Breath acetone is a promising biomarker of diabetes mellitus. With an integrated standalone, on-site cavity ringdown breath acetone analyzer, LaserBreath-001, we tested breath samples from 23 type 1 diabetic (T1D) patients, 312 type 2 diabetic (T2D) patients, 52 healthy subjects. In the cross-sectional studies, the obtained breath acetone concentrations were higher in the diabetic subjects compared with those in the control group. No correlation between breath acetone and simultaneous BG was observed in the T1D, T2D, and healthy subjects. A moderate positive correlation between the mean individual breath acetone concentrations and the mean individual BG levels was observed in the 20 T1D patients without ketoacidosis. In a longitudinal study, the breath acetone concentrations in a T1D patient with ketoacidosis decreased significantly and remained stable during the 5-day hospitalization. The results from a relatively large number of subjects tested indicate that an elevated mean breath acetone concentration exists in diabetic patients in general. Although many physiological parameters affect breath acetone concentrations, fast (<1 min) and on site breath acetone measurement can be used for diabetic screening and management under a specifically controlled condition.
Fiber loop ringdown technique has shown promise in biomedical applications in recent studies. In the present work, fiber loop ringdown sensors using the evanescent field as the sensing mechanism have been fabricated and tested in actual human urines for the first time. In order to evaluate the sensors’ performance, the sensors were comparatively tested in healthy human urines, synthetic urine solutions, and diabetic urines. Due to different features or chemical compositions of each urine sample, the sensors experience different optical losses, equivalently, different ringdown times. The comparative results show that evanescent field-fiber loop ringdown glucose sensors can discriminate the three different urine samples by displaying different ringdown times. The evanescent field-fiber loop ringdown glucose sensors had fast response, good reproducibility, and high sensitivity. The promising results imply that the evanescent field-fiber loop ringdown sensors have potential for near real-time detection of diabetic urines.
Real-time detection and identification of bio-aerosol particles are crucial for the protection against chemical and
biological agents. The strong elastic light scattering properties of airborne particles provides a natural means for rapid,
non-invasive aerosol characterization. Recent theoretical predictions suggested that variations in the polarization
dependent angular scattering cross section could provide an efficient means of classifying different airborne particles. In
particular, the polarization dependent scattering cross section of aggregate particles is expected to depend on the shape
of the primary particles. In order to experimentally validate this prediction, we built a high throughput, sampling system,
capable of measuring the polarization resolved angular scattering cross section of individual aerosol particles flowing
through an interrogating volume with a single shot of laser pulse. We calibrated the system by comparing the
polarization dependent scattering cross section of individual polystyrene spheres with that predicted by Mie theory. We
then used the system to study different particles types: Polystyrene aggregates composed 500 nm spheres and <i>Bacillus
subtilis</i> (<i>BG, Anthrax simulant</i>) spores composed of elongated 500 nm × 1000 nm cylinder-line particles. We found that
the polarization resolved scattering cross section depends on the shape of the constituent elements of the aggregates.
This work indicates that the polarization resolved scattering cross section could be used for rapid discrimination between
different bio-aerosol particles.
Evanescent field-fiber loop ringdown (EF-FLRD) is a relatively new hybrid sensing technique which combines a versatile sensing mechanism with a sensitivity-enhanced ringdown detection scheme. An array of low cost, fast response, and high sensitivity biosensors based on the EF-FLRD technique can be developed. In this work, new fiber loop ringdown glucose sensors using refractive index-difference evanescent field attenuation effect as a sensing mechanism are described. The sensor head consists of either a section of partially-etched bare single mode fiber or a section of the etched fiber with glucose oxidase (GOD) immobilized on the etched fiber surface. Effects of the sensor head, with and without the immobilized GOD, on the sensor's performance are comparatively examined. The sensors' responses to standard glucose solutions and synthetic urines in different glucose concentrations ranging from 50 mg/dl to 10 g/dl are studied. The sensors, with or without the immobilized GOD, showed a linear response to glucose concentrations in the range of 100 mg/dl to 1 g/dl, but a nonlinear response in the higher glucose concentration ranging from 1 to 10 g/dl. The detection sensitivities of the sensors for the glucose solutions and artificial urine samples are 75 and 50 mg/dl respectively, and the sampling rate of the sensors is 10 to 100 Hz. Estimated theoretical detection sensitivity of the EF-FLRD glucose sensors is 10 mg/dl, which is approximately 17 times lower than the glucose renal threshold concentration.
We report a new type of refractive index-based biosensor using a fiber loop ringdown evanescent field (FLRD-EF) sensing scheme, in which the sensing signal is a time constant and detection sensitivity is enhanced by the multipass nature of the ringdown technique. Bulk index-based detections of three different single strand DNAs and one type of bacteria are demonstrated for the FLRD-EF sensors that utilize a partially-etched single mode fiber as the sensor head. Stepwise coating of the sensor head with poly-L-lysine and a probe DNA has enabled surface index-based label-free target DNA sensing. We expect an array of FLRD-EF biosensors to be created, which are superior to counterparts in terms of simplicity, low cost, and high sensitivity.
Fiber loop ringdown (FLRD), a uniform time-domain sensing scheme, has potential to help address the three key
issues: Power losses, light intensity fluctuations, and high terminal equipment costs, in the development of fiber
optic sensor networks for simultaneously sensing multiple quantities, including pressure, temperature, strain,
chemical species, etc. with fast response, high sensitivity, and significantly reduced costs. Performance and design
of a cluster of individual FLRD-based fiber optic sensors are presented. Multiplexing those individual FLRD sensor
units into a large scale sensor system for multi-function sensing is proposed. System configuration, operation, and
advantages are discussed.
Fiber loop ringdown spectroscopy is an emerging technique, introduced in the last few years, and has demonstrated its promise in optic fiber sensor development for a variety of applications. This paper describes a new double fiber loop ringdown system, consisting of an electronic portion and two fiber loops, which can detect environmental changes in each fiber loop simultaneously. We present a theoretical simulation of the optical output of the double loop ringdown system. The simulation is modeled by the superposition of each of the individual ringdown waveforms represented by a single exponential decay and an interference term that is characterized by a Bessel function. The theoretical results are in good agreement with the experimental observations. This method may be useful for signal processing in the double fiber loop ringdown system, which is developed for simultaneous sensing in separate locations.
A new method of developing fiber temperature sensors using a fiber Bragg grating-loop ringdown scheme is introduced. With this new technique, temperature measurements are converted to measuring time constants. Temperature sensing up to 593°C has been demonstrated using a proof-of-concept device. The sensor's stability, repeatability, sensitivity, and dynamic range are also explored.