Accessing analytes in biofluids for peripheral biochemical monitoring.

Peripheral biochemical monitoring involves the use of wearable devices for minimally invasive or noninvasive measurement of analytes in biofluids such as interstitial fluid, saliva, tears and sweat. The goal in most cases is to obtain measurements that serve as surrogates for circulating analyte concentrations in blood. Key technological developments to date include continuous glucose monitors, which use an indwelling sensor needle to measure glucose in interstitial fluid, and device-integrated sweat stimulation for continuous access to analytes in sweat. Further development of continuous sensing technologies through new electrochemical sensing modalities will be a major focus of future research. While there has been much investment in wearable technologies to sense analytes, less effort has been directed to understanding the physiology of biofluid secretion. Elucidating the underlying biology is crucial for accelerating technological progress, as the biofluid itself often presents the greatest challenge in terms of sample volumes, secretion rates, filtration, active analyte channels, variable pH and salinity, analyte breakdown and other confounding factors.

Continuous, quantifiable, and simple osmotic preconcentration and sensing within microfluidic devices.

Insurmountable detection challenges will impede the development of many of the next-generation of lab-on-a-chip devices (e.g., point-of-care and real-time health monitors). Here we present the first membrane-based, microfluidic sample preconcentration method that is continuous, quantifiable, simple, and capable of working with any analyte. Forward osmosis rapidly concentrates analytes by removing water from a stream of sample fluid. 10-100X preconcentration is possible in mere minutes. This requires careful selection of the semi-permeable membrane and draw molecule; therefore, the osmosis performance of several classes of membranes and draw molecules were systematically optimized. Proof-of-concept preconcentration devices were characterized based on their concentration ability and fouling resistance. In-silico theoretical modeling predicts the experimental findings and provides an engineering toolkit for future designs. With this toolkit, inexpensive ready-for-manufacturing prototypes were also developed. These devices provide broad-spectrum detection improvements across many analytes and sensing modalities, enabling next-generation lab-on-a-chip devices.

Modeling Glucose Transport From Systemic Circulation to Sweat.

Sweat sensing may provide a noninvasive means of estimating blood biomarker levels if a number of technological hurdles can be overcome. This report describes progress on a physiologically based transport model relating sweat glucose and key electrolyte concentrations to those in blood. Iontophoretically stimulated sweat glucose and fasted blood glucose were simultaneously measured in 2 healthy human subjects. Sweat glucose was measured with a novel, prototype skin sweat collection/analysis system and blood glucose with a commercial fingerstick glucometer. These data, in combination with data from 3 published studies, were used to calibrate a dynamic mathematical model for glucose transport and uptake in human skin, followed by extraction into sweat. Model simulations revealed that experimental and literature sweat glucose values were well represented under varying physiologic conditions. The glucose model, calibrated under a variety of experimental conditions including electrical enhancement, revealed a 10 min blood-to-sweat lag time and a sweat/blood glucose level ranging from 0.001 to 0.02, depending on the sweat rate. These values are consistent with those reported in the literature. The developed model satisfactorily described the sweat-to-blood relationship for glucose concentrations measured under different conditions in 4 human studies including the present pilot study. The algorithm may be used to facilitate sweat biosensor development.

Enhancing glucose flux into sweat by increasing paracellular permeability of the sweat gland.

Non-invasive wearable biosensors provide real-time, continuous, and actionable health information. However, difficulties detecting diluted biomarkers in excreted biofluids limit practical applications. Most biomarkers of interest are transported paracellularly into excreted biofluids from biomarker-rich blood and interstitial fluid during normal modulation of cellular tight junctions. Calcium chelators are reversible tight junction modulators that have been shown to increase absorption across the intestinal epithelium. However, calcium chelators have not yet been shown to improve the extraction of biomarkers. Here we show that for glucose, a paracellularly transported biomarker, the flux into sweat can be increased by >10x using citrate, a calcium chelator, in combination with electroosmosis. Our results demonstrate a method of increasing glucose flux through the sweat gland epithelium, thereby increasing the concentration in sweat. Future work should examine if this method enhances flux for other paracellularly transported biomarkers to make it possible to detect more biomarkers with currently available biosensors.

Fungicide contamination reduces beneficial fungi in bee bread based on an area-wide field study in honey bee, Apis mellifera, colonies.

Fermentation by fungi converts stored pollen into bee bread that is fed to honey bee larvae, Apis mellifera, so the diversity of fungi in bee bread may be related to its food value. To explore the relationship between fungicide exposure and bee bread fungi, samples of bee bread collected from bee colonies pollinating orchards from 7 locations over 2 years were analyzed for fungicide residues and fungus composition. There were detectable levels of fungicides from regions that were sprayed before bloom. An organic orchard had the highest quantity and variety of fungicides, likely due to the presence of treated orchards within bees' flight range. Aspergillus, Penicillium, Rhizopus, and Cladosporium (beneficial fungi) were the primary fungal isolates found, regardless of habitat differences. There was some variation in fungal components amongst colonies, even within the same apiary. The variable components were Absidia, Alternaria, Aureobasidium, Bipolaris, Fusarium, Geotrichum, Mucor, Nigrospora, Paecilomyces, Scopulariopsis, and Trichoderma. The number of fungal isolates was reduced as an effect of fungicide contamination. Aspergillus abundance was particularly affected by increased fungicide levels, as indicated by Simpson's diversity index. Bee bread showing fungicide contamination originated from colonies, many of which showed chalkbrood symptoms.

Water balance characteristics of pupae developing in different size maggot masses from six species of forensically important flies.

The impact of maggot mass size on body water content, net transpiration rate, and dehydration tolerance of fly pupae was examined in six species of necrophagous flies. Species that spent more time on food as larvae, produced pupae with high body water contents. Dehydration tolerance limits of pupae were modest, matching the moisture-rich conditions of decaying carrion for larvae. Protophormia terraenovae pupariates on food as it dries, and this was reflected by pupae having the highest body water content and lowest net transpiration rate. Megaselia scalaris featured the lowest body water content and highest dehydration tolerance, implying that this species is arid-suited, which matches its ability to feed and colonize on post-decay carrion. Lucilia illustris was the most sensitive to larval overcrowding, resulting in a dramatic decrease in pupal size, early dispersal from food, fed less and had fast net transpiration rates. By contrast, Lucilia sericata was the most resistant, by showing no pupal size decrease and no change in net transpiration rate. Other species were between these extremes, requiring larger maggot mass sizes to produce the effect of decreasing pupal size and increasing net transpiration rate. We conclude: (1) the pupa's response to overcrowding and water balance profile are species-specific, varying according to pupal size and net transpiration rate as independent characteristics; (2) water balance profile of the pupae reflects the behavior and microhabitat of the larva; and (3) danger of lethal desiccation to smaller-sized pupae is circumvented by a faster developmental rate rather than enhanced water conservation.

Multiple traumatic insemination events reduce the ability of bed bug females to maintain water balance.

To examine how traumatic insemination, a wounding process to females inflicted by males during copulation, reduces the longevity of females of the bedbug, Cimex lectularius, we assessed if multiple bouts of mating impact water relations of females by measuring net transpiration water loss rates. Our studies show that net transpiration rate of females correlates with frequency of mating (small increase after exposure to low numbers of males; large increase after exposure to large numbers of males), and this is reflected by reduced female survivorship for as much as 22 days at 75% RH, 25°C. Water loss occurs up to 28% more rapidly in females after being held with large groups of males. Females that were exposed to males having their paramere removed, females exposed only to other females, and females kept in isolation (unmated) exhibited no reduction in ability to retain water, indicating that traumatic insemination was responsible for the net transpiration rate increase. Mechanical piercing of the female's abdominal wall leads to increased net transpiration rates for longer periods than puncturing the ectospermalege (regular mating site), implying that inaccurate copulation by males is extremely detrimental to the water balance of females and that the ectospermalege is uniquely modified to seal off more quickly to prevent excess water loss. Mating frequency and the associated increased water loss is considerably reduced by the addition of bed bug alarm pheromone components. Thus, females experience elevated water stress due to traumatic insemination, especially at high levels and when males fail to pierce the ectospermalege, and water loss prevention, likely by more rapid sealing of the wound, is a novel function of the ectopsermalege.