noninvasively diagnose the DFU in real time, as it detects changes in local blood volume fraction and oxygenation state level that occur when tissue becomes diseased or ulcerated. Since foot soles have a thicker epidermis and deeper blood vessels/capillaries than other parts of the body, a spatially resolved fiber-optic probe (SRFP) is needed to detect the optimal spatially resolved diffuse reflectance (SRDR) signal from the local site of the ulcer for DFU diagnosis. Therefore, herein, an SRFP consisting of a linear array of seven 400-mu m fibers with detector-source (D-S) fiber separation (rho) ranging from 0.8 to 4.8 mm was designed, fabricated, tested, and evaluated for SRDR measurement from a standard reflectance plate of barium sulfate (BaSO4) and foot sole of 27 healthy human subjects. The variation in SRDR spectra for each detector and source fiber pair measured with BaSO4 was found to be less than 1.6\%. In-vivo measurements from the foot sole demonstrate that the fabricated probe has the ability to spatially resolve and distinguish the SRDR spectra from sites, namely, the fifth metatarsal, ball of great joint, calcaneum, and great toe. Experimentally and theoretically, the detector and source fiber pair of rho=1.6 and 2.4 mm were optimal for SRDR measurements from a human foot. To evaluate and validate the performance of SRFP in a context relevant to DFU diagnosis, further SRDS measurements were performed on the solid tissue phantoms that mimic the optical properties of the normal and diabetic foot sole, and their results are statistically found different. Preliminary results suggest that developed SRFP can be explored for DRS measurement from foot ulcer patients to confirm its potential clinical applicability.

}, keywords = {diabetic foot ulcer, diffuse reflectance spectroscopy, foot sole, spatially resolved fiber-optic probe, tissue phantom}, issn = {0091-3286}, doi = {10.1117/1.OE.63.4.044103}, author = {Kumar, Ajay and Hattale, Gangadhar and Pawar, Dnyandeo and Kanawade, Rajesh} } @article {49243, title = {Normal and diabetic foot sole skin mimicking tissue phantom fulfillment for spectroscopic-based DFU diagnostics perspective}, journal = {AIP ADVANCES}, volume = {14}, year = {2024}, month = {JUN }, type = {Journal Article}, keywords = {OPTICAL-PROPERTIES, STATE}, doi = {10.1063/5.0206988}, author = {Kumar, Ajay and Hattale, Gangadhar and Hinge, Sarika and Kulkarni, Gauri and Late, Dattatray J. and Kanawade, Rajesh} } @article {49658, title = {Polymeric PEI/PEG coated optical fiber fabry-perot interferometer for CO2 detection}, journal = {IEEE Sensors Journal}, volume = {24}, year = {2024}, month = {DEC }, pages = {40883-40889}, type = {Article}, abstract = {

Monitoring carbon dioxide (CO2) gas is essential for numerous applications, but the detection of CO2 in miniaturized devices presents significant challenges. In this study, a polyethyleneimine/poly(ethylene glycol) (PEI/PEG) coated optical fiber Fabry-Perot interferometer (FPI) and its charge transfer process toward CO2 are investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to analyze the surface morphology and vibration bands of the PEI/PEG composite. The PEI/PEG composite Fabry-Perot (FP) cavity of length similar to 13 mu m is coated at the distal end of the single-mode fiber using a dip coating technique. A highly sensitive optical and low-cost FPI probe fabrication has displayed a linear sensitivity of 17.10 nm/\% in the range of 0.31\%-1.25\% CO2 gas. The response and recovery times of the sensor are in a few tens of seconds. The enhanced performance of the sensor is primarily due to the protonation and charge transfer between CO2 gas molecules and PEI/PEG composite. Due to low-cost fabrication and high sensitivity, this FPI sensor can be used in a range of potential applications in bioprocessing, healthcare, and environmental monitoring.

}, keywords = {dip coating, Fresnel{\textquoteright}s reflection, Interference, monitoring, Optical fiber sensors, Optical fibers, polymer composite, Polymers, refractive index, sensitivity, Sensor phenomena and characterization, sensors, swelling, Temperature sensors}, issn = {1530-437X}, doi = {10.1109/JSEN.2024.3478088}, author = {Pawar, Dnyandeo and Lo Presti, Daniela and Lemma, Enrico D. and Rainer, Alberto and Kumar, Ajay and Kanawade, Rajesh and Silvestri, Sergio and Schena, Emiliano and Massaroni, Carlo} } @article {49552, title = {Investigating the visible range photoresponse of an organic single-crystal analogue of the green fluorescent protein}, journal = {Nanoscale}, volume = {17}, year = {2025}, month = {APR}, pages = {8614-8623}, type = {Article}, abstract = {

The growing demand for lightweight, flexible, semi-transparent and low-cost photodetectors (PDs) in wearable electronics and optical communication systems has prompted studies to investigate organic materials as feasible alternatives to conventional inorganic PDs. However, modern organic PDs often face responsivity, detectivity, and photoresponse speed limitations, particularly in the visible range. Here, we present the photoresponse of an organic single-crystal analogue of the green fluorescent protein (GFP) chromophore photodetector, fabricated on a silicon nitride substrate. A significant increase in photocurrent was detected upon illumination with visible wavelengths (532 nm, 630 nm, and halogen light). A remarkably consistent and repeatable photoresponse was obtained during the ON and OFF illumination cycles. The device showed the dependence of photocurrent on the applied bias voltages. The measured photocurrent, responsivity, detectivity, rise time, decay time, noise equivalent power and external quantum efficiency are studied for different wavelengths. Strikingly, the fabricated device demonstrates excellent performance in the visible region compared to several conventional organic and inorganic PDs. The observed responsivity and detectivity values for the device are 98 mA W-1 and 7.94 x 108 Jones, respectively. Furthermore, the device also exhibits rapid photoresponse dynamics with a rise time of 180 ms and a decay time of 152 ms. The excellent photodetection features indicate that the single crystal GFP could serve as a versatile broadband material for future applications in optoelectronics.

}, issn = {2040-3364}, doi = {10.1039/d4nr05252h}, author = {Virole, Vishal and Dabke, Niteen and Verma, Sahil and Kumar, Ajay and Pandya, Rinu and Husale, Sudhir and Vanka, Kumar and Gonnade, Rajesh and Kanawade, Rajesh} } @article {49586, title = {Real-time estimation of blood oxygenation parameters from human foot sole during leg elevation: a preliminary study with diffuse reflectance spectroscopy}, journal = {Optics and Laser Technology}, volume = {181}, year = {2025}, month = {FEB}, pages = {111706}, type = {Article}, abstract = {

This study investigated the applicability of diffuse reflectance spectroscopy (DRS) for real-time and non-invasive measurement of blood oxygenation parameters (BOPs) such as reduced hemoglobin (RHb), oxyhemoglobin (HbO(2)), and oxygen saturation (SO2) from human foot sole during leg elevation. Seventeen (17) healthy male subjects aged between 21 to 39 years were included in this study. Diffuse reflectance spectra were recorded from measurement sites namely the 5th metatarsal, ball of great joint, calcaneum, and great toe of the human foot sole w.r.t. leg elevation angles such as 0(0), 15(0), 30(0), 45(0), and 60(0), respectively. The localized BOPs were derived from the recorded spectra. In addition, blood hemodynamic parameters (BHPs) such as heart rate (HR), SO2, perfusion index (PI), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were also measured for each elevating angle. To study and assess the changes in BOPs and BHPs w.r.t. leg elevation, a One-way ANOVA test followed by a Tukey HSD post-hoc test was performed. We observed a statistically significant increase in RHb (p \< 0.001) and a decrease in HbO(2) (p \< 0.001) after 45 degrees of leg elevation, however, there was no statistically significant difference in SO2 (p = 0.74) and HR (p = 0.84) for each measurement site w.r.t. leg elevation, respectively. Furthermore, PI (p \< 0.01), ankle SBP (p \< 0.001) and DBP (p \< 0.001) were decreased w.r.t. leg elevation. The obtained results are in agreement with the literature. The preliminary results suggest that DRS has the potential for real-time estimation of BOPs from the local sites of healthy human foot soles during leg elevation. Thus, it opens the possibility of DRS to monitor and evaluate the diagnosis and treatment of ischemia and edema during leg elevation of patients through BOPs measurement.

}, keywords = {diabetic foot ulcer, diffuse reflectance spectroscopy, Leg elevation, Oxygen saturation, Oxyhemoglobin, Reduced hemoglobin}, issn = {0030-3992}, doi = {10.1016/j.optlastec.2024.111706}, author = {Kumar, Ajay and Lohchab, Viney and Pawar, Dnyandeo and Someshwar, Vimal and Mathe, Vikas and Husale, Sudhir and Kanawade, Rajesh} }