Intrinsic optical sectioning with upconverting nanoparticles.

Multiphoton microscopy is a powerful technique for imaging due to its deep penetration, low scattering and sectioning power, allowing control on all three axes for both imaging and molecular actuation, but involves expensive femtosecond lasers. We show that lanthanide-based Upconverting Nanoparticles offer an under $1000 solution with the main advantages of multiphoton imaging, including direct optical sectioning in complex 3D samples.

Transient photocyclization in ruthenium(ii) polypyridine complexes of indolamines.

Ruthenium polypyridine complexes have proved to be useful caging groups for visible-light photodelivery of biomolecules. In most photoreactions, one ligand is expelled upon irradiation, yielding ruthenium mono-aqua complexes and no other photoproduct. In this work we show that a long-lived transient photoproduct is generated when the ruthenium complexes involve indolamines. The spatial conformation of this species is compatible with a cyclic structure that contains both the amine and the normally non-coordinating aromatic ring coordinated to the ruthenium center.

In vivo photorelease of GABA in the mouse cortex.

Electrical stimulation has been used for more than 100 years in neuroscientific and biomedical research as a powerful tool for controlled perturbations of neural activity. Despite quickly driving neuronal activity, this technique presents some important limitations, such as the impossibility to activate or deactivate specific neuronal populations within a single stimulation site. This problem can be avoided by pharmacological methods based on the administration of receptor ligands able to cause specific changes in neuronal activity. However, intracerebral injections of neuroactive molecules inherently confound the dynamics of drug diffusion with receptor activation. Caged compounds have been proposed to circumvent this problem, for spatially and temporally controlled release of molecules. Caged compounds consist of a protecting group and a ligand made inactive by the bond between the two parts. By breaking this bond with light of an appropriate wavelength, the ligand recovers its activity within milliseconds. To test these compounds in vivo, we recorded local field potentials (LFPs) from the cerebral cortex of anesthetized female mice (CF1, 60-70 days, 20-30 g) before and after infusion with caged γ-amino-butyric-acid (GABA). After 30 min, we irradiated the cortical surface with pulses of blue light in order to photorelease the caged GABA and measure its effect on global brain activity. Laser pulses significantly and consistently decreased LFP power in four different frequency bands with a precision of few milliseconds (P < 0.000001); however, the inhibitory effects lasted several minutes (P < 0.0043). The technical difficulties and limitations of neurotransmitter photorelease are presented, and perspectives for future in vivo applications of the method are discussed.

In vivo photorelease of GABA in the mouse cortex

Electrical stimulation has been used for more than 100 years in neuroscientific and biomedical research as a powerful tool for controlled perturbations of neural activity. Despite quickly driving neuronal activity, this technique presents some important limitations, such as the impossibility to activate or deactivate specific neuronal populations within a single stimulation site. This problem can be avoided by pharmacological methods based on the administration of receptor ligands able to cause specific changes in neuronal activity. However, intracerebral injections of neuroactive molecules inherently confound the dynamics of drug diffusion with receptor activation. Caged compounds have been proposed to circumvent this problem, for spatially and temporally controlled release of molecules. Caged compounds consist of a protecting group and a ligand made inactive by the bond between the two parts. By breaking this bond with light of an appropriate wavelength, the ligand recovers its activity within milliseconds. To test these compounds in vivo, we recorded local field potentials (LFPs) from the cerebral cortex of anesthetized female mice (CF1, 60-70 days, 20-30 g) before and after infusion with caged γ-amino-butyric-acid (GABA). After 30 min, we irradiated the cortical surface with pulses of blue light in order to photorelease the caged GABA and measure its effect on global brain activity. Laser pulses significantly and consistently decreased LFP power in four different frequency bands with a precision of few milliseconds (P < 0.000001); however, the inhibitory effects lasted several minutes (P < 0.0043). The technical difficulties and limitations of neurotransmitter photorelease are presented, and perspectives for future in vivo applications of the method are discussed.

Layer-by-layer self-assembly of glucose oxidase and Os(Bpy)2CIPyCH2NH-poly(allylamine) bioelectrode.

The uptake of glucose oxidase (GOx) onto a polycationic redox polymer (PAA-Os)-modified surface, by adsorption from dilute aqueous GOx solutions, was followed by the quartz crystal microbalance (QCM) and shows double exponential kinetics. The electrochemistry of the layer-by-layer-deposited redox-active polymer was followed by cyclic voltammetry in glucose-free solutions, and the enzyme catalysis mediated by the redox polymer was studied in beta-D-glucose-containing solutions. AFM studies of the different layers showed the existence of large two dimension enzyme aggregates on the osmium polymer for 1 microM GOx and less aggregation for 50 nM GOx solutions. When the short alkanethiol, 2,2'-diaminoethyldisulfide was preadsorbed onto gold, a monoexponential adsorption law was observed, and single GOx enzyme molecules could be seen on the surface where the enzyme was adsorbed from 50 nM GOx in water.

Electrochemical quartz crystal impedance study of redox hydrogel mediators for amperometric enzyme electrodes.

Quartz crystal impedance around the resonant frequency at 10 MHz of a composite quartz crystal resonator has been studied simultaneously with cyclic voltammetry. A modified quartz crystal with a redox hydrogel (poly(allylamine)-ferrocene cross-linked with glucose oxidase) and immersed in liquid electrolyte was used. Impedance parameters (R(f) and X(L)((f))) of the surface redox gel film were obtained by fitting the resonator transfer function |V(o)/V(i)| vs ω to a BVD equivalent circuit and analyzed with the multiple nonpiezoelectric layer model of Martin. Two limiting hydrogel layers of the same composition were studied while oxidizing and reducing the ferrocene/ferricenium moieties attached to the swollen polymer backbone: thin and thick redox hydrogel films. For the thin films, the Sauerbrey approximation was valid. The mass/thickness and film viscosity changes that resulted from the anion and water exchange were evaluated while redox switching the polymer on the assumption of negligible storage modulus G' and a density of 1. For thick gel layers, on the other hand, the penetration depth of the acoustic wave was far less than the film thickness, and a liquid-like behavior was apparent. Film storage modulus and film loss modulus were simultaneously evaluated with the cyclic voltammetry.

Electrical Communication between Electrodes and Enzymes Mediated by Redox Hydrogels.

Different redox polymers based on poly(allylamine) with covalently attached ferrocene and pyridine groups that coordinate iron and ruthenium complexes were prepared, and hydrogels were obtained by cross-linking them with epichlorohydrin. Charge propagation from the underlying electrode, through the redox polymer and electrical communication with the enzyme FADH(2) of glucose oxidase, was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The effects of electrolyte composition, concentration of enzyme and substrate, and electrode potential are reported. The role of different redox mediators covalently attached to the polymer backbone is discussed in terms of driving force and electrostatic barriers.