Investigation of the potential of deep eutectic solvents (DES) as alternative solvents in antimicrobial photodynamic therapy

Cátia Vieira, Maria Bartolomeu, Sónia N. Pedro, Ana T. P. C. Gomes, Cristina J. Dias, Sara R. D. Gamelas, Leandro M. O. Lourenço, Carmen S. R. Freire, M. Graça P. M. S. Neves, M. Amparo F. Faustino, Adelaide Almeida

Research output: Contribution to conferenceAbstractpeer-review



Antimicrobial Photodynamic Therapy (aPDT) is gaining recognition as an effective approach for the photoinactivation of a broad spectrum of microorganisms [1,2]. Due to their apolar behavior, photosensitizers (PS) often have low solubility in aqueous media requiring the use of toxic organic solvents that are incompatible with their application in the field [4]. In this study, the potential of Deep Eutectic Solvents (DES) to prepare formulations of one chlorin (bearing five cationic charges) and two porphyrins (neutral THPP, and tetra cationic Tetra-Py(+)-Me) poorly water-soluble was investigated. To this purpose, formulations of each PS were prepared in DMSO and three DES (betaine:glycerol, proline:xylitol and betaine:citric acid) and their physio-chemical properties, cytotoxicity for mammalian cells, and photodynamic action towards Escherichia coli, as a gramnegative bacterium model, were evaluated. The physico-chemical experiments revealed that all PS were soluble in the selected DES. However, PS stability varied highly depending on the solvent used. In dark conditions, chlorin remained stable in DES formulations while strong aggregation was observed in DMSO. In contrast, THPP showed better stability in the former solvent. Tetra-cationic porphyrin was stable in the dark regardless of the solvent used, but upon irradiation, DES formulations increased this PS photostability. Regarding the biological experiments, betaine:glycerol and proline:xylitol formulations lacked toxicity towards mammalian cells and improved Tetra-Py(+)Me photodynamic activity against E. coli. On the other hand, betaine:citric acid formulation, although highly toxic to Vero cells, enhanced the photodynamic action of both THPP and Tetra-Py(+)-Me. Overall, these findings indicate that DES have a high potential to prepare formulations of PS with low solubility in aqueous solutions and, in some cases, can improve their antimicrobial photodynamic activity.
Original languageEnglish
Number of pages1
Publication statusPublished - Aug 2023
Event20th Congress of the European Society for Photobiology - Institut national des sciences appliquées, Lyon, France
Duration: 27 Aug 202331 Aug 2023


Conference20th Congress of the European Society for Photobiology


  • Deep Eutetic Solvents
  • Antimicrobial photodynamic therapy (aPDT)
  • Porphyrin
  • Chlorin
  • Escherichia coli


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