Infrared spectroscopy is a spectroscopic technique for the structural analysis of chemical compounds. It is also used to detect substances in chemical and biological samples. In medicine, for example, it is used to monitor oxygen levels in the blood of intensive care patients.
What is infrared spectroscopy?
Infrared spectroscopy is a spectroscopic technique for the structural analysis of chemical compounds. In medicine, for example, it is used to monitor oxygen levels in the blood of intensive care patients. Infrared spectroscopy (IR spectroscopy) is based on the excitation of energy states in molecules by infrared radiation in the wavelength range from 800 nm to 1 mm. The principle of the measurement is the absorption of radiation in a specific wavelength range to excite discrete vibrational and rotational states of functional groups. The absorbed region is displayed as a peak in the IR spectrum. Since the vibrational states are characteristic of specific atoms and groups of atoms, the location of the peaks provides information about the structure of the molecules. Several techniques can be used for measurement. For example, in the transmission technique, the infrared radiation passes through the sample before the absorption spectrum is recorded. After the reflection technique, the reflected radiation is examined spectroscopically. Furthermore, there are also methods for recording emission spectra. Infrared spectroscopy is divided into three wavelength ranges: near infrared (NIRS) from 0.8 to 2.5 micrometers, mid or classical infrared from 2.5 to 25 micrometers, and far infrared from 25 to 1000 micrometers.
Function, effect and objectives
Today, infrared spectroscopy is used in many fields of industry, research or medicine. Especially near-infrared spectroscopy has some advantages over the other two forms. Due to its higher energy, the near infrared light can better traverse the samples or at least has a greater penetration depth. Because of this advantage alone, NIRS is often used in medicine. NIRS is ideal for determining the water content in many samples. Thus, the moisture as well as the protein and fat content of many foods can be determined well. It is therefore used in process control in the food and pharmaceutical industries. For more than 30 years, near-infrared spectroscopy has been firmly integrated as an imaging technique in medicine and neuroscience. It is used to monitor the oxygen content in the blood, the blood flow or the blood volume of various organs and tissues. Especially brain, muscles or chest are examined with this method. The success of this method for determining the oxygen content is based on the different absorption behavior of oxygenated and deoxygenated hemoglobin. IR spectra are recorded as part of a monitoring process, documenting the changes in oxygen content over time. At the same time, these values can be displayed using imaging techniques. This principle is also used to monitor blood flow and blood volume in emergency patients. As a result, NIRS is now increasingly being used in emergency and intensive care medicine to ensure a continuous supply of oxygen to the patient. The method has also proven its worth for measuring brain activity. In determining it, the dynamic changes in the oxygen concentration of the blood in the brain are measured through the skullcap. This is possible because the near infrared light has a great penetration depth. Based on the concentration changes of oxygen, the strength of brain activity can be inferred. The assumption is that a high oxygen content in a particular brain area indicates increased activity there. In this way, neurological diseases are to be detected. Furthermore, scientific studies are being conducted to further investigate the relationship between oxygen demand and brain activity. Since the structure and interaction of proteins, carbohydrates, lipids and nucleic acids can provide clues to diseases such as Alzheimer’s disease, multiple sclerosis, arthritis or certain types of cancer, scientific studies have also been undertaken for some time to elucidate the structure of these substances in tissue using IR spectroscopy.Special emphasis is placed on the classification of tissue types without the need for staining techniques. Body fluids such as saliva, blood plasma, urine or synovial fluid can also be analyzed for glucose, lipids, cholesterol, urea, protein or phosphate using IR spectroscopy. Scientific studies are still being carried out to expand glucose determination by using infrared spectroscopy. The aim is to rapidly determine the blood glucose concentration of diabetic patients.
Risks, side effects, and hazards
No hazards are expected when using IR spectroscopy in medical diagnostics. It is a noninvasive painless method without any additional radiation exposure. Due to the low energy, exposure of the genetic material is excluded. In principle, humans are constantly exposed to infrared radiation (heat radiation). The good tolerance of the method is the ideal prerequisite for its wide application in medicine. However, its all-encompassing application still has its limits today. In combination with other imaging techniques, however, considerable success has been achieved in diagnostics. As mentioned above, efforts are currently being made to optimize glucose determination in diabetics. In particular, non-invasive methods such as IR spectroscopy should ensure rapid analysis. To date, however, no breakthrough has been achieved in this area. A great deal of research work also remains to be done in other areas. For example, the measurement of brain activity highlights the non-uniqueness of the inverse problem. After all, brain activity is not registered directly, but only the change in oxygen concentration in the blood. Therefore, only an increased activity can be concluded. To verify the correlation, further studies and comparisons with other methods have to be performed. In general, only near-infrared spectroscopy (NIRS) is suitable for use in medicine. Mid- and far-infrared light radiation does not have the ability to penetrate deep into tissue.