The possibility to monitor DA levels by a simple smartphone leads to the easy homemade DA monitoring. The novelty of this proposed sensor is the possibility to detect DA by supramolecular approach, obtaining a reusable device able to be used with a smartphone as detector. Notably, the picomolar limit of detection allows the detection of DA concentrations in real saliva samples. This sensor shows, on siloxane-based polymeric solid state, good linearity range (10 mM–100 pM), low limit of detection value (1 pM, corresponding to 87 fg of DA) and excellent selectivity for DA respect to the other common analytes contained in the saliva. Here, we report the first example of DA detection by a reusable solid device exploiting a quinoxaline cavitand as supramolecular receptor, by using a smartphone as detector.

To the best of our knowledge, only a few examples of non-covalent sensing of DA have been reported, also exploiting cyclodextrins, calixarenes, pillararenes and cucurbiturils in these cases with micromolar ranges of linearity and limits of detection. This goal can be achieved by exploiting the principle of supramolecular chemistry, and in particular the non-covalent interactions between a receptor/host (sensor) and the analyte/guest (DA). In this context, the possibility to restore the starting sensor leads to the opportunity to reuse the device. Few examples of smartphone-based methods able to determine the DA concentration, in micromolar ranges, have been reported. In addition, the use of a simple smartphone as detector leads to the possibility to a “homemade” DA levels detection. To this end, optical or colorimetric sensors are more useful. The possibility to obtain a point-of-care DA detection method is undoubtedly interesting and useful for a rapid screening of the DA levels in blood, saliva and urine.

However, these techniques require expert personal, high-cost, long and complicated analysis. Different DA detection methods have been reported, including chromatographic, electrophoretic, electrochemical and methods based on Surface Plasmon Resonance. In normal conditions, the DA concentration in plasma is around 20 ng/mL, 18.9 pg/mL in saliva and is 0.2–1 mg/mL in human urine. For these reasons, DA sensing is crucial to monitoring the human health condition. In particular, alteration of DA levels can be related to different diseases, such as Alzheimer, schizophrenia, Parkinson, Huntington attention-deficit hyperactivity disorder and paragangliomas. Dopamine (DA), a phenethylamine derivative produced by the adrenal medulla, is fundamental in many brain functions.

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