Label-Free Tapered Fiber Optic Sensor for Real-Time In Situ Detection of Cell Activity

In the field of biomedicine, the nondestructive and label-free detection of individual living cells has been long pursued. We propose a tapered fiber optic biosensor (TFOB) and perform theoretical and simulation analyses of the optical intensity distribution of the fiber tip, which gradually becomes thinner to expose the evanescent field around it. The fiber tip becomes a highly sensitive sensing element that acts as a transduction mechanism for the evanescent field. It translates the intensity change of the evanescent field around the tapered fiber into changes in output power. The experimental results show that the developed TFOB can detect vibration signals with amplitudes as low as 3 nm and achieve nondestructive, label-free measurements of respiratory vibrations of pasta yeast cells. Results show the periodic motion of yeast cells in the range of 300–550 Hz. Meanwhile, inactivated yeast cells have no characteristic frequencies evident in the spectrum. This nanoscale fiber optic sensor offers potential technical support for cell activity detection and pathological analysis.