Immobilizing Gold Nanoparticles in Mesoporous Silica Covered Reduced Graphene Oxide: A Hybrid Material for Cancer Cell Detection through Hydrogen Peroxide Sensing

A new kind of two-dimensional (2-D) hybrid material (RGO-PMS@AuNPs), fabricated by the immobilization of ultrasmall gold nanoparticles (AuNPs, ∼3 nm) onto sandwich-like periodic mesopourous silica (PMS) coated reduced graphene oxide (RGO), was employed for both electrocatalytic application and cancer cell detection. The hybrid-based electrode sensor showed attractive electrochemical performance for sensitive and selective nonenzymatic detection of hydrogen peroxide (H₂O₂) in 0.1 M phosphate buffered saline, with wide linear detection range (0.5 μM to 50 mM), low detection limit (60 nM), and good sensitivity (39.2 μA mM^–1 cm^–2), and without any interference by common interfering agents. In addition, the sensor exhibited a high capability for glucose sensing and H₂O₂ detection in human urine. More interestingly, the hybrid was found to be nontoxic, and the electrode sensor could sensitively detect a trace amount of H₂O₂ in a nanomolar level released from living tumor cells (HeLa and HepG2). Because the hybrid presents significant properties for the detection of bioactive species and certain cancerous cells by the synergistic effect from RGO, PMS, and AuNPs, it could be able to serve as a versatile platform for biosensing, bioanalysis, and biomedical applications

Cancer Cell Detection and Therapeutics Using Peroxidase-Active Nanohybrid of Gold Nanoparticle-Loaded Mesoporous Silica-Coated Graphene

Development of efficient artificial enzymes is an emerging field in nanobiotechnology, since these artificial enzymes could overcome serious disadvantages of natural enzymes. In this work, a new nanostructured hybrid was developed as a mimetic enzyme for in vitro detection and therapeutic treatment of cancer cells. The hybrid (GSF@AuNPs) was prepared by the immobilization of gold nanoparticles (AuNPs) on mesoporous silica-coated nanosized reduced graphene oxide conjugated with folic acid, a cancer cell-targeting ligand. The GSF@AuNPs hybrid showed unprecedented peroxidase-like activity, monitored by catalytic oxidation of a typical peroxidase substrate, 3,3′,5,5′-tetramethylbenzidine (TMB), in the presence of H₂O₂. On basis of this peroxidase activity, the hybrid was utilized as a selective, quantitative, and fast colorimetric detection probe for cancer cells. Finally, the hybrid as a mimetic enzyme was employed for H₂O₂- and ascorbic acid (AA)-mediated therapeutics of cancer cells. In vitro experiments using human cervical cancer cells (HeLa cells) exhibited the formation of reactive oxygen species (OH^• radical) in the presence of peroxidase-mimic GSF@AuNPs with either exogenous H₂O₂ or endogenous H₂O₂ generated from AA, leading to an enhanced cytotoxicity to HeLa cells. In the case of normal cells (human embryonic kidney HEK 293 cells), the treatment with the hybrid and H₂O₂ or AA showed no obvious damage, proving selective killing effect of the hybrid to cancer cells

A Taco Complex Derived from a Bis-Crown Ether Capable of Executing Molecular Logic Operation through Reversible Complexation

As learned from natural systems, self-assembly and self-sorting help in interconnecting different molecular logic gates and thus achieve high-level logic functions. In this context, demonstration of important logic operations using changes in optical responses due to the formation of molecular assemblies is even more desirable for the construction of a molecular computer. Synthesis of an appropriate divalent as well as a luminescent crown ether based host <b>1</b> and paraquat derivatives, <b>2</b>(PF₆)₂ and <b>3</b>(PF₆)₂, as guests helped in demonstrating a reversible [3]­(taco complex) (<b>1</b>·{<b>2</b>(PF₆)₂}₂ or <b>1</b>·{<b>3</b>(PF₆)₂}₂) formation in nonpolar solvent. Detailed ¹H NMR studies revealed that two paraquat units were bound cooperatively by the two crown units in <b>1</b>. Because of preorganization, the flexible host molecule <b>1</b> adopts a folded conformation, where each of two paraquat units remain sandwiched between the two aromatic units of each folded crown ether moiety in <b>1</b>. Disassembly of the “taco” complex in the presence of KPF₆ and reassembly on subsequent addition of DB18C6 was initially demonstrated by ¹H NMR spectral studies, which were subsequently corroborated through luminescence spectral studies. Further, luminescence spectral responses as output signals with appropriate and two independent molecular inputs could be correlated to demonstrate basic logic operation like OR and YES gates, while the results of the three molecular inputs could be utilized to demonstrate important logic operation like an INHIBIT gate

Recognition of Hg²⁺ Ion through Restricted Imine Isomerization: Crystallographic Evidence and Imaging in Live Cells

A newly synthesized imine-based receptor (<b>L</b>) showed remarkable specificity toward the Hg²⁺ ion in aqueous media over other metal ions. Coordination of <b>L</b> to Hg²⁺ induces a <i>turn-on</i> fluorescence response. This was explained based on the restricted imine isomerization along with PET on coordination to Hg²⁺. X-ray structural evidence tends to favor a C–C bond rotation rather than CN isomerization for adopting a favorable conformation in <b>L</b> for coordination to Hg²⁺. This reagent could be used for imaging the accumulation of Hg²⁺ ions in HeLa cells

Recognition of Hg²⁺ Ion through Restricted Imine Isomerization: Crystallographic Evidence and Imaging in Live Cells

A newly synthesized imine-based receptor (<b>L</b>) showed remarkable specificity toward the Hg²⁺ ion in aqueous media over other metal ions. Coordination of <b>L</b> to Hg²⁺ induces a <i>turn-on</i> fluorescence response. This was explained based on the restricted imine isomerization along with PET on coordination to Hg²⁺. X-ray structural evidence tends to favor a C–C bond rotation rather than CN isomerization for adopting a favorable conformation in <b>L</b> for coordination to Hg²⁺. This reagent could be used for imaging the accumulation of Hg²⁺ ions in HeLa cells

Molecular Interactions, Proton Exchange, and Photoinduced Processes Prompted by an Inclusion Process and a [2]Pseudorotaxane Formation

Appropriate design of the host and guest components allows formation of a novel [2]­pseudorotaxane complex with an interrupted photoinduced electron transfer (PET)-coupled fluorescence resonance energy transfer (FRET) response. This is the first example of an inclusion complex with NO₆-based azacrown ether as the host unit (H). Different guest molecules (G1, G2, G3, and G4) with varying stopper size are used for the studies. Unlike G1, G2, and G3, G4 with a relatively bulkier stopper fails to form a [2]­pseudorotaxane complex. Isothermal titration microcalorimetry measurements reveal a systematic increase in the association constant for H·G1, H·G2, and H·G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H·G1/H·G2/H·G3 is exclusively driven by a large positive entropic gain (<i>T</i>Δ<i>S</i> = 19.69/26.80/21.81 kJ·mol^–1), while the enthalpy change is slightly negative for H·G1/H·G3 (−2.61/–1.97 kJ·mol^–1) and slightly positive for H·G2 (Δ<i>H</i> = 5.98 kJ·mol^–1). For these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is attributed to the subtle differences in acidity of the NH₂⁺ unit of the guest molecules and thus the proton exchange ability between the host and respective guest. This is substantiated by the results of the computational studies