In order to better test the possibility of using HCR to amplify the label-free detection of the DNA target, a further experiment was performed on the Biacore SPR X100. Target_Giardia was
injected at different concentrations over Probe_Giardia, followed by a second injection of Hairpin1_Giardia/Hairpin2_Giardia mix (both 1 μM) for the HCR. As shown in Fig. 2, for low Target_Giardia concentrations (0.1 nM and 1 nM), the signal after target binding remains practically indistinguishable from the background signal. However, the subsequent HCR reaction determines a visible signal increase for a Target_Giardia concentration of 1 nM. Here, the
dispersion of the SPR signal also increases, albeit not linearly with the signal: the global effect is an improvement of the limit of
detection in this concentration range