Henry Bruhns

Photoacoustic Spectroscopy for the Determination of Lung Cancer Biomarkers-A Preliminary Investigation

With 1.6 million deaths per year, lung cancer is one of the leading causes of death worldwide. One reason for this high number is the absence of a preventive medical examination method. Many diagnoses occur in a late cancer stage with a low survival rate. An early detection could significantly decrease the mortality. In recent decades, certain substances in human breath have been linked to certain diseases. Different studies show that it is possible to distinguish between lung cancer patients and a healthy control group by analyzing the volatile organic compounds (VOCs) in their breath. We developed a sensor based on photoacoustic spectroscopy for six of the most relevant VOCs linked to lung cancer. As a radiation source, the sensor uses an optical-parametric oscillator (OPO) in a wavelength region from 3.2 µm to 3.5 µm. The limits of detection for a single substance range between 5 ppb and 142 ppb. We also measured high resolution absorption spectra of the biomarkers compared to the data currently available from the National Institute of Standards and Technology (NIST) database, which is the basis of any selective spectroscopic detection. Future lung cancer screening devices could be based on the further development of this sensor.

Photoacoustic detection of volatile organic compounds

We present first results of a research project that has the goal to develop an analyzer for volatile organic compounds (VOCs) with extraordinarily high detection sensitivity and detection selectivity. Due to its high potential concerning these two key parameters, optical spectroscopy is employed. The new detection scheme is based on photoacoustic spectroscopy (PAS). PA detection utilizes the fact, that the excitation energy of light absorbing molecules is essentially transferred into kinetic energy of the surrounding molecules via inelastic collisions. This causes a local pressure increase in the absorbing gas. If the excitation source is modulated, a sound wave is generated that can be detected by a microphone and phase-sensitively measured using a lock-in amplifier. A considerable challenge of this project is represented by the broad and strongly overlapping absorption bands of the hydrocarbons. Discrimination of the VOCs is possible only by using a spectrally tunable monochromatic radiation source in combination with a sophisticated data analysis algorithm. Therefore, we apply an optical parametric oscillator (OPO) with spectral emission between 3 and 4 μm.