Dora Balogh

Analysis of Telomerase by the Telomeric Hemin/G-Quadruplex-Controlled Aggregation of Au Nanoparticles in the Presence of Cysteine

Telomeres are guanosine-rich nucleic-acid chains that fold, in the presence of K(+) ions and hemin, into the telomeric hemin/G-quadruplex structure, exhibiting horseradish peroxidase mimicking functions. The telomeric hemin/G-quadruplex structures catalyze the oxidation of thiols (e.g., l-cysteine) into disulfides (e.g., cystine). As l-cysteine stimulates the aggregation of Au nanoparticles (NPs), accompanied by absorbance changes from red (individual Au NPs) to blue (aggregated Au NPs), the process is implemented to quantitatively analyze the activity (content) of telomerase, a versatile biomarker for cancer cells. Telomerase extracted from 293T cancer cells catalyzes, in the presence of a dNTPs mixture and an appropriate primer probe, the telomerization process, leading to the generation of catalytic telomeric hemin/G-quadruplex chains that control the l-cysteine-mediated aggregation of Au NPs. The extent of aggregation is thus controlled by the concentration of telomerase. The method enabled the detection of telomerase with a detection limit of 27 cells/μL. The spectral changes accompanying the aggregation of Au NPs are further supported by transmission electron microscopy imaging.

Helquat-Induced Chiroselective Aggregation of Au NPs

Au nanoparticles (NPs) are functionalized with chiral (R) or (S) binaphthol phenylboronic acid ligands, (1a) or (1b). The (R)- or (S)-binaphthol phenylboronic acid ligands form donor-acceptor complexes with the chiral dicationic helicene, helquat (P)-HQ(2+) or (M)-HQ(2+), (2a) or (2b). The association constants between (1a)/(2a) and (1a)/(2b) correspond to (7.0 ± 0.5) × 10(5) M(-1) and (2.5 ± 0.3) × 10(5) M(-1), respectively, whereas the association constants between (1b)/(2b) and (1b)/(2a) correspond to (4.0 ± 0.5) × 10(5) M(-1) and (1.8 ± 0.3) × 10(5) M(-1), respectively. Chiroselective aggregation of chiral binaphthol phenylboronic acid-capped Au NPs triggered by the chiral helquats, is demonstrated.

Electrochemically triggered Au nanoparticles "sponges" for the controlled uptake and release of a photoisomerizable dithienylethene guest substrate.

1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges. The closed isomer is stabilized in the imprinted sites of the bis-aniline-bridged Au NPs composite by donor-acceptor interactions. The electrochemical oxidation of the bis-aniline bridging units to the quinoid acceptor state leads to imprinted sites that lack affinity interactions for the binding of the closed state to the matrix, leading to the release of the closed photoisomer to the electrolyte solution. By the cyclic reduction and oxidation of the bridging units to the bis-aniline and quinoid states, the reversible electrochemically controlled uptake and release of the closed photoisomer is demonstrated. The quantitative uptake and release of the closed isomer to and from the imprinted Au NPs composites is followed by application of CdSe/ZnS quantum dots as auxiliary probes. Similarly, by the reversible photochemical isomerization of the closed substrate to the open substrate (λ > 530 nm) and the reversible photoizomerization of the open substrate to the closed state (λ = 302 nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated. Finally, we demonstrate that the electrochemically stimulated uptake and release of the closed substrate to and from the imprinted Au NPs composite controls the wettability of the resulting surface.

DNA Sensors and Aptasensors Based on the Hemin/G‐quadruplex‐Controlled Aggregation of Au NPs in the Presence of L‐Cysteine

L-cysteine induces the aggregation of Au nanoparticles (NPs), resulting in a color transition from red to blue due to interparticle plasmonic coupling in the aggregated structure. The hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme catalyzes the aerobic oxidation of L-cysteine to cystine, a process that inhibits the aggregation of the NPs. The degree of inhibition of the aggregation process is controlled by the concentration of the DNAzyme in the system. These functions are implemented to develop sensing platforms for the detection of a target DNA, for the analysis of aptamer-substrate complexes, and for the analysis of L-cysteine in human urine samples. A hairpin DNA structure that includes a recognition site for the DNA analyte and a caged G-quadruplex sequence, is opened in the presence of the target DNA. The resulting self-assembled hemin/G-quadruplex acts as catalyst that controls the aggregation of the Au NPs. Also, the thrombin-binding aptamer folds into a G-quadruplex nanostructure upon binding to thrombin. The association of hemin to the resulting G-quadruplex aptamer-thrombin complex leads to a catalytic label that controls the L-cysteine-mediated aggregation of the Au NPs. The hemin/G-qaudruplex-controlled aggregation of Au NPs process is further implemented for visual and spectroscopic detection of L-cysteine concentration in urine samples.

Light-induced and redox-triggered uptake and release of substrates to and from mesoporous SiO2 nanoparticles

The photonic- and redox-triggered cyclic uptake and release of organic substrates in functionalized mesoporous SiO2 nanoparticles (NPs) is demonstrated. The mesoporous SiO2 NPs are functionalized with nitrospiropyran photoisomerizable units. Rhodamine B is encapsulated in the channels of the SiO2 NPs and trapped by the hydrophobic nitrospiropyran capping units. Photoisomerization of the capping units to the protonated nitromerocyanine groups opens the channels and releases the encapsulated dye. Similarly, modification of the SiO2 channels by chloronaphthoquinone units traps eosin Y in the channels, by means of donor-acceptor interactions. The reduction of the quinone units to the chloronaphth hydroquinone donor groups opens the channels and releases the encapsulated substrate. The novelty of the study rests on the demonstration of the reversible and cyclic photostimulated or redox-activated uptake and release of substrates from the mesoporous SiO2 NPs.

pH-controlled release of substrates from mesoporous SiO2 nanoparticles gated by metal ion-dependent DNAzymes

The pH-controlled release of substrates from mesoporous SiO2 nanoparticles, MP-SiO2 NPs, is demonstrated by capping the pores with the Mg2+- or UO2 2+-dependent DNAzyme sequences and unlocking of the pores with Mg2+ ions or UO2 2+ ions at appropriate pH values. While the Mg2+-dependent DNAzyme reveals high activity at pH = 7.2, moderate activity at pH = 6.0, and it lacks activity at pH = 5.2, the UO2 2+-dependent DNAzyme reveals high activity at pH = 5.2, moderate activity at pH = 6.0, and it is catalytically inactive at pH = 7.2. Accordingly, the MP-SiO2 NPs were loaded with methylene blue, MB+, or thionine, Th+, and locked in the pores by the Mg2+- and UO2 2+-dependent DNAzyme sequences, respectively. The pH-programmed release of MB+ or Th+ from the loaded NPs proceeds, in the presence of Mg2+ ions or UO2 2+ ions, at pH = 7.2 and pH = 5.2, using the Mg2+- and UO2 2+-dependent DNAzyme as catalysts that cleave the protecting caps and unlock the pores, respectively. At pH = 6.0 the MB+- and Th+-loaded NPs are concomitantly unlocked by the two DNAzymes. The unlocking processes are selective and other metal ions do not stimulate the release processes.