RESUMEN
The detection of small numbers of magnetic spins is a significant challenge in the life, physical and chemical sciences, especially when room temperature operation is required. Here we show that a proximal nitrogen-vacancy spin ensemble serves as a high precision sensing and imaging array. Monitoring its longitudinal relaxation enables sensing of freely diffusing, unperturbed magnetic ions and molecules in a microfluidic device without applying external magnetic fields. Multiplexed charge-coupled device acquisition and an optimized detection scheme permits direct spin noise imaging of magnetically labelled cellular structures under ambient conditions. Within 20 s we achieve spatial resolutions below 500 nm and experimental sensitivities down to 1,000 statistically polarized spins, of which only 32 ions contribute to a net magnetization. The results mark a major step towards versatile sub-cellular magnetic imaging and real-time spin sensing under physiological conditions providing a minimally invasive tool to monitor ion channels or haemoglobin trafficking inside live cells.
RESUMEN
We present a solid state magnetic field imaging technique using a two-dimensional array of spins in diamond. The magnetic sensing spin array is made of nitrogen vacancy (NV) centers created at shallow depths. Their optical response is used for measuring external magnetic fields in close proximity. Optically detected magnetic resonance is read out from a 60 x 60 microm(2) field of view in a multiplexed manner using a charge coupled device camera. We experimentally demonstrate full two-dimensional vector imaging of the magnetic field produced by a pair of current carrying microwires. The presented wide-field NV magnetometer offers, in addition to its high magnetic sensitivity and vector reconstruction, an unprecedented spatiotemporal resolution and functionality at room temperature.
Asunto(s)
Magnetismo/métodos , Simulación por Computador , Instalación Eléctrica , Electrónica/métodos , Fluorescencia , Microtecnología/instrumentación , Método de Montecarlo , Nitrógeno/química , Óptica y Fotónica/métodos , Programas Informáticos , Marcadores de Spin , Temperatura , Factores de TiempoRESUMEN
In the last decade, the structures of many components of the photosynthetic apparatus of purple bacteria, as well as the mutual organization of these components within the purple membrane, were resolved. One key question that emerged concerned the assembly of the core complex consisting of the reaction center (RC) and the light-harvesting 1 (LH1) complex. In some species, like Rhodobacter sphaeroides, the ring-shaped LH1 complex was found to be open, whereas other species, like Rhodospirillum rubrum, have a closed ring surrounding the reaction center. This poses the question of how the ubiquinone molecule that transports electrons and protons from the RC to the cytochrome bc(1) complex overcomes the apparent barrier of the LH1 ring. In this study, we investigated how, in the case of a closed LH1 ring, the ubiquinone molecule diffuses through the LH1 ring. For this purpose, the LH1 structure of R. rubrum was modeled and the potential of mean force along the diffusion pathway through the LH1 was determined by steered molecular-dynamics simulations. The potential was reconstructed using the fluctuation theorem in combination with the stiff spring approximation. An upper limit for the mean first-passage time for diffusion of ubiquinone through the LH1 ring, based on a worst-case scenario potential, was calculated as approximately 8 x 10(-3) s, which is still in agreement with known turnover rates of RC and RC-LH1 complexes in the range of approximately 1000 Hz.
Asunto(s)
Rhodospirillum rubrum/metabolismo , Ubiquinona/química , Transporte Biológico , Simulación por Computador , Electrones , Complejos de Proteína Captadores de Luz , Membrana Dobles de Lípidos/química , Modelos Químicos , Modelos Moleculares , Modelos Estadísticos , Conformación Molecular , Fosfatidilcolinas/química , Conformación Proteica , ProtonesRESUMEN
Low values obtained in the microbiological assay of serum folate are often due to the presence of antibiotics in the test serum. The assay has been modified to permit consistent recognition of the presence and extent of such contamination. Other assay variables have been investigated and a quality control system devised which rapidly identifies the presence of inconsistencies in any one assay batch. The system further allows for the reporting of some clinically useful results from an imperfect assay batch thus reducing the necessity for reassay of some test sera.
