  The achievement of all-fibre functional nano-modules for subcellular
label-free measurement has long been pursued due to the limitations of
manufacturing techniques. In this paper, a compact all-fibre label-free
nano-sensor composed of a fibre taper and zinc oxide nano-gratings is designed
and applied for the early monitoring of apoptosis in single living cells.
Because of its nanoscale dimensions, mechanical flexibility and minimal
cytotoxicity to cells, the sensing module can be loaded in cells for long-term
in situ tracking with high sensitivity. A gradual increase in the nuclear
refractive index during the apoptosis process is observed, revealing the
increase in molecular density and the decrease in cell volume. The strategy
used in this study not only contributes to the understanding of internal
environmental variations during cellular apoptosis but also provides a new
platform for non-fluorescent all-fibre devices to investigate cellular events
and to promote new progress in fundamental cell biochemical engineering.
