Neuroscience

Imaging dopamine with MRI

Magnetic resonance imaging (MRI) is a powerful, noninvasive technology for studying the brain. But neurotransmitters such as dopamine have not been directly observed by MRI. Shapiro et al. now report the directed evolution of a MRI contrast agent specific for dopamine, based on the heme domain from a bacterial cytochrome. The probe allowed the researchers to image depolarization-triggered dopamine release in live animal brains.

Shapiro, M.G. et al. Nat. Biotechnol. 28, 264–270 (2010).

Chemical biology

More potent CALI reagents

Tools for inactivating protein function in cells, chromophore-assisted light inactivation (CALI) reagents, contain a protein-targeting moiety and a chromophore that generates singlet oxygen when irradiated with light. These tools, however, generally suffer from poor targeting efficiency and poor singlet oxygen generation. Lee et al. describe highly potent CALI reagents made by tacking a Ru(II)(tris-bipyridyl)2+ derivative, a very efficient photocatalyst for generating singlet oxygen, to a highly selective protein-targeting peptoid.

Lee, J. et al. Nat. Chem. 6, 258–260 (2010).

Spectroscopy

Introducing SHINERS

Surface-enhanced Raman scattering (SERS) is a useful approach for enhancing Raman signals by distributing metal nanoparticles over a surface, but the nanoparticles often stick to each other and to the material being studied. Li et al. now introduce shell-isolated, nanoparticle-enhanced Raman spectroscopy, or SHINERS. Gold nanoparticles are coated with an ultrathin alumina or silica shell; the nanoparticles are spread over the surface without sticking, yet they conform to the surface contours and facilitate single-molecule detection.

Li, J.F. et al. Nature 464, 392–395 (2010).

Imaging and visualization

New red fluorescent proteins

The titanium-sapphire lasers used in two-photon microscopy have low power output in the excitation wavelength range for red fluorescent proteins, limiting their application. Piatkevich et al. introduce two new monomeric red fluorescent proteins, named LSS-mKate1 and LSS-mKate2. These proteins have large Stokes shifts, allowing efficient excitation by titanium-sapphire lasers, in addition to high pH stability, photostability and rapid chromophore maturation, making them useful for multicolor intravital imaging.

Piatkevich, K.D. et al. Proc. Natl. Acad. Sci. USA 107, 5369–5374 (2010).

Cell biology

Levitating cell cultures

Souza et al. describe a method for three-dimensional tissue culture by magnetic cell levitation. The cells are incubated with a hydrogel made up of gold, magnetic iron oxide nanoparticles and bacteriophages. By controlling the magnetic field, the researchers can manipulate the three-dimensional geometry of the cell culture to better represent the in vivo tissue structure.

Souza, G.R. et al. Nat. Nanotechnol. 5, 291–296 (2010).