Paper spray ionization devices for direct, biomedical analysis using mass spectrometry.

Paper spray ionization has been developed as a direct, fast and low-cost sampling and ionization method for qualitative and quantitative mass spectrometric (MS) analysis of complex mixtures. Analyte ions are generated by applying a high voltage and a small volume (~10 µL) of spray solvent onto a porous substrate. The sample can be preloaded onto the paper or mixed into the spray solution. The geometry of the paper and the method of supplying the necessary internal standard are important factors that affect the ionization efficiency and subsequently the sensitivity and quantitation accuracy of the analytical data. As the cut angle of the paper tip is changed, the spray plume, the total spray current and the electric field intensity at the tip all vary correspondingly, with resulting differences in signal intensity. Sample load is another important factor for obtaining a stable MS signal and accurate quantitative results. The optimal sample load was found to be dependent on the paper size. The dissolution and spray process was also investigated and analyte transfer on paper was shown to be largely associated with bulk solution flow towards the spray tip. The information gathered from these systematic studies provides guidance for the design and optimization of a disposable sample cartridge for paper spray MS, a device which potentially is suitable for fast clinical analysis, especially for point-of-care diagnostics.

Circular arrays of polymer-based miniature rectilinear ion traps.

The design and operation of an annular array of parallel, miniature rectilinear ion traps (RITs) is discussed. Stereolithography apparatus (SLA), a previously validated method for ion trap fabrication, was applied here to construct an array of mass analyzers and their mounting hardware. Two versions of the array were tested, using either six or twelve stretched RITs (x0 = 1.66 mm, y0 = 1.33 mm, z = 16.66 mm) mounted in parallel about the circumference of a circle with the interior and exterior x-electrode planes oriented tangential to the inner and outer annulus rings, respectively. The arrangement of the ion traps is such that the ions are radially ejected just above the throat of a centrally located electron multiplier detector into which they are accelerated. The mass analyzer array was mounted in a custom vacuum manifold. The resolution, mass-to-charge ratio (m/z) range, and MS/MS capabilities were tested using electrospray ionization (ESI). The devices were tested in two configurations: (i) separate ion sources for each trap, and (ii) a single ion source for the entire array.

Halo ion trap mass spectrometer.

We describe a novel radio frequency ion trap mass analyzer based on toroidal trapping geometry and microfabrication technology. The device, called the halo ion trap, consists of two parallel ceramic plates, the facing surfaces of which are imprinted with sets of concentric ring electrodes. Radii of the imprinted rings range from 5 to 12 mm, and the spacing between the plates is 4 mm. Unlike conventional ion traps, in which hyperbolic metal electrodes establish equipotential boundary conditions, electric fields in the halo ion trap are established by applying different radio frequency potentials to each ring. The potential on each ring can be independently optimized to provide the best trapping field. The halo ion trap features an open structure, allowing easy access for in situ ionization. The toroidal geometry provides a large trapping and analyzing volume, increasing the number of ions that can be stored and reducing the effects of space-charge on mass analysis. Preliminary mass spectra show resolution (m/Deltam) of 60-75 when the trap is operated at 1.9 MHz and 500 Vp-p.

Magneto-optical observation of picosecond dynamics of single nanomagnets.

We report measurements of picosecond dynamics of individual nickel nanomagnets as a function of magnet dimension, aspect ratio, and magnetic environment. Spatial sensitivity to nanomagnet diameters as small as 125 nm is achieved by use of cavity enhancement of the magneto-optic Kerr effect (CE-MOKE). The importance of single-particle measurements without ensemble effects for extracting the size dependence of the intrinsic nanomagnet material properties is demonstrated.