Non-invasive methods for early diagnosis of skin cancer are highly valued. One possible approach is to monitor relevant biomarkers such as tryptophan (Trp) and kynurenine (Kyn), on the skin surface. The primary aim of this in vitro investigation was, therefore, to examine whether reverse iontophoresis (RI) can enhance the extraction of Trp and Kyn, and to demonstrate how the Trp/Kyn ratio acquired from the skin surface reflects that in the epidermal tissue. The study also explored whether the pH of the receiver medium impacted on extraction efficiency, and assessed the suitability of a bicontinuous cubic liquid crystal as an alternative to a simple buffer solution for this purpose. RI substantially enhanced the extraction of Trp and Kyn, in particular towards the cathode. The Trp/Kyn ratio obtained on the surface matched that in the viable skin. Increasing the receiver solution pH from 4 to 9 improved extraction of both analytes, but did not significantly change the Trp/Kyn ratio. RI extraction of Trp and Kyn into the cubic liquid crystal was comparable to that achieved with simple aqueous receiver solutions. We conclude that RI offers a potential for non-invasive sampling of low-molecular weight biomarkers and further investigations in vivo are therefore warranted.

For the commercial‐scale isolation of phytochemicals, a suitable plant biomass source (including species, origin, growing season, etc.) must be identified, and frequent analytical verification is required to ensure that the phytochemicals are present at predefined minimum threshold concentrations. While the latter are typically assessed in the laboratory, a more efficient and less resource‐intensive approach would involve non‐destructive and environmentally friendly measurements in situ. Reverse iontophoretic (RI) sampling offers a potential solution to this challenge. Objective We aimed to demonstrate the non‐destructive, RI sampling of phytochemicals of interest from biomass from four different sources. Materials and methods RI experiments were performed in side‐by‐side diffusion cells using a current density of 0.5 mA/cm2, for a predetermined time in a defined pH environment, using (1) fresh leaves from Mangifera indica and Centella asiatica and (2) isolated peel from Punica granatum and Citrus sinensis. Results Mangiferin, madecassoside, punicalagin, ellagic acid, and hesperidin were extracted from the different biomasses by RI. The amounts extracted ranged from 0.03 mg/100 mg of biomass for the cathodal extraction of madecassoside to 0.63 mg/100 mg of biomass for the anodal extraction of punicalagin. A linear relationship (r2 = 0.73) between the RI‐extracted quantities of punicalagin and those determined using conventional methods was demonstrated. Conclusion The non‐destructive, in situ measurement of phytochemical levels by RI represents a feasible approach for timing the harvesting process.

Reverse iontophoresis facilitated the extraction of phytochemicals from intact pomegranates in a non-destructive manner. These phytochemicals were subsequently identified using liquid chromatography coupled to untargeted mass spectrometry (LC-MS).