Diamond Nanoparticles-Porphyrin mTHPP Conjugate as Photosensitizing Platform: Cytotoxicity and Antibacterial Activity.

Carolina Ramos Hurtado,Gabrielle Lupeti De Cena,Ncediwe Tsolekile,Alexandre Vieira Silva,Verônica Ribeiro Dos Santos,Rafaela Campos Queiroz,Gabriela Ramos Hurtado,Katia Conceição,Vladimir Trava-Airoldi,Milton Faria Diniz,Oluwatobi Samuel Oluwafemi,Dayane Batista Tada,Maurício Da Silva Baptista

doi:10.3390/nano11061393

Abstract

Conjugation of photosensitizers (PS) with nanoparticles has been largely used as a strategy to stabilize PS in the biological medium resulting in photosensitizing nanoparticles of enhanced photoactivity. Herein, (Meso-5, 10, 15, 20-tetrakis (3-hydroxyphenyl) phorphyryn (mTHPP) was conjugated with diamond nanoparticles (ND) by covalent bond. Nanoconjugate ND-mTHPP showed suitable stability in aqueous suspension with 58 nm of hydrodynamic diameter and Zeta potential of −23 mV. The antibacterial activity of ND-mTHPP was evaluated against Escherichia coli for different incubation times (0–24 h). The optimal activity was observed after 2 h of incubation and irradiation (660 nm; 51 J/cm2) performed right after the addition of ND-mTHPP (100 μg/mL) to the bacterial suspension. The inhibitory activity was 56% whereas ampicillin at the same conditions provided only 14% of bacterial growth inhibition. SEM images showed agglomerate of ND-mTHPP adsorbed on the bacterial cell wall, suggesting that the antimicrobial activity of ND-mTHPP was afforded by inducing membrane damage. Cytotoxicity against murine embryonic fibroblast cells (MEF) was also evaluated and ND-mTHPP was shown to be noncytotoxic since viability of cells cultured for 24 h in the presence of the nanoconjugate (100 μg/mL) was 78%. Considering the enhanced antibacterial activity and the absence of cytotoxic effect, it is possible to consider the ND-mTHPP nanoconjugate as promising platform for application in antimicrobial photodynamic therapy (aPDT).

Highlights

Diamond nanoparticles (ND) are carbon-based materials that have attracted significant attention due to their excellent mechanical properties, chemical inertia of the diamond core, high biocompatibility and fluorescence when nitrogen vacancy centers are present in their crystalline lattice [1,2,3,4,5,6]
1707 cm−1 corresponds to the stretching vibrational mode of the C=O bond of the carboxyl of the carboxylic group from the ND-COOH surface. This band was shifted to a higher wave number, 1728 cm−1, in the spectrum of nanoconjugate ND-mTHPP, which could be assigned to the stretching vibrational mode of the C=O bond of the ester bond
Another piece of evidence of the ester bond formation was the shift of the band at 1098 cm−1 (NDCOOH) to smaller wave number (1021 cm−1 ) after the conjugation, which represents the change from the vibrational modes of the C–O bond of carboxylic acids to the C–O of the ester chemical group

Summary

Introduction

Diamond nanoparticles (ND) are carbon-based materials that have attracted significant attention due to their excellent mechanical properties, chemical inertia of the diamond core, high biocompatibility and fluorescence when nitrogen vacancy centers are present in their crystalline lattice [1,2,3,4,5,6]. The application of ND in the most diverse field of materials engineering has been further expanded by ND surface functionalization with reactive chemical groups affording the modulation of hydrophobicity and (bio) molecular interaction. Depending on the synthetic route, ND may have different surface chemical groups. ND with hydrogenated surface were obtained from leftover of HFCVD system by ultrasonic cavitation [12] and high-energy mill grinding [13]. The ND obtained by explosive detonation have high surface density of oxidized chemical groups that are highly reactive and enable the coupling of different types of molecules [14,15,16,17]

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Discussion

Conclusion