Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition

Nonenzymatic glucose sensors employing multiwalled carbon nanotubes (MWNTs) with highly dispersed Pt-M (M = Ru and Sn) nanoparticles (Pt-M@PVP-MWNTs) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these nonenzymatic sensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (A mM−1), linear range (mM), and detection limit (mM) (S/N = 3) of the glucose sensor with the Pt-Ru catalyst in NaOH electrolyte were determined as 18.0, 1.0–2.5, 0.7, respectively. The corresponding data of the sensor with Pt-Sn catalyst were 889.0, 1.00–3.00, and 0.3, respectively. In addition, these non-enzymatic sensors can effectively avoid interference arising from the oxidation of the common interfering species ascorbic acid and uric acid in NaOH electrolyte. The experimental results show that such sensors can be applied in the detection of glucose in commercial red wine samples

Hybrid Metallic Nanostructures for Bio and Analytical Applications

Different hybrid nanoparticles (NPs), including FeM (M=Ni, Au, Pt, Pd) and Fe-biomolecules (biomolecule=glucose oxidase, p53p protein), have been synthesized by a surfactant-free, single-step electrochemical method. FeNi bimetallic NP systems have been chosen as the starting point of the present study. Shape evolution and phase transformation of FeNi NPs obtained by changing their composition is demonstrated. It has been shown that the shape evolution of NPs from concave cube to truncated sphere occurs concurrently with the phase transformation from bcc to fcc. In-situ formation of a very thin Ni-doped FeOOH outer layer and NiFe2O4 intermediate layer on the skin of the NPs is observed, the latter of which passivates the surface and dramatically enhances the air stability. Furthermore, bimetallic FeNi concave nanocubes with high Miller index planes have been obtained through controlled triggering of the different growth modes of Fe and Ni. Taking advantage of the higher activity of the high-index planes, mono-dispersed concave nanocages have been fabricated by introducing a material-independent electroleaching process. With the high-index facets exposed, these concave nanocubes and nanocages are found to be 10 and 100-fold, respectively, more active toward electrochemical detection of 4-aminophenol than cuboctahedrons which provides a label-free sensing approach to monitoring toxins in water and pharmaceutical wastes. In addition, the shape-dependent magnetic properties of a bimetallic system have been studied for FeNi NPs with well-defined concave cubic and octahedron shapes. The alloy composition was chosen to be close to that of Invar FeNi alloys (35% Ni content) but with concurrent presence of both bcc and fcc phases, in order to investigate the role of phase combination in controlling the magnetic properties. The role of the two phases in governing the magnetic properties has also been studied for both bulk and nanoalloys by large-scale density function theory (DFT) calculations using Vienna Ab-initio Simulation Package (VASP, Version 5.2), which provides a new complementary approach to understanding the magnetic properties of alloy materials. To extend the aforementioned method to other hybrid and bimetallic systems, FePt NPs with different compositions (Fe25Pt75, Fe30Pt70, Fe35Pt65) have been synthesized and their chemical sensing investigated for the electro-oxidation of vitamin C. The FePt alloy NPs are found to be superior catalysts for vitamin C electro-oxidation than Pt NPs and are significantly more selective for the detection of vitamin C against other common interference species, including dopamine, citric acid, uric acid, glucose, and NaCl. Enhancement in sensor performance can be attributed to the increase in specific surface area due to reduction of nanocrystallite size and to modification in the Pt electronic structure as a result of nanoalloying. We also synthesize bimetallic FeAu, FePd, and AuPt NPs and investigate their electrochemical properties for As(III) detection. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, Pd) than pristine noble metal NPs (without Fe alloying), with the best performance found for FePt NPs. The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), acting as the most detrimental interfering ion for As detection. The versatility of the method for hybridization of different components is demonstrated by synthesizing size-specific hybrid NPs based on Fe-biomolecules. We have chosen an anticancer peptide (p53p, MW 1.8 kDa) and an common enzyme (glucose oxidase, MW 160 kDa) as model molecules to illustrate the versatility of the method towards different types of molecules over a large size range. We show that the electrostatic interaction for complex formation of metal hydroxide ion with the partially charged side of the biomolecule in the solution is the key to hybridization of metal-biomolecule materials to form complexes as the building blocks. These hybrid NPs with controllable sizes ranging from 30 nm to 3.5 μm are found to exhibit superparamagnetic behavior, which is a big challenge for particles in this size regime. As an example of greatly improved properties and functionality of the new hybrid material, in-vitro toxicity assessment of Fe-glucose oxidase hybrid NPs shows no adverse effect, while the Fe-p53p hybrid NPs are found to selectively bind to cancer cells. The present work therefore definitely demonstrates the general applicability of the hybridization method for synthesis of metallic hybrid NPs with magnetic properties for different applications, including chemical sensing, magnetic resonance imaging contrast agents, and targeted drug delivery carriers

Interacción de nanoestructuras de carbono o metálicas con (bio)moléculas y su aplicación al desarrollo de sensores

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Analitica y Análisis Instrumental . Fecha de lectura: 26-10-201

Nanocatalytic CePO4·H2O (Rhabdophane): Mitochondrial-Targeting, Cell-Discriminative, ROS-Mediated Cancer Therapy

Nanocatalytic tumor therapies involve established strategies to increase the concentration of endogenous oxygen species (ROS) H2O2 to cytotoxic levels. These strategies are based on increasing the ROS levels through stimuli from drugs, the action of ROS-producing agents, and nanoparticulate catalysis. However, these techniques frequently are indiscriminatory, being cytotoxic to diseased cells and normal cells alike, leading to significant unwanted side-effects. The present work reports a new paradigm strategy based upon the catalytic action of a cell-discriminative, ROS-mediating, autophagy-suppressive nanoparticle, which is CePO4·H2O (rhabdophane). CePO4·H2O nanoparticles were synthesised using CeNO3·6H2O precipitated in an aqueous solution of sodium tripolyphosphate (STPP) at room temperature. The nanoparticles were well crystallised, equiaxed (~10-35 nm), of positive surface charge, and of general valence ratio 〖"Ce" 〗_"0.8" ^"3+" 〖"Ce" 〗_"0.2" ^"4+" 〖"PO" 〗_"4.1" . Materials characterisation involved particuological (hydrodynamic particle size, surface area, zeta potential), mineralogical (X-ray diffraction, laser Raman microspectroscopy), chemical (X-ray photoelectron spectroscopy), structural (Fourier transform infrared spectroscopy), and microstructural (transmission electron microscopy) analyses. Biological characterisation involved examination of the effects on HT-1080 fibrosarcoma cells and MRC-5 normal fibroblasts in terms of cellular interactions (cell viability by MTT assay), cellular uptake and trafficking (confocal laser scanning microscopy, biological transmission electron microscopy, flow cytometry), ROS generation (confocal laser scanning microscopy, flow cytometry), apoptosis (annexin V-FITC assay), gene expression (q-RT-PRC), and protein expression (western blot analyses). The key observations and conclusions from the biological evaluation are as follows: Discriminative Cytotoxicity: CePO4·H2O nanoparticles are the first to exhibit discriminative cytotoxicity: At 24 h, fibrosarcoma HT-1080 cell viability is ~10% but MRC-5 normal cell viability is ~45%. Discriminative Uptake: CePO4·H2O nanoparticles are the first, without the use of a targeting ligand, to be internalized readily by cancer cells but scarcely by normal cells. Self-Targeting: CePO4·H2O nanoparticles are trafficked toward the mitochondrial environment and possibly the converse trafficking. Mitochondrial Starvation: The preceding proximity between CePO4·H2O nanoparticles and cancer cell leads to increased phosphate concentration in the cellular environment, the concentration gradient of which effectively starves the mitochondria, leading to mitochondrial stress and dysfunction. Discriminative ROS Generation: CePO4·H2O nanoparticles are the first to demonstrate elevated cellular ROS in cancer cells by multiple mechanisms while normal cells exhibit only a low level of such elevation. Autophagy Suppression: CePO4·H2O nanoparticles suppress autophagy, thereby increasing cellular stress and suppressing cancer cell survival, thus offering a complement to mitochondrial starvation. Redox Switching: CePO4·H2O nanoparticles are the first nonmetallic nanoparticles to balance redox switching through simple electronic charge compensation rather than more complex ionic charge compensation. Biocompatibility: As hydrated phosphates, CePO4·H2O nanoparticles are more biocompatible than metals or oxides, suggesting greater feasibility of renal clearance. These advantages derive from the key role of the redox and defect equilibria arising from the oxidation reaction Ce3+ → Ce4+ + e′, which is induced by the acidic pH environment of the cancer call versus the stability of the Ce3+ valence in the basic pH environment of the normal cell. The former both elevates the ROS level and disrupts the electron transfer chain. Ultimately, the suppression of the proliferation of cancer cells derives from the cross-talk involving cellular ROS elevation, autophagy suppression, and their mitochondrial control