3 research outputs found
Smart Mesoporous SiO<sub>2</sub> Nanoparticles for the DNAzyme-Induced Multiplexed Release of Substrates
The fluorescent dyes methylene blue, MB<sup>+</sup>,
and thionine,
Th<sup>+</sup>, can be trapped in the pores of mesoporous silica,
MP-SiO<sub>2</sub>, by means of functional nanostructures consisting
of the Mg<sup>2+</sup>- or Zn<sup>2+</sup>-dependent DNAzyme sequences.
In the presence of Mg<sup>2+</sup> or Zn<sup>2+</sup> ions the respective
DNAzymes are activated, leading to the specific cleavage of the respective
caps, and the selective release of MB<sup>+</sup> or Th<sup>+</sup>. The enlargement of the conserved loop domains of the Mg<sup>2+</sup>- or Zn<sup>2+</sup>-dependent DNAzyme sequences with foreign nucleotides
prohibits the formation of active DNAzymes and eliminates the release
of the respective dyes. This is due to the flexibility of the loops
that lacks affinity for the association of the ions. The insertion
of aptamer sequences (e.g., the adenosine-5′-triphosphate (ATP)
aptamer) or ion-binding sequences (e.g., T-rich Hg<sup>2+</sup> ion-binding
domains) as foreign components to the loop regions allows the formation
of active Mg<sup>2+</sup>- or Zn<sup>2+</sup>-dependent DNAzyme structures
through the cooperative formation of aptamer-ATP complexes or T-Hg<sup>2+</sup>-T bridges. These aptamer–substrate complexes or T-Hg<sup>2+</sup>-T bridges allosterically stabilize and activate the DNAzymes,
thus allowing the selective release of the fluorescent substrates
MB<sup>+</sup> or Th<sup>+</sup>. The metal ion-driven DNAzyme release
of substrates from the pores of MP-SiO<sub>2</sub>, and particularly
the allosteric activation of the DNAzymes through cooperative aptamer–substrate
complexes or metal-ion bridges, has important future nanomedical implications
for targeted release of drugs. This is demonstrated with the triggered
release of the anticancer drug, doxorubicin, by the Mg<sup>2+</sup>-DNAzyme-locked pores or by the aptamer-ATP complex-triggered activation
of the Mg<sup>2+</sup>-dependent DNAzyme
Light-Induced Aggregation of Gold Nanoparticles and Photoswitching of Silicon Surface Potential
Hybrid
nanomaterials having tunable properties that can be reversibly
conducted by external stimuli, in a particular light, are of great
importance since they enable synergetic behavior between their components
and enable the design of stimuli responsive “smart”
materials and surfaces. Here we describe the formation of organic–inorganic
hybrid nanoparticles that photochemically aggregate and their effect
on the electronic properties of a semiconducting surface, as a function
of external irradiation. The inorganic component consists of 3 nm
gold nanoparticles while the organic component is a covalently attached,
photochromic spiropyran derivative. Aggregation/deaggregation patterns
in solution were obtained and analyzed by UV–vis spectroscopy
and transmission electron microscopy upon photoswitching. The assembly
of spiropyran-modified gold nanoparticles on an Si/SiO<sub>2</sub> surface proved useful in phototuning the electronic properties of
semiconductors measured by contact potential difference
Biocatalytic Release of an Anticancer Drug from Nucleic-Acids-Capped Mesoporous SiO<sub>2</sub> Using DNA or Molecular Biomarkers as Triggering Stimuli
DNA-gated mesoporous SiO<sub>2</sub> nanoparticles, MP-SiO<sub>2</sub> NPs, loaded with rhodamine B, RhB, act as “smart” materials that reveal complementary “sense” and “release” functionalities. The unlocking of the DNA pore-capping units is achieved by the biocatalytic cleavage of the DNA, and the unlocking process is amplified by the regeneration of the analyte-trigger. The RhB-loaded MP-SiO<sub>2</sub> NPs are capped with nucleic acid hairpin structures that lock the RhB in the pores. Opening of the hairpin structures by a nucleic acid analyte trigger or by the formation of an aptamer–substrate (ATP) complex leads to the formation of duplex structures being cleaved by exonuclease III, Exo III, or the nicking enzyme, Nb. BbvCI. This results in the regeneration of the target analytes, the autonomous unlocking of the pores, and the release of RhB. The systems reveal selectivity, and one-, two-, three-base mutations in the target DNA, or substitution of ATP with other triphosphate nucleotides, prohibit the unlocking of the pores. In analogy to the biocatalytic release of the model fluorophore substrates, the anticancer drug camptothecin, CPT, was entrapped in the pores and locked by the <b>1</b> or <b>11</b> hairpin structures. The drug was released from the pores in the presence of the nucleic acid <b>2</b> or ATP and the Exo III, as biocatalyst. Similarly, CPT locked in the pores by the <b>6</b> or <b>12</b> hairpins were released from the pores in the presence of ATP and Nb. BbvCI, as nicking enzyme, respectively. The effects of the CPT-loaded MP-SiO<sub>2</sub> NPs, capped with the ATP-dependent lock <b>6</b>, on the viability of MDA-231 breast cancer cells and MCF-10a normal breast cells were examined. We find that after 48 h, 65% cell death was observed for the MDA-231 cancer cells, where only 25% cell death was observed for the normal cells. The higher cell death of the cancer cells correlates well with the enhanced metabolic synthesis of ATP in the cancerous cells