Many transfection techniques can deliver biomolecules into cells, but the dose cannot be controlled precisely. Delivering well-defined amounts of materials into cells is important for various biological studies and therapeutic applications. Here, we show that nanochannel electroporation can deliver precise amounts of a variety of transfection agents into living cells. The device consists of two microchannels connected by a nanochannel. The cell to be transfected is positioned in one microchannel using optical tweezers, and the transfection agent is located in the second microchannel. Delivering a voltage pulse between the microchannels produces an intense electric field over a very small area on the cell membrane, allowing a precise amount of transfection agent to be electrophoretically driven through the nanochannel, the cell membrane and into the cell cytoplasm, without affecting cell viability. Dose control is achieved by adjusting the duration and number of pulses. The nanochannel electroporation device is expected to have high-throughput delivery applications.

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We have trapped single molecular ions in a precision Penning trap and, using cyclotron resonance techniques, have measured the mass ratio M(CO + )/M(N2 + ) to be 0.999 598 8876(4). Accuracy is limited at 4xl0~1 0 predominantly by temporal instability in the magnetic field. All other systematic sources of error are AM/M^S 10 ~1 0 . PACS numbers: 35.10.Bg, 07.75.+hThe Penning trap, with its strong uniform magnetic field and its much weaker electric field, has been used to perform a number of very accurate quantitative experiments. 1-4 We have used a Penning trap for mass spectroscopy using single-ion cyclotron resonance (SICR). The absence of ion-ion interaction makes systematics easy to understand; hence SICR is the most accurate method of comparing mass. The AM/M-4x 10 ~1 0 result reported here, limited predominantly by the temporal drift in the magnetic field, is a factor of 6 better than the value from current tables, 5 and may be the most accurate ion mass comparison to date.A hyperbolic Penning trap 6 consists of three main electrodes, all hyperbolic surfaces of rotation, which provide a restoring electric field which is linear with displacement along the axis of rotation. The much stronger axial magnetic field confines the particle radially. For a single charged particle there are three normal modes, one (the "axial" mode) that is aligned with the magnetic field, and two perpendicular to it. The perpendicular ("radial") modes are the electric field-modified cyclotron motion at frequency v' c and the slower magnetron orbit, due basically toExB drift.The ratio of the cyclotron frequencies for two different ion species, when corrected for electric field effects, is simply the inverse of their mass ratio. Our approach, then, is to compare the cyclotron frequencies of alternately loaded single ions. For an M -28 amu ion, the cyclotron, axial, and magnetron frequencies in our trap are, respectively, v^4.5 MHz, v z = 160 kHz, and v m ^2.8 kHz.Our trap hangs vertically in the bore of an 8.5-T superconducting Oxford magnet. The magnet has superconducting shims and a custom Dewar in the bore which allows us to cycle the trap from room temperature to 4.2 K while keeping the magnet itself cold. The main electrodes are precision-machined oxygen-free high-conductivity copper, plated with gold and coated with a layer of graphite particles (Aquadag) to minimize surface patch effects. The three main electrodes are spaced by machinable ceramic (MACOR) rings on which are painted guard ring electrodes, used to shim out higher-

Neutral sodium atoms have been continuously loaded into a 0. 1-k-deep superconducting magnetic trap with laser light used to slow and stop them. At least 1x10 atoms were trapped with a decay time of 2 -, ' min. The fluorescence of the trapped atoms was studied as a function of time; possible loss mechanisms from the trap are discussed.PACS numbers: 32.80.PjTrapping neutral atoms and cooling them to microkelvin temperatures will make possible a variety of experiments including precision spectroscopy, atomic collision studies in the s-wave-only regime, and studies of collective behavior including, possibly, Bose condensation. This Letter reports several important advances toward the accomplishment of such experiments. We have continuously stopped thermal sodium atoms with laser light and continuously loaded them into a 0. 1-K-deep superconducting magnetic trap. The continuous loading process has allowed us to accumulate up to 1&10 trapped atoms. This is 4 orders of magnitude more than for the previous magnetic trapping results of Migdall et al. , ' and 6 orders of magnitude more than Chu et al. obtained with use of an optical trap. We have observed trapping times of up to 2 -, ' min. -2 orders of magnitude greater than in these previous experiments -and studied the fluorescence of the trapped atoms. These increases in trapping time and number of trapped atoms will permit useful experiments with the trapped atoms for the first time. The trap has the added feature of having a uniform magnetic field at its bottom, opening up the possibility of precision spectroscopy of the trapped atoms.The arrangement of longitudinal magnetic fields, laser beams, and fluorescence detectors used in our experiment is shown in Fig. 1. The magnetic fields are generated by superconducting magnets operated in a persistent mode.

Enhanced glioma-stem-cell (GSC) motility and therapy resistance are considered to play key roles in tumor cell dissemination and recurrence. As such, a better understanding of the mechanisms by which these cells disseminate and withstand therapy could lead to more efficacious treatments. Here, we introduce a novel micro-/nanotechnology-enabled chip platform for performing live-cell interrogation of patient-derived GSCs with single-clone resolution. On-chip analysis revealed marked intertumoral differences (>10-fold) in single-clone motility profiles between two populations of GSCs, which correlated well with results from tumor-xenograft experiments and gene-expression analyses. Further chip-based examination of the more-aggressive GSC population revealed pronounced interclonal variations in motility capabilities (up to ∼4-fold) as well as gene-expression profiles at the single-cell level. Chip-supported therapy resistance studies with a chemotherapeutic agent (i.e., temozolomide) and an oligo RNA (anti-miR363) revealed a subpopulation of CD44-high GSCs with strong antiapoptotic behavior as well as enhanced motility capabilities. The living-cell-interrogation chip platform described herein enables thorough and large-scale live monitoring of heterogeneous cancer-cell populations with single-cell resolution, which is not achievable by any other existing technology and thus has the potential to provide new insights into the cellular and molecular mechanisms modulating glioma-stem-cell dissemination and therapy resistance.