An analysis of the spatio-temporal behavior of COVID-19 patients using activity trajectory data.

During the global pandemic, COVID-19 patients' activity trajectories and actions emerge as revelatory conduits elucidating their spatiotemporal behavior and transmission dynamics. This study analyzes COVID-19 patients' behavior in Nanjing and Yangzhou, China, by using patient activity trajectory data in conjunction with complex network theory. The main findings are as follows: (1) The evaluation of the activity network structure of patients revealed that "residential areas" and "vegetable markets" had the highest betweenness centrality, indicating that these are the primary nodes of COVID-19 transmission. (2) The power-law distribution of the degree distribution of nodes for different facility types revealed that residential areas, vegetable markets, and shopping malls had the most scale-free characteristics, indicating that a large number of patients visited these three facility types at a few access points. (3) Community detection showed that patient visitation sites in Nanjing and Yangzhou were divided into five or six communities, with the largest community containing the outbreak origin and several residential areas surrounding it. (4) Patients had fewer activities across administrative regions but more activities across the life circle when the pandemic broke out in the suburbs, and more activities across administrative regions but fewer activities across the life circle when the pandemic broke out in the central city. Based on these findings, this paper makes recommendations for future pandemic preparedness in an effort to achieve effective pandemic control and reduce the damage caused by pandemics. Overall, this study provides insights into understanding the transmission patterns of COVID-19 and may inform future pandemic control strategies.

All-printed stretchable electrochemical devices.

The fabrication and characterization of all-printed, inexpensive, stretchable electrochemical devices is described. These devices are based on specially engineered inks that can withstand severe tensile strain, as high as 100%, without any significant effect on their electrochemical properties. Such stretchable electrochemical devices should be attractive for diverse sensing and energy applications.

Biocompatible enzymatic roller pens for direct writing of biocatalytic materials: "do-it-yourself" electrochemical biosensors.

The development of enzymatic-ink-based roller pens for direct drawing of biocatalytic sensors, in general, and for realizing renewable glucose sensor strips, in particular, is described. The resulting enzymatic-ink pen allows facile fabrication of high-quality inexpensive electrochemical biosensors of any design by the user on a wide variety of surfaces having complex textures with minimal user training. Unlike prefabricated sensors, this approach empowers the end user with the ability of "on-demand" and "on-site" designing and fabricating of biocatalytic sensors to suit their specific requirement. The resulting devices are thus referred to as "do-it-yourself" sensors. The bio-active pens produce highly reproducible biocatalytic traces with minimal edge roughness. The composition of the new enzymatic inks has been optimized for ensuring good biocatalytic activity, electrical conductivity, biocompati-bility, reproducible writing, and surface adherence. The resulting inks are characterized using spectroscopic, viscometric, electrochemical, thermal and microscopic techniques. Applicability to renewable blood glucose testing, epidermal glucose monitoring, and on-leaf phenol detection are demonstrated in connection to glucose oxidase and tyrosinase-based carbon inks. The "do-it-yourself" renewable glucose sensor strips offer a "fresh," reproducible, low-cost biocatalytic sensor surface for each blood test. The ability to directly draw biocatalytic conducting traces even on unconventional surfaces opens up new avenues in various sensing applications in low-resource settings and holds great promise for diverse healthcare, environmental, and defense domains.

Tattoo-based noninvasive glucose monitoring: a proof-of-concept study.

We present a proof-of-concept demonstration of an all-printed temporary tattoo-based glucose sensor for noninvasive glycemic monitoring. The sensor represents the first example of an easy-to-wear flexible tattoo-based epidermal diagnostic device combining reverse iontophoretic extraction of interstitial glucose and an enzyme-based amperometric biosensor. In-vitro studies reveal the tattoo sensor's linear response toward physiologically relevant glucose levels with negligible interferences from common coexisting electroactive species. The iontophoretic-biosensing tattoo platform is reduced to practice by applying the device on human subjects and monitoring variations in glycemic levels due to food consumption. Correlation of the sensor response with that of a commercial glucose meter underscores the promise of the tattoo sensor to detect glucose levels in a noninvasive fashion. Control on-body experiments demonstrate the importance of the reverse iontophoresis operation and validate the sensor specificity. This preliminary investigation indicates that the tattoo-based iontophoresis-sensor platform holds considerable promise for efficient diabetes management and can be extended toward noninvasive monitoring of other physiologically relevant analytes present in the interstitial fluid.

Non-invasive mouthguard biosensor for continuous salivary monitoring of metabolites.

The present work describes the first example of a wearable salivary metabolite biosensor based on the integration of a printable enzymatic electrode on a mouthguard. The new mouthguard enzymatic biosensor, based on an immobilized lactate oxidase and a low potential detection of the peroxide product, exhibits high sensitivity, selectivity and stability using whole human saliva samples. Such non-invasive mouthguard metabolite biosensors could tender useful real-time information regarding a wearer's health, performance and stress level, and thus hold considerable promise for diverse biomedical and fitness applications.

Mechanisms for enhanced performance of platinum-based electrocatalysts in proton exchange membrane fuel cells.

As a new generation of power sources, fuel cells have shown great promise for application in transportation. However, the expensive catalyst materials, especially the cathode catalysts for oxygen reduction reaction (ORR), severely limit the widespread commercialization of fuel cells. Therefore, this review article focuses on platinum (Pt)-based electrocatalysts for ORR with better catalytic performance and lower cost. Major breakthroughs in the improvement of activity and durability of electrocatalysts are discussed. Specifically, on one hand, the enhanced activity of Pt has been achieved through crystallographic control, ligand effect, or geometric effect; on the other hand, improved durability of Pt-based cathode catalysts has been realized by means of the incorporation of another noble metal or the morphological control of nanostructures. Furthermore, based on these improvement mechanisms, rationally designed Pt-based nanoparticles are summarized in terms of different synthetic strategies such as wet-chemical synthesis, Pt-skin catalysts, electrochemically dealloyed nanomaterials, and Pt-monolayer deposition. These nanoparticulate electrocatalysts show greatly enhanced catalytic performance towards ORR, aiming not only to outperform the commercial Pt/C, but also to exceed the US Department of Energy 2015 technical target ($30/kW and 5000 h).

Electrochemical tattoo biosensors for real-time noninvasive lactate monitoring in human perspiration.

The present work describes the first example of real-time noninvasive lactate sensing in human perspiration during exercise events using a flexible printed temporary-transfer tattoo electrochemical biosensor that conforms to the wearer's skin. The new skin-worn enzymatic biosensor exhibits chemical selectivity toward lactate with linearity up to 20 mM and demonstrates resiliency against continuous mechanical deformation expected from epidermal wear. The device was applied successfully to human subjects for real-time continuous monitoring of sweat lactate dynamics during prolonged cycling exercise. The resulting temporal lactate profiles reflect changes in the production of sweat lactate upon varying the exercise intensity. Such skin-worn metabolite biosensors could lead to useful insights into physical performance and overall physiological status, hence offering considerable promise for diverse sport, military, and biomedical applications.

Tattoo-based potentiometric ion-selective sensors for epidermal pH monitoring.

This article presents the fabrication and characterization of novel tattoo-based solid-contact ion-selective electrodes (ISEs) for non-invasive potentiometric monitoring of epidermal pH levels. The new fabrication approach combines commercially available temporary transfer tattoo paper with conventional screen printing and solid-contact polymer ISE methodologies. The resulting tattoo-based potentiometric sensors exhibit rapid and sensitive response to a wide range of pH changes with no carry-over effects. Furthermore, the tattoo ISE sensors endure repetitive mechanical deformation, which is a key requirement of wearable and epidermal sensors. The flexible and conformal nature of the tattoo sensors enable them to be mounted on nearly any exposed skin surface for real-time pH monitoring of the human perspiration, as illustrated from the response during a strenuous physical activity. The resulting tattoo-based ISE sensors offer considerable promise as wearable potentiometric sensors suitable for diverse applications.

Ultrasensitive and selective non-enzymatic glucose detection using copper nanowires.

In the pursuit of more economical electrocatalysts for non-enzymatic glucose sensors, one-dimensional Cu nanowires (Cu NWs) with uniform size distribution and a large aspect ratio (>200) were synthesized by a facile, scalable, wet-chemistry approach. The morphology, crystallinity, and surface property of the as-prepared Cu NWs were examined by SEM, XRD, and XPS, respectively. The electrochemical property of Cu NWs for glucose electrooxidation was thoroughly investigated by cyclic voltammetry. In the amperometric detection of glucose, the Cu NWs modified glassy carbon electrode exhibited an extraordinary limit of detection as low as 35 nM and a wide dynamic range with excellent sensitivity of 420.3 µA cm(-2) mM(-1), which was more than 10,000 times higher than that of the control electrode without Cu NWs. The performance of the developed glucose sensor was also independent to oxygen concentration and free from chloride poisoning. Furthermore, the interference from uric acid, ascorbic acid, acetaminophen, fructose, and sucrose at the level of their physiological concentration were insignificant, indicating excellent selectivity. Finally, good accuracy and high precision for the quantification of glucose concentration in human serum samples implicate the applicability of Cu NWs in sensitive and selective non-enzymatic glucose detection.

Pt nanoflower/polyaniline composite nanofibers based urea biosensor.

Hybrid materials with special structures are of great interest because of their superior properties compared with their pure counterparts. Hybrid polyaniline (PANi) nanofibers with integrated Pt nanoflowers are studied in this research. PANi is prepared by in situ polymerization of aniline on an electrospun nanofiber template in an acidic solution with ammonium persulfate (APS) as the oxidant. Pt nanoflowers are further electrodeposited onto the PANi nanofibers backbone by cyclic voltammetry (CV), resulting in novel functionalized hybrid nanofibers. The coverage of Pt nanoflowers on PANi nanofibers can be facilely controlled by adjusting the electrodeposition conditions. The factors affecting Pt nanoflowers formation are further investigated. As a demonstration, urease is immobilized onto the Pt/PANi hybrid nanofibers and the composite was employed as the sensing platform for urea detection in a flow-injection-analysis (FIA) system. The detection of urea shows a wide linear range (up to 20 mM), a good limit of detection of 10 µM (S/N=3), and an excellent anti-interference property against chloride ion. In addition, it was found that the response to urea was attributed not only to the conductivity change of PANi due to the interaction between PANi and ammonia (liberated from the enzymatic reaction), but also to the interaction between Pt nanoflowers and amine groups in urea. The strategy developed in this study can be extended to synthesize other composite nanofibers consisting of conducting polymer and metal nanoparticles for a wide range of sensing applications.

Microbial biosensors: a review.

A microbial biosensor is an analytical device which integrates microorganism(s) with a physical transducer to generate a measurable signal proportional to the concentration of analytes. In recent years, a large number of microbial biosensors have been developed for environmental, food, and biomedical applications. Starting with the discussion of various sensing techniques commonly used in microbial biosensing, this review article concentrates on the summarization of the recent progress in the fabrication and application of microbial biosensors based on amperometry, potentiometry, conductometry, voltammetry, microbial fuel cell, fluorescence, bioluminescence, and colorimetry, respectively. Prospective strategies for the design of future microbial biosensors will also be discussed.

Effect of inoculum types on bacterial adhesion and power production in microbial fuel cells.

Microbial fuel cell (MFC) is an emerging biotechnology to convert the organic substrates in wastewater to electricity by anaerobic electrogenic bacteria. The main challenge for MFC research is to elucidate the fundamental mechanisms of electron generation and transfer and to apply these mechanisms to improve the power production in the engineering operation. This study extensively investigated the effects of three inocula (Geobacter sulfurreducens, soil, and wastewater) on the power production and electrochemical characteristics (i.e., internal resistances, Coulombic Efficiency) of MFCs. The results showed that the extents of bacterial adhesion varied between mixed cultures (soil) and pure cultures (G. sulfurreducens). The voltage output increased 30% when bacterial adhesion was well-developed in the soil inocula. Meanwhile, the inoculum types clearly affected the internal resistance (R(in)) and power production of MFCs. Pure culture inoculum (G. sulfurreducens) had the lowest R(in) (165 Omega) and the highest Coulombic Efficiency (CE, 25.8%) and Energy Conversion Efficiency (ECE, 7.2%), while the mixed culture inocula (soil) with the high concentration of nonelectrogenic bacteria, exhibited the highest R(in) (620 Omega), lowest CE (9.2%) and lowest ECE (2.4%). Additionally, a second-order correlation was established between the anode potential (P(A)) and power output while an exponential correlation was established between the difference between anode and cathode potentials (DeltaP(C-A)) and power output.

Preparation, Characterization and Sensitive Gas Sensing of Conductive Core-sheath TiO(2)-PEDOT Nanocables.

Conductive core-sheath TiO(2)-PEDOT nanocables were prepared using electrospun TiO(2) nanofibers as template, followed by vapor phase polymerization of EDOT. Various techniques were employed to characterize the sample. The results reveal that the TiO(2) core has an average diameter of ∼78 nm while the PEDOT sheath has a uniform thickness of ∼6 nm. The as-prepared TiO(2)-PEDOT nanocables display a fast and reversible response to gaseous NO(2) and NH(3) with a limit of detection as low as 7 ppb and 675 ppb (S/N=3), respectively. This study provides a route for the synthesis of conductive nanostructures which show excellent performance for sensing applications.