Fig. 5: Experimental characterization of Pb²⁺ sensor performance.

a Wavelength spectrum of the sensor, when DI water is applied into the sensor assembly (as shown in Fig. 1d). b Calibration curve of the sensor when exposed to reference Pb²⁺ concentration of 0, 5, 25, 125, 625, 2625, 12625, 62625, 262625 ppb via a cumulative testing approach (see Methods). Error bars pertaining to six independent measurements (n = 6) are indicated, where the bottom and top edges of the boxplot correspond to the 25^th and 75^th percentile of the data. The minimum and maximum points of the data are indicated by the extension to which the whiskers of the boxplot are extended to. The mean of the data is indicated by the red point. c A set of optical fringe minima corresponding to the tested concentrations in the calibration curve (Fig. 5b). d Fig. 5c, zoomed-in at concentrations of 0, 5, 25 ppb. Validation of the calibration curve (Fig. 5b) at reference concentrations of e, 80 ppb, f. 1 ppb and g, 10 ppb, h, 62 ppm. For the detection of Pb²⁺ concentration via the sensor in Fig. b–h, the pH of the analyte is maintained at 6.8 (see Methods). DI water is used.