Continuous glucose sensing with fluorescent thin-film hydrogels. 2. Fiber optic sensor fabrication and in vitro testing

Fiber Optic Sensors: A Review for Glucose Measurement

Diabetes mellitus is a chronic metabolic disorder, being globally one of the most deadly diseases. This disease requires continually monitoring of the body's glucose levels. There are different types of sensors for measuring glucose, most of them invasive to the patient. Fiber optic sensors have been proven to have advantages compared to conventional sensors and they have great potential for various applications, especially in the biomedical area. Compared to other sensors, they are smaller, easy to handle, mostly non-invasive, thus leading to a lower risk of infection, high precision, well correlated and inexpensive. The objective of this review article is to compare different types of fiber optic sensors made with different experimental techniques applied to biomedicine, especially for glucose sensing. Observations are made on the way of elaboration, as well as the advantages and disadvantages that each one could have in real applications.

Real-time dynamic sensing with an on-chip nanophotonic sensor

We demonstrate a nanophotonic sensor for real-time monitoring of fluid flows. The sensor is based on a silicon photonic crystal cavity with a well aligned micro fluidic channel for fluid-injection. The simulated resonant wavelength shift of the sensor with residual oil in holes is 9.0 nm, and the observed experimental shift under the same condition is 10.0 nm. An alternating fluid delivery is applied in a dynamic sensing experiment with syringe pump controlled ratios of water and oil. Excellent agreement between the measured data and the video images of fluidic streams in the optofluidic cell is found.

Recent advances in fluorescent arylboronic acids for glucose sensing

Continuous glucose monitoring (CGM) is crucial in order to avoid complications caused by change in blood glucose for patients suffering from diabetes mellitus. The long-term consequences of high blood glucose levels include damage to the heart, eyes, kidneys, nerves and other organs, among others, caused by malign glycation of vital protein structures. Fluorescent monitors based on arylboronic acids are promising candidates for optical CGM, since arylboronic acids are capable of forming arylboronate esters with 1,2-cis-diols or 1,3-diols fast and reversibly, even in aqueous solution. These properties enable arylboronic acid dyes to provide immediate information of glucose concentrations. Thus, the replacement of the commonly applied semi-invasive and non-invasive techniques relying on glucose binding proteins, such as concanavalin A, or enzymes, such as glucose oxidase, glucose dehydrogenase and hexokinases/glucokinases, might be possible. The recent progress in the development of fluorescent arylboronic acid dyes will be emphasized in this review.

A unique, two-component sensing system for fluorescence detection of glucose and other carbohydrates

In our glucose-sensing system, a boronic acid-modified viologen molecule quenches the fluorescence of a separate dye molecule. When glucose or other monosaccharides are added and bind to the boronic acid, the quenching ability of the viologen is diminished and fluorescence increases. Thus, changes in the fluorescence of the dye can be correlated with changing glucose concentration. Quenching and sugar-sensing results are explained by an electrostatic interaction between dye and quencher. This modular system can be configured in a nearly unlimited number of ways through substitution and multiplexing of the two fundamental quencher and dye components. Significantly, fluorescent quantum dots (QDs) can also be used as the reporter component. The system can also be immobilized in a hydrogel polymer to provide real-time, reversible sugar sensing.

Materials for diabetes therapeutics

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels).

A NEW CLASS OF THIN FILM HYDROGELS PRODUCED BY PLASMA POLYMERIZATION

A simple, direct route to preparation of surface immobilized hydrogel films is described. Specifically, low pressure RF pulsed plasma polymerization of 1-amino-2-propanol and 2-(ethylamino)ethanol monomers produced thin hydrogel films deposited on substrates located in the plasma reactor. The successful syntheses were carried out under plasma conditions which not only yield the hydrogel but are also sufficiently energetic to produce films strongly grafted to the substrates. The polymer films obtained exhibit the thermoresponsive property of hydrogels, as shown by film color change with temperature. Additional evidence for the phase transition properties of these films was obtained using water contact angle and capillary rise measurements. The plasma polymerization approach provides an unusually simple route to synthesis of hydrogels in which the films are pin-hole free and are of easily controlled thickness. An important added advantage, particularly for applications involving biomaterials, is the conformal property of the plasma generated polymer films. The results obtained suggest that this approach should be applicable to a variety of other monomers and, based on differences observed with the present two monomers, suggest synthesis of films which exhibit a range of phase transition temperatures.

Using an Indicator Displacement Assay to Monitor Glucose Oxidase Activity in Blood Serum

[diagram: see text] Using a boronic acid receptor that was previously found to have high affinity for gluconic acid, we created a colorimetric indicator displacement assay (IDA) that can report the concentration of the product of glucose oxidase (GOx) catalyzed glucose oxidation. The color change obtained directly reflects the concentration of glucose. Our sensing ensemble was then successfully applied to determine the glucose concentration in human serum, which offers a facile, colorimetric, sensitive, and accurate glucose test.

Recent progress in analytical instrumentation for glycemic control in diabetic and critically ill patients

Implementing strict glycemic control can reduce the risk of serious complications in both diabetic and critically ill patients. For this reason, many different analytical, mainly electrochemical and optical sensor approaches for glucose measurements have been developed. Self-monitoring of blood glucose (SMBG) has been recognised as being an indispensable tool for intensive diabetes therapy. Recent progress in analytical instrumentation, allowing submicroliter samples of blood, alternative site testing, reduced test time, autocalibration, and improved precision, is comprehensively described in this review. Continuous blood glucose monitoring techniques and insulin infusion strategies, developmental steps towards the realization of the dream of an artificial pancreas under closed loop control, are presented. Progress in glucose sensing and glycemic control for both patient groups is discussed by assessing recent published literature (up to 2006). The state-of-the-art and trends in analytical techniques (either episodic, intermittent or continuous, minimal-invasive, or noninvasive) detailed in this review will provide researchers, health professionals and the diabetic community with a comprehensive overview of the potential of next-generation instrumentation suited to either short- and long-term implantation or ex vivo measurement in combination with appropriate body interfaces such as microdialysis catheters.