System Bits: March 1

Quantum dot solids; cell-sorting diagnostics; cell phone molecule counting.

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Current generation silicon wafer
While the single-crystal silicon wafer changed the nature of communication 60 years ago, a group of Cornell researchers is now hoping its work with quantum dot solids can usher in a new era in electronics.

In what could be the first step toward discovering and developing artificial materials with controllable electronic structure, the team has fashioned 2D superstructures out of single-crystal building blocks: Through a pair of chemical processes, the lead-selenium nanocrystals are synthesized into larger crystals, then fused together to form atomically coherent square superlattices.

They said the difference between these and previous crystalline structures is the atomic coherence of each 5nm crystal, as they’re not connected by a substance between each crystal; they’re connected to each other.

Further, the researchers said electrical properties of these superstructures could be superior to existing semiconductor nanocrystals, and they anticipate their use in energy absorption and light emission.

Magnetic ratcheting system could help prepare medical therapies
In a development that could lead to a simple, rapid automation of cell analysis, as well as an easier way to separate therapeutic cells from non-therapeutic or contaminating cells, researchers at UCLA have developed a new way to separate and organize cells suspended in fluid samples by their subtle biochemical differences.

Cell sorting is widely used in life sciences research and in diagnostic and industrial processing, such as to isolate progenitor or stem cells from tissues or in vitro cultures that can be delivered back to a patient to heal injuries or attack tumor cells. The magnetic ratcheting system developed at UCLA can distinguish between subtly different cells so that only the correct, therapeutic cells are used for treatments.

Progressively spaced micropillars in the new magnetic ratcheting system for sorting cells. (Source: UCLA)

Progressively spaced micropillars in the new magnetic ratcheting system for sorting cells.
(Source: UCLA)

The system consists of a microchip of permalloy micropillar arrays with increasing lateral pitch and a mechatronic device to generate a cycling magnetic field. Particles with higher iron oxide content separate and equilibrate along the miropillar array at larger pitches.

The researchers see this magnetic ratcheting technology as a new approach to an automated system that could fit on a glass chip, known as a “lab on a chip,” where samples such as blood could be rapidly analyzed with resolutions as fine as single cells.

Counting molecules with a cell phone
To help bring emerging diagnostic capabilities out of laboratories and to the point of care, researchers in the lab of Rustem Ismagilov, Caltech’s Ethel Wilson Bowles and Robert Bowles Professor of Chemistry and Chemical Engineering and director of the Jacobs Institute for Molecular Engineering for Medicine, are inventing new technologies including diagnostic devices in which the results are robust against a variety of environmental conditions and user errors.

To address this need, the researchers have invented a new visual readout method that uses analytical chemistries and image processing to provide unambiguous quantification of single nucleic-acid molecules that can be performed by any cell-phone camera.

The work utilizes a microfluidic technology called SlipChip, which was invented in the Ismagilov lab several years ago. A SlipChip serves as a portable lab-on-a-chip and can be used to quantify concentrations of single molecules. Each SlipChip encodes a complex program for isolating single molecules (such as DNA or RNA) along with chemical reactants in nanoliter-sized wells. The program also controls the complex reactions in each well: the chip consists of two plates that move—or “slip”—relative to one another, with each “slip” joining or separating the hundreds or even thousands of tiny wells, either bringing reactants and molecules into contact or isolating them. The architecture of the chip enables the user to have complete control over these chemical reactions and can prevent contamination, making it an ideal platform for a user-friendly, robust diagnostic device, the researchers asserted.

Interestingly, the visual readout method builds upon this SlipChip platform: Special indicator chemistries are integrated into the wells of the SlipChip device such that after an amplification reaction—a reaction that multiplies nucleic-acid molecules—wells change color depending on whether the reaction in it was positive or negative—and the readout process can be used with any cell phone camera.

Wells turn blue if a particular nucleic acid molecule is present. A cell-phone image of the wells can then undergo ratiometric spectral processing to provide a quantification of target molecules. (Source: Ismagilov Lab)

Wells turn blue if a particular nucleic acid molecule is present. A cell-phone image of the wells can then undergo ratiometric spectral processing to provide a quantification of target molecules.
(Source: Ismagilov Lab)