We report on a selective and nondestructive measurement of mRNA ͑messenger ribonucleic acid͒ expression levels within a living cell. We first modify an atomic force microscope tip to create a tapered nanoscale coaxial cable. Application of an ac ͑alternating potential͒ between the inner and outer electrodes of this cable creates a dielectrophoretic force attracting mRNA molecules toward the tip-end which is pretreated with gene specific primers. We selectively extracted and analyzed both high ͑ϳ2500͒ and extremely low ͑110͒ copy number mRNA from a living cell mRNA in less than 10 s. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3213343͔ Atomic force microscopes ͑AFMs͒ have been used for both injecting 1 and manipulating 2-5 molecules. We present initial results on the use of an AFM for determining very low and high copy number messenger ribonucleic acid ͑mRNA͒ expression levels within a living cell. The technique is based on the use of a modified AFM probe-a dielectrophoretic nanotweezer ͑DENT͒-for attracting mRNA molecules toward its end. It gives us the flexibility to extract mRNA from within compartments of a single cell-in our case the nucleus. The DENT can be viewed as a nanoscale, tapered, coaxial cable integrated into an AFM probe. Application of an ac electric field between the inner and outer electrodes of the DENT creates a large electric field gradient at the probe tip resulting in a dielectrophoretic attractive force on mRNA molecules. Selective mRNA extraction was achieved by combing the dielectrophoretic attractive force with chemical derivatization of the probe surface-using gene specific oligonucleotide primers tailored to hybridize specific target mRNAs of interest.DENTs were built using commercially available conical, highly doped ͑resistivity 4 -6 ⍀ cm͒ silicon AFM probes ͑k ϳ 1.5 N / m͒. We start by growing a 20 nm thick layer of thermal SiO 2 on the AFM probes. This serves to electrically insulate the entire silicon probe including the AFM cantilever and handling chip. In the second step, we e-beam evaporate a 10 nm titanium adhesion layer followed by a 20 nm film of platinum onto the side of the cantilever that contains the probe tip. In the final step, we polish the end of the Pt coated tip until the doped silicon tip is just exposed. The last step was performed by scanning the tip in contact with a flat sapphire surface for about 5 min using a loading force of 7.5ϫ 10 −7 N in the AFM setup. Figure 2͑a͒ shows the scanning electron micrograph of the tip in its final form.Chemical modification of the probe surface was achieved by immobilizing gene specific primers complementary to the mRNA of interest using standard biotinstreptavidin chemistry. 6 First the cantilevers were cleaned using solvents for 5 min and air dried. Next, the samples were transferred to an ultraviolet ͑UV͒ chamber and irradiated for 60-75 min. A mixture of 5% ͓aminopropyltriethoxysilane ͑APTES͔͒ in ethanol was prepared, the samples were immersed in the APTES solution for 3 h, then washed in 100% ethanol solution...

The current gold standard for detecting or quantifying target analytes from blood samples is the ELISA (enzyme-linked immunosorbent assay). The detection limit of ELISA is about 250 pg/ml. However, to quantify analytes that are related to various stages of tumors including early detection requires detecting well below the current limit of the ELISA test. For example, Interleukin 6 (IL-6) levels of early oral cancer patients are <100 pg/ml and the prostate specific antigen level of the early stage of prostate cancer is about 1 ng/ml. Further, it has been reported that there are significantly less than 1pg/mL of analytes in the early stage of tumors. Therefore, depending on the tumor type and the stage of the tumors, it is required to quantify various levels of analytes ranging from ng/ml to pg/ml. To accommodate these critical needs in the current diagnosis, there is a need for a technique that has a large dynamic range with an ability to detect extremely low levels of target analytes (

This study reports a sensitive, low-cost and speedy circulating microRNA (miRNA) detection method called iLluminate-miRNA, for potential clinical applications at point-of-care. The central component of the iLluminate-miRNA is the low-cost disposable device that has a combination of microscale and nanoscale metallic structures. These structures are powered with low energy (

Reactions between metals and chloride solutions have been shown to exhibit magnetic field fluctuations over a wide range of size and time scales. Power law behavior observed in these reactions is consistent with models said to exhibit self-organized criticality. Voltage fluctuations observed during the dissolution of magnesium and aluminum in copper chloride solution are qualitatively similar to the recorded magnetic signals. In this paper, distributions of voltage and magnetic peak sizes, noise spectra, and return times are compared for both reactions studied.

We present a plastic microfluidic device with integrated nanoscale magnetic traps (NSMTs) that separates magnetic from non-magnetic beads with high purity and throughput, and unprecedented enrichments. Numerical simulations indicate significantly higher localized magnetic field gradients than previously reported. We demonstrated >20 000-fold enrichment for 0.001% magnetic bead mixtures. Since we achieve high purity at all flow-rates tested, this is a robust, rapid, portable, and simple solution to sort target species from small volumes amenable for pointof-care applications. We used the NSMT in a 96 well format to extract DNA from small sample volumes for quantitative polymerase chain reaction (qPCR). V C 2013 American Institute of Physics.

We report on harmonic generation by budding yeast cells in response to a sinusoidal electric field, which is seen to be minimal when the field amplitude is less than a threshold value. Surprisingly, sodium metavanadate, an inhibitor of P-type ATPases reportedly responsible for nonlinear response in yeast, reduces the threshold field amplitude, increasing harmonic generation at low amplitudes while reducing it at large amplitudes, whereas the addition of glucose dramatically increases the production of even harmonics. Finally, a simple model is proposed to interpret the observed behavior.

We present an efficient and fast method for selective and localized electroporation of a single living cell from a population of millions to tens of cells using the modified tip of an atomic force microscope. Electroporation was observed in real time using an inverted microscope. This technique is proposed as a tool for efficient and controlled delivery of biomolecules, proteins, drugs, and genes.

Magnetic detection of the nonlinear response of cell suspensions to oscillating electrical fields is reported. It has been shown that H+-ATPase, which is located in plasma membrane of yeast cells, generates harmonics of the fundamental frequency when electrically excited at certain frequencies and field strengths. Electrode polarization may cause erroneous results, especially when using a conventional four-probe setup. In this letter we use highly sensitive superconducting quantum interference device magnetometers to detect the cells’ nonlinear response and to avoid electrode polarization effects. Experiments were carried out using yeast (Saccharomyces cerevisiae, 108cells∕ml) cells with excitation voltages and frequencies between 1–5V∕cm and 10–300 Hz, respectively.