Early Detection of Severe Acute Respiratory Syndrome Coronavirus 2 Variants Using Traveler-based Genomic Surveillance at 4 US Airports, September 2021-January 2022.

We enrolled arriving international air travelers in a severe acute respiratory syndrome coronavirus 2 genomic surveillance program. We used molecular testing of pooled nasal swabs and sequenced positive samples for sublineage. Traveler-based surveillance provided early-warning variant detection, reporting the first US Omicron BA.2 and BA.3 in North America.

Metabolic cost of rapid adaptation of single yeast cells.

Cells can rapidly adapt to changing environments through nongenetic processes; however, the metabolic cost of such adaptation has never been considered. Here we demonstrate metabolic coupling in a remarkable, rapid adaptation process (1 in 1,000 cells adapt per hour) by simultaneously measuring metabolism and division of thousands of individual Saccharomyces cerevisiae cells using a droplet microfluidic system: droplets containing single cells are immobilized in a two-dimensional (2D) array, with osmotically induced changes in droplet volume being used to measure cell metabolism, while simultaneously imaging the cells to measure division. Following a severe challenge, most cells, while not dividing, continue to metabolize, displaying a remarkably wide diversity of metabolic trajectories from which adaptation events can be anticipated. Adaptation requires a characteristic amount of energy, indicating that it is an active process. The demonstration that metabolic trajectories predict a priori adaptation events provides evidence of tight energetic coupling between metabolism and regulatory reorganization in adaptation. This process allows S. cerevisiae to adapt on a physiological timescale, but related phenomena may also be important in other processes, such as cellular differentiation, cellular reprogramming, and the emergence of drug resistance in cancer.

Development and validation of a glass-silicon microdroplet-based system to measure sulfite concentrations in beverages.

Sulfite is often added to beverages as an antioxidant and antimicrobial agent. In fermented beverages, sulfite is also naturally produced by yeast cells. However, sulfite causes adverse health effects in asthmatic patients and accurate measurement of the sulfite concentration is therefore very important. Current sulfite analysis methods are time- and reagent-consuming and often require costly equipment. Here, we present a system allowing sensitive, ultralow-volume sulfite measurements based on a reusable glass-silicon microdroplet platform on which microdroplet generation, addition of enzymes through chemical-induced emulsion destabilization and pillar-induced droplet merging, emulsion restabilization, droplet incubation, and fluorescence measurements are integrated. In a first step, we developed and verified a fluorescence-based enzymatic assay for sulfite by measuring its analytical performance (LOD, LOQ, the dynamic working range, and the influence of salts, colorant, and sugars) and comparing fluorescent microplate readouts of fermentation samples with standard colorimetric measurements using the 5,5'-dithiobis-(2-nitrobenzoic acid) assay of the standard Gallery Plus Beermaster analysis platform. Next, samples were analyzed on the microdroplet platform, which also showed good correlation with the standard colorimetric analysis. Although the presented platform does not allow stable reinjection of droplets due to the presence of a tight array of micropillars at the fluidics entrances to prevent channel clogging by dust, removing the pillars, and integrating miniaturized pumps and optics in a future design would allow to use this platform for high-throughput, automated, and portable screening of microbes, plant, or mammalian cells. Graphical abstract ᅟ.

Activity-Fed Translation (AFT) Assay: A New High-Throughput Screening Strategy for Enzymes in Droplets.

There is an increasing demand for the development of sensitive enzymatic assays compatible with droplet-based microfluidics. Here we describe an original strategy, activity-fed translation (AFT), based on the coupling of enzymatic activity to in vitro translation of a fluorescent protein. We show that methionine release upon the hydrolysis of phenylacetylmethionine by penicillin acylase enabled in vitro expression of green fluorescent protein. An autocatalytic setup where both proteins are expressed makes the assay highly sensitive, as fluorescence was detected in droplets containing single PAC genes. Adding a PCR step in the droplets prior to the assay increased the sensitivity further. The strategy is potentially applicable for any activity that can be coupled to the production of an amino acid, and as the microdroplet volume is small the use of costly reagents such as in vitro expression mixtures is not limiting for high-throughput screening projects.

Toward point-of-care diagnostics: Running enzymatic assays on a photonic waveguide-based sensor chip with a portable, benchtop measurement system.

We demonstrate a portable, compact system to perform absorption-based enzymatic assays at a visible wavelength of 639 nm on a photonic waveguide-based sensor chip, suitable for lab-on-a-chip applications. The photonic design and fabrication of the sensor are described, and a detailed overview of the portable measurement system is presented. In this publication, we use an integrated photonic waveguide-based absorbance sensor to run a full enzymatic assay. An assay to detect creatinine in plasma is simultaneously performed on both the photonic sensor on the portable setup and on a commercial microplate reader for a clinically relevant creatinine concentration range. We observed a high correlation between the measured waveguide propagation loss and the optical density measurement from the plate reader and measured a limit-of-detection of 4.5 µM creatinine in the sensor well, covering the relevant clinical range for creatinine detection.

Small-molecule autocatalysis drives compartment growth, competition and reproduction.

Sustained autocatalysis coupled to compartment growth and division is a key step in the origin of life, but an experimental demonstration of this phenomenon in an artificial system has previously proven elusive. We show that autocatalytic reactions within compartments-when autocatalysis, and reactant and solvent exchange outpace product exchange-drive osmosis and diffusion, resulting in compartment growth. We demonstrate, using the formose reaction compartmentalized in aqueous droplets in an emulsion, that compartment volume can more than double. Competition for a common reactant (formaldehyde) causes variation in droplet growth rate based on the composition of the surrounding droplets. These growth rate variations are partially transmitted after selective division of the largest droplets by shearing, which converts growth-rate differences into differences in droplet frequency. This shows how a combination of properties of living systems (growth, division, variation, competition, rudimentary heredity and selection) can arise from simple physical-chemical processes and may have paved the way for the emergence of evolution by natural selection.

New generation of amino coumarin methyl sulfonate-based fluorogenic substrates for amidase assays in droplet-based microfluidic applications.

Droplet-based microfluidics is a powerful tool for biology and chemistry as it allows the production and the manipulation of picoliter-size droplets acting as individual reactors. In this format, high-sensitivity assays are typically based on fluorescence, so fluorophore exchange between droplets must be avoided. Fluorogenic substrates based on the coumarin leaving group are widely used to measure a variety of enzymatic activities, but their application in droplet-based microfluidic systems is severely impaired by the fast transport of the fluorescent product between compartments. Here we report the synthesis of new amidase fluorogenic substrates based on 7-aminocoumarin-4-methanesulfonic acid (ACMS), a highly water-soluble dye, and their suitability for droplet-based microfluidics applications. Both substrate and product had the required spectral characteristics and remained confined in droplets from hours to days. As a model experiment, a phenylacetylated ACMS was synthesized and used as a fluorogenic substrate of Escherichia coli penicillin G acylase. Kinetic parameters (k(cat) and K(M)) measured in bulk and in droplets on-chip were very similar, demonstrating the suitability of this synthesis strategy to produce a variety of ACMS-based substrates for assaying amidase activities both in microtiter plate and droplet-based microfluidic formats.

Rapid Quantification of Plasma Creatinine Using a Novel Kinetic Enzymatic Assay.

BACKGROUND: Enzymatic assays are among the most common diagnostic tests performed in the clinical laboratory. Enzymatic substrate analysis is most commonly measured using endpoint methods; however, modulating the reaction kinetics allows fine control of the reaction rate, which can be adjusted based on specific monitoring technologies. METHODS: We developed and optimized an enzymatic method for measurement of creatinine in plasma, using commonly paired enzymes of creatininase (Crtnnase), creatinase (Crtase), sarcosine oxidase (SOX), ascorbate oxidase (AOX), and horseradish peroxidase (HRP). The novel aspect of the assay is that it is fast and uses SOX as the limiting enzyme. The assay performance was assessed with respect to precision, accuracy, and interferences. RESULTS: The intrarun %CV (n = 12) was approximately 5% for each concentration tested, with biases ranging from -3 to -9%. The interrun %CV (n = 39) ranged from 5 to 8%, with biases ranging from -2 to -6%. During the accuracy assessment (n = 127), only 4 samples did not meet the minimum acceptability criteria. Minimal interference was observed, except at low creatinine concentrations with elevated creatine. CONCLUSION: Our novel and versatile enzymatic assay to measure plasma creatinine using kinetic analysis with SOX as the limiting enzyme is rapid (<2 mins), sensitive, and specific and demonstrates excellent concordance with the laboratory standard. We anticipate this rapid kinetic assay to be compatible with emerging technologies in the field of portable diagnostic devices, such as the usage of silicon photonics to monitor biochemical reactions.