Herein, we fabricated nanoparticles of doped carbon dots with nitrogen (N-CDs) with an ecofriendly and easy approach, yielding spherical nanoparticles (mean size: 19 nm). N-CDs were further characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. In addition, we developed a fluorometric method for determination of dopamine (DA) in human fluids at nanomolar concentrations (rapid and highly sensitive). The quenching effect over the emission of the doped CDs at 438 nm was the basis of the quantification of DA. A linear trend between 0 and 652 nM was the range of application with a detection limit at 4 nM, acceptable accuracy (>80%), and precision (relative standard deviation < 10%), showing a highest selectivity with related analytes. The obtained sensing method was applied for DA determination in human fluids (urine and serum samples) with acceptable accuracy. In order to understand the interaction of DA with the nanoparticles of N-CDs, we applied density functional theory. The bonding between the −NH3 + moiety of DA and the corresponding N-CD surface ligand consists of the formation of hydrogen bonds. It is demonstrated that the selected geometrical models explain the spectroscopic experiments performed on such nanoparticles.

Unlike humans, some animals have evolved a physiological ability to deposit porphyrins, which are pigments produced during heme synthesis in cells, in the skin and associated integument such as hair. Given the inert nature and easiness of collection of hair, animals that present porphyrin-based pigmentation constitute unique models for porphyrin analysis in biological samples. Here we present the development of a simple, rapid, and efficient analytical method for four natural porphyrins (uroporphyrin I, coproporphyrin I, coproporphyrin III and protoporphyrin IX) in the Southern flying squirrel Glaucomys volans, a mammal with hair that fluoresces and that we suspected has porphyrin-based pigmentation. The method is based on capillary liquid chromatography-mass spectrometry (CLC-MS), after an extraction procedure with formic acid and acetonitrile. The resulting limits of detection (LOD) and quantification (LOQ) were 0.006–0.199 and 0.021–0.665 µg mL−1, respectively. This approach enabled us to quantify porphyrins in flying squirrel hairs at concentrations of 3.6–353.2 µg g−1 with 86.4–98.6% extraction yields. This method provides higher simplicity, precision, selectivity, and sensitivity than other methods used to date, presenting the potential to become the standard technique for porphyrin analysis.