%0 Journal Article %J Journal of Magnetic Resonance %D 2007 %T Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal %A Garcia, S. %A Chavez, L. %A Lowery, T. J. %A Han, S. I. %A Wemmer, D. E. %A Pines, A. %K resonance %X

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time. (c) 2006 Elsevier Inc. All rights reserved.

%B Journal of Magnetic Resonance %V 184 %P 72-77 %8 Jan %@ 1090-7807 %G English %U ://WOS:000243568900009 %N 1 %M WOS:000243568900009 %! Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal %R Doi 10.1016/J.Jmr.2006.09.010 %0 Journal Article %J Science %D 2002 %T Liquid-state NMR and scalar couplings in microtesla magnetic fields %A McDermott, R. %A Trabesinger, A. H. %A Mück, M. %A Hahn, E. L. %A Pines, A. %A Clarke, J. %K resonance %X

We obtained nuclear magnetic resonance (NMR) spectra of liquids in fields of a few microtesla, using prepolarization in fields of a few millitesta and detection with a dc superconducting quantum interference device (SQUID). Because the sensitivity of the SQUID is frequency independent, we enhanced both signal-to-noise ratio and spectral resolution by detecting the NMR signal in extremely tow magnetic fields, where the NMR tines become very narrow even for grossly inhomogeneous measurement fields. In the absence of chemical shifts, proton-phosphorous scalar (J) couplings have been detected, indicating the presence of specific covalent bonds. This observation opens the possibility for "pure J spectroscopy" as a diagnostic tool, for the detection of molecules in low magnetic fields.

%B Science %V 295 %P 2247-2249 %8 Mar 22 %@ 0036-8075 %G English %U ://WOS:000174561700039 %N 5563 %M WOS:000174561700039 %! Liquid-state NMR and scalar couplings in microtesla magnetic fields %R Doi 10.1126/Science.1069280 %0 Journal Article %J Science %D 1996 %T Enhancement of solution NMR and MRI with laser-polarized xenon %A Navon, G. %A Song, Y. Q. %A Room, T. %A Appelt, S. %A Taylor, R. E. %A Pines, A. %K resonance %X

Optical pumping with laser light can be used to polarize the nuclear spins of gaseous xenon-129. When hyperpolarized xenon-129 is dissolved in liquids, a time-dependent departure of the proton spin polarization from its thermal equilibrium is observed, The variation of the magnetization is an unexpected manifestation of the nuclear Overhauser effect, a consequence of cross-relaxation between the spins of solution protons and dissolved xenon-129. Time-resolved magnetic resonance images of both nuclei in solution show that the proton magnetization is selectively perturbed in regions containing spin-polarized xenon-129. This effect could find use in nuclear magnetic resonance spectroscopy of surfaces and proteins and in magnetic resonance imaging.

%B Science %V 271 %P 1848-1851 %8 Mar 29 %@ 0036-8075 %G English %U ://WOS:A1996UC77800041 %N 5257 %M WOS:A1996UC77800041 %! Enhancement of solution NMR and MRI with laser-polarized xenon %R Doi 10.1126/Science.271.5257.1848 %0 Journal Article %J Journal of Physical Chemistry %D 1994 %T Probing Cds Nanocrystal Surfaces with Laser-Polarized Xenon %A Bowers, C. R. %A Pietrass, T. %A Barash, E. %A Pines, A. %A Grubbs, R. K. %A Alivisatos, A. P. %K resonance %X

This paper describes the application of optically pumped xenon NMR to probe the surface of semiconductor nanocrystals by physisorption at 123 K. These experiments were made possible by using highly spin ordered Xe-129, prepared by optical pumping and spin exchange of a rubidium xenon gas mixture, to increase the NMR signal strength. CdS nanocrystals were prepared by regulated growth in inverse micelles and precipitated by surface derivatization with thiophenol. Nanocrystals of 11.8, 12.8, and 23 Angstrom radii with 26%, 63%, and 57% thiophenol surface coverage, respectively, were characterized. Within this sample parameter space, the Xe-129 spectra, recorded at varying xenon coverages, depended strongly on thiophenol surface coverage but were not sensitive to the crystallite size. In addition, the nanocrystals with low thiophenol coverage yielded a xenon line shape consisting of two components, interpreted as xenon signals arising from distinct surface domains. These domains are presumably formed by the aggregation of thiophenol molecules on the nanocrystal surface when the thiophenol coverage is incomplete, a model which is consistent with existing X-ray photoelectron spectroscopy and liquid state H-1 NMR data.

%B Journal of Physical Chemistry %V 98 %P 9400-9404 %8 Sep 22 %@ 0022-3654 %G English %U ://WOS:A1994PH55900008 %N 38 %M WOS:A1994PH55900008 %! Probing Cds Nanocrystal Surfaces with Laser-Polarized Xenon %R Doi 10.1021/J100089a008 %0 Journal Article %J Chemical Physics Letters %D 1993 %T Squid-Nqr of N-14 in Amino-Acids and Small Peptides %A Werner, U. %A Black, B. %A Ziegeweid, M. %A Pines, A. %K resonance %X

We present a technique for the study of nuclear quadrupole resonance of N-14 interacting with low electric field gradients as found, for example, in amino acids. A superconducting quantum interference device (SQUID) is used to detect directly small NMR signals via cross relaxation of the N-14 polarization to adjacent proton spins, eliminating the need for field cycling. When one nitrogen quadrupolar transition matches the proton Zeeman splitting, the remaining two quadrupolar transitions can be observed by sweeping a saturating rf field through resonance. In addition, signal enhancement by simultaneous excitation of two nitro n resonances helps to identify connected transitions.

%B Chemical Physics Letters %V 209 %P 17-21 %8 Jun 25 %@ 0009-2614 %G English %U ://WOS:A1993LH24600003 %N 1-2 %M WOS:A1993LH24600003 %! Squid-Nqr of N-14 in Amino-Acids and Small Peptides %R Doi 10.1016/0009-2614(93)87194-8