Examples of mPOF used in liquid-based sensing. (a) Selective detection of α-CRP antibody through binding to the fibre, compared to α-streptavidin antibodies which do not bind, and to a clean fibre to which neither bind. (b) Additional microstructure in the core increases overlap between the evanescent field of the light and the liquid. (c) Exposed core fibre that does not require filling. (d) Fluorescence spectroscopy of single particles trapped using an optical trap inside the core of an HC-mPOF. The fluorescence at different times indicated photobleaching. Lower panels show the fibre cross-section and an example of a trapped particle inside the core. The arrow (coincidentally) indicates the direction of the trapping beam. Adapted from (a) [43], (b) [119], (c) [120], and (d) [125].