Global priorities for large-scale biomarker-based prospective cohorts.

The focus of this paper is on strategic approaches for establishing population-based prospective cohorts that collect and store biological samples from very large numbers of participants to help identify the determinants of common health outcomes. In particular, it aims to address key issues related to investigation of genetic, as well as social, environmental, and ancestral, diversity; generation of detailed genetic and other types of assay data; collection of detailed lifestyle and environmental exposure information; follow-up and characterization of incident health outcomes; and overcoming obstacles to data sharing and access (including capacity building). It concludes that there is a need for strategic planning at an international level (rather than the current ad hoc approach) toward the development of a carefully selected set of deeply characterized large-scale prospective cohorts that are readily accessible by researchers around the world.

Long-Term In Vivo Oxygen Sensors for Peripheral Artery Disease Monitoring.

Tracking of tissue oxygenation around chronic foot wounds may help direct therapy decisions in patients with peripheral artery disease (PAD). Novel sensing technology to enable such monitoring was tested over 9 months in a Sinclair mini-pig model. No adverse events were observed over the entire study period. Systemic and acute hypoxia challenges were detected during each measurement period by the microsensors. The median time to locate the sensor signal was 13 s. Lumee Oxygen microsensors appear safe for long-term repeated oxygen measurements over 9 months.

Glucose-sensitive nanofiber scaffolds with an improved sensing design for physiological conditions.

Continuous physiological monitoring of electrolytes and small molecules such as glucose, creatinine, and urea is currently unavailable but achieving such a capability would be a major milestone for personalized medicine. Optode-based nanosensors are an appealing analytical platform for designing in vivo monitoring systems. In addition to the necessary analytical performance, such nanosensors must also be biocompatible and remain immobile at the implantation site. Blood glucose in particular remains a difficult but high-value analyte to monitor continuously. Previously, we developed glucose-sensitive nanosensors that measure glucose by a competitive binding mechanism between glucose and a fluorescent dye to 4-carboxy-3-fluorophenyl boronic acid. To improve the sensitivity and residency time of our reported sensors, we present here a series of new derivatives of 4-carboxy-3-fluorophenyl boronic acid that we screened in a macrosensor format before translating into a nanofiber format with electrospinning. The lead candidate was then implanted subdermally and its residency time was compared to spherical nanosensor analogues. The nanofiber scaffolds were markedly more stable at the implantation site whereas spherical nanosensors diffused away within three hours. Based on the enhanced sensitivity of the new boronic acids and the residency time of nanofibers, this sensor configuration is an important step towards continuous monitoring of glucose and other analytes.

Gel encapsulation of glucose nanosensors for prolonged in vivo lifetime.

BACKGROUND: Fluorescent glucose-sensitive nanosensors have previously been used in vivo to track glucose concentration changes in interstitial fluid. However, this technology was limited because of loss of fluorescence intensity due to particle diffusion from the injection site. In this study, we encapsulated the nanosensors into injectable gels to mitigate nanosensor migration in vivo. METHODS: Glucose-sensitive nanosensors were encapsulated in two different commercially available gelling agents: gel 1 and gel 2. Multiple formulations of each gel were assessed in vitro for their nanosensor encapsulation efficiency, permeability to glucose, and nanosensor retention over time. The optimal formulation for each gel, as determined from the in vitro assessment, was then tested in mice, and the lifetime of the encapsulated nanosensors was compared with controls of nanosensors without gel. RESULTS: Five gel formulations had encapsulation efficiencies of the nanosensors greater than 90%. Additionally, they retained up to 20% and 40% of the nanosensors over 24 h for gel 1 and gel 2, respectively. In vivo, both gels prevented diffusion of glucose nanosensors at least three times greater than the controls. CONCLUSIONS: Encapsulating glucose nanosensors in two injectable gels prolonged nanosensor lifetime in vivo; however, the lifetime must still be increased further to be applicable for diabetes monitoring.

Biodegradable optode-based nanosensors for in vivo monitoring.

Optode-based fluorescent nanosensors are being developed for monitoring important disease states such as hyponatremia and diabetes. However, traditional optode-based sensors are composed of nonbiodegradable polymers such as poly(vinyl chloride) (PVC) raising toxicity concerns for long-term in vivo use. Here, we report the development of the first biodegradable optode-based nanosensors that maintain sensing characteristics similar to those of traditional optode sensors. The polymer matrix of these sensors is composed of polycaprolactone (PCL) and a citric acid ester plasticizer. The PCL-based nanosensors yielded a dynamic and reversible response to sodium, were tuned to respond to extracellular sodium concentrations, and had a lifetime of at least 14 days at physiological temperature. When in the presence of lipase, the nanosensors degraded within 4 h at lipase concentrations found in the liver but were present after 3 days at lipase concentrations found in serum. The development of biodegradable nanosensors is not only a positive step towards their future use in in vivo applications, but they also represent a new sensor platform that can be extended to other sensing mechanisms.

Fluorescent nanoparticles for the measurement of ion concentration in biological systems.

Tightly regulated ion homeostasis throughout the body is necessary for the prevention of such debilitating states as dehydration.(1) In contrast, rapid ion fluxes at the cellular level are required for initiating action potentials in excitable cells.(2) Sodium regulation plays an important role in both of these cases; however, no method currently exists for continuously monitoring sodium levels in vivo (3) and intracellular sodium probes (4) do not provide similar detailed results as calcium probes. In an effort to fill both of these voids, fluorescent nanosensors have been developed that can monitor sodium concentrations in vitro and in vivo.(5,6) These sensors are based on ion-selective optode technology and consist of plasticized polymeric particles in which sodium specific recognition elements, pH-sensitive fluorophores, and additives are embedded.(7-9) Mechanistically, the sodium recognition element extracts sodium into the sensor. (10) This extraction causes the pH-sensitive fluorophore to release a hydrogen ion to maintain charge neutrality within the sensor which causes a change in fluorescence. The sodium sensors are reversible and selective for sodium over potassium even at high intracellular concentrations.(6) They are approximately 120 nm in diameter and are coated with polyethylene glycol to impart biocompatibility. Using microinjection techniques, the sensors can be delivered into the cytoplasm of cells where they have been shown to monitor the temporal and spatial sodium dynamics of beating cardiac myocytes.(11) Additionally, they have also tracked real-time changes in sodium concentrations in vivo when injected subcutaneously into mice.(3) Herein, we explain in detail and demonstrate the methodology for fabricating fluorescent sodium nanosensors and briefly demonstrate the biological applications our lab uses the nanosensors for: the microinjection of the sensors into cells; and the subcutaneous injection of the sensors into mice.

The design and development of fluorescent nano-optodes for in vivo glucose monitoring.

BACKGROUND: The advent of fluorescent nanosensors has enabled intracellular monitoring of several physiological analytes, which was previously not possible with molecular dyes or other invasive techniques. We have extended the capability of these sensors to include the detection of small molecules with the development of glucose-sensitive nano-optodes. Herein, we discuss the design and development of glucose-sensitive nano-optodes, which have been proven functional both in vitro and in vivo. METHODS: Throughout the design process, each of the sensor formulations was evaluated based on their response to changes in glucose levels. The percent change in signal, sensor reversibility, and the overall fluorescence intensity were the specific parameters used to assess each formulation. RESULTS: A hydrophobic boronic acid was selected that yielded a fully reversible fluorescence response to glucose in accordance with the sensor mechanism. The change in fluorescence signal in response to glucose was approximately 11%. The use of different additives or chromophores did not improve the response; however, modifications to the plasticized polymeric membrane extended sensor lifetime. CONCLUSIONS: Sensors were developed that yielded a dynamic response to glucose and through further modification of the components, sensor lifetime was improved. By following specific design criteria for the macrosensors, the sensors were miniaturized into nano-optodes that track changes in glucose levels in vivo.

Fluorescent nano-optodes for glucose detection.

We have designed fluorescent nanosensors based on ion-selective optodes capable of detecting small molecules. By localizing the sensor components in a hydrophobic core, these nanosensors are able to monitor dynamic changes in concentration of the model analyte, glucose. The nanosensors demonstrated this response in vitro and also when injected subcutaneously into mice. The response of the nanosensors tracked changes in blood glucose levels in vivo that were comparable to measurements taken using a glucometer. The development of these nanosensors offers an alternative, minimally invasive tool for monitoring glucose levels in such fields as diabetes research. Furthermore, the extension of the ion-selective optode sensor platform to small molecule detection will allow for enhanced monitoring of physiological processes.