Aims and Background: The number of pathogenic microorganisms has been increasing
over the years, and so as resistance of these microorganisms are developing against various antibiotics.
Antimicrobial photodynamic therapy (aPDT), also called photodynamic inactivation, is emerging
as a promising alternative to treatments based on conventional antibiotics. Recent patents on structured
silver mesoporous silica nanoparticles having antimicrobial activity (WO2010/071831 A2), photosensitiser
modified core-shell structure nanocomposites (CN 103536935(A)), and Chitosan-coated
magnetic mesoporous silica nanoparticles (MSN) (CN 104785214(A)) helped in selecting method of
synthesis of MSN and photosensitizers.
Materials and Methods: MSN were synthesised by Sol-Gel method and amino functionalised (APTES).
Methylene blue (MB) and ortho-toluidine blue (O-TB) were used as photosensitisers. Different
batches were synthesised. The final product was characterised by using FTIR, BET, SEM, time resolved
fluorescence. The photosensitiser loaded MSN were illuminated by LED based lamp emitting
red light at 620± 20nm for different time lengths viz 15 min and 30 mins. Fluorescence studies and antimicrobial
assays were carried out as per 72 well plate method I.P, 2014 using, gram negative E. coli
(ATCC no. 8739), S. aureus (ATCC no. 7447) and gram positive P. aeruginosa (ATCC no. 9027)
Results: MB and O-TB were successfully adsorbed on APTES functionalised MSN. Different exposure
time length of the photosensitisers to red light showed different zone of inhibition. MB and O-TB
loaded MSN showed significant increase in zone of inhibition after irradiation as compared to MB and
O-TB loaded on MSN without exposure to light.
Conclusion: MB and O-TB adsorbed on APTES functionalized mesoporous silica nanoparticles were
capable of efficiently inactivating E. coli, P. aeruginosa, S. aureus bacteria upon exposure to red light
(620± 20nm wavelength) at a much lower concentration. Mesoporous silica nanoparticles played an
important role in aPDT due to their high surface area and porous structure. Also, APTES functionalization
resulted in the pore expansion of MSN, thereby increasing the loading capacity of the photosensitizer
on MSN. From the results obtained it can be concluded that O-TB loaded MSN showed higher activity
against gram negative and positive microorganisms microorganism as compared to that of MB.