Flattened infrared fiber-optic sensors for the analysis of micrograms of insoluble solid particles in solution or in a dry state

Highly sensitive absorption measurements on various samples may be carried out by Fiber-optic Evanescent Wave Spectroscopy (FEWS) in the mid-IR. Such measurements have already been done on solids, liquids and gases, using chalcogenide glass fibers or crystalline fibers. Segments of crystalline AgClBr fibers may be used as sensors of much higher sensitivity if their middle sections are pressed to form flat waveguides. We carried out measurements on micrograms of insoluble or slightly soluble particles in water, when they sedimented on the flattened parts of such sensors. Measurements were also carried out on few micrograms of dry particles that had been pressed onto the flattened parts. Flattened fiber sensors may therefore be used for measurements on micrograms of particles and they can be used for identifying the chemical nature of particles of organic, inorganic or biological materials and for studying their properties. The FEWS method, based on flattened mid-IR fiber sensors, is simple, inexpensive and does not require sample processing. It would be useful for measurements on very small quantities of particles for biomedical applications, for environmental protection, for drug enforcement agencies and for homeland security.