Of microchemistry and molecules: Electronic microfluidic device synthesizes biocompatible probes

The research team, led by Professors R. Michael van Dam and Pei Yuin Keng in UCLA’s Crump Institute for Molecular Imaging and Professor CJ Kim in the Mechanical and Aerospace Engineering Department, faced a particularly challenging issue in developing their digital microfluidic device and applying it to microscale chemical synthesis. “When working with organic solvents at small volume scales – especially those that are volatile – evaporation is a significant problem in the relatively open configuration of EWOD chips,” van Dam tells PhysOrg.com. “Unwanted evaporation can change concentrations, dry the sample, and so on, leading to imprecise control over the chemical process and low reproducibility of the chemistry. Our main challenge was in overcoming this effect.”

Controlling liquids via electrowetting is very attractive due to the absence of moving parts, as well as the ease of integrating droplet actuation with heating and sensing. “It had been shown a few years ago that organic solvents can be manipulated on the same chips as water droplets, although not exactly by pure electrowetting,” van Dam continues. “Indeed, we didn’t have any problems moving droplets. Rather, the main operational challenges we encountered were related to on-chip mixing of liquids with solid residues, and the well-controlled evaporation of solvents at temperatures above the solvent boiling point.” This is due to the fact that under such superheated conditions, liquids can undergo bumping – the bursting of droplets and loss of reagents out of the chip.

The team explored a number of ideas to address the issue of undesired evaporation during reaction steps. “Altering the chip and droplet geometry to limit evaporation was somewhat effective, but also adversely impacted the ability to evaporate solvents during steps where evaporation was actually desired,” van Dam explains. Replenishing the solvent by loading additional droplets is a promising approach – but other technical challenges would then need to be addressed, such as how to avoid a drop in reaction temperature when a new droplet is added, and how to effectively mix the incoming droplet with the existing reaction mixture.

“The real breakthrough in the application we presented was realizing that we could alter the solvent without encountering the same difficulties associated with doing so at the macroscale. Since our reaction volume is so small, we could effectively evaporate dimethyl sulfoxide (DMSO) – a very non-volatile solvent – at a modest temperature.” At the macroscale, DMSO is typically avoided because it is very difficult to remove quickly – a concern in certain applications where synthesis time is critical, such as synthesis of positron emission tomography (PET) probes – and more volatile solvents are selected instead. However, van Dam points out, for some applications, the length of time would be less critical – for example, chemical and pharmaceutical production processes can take days, weeks or months.

Moreover, adds van Dam, the team is developing several additional innovations to enhance the current experimental design. “One area we’re working on is increasing the level of automation,” van Dam illustrates. “Once the droplets of chemicals are on-chip, they’re manipulated electronically, so sophisticated sequences of operations can readily be automated. In contrast,” he continues, “in our proof-of-concept synthesis chip, the necessary steps of adding reagents to the chip and extracting the final product are performed by pipetting or other manually-operated techniques. Increased overall automation is therefore critical to making the platform user-friendly and safe.

Another area of investigation is in situ sensing of liquid droplets. “With a very simple modification of the EWOD voltage driving circuit, it’s possible to monitor the AC current through the droplet, says van Dam. “This small current gives information about impedance, which in turn is related to droplet volume and composition. Other groups have shown how verifying that droplets have actually moved as instructed can increase the fidelity of on-chip assays and we’re planning to extend this principle to verify that the correct liquid is in the correct location and to perform real-time monitoring of chemical process variables.” This could be used, for example, to increase the reliability of on-chip microchemical production or provide an integrated readout for a chemical assay.

Van Dam also notes that microscale will eventually transition to nanoscale. “There are research efforts underway to shrink the size of electrodes and droplets handled by EWOD microfluidic devices to subnanoliter volumes. The microchemistry principles we presented could likely be scaled down to operate on these devices.”

On the other hand, van Dam points out that an in silico simulation model would be difficult to derive, given the current general lack of understanding of microscale chemistry in droplets. “For example,” he relates to PhysOrg, “one surprising result we observed was the need to use somewhat higher reagent concentrations in droplets compared to what is normally used at the macroscale to achieve comparable reaction yields. Our microchemistry platform could perhaps be used to study microscale chemistry and gather data that could lead to development of a simulation.”

One of the next steps in the group’s work is to increase the level of automation as mentioned above. “We envision a compact, benchtop system that, if loaded with the right reagents, could produce a variety of compounds on demand at the push of a button. We’re also pursuing applications of this device – in particular for the production of PET probes. Unlike most chemicals which can be produced in large batches and stored, these compounds are short-lived and require production just prior to use for medical imaging.” Currently, the production of PET probes requires expensive, complicated, and bulky equipment and infrastructure.

“Commercial networks of radiopharmacies have invested in this equipment and produce and ship the probes daily to supply hospitals, imaging centers, and research labs,” van Dam adds. “Making large batches that are divided among numerous customers provides economy of scale that makes these probes affordable, but at a cost – these radiopharmacies provide only a small number of different probes. But as we move into an era of personalized medicine, it will become increasingly important to have a diversity of diagnostic probes available so that patients can be matched to the correct drugs.” Compact, inexpensive, benchtop chemistry systems could be transformative, in that clinicians and researchers could afford to produce exactly the probes they want, when they want.

 Van Dam also points out that although these techniques have been demonstrated in the context of medical diagnostics, many different areas could also be served by performing microchemistry on EWOD. “Small scale chemistry could be useful to chemists doing natural products synthesis, where reagents and intermediates can be very costly due to the large number of reaction steps, and time, needed to produce them,” he adds. “It’s also likely that the ability to handle chemicals and organic solvents on-chip could lead to new assays in a variety of areas such as contaminant detection, environmental monitoring, and quality control in chemical production.” The techniques might also be useful for optofluidics due to the use of organic and high-index liquids in such devices.

“EWOD chips enable programmable control of liquids and thus a single chip design may be capable of supporting a wide range of reactions and assays with only software changes,” van Dam concludes. “By not having to produce a different chip for each application, cost could be substantially reduced.”

More information: Micro-chemical synthesis of molecular probes on an electronic microfluidic device. PNAS January 17, 2012 vol. 109 no. 3 690-695, doi: 10.1073/pnas.1117566109

Copyright 2012 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Chemists develop compounds capable of forming heath-resistant, economic and biocompatible gels

 Eating a yogurt or a jelly, using a pharmaceutical or cosmetic cream or shampoo... are just some of the numerous everyday actions in which we use gels developed through a process of gelation. Researchers from Universitat Jaume I have patented a new family of compounds that enables to develop gels more resistant to high temperatures with a higher level of biocompatibility and able to work with a variety of organic solvents, and all this with an easy synthesis, scalable and low cost.

This family of compounds has significant applications in industries such as pharmaceuticals and cosmetics or food industry, among others.

A jellifying agent is a substance that when is added to a liquid, transforms it into ice. When the liquid used is water, it is called hydrogel. But if the solvents used are organic compounds, they use organojellifying compounds such as the developed by the group Sustainable chemistry: supported reactants and catalysts. Supramolecular chemistry from the UJI, led by the chair professor Santiago Luis. 'Normally, when we develop a compound or family compounds able to form organogels, they only act in such a way in a very small number of solvents. The fundamental difference is that our group of compounds is capable of forming gels with a very high range of solvents', the researcher explains.

Another contribution of the compound is its ability to maintain stability at temperatures up to 100° C, thus allowing the products to keep their properties. In addition, the basic chemical structures that form compounds are amino acids, which provide products that are in most cases biocompatible. 'As they have units easily acceptable by the biological world, they don't have incompatibility, allergies or toxicities problems," Santiago Luis stresses.

To all these advantages, we have to add the fact that these compounds with a jellifying action at low concentrations are cheap.

Story Source:

The above story is reprinted from materials provided by Universitat Jaume I.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Note: If no author is given, the source is cited instead.

Gallium nitride is non-toxic, biocompatible; holds promise for implants, research finds

 Researchers from North Carolina State University and Purdue University have shown that the semiconductor material gallium nitride (GaN) is non-toxic and is compatible with human cells -- opening the door to the material's use in a variety of biomedical implant technologies.

GaN is currently used in a host of technologies, from LED lighting to optic sensors, but it is not in widespread use in biomedical implants. However, the new findings from NC State and Purdue mean that GaN holds promise for an array of implantable technologies -- from electrodes used in neurostimulation therapies for Alzheimer's to transistors used to monitor blood chemistry.

"The first finding is that GaN, unlike other semiconductor materials that have been considered for biomedical implants, is not toxic. That minimizes risk to both the environment and to patients," says Dr. Albena Ivanisevic, who co-authored a paper describing the research. Ivanisevic is an associate professor of materials science and engineering at NC State and associate professor of the joint biomedical engineering program at NC State and the University of North Carolina at Chapel Hill.

Researchers used a mass spectrometry technique to see how much gallium is released from GaN when the material is exposed to various environments that mimic conditions in the human body. This is important because gallium oxides are toxic. But the researchers found that GaN is very stable in these environments -- releasing such a tiny amount of gallium that it is non-toxic.

The researchers also wanted to determine GaN's potential biocompatibility. To do this they bonded peptides -- the building blocks that make up proteins -- to the GaN material. Researchers then placed peptide-coated GaN and uncoated GaN into cell cultures to see how the material and the cells interacted.

Researchers found that the peptide-coated GaN bonded more effectively with the cells. Specifically, more cells bonded to the material and those cells spread over a larger area.

"This matters because we want materials that give us some control over cell behavior," Ivanisevic says. "For example, being able to make cells adhere to a material or to avoid it.

"One problem facing many biomedical implants, such as sensors, is that they can become coated with biological material in the body. We've shown that we can coat GaN with peptides that attract and bond with cells. That suggests that we may also be able to coat GaN with peptides that would help prevent cell growth -- and keep the implant 'clean.' Our next step will be to explore the use of such 'anti-fouling' peptides with GaN."

The paper, "Gallium Nitride is Biocompatible and Non-Toxic Before and After Functionalization with Peptides," is forthcoming from Acta Biomaterialia and was co-authored by Ph.D. students Scott A. Jewett and Matthew S. Makowski; undergraduate Benjamin Andrews; and Michael J. Manfra -- all of Purdue. The research was funded by the National Science Foundation.

NC State's Department of Materials Science and Engineering, and joint Department of Biomedical Engineering, are part of the university's College of Engineering.

Story Source:

The above story is reprinted from materials provided by North Carolina State University.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Scott A. Jewett, Matthew S. Makowski, Benjamin Andrews, Albena Ivanisevic, Michael J. Manfra. Gallium Nitride is Biocompatible and Non-Toxic Before and After Functionalization with Peptides. Acta Biomaterialia, 2011; DOI: 10.1016/j.actbio.2011.09.038

Click chemistry with copper -- a biocompatible version

Berkeley Lab researchers have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living cells.

Biomolecular imaging can reveal a great deal of information about the inner workings of cells and one of the most attractive targets for imaging are glycans – sugars that are ubiquitous to living organisms and abundant on cell surfaces. Imaging a glycan requires that it be tagged or labeled. One of the best techniques for doing this is a technique called click chemistry. The original version of click chemistry could only be used on cells in vitro, not in living organisms, because the technique involved catalysis with copper, which is toxic at high micromolar concentrations. A copper-free version of click chemistry that can safely be used in living organisms is available, but it is not always optimal in terms of reaction kinetics and target specificity. Now, a variation of click chemistry has been introduced that retains the copper catalyst of the original reaction - along with its speed and specificity – but is safe for cells in vivo.

Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the Albert Einstein College of Medicine at Yeshiva University in New York, have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living organisms. Compared to the copper-free click chemistry reaction, which can take up to an hour, the ligand-accelerated copper-catalyzed click chemistry reaction can achieve effective labeling within 3-5 minutes. The presence of the copper catalyst also enables this new formulation of click chemistry to be more target-specific with fewer background side reactions.

"The discovery of this new accelerating ligand for copper-catalyzed click chemistry should provide an effective complimentary tool to copper-free click chemistry," says Yi Liu, a chemist with Berkeley Lab's Molecular Foundry and the co-leader of this research with Peng Wu, of the Albert Einstein College of Medicine.

"While copper-free click chemistry may have advantages for whole animal imaging experiments such as imaging in mice," Liu says, "our ligand-accelerated copper reaction is better suited for enriching glycoproteins for their identification."

The ligand-accelerated copper-catalyzed reaction was used to label glycans in recombinant glycoproteins, glycoproteins in cell lysates, glycoproteins on live cell surfaces, and glycoconjugates in live zebrafish embryos. Because a zebrafish embryo is transparent in the first 24 hours of its development, it allows labeled glycans to be detected via molecular imaging techniques, making it a highly useful model for developmental biology studies.

"Based on our results," says Peng Wu, "we believe that ligand-accelerated copper-catalyzed click chemistry represents a powerful and highly adaptive bioconjugation tool that holds great promise for further improvement with the discovery of more versatile catalyst systems."

Click chemistry, which was introduced in 2002 by the Nobel laureate chemist Barry Sharpless of the Scripps Research Institute, utilizes a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction that makes it possible for certain chemical building blocks to "click" together in an irreversible linkage, analogous to the snapping together of Lego blocks. While the technique immediately proved valuable for attaching small molecular probes to various biomolecules in a test tube or on fixed cells, it could not be used for biomolecule labeling in live cells or organisms because of the copper catalyst.

In 2007, Carolyn Bertozzi, a chemist who holds joint appointments with Berkeley Lab, the University of California (UC) Berkeley, and the Howard Hughes Medical Institute, led a research effort that produced a copper-free version of click chemistry. In this version, glycans were metabolically labeled with azides - a functional group featuring three nitrogen atoms - via reactions that were carried out through the use of cyclooctyne reagents that required no copper catalyst. With their latest reagent, biarylazacyclooctynone (BARAC), Bertozzi and her group have provided a copper-free click chemistry technique that delivers relatively fast reaction kinetics and the bioorthogonality needed for biomolecule labeling. However, the technique can only be used on biomolecules that can be tagged with azides.

"Our bio-benign ligand-accelerated copper-catalyzed click chemistry reaction liberates bioconjugation from the limitation where ligations could only be accomplished with azide-tagged biomolecules," Liu says. "Now terminal alkyne residues can also be incorporated into biomolecules and detected in vivo."

Provided by Lawrence Berkeley National Laboratory (news : web)

Click chemistry with copper: A biocompatible version

Biomolecular imaging can reveal a great deal of information about the inner workings of cells and one of the most attractive targets for imaging are glycans -- sugars that are ubiquitous to living organisms and abundant on cell surfaces. Imaging a glycan requires that it be tagged or labeled. One of the best techniques for doing this is a technique called click chemistry. The original version of click chemistry could only be used on cells in vitro, not in living organisms, because the technique involved catalysis with copper, which is toxic at high micromolar concentrations.

A copper-free version of click chemistry that can safely be used in living organisms is available, but it is not always optimal in terms of reaction kinetics and target specificity. Now, a variation of click chemistry has been introduced that retains the copper catalyst of the original reaction -- along with its speed and specificity -- but is safe for cells in vivo.

Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the Albert Einstein College of Medicine at Yeshiva University in New York, have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living organisms. Compared to the copper-free click chemistry reaction, which can take up to an hour, the ligand-accelerated copper-catalyzed click chemistry reaction can achieve effective labeling within 3-5 minutes. The presence of the copper catalyst also enables this new formulation of click chemistry to be more target-specific with fewer background side reactions.

"The discovery of this new accelerating ligand for copper-catalyzed click chemistry should provide an effective complimentary tool to copper-free click chemistry," says Yi Liu, a chemist with Berkeley Lab's Molecular Foundry and the co-leader of this research with Peng Wu, of the Albert Einstein College of Medicine.

"While copper-free click chemistry may have advantages for whole animal imaging experiments such as imaging in mice," Liu says, "our ligand-accelerated copper reaction is better suited for enriching glycoproteins for their identification."

The ligand-accelerated copper-catalyzed reaction was used to label glycans in recombinant glycoproteins, glycoproteins in cell lysates, glycoproteins on live cell surfaces, and glycoconjugates in live zebrafish embryos. Because a zebrafish embryo is transparent in the first 24 hours of its development, it allows labeled glycans to be detected via molecular imaging techniques, making it a highly useful model for developmental biology studies.

"Based on our results," says Peng Wu, "we believe that ligand-accelerated copper-catalyzed click chemistry represents a powerful and highly adaptive bioconjugation tool that holds great promise for further improvement with the discovery of more versatile catalyst systems."

Click chemistry, which was introduced in 2002 by the Nobel laureate chemist Barry Sharpless of the Scripps Research Institute, utilizes a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction that makes it possible for certain chemical building blocks to "click" together in an irreversible linkage, analogous to the snapping together of Lego blocks. While the technique immediately proved valuable for attaching small molecular probes to various biomolecules in a test tube or on fixed cells, it could not be used for biomolecule labeling in live cells or organisms because of the copper catalyst.

In 2007, Carolyn Bertozzi, a chemist who holds joint appointments with Berkeley Lab, the University of California (UC) Berkeley, and the Howard Hughes Medical Institute, led a research effort that produced a copper-free version of click chemistry. In this version, glycans were metabolically labeled with azides -- a functional group featuring three nitrogen atoms -- via reactions that were carried out through the use of cyclooctyne reagents that required no copper catalyst. With their latest reagent, biarylazacyclooctynone (BARAC), Bertozzi and her group have provided a copper-free click chemistry technique that delivers relatively fast reaction kinetics and the bioorthogonality needed for biomolecule labeling. However, the technique can only be used on biomolecules that can be tagged with azides.

"Our bio-benign ligand-accelerated copper-catalyzed click chemistry reaction liberates bioconjugation from the limitation where ligations could only be accomplished with azide-tagged biomolecules," Liu says. "Now terminal alkyne residues can also be incorporated into biomolecules and detected in vivo."

This work was supported by a grant from the National Institutes of Health, and in part as a User Project at the Molecular Foundry, which is funded through DOE's Office of Science.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Christen Besanceney-Webler, Hao Jiang, Tianqing Zheng, Lei Feng, David Soriano del Amo, Wei Wang, Liana M. Klivansky, Florence L. Marlow, Yi Liu, Peng Wu. Increasing the Efficacy of Bioorthogonal Click Reactions for Bioconjugation: A Comparative Study. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201101817

Soft memory device opens door to new biocompatible electronics

 Researchers from North Carolina State University have developed a memory device that is soft and functions well in wet environments -- opening the door to a new generation of biocompatible electronic devices.

"We've created a memory device with the physical properties of Jell-O," says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper describing the research.

Conventional electronics are typically made of rigid, brittle materials and don't function well in a wet environment. "Our memory device is soft and pliable, and functions extremely well in wet environments -- similar to the human brain," Dickey says.

Prototypes of the device have not yet been optimized to hold significant amounts of memory, but work well in environments that would be hostile to traditional electronics. The devices are made using a liquid alloy of gallium and indium metals set into water-based gels, similar to gels used in biological research.

The device's ability to function in wet environments, and the biocompatibility of the gels, mean that this technology holds promise for interfacing electronics with biological systems -- such as cells, enzymes or tissue. "These properties may be used for biological sensors or for medical monitoring," Dickey says.

The device functions much like so-called "memristors," which are vaunted as a possible next-generation memory technology. The individual components of the "mushy" memory device have two states: one that conducts electricity and one that does not. These two states can be used to represent the 1s and 0s used in binary language. Most conventional electronics use electrons to create these 1s and 0s in computer chips. The mushy memory device uses charged molecules called ions to do the same thing.

In each of the memory device's circuits, the metal alloy is the circuit's electrode and sits on either side of a conductive piece of gel. When the alloy electrode is exposed to a positive charge it creates an oxidized skin that makes it resistive to electricity. We'll call that the 0. When the electrode is exposed to a negative charge, the oxidized skin disappears, and it becomes conducive to electricity. We'll call that the 1.

Normally, whenever a negative charge is applied to one side of the electrode, the positive charge would move to the other side and create another oxidized skin -- meaning the electrode would always be resistive. To solve that problem, the researchers "doped" one side of the gel slab with a polymer that prevents the formation of a stable oxidized skin. That way one electrode is always conducive -- giving the device the 1s and 0s it needs for electronic memory.

The paper was published online July 4 by Advanced Materials. The paper was co-authored by NC State Ph.D. students Hyung-Jun Koo and Ju-Hee So, and NC State INVISTA Professor of Chemical and Biomolecular Engineering Orlin Velev. The research was supported by the National Science Foundation and the U.S. Department of Energy.

NC State's Department of Chemical and Biomolecular Engineering is part of the university's College of Engineering.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by North Carolina State University.

Journal Reference:

Hyung-Jun Koo, Ju-Hee So, Michael D. Dickey, Orlin D. Velev. Towards All-Soft Matter Circuits: Prototypes of Quasi-Liquid Devices with Memristor Characteristics. Advanced Materials, 2011; DOI: 10.1002/adma.201101257