News Column

Patent Issued for Glucose Sensor Calibration

June 25, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventors Crane, Barry Colin (Oxfordshire, GB); Paterson, William (Oxfordshire, GB), filed on November 16, 2011, was published online on June 10, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8746031 is assigned to Lightship Medical Limited (London, GB).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The use of glucose sensors in the medical field is widespread. The regular monitoring of blood glucose levels of diabetic patients at home as well as the use of glucose monitoring in intensive care units are two primary examples. The usual aim in developing a glucose sensor is to produce a digital electronic signal, which is proportional to the glucose concentration. The sensor usually comprises two main components, a chemical or biological part that reacts or complexes with the glucose (ideally specifically) to form new chemical or biological products or changes in energy that can be detected by means of the second component, a transducer. The chemical/biological component can be said to act as a receptor/indicator for glucose. A variety of transduction methods can be used including electrochemical (such as potentiometric, amperometric, conductimetric, impedimetric), optical, calorimetric and acoustic. After transduction the signal is usually converted to an electronic digital signal.

"Since the signal generated by the chemical/biological reaction with the analyte is usually dependent not only on the concentration of the analyte but also on the characteristics of the sensor itself, such sensors usually require calibration before they can be utilised quantitatively. The way in which the signal varies with the analyte concentration determines the shape of the calibration curve (signal versus analyte concentration) and may define the number of calibration points. Typical calibration curves can be straight line, exponential, s-shaped etc and the principal of calibration applies to all methodologies of transduction for chemical or biological sensors.

"Ideally, the sensor should be calibrated just before its use since some sensor characteristics that can affect the calibration curve vary with time (ageing effect). It is often the case that the time between sensor manufacture and use can be many months, so calibration at the point of manufacture can lead to inaccuracies in the end result. This means that the attendant clinician or nurse, or the home user, will be required to perform the calibration themselves. In order to maximise user compliance, the calibration process should be simple to perform, ideally invisible to the person performing the calibration, and be quickly completed.

"Typical calibration techniques currently in use require the sensor to be inserted into three solutions having differing, but known, glucose concentrations (one of which may be zero), a reading to be taken for each solution, and a calibration curve to be generated. Since glucose has a tendency to degrade when sterilised in an aqueous solution, commonly the glucose solutions must be made up at the time of calibration by the addition of solid glucose to water or a solution such as saline. The entire calibration process is therefore both complicated and time consuming. Calibration of many currently available glucose sensors could 25 minutes or more to complete. There is therefore a need for a more rapid calibration technique for a glucose sensor, in order to improve user compliance."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The present inventors have found that the time needed for calibration of a glucose sensor can be reduced by preparing the calibration solutions in a particular manner. Specifically, the calibration solutions are prepared by the addition of both alpha and beta glucose to water or an aqueous solution.

"As is well known, glucose exists in two predominant forms (isomers), termed the alpha and beta forms. In aqueous solution, the two forms will equilibrate by mutarotation of the glucose molecule. The resulting ratio of the two forms will be approximately 64:36 (beta:alpha). In the solid state, however, glucose is usually supplied in the alpha form. This means that when alpha glucose is added to water or an aqueous solution, it takes a period of time for the two forms to equilibrate (full equilibration can take a matter of hours).

"Glucose sensors contain a receptor which has an affinity for glucose. Such receptors typically also have a greater affinity for either the alpha or beta form. This means that when calibration is carried out by the usual technique of addition of alpha glucose to water, the rate at which the sensor signal stabilises in the resulting solution is dependent on the rate of mutarotation.

"The present inventors have shown that by the preparation of calibration solutions for a glucose sensor by adding both the alpha and beta forms to water or an aqueous solution, the rate of stabilisation of the sensor signal and hence the rate of calibration can be reduced.

"The present invention accordingly provides a method of calibrating a glucose sensor, which method comprises: (a) preparing a first glucose-containing calibration solution by combining water or an aqueous solution with alpha and beta glucose, the alpha and beta glucose being provided in solid form; (b) exposing a glucose sensor to said first glucose-containing calibration solution and determining the sensor output; exposing the glucose sensor to one or more further calibration solutions having different glucose concentrations from each other and from said first glucose-containing calibration solution (said different glucose concentration optionally being zero) and determining the sensor output for the or each calibration solution; and (d) determining a calibration curve from the sensor output data collected in steps (b) and .

"Step may be carried out either before or after steps (a) and/or (b).

"Also provided is a calibration kit comprising a first compartment (1) containing water or an aqueous solution; a second compartment (2) containing glucose in solid form; and an optional third compartment (3) containing glucose in solid form, wherein at least one of the second and third compartments contains alpha glucose and at least one of the second and third compartments contains beta glucose, and wherein the first compartment is separated from the glucose-containing compartment(s) by a water impermeable dividing material.

"Also provided is a glucose sensor kit comprising a glucose sensor and the calibration kit of the invention."

URL and more information on this patent, see: Crane, Barry Colin; Paterson, William. Glucose Sensor Calibration. U.S. Patent Number 8746031, filed November 16, 2011, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8746031.PN.&OS=PN/8746031RS=PN/8746031

Keywords for this news article include: Lightship Medical Limited.

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Source: Journal of Engineering