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Engineered Pacifier Measures Glucose in Saliva

Pacifiers can soothe fussy babies and help keep parents sane. Now researchers have turned these baby care must-haves into high-tech sensors that could track levels of glucose and other chemicals in a baby’s saliva.

Monitoring sick or preterm babies can be difficult. Keeping tab on infants’ vital signs typically requires rigid electrodes stuck to babies’ sensitive skin and connected to monitors via a tangle of wires. Measuring blood levels of chemicals like glucose, lactate, and sodium, meanwhile, means pricking the heel or an intravenous blood draw.

Wireless non-invasive technologies offer a gentler touch. Researchers have recently tested soft, tattoo-like wireless sensors that can measure blood oxygen levels, heart and breathing rate, and temperature. Other technologies already on the market include a smart sock that can monitor heart rate and oxygen levels, and temperature-tracking Bluetooth pacifiers.

But all these devices measure physical parameters, says Joseph Wang, a nanoengineer at the University of California San Diego. “Our pacifier is the first example of a device that measures chemistry markers.”

Wang, Alberto Escarpa of the University of Alcalá, and colleagues made the binky biosensor by combining silicone nipples from commercial pacifiers with a custom 3-D printed back end that contains an electrochemical sensor. “The beauty of this pacifier is that everything electronic is outside the mouth so it’s very baby friendly,” Wang says, and the electronics add unnoticeable weight.

They bored a 4 mm wide channel in the silicone nipple and inserted a small PVC tube into it. The tube contains a series of three polystyrene valves shaped like pipette tips that keep saliva from flowing back into the baby’s mouth.

Sucking squeezes the nipple, drawing in saliva and forcing it to the back of the tube. There, behind the mouthpiece, it drops into a small 3-D printed chamber in the pacifier cap where it contacts the tip of a disposable electrode coated with an enzyme that oxidizes glucose. This reaction changes the electric current in proportion to glucose levels.

The back side of the electrode strip connects to electronics in the pacifier cap that measure the current and transmit the data to a smartphone using Bluetooth signals. Putting a different enzyme on the electrode tip could allow the pacifier to measure other chemical biomarkers, Wang says.

The researchers haven’t tested the pacifier on infants yet. With an adult volunteer using the pacifier, it took about five minutes for the saliva to contact the enzyme and the device to generate the glucose signal. The team also tested the device by squeezing saliva samples into the tube manually. They used samples from before and after a meal in four people with type I diabetes. The measurements closely matched those from a glucose sensor using fingertip blood.

The pacifier sensor faces several challenges before it can be used in hospitals. For one, it could be prone to getting dirty. Protective coatings could help keep the saliva-collecting channel and chamber bacteria-free, the researchers say. To make it safe for babies, they also plan to integrate the valves into a single-piece silicone nipple so that there are no small ingestible pieces.

“I think this is a highly innovative approach that could impact the personalized healthcare of babies,” says Wei Gao, a medical engineer at the California Institute of Technology. He says that the technique could be adapted into other types of portable biosensors to analyze saliva in elderly patients with chronic diseases. It could, for instance, be turned into a single-use device that adults can spit on for rapid screening of chemicals in saliva, Wang says.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on October 16, 2019.

Adhesive Tape–Based Method Could Help Screen Skin Cells for Melanoma

Melanoma is the deadliest form of skin cancer and not something on which dermatologists like to take chances. When they see a suspicious-looking mole on the tip of a patient’s nose, they biopsy it and send it off for testing. But those biopsies come back negative at least 75% of the time—good news, but at the price of a snip and occasional scar. Now, researchers are aiming to decrease the need for biopsies by turning to a screening method that uses adhesive tape. The tape pulls off a layer of cells and then gets put through a scanning electrochemical microscope (SECM) to check for a known melanoma biomarker.

One company, DermTech, currently markets an adhesive tape to physicians that screens for melanoma via known genetic mutations. But once the sample is collected, the tape must be mailed to a lab where the cells are removed and tested for overexpression of melanoma-specific genes. Also, this approach loses all information about size and shape of the tumors. The new approach, says Hubert H. Girault of the Swiss Federal Institute of Technology, Lausanne, allows cells to stay in place on the tape, acting as a map of the skin’s surface.

Girault and his colleagues used the adhesive tape from DermTech, adhered it to the skin of mice with different stages of melanoma, circled the location of the lesions on the other side of the tape, and removed it. Then, they created a labeling system to tag tyrosinase, an enzyme that is overexpressed in Stage II melanoma cells and present in high concentrations relative to noncancerous cells. The label links tyrosinase via two antibodies to an enzyme that catalyzes a redox reaction, the results of which can be picked up by the SECM’s sensor as it moves across the tape, indicating the exact location of the tyrosinase. The approach reliably identified Stage II melanomas in 10 out of 10 mice. Detection of earlier stage lesions, however, was less consistent.

Unlike DermTech’s approach, the SECM analysis preserves topological information from the tumors, Girault says. “Because we do imaging, we can see if the spot is growing and if it’s heterogeneous,” which is an indication that the cancer is advancing from one stage to the next. And although they used tape designed for removing skin cells for their analysis, Girault says, “Scotch tape works just as well.”

While that sounds good in principle, dermatologists are wary. “The technology is exciting, and I’m excited for it to grow and be validated to the point where it could reduce the number of biopsies,” says Ali Hendi, a dermatologist in Chevy Chase, Maryland, and author of the Atlas of Skin Cancers. He notes that there is room for such a screening test, but it needs to be proved extensively. “The gold standard is a biopsy,” he says. “The worst fear of a dermatologist is to miss a melanoma and for that melanoma to become advanced and kill a patient. To get around that, the test really has to be validated, and the false negative has to be really low.”

Screening technologies, particularly ones administered outside a clinic, say Hendi and other dermatologists, are no match for an in-person visit with a physician who knows what to look for and could quickly perform a biopsy or even a noninvasive exam such as dermatoscopy, a newer technique that uses polarized and nonpolarized light to examine skin surface structure and pigmentation.

In areas where dermatologists are in short supply and it takes months to get an appointment, however, the calculus changes. “In areas where access is an issue, it could be helpful,” says Vishal Patel, a dermatologist, and oncologist at the George Washington University School of Medicine and Health Sciences. But, he notes, “screening tests like this need to be administered by a clinician…not [performed] in lieu of one.”

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on October 14, 2019.

The First Fully Printed Electronics Roll Off Printers Ready to Use

Interest in printed electronics has surged in the past decade as a way to mass-produce RFID tags and sensors at a low cost. But printing digital logic devices on a substrate today involves multiple steps beyond the printer, such as rinsing or curing in an oven. Now, researchers have made the first fully printed transistors—ones that emerge from a printer with all of their components in place, ready to be used.

Work on printed circuitry typically has focused on inkjet printers, which use tiny nozzles to deposit ink droplets onto a substrate. The inks are suspensions of different materials—conductive nanoparticles, semiconducting carbon nanotubes, or insulating polymers—used to print different layers of thin-film transistors over several runs through the printer. But after printing, the process requires washing away unwanted materials and heating at high temperature to cure the insulating layer.

To get rid of those extra steps, Aaron D. Franklin, an electrical and computer engineer at Duke University, and his colleagues used a technique called aerosol jet printing. Their new process allows all of the steps to happen in place at the printer. Everything is done at temperatures less than 80 °C, which lets the researchers print transistors on paper.

Aerosol jet printing uses pressure and an inert gas to break up the ink into microscopic droplets “like aerosol hair spray,” Franklin says. “This makes it possible to print in smaller lines and to dry more rapidly because you are minimizing droplet size and the volume of background solvent.” That means less unwanted material to rinse off or evaporate outside a printer.

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Credit: Shiheng Lu/Duke University
A cross-section of a transistor printed with a new aerosol jet printing technique shows two electrode layers of silver nanowires (top and bottom) sandwiching an insulator layer printed with hexagonal boron nitride flakes (middle). There is no mixing of the layers, which is an issue with conventional printing methods.

The team first printed layers of carbon nanotubes on paper and plastic substrates to form the conductive channel of a transistor. Without removing the substrate from the printer, the researchers placed a few drops of toluene for 20 s on the substrate, gently warmed it at 80 °C, and blow-dried it with a nitrogen gun to remove excess material. Then they printed electrodes using water-based silver nanowire ink.

The next layer marked a key advance: printing a quality insulator film using an ink of 2-D hexagonal boron nitride (h-BN) flakes. “One of the most challenging areas for printed logic devices has been the development of a good, patterned insulator layer,” says Ioannis Kymissis, an electrical engineer at Columbia University who was not involved in the work.

Printed h-BN layers normally require baking at 180 °C for 2 h to create a smooth film with flat, well-arranged flakes that gives good insulating properties. And a critical concern is to avoid the mixing of the h-BN inks with the silver nanowire inks above and below, which would lead to defective transistors.

To overcome these problems, the Duke engineers added hydroxypropyl methylcellulose to their h-BN ink, which makes the ink thicker and keeps it from mixing with the silver nanowire layer below. The process, to their surprise, gave high-quality insulating h-BN layers that did not blend with the silver nanowires and did not need heating. The researchers believe the binder helps the microdroplets spread out and stick to the surface, laying down the flakes in a structured way as they are being printed. “This is an exciting discovery,” Franklin says.

Finally, the researchers printed the last electrode layer on top of the insulator and then tested the devices using standard current-voltage measurements. The devices maintained their performance after being bent 1,000 times.

The aerosol jet printing process isn’t fast enough for high-volume manufacturing, but it could be used to make custom, on-the-fly electronics or paper-based sensors. The method could also print biomolecules, Franklin says, to create a customized array of biosensors on an electronic bandage for monitoring a patient.

The fully printed, mechanically flexible devices show “outstanding overall performance,” Kymissis says, “and pulling all of this together makes for a significant advance in the field.”

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on October 07, 2019.

Single-Atom Switcheroo Yields Fluorescent Dyes Activated by Visible Light

Researchers have developed a simple method for making fluorescent dyes of many colors that can be activated by visible light. The method involves switching out a single oxygen atom in existing fluorescent dyes for a sulfur atom, which makes them photoactivatable. The approach provides a new set of tools for visualizing how proteins and other molecules behave in living cells without damaging tissue.

Today’s light microscopes are so powerful that they can track molecules at nanometer-scale resolution as a cell conducts its business. Researchers want to be able to turn fluorescent dyes on and off in order to selectively light up and track specific molecules over time in living cells. But scientists have struggled to capture these close-ups because the photoactivatable dyes commonly used for labeling molecules have some major limitations: the dyes can be bulky, so they can’t label smaller molecules with good resolution, and they need to be activated with high-energy laser light. The intense illumination damages DNA and mitochondria and causes proteins to cross-link. It also bleaches the fluorescence that the dyes deliver. So dyes that can be triggered with low-power visible light would be a boon for biological imaging in living tissue.

Previous work had shown that trading the carbonyl group for a thiocarbonyl group in a dye can quench fluorescence nearby. In the new study, Han Xiao, a chemist and bioengineer at Rice University, and his team demonstrated that if the thiocarbonyl group is incorporated into the conjugated system of an ordinary, nonphotoactivatable fluorescent dye, the dye can be photo-oxidized with visible light. Xiao and his team used a one-step chemical reaction involving a thionating agent called Lawesson’s reagent to switch the carbonyl group’s oxygen to sulfur, essentially suppressing the glow.

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Credit: J. Am. Chem. Soc.
A photoactivated red dye (bottom left) labels lipid droplets in a cell just like a commercial nonphotoactivatable green dye (top right). Brown shows the colocalization of the dyes (bottom right). Cell nuclei are stained blue.

Unleashing the fluorescence simply involves flashing a dye solution with low-intensity visible light of a wavelength the same or shorter than that emitted by the dye, Xiao explains. If the dye is red, for example, a red, green, or blue light would activate it. “The chemistry we are using is really simple,” Xiao says. The photoactivation requires just visible light and oxygen, which is present at sufficient levels naturally dissolved in saline buffer.

Xiao’s team used the approach to create light-activated versions of common red, green, blue, and purple dyes that can be made to target different biomolecules or parts of the cell. They used one of the dyes to visualize lipid droplets and another to mark specific sites within a protein. They also demonstrated that they could use two different dyes simultaneously to label different parts of a lipid droplet.

Luke D. Lavis, a biochemist at Janelia Research Campus, says he likes the paper because the fluorescence quenching is accomplished with substitution of a single atom, so the resulting molecule is small. Researchers could encode such a molecule into a protein that could then be made to fluoresce without using any additional reagents.

A huge variety of nonphotoactivatable dyes exist, and most of them should respond to this strategy, Xiao says. “The beauty of our chemistry is that you don’t need a really strong light source. You can use an LED you get from Amazon, and it works.”

Xiao’s team is continuing to make more dyes using the approach. They are also testing the strategy for near-infrared dyes, which can penetrate tissue more deeply.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on September 30, 2019.

Wetland Microbe Detoxifies PFAS Contaminants

Toxic fluorinated chemicals known as per- and polyfluoroalkyl substances (PFAS) have triggered a public health challenge due to their widespread contamination of drinking water. Some scientists have dubbed these compounds “forever chemicals” because they have been virtually immune to microbial degradation—until now. A new study reports that over a 100-day period in the lab, a wetland bacterium removed the fluorine atoms from up to 60% of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), rendering the substances harmless. The results offer the first glimpse that sites contaminated with PFAS could potentially be cleaned up using bioremediation.

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PFOA and PFOS are just two out of more than 4,700 fluorinated surfactants in the PFAS family. Manufacturers once used PFOA in firefighting foamsand to make Teflon. Companies also added PFOS to firefighting foams and stain repellents. US manufacturers phased out the two compounds after scientists linked them to cancer and endocrine disruption. But they remain the most common PFAS contaminating the environment, released into ground and surface water by the fluorochemical industries and the use of firefighting foams for training and to suppress fires.

With the US Environmental Protection Agency and a growing number of states establishing health advisory levels for PFOA and PFOS in drinking water, scientists are keen to develop bioremediation technologies to eliminate these substances. But the compounds resist degradation because their carbon-fluorine bond is the strongest single bond to carbon—and the key to their persistence in the environment, says Peter R. Jaffé, an environmental engineer at Princeton University. To date, scientists have identified only a few microbes that can partially break down PFOA and PFOS. Because these organisms are unable to attack the C–F bond, however, they just produce smaller perfluorinated compounds that still aren’t degradable, he says.

Jaffé and his Princeton colleague Shan Huang, lead author of the study, had been working with a strain of Acidimicrobium bacteria called A6 that they plucked from a New Jersey wetland. A6, which thrives in an iron- and ammonium-rich environment, performs a reaction known as Feammox, in which it transfers electrons from ammonium to ferric iron, reducing it to ferrous iron. The scientists wondered if the Feammox reaction could reduce the C–F bonds in PFOA and PFOS, thereby breaking them and producing less toxic fluoride ions. Low concentrations of fluoride are often added to drinking water to prevent tooth decay. “So, we decided to test exposing A6 to PFOA and PFOS,” Jaffé says.

The team cultured A6 in the lab with iron and ammonium, with and without PFOA and PFOS. The researchers tracked the concentrations of the two PFAS over time using liquid chromatography–tandem mass spectrometry. The scientists also monitored levels of iron, ammonium, and fluoride with ion chromatography. After 100 days, 60% of the PFOA and PFOS were gone. By comparing the ratio of ferrous iron produced to ammonium removed from the cultures, the researchers determined that A6 was transferring electrons to the PFAS to liberate fluoride ions instead of passing electrons over to ferric iron to produce ferrous iron.

“Although the defluorination is slow, this Feammox research is potentially transformative,” showing for the first time that these fluorinated compounds can be biodegraded, says William Cooper, an environmental chemist at the University of California, Irvine. Compared with pumping groundwater and applying chemical or physical treatments, biological remediation can be done in place relatively easily and more cheaply, he says.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on September 20, 2019.

Metal-Organic Framework Could Cut Chiral Chromatography Costs

Enantiomeric drug molecules are like the Z-shaped pieces in Tetris—typically, only one of them will be the right fit. In drug discovery, chemists separate these enantiomers, which often exhibit different biological activity from each other, through high-performance liquid chromatography columns packed with specialized chiral stationary phases. But these columns are usually only compatible with either polar or nonpolar solvent mixtures, meaning chemists sometimes have to switch between columns to find the right solvent system. Now, a team of researchers demonstrates a reusable and scalable metal-organic framework (MOF) that can be used to do chiral separations with both polar and nonpolar solvents.

MOFs have been used in chiral separations before, but they haven’t been commercialized for this application, likely because of their poor stability and the high cost of their chiral organic components. To address these issues, José Ramón Galán-Mascarós of the Institute of Chemical Research of Catalonia and colleagues synthesized a water-stable MOF composed of copper atoms linked with modified L-histidine molecules. The enantiomers of a compound each interact slightly differently with the chiral histidine groups, with one slowing down more than the other as they pass through the MOF, allowing the material to separate the two molecules from each other. Histidine is a relatively inexpensive amino acid, and by placing triazole groups on the histidine linkers, researchers were able to increase the metal-nitrogen coordination and boost the MOF’s thermal and chemical stability. Galán-Mascarós’s lab teamed up with Melissa M. Reynolds of Colorado State University and other collaborators to test the performance of the triazole acid metal-organic framework (TAMOF-1) in chiral separations.

The team showed that the TAMOF-1-packed column could separate the enantiomers of the pain-relieving drug ibuprofen and of the infamous medication thalidomide, which was used to treat morning sickness until scientists discovered that one of its enantiomers could cause birth defects.

Using a standard chiral mixture, the team also compared the separation capabilities of the TAMOF-1 column to three commercial chiral columns and found that the TAMOF-1 column performed as well as the others at separating the compounds. However, since most chiral columns can only handle mostly polar or nonpolar solvent mixtures, researchers have to invest in a range of columns to cover a range of different analytes, depending on what solvents will separate them. Using the TAMOF-1 column, however, researchers could switch among solvent systems simply by flushing the column with the appropriate solvent. “We have used these columns many, many times, and we still haven’t worn them out,” Reynolds says.

“The chemistry employed in the synthesis of this new material is easy and flexible enough to allow future chiral MOFs based on modified amino acids, allowing scaled-up synthesis of this and new daughter structures,” says David Fairen-Jimenez of the University of Cambridge. This could expand the range of molecules that could be separated using this technique.

Yong Cui, an expert in metal-organic frameworks at Shanghai Jiao Tong University, says TAMOF-1’s stability, simple preparation, and excellent separation capabilities make it a promising chiral stationary phase for purifying enantiomeric drugs.

Galán-Mascarós and collaborators founded a start-up, Orchestra Scientific, to develop TAMOF-1, which has been synthesized on a 10 kg scale, for commercial use as a stationary phase in chiral chromatographic separations.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on September 16, 2019.

Microtubule Protein Level Predicts Drugs’ Effectiveness Against Brain Cancer Cells

Certain chemotherapy drugs, including paclitaxel (Taxol), block cancer cell division by targeting microtubules—structural polymers that are critical for cell division and other functions. Such microtubule-targeting agents (MTAs) are promising drug candidates against glioblastoma, an aggressive brain cancer, but they have not reached the clinic in part because of highly variable results in the lab. Now, researchers have found one reason why MTAs do not stop the growth of all glioblastoma cells: different levels of microtubule proteins in these cells affect their susceptibility to MTAs.

Microtubules contain polymerized tubulin dimers made of an α-tubulin and a β-tubulin, each of which comes in several forms. Although researchers know that MTAs bind to tubulins to disrupt microtubule function, not much is known about how a cell’s tubulin profile might impact the drugs’ effectiveness. So Lenka Munoz of the University of Sydney and her team analyzed 15 glioblastoma cell lines and characterized the amounts of tubulin proteins using immunoassays. Then they tested four small MTAs that can potentially cross the blood-brain barrier—colchicine, nocodazole, tivantinib, and CMPD1—against the cell lines. In all cases, cells with higher α- and β-tubulin levels were more susceptible to MTAs—including the 12 lines of stem-cell-like glioblastoma cells that the team tested. In the battle against the notoriously aggressive cancer, these cells are of particular interest because they can escape chemotherapy and cause a recurrence of the cancer.

To validate their finding, the researchers also tested three MTAs commonly used in the clinic: paclitaxel, vinblastine, and ixabepilone. In four key stem-cell-like cell lines that survived these drugs, tubulin levels were as much as 20% lower than lines that were effectively killed by MTAs, the researchers found. Why cells have different levels of tubulin is not known, Munoz says.

In addition, the researchers observed that cells with low tubulin levels and high MTA tolerance had more physical and molecular features typically found in nonproliferating, dormant cancer cells. This suggests to the researchers that low-tubulin-containing cells somehow convert to a dormant state during which they do not divide. That way, the cells survive MTA treatment and can proliferate once the MTA therapy is finished.

The team is working to understand the molecular mechanisms behind this switch to dormancy, information that researchers could use to design drugs to prevent cancer cells from going into that state, Munoz says. She says physicians could then use such drugs along with MTAs to eradicate all cells within a brain tumor.

Maria G. Castro, a brain cancer scientist at the University of Michigan Medical School who does both basic and translational research, calls the data from this study “exciting” and says that this work paves the way for personalized therapy when using MTAs to treat brain cancer. The next critical steps would be to test the findings in animal models using cells with different MTA sensitivity, she says.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on September 10, 2019.

Nanocones Extend the Graphene Toolbox

Graphene, buckyballs, and carbon nanotubes now have a new family member, the nanocone, adding to the types of all-carbon nanostructures with remarkable electronic and optical characteristics and bringing its own promising properties. Such molecules could be useful for developing efficient organic solar cells or as sensor molecules.

Organic chemist Frank Würthner and postdoctoral researcher Kazutaka Shoyama of the University of Würzburg came up with the method for synthesizing the nanocones, which are 1.68 nm in diameter and 0.432 nm tall. A five-atom ring of carbons forms the cone’s tip. The team used a cross-coupling annulation cascade to add hexagons around the edges of the ring until the molecule grew to 80 carbons. The team added five nitrogen atoms around the periphery of the cone, increasing the crystal’s solubility.

The cones could prove more soluble in organic solvents than graphene; solubility is necessary for making thin-films to build devices, such as solar cell components, out of the material. The nanocones also absorbed light across most of the visible spectrum better than fullerenes. Like fullerenes, they were also electron poor. Those two properties could make them useful for creating efficient organic solar cells, the authors say, and the nanocones’ fluorescence could make them useful in sensor applications. The overall yield of the full-size cone was low, however, just 0.6%, because of the strain induced by the molecule’s cone shape.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on September 3, 2019.

New Device Uses Carbon Nanotubes to Detect Marijuana in Human Breath

As the number of states legalizing marijuana grows, so do concerns that users may drive under the influence of the drug. A breathalyzer-type instrument—like the ones used to test for alcohol impairment—would permit a fast, accurate, and noninvasive means to test drivers’ breath for the main psychoactive compound in marijuana, tetrahydrocannabinol (THC). Now, researchers have designed a sensitive, handheld prototype THC detector that contains a sensor made of carbon nanotubes.

Current efforts to detect THC in breath involve analytical techniques such as colorimetric detection or miniaturized mass spectrometry. But THC pharmacodynamics expert Marilyn A. Huestis of Thomas Jefferson University, who was not involved in the study, says carbon nanotube–based sensors have the potential to offer unprecedented sensitivity. Carbon nanotubes have a large surface area to bind molecules, making them excellent sensors. They are also stable in the face of high temperatures and humidity.

These properties motivated Alexander Star of the University of Pittsburgh and colleagues to fabricate a sensor out of semiconducting carbon nanotubes. They built a 3-D printed case around it, creating a device similar to an alcohol breathalyzer. With their prototype, the researchers can measure the change in the nanotubes’ electrical resistance when molecules bind to them and get released.

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Credit: ACS Sens.
Researchers built a handheld, battery-powered prototype breathalyzer for detecting THC.

To be practical, the sensor would need to differentiate THC from the mixture of other chemicals in human breath. So Star’s team exposed the sensor to such a mix, including compounds like carbon dioxide, water, ethanol, and acetone. They discovered they could distinguish THC from these other compounds by monitoring how long it took the sensor to return to its normal voltage after the bound THC molecules were released from the nanotubes. Different species were released at different rates over time, but THC stayed bound the longest. They trained a machine learning algorithm to sift through these recovery traces, sorting their lab-made vapor samples into those that contained THC and those that did not.

The researchers then tested their breathalyzer prototype using samples taken from a human volunteer and showed that it performed comparably to mass spectrometry, the gold standard for detecting breath components, though it’s much less portable.

Huestis says the next step is to ensure the device is specific for THC and doesn’t get confused between other drugs like cocaine or nonpsychoactive cannabinoids with similar chemical structures.

The prototype cannot yet deduce exact concentrations of THC from random mixtures of unknown compounds, but Huestis points out that US lawmakers have not instituted a standardized legal limit for marijuana, so currently there is not a target concentration for detection. And because THC affects chronic and daily users differently, “there is no one number that differentiates ‘cannabis-impaired’ from ‘non-impaired,’” she says. She advises that THC breathalyzers be paired with behavioral tests to gauge intoxication.

Carbon nanotube expert Meyya Meyyappan of NASA’s Ames Research Center, who was not involved in the study, says the high sensitivity of the researchers’ prototype instrument is a great start. “This is a good story,” he says. “It can go places.”

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on August 18, 2019.

Polymer Nanoparticles Block Underarm Odors

Typical deodorants work by killing the bacteria responsible for the stink. A polymer-based deodorant could capture odor precursors in the underarm before they start to smell, without disturbing the microbes that live on the skin.

Polymer nanoparticles could provide a new way to fight underarm odor without disturbing the balance of skin bacteria or causing irritation.

Underarm smell is mainly caused by a couple of volatile fatty acids, (E)-3-methyl-2-hexenoic acid and 3-hydroxy-3-methyl-hexanoic acid. They are produced when bacteria living on the skin break down precursor molecules—glutamine conjugates of these fatty acids— that are found in sweat; by themselves, these precursors have no odor. “When bacteria cleave them into smaller molecules, they start to smell. That is where body odor comes from,” says Karsten Haupt, a nanobiotechnologist at the University of Technology of Compiègne.

Sweat contains these glutamine conjugates of two volatile fatty acids. Molecularly imprinted polymers can bind these molecules, preventing bacteria from cleaving them to produce the fatty acids, which are responsible for body odor.

Typical deodorants tackle the stink by going after the bacteria with a bactericide such as triclosan or chlorhexadine. But researchers worry using those may disrupt the balance of healthful bacteria on the skin or lead to the evolution of resistant bacteria. Antiperspirants, on the other hand, contain aluminum salts to stanch the flow of sweat from the pores. But that can lead to skin irritation, and some people want to avoid products that block pores with these ingredients.

The new approach relies on molecularly imprinted polymers (MIPs). MIPS are made by combining a template molecule with monomers and free radical species to induce polymerization. As the polymer forms, molecular interactions mold it around the template molecule. Removing the template leaves behind a polymer shaped to bind to molecules that resemble the template. MIPs have been used for years in applications such as biosensors and immunoassays.

Aided by funding from L’Oreal, Haupt and Bernadette Tse Sum Bui, a research engineer at France’s National Center for Scientific Research, showed in 2016 that they could build MIPs that capture molecules involved in underarm odor. The researchers created MIPs about 600 nm in diameter that could bind to the glutamine group in the odor precursor molecules. That binding made it impossible for bacteria to access the precursors, so they couldn’t produce the smelly breakdown products. The bacteria can still use other components of the sweat as a food source.

For the new study, the researchers tested the biocompatibility of the MIPs by culturing three types of skin bacteria in the presence and absence of MIPs. Growth rates were the same, suggesting the MIPs do not alter the skin microbiome. They also mixed MIPs in with cultured skin cells, then looked to see whether the cells had produced cytokines, a marker of inflammation. They did not. Haupt says that shows the material is safe for both skin and bacteria.

Ken Shimizu, a chemist at the University of South Carolina who works on MIP-based sensors, says factors that make MIPs unsuitable for many pharmaceutical applications, such as their inability to permeate membranes, are actually advantages for this application. “This is a clever use of MIPs,” he says. “The principle of using benign ways of modifying the behavior of bacterial products without killing them has great potential.”

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on August 08, 2019.