INTEGRATED ELECTRODE FOR SAMPLING OF LACTATE AND OTHER ANALYTES

Abstract

The invention provides a biosensor for at least partial insertion in a fetal scalp, for monitoring an analyte in the body of the fetus, wherein the biosensor comprises a needle and a microdialysis element for sampling the analyte. The invention also provides a sensing system comprising the biosensor, configured to flow a liquid through the microdialysis element. The invention can be used for e.g. lactate sensing as well as releasing a pharmaceutical. Hence, the biosensor and/or sensing system may also be used for delivery of a pharmaceutical or nutrient to a fetus.

Claims

1. A biosensor for at least partial insertion in a fetal scalp, for monitoring an analyte in the body of the fetus, wherein the biosensor comprises a needle and a microdialysis element for sampling the analyte.

2. The biosensor according to claim 1, wherein the microdialysis element is integrated in the needle.

3. The biosensor according to claim 1, comprising an electrode.

4. The biosensor according to claim 1, wherein the microdialysis element is integrated in the electrode.

5. The biosensor according to claim 3, wherein the needle comprises the electrode and the microdialysis element.

6. The biosensor according to claim 3, wherein the electrode has a single or double helix configuration.

7. The biosensor according to claim 1, wherein the microdialysis element comprises a membrane having a cut-off selected from the range of 5-200 kDa.

8. A sensing system comprising the biosensor according to claim 1, configured to flow a liquid through the microdialysis element.

9. The sensing system according to claim 8, wherein the sensing system includes an analysis unit, configured to sense an analyte in the liquid returning from the microdialysis element.

10. The sensing system according to claim 8, further configured to measure with the electrode one or more of CTG and STAN.

11. The sensing system according to claim 8, configured for continuously monitoring or configured for periodically monitoring an analyte in the body of the fetus.

12. The sensing system according to claim 8, wherein the sensing system is configured to sense lactate as analyte.

13. The sensing system according to claim 8, wherein the sensing system is configured to perform an ELISA analysis.

14. The sensing system according to claim 8, wherein the sensing system is configured to perform an enzymatic (assay) analysis.

15. The sensing system according to claim 8, wherein the sensing system is configured to perform chromatographic analysis.

16. The sensing system according to claim 8, wherein the sensing system is configured to perform mass spectrometric analysis, especially MSMS analysis.

17. The sensing system according to claim 8, wherein the biosensor comprises a hollow membrane with a hollow tube (especially a tube in tube configuration) arranged in part of the cavity enclosed by the membrane, wherein the sensing system is configured to flow dialysis liquid via the hollow tube into the hollow membrane, and wherein the sensing system is configured to retrieve dialysis liquid that flow along the membrane back to an analysis unit.

18. The sensing system according to claim 17, wherein the analysis unit comprises one or more of an ELISA, an enzymatic assay, a chromatographic unit and a mass spectrometric unit.

19. The sensing system according to claim 8, further comprising a storage unit, functionally coupled with the biosensor, and configured to store a sample sampled with the biosensor.

20. A method of using the biosensor according to claim 1, comprising sensing lactate and/or one or more other analytes in the scalp of a baby during giving birth.

21. A method of using the biosensor according to claim 1, comprising for sensing neurotransmitters in tissue of an animal.

22. The method of using the biosensor according to claim 1, comprising delivery of a pharmaceutical or nutrient to a fetus.

23. A method of using the biosensor according to claim 8, comprising sensing lactate and/or one or more other analytes in the scalp of a baby during giving birth.

24. A method of using the biosensor according to claim 8, comprising sensing neurotransmitters in tissue of an animal.

25. A method of using the biosensor according to claim 8, comprising delivery of a pharmaceutical or nutrient to a fetus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0024] FIG. 1a-2c schematically depict some aspects of the biosensor; and

[0025] FIGS. 3a-4c show some results.

[0026] The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] For adequate monitoring of e.g. lactate and/or other analytes, the microdialysis membrane needs to be inserted in the fetal scalp. To this end the microdialysis membrane can either be incorporated into (one of) the recording electrode(s) (FIG. 1a. Left) or can be incorporated into a scalp penetrating needle, that is located adjacent to the electrode(s), such as in the middle of a (helix) electrode (FIG. 1b Right). In the version where the microdialysis membrane is incorporated in a scalp penetrating needle, the needle will penetrate the scalp when the electrodes are screwed in. FIGS. 1a-1b schematically depict embodiments of a (regular) fetal scalp electrode, indicated with reference 102, like a fetal scalp electrode configured for CTG analysis and/or STAN analysis, wherein the micro dialysis probe (also indicated herein as dialysis probe), indicated with reference 103, is indicated. Reference 100 indicates the biosensor.

[0028] A fetal scalp electrode (FSE) may especially monitor the fetal heart rate (FHR) directly and continuously during the intrapartum period. They accurately measure beat-to-beat variability and display the fetal electrocardiogram (fECG) waveform. The fetal scalp electrode allows electronic fetal monitoring (EFM). The electrode may e.g. include a single helix configuration (see FIGS. 1a/1b), or optionally a double helix configuration. Internal fetal monitoring especially involves placing an electrode directly on the fetal scalp through the cervix. This test is performed to evaluate fetal heart rate and variability between beats, especially in relation to the uterine contractions of labor. Internal monitoring differs from external monitoring. Instead of both leads being strapped to the outside of the woman's body, the Doppler lead is replaced by a smaller lead that is placed inside the woman's vagina and attached to the head of the baby. The internal lead is called a fetal scalp electrode (or FSE). It is especially only used to monitor the baby's heart rate during labour, usually if external monitoring is not being reliable (but sometimes if the caregiver prefers internal to external monitoring). A fetal scalp clip, or electrode, may be a small, circular, corkscrew-shaped needle attached to a coated wire. The clip may be covered with a long, protective, flexible, plastic covering and guided up through the mother's vagina by the caregiver doing an internal examination. This procedure should not be any more uncomfortable than a normal vaginal examination. The waters need to be broken to attach an FSE to the baby's head. If they are not already broken, this will need to be done to allow the electrode to be attached. The needle is gently rotated into the skin on the baby's scalp (or bottom if the baby is breech). The internal electrode monitors the baby's heart rate more accurately than an external Doppler. Once the clip is attached, the plastic cover is removed, leaving just the wire. The fetal scalp clip may have two colored wires attached. The wires are connected to the lead with a small conducting device (about the size of a match-box), strapped to the woman's thigh. The conducting device has conducting gel applied to it (like the gel used in ultrasounds). The lead is then plugged into the monitor to produce the readouts.

[0029] The electrode, especially for fetal monitoring or like application, may comprise an electrically conductive electrode lead having means at one end thereof to transmit a signal to a recording or related means, said lead being provided at its opposite end with a reversely reentrant, sharpened and barbed formation to embed in a skin area of a fetus, a second electrode lead generally paralleling said first lead and also provided with means at an end thereof to transmit a signal to said recording means, and a sheath encircling said leads and exposing said opposite end of said first-named lead.

[0030] In such electrode(s) the microdialysis element may be incorporated, such as in a recording electrode or in a separate needle (or both)(see also above).

[0031] The dialysis membrane, indicated with reference 103a which is comprised by the biosensor 100, typically has a molecular weight cut-off of 5 KDa to 200 KDa. The membrane may be closed off on one side, e.g. with glue. By inserting a (thin) hollow tube 101, such as a fused silica tube, into the membrane, ringer's solution or saline can be perfused through the inner side of the membrane. The open surface of the membrane 103a will typically be (over a length of) 1-5 mm, which is enough to sample recover lactate and/or other analytes from the scalp for quantification (FIGS. 2a-2b). This application can also be used in other target tissues, like regular skin or bone.

[0032] Hence, a (dialysis) liquid (herein also indicated as perfusate) is flowed in the internal of the microdialysis element along the dialysis membrane, thereby entraining (bio)molecules at the other side of the membrane when the membrane is in contact with body tissue and/or a body fluid.

[0033] FIGS. 1a-1b. Fetal scalp electrode for CTG and STAN analysis, in which a microdialysis membrane is incorporated. The dotter area in FIG. 1a marks the position where the membrane is in contact with the extracellular fluid (during use). Left picture 1a shows the membrane incorporated into the CTG/STAN electrode. Right picture 1b shows an additional skin penetrating needle type micro dialysis probe, in which the membrane is incorporated. Hence, in both embodiments the micro dialysis probe is incorporated in the biosensor for CTG and/or STAN, herein also indicated as (regular) fetal scalp electrode. However, in the former (1a) the micro dialysis probe is integrated in the actual electrode(s) 102, whereas in the latter (1b) the micro dialysis probe is arranged adjacent to the actual electrode(s) 102 for CTG and/or STAN analysis, such as within the helix shaped electrode 102.

[0034] FIG. 2a depicts an embodiment and some aspects of the dialysis procedure in both configurations of FIG. 1 or other configurations. Here, FIG. 2a especially shows a configuration of dialysis membranes incorporated in CTG/STAN electrode 102, though a similar configuration may also be used for the separate probe as depicted in FIG. 1b. Reference 102a indicates a surface of the electrode 102. Dialysis liquid is transported to tube 104, which is arranged within the micro dialysis probe 103. The probe comprises membrane 103a. The dialysis fluid will leave the tube 104 and flow back, along the membrane 103a. The dialysis liquid may be forced back by a closure 107 at an end of the micro dialysis probe, such as a glue stop. While flowing along the membrane 103a, exchange 105 of (small) molecules will occur between the dialysis liquid and external fluid. Fluid can be collected when leaving 108 the dialysis probe 103. An opposite flow of the fluid within the dialysis probe 103 is also possible. FIG. 2b schematically depicts a cross-section of FIG. 2a at the membrane 103a. Referring to FIGS. 2a-2b, part of the electrode surface 102a is open, such as over a length of 1-5 mm, such that the membrane 103a can be exposed to body tissue and body fluid. Fluid that is collected downstream from the membrane (see reference 108 ) may be analyzed as above.

[0035] FIG. 2c schematically depicts a system 1000 with a biosensor 100 functionally coupled to an analysis unit 1100. Here, the analysis unit 1100 is optionally (also) configured to measure e.g. a CTG signal, using e.g. a voltage source or electro physiological measuring device 1110. Further, a dialysis fluid source 120 is functionally coupled with the biosensor 100 to provide the fluid, which returns to the analysis unit to be analyzed with a dialysis fluid analysis unit, comprised by the analysis unit 1100. Further, the term analysis unit may also refer to a plurality of such units, which may especially be functionally coupled. For instance, the analysis unit may include a chromatographic unit and a mass spectrometric unit. Hence, optionally the system may be configured to sample with the biosensor and to measure CTG and/or STAN.

[0036] Note that the unit 1100 may optionally also be configured to provide a nutrient and/or pharmaceutical. In such instance the unit 1100 may be defined as delivery unit. Further the unit 1100 is not necessarily configured to sense also via the electrode (functionality). For instance, the unit may be configured to (1) sense the analyte via the biosensor, and/or (2) to provide a nutrient and/or pharmaceutical via the biosensor, and optionally also to measure CTG and/or STAN. Instead of nutrient and/or pharmaceutical, also one or more of a contrast liquid or radioactive isotope, etc. may be included in the dialysis liquid.

[0037] Note however that the same principle may be used to release active components, like a pharmaceutical or a nutrient. Even, during application both functions may be applied, i.e. monitoring by e.g. lactate sensing as well as releasing a pharmaceutical. Hence, the biosensor and/or sensing system may also be used for delivery of a pharmaceutical or nutrient to a fetus.

Experimental

[0038] Adult male wild type wistar rats were used for the experiments (500 g). Animals were anaesthetized using isoflurane (oxygen 0.8 l/min, nitrogen 0 l/min). After shaving, microdialysis probes were inserted in the skin of the back of the animal and fixated with a suture. A pulse oximeter was clamped on the tail of the animal to monitor oxygenation and heart rate. A jugular vena cannula was inserted to draw blood samples (100 microl each), for analysis of lactate and saturation (Abbott analyzer).

[0039] Dialysis was performed using sterile saline solution (dialysis liquid) at 1.5 microl/min Samples were collected in 300 microl polypropylene vials, for lactate analysis. After stabilization of 15 min, sampling was started.

Analysis

[0040] Lactate, pH and saturation in blood samples was analyzed using a handheld Abbott analyzer. Lactate from dialysis samples was quantified with an enzymatic assay in a 96 well plate (reagents CMA).

Results

Peripheral Lactate

[0041] Upon decreasing of oxygenation (t=0 min) using increased nitrogen (0.8 l/min) and decreased oxygen (0.05 l/min), a saturation could be reduced to below 40% for an hour. Blood lactate levels simultaneously increased 2.5 fold (FIG. 3.). Upon restoration of saturation using 0.8 l/min oxygen, lactate levels returned to baseline levels rapidly. Blood pH, slowly decreased over the course of the experiment, and did not return to baseline for the 20 min when the animal was at restored saturation. FIG. 3 shows on the x-axis the time in minutes and on the y-axis lactate (L) in mM. Curve I (closed diamonds) indicates the saturation, curve II (closed squares) indicates lactate, and curve III (closed triangles) indicates the pH-7. 100% oxygenation is indicated with 1. The pH is the pH-7; i.e. the start pH is thus at 7.5.

Microdialysis of Lactate

[0042] FIG. 4a depicts the lactate levels as measured in dialysate and blood. The upper panel shows the absolute values of lactate from blood and dialysates (y-axis Lactate (L) in mM; and x-axis time in minutes). With a recovery of the dialysis membrane for lactate (II) of about 5%, levels corrected for recovery match blood lactate levels (I). Dialysis lactate levels increased at the same time that blood lactate levels increased, indicating that microdialysis can be used as alternative for blood lactate analysis. The lower panel 4b shows the effects represented as % of basal level (BL) (y-axis % of basal level (BL); and x-axis time in minutes). The high peak at about 50 minutes is an artefact.

Recovery Experiment

[0043] Recovery was performed by inserting a CTG electrode with integrated microdialysis membrane in a stirred saline solution containing 10 mM of lactate. A 200 m outer diameter microdialysis membrane with 18 kDa cutoff was applied.

TABLE-US-00001 Dialysis flow Relative recovery (mean sem) 1.5 microliter per minute 22.74 2.27% (n = 4).sup.(1) 5 microliter per minute 8.90 0.64% (n = 2) .sup.(1)Relative to 10 mM external lactate concentration. Hence, with 22% one measures 2.2 mM when using the biosensor in the 10 mM lactate bath.

[0044] The data are also shown in FIG. 4c, with I indicating the blood lactate level, II indicating the concentration in the actual microdialysis fluid, and III indicating the corrected concentration of lactate in dialysis fluid after correction for recovery 22.74%.

[0045] Hence, the invention provides a biosensor for at least partial insertion in a body, especially a fetal body, such as in a fetal scalp, for monitoring an analyte, such as in the body of the fetus, wherein the biosensor comprises a needle and a micro dialysis element (herein also indicated as micro dialysis probe) for sampling the analyte. The invention also provides a sensing system comprising the biosensor according to any one of the preceding system, configured to flow a liquid through the micro dialysis element. The sensing system may include one or more units configured to analyze the liquid that flows back from the biosensor. Further, the sensing system may include a unit to flow the dialysis liquid through the biosensor. For instance, the biosensor may comprise a hollow membrane with a hollow tube (especially a tube in tube configuration) arranged in part of the cavity enclosed by the membrane (see also FIGS. 2a-2b), wherein the sensing system is configured to flow dialysis liquid via the hollow tube into the hollow membrane, and wherein the sensing system is configured to retrieve dialysis liquid that flow along the membrane back to an analysis unit. The invention also provides the use of the biosensor as defined herein or the sensing system according as defined herein, for sensing lactate in the scalp of a baby during giving birth. Especially, the fetal scalp is of a human fetus. The invention is further defined in the accompanying claims.