Supporting Information for:
Silica nanocapsules with redox-responsive delivery
Johannes Fickert, David Schaeffel, Kaloian Koynov, Katharina Landfester, Daniel Crespy*
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
Experimental Section
Materials
Bis[3-(triethoxysilyl)propyl] tetrasulfide TESPT (Sigma Aldrich, 90%), cetyltrimethylammonium chloride CTMA-Cl (Acros Organics, 99%), hexadecane HD (Sigma Aldrich, 99%), tetraethoxysilane TEOS (Alfa Aesar, 98%), tris(2-carboxyethyl)phosphine hydrochloride TCEP (Sigma Aldrich, 98%), N-(2,6-diisopropylphenyl)perylene-3,4-dicarbonacidimide PMI (BASF) were used as received. Demineralized water was used throughout the work.
Preparation of the nanocapsules
Known amounts of precursors (TEOS, TESPT) were mixed with 0.66 g of HD or 0.33 g and 0.33 g of HD, and were stirred with 30 mL of a 0.77 mg∙mL-1 aqueous solutions of CTMA-Cl for 5 min. The emulsion was sonicated under ice cooling for 120 s at 70% amplitude in a pulse regime (30 s sonification, 10 s pause) using a Branson 450 W sonifier and a 1/2” tip. The resulting miniemulsions were stirred at room temperature at 1000 rpm overnight to obtain the silica nanocapsules. The different compositions of the capsules are summarized in Table 1.
Table S1. Compositions for the functional nanocapsules and their hydrodynamic diameters.
Entry / TEOS [g] / TESPT [g] / Dh [nm]JF201-1 / 1.0 / 1.0 / 210 ± 70
JF201-2 / 1.5 / 0.5 / 200 ± 60
JF215-1 / 1.0 / 1.0 / 250 ± 150
Reduction of the disulfide bonds
4 g of dispersion JF201-1 and 6 mL of a 60.8 mg∙mL-1 aqueous solutions of TCEP nTCEP=3∙nTESPT were mixed and stirred for 24 h at 1000 rpm. Some treated dispersions were washed by a 3 times repeated procedure of centrifugation (10 min at 5000 rpm) followed by redispersion in 10 mL of a 0.77 mg∙mL-1 aqueous solution of CTMA-Cl.
Kinetics of the cleavage of the disulfide bonds
The whole procedure was carried out under argon atmosphere and with a degassed dispersion and degassed water to protect the TCEP from oxygen. 4 g of dispersion JF201-1 and 6 mL of a 60.8 mg∙mL-1 aqueous solutions of TCEP were mixed with 20 mg potassium phosphate used as internal standard for 31P-NMR spectroscopy and stirred at 1000 rpm. Aliquots were taken at fixed time intervals and directly measured by 31P-NMR spectroscopy. The signal of TCEP appearing at 16.66 ppm was monitored in time.
Measurements of the release by fluorescence correlation spectroscopy (FCS)
The release of fluorescent dye (perylene) from the silica nanocapsules was monitored by FCS. The nanocapsules loaded with the perylene dye were prepared as aforementioned except that the dispersed phase consisted in a known amount of the precursors TEOS and TESPT (Table S1) mixed with 0.33 g HD and 0.33 g of a 1.45∙10-5 mg∙mL-1 solution of PMI in xylene. After preparation of the nanocapsules, 4 g of dispersions and 6 mL of a 60.8 mg∙mL-1 aqueous solutions of TCEP were mixed and stirred for 24 h at 1000 rpm. For the FCS measurements, the samples were diluted 50 times in water and THF.
The experiments were conducted on IX70 inverted microscope with a FluoView300 confocal laser scanning unit (Olympus) which was combined with a FCS unit (PicoQuant) consisting of a single-photon avalanche diode (τ-SPAD) and the time-correlated single-photon counting card TimeHarp 200. Excitation was accomplished using an argon-ion laser at λ = 488 nm (8mW, CVI Melles Griot) and the fluorescence was detected after filtering with a LP488R Raman Edge long-pass filer. The oil immersion objective Olympus PLAPON 60XOTIRFM, 60x/NA 1.45 was used throughout the studies.
Figure S1. Reaction scheme for the reduction of the disulfide bonds by TCEP.
a. b. c.
Figure S2. Nanocapsules of JF201-1 a: after addition of TCEP (TEM), b-c: after addition of TCEP and centrifugation (TEM and SEM).
Evaluation procedure of the FCS data
The measured temporal fluctuations of the fluorescence intensity δF(t) caused by the diffusion of the fluorescent species through the detection volume V are used for the construction of an experimental autocorrelation curve:
Gτ=1+δF(t)δF(t+τ)/F(t)2 (S1)
It has been shown theoretically [1] that for an ensemble of m different types of freely diffusing fluorescent species the autocorrelation curve has the following analytical form:
Gτ=1+1Ni=1mfi1+tτDi1+tS2τDi (S2)
Here N is the average number of tracers in V and S = zoro is the so called structural parameter describing the ratio between the lateral to radial dimension of V. τDi and fi are the mean diffusion time of a tracer of species i through V and their fraction, respectively. By fitting the experimental autocorrelation curve (Eq. S1) with the analytical model (Eq. S2) and knowing V and S from reference measurements using dyes with known diffusion coefficients the respective diffusion coefficient Di=ro2+Ri24τDi and hydrodynamic radius Ri can be evaluated using an iteration procedure [1] involving also the Stokes-Einstein equation. In the case of one type of fluorescent species only (m=1) the species concentration NV and fluorescent brightness <F>/N can also be calculated.
Table S2. Composition of the fluorescent miniemulsions and hydrodynamic radii of the corresponding droplets measured by DLS.
Entry / TEOS [g] / TESPT [g] / Rh [nm]JF220-1 / 2.0 / 0.0 / 110 ± 50
JF220-2 / 1.0 / 1.0 / 100 ± 50
JF220-3 / 1.5 / 0.5 / 90 ± 40
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