Fig. 1. Carbon nanodots concentration determination through UV-Vis and fluorescence emission spectrophotometry.

a Sketch of the N-, S-, and R-CNDs. b Absorption A₂₈₀ at 280 nm of CNDs dissolved in water at the mass concentration C_CNDs (determined by weighting). The A₂₈₀(C_CNDs) curve was fitted with linear regression to yield the slope ß_A,j (mL μg^–1) = ΔA₂₈₀(j) ΔC_CNDs^–1 (j = R-CND, S-CND, N-CND). R² indicates the fitting reliability with linear regression (perfect fit: R² = 1). Data for the absorption at 405 nm (A₄₀₅) are shown in Supplementary Fig. 6. c Integrated fluorescence emission I_max ranging from 425 to 475 nm (excitation wavelength λ_ex = 405 nm) of CNDs dissolved in water at the mass concentration C_CNDs. The I_max(C_CNDs) curve was fitted with linear regression to yield the slope ß_I,j (mL μg^–1) = ΔI_max(j) ΔC_CNDs^–1 (j = R-CND, S-CND, N-CND). From these slopes, first the percentual differences Δß_i,j in the slopes between the R-CND and S-CND sample to the N-CND sample were derived for the absorption and intensity measurements as Δß_i,j = (ß_i,N-CND − ß_i,j) ß_i,N-CND^–1 (i = A, I; j = R-CND, S-CND), and then the deviation Δß_j in these differences between the absorption and intensity measurements were obtained as Δß_j = |Δß_A,j − Δß_I,j| (j = R-CND, S-CND). The percentual error in concentration determination was defined as the maximum of these values as ΔC_CNDs C_CNDs^–1 = max(Δß_R-CND, Δß_S-CND). The values are enlisted in Table 1. The shown data were obtained with batch #1.