The MOF can for example be endlessly single-mode [5] and it can be designed to guide either in a solid core through index guiding or in a hollow core through the photonic bandgap effect [6].MOF biosensors Ponatinib TNKS1 have the advantage that bio-chemical reactions and definition of sensor layers can be performed inside the air holes. Biological samples may hence be probed by the optical field without removing the fiber coating and cladding, thus maintaining Inhibitors,Modulators,Libraries the robustness of the fiber. In addition, the sample volume can be minute (nanoliters), due to the small cladding holes. In general, biosensing with MOFs fall into two categories:(1)Evanescent wave sensing of samples in the holes through the evanescent tail of the field propagating in the solid material.
Typically this is done in the cladding holes of an index-guiding MOF.
(2)Sensing Inhibitors,Modulators,Libraries Inhibitors,Modulators,Libraries samples in the core of a hollow-core originally bandgap-guiding MOF with the fundamental mode then propagating with most of its power in the sample.Evanescent wave sensing with MOFs was first proposed by Monro et al., who numerically studied a MOF with a periodic triangular arrangement of cladding holes and showed that the overlap of the optical mode with the holes could be made sufficiently large if the pitch Inhibitors,Modulators,Libraries �� (hole-to-hole separation) could be made small enough and the relative hole diameter d/�� could be made small enough [7,8]. For �� = 750 nm and d/�� = 0.7 the overlap was for example 20% at a wavelength of 1,550 nm and decreasing with decreasing wavelength [7].
It was later Inhibitors,Modulators,Libraries shown by Du Inhibitors,Modulators,Libraries and co-workers that a 3-hole steering-wheel Entinostat solid-core MOF design could give an even larger Inhibitors,Modulators,Libraries overlap of 29% at 1,500 nm and that the overlap increases when water was infiltrated in the fiber [9,10].A large field overlap with the sample is essential for a good fiber-optical biosensor. Hollow-core bandgap MOFs with sample liquids in the core and the optical field guided in the core can have more than a 90% overlap and are thus potentially very attractive for biosensing, as proposed by Fini [11] and first demonstrated for gas sensing [12] and later for surface-enhanced Raman scattering (SERS) [13�C15].
However, with liquid in the core the optical losses are typically very Anacetrapib large in these biosensors, often selective filling is needed [11,14], and stringent requirements must be met on the periodicity of the holes in the cladding, whereas this is not the case for index guiding MOFs, Idelalisib CLL where the hole-structure can even be random [16].
Evanescent-wave MOF sensors were first used for gas sensing [16,17] and in 2004 for sensing of fluorophore-labeled biomolecules in aqueous solutions [18]. The MOF biosensor used reference 2 in [18] and later in the chip-based version [3] was special in that a hollow-core bandgap MOF was used, but filled uniformly in both core and cladding, while the fiber was excited in such a way, that the light was guided in all the tiny interstices between the holes.