using the method modified from the works of Lapidot20 and
Ahn.39 The encapsulation was carried out at a 1 : 2 and 1 : 1
(w/w) ratio of citronellal : TES4C. For encapsulation, at (w/w)
ratio of 1 : 2 citronellal : TES4C, citronellal (0.20 g), TES4C
(0.40 g) and APTES (0.08 g) were co-dissolved in 4 ml ethanol.
The obtained clear solution was dropped slowly (1 ml minꢀ1) into
the stirred water (16 ml, stirring rate ꢁ700 rpm), and the
suspension stirred for 24 h at room temperature, before being
centrifugally filtered (MWCO 100,000, Amicon Ultra-15, Milli-
pore, Ireland) to collect the citro-PTES4C-1 spheres. The
obtained spheres were then redissolved in water to a final volume
of 20 ml. Encapsulation at a citronellal : TES4C (w/w) ratio of
1 : 1 was carried out similarly, except that 0.40 g of citronellal
was used instead of 0.20 g and the obtained product was called
citro-PTES4C-2.
PF measurement using an SPF Analyzer (Optometrics, SPF-
290s, MA, USA). PTES24C and EHMC were also subjected to
the same measurement using the same protocol (see Table 2 for
the amount of PTES24C and EHMC used).
Acknowledgements
The authors thank the Ratchadaphisesomphot endowment fund,
the Special Task force for Activating Research from the center-
nary academic development project, Chulalongkorn University,
the Commission of Higher Education-Thailand Research Fund
(BRG5280004), Thai Government Stimulus Package
2
(TKK2555), for financial support. The authors are also very
grateful for the English corrections from Robert Butcher of the
Publication Counseling Unit, Faculty of Science, Chulalongkorn
University, and the SPF and UVA-PF measurements from the
Institute of Beauty and Health Sciences Co., Ltd.
Citronellal loadings in citro-PTES4C-1 and citro-PTES4C-2
were determined by directly evaluating the amount of citronellal
in the obtained particles following extraction of the encapsulated
citronellal nanoparticles with hexane. Five ml of hexane was
added to 1.0 ml of the obtained suspensions, vigorously shaken,
sonicated for 30 min, and left at 30 ꢄC for 12 h before the hexane
layer was withdrawn and the amount of citronellal in the hexane
layer was determined by UV absorption spectroscopy with the
aid of a calibration curve. The loading capacities were then
calculated as follows:
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This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 7922–7930 | 7929