Near-infrared spectroscopy (NIRS) is a non-invasive analytical technique that uses light to determine the composition of various substances. It operates by shining light from the near-infrared region of the electromagnetic spectrum onto or through a sample. This method provides insights into the chemical and physical properties of materials, making it a valuable tool across many fields.
The Science of Near-Infrared Light
NIRS functions by directing near-infrared light, ranging from 700 to 2500 nanometers, onto a sample. This light interacts with the molecular bonds within the material, causing them to vibrate in specific ways. Molecules containing bonds like O-H (water), N-H (proteins), and C-H (fats and other organic compounds) absorb and scatter this light uniquely.
Each molecule possesses a distinct “light signature” based on how it absorbs particular wavelengths. The NIRS instrument measures the intensity of the light that is absorbed, reflected, or transmitted through the sample. This pattern is then analyzed to identify and quantify chemical constituents. The technique is non-destructive, requiring minimal or no sample preparation, which makes it suitable for rapid analysis across diverse materials.
Medical and Brain Imaging Applications
Near-infrared spectroscopy has found diverse applications within medical and biological contexts, leveraging its safe nature. Functional near-infrared spectroscopy (fNIRS), a specialized form, measures brain activity by detecting changes in hemoglobin concentration in the cerebral cortex. This occurs because oxygenated and deoxygenated hemoglobin absorb near-infrared light differently, allowing researchers to infer localized brain function.
fNIRS is utilized in cognitive science to study brain responses during various tasks. In clinical settings, it helps diagnose and monitor neurological disorders, including conditions like depression, anxiety, and stroke. The portability of fNIRS systems, often worn as caps, enables monitoring in natural environments where movement is allowed, unlike more restrictive imaging methods. NIRS is also applied in sports science to assess muscle oxygenation, providing real-time data on metabolism and fatigue response, which aids coaches and trainers in optimizing training and recovery. In neonatal care, NIRS monitors the brains of premature infants, assessing cerebral oxygenation and blood flow to detect brain injuries. It provides continuous, bedside monitoring, particularly beneficial for this vulnerable population.
Industrial and Agricultural Uses
Near-infrared spectroscopy demonstrates its versatility across various industrial and agricultural sectors. In agriculture, NIRS is employed for analyzing grain to determine protein, moisture, starch, and fat content. This helps in assessing quality, optimizing harvest times, and informing storage and processing decisions. The technology also evaluates fruit ripeness on the vine by measuring dry matter and sugar content, ensuring optimal harvesting for fresh consumption or processing.
Within the pharmaceutical industry, NIRS plays a role in quality control throughout manufacturing. It verifies the chemical composition of raw materials and finished products, such as tablets, ensuring consistency and purity. This includes identifying active pharmaceutical ingredients and excipients, and monitoring processes like blending and granulation in real-time. In food science, NIRS helps determine the fat, protein, and moisture content in products like milk and meat. For instance, it can standardize milk fat-to-protein ratios for cheese production or analyze minced meat for protein and fat levels, even detecting adulteration by identifying different meat species.
Information Gathered from NIRS
Near-infrared spectroscopy primarily provides quantitative data regarding chemical concentrations and physical properties of a sample. Unlike imaging techniques that produce pictures, NIRS generates spectral data processed to yield specific numerical values. This output directly reflects the molecular composition of the analyzed material.
For medical applications, particularly brain imaging, NIRS delivers data on the concentrations of oxygenated and deoxygenated hemoglobin. These measurements indicate changes in blood flow and oxygen usage within tissues. In agricultural contexts, the technology quantifies parameters such as moisture percentage, protein content, and fat levels in grains and produce. For food science, NIRS provides precise percentages of fat, protein, and carbohydrates in milk, meat, or other food items. This data allows for detailed analysis of material composition, quality assessment, and process monitoring across diverse applications.