Ultrafine-fiber thermistors for microscale biomonitoring

We have prepared spinel Mn1.4Co0.9Ni0.5Cu0.2O4 (MCNC) film thermistors on ultrafine aramid (poly-p-phenylene-terephthalamide) fibers using a photocrystallization technique with KrF laser irradiation at room temperature. We coated a phi 15 mu m diameter aramid fiber using an MCNC nanoparticle dispersion, and we employed KrF laser irradiation to crystallize the MCNC film on the fiber surface. The resulting ultrafine-fiber thermistor showed a good semiconducting behavior with a high thermistor constant of 2767.3 K. It also exhibited a very rapid response time of only ca. 100 ms, and the rise and drop rates were almost equivalent. These rapid responses were observed due to the small heat capacity that resulted from the minuscule cross-sectional area (S) of the fiber substrate. Thermal-transfer simulations showed that the phi 15 mu m-core fiber thermistor can detect temperature variations of microscopic objects more reliably than a sheet-type thermistor with a substrate thickness of 60 mu m. Using temperature simulations of both fiber- and sheet-type thermistors, we also confirmed that the equivalence of the rise and drop timescales (tau(r) and tau(d)) of the response was not influenced by undesirable heat flow to/from the substrates. It is very important for tau(d)/tau(r) to approach 1.0 and for the value of S to be reduced as much as possible, as tau(d)/tau(r) is proportional to log S. The phi 15 mu m-core fiber thermistor achieved a small tau(d)/tau(r) value of only 1.12. The rapid and accurate temperature responses of the ultrafine MCNC fiber thermistors make them promising candidates for microscopic temperature sensors.

Automated summary

We synthesized MCNC film thermistors on aramid fibers using a photocrystallization technique with KrF laser irradiation. The resulting ultrafine-fiber thermistor showed good semiconducting behavior, rapid response time, and equivalent rise and drop rates, due to the small heat capacity of the fiber substrate. Thermal-transfer simulations demonstrated that the fiber thermistor outperformed sheet-type thermistors in detecting temperature variations of microscopic objects. These ultrafine MCNC fiber thermistors with rapid and accurate temperature responses have potential applications as microscopic temperature sensors.