Many biosensing and imaging systems use fluorescence detection. In this paper we presented the synthesis of biotin-endfunctionalized highly fluorescent water-soluble polymers for use in biotin–avidin systems. Statistical polymers of N-acryloylmorpholine (NAM) and N-acryloxysuccinimide (NAS) were prepared by RAFT polymerization using a biotinylated chain transfer agent that ensured 95% end-functionalization of the chains. They were further labeled with a lucifer yellow (LY) dye, yielding 7 to 62 LY fluorophores per polymer chain. The resulting polymers exhibited reduced fluorescence self-quenching, with 7- to 43-fold higher brightness than free LY dye. In addition, they featured low pH sensitivity and very good photobleaching resistance. Moreover, we showed that a more extended polymer conformation was beneficial to the binding of the terminal biotin with streptavidin. This work paves the way for the development of polymers for signal amplification in biosensing assays, labeling of biotin-receptors at cell surfaces in some cancer studies, labeling of antibodies and microscopy imaging purposes. This work originated the following joint patents with the company BioMerrieux: US8133411B2, 2012; US2008290321, 2008; EP1899434, 2008; WO2007003781, 2007; and FR2887892, 2007.
This work was cover of Polymer Chemistry2013, 4.
Integrated optical detection of autonomous capillary microfluidic immunoassays: a hand-held point-of-care prototypeBiosensors and Bioelectronis, 57, 284(2014)|www|
Cross-sectional SEM image of a photocathode
In this work we present a point-of-care prototype system by integrating capillary microfluidics with a microfabricated photodiode array and electronic instrumentation into a hand-held unit. The capillary microfluidic device is capable of autonomous and sequential fluid flow, including control of the average fluid velocity at any given point of the analysis. To demonstrate the functionality of the prototype, a model chemiluminescence ELISA was performed. The performance of the integrated optical detection in the point-of-care prototype is equal to that obtained with traditional bench-top instrumentation. The prototype performed integrated chemiluminescence ELISA detection in about 15 minutes with a limit-of-detection of ≈2 nM with an antibody-antigen affinity constant of ≈2x107 M-1.
A U.S. patent related to this technology is pending.
On the Stability Enhancement of Cuprous Oxide Water Splitting Photocathodes by Low Temperature Steam Annealing João Azevedo et al., Energy & Environmental Science|www|
Given the intermittent nature of solar radiation, large-scale use of solar energy requires an efficient energy storage solution. So far, the only practical way to store such large amounts of energy is in the form of a chemical energy carrier, i.e., a fuel. Photoelectrochemical (PEC) cells offer the ability to convert solar energy directly into chemical energy in the form of hydrogen. Cuprous oxide (Cu2O) is being investigated for photoelectrochemical solar water splitting since it has a band gap of 2.0 eV with favorable energy band positions for water cleavage, it is abundant and environmentally friendly. A major challenge with Cu2O is the limited chemical stability in aqueous environments. We present a simple and low-cost treatment to create a highly stable photocathode configuration for H2 production, consisting of a steam treatment of the multilayer structures. The role of this treatment was investigated and the optimized electrodes showed photocurrents over –5 mA cm–2 with 90% stability over more than 50 h of light chopping (biased at 0 VRHE in pH 5 electrolyte).
Dynamic and structural properties of orthorhombic rare-earth manganites under high pressure PHYSICAL REVIEW B90, 054104 (2014) |www|
The present work reports a high-pressure study of orthorhombic rare-earth manganites AMnO3 using Raman scattering (for A = Pr, Nd, Sm, Eu, Tb, and Dy) and synchrotron x-ray diffraction (XRD), for A = Pr, Sm, Eu, and Dy. In all cases, a phase transition was evidenced by the disappearance of the Raman signal at a critical pressure that depends on the A cation. For the compounds with A = Pr, Sm, and Dy, XRD confirms the presence of a corresponding structural transition to a noncubic phase, so that the disappearance of the Raman spectrum can be interpreted as an insulator-to-metal transition. We analyze the compression mechanisms at work in the different manganites via the pressure dependence of the lattice parameters, the shear strain in the ac plane, and the Raman bands associated with out-of-phase MnO6 rotations and in-plane O2 symmetric stretching modes. Our data show a crossover across the rare-earth series between two different kinds of behavior. For the smaller A cations considered in this study (Dy and Tb), the compression is nearly isotropic in the ac plane, with only small evolutions of the tilt angles and cooperative Jahn-Teller distortion. As the radius of the A cation increases, the pressure-induced reduction of Jahn-Teller distortion becomes more pronounced and increasingly significant as a compression mechanism, while the pressure-induced tilting of octahedra chains becomes conversely less pronounced. We finally discuss our results in light of the notion of chemical pressure and show that the analogy with hydrostatic pressure works quite well for manganites with the smaller A cations considered in this paper but can be misleading with large A cations.
Electrostatically driven lipid–lysozyme mixed fibers display a multilamellar structure without amyloid features. Soft Matter,2014, 10(6),840-850 |www|
Understanding the interactions between anionic lipid membranes and amyloidogenic proteins/peptides is key to elucidate the molecular mechanisms underlying the membrane-driven amyloid fiber formation. Here, hen egg-white lysozyme was used as a model protein to test whether this same process also occurs with non-amyloidogenic lipid-binding proteins/peptides. A complementary set of biophysical techniques was employed to study the structure and dynamics of the lipid–lysozyme mixed fibers produced at a low lipid/protein molar ratio that have been proposed earlier to present “amyloid-like” characteristics. The multilamellar architecture of these elongated mesoscopic structures was established by performing time-resolved Förster resonance energy transfer measurements, at both bulk (ensemble) and single-fiber level. The predominantly oligomeric lysozyme and phospholipids were both found to display significantly decreased lateral mobility when embedded in these mixed fibers. Notably, two-photon microscopy of Laurdan revealed that a pronounced membrane surface dehydration/increased molecular interfacial packing was produced exclusively in these elongated mixed supramolecular fibers present in the highly polymorphic samples. Infrared spectroscopic studies of lysozyme in these samples further showed that this protein did not exhibit a rich β-sheet structure characteristic of amyloid fibrils. These results support the conclusion that negatively charged lipid membranes do not have the general ability to trigger amyloid fibril formation of non-amyloidogenic proteins.
This work was back cover of Soft Matter 2014 10(6)
Fluorescent “rhodamine-like” hemicyanines derived from the 6-(N,N-diethylamino)-1,2,3,4-tetrahydroxanthylium system Dyes and Pigments, 2015, 112, 73. |www|
Two new compounds derivatives of the “rhodamine-like” heterocyclic system 6-(N,N-diethylamino)-1,2,3,4-tetrahydroxanthylium were synthesized, bearing an aniline fragment in the conjugation chain. Their spectral-luminescent properties were investigated; fluorescence quantum yields and lifetimes were obtained for each dye in three different solvents. Dye 3a presents the highest fluorescence quantum yield in dichloromethane (φF = 0.60). In contrast with classic rhodamines, a large Stokes shift was detected, compatible with a mechanism of deactivation involving twisted intramolecular charge transfer interactions. These rhodamine-like compounds exhibit very low quantum yield of singlet oxygen formation (φΔ = 0.07 for 3a), similar to what is observed for other hemicyanines. Triplet–triplet absorption spectra were also obtained, as well as the quantum yield of intersystem crossing (φT = 0.10 for 3a). Photostability was evaluated under visible and laser irradiation and dye 3a proved to be the most stable one, making it a good candidate to be used as imaging agent.