Use of liposomes encapsulating drug
nanocrystals for the treatment
of diseases like cancer and pulmonary infections is gaining attention.
The potential therapeutic benefit of these engineered formulations
relies on maintaining the physical integrity of the liposomes and
the stability of the encapsulated drug. With the significant advancement
in the microscopic and analytical techniques, analysis of the size
and size distribution of these nanosized vesicles is possible. However,
due to the limited spatial resolution of conventional vibrational
spectroscopy techniques, the chemical composition of individual nanosized
liposome cannot be resolved. To address this limitation, we applied
atomic force microscopy infrared spectroscopy (AFM-IR) to assess the
chemical composition of individual liposomes encapsulating ciprofloxacin
in dissolved and nanocrystalline form. Spatially resolved AFM-IR spectra
acquired from individual liposomes confirmed the presence of peaks
related to N–H bending vibration, C–N stretching and
symmetric, and asymmetric vibration of the carboxyl group present
in the ciprofloxacin. Our results further demonstrated the effectiveness
of AFM-IR in differentiating the liposome containing ciprofloxacin
in dissolved or nanocrystalline form. Spectra acquired from dissolved
ciprofloxacin had peaks related to the ionised carboxyl group, i.e.,
at 1576 and 1392 cm–1, which were either absent
or far weaker in intensity in the spectra of liposomal sample containing
ciprofloxacin nanocrystals. These findings are highly significant
for pharmaceutical scientists to ascertain the stability and physicochemical
composition of individual liposomes and will facilitate the design
and development of liposomes with greater therapeutic benefits.
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