SUBCUTANEOUS GLUCOSE SENSOR

1 . A glucose sensor for measurement of glucose in subcutaneous tissue, the sensor comprising:

a probe for subcutaneous insertion, the probe containing an indicator system comprising a receptor for selectively binding to glucose and a fluorophore associated with said receptor, wherein the fluorophore has a fluorescence lifetime of less than 100 ns;

a detector head which is optically connected to the probe and which is for location outside the body;

a light source; and

a detector arranged to receive fluorescent light emitted from the indicator system,

wherein the light source and detector are optionally located within the detector head;

wherein the sensor is arranged to measure glucose concentration in subcutaneous tissue by monitoring the fluorescence lifetime of the fluorophore.

2 . A sensor according to claim 1 , wherein the detector is a single photon avalanche diode.

3 . A sensor according to claim 2 , further comprising:

a driver arranged to modulate the light source intensity at a first frequency;

a bias voltage source arranged to apply a bias voltage to the single photon avalanche diode, wherein the bias voltage is modulated at a second frequency, different from the first frequency, and wherein the bias voltage is above the breakdown voltage of the single photon avalanche diode; and

a signal processor arranged to determine information related to a fluorescence lifetime of the fluorophore based on at least the output signal of the single photon avalanche diode.

4 . A sensor according to claim 1 wherein the receptor is an enzyme or a compound containing one or more boronic acid groups.

5 . A sensor according to claim 1 , wherein the fluorophore has a fluorescence lifetime of 30 ns or less.

6 . A sensor according to claim 1 , wherein the fluorophore has a fluorescence lifetime of 20 ns or more.

7 . A sensor according to claim 1 , wherein the fluorophore is a non-metallic fluorophore.

8 . A sensor according to claim 1 , wherein the indicator system comprises a fluorophore-receptor construct which is bound to a hydrogel.

9 . A sensor according to claim 8 , wherein the hydrogel is a fluid hydrogel having a water content of at least 30% w/w.

10 . A sensor according to claim 1 , wherein the indicator system is provided as an aqueous solution.

11 . A sensor according to claim 1 , comprising (a) a non-disposable detector head and (b) a disposable probe unit comprising the probe and a connector arranged to connect the probe to the detector head.

12 . A sensor according to claim 1 , further comprising a reader unit arranged to connect to, or receive data from, the detector head, wherein the light source and detector are optionally located within the reader unit.

13 . A sensor according to claim 12 , wherein the detector head comprises the light source and detector and additionally comprises a power supply and a transmitter arranged to wirelessly transmit data relating to the output of the detector to a receiver, and wherein the reader unit comprises a receiver arranged to receive data transmitted by the transmitter.

14 . A sensor according to claim 1 , further comprising a microprocessor arranged for controlling the sensor to provide two or more measurements of glucose concentration at defined intervals and a memory arranged for storing information on the fluorescence lifetime data, or glucose concentration.

15 . A disposable probe unit for use in a glucose sensor as defined in claim 1 , comprising (a) a probe for subcutaneous insertion, the probe containing an indicator system as defined in any one of claims 1 or 4 to 10 , and (b) a connector arranged to optically connect the probe to a detector head comprising, or being itself further optically connected to, a light source and a detector.

16 . A detector head adapted for connection to a separate probe unit, wherein the detector head comprises a detector which is a single photon avalanche diode, the detector being arranged to receive light from the probe unit, the detector head being adapted to monitor fluorescence lifetimes of less than 100 ns.

17 . A detector head according to claim 16 , wherein the detector is adapted to monitor fluorescence lifetimes of 20 ns or more.

18 . A method of measuring glucose concentration in subcutaneous tissue, which comprises

(a) inserting the probe of a sensor as defined in claim 1 into subcutaneous tissue;

(b) providing incident light to the indicator system from the light source;

(c) receiving fluorescent light, emitted from the indicator system in response to the light incident on the indicator system from the light source, using the detector and generating an output signal; and

(d) determining information related to the fluorescence lifetime of the fluorophore based on at least the output signal of the detector.

19 . A method according to claim 18 , which further comprises (e) wirelessly transmitting data relating to the output signal of the detector or to the fluorescence lifetime of the fluorophore, to a receiver located in a reader unit, wherein step (e) may be carried out either before or after step (d).

20 . A method according to claim 18 wherein the detector is a single photon avalanche diode and the method further comprises the steps of:

(f) modulating the light source intensity at a first frequency; and

(g) applying a bias voltage to the single photon avalanche diode, wherein the bias voltage is modulated at a second frequency, different from the first frequency, and wherein the bias voltage is above the breakdown voltage of the single photon avalanche diode.

21 . A method according to claim 18 , wherein glucose concentration is monitored continuously by carrying out at least steps (b), (c) and (d) two or more times at defined intervals and storing the obtained information in a memory.