Elisa Biavardi

Single-molecule-magnet carbon-nanotube hybrids.

Carbon nanotubes (CNTs) hold great promise for sensing and nanoelectronics, as core components of chemical and biological ultra-sensitive probes and of field-effect transistors (FETs). CNT–SQUID devices in particular could constitute magnetic detectors with single-molecule sensitivity, thus offering a viable route to the long-sought readout of magnetic information stored in individual single-molecule magnets (SMMs). SMMs are metal-ion clusters with a large easy-axis magnetic anisotropy, exhibiting a magnetic hysteresis loop at low temperature and suggested as components for quantum computing and molecular spintronics. To date, the chemistry needed to bridge the domains of CNTs and SMMs has remained unexplored. CNT hybrids with gold or magnetic nanoparticles, proteins, enzymes, or luminescent molecules are currently under intense investigation. 8] The resulting materials usually entail a large number of nanoparticles or molecules per CNT, whereas CNT–SMM detectors and spintronic devices require the sequential addition of a small but very controlled number of nanomagnets. Grafting through covalent bonds might introduce electron scattering centers that may limit the performance of CNT devices. By contrast, noncovalent p-stacking interactions with pristine CNTs should largely preserve the CNT conductance, while guaranteeing SMM–CNT interaction. Herein we report the assembly of CNT–SMM hybrids using a tailor-made tetrairon(III) SMM, [Fe4(L)2(dpm)6] (1; Hdpm= dipivaloylmethane), designed to graft onto the walls of CNTs. The ligand L (H3L= 2-hydroxymethyl-2-(4(pyren-1-yl)butoxy)methylpropane-1,3-diol), features an alkyl chain with a terminal pyrenyl group and was synthesized as in Figure 1a. Reduction of 4-pyren-1-yl-butyric acid gives 4-(1-pyrenil)butanol, which is then coupled with 4-bromomethyl-1-methyl-2,6,7-trioxa-bicyclo[2.2.2]octane. A twosteps deprotection of the trimethylol function affords H3L, which is finally treated with the preformed complex [Fe4(OMe)6(dpm)6] (2) to give 1 in excellent yield (95%). The molecular structure of 1 (Figure 1b,c), determined by single-crystal X-ray diffraction, shows a tetrairon(III) propeller-like core with idealized D3 symmetry held together by two triply deprotonated H3L ligands lying at opposite sides of the molecular plane (see Supporting Information). The molecular size of 1 is 1.6–2.3 nm (av.: 1.9 nm). Low-temperature high-frequency (HF)-EPR spectra at 190 and 230 GHz (Figure 2a) and variable-temperature magnetic-susceptibility measurements show the presence of an S= 5 high-spin ground state with an easy-axis magnetic anisotropy (D= 0.409 cm ; Supporting Information). Indeed, single-crystal magnetic measurements reveal a hysteresis loop below 1 K with characteristic quantum-tunneling steps (Figure 2b), confirming the SMM behavior. CNT–FETs were obtained by electron-beam lithography on degenerately n-doped silicon wafers covered with a 300 nm thick SiO2 layer. Single CNTs were located by atomic force microscopy (AFM) and connected by palladium leads separated by 300 nm gaps. The hybrids were then produced by immersion of the CNT–FETs in a 3.1 10 m solution of 1 in 1,2-dichloroethane (DCE) for 30 min, followed by extensive washing with pure DCE. H NMR, ESI-MS, and fluorescence techniques demonstrate that the complex is completely stable in solution in the conditions used for the deposition (Supporting Information). The grafting was reiterated to follow the progressive addition of SMMs. After each treatment a few SMMs were found to stick onto the CNT (Figure 3a), while some others were also located on the surrounding surface. The isostructural complex containing H3L’= 2-hydroxymethyl-2-phenylpropane-1,3-diol did not graft onto CNTs in the same experimental conditions. This result is a strong indication that 1 has been grafted as a result of the pyrenyl functionalities. [*] Dr. L. Bogani, Dr. N. Bendiab, Dr. W. Wernsdorfer Institut N el, CNRS 25 Av. des Martyrs, 38042 Grenoble, Cedex 9 (France) Fax: (+33)4-7688-1191 E-mail: lbogani@hotmail.com

Fully reversible guest exchange in tetraphosphonate cavitand complexes probed by fluorescence spectroscopy

We report here the monitoring of reversible guest inclusion in phosphonate cavitands through a large increase in luminescence intensity caused by the modulation of the exoergonicity of an electron-transfer reaction.

Exclusive recognition of sarcosine in water and urine by a cavitand-functionalized silicon surface

A supramolecular approach for the specific detection of sarcosine, recently linked to the occurrence of aggressive prostate cancer forms, has been developed. A hybrid active surface was prepared by the covalent anchoring on Si substrates of a tetraphosphonate cavitand as supramolecular receptor and it was proven able to recognize sarcosine from its nonmethylated precursor, glycine, in water and urine. The entire complexation process has been investigated in the solid state, in solution, and at the solid–liquid interface to determine and weight all the factors responsible of the observed specificity. The final outcome is a Si-based active surface capable of binding exclusively sarcosine. The complete selectivity of the cavitand-decorated surface under these stringent conditions represents a critical step forward in the use of these materials for the specific detection of sarcosine and related metabolites in biological fluids.

Cavitand‐Grafted Silicon Microcantilevers as a Universal Probe for Illicit and Designer Drugs in Water

The direct, clean, and unbiased transduction of molecular recognition into a readable and reproducible response is the biggest challenge associated to the use of synthetic receptors in sensing. All possible solutions demand the mastering of molecular recognition at the solid-liquid interface as prerequisite. The socially relevant issue of screening amine-based illicit and designer drugs is addressed by nanomechanical recognition at the silicon-water interface. The methylamino moieties of different drugs are all first recognized by a single cavitand receptor through a synergistic set of weak interactions. The peculiar recognition ability of the cavitand is then transferred with high fidelity and robustness on silicon microcantilevers and harnessed to realize a nanomechanical device for label-free detection of these drugs in water.

Thermodynamics of host–guest interactions between methylpyridinium salts and phosphonate cavitands

In this work, the properties of complexation of tetraphosphonate cavitands towards methylpyridinium guests were investigated via isothermal titration calorimetry (ITC). For this purpose, Tiiii[C3H7, CH3, Ph], Tiiii[C3H7, H, Ph], TSiiii[C3H7, H, Ph] hosts and three different methylpyridinium guests were synthesised. The role of the following parameters in the host–guest complexation was investigated: (i) solvation, (ii) nature of the guest counterion, (iii) presence of substituents in the apical positions of the receptor, and (iv) P = O versus P = S bridging units. The results showed that (i) switching from dichloroethane to methanol leads to a decrease of the association constant due to the competitive nature of the solvent, (ii) the guest counterion does not affect the thermodynamics of the process, (iii) the apical methyl groups enhance the binding affinity of the receptor and (iv) the comparison between phosphonate and thiophosphonate hosts clearly demonstrates that cation–dipole interactions are necessary for binding.

Cavitands Endow All-Dielectric Beads With Selectivity for Plasmon-Free Enhanced Raman Detection of Nε-Methylated Lysine.

SiO2/TiO2 microbeads (T-rex) are promising materials for plasmon-free surface-enhanced Raman scattering (SERS), offering several key advantages in biodiagnostics. In this paper we report the combination of T-rex beads with tetraphosphonate cavitands (Tiiii), which imparts selectivity toward Nε-methylated lysine. SERS experiments demonstrated the efficiency and selectivity of the T-rex-Tiiii assays in detecting methylated lysine hydrochloride (Nε-Me-Lys-Fmoc) from aqueous solutions, even in the presence of the parent Lys-Fmoc hydrochloride as interferent. The negative results obtained in control experiments using TSiiii ruled out any other form of surface recognition or preferential physisorption. MALDI-TOF analyses on the beads exposed to Nε-Me-Lys-Fmoc revealed the presence of the Tiiii•Nε-Me-Lys-Fmoc complex. Raman analyses based on the intensity ratio of Nε-Me-Lys-Fmoc and cavitand-specific modes resulted in a dose-response plot, which allowed for estimating the concentration of Nε-methylated lysine from initial solutions in the 1 × 10(-3) to 1 × 10(-5) M range. These results can set the basis for the development of new Raman assays for epigenetic diagnostics.

An electrochemiluminescence-supramolecular approach to sarcosine detection for early diagnosis of prostate cancer

Monitoring Prostate Cancer (PCa) biomarkers is an efficient way to diagnosis this disease early, since it improves the therapeutic success rate and suppresses PCa patient mortality: for this reason a powerful analytical technique such as electrochemiluminescence (ECL) is already used for this application, but its widespread usability is still hampered by the high cost of commercial ECL equipment. We describe an innovative approach for the selective and sensitive detection of the PCa biomarker sarcosine, obtained by a synergistic ECL-supramolecular approach, in which the free base form of sarcosine acts as co-reagent in a Ru(bpy)3(2+)-ECL process. We used magnetic micro-beads decorated with a supramolecular tetraphosphonate cavitand (Tiiii) for the selective capture of sarcosine hydrochloride in a complex matrix like urine. Sarcosine determination was then obtained with ECL measurements thanks to the complexation properties of Tiiii, with a protocol involving simple pH changes - to drive the capture-release process of sarcosine from the receptor - and magnetic micro-bead technology. With this approach we were able to measure sarcosine in the μM to mM window, a concentration range that encompasses the diagnostic urinary value of sarcosine in healthy subjects and PCa patients, respectively. These results indicate how this ECL-supramolecular approach is extremely promising for the detection of sarcosine and for PCa diagnosis and monitoring, and for the development of portable and more affordable devices.

A New Sensitive and Fast Detection System for Amphetamine Type Stimulants (ATS), Based on Gas-Chromatography (GC) and Hollow Fiber Infrared Absorption Spectroscopy (HF-IRAS)

A new detection system for ATS and their precursors has been designed and a bench-top demonstrator has been realized. A test campaign has been performed in order to assess the overall system behavior, and the results confirmed the feasibility of this type of device.

Toward street detection of amphetamines

It would be beneficial to detect amphetamine-type stimulants (ATS) and precursors not only in a forensic lab, but also via field sensors. These would be used by customs and law enforcement units in their daily fight against the trafficking and street distribution of illicit drugs. Such sensors would need to combine hand-portability, high sensitivity, fast response, low false alarm rates, and robustness, together with the ability to analyze substances with a range of different chemo-physical characteristics, and to establish chemical similarities between an unknown substance—potentially a new ATS molecule—and a known set of drugs banned or controlled by law. Together, gas chromatography (GC) and IR absorption spectroscopy (IRAS) combine the chemical separation power of GC with the chemical identification ability associated with the analysis of molecular roto-vibrational transitions. GC-IRAS represents one of the most powerful techniques for the identification of amphetamines.1 So far, however, GC-IRAS has been implemented essentially as bench-top instrumentation for forensic applications2 and ‘bulk’ analysis. With ‘DIRAC’ funding from the European Commission,3 we are developing a GC-IRAS sensor that features hand-portability and fast response, together with the ability to analyze both bulk and traces, with nanogram-level sensitivity.4 Sensitivity is greatly improved by matching the high radiation and spectral resolving power of a tunable external cavity-quantum cascade laser (EC-QCL),5 with the very small interrogation volume ( 70 l) of an IR hollow fiber (HF).6 The HF-IRAS module is efficiently coupled to a silicon-micro-machined (SMM) device that pre-concentrates the vapors of interest, and separates Figure 1. Sensor operational scheme. VPC–GC: Vapor phase preconcentrator gas chromatography. HF–IRAS: Hollow fiber infrared absorption spectroscopy.