International audienceWell-ordered periodic mesoporous organosilicas (PMOs) of the MCM-41 type of structure containing framework Ni(II) complexes (Ni@PMOs) were synthesized via a one-pot synthesis route in mild conditions, using cheap and environmental friendly reactants. These materials were obtained using the N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTMS) ligand in three different molar ratios of Ni, X = 1, 2, 3 and co-condensed with sodium silicate in the presence of cetyltrimethylammonium tosylate as a templating agent. The latter named OP-Ni-1, OP-Ni-2 and OP-Ni-3, respectively, were submitted to a treatment using a mixture of chlorotrimethylsilane (CTMS) and hexamethyldisilazane (HMDSA) that simultaneously removed the surfactant and capped the silanol groups leading to materials OP-Ni-1TA, OP-Ni-2TA and OP-Ni-3TA (∼2 wt% Ni content). For comparison, a series of mesoporous materials were prepared via a post-synthesis route to locate the Ni(II) complexes in the channel (∼2.4 wt% Ni). The latter were prepared using the “molecular stencil patterning” (MSP) technique based on sequential grafting of trimethylsilyl (TMS) groups and the same ligand cited above using AAPTMS/Ni molar ratios of 2 and 3. These steps lead to intermediate materials LUS to LUS-PSE and final materials LUS-MSP-Ni-2 and LUS-MSP-Ni-3. Both series of materials were thoroughly investigated in terms of (i) coordination state compared to molecular analogues, (ii) Ni(II) to Cu(II) exchange ability and (iii) coordination accessibility using ethylenediamine (en) or thiocyanate (SCN−) as probe ligands. All materials were investigated using XRD, TEM, N2 sorption isotherms, UV-visible, FT-IR and EPR spectroscopies. In particular, FT-IR and EPR data were treated quantitatively to monitor both the TMS loading and the concentration of isolated Cu(II) in conjunction with elemental analysis. Pore size decrease, pore volume reduction, nickel to copper exchangeability (> 90%) and ligand accessibility were observed for materials LUS-MSP-Ni-2 and LUS-MSP-Ni-3 as expected with grafted Ni(II) complexes located in the channel. By contrast, a clear opposite trend, observed for Ni@PMOs, OP-Ni-1, OP-Ni-2 and OP-Ni-3, was fully consistent with a complete insertion and captation of the Ni complexes in the siliceous pore walls despite the very small thickness (ca. 1.4 nm) of the wall. This is explained by the state of Ni(II) both in terms of coordination and cavity effect. Indeed, both absence of counterion coming from the solution (nitrate) and bathochromic shift of the d-d electronic transitions, are consistent with the presence of silanolate groups counterbalancing the electrical charges and mainly leading to neutral framework species of formula, [Ni(AAPS)2(SiO)2], [Ni(AAPS)(OL)2(SiO)2], with neutral ligand OL = H2O, SiOH, SiOSi and AAPS = N-(2-aminoethyl)-3-aminopropylsilyl moities
The paper shows the different methods to attach a molecule to detect streptavidin to a dielectric particle made of a rare-earth oxide core and a polysiloxane shell containing fluorescein. First, the detection of streptavidin binding on a biotinylated gold substrate can be achieved in three ways: the shift of the surface plasmon resonance of the substrate and the double luminescence (organic and inorganic) of the core/shell particle. Second, these detections are efficient even after elimination upon thermal annealing of all the undesired molecules that skew the assays. Finally, the particle that ballasts the protein enhances its binding kinetics and increases the localized surface plasmon resonance shift that detects the binding.
Peroxidase labeled streptavidin was immobilized onto the surface of bulk and clusterlike metal films at a distance controlled by a peptide chain with a length between 1.3 and 7.8nm. Luminol chemiluminescence which occurred at peroxidase vicinity depends on the metal nanostructure. When peroxidase is attached on a bulklike film, chemiluminescence increases monotonously with the distance because of a decrease of the light emission quenching by metal. When peroxidase is attached on a clusterlike film, chemiluminescence undergoes a complex variation with the metal/catalyst distance evidencing a competition between the already mentioned quenching process and a nanostructure-induced catalysis enhancement.
The paper shows how polysiloxane particles encapsulating fluorophores can be successfully used to detect biotin-streptavidin binding by two types of technique. After functionalization of the particles by streptavidin, the fixation of the biomolecule can indeed be detected by a shift of the localized surface plasmon resonance of the biotinylated gold dots used as substrate and by the luminescence of the fluorophores evidenced by scanning near-field optical microscopy. The development of particles allowing such a double detection opens a route for increasing the reliability of biological detection and for multi-labelling strategies crossing both detection principles.
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