Biosensors waveguide studies

In contrast to SPFS, SPR, and SPDS are tools that can study biomolecular interactions without external labels. They share the same category of label-free biosensors with the reflectometry interference spectroscopy (RIfS) [46], waveguide spectroscopy [47], quartz crystal microbalance (QCM) [48], micro-cantilever sensors [49], etc. Although the label-free sensors cannot compete with SPFS in terms of sensitivity [11], they are however advantageous in avoiding any additional cost/time in labeling the molecules. In particular, the label-free detection concept eliminates undue detrimental effects originating from the labels that may interfere with the fundamental interaction. In this sense, it is worthwhile to develop and improve such sensors as instruments complementary to those ultra-sensitive sensors that require labels. 

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