Biosensor development

Review Article - Diabetes Technology in the Hospital: An Update

PURPOSE OF REVIEW

There have been many developments in diabetes technology in recent years, with continuous glucose monitoring (CGM), insulin pump therapy (CSII) and automated insulin delivery (AID) becoming progressively accepted in outpatient diabetes care. However, the use of such advanced diabetes technology in the inpatient setting is still limited for several reasons, including logistical challenges and staff training needs. On the other hand, hospital settings with altered diet and stress-induced hyperglycemia often pose challenges to tight glycemic control using conventional treatment tools. Integrating smarter glucose monitoring and insulin delivery devices into the increasingly technical hospital environment could reduce diabetes-related morbidity and mortality. This narrative review describes the most recent literature on the use of diabetes technology in the hospital and suggests avenues for further research.

RECENT FINDINGS

Advanced diabetes technology has the potential to improve glycemic control in hospitalized people with and without diabetes, and could add particular value in certain conditions, such as nutrition therapy or perioperative management. Taken together, CGM allows for more accurate and patient-friendly follow-up and ad hoc titration of therapy. AID may also provide benefits, including improved glycemic control and reduced nursing workload. Before advanced diabetes technology can be used on a large scale in the hospital, further research is needed on efficacy, accuracy and safety, while implementation factors such as cost and staff training must also be overcome.

Electrospun Nanofibers for Label-Free Sensor Applications

Electrospinning is a simple, low-cost and versatile method for fabricating submicron and nano size fibers. Due to their large surface area, high aspect ratio and porous structure, electrospun nanofibers can be employed in wide range of applications. Biomedical, environmental, protective clothing and sensors are just few. The latter has attracted a great deal of attention, because for biosensor application, nanofibers have several advantages over traditional sensors, including a high surface-to-volume ratio and ease of functionalization. This review provides a short overview of several electrospun nanofibers applications, with an emphasis on biosensor applications. With respect to this area, focus is placed on label-free sensors, pertaining to both recent advances and fundamental research. Here, label-free sensor properties of sensitivity, selectivity, and detection are critically evaluated. Current challenges in this area and prospective future work is also discussed.

Consistency of Continuous Ambulatory Interstitial Glucose Monitoring Sensors

AIMS

The abdominal region is the most common location for continuous glucose monitor (CGM) sensor insertion. However, a paucity of post-marketing data is available to demonstrate intra-individual consistency of CGM readings at different abdominal insertion sites.

METHODS

Healthy adults (fasting glucose (FG) < 5.5 mmol/L; BMI < 30 kg/m²) were recruited and a CGM sensor was placed on each side of the abdomen. Postprandial and continuous 48-h interstitial glucose levels were analyzed.

RESULTS

There was no significant difference in the 3-h postprandial glucose (PPG) level derived from the left versus right CGM, which remained non-significant after adjusting for waist circumference or FG. Among the glucose levels recorded over 48-h, values on the left site were greater in 3.6% of the data points (p < 0.05). After adjusting for waist circumference, only 0.5% of the glucose values remained significantly greater on the left (p < 0.05). When adjusted for FG, similar results were observed. For both PPG and 48-h readings, the mean absolute relative difference was not significant between the two abdominal sites.

CONCLUSIONS

CGM-derived glucose measures were highly consistent between the left and right abdomen during both the postprandial and post-absorptive periods.

Specific Interaction of Influenza Virus with Organized Assemblies of Polydiacetylenes

Supramolecular organizates of liposomes and Langmuir-Blodgett (LB) films are described which are capable of specifically binding to pathogens such as influenza virus. The specific interaction is between the hemagglutinin protein of the virus and an α-C-glycoside of sialic acid expressed on the surface of the liposome or LB film. Sialic acidcontaining liposomes were found to inhibit influenza virus infectivity in cell culture, and may provide a basis for new materials which act as therapeutic agents. Sialic acid-containing LB films also specifically bind to the influenza virus. In this case, the conjugated polymer backbone acts as a built-in reporter of the binding event, measurable by a chromatic change in the visible absorption spectrum. These films may provide a basis for new materials which act as direct detectors of binding

A tale of two compartments: interstitial versus blood glucose monitoring

Self-monitoring of blood glucose was described as one of the most important advancements in diabetes management since the invention of insulin in 1920. Recent advances in glucose sensor technology for measuring interstitial glucose concentrations have challenged the dominance of glucose meters in diabetes management, while raising questions about the relationships between interstitial and blood glucose levels. This article will review the differences between interstitial and blood glucose and some of the challenges in measuring interstitial glucose levels accurately.

Chemiluminescence biosensor system for lactic acid using natural animal tissue as recognition element

A new method based on natural animal tissue porcine kidney as recognition element for chemiluminescence sensing of lactic acid is proposed in this paper. The principle for lactic acid sensing is that lactic acid is oxidized by oxygen under the catalysis of alpha-hydroxy acid oxidase in the tissue column to produce hydrogen peroxide, which can react with luminol in the presence of potassium ferricyanide to generate a CL signal. The experimental results show that the CL emission intensity was linear with lactic acid concentration in the range of 1-1000 micromol/L and the detection limit (3sigma) for lactic acid was 0.2 micromol/L. The biosensor could be used continuously for 6h with no significant changes in the response. More than 240 measurements were carried out during this time. A complete analysis, including sampling and washing, could be performed in 1.5 min with a relative standard deviation of 1.12% for 100 micromol/L lactic acid. The reproducibility among tissue columns was satisfactory (RSD among columns is less than 5%). The biosensor has been applied successfully to the analysis of lactic acid in plasma and milk samples.

Diffusion and transfer of antibody proteins from a sugar-based hydrogel

Diffusion of antibody protein from hydrogel films and hydrogel encapsulated in a microcapillary was studied. Thin hydrogel films were formed by crosslinking 6-acryloyl-B-O-methylgalactoside with N,N'-methylene-bis-acrylamide and the diffusive transport of monoclonal antimouse IgG-FITC into and out of the hydrate films was measured. Diffusion coefficients in 2 and 4% crosslinked hydrogel films were measured. The measured diffusion constants determined for IgG in both the 2 and 4% hydrogel films were comparable to the free diffusion of IgG in bulk water (Dmean approximately 10(-7) cm2/s). In addition, 2% crosslinked hydrogels were prepared in a capillary tube and the transport of antimouse IgG-FITC into and out of the hydrated hydrogel was measured. Kinetic analysis indicated that the protein transport through the capillary hydrogel was faster than would be expected for a simple diffusion process. Finally, by utilizing the diffusion of antibody from the capillary hydrogel, transfer of antibody to a silica surface was demonstrated. A capillary hydrogel loaded with antimouse IgG-FITC was used to transfer the protein to a silica surface forming a 30-micron spot of antibody, which was imaged using fluorescence microscopy. These results may lead to the development of a nonlithographic method of patterning antibodies on surfaces for use in integrated microimmunosensors.

Biosensors for food analysis

Concerning speed, cost and on-line capabilities, biosensors offer attractive alternatives to existing methods for food analysis. They make monitoring and control of manufacturing processes possible. Furthermore, portable biosensors could be used for monitoring in manufacturing, retail and distribution of foods. An overview is given about existing biosensors for foodstuffs that could find applications in food industry.

Microbiosensors using electrodes made in Si-technology

The combination of electrochemical transducers made in silicon technology with chemical and biochemical components has been used to manufacture miniaturized sensor structures. Three different types of sensors have been developed and optimized for practical use; (i) an ion-selective sensor, (ii) a glucose enzyme sensor, (iii) a redox-amplifying sensor for immunosensing. The immunodetection based on the redox recycling of mediator molecules is shown for low and high molecular weight analytes. The sensors have been integrated with miniaturized fluidic components and combined with sensor-related electronics and a common microcontroller.

Z-membranes: artificial organelles for overexpressing recombinant integral membrane proteins

We have expressed a fusion protein formed between the avian infectious bronchitis virus M protein and the bacterial enzyme beta-glucuronidase in transgenic tobacco cells. Electron microscope images of such cells demonstrate that overexpression of this fusion protein gives rise to a type of endoplasmic reticulum membrane domain in which adjacent membranes become zippered together apparently as a consequence of the oligomerizing action of beta-glucuronidase. These zippered (Z-) membranes lack markers of the endoplasmic reticulum (NADH cytochrome c reductase and ribosomes) and accumulate in the cells in the form of multilayered scroll-like structures (up to 2 micrometers in diameter; 20-50 per cell) without affecting plant growth. The discovery of Z-membranes has broad implications for biology and biotechnology in that they provide a means for accumulating large quantities of recombinant membrane proteins within discrete domains of native membranes.

Biosensors for chemical and biological agents of defence interest

This review discusses current developments in biosensors for toxic materials of defence interest with particular emphasis on the biological element of such devices. A wide variety of synthetic chemicals, toxins of plant or animal origin and biological materials--including various disease micro-organisms as well as some bacterial exotoxins--have either been used as warfare agents or are perceived as having the potential to be used for that purpose. Although an enormous effort is being put into developing biosensors, relatively few analytes, especially toxic materials, can yet be measured by commercially available devices. The factors which currently mitigate against the use of enzyme, natural receptor or antibody based biosensors for unattended continuous environmental monitoring of toxic materials include the inherent instability and availability of suitable proteins and--for receptors and antibodies--the essentially irreversible nature of the binding event, which necessitates a continuous supply of reagents for sequential measurements. Assays involving antibody or DNA based biosensors are time consuming when working in a hazardous environment. Nevertheless, biosensors are capable of being used for extremely sensitive and specific on-site measurements of contamination by specific toxic materials. Methods for improving the stability, extending the range and altering the binding characteristics of sensing molecules are discussed.

Evanescent wave biosensors. Real-time analysis of biomolecular interactions

Optical biosensors, based on evanescent wave technology, are analytical devices that measure the interactions between biomolecules in real time, without the need for any labels. Specific ligands are immobilized to a sensor surface, and a solution of receptor or antibody is injected over the top. Binding is measured by recording changes in the refractive index, caused by the molecules interacting near the sensor surface within the evanescent field. Evanescent wave-based biosensors are being used to study an increasing number of applications in the life sciences, including the binding and dissociation kinetics of antibodies and receptor-ligand pairs, protein-DNA and DNA-DNA interactions, epitope mapping, phage display libraries, and whole cell- and virus-protein interactions. There are currently four commercially available evanescent wave biosensors on the market. This article describes the technology behind their sensing techniques, as well as the range of applications in which they are employed.