Compact all-fiber photoacoustic spectrometer for intravascular gas detection comparable to laboratory-based systems

Compact spectroscopic systems capable of detecting trace concentrations at parts per billion (ppb) levels are of paramount importance in applications ranging from environmental monitoring and industrial process control to biomedical diagnostics. However, existing benchtop spectroscopy systems are too large, complex, and impractical for use in confined spaces. Additionally, traditional laser spectroscopy techniques use large components such as light sources, mirrors, detectors, and gas cells to detect light absorbed or scattered by the sample, making them minimally invasive, such as in intravascular diagnostics. Not suitable for scenarios where sex is required.

In a study published in the journal Advanced Photonics, Chinese researchers have developed an innovative miniature all-fiber device designed to detect trace gases at ppb levels and analyze nanoliter-sized samples with millisecond response times. We have introduced a photoacoustic spectrometer (FPAS). For continuous intravascular gas analysis.

“We are committed to the important challenge of reducing current photoacoustic spectrometers to microscale sizes while maintaining high sensing performance, especially in minimally invasive intravascular diagnostics and lithium battery condition monitoring. We tried to address the challenges,” explains Professor Bai-Ou Guan of Jinan University. Corresponding author of the article.

While current laser spectroscopy systems are mostly open-path configurations with inherent scale-down sensitivities to match the device footprint, the proposed FPAS allows It works by using photoacoustic spectroscopy (PAS) to detect the sound waves produced by the .

Instead of using large resonant gas cells for acoustic amplification or large microphones to increase acoustic sensitivity, as traditional PAS systems do, all-fiber photoacoustic spectrometers use laser-patterned elastic membranes. integrated into a single optical fiber tip with a section of silica capillary into a microscale Fabry-Perot (FP) cavity.

The silica cavity acts as a rigid boundary for sound, effectively trapping and accumulating the sound waves generated by the gas molecules in a flexible membrane. This local acoustic amplification compensates for the sensitivity loss caused by the reduction in membrane diameter, resulting in a size-independent photoacoustic response.

Furthermore, both the pump and probe light beams are directly delivered through the same fiber for excitation and detection of the photoacoustic signal, avoiding bulky free-space optics for light delivery.

The FP cavity is only 60 micrometers long (1 μm = 10-6 m) and 125 μm in diameter, making this system very compact. Despite its small size, the detection limit for acetylene gas is as low as 9 ppb, which is about the same sensitivity as larger conventional laboratory spectrometers. The short cavity length also enables ultra-fast measurements with a response time of 18 ms. This is two to three orders of magnitude faster than traditional photoacoustic spectroscopy systems.

By inserting FPAS into the tail vein, the researchers monitored carbon dioxide (CO2) concentrations in flowing gas in real time, detected fermentation in yeast solutions with samples as small as 100 nanoliters, and were able to detect fermentation in vivo. successfully tracked dissolved CO2 levels in the blood vessels of rats. syringe.

“This spectrometer effectively measures CO2 levels under hypoxic (hypoxia) and hypercapnic (high CO2) conditions and has the potential to monitor intravascular blood gases in real time without the need for blood sample collection. ” explained Jun Ma, an associate professor at Jinan University.

Additionally, optical fibers can be easily connected to low-cost distributed feedback laser sources and integrated with existing fiber optic networks, making the system a cost-effective, compact, and flexible spectroscopy solution.

The proposed miniature spectrometer enables laboratory-level precision in a microscale probe format due to the requirements of small size, high sensitivity, and low sample volume, continuous intravascular blood gas monitoring, and minimally invasive use of lithium-ion batteries. It may be applicable to applications such as health evaluation. , and remote detection of explosive gas leaks in very confined spaces.