Fig. 8
Combined sensor geometry and connectivity network elicit signal reproducibility and sensitivity. a The mechanical force obtained from 500 pM of Van. The orange, green, and wine colors represent data obtained from three separate nanomechanical cantilever sensors. b The mechanical force from 20 (blue), 50 (red), and 500 nM (green) Van. In a and b, the negative signal is associated with a compressive mechanical force on the gold top surface causing the cantilever to bend down. c The plot showing the measured mechanical force obtained from capture molecules using narrow geometrical width (green) and broad geometrical width (purple) of nanomechanical cantilever sensors. The data are described by Eq. (3) for Kd = 0.5 ± 0.2 µM (green diamond symbol, narrow nanomechanical cantilever sensors) and for Kd = 0.5 ± 0.2 µM (purple diamond symbol, broad sensing elements). The error bars shown represent the standard deviation of the mechanical force obtained from four separate cantilever chips each with eight cantilevers totaling 32 measurements. d The mechanical force obtained from 0.2 (blue), 5 (pink), and 100 fg per ml (green) immunoglobulin G (IgG). The positive signal is associated with tensile mechanical force on the sensing element causing the cantilever to bend upward. In a, b, and d, the shaded areas represent the time frame during which the phosphate-buffered saline solution was injected without analytes to establish a baseline. The reference signal is shown in black. The results show that by altering the dimensions of the sensing element and surface chemistries, whilst maintaining the continuous connectivity with the hinge, the limit of detection of proteins is significantly improved down to sub-femtogram levels without compromising the signal reproducibility or the need to use labels
