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).

Nanodiamonds (NDs) are amongst the most investigated carbon-based nanostructures due to their chemical stability and favorable mechanical properties. Despite the number of works on methods for NDs production, one of the main challenges is to achieve their colloidal stability in aqueous suspension. Additionally, NDs are normally obtained by expensive, complex and time-consuming process. Herein, it was presented a facile method to obtain NDs in aqueous suspension by using columnar structure diamond from Hot-Filament Chemical Vapour Deposition reactor (HFCVD). CVD diamond leftover thick film from CVDVale Company was used. Therefore, this method has the advantage of being not only practical but also cost-effective since it brings a profitable use of CVD diamond leftover. The Diamond thick film was submitted to ultrasonic cavitation in the presence and absence of ZrO 2 microbeads in aqueous medium. The NDs hydrodynamic diameter and the stability in aqueous suspension were monitored by light scattering, size and morphology were analyzed by transmission electronic microscopy. Considering the wide application of NDs in biomedical devices, cytotoxicity of aqueous suspensions of NDs was evaluated against murine embryonic fibroblast cells. Furthermore, NDs were functionalized with hydrogen and carboxyl groups. NDs aqueous suspension of straight size distribution was obtained even in the absence of ZrO 2 beads, indicating that they may be dispensable in order to decrease NDs size. NDs of average hydrodynamic diameter of 22 nm and − 35 mV of Zeta-potential were obtained after ultrasonic cavitation followed by 2 h of centrifugation, not demonstrating cytotoxicity to cells at very low (0.05-0.5 μg/mL) nor at higher concentrations (116 μg/mL). Nevertheless, NDs showed a moderate cytotoxicity at intermediary concentration range (0.5-2.2 μg/mL). From our knowledge, this is the first work that reports on a facile method for providing NDs aqueous suspension with high colloidal stability from HFCVD diamond leftover.