A low-cost optoacoustic sensor for environmental monitoring.

Attention to Black Carbon (BC) has been rising due to its effects on human health as well its contribution to climate change. Measurements of BC are challenging, as currently used devices are either expensive or impractical for continuous monitoring. Here, we propose an optoacoustic sensor to address this problem. The sensor utilizes a novel ellipsoidal design for refocusing the optoacoustic signal with minimal acoustic energy losses. To reduce the cost of the system, without sacrificing accuracy, an overdriven laser diode and a Quartz Tuning Fork are used as the light source and the sound detector, respectively. The prototype was able to detect BC particles and to accurately monitor changes in concentration in real time and with very good agreement with a reference instrument. The response of the sensor was linearly dependent on the BC particles concentration with a normalized noise equivalent absorption coefficient (NNEA) for soot equal to 7.39 × 10−9 W cm−1 Hz−1/2. Finally, the prototype was able to perform NO2 measurements, demonstrating its ability to accurately monitor both particulate and gaseous pollutants. The proposed sensor has the potential to offer a significant economic impact for BC environmental measurements and source appointment technologies

Continuous wave laser diodes enable fast optoacoustic imaging.

Pulsed laser diodes may offer a smaller, less expensive alternative to conventional optoacoustic laser sources; however they do not provide pulse rates faster than a few tens of kHz and emit at wavelengths only within the near-infrared region. We investigated whether continuous wave (CW) laser diodes, which are available in visible and near-infrared regions, can be good optoacoustic light sources when overdriven with a peak current >40-fold higher than the CW absolute maximum. We found that overdriven CW diodes provided ∼10 ns pulses of ∼200 nJ/pulse and repetition rates higher than 600 kHz without being damaged, outperforming many pulsed laser diodes. Using this system, we obtained images of phantoms and mouse ear and human arm in vivo, confirming their use in optoacoustic imaging and sensing

Capsule optoacoustic endoscopy for esophageal imaging.

Detection and monitoring of esophageal cancer severity require an imaging technique sensitive enough to detect early pathological changes in the esophagus and capable of analyzing the esophagus over 360 degrees in a non-invasive manner. Optoacoustic endoscopy (COE) has been shown to resolve superficial vascular structure of the esophageal lumen in rats and rabbits using catheter-type probes. Although these systems can work well in small animals, they are unsuitable for larger lumens with thicker walls as required for human esophageal screening, due to their lack of position stability along the full organ circumference, sub-optimal acoustic coupling and limited signal-to-noise ratio (SNR). In this work, we introduce a novel capsule COE system that provides high-quality 360 degrees images of the entire lumen, specifically designed for typical dimensions of human esophagus. The pill-shaped encapsulated probe consists of a novel and highly sensitive ultrasound transducer fitted with an integrated miniature pre-amplifier, which increases SNR of 10 dB by minimizing artifacts during signal transmission compared to the configuration without the preamplifier. The scanner rotates helically around the central axis of the probe to capture three-dimensional images with uniform quality. We demonstrate for the first time ex vivo volumetric vascular network images to a depth of 2 mm in swine esophageal lining using COE. Vascular information can be resolved within the mucosa and submucosa layers as confirmed by histology of samples stained with hematoxylin and eosin and with antibody against vascular marker CD31. COE creates new opportunities for optoacoustic screening of esophageal cancer in humans

Low-cost single-point optoacoustic sensor for spectroscopic measurement of local vascular oxygenation.

Optical sensors developed for the assessment of oxygen in tissue microvasculature, such as those based on near-infrared spectroscopy, are limited in application by light scattering. Optoacoustic methods are insensitive to light scattering, and therefore, they can provide higher specificity and accuracy when quantifying local vascular oxygenation. However, currently, to the best of our knowledge, there is no low-cost, single point, optoacoustic sensor for the dedicated measurement of oxygen saturation in tissue microvasculature. This work introduces a spectroscopic optoacoustic sensor (SPOAS) for the non-invasive measurement of local vascular oxygenation in real time. SPOAS employs continuous wave laser diodes and measures at a single point, which makes it low-cost and portable. The SPOAS performance was benchmarked using blood phantoms, and it showed excellent linear correlation (R2 = 0.98) with a blood gas analyzer. Subsequent measurements of local vascular oxygenation in living mice during an oxygen stress test correlated well with simultaneous readings from a reference instrument