pH SENSOR FOR TISSU E-FLAP-ORGAN BLOOD FLOW CHANGE AND ISCHEMIA DETECTION

Abstract

The invention relates to a pH sensor that can be embedded within a flap, allows wired or wireless operation, is biocompatible, does not require an additional power source thanks to its Schottky diode structure, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents. The pH sensor subject to the invention is suitable for use in the healthcare field, in areas dealing with tissue transplantation such as plastic surgery, hand surgery, and transplant surgery.

Description

[0001] pH SENSOR FOR TiSSU E-FLAP-ORGAN BLOOD FLOW CHANGE AND ISCHEMIA DETECTION TECHNICAL FIELD

[0002] The invention relates to a pH sensor that can be embedded within a flap, can allow wired or wireless operation, is biocompatible, does not require an additional power source thanks to its Schottky diode structure, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents. The pH sensor subject to the invention is suitable for use in the healthcare field, in areas dealing with tissue transplantation such as plastic surgery, hand surgery, and transplant surgery.

[0003] PRIOR ART

[0004] Free flap surgery is a reconstructive technique that involves the transfer of living tissue from one part of the body to another in order to repair defects caused by trauma, cancer resection, or congenital anomalies. This technique involves separating a tissue flap from its blood supply, known as the donor site, and reconnecting it to a recipient site where new blood vessels will form and nourish the transplanted tissue. Today, free flap surgery is a complex and sophisticated technique that requires a high level of skill and experience to be performed successfully. The development of monitoring techniques, imaging modalities, and computer-assisted planning systems has further increased the safety and effectiveness of free flap surgery. The success of free flap surgery depends on many factors, such as the patient’s medical history, the complexity of the procedure, and the expertise of the surgical team. An important aspect affecting the success of free flap surgery is the monitoring of flap viability. The blood supply of the flap must be closely monitored to ensure adequate perfusion and oxygenation, because disruption of blood flow can lead to flap necrosis and failure. Various monitoring techniques, including clinical examination, Doppler ultrasound, and near-infrared spectroscopy, are available to assess flap viability and allow early intervention in case of compromise. In the current technique, there is no generally accepted monitoring device for free tissue transfers performed in plastic surgery, and tissue perfusion in these procedures is followed by clinical observation. In the known state of the art, clinical monitoring is used as the gold standard in flap followup. In this process, especially with the highest probability in the early postoperative first 72 hours, the flap must be routinely evaluated for arterial or venous insufficiency during thefirst week, and clinical parameters such as capillary refill, turgor, and temperature are checked hourly. In addition to being subjective, the main limitations of the use of clinical monitoring include the need for expertise to interpret clinical signs, unsuitability for use in buried flaps, and the lack of qualitative / objective values it produces. The unsuitability of clinical monitoring for evaluating buried flaps is a limitation frequently noted especially in head and neck surgery. Therefore, it is necessary to discover and develop laboratory-technological flap monitoring modalities that do not vary from person to person in an objective manner. Among noninvasive flap monitoring technologies, NIRS, laser Doppler, handheld Doppler, and duplex ultrasonography have limitations such as high cost and the requirement for experienced personnel for interpretation. The main limitations of invasive flap monitoring technologies include complex surgical technique, unsuitable equipment design and malfunction, and high cost. Today, the use of clinical observation and handheld Doppler devices, which are still considered the gold standard among monitoring methods, requires experienced personnel, does not allow continuous monitoring of the tissue, and may vary depending on the evaluator. In the current technique, the devices and methods used in free tissue transfers performed in plastic surgery have many disadvantages. Methods such as laser Doppler flowmetry and thermal imaging among these devices require competent and experienced personnel in their field. These devices are not manufactured domestically and are costly to procure. In addition, the devices require external access to the tissue; therefore, they do not offer monitoring capability for tissue and organ transplants that have no connection with the exterior of the body. For Color Doppler Ultrasonography, devices may not be available in every center, and they also require follow-up by a radiology specialist competent in the field outside the surgical and follow-up specialty, and do not provide continuous monitoring. Devices such as tissue oximeters and spectroscopy require the provision of a light source (in the infrared spectrum) to the transplanted tissue. Therefore, their use is not possible in buried tissue transplants, that is, those with no connection to the outside. At the same time, they may also be affected by oxygen deficiency occurring in the patient rather than in the tissue, and may cause false positives. Implanted Doppler probes and devices such as flow couplers require a significant learning curve since they are placed around the microvascular anastomosis, and incorrect placement may impair tissue perfusion. Even if no problem is observed after placement, they are not manufactured domestically, access is limited, costs are high, and significant complications have been reported. Devices such as fluorescence imaging, magnetic resonance, scintigraphy, and contrast-enhanced Doppler are not suitable for frequent measurements because they require contrast agent injection into patients, specialized imaging devices, and expert physicians competent in interpretation. At the same time, they do not provide continuous measurement. Microdialysis requiresobtaining samples from the transplanted tissue for biochemical investigation; therefore, it does not provide continuous measurement. The technique is technically complicated, difficult to interpret, and obtaining biochemical results is time-consuming. pH measurement modalities to date have been limited to small case series and have been reported to yield meaningful results in experimental studies. However, the main problem associated with pH measurement is the delayed acquisition of responses and the requirement to insert an external microelectrode into the tissue for measurement. In addition, to date, the smallest electrode in the known state of the art is 3 cm in length. The most commonly used methods for measuring tissue oxygenation are spectroscopy-based. This approach requires an external light source directed to the tissue; therefore, this approach is limited to skin-derived tissues outside the body. In the known state of the art, the response obtained in pH measurement modalities measures only the closed-circuit current resulting from ischemia-induced proton increase in the interstitial fluid. These sensors are standard measurement sensors placed on open wounds in wound care models. None of these sensors are intended for postoperative follow-up. They have been used for chronic wound care and intraoperative monitoring purposes.

[0005] In the known state of the art, patent document US9314165B2 describes a method and system for monitoring tissue oxygenation levels. The method and system described in this document may include one or more near-infrared compartment sensors, each of which may be equipped with a compartment alignment mechanism and a central scanning depth indicator, so that each sensor can be precisely positioned over a compartment of a living organism. The system may consist of hardware or software or both, and may adjust one or more algorithms depending on whether the monitored tissue is traumatized or healthy. The system may also monitor the relationship between blood pressure and oxygenation levels and may activate alarms based on predetermined conditions related to oxygenation levels or blood pressure or both. The method in question measures oxygenation measurements using the near-infrared method. Its use specifically in tissue transplants has not been reported. There is no operating mechanism related to pH measurement or ischemic metabolites.

[0006] In another known state of the art, patent document US8622918B1 describes a method and a device for assessing the viability of tissues such as flap tissue. The method in question for assessing flap tissue viability includes obtaining an oxygen saturation level associated with a first position on the flap tissue, determining whether the oxygen saturation level is below a first level, and, if the oxygen saturation level is below the first level, identifying the first position as having poor blood supply. This method aims to measure oxygen saturationlevels and to report impairment of tissue perfusion based on the measurement of oxygen saturation differences between two different regions, namely a non-intervened region and a flap-applied region. There is no operating mechanism related to pH measurement or ischemic metabolites.

[0007] In another known state of the art, patent document W02020101680A1 describes a system including a Doppler blood flow monitoring device, a signal generation module, a signal receiving module, a signal filtering module, a signal conversion module, at least one speaker, and a user interface. The signal generation module is configured to send a signal to a probe positioned in a probe housing on a vascular coupling element positioned around a patient’s vessel. The signal filtering module is configured to filter the return signal. The signal conversion module is configured to convert the filtered signal into an audible indicator and a visual indicator corresponding to a characteristic of blood flow in the patient’s vessel. The at least one speaker is configured to emit the first audible indicator. In addition, the user interface is configured to display the visual indicator. In this document, it is intended to use Doppler ultrasonography determinations in flap monitoring. Although there is no reference to pH measurement in the tissue, it is a method intended for use in flap monitoring. However, there is no method by which it can be used in buried flaps and internal organ transplants, because it is connected to the exterior of the body.

[0008] The limitations and inadequacies of the solutions in the current state of the art, the inability of the modalities claimed to be usable for flap monitoring to determine flap viability through the determination of pH or ischemia-related acidosis, and the disadvantages of these modalities in general such as being connected to the exterior of the body, requiring a light source, and needing to be positioned close to the flap’s nourishing vessel, which may put circulation at risk have made it necessary to develop an improvement in this field.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The invention relates to a pH sensor that can be embedded within a flap, allows wired or wireless operation, is biocompatible, does not require an additional power source thanks to its Schottky diode structure, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents.

[0011] One objective of the invention is to develop a sensor capable of performing the measurement of a different parameter that can provide reliable measurements byabandoning oxygenation, in order to detect circulation in buried or internal organ transplants. For this purpose, a pH sensor has been developed in the invention. Since every minute is critical in free tissue transfers, the invention aims to measure the increase in the amount of protons causing the pH change rather than the pH value of the tissue itself.

[0012] Another objective of the invention is to develop a pH sensor that does not require an additional power source. The pH sensor subject to the invention has Schottky diode structures. The Schottky diode property eliminates the need for an external battery, particularly in wired use. The sensor in question is capable of taking continuous measurements by being placed within the tissue.

[0013] Another objective of the invention is to eliminate the requirement for experienced personnel or specialists from another discipline in flap monitoring. The pH sensor in question eliminates this requirement through measurements performed based on quantified values. Thus, the mentioned pH sensor provides an objective technique in addition to the subjective, that is, operator-dependent techniques of the current state of the art.

[0014] In the invention, it is aimed to develop a pH sensor for use in flap monitoring applications that is used to determine whether the tissue is perfused, does not directly measure oxygen level and carbon dioxide level that are dependent on external factors, is not affected by ambient and patient temperature like thermal imaging and other temperature measurement techniques, does not require a connection from the external surface into the tissue, can be embedded within the tissue, responds to acidosis occurring in cases of impaired blood flow by measuring proton changes in the interstitial fluid, provides continuous measurement capability, allows wireless data transmission when necessary, enables early warning by recognizing proton flow at the nanomolar level compared to conventional pH measurement modalities, measures the increase in the amount of protons causing the pH change rather than the tissue pH value itself, and does not require any external power source.

[0015] Another objective of the invention is to develop a pH sensor that can also be used in organ transplants, which have characteristics similar to free flaps. While in free flaps a vascularized tissue taken from the patient’s own body is transplanted to another region, in organ transplants tissue taken from another person is transplanted. Similarly, this sensor can be used to monitor tissue viability.BRIEF DESCRIPTION OF THE FIGURES

[0016] Figure 1. Schematic view of the pH sensor subject to the invention

[0017] Figure 2. Current-voltage characteristics of the Au / GS / nSi Schottky diode structure in different liquid environments ((3): pH 8.3 NaHCO3, (2): pH 7.8 base, (0): air, (1): pH 6.4 acid)

[0018] Figure 3. Time-dependent short-circuit current variation of the Au / GS / nSi Schottky diode structure in different liquid environments ((1): pH 6.4 acid, (2): pH 7.8 base, (3): pH 8.3 NaHCO3)

[0019] Figure 4. Normalized current increase signals observed from the moment of occlusion in different numbered animals belonging to the arterial group in in vivo experiments

[0020] DEFINITION OF THE ELEMENTS / PARTS CONSTITUTING THE INVENTION

[0021] 1. Silver (Ag) ohmic contact

[0022] 2. Gold (Au) layer

[0023] 3. Porous silicon (PS) layer

[0024] 4. n-type silicon (nSi) layer

[0025] 5. Indium (In) ohmic contact

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] The invention relates to a pH sensor that can be embedded within a flap, allows wired operation or wireless operation via transmitters that allow data transmission as defined in the literature, is biocompatible, does not require an additional power source thanks to its Schottky diode-based fuel cell-type structure, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents. The present sensor must be removed after it has completed fulfilling its intended purpose. In the invention, a sensor has been developed that measures the change in short-circuit current generated by conductivity / capacitance changes created in a porous silicon-based sensor by H+ions formed during ischemia and subsequent acidosis. When acidosis occurs, the H+ions formed create conductivity / capacitance changes in the porous silicon-based sensor. This, in turn, causes the formation / change of short-circuit current.The pH sensor subject to the invention comprises:

[0028] • a silver (Ag) ohmic contact (1 ),

[0029] • a gold (Au) layer (2) as the catalyst layer of the Schottky diode metal layer,

[0030] • a porous silicon (PS) layer (3) as the pH-sensitive defective interface of the Schottky diode semiconductor layer,

[0031] • an n-type silicon (nSi) layer (4) as the substrate of the Schottky diode semiconductor layer,

[0032] • an indium (In) ohmic contact (5).

[0033] The pH sensor subject to the invention comprises a gold (Au) layer / porous silicon (PS) layer / n-type silicon (nSi) layer (Au / PS / nSi) Schottky diode metal / semiconductor diode structure.

[0034] In one embodiment of the invention, the pH sensor in question comprises:

[0035] • a silver (Ag) ohmic contact (1 ),

[0036] • a 0.350 micrometer gold (Au) layer (2) as the catalyst layer of the Schottky diode metal layer,

[0037] • a 20 micrometer porous silicon (PS) layer (3) as the pH-sensitive defective interface of the Schottky diode semiconductor layer,

[0038] • a 550 micrometer n-type silicon (nSi) layer (4) as the substrate of the Schottky diode semiconductor layer,

[0039] • a 100 micrometer indium (In) ohmic contact (5).

[0040] The pH sensor subject to the invention has a structure that can be embedded within a flap, allows wired or wireless operation, is biocompatible, does not require an additional power source within the interstitial fluid due to its Schottky diode structure, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents. The pH sensor subject to the invention provides continuous measurement, either indirectly (pH change due to changes in ion quantity and an increase in short-circuit current) or directly through pH values, by being embedded in the transplanted tissue in a biocompatible manner, either wired or wirelessly. As a result of measurements performed based on quantified values, the requirement for experienced personnel or specialists from another discipline is eliminated. The pH sensor subject to the invention presents an objective technique in addition to the subjective, that is, operator-dependent techniques defined in the literature among post-microsurgical follow-up methods. The pH sensor in question offers a solution in the field of tissue monitoring that is completely different from innovative but expensive materials andmethods. The pH sensor subject to the invention has Schottky diode structures. The Schottky diode property eliminates the need for an external battery, particularly in wired use. The sensor in question has the capability to take continuous measurements by being placed within the tissue. The pH sensor subject to the invention does not directly measure oxygen level and carbon dioxide level, which are used to determine whether the tissue is perfused and are dependent on external factors, is not affected by ambient and patient temperature like thermal imaging and other temperature measurement techniques, does not require a connection from the external surface into the tissue, can be embedded within the tissue, responds to acidosis occurring in cases of impaired blood flow by measuring proton changes in the interstitial fluid, provides continuous measurement capability, allows wireless data transmission when necessary, enables early warning by recognizing proton flow at the nanomolar level compared to conventional pH measurement modalities, and does not require any external power source thanks to its Schottky diode structure.

[0041] In the invention, it is aimed to measure the increase in the amount of protons causing the pH change rather than the pH value of the tissue. For this reason, the single-crystal silicon-based sensors used are Schottky diode devices in an Au / PS / nSi structure formed by a porous silicon (PS) layer created on the single-crystal silicon surface by an electrochemical anodization process and a gold (Au) metal electrode coated thereon. Porous silicon is a material that attracts attention particularly in gas and humidity sensor applications due to its proton conductivity property and unique surface chemical bond distribution, consisting of a spongy silicon network covered with nano- to micro-sized pores and having a high surface area of about 103m2 / cm3compared to single-crystal silicon. It is known from literature studies that the metal / PS / nSi Schottky diode structure generates short-circuit current and open-circuit voltage in hydrogen-containing liquids without the need for any external power source. The diode surface in contact with the flap tissue fluid takes the liquid into the pores through the PS structure surface and generates short-circuit current like a fuel cell. In this process, changes in the hydrogen content of the contacting liquid generate a signal by changing the internal electric field of the diode and thus the short-circuit current. An increase in the acidity of the environment or an increase in H+ion concentration increases the diode short-circuit current, whereas an increase in negative ions, on the contrary, decreases the diode short-circuit current. Au was selected due to its noble metal nature and catalytic effect. The structure is open to further development with different metals and catalytic layers capable of forming a diode structure. In this manner, improvements are being studied with metals (silver, platinum, palladium) and layers such as graphene and graphene oxide to increase catalytic effect. The metal (Au) / PS / nSiintegrated diode structure is inseparable, and ohmic contacts (Ag, In) are essential for measuring the sensor response.

[0042] In the experimental approach of the pH sensor subject to the invention, it has been demonstrated in in vivo and in vitro studies that the sensor is sensitive to ischemia and the metabolic consequences it causes. In the experiments, following a two-stage process consisting initially of in vitro experiments and in vivo studies conducted in three animals for sensor and animal model optimization, in vivo experiments of the final sensor model were initiated.

[0043] The in vivo experimental procedure applied in the development of the pH sensor subject to the invention and its translation into the clinical scenario are as follows:

[0044] The procedural steps applied in the experimental model of the pH sensor subject to the invention include:

[0045] • elevation of the rat groin flap,

[0046] • verification of perfusion,

[0047] • placement of the sensor beneath the flap,

[0048] • performance of baseline measurement,

[0049] • continuous measurement for 20 minutes,

[0050] • application of micro-clamp occlusion of the relevant vessel for 20 minutes and evaluation of the signal.

[0051] In the clinical scenario of the pH sensor subject to the invention, the procedural steps are as follows:

[0052] • completion of the free tissue transfer procedure,

[0053] • confirmation that the vascular anastomoses are functioning,

[0054] • embedding and fixation of the sensor within the flap tissue,

[0055] • performance of baseline measurement,

[0056] • continuous measurement,

[0057] • detection of a signal peak as ischemia or vessel occlusion,

[0058] • flap assessment (clinical evaluation and use of additional follow-up methods), • performing reoperation and revascularization if necessary.

[0059] In the first stage of the study, n-type single-crystal silicon was first cleaned using an organic solvent. An electrochemical etching process was created under illumination with a constant current density in an anodization cell in which silicon acted as the anode in asolution containing hydrofluoric acid and water, while a platinum wire acted as the cathode. The anodization process was carried out for the targeted duration. An indium ohmic contact is placed on the nSi side of the prepared PS / nSi structure. Thus, the PS surface is coated with metals such as gold and platinum under vacuum using the electron-beam evaporation technique. The metal / PS / nSi diode structure with prepared contacts is placed onto a suitable substrate. For example, all parts except the front PS surface are coated with wax to prevent unwanted interactions when operating in a liquid environment.

[0060] The production method of the pH sensor subject to the invention comprises the following process steps:

[0061] i. cleaning the surface oxide and organic contamination of n-type crystalline silicon using organic solvents,

[0062] ii. carrying out an electrochemical etching process under illumination at a constant current density in an anodization cell in which silicon acts as the anode in a solution, while a platinum wire acts as the cathode,

[0063] iii. performing the anodization process for 1-200 minutes or for 30 minutes, iv. placing an indium ohmic contact on the nSi side of the prepared porous silicon / n- type silicon (PS / nSi) structure,

[0064] v. coating the porous silicon (PS) surface with metals such as gold and platinum under vacuum using the electron-beam evaporation technique,

[0065] vi. placing the metal / PS / nSi diode structure with prepared contacts onto a suitable substrate,

[0066] vii. coating all parts except the PS surface with wax in order to prevent unwanted interactions when operating in a liquid environment.

[0067] In one embodiment of the invention, in step (i) of the method in question, hydrofluoric acid (HF) is used to clean the surface oxide, and acetone and isopropanol are used to remove organic contamination.

[0068] In one embodiment of the invention, in step (ii) of the method in question, the electrochemical etching process is carried out at a constant current density of J = 1-50 mA-crn-2.

[0069] In one embodiment of the invention, in step (ii) of the method in question, the solution contains hydrofluoric acid and water.Using the indium rear contact and the metal front contact, short-circuit current measurements of the metal / PS / nSi structure as a function of time were performed using a Keithley 640 electrometer device. Although it was not possible to create an exact one-to-one equivalent of the measurements performed within the flap under room conditions, the current-voltage characteristics and time-dependent short-circuit current (Isc) variation of the sensors were measured within liquids in the living pH range (8.3-6.4) and at room conditions by dropping the liquids onto the surface, using a Keithley 2400 device.

[0070] In Figure 1 , a schematic view of the pH sensor subject to the invention is provided. Ag and indium are ohmic contact points. The basic Schottky diode-structured sensor is in Metal / Semiconductor form. The diode metal is Au (gold), and the semiconductor is GS / nSi.

[0071] When the current-voltage characteristics of the Au / GS / nSi structure were examined in room conditions, pH 6.4 acidic solution, pH 7.8 basic solution, and pH 8.3 NaHCO3buffer solution, it was measured that the devices exhibited Schottky diode characteristics in all environments, and the graph is given in Figure 2. When the current-voltage characteristics of the Au / GS / nSi-structured sensor were examined under room conditions, in pH 6.4 acidic, pH 7.8 basic, and pH 8.3 NaHCO3buffer solutions with the liquid contacting the front Au / GS surface, it was observed that the amount of current provided by the device varied according to the amount of voltage applied to the circuit, and it was determined that the device exhibited Schottky diode characteristics in all environments. When the short-circuit currents of the structure in liquids with the relevant three different pH values were measured as a function of time without any external supply, it was determined in Figure 3 that, particularly in the acidic medium, a process was observed in which the current increased within the first 1 minute reaching up to 8.5 pA, then rapidly decreased, and reached saturation at a constant value of 1-1.5 pA. These measurements indicated that when placed in liquid environments, the above-mentioned process first occurred, and when oxygen and other molecules reached the GS interface, the process proceeded in the reverse direction at the reactive GS interface. However, when placed in the NaHCO3environment, it was determined that the short-circuit current slowly increased from 0.4 pA to 1.2 pA and then approximately stabilized. This situation was considered to direct the process in such a way that, following the formation of an acidic environment on the surface as shown by the reactions given below on the surface of the NaHCO3structure, a lower short-circuit current would be reached compared to the acidic environment. When the short-circuit currents generated by the sensor structure in liquids with the relevant three different pH values were measured as a function of time without any external supply, it was again observed that in pH 6.4 acidic medium the current increased within the first 1 minutereaching 8.5 pA, then rapidly decreased and reached saturation at a constant value of 11.5 pA; in pH 7.8 basic medium it increased more weakly and more rapidly compared to the acidic medium and then decreased and stabilized more rapidly than in the acidic medium; and in pH 8.3 NaHCO3it was observed that the short-circuit current increased weakly and then approximately stabilized.

[0072] In the second stage of the experimental study, using a rat groin flap model designed in three groups of five animals each, on a total of 15 rats, the sensor’s ability to detect ischemia at an early stage was determined by occluding the artery of the groin flap (ART group), the vein (VEN group), and both vessels (pedicle, PED group) (Table 1). In order to create an environment that could be embedded within the flap in the clinical scenario, the elevated groin flaps were placed over the sensor. The underlying reason for the sensor appearing large relative to its size can be explained in this manner.

[0073] Table 1. Experimental groups

[0074] Experimental and Control Number of Animals Number of Repetitions Groups per Group

[0075] Group ART 5 Artery, Artery, Vein, Pedicle Group VEN 5 Vein, Vein, Artery, Pedicle Group PED 5 Pedicle, Pedicle, Artery,

[0076] Vein

[0077]

[0078] In order to minimize excessive animal use and to collect more recordings, different vessel measurements of 20 minutes were also included in each animal. However, in accordance with the intended purpose of the sensor and in order to mimic the clinical scenario, the data obtained during the first occlusion and the release of the first occlusion were taken into consideration. The results belonging to the arterial occlusion group are given in Figure 4. As can be read from the graph, the average time elapsed to obtain an ischemia-related signal from the flap tissue on the sensor after clamping is 105 seconds, that is, less than 2 minutes. The moments of occlusion are indicated by circular symbols. It was measured that the occlusion signal began to appear on average 105 s after occlusion, approximately between 60-214 s, and that the signal peak was completed on average at 386 s, approximately between 200-720 s.

Claims

CLAIMS1. A pH sensor that can be embedded within a flap, allows wired or wireless operation, is biocompatible, and is capable of detecting the increase in tissue acidity caused by changes in blood flow and ischemia through ion exchange and closed-circuit currents, characterized in that it comprises:• a silver (Ag) ohmic contact (1 ),• a gold (Au) layer (2) as the catalyst layer of the Schottky diode metal layer, • a porous silicon (PS) layer (3) as the pH-sensitive defective interface of the Schottky diode semiconductor layer,• an n-type silicon (nSi) layer (4) as the substrate of the Schottky diode semiconductor layer,• an indium (In) ohmic contact (5).

2. A pH sensor according to claim 1, characterized in that it comprises a gold (Au) layer / porous silicon (PS) layer / n-type silicon (nSi) layer (Au / PS / nSi) Schottky diode metal / semiconductor diode structure.

3. A pH sensor according to claim 1 , characterized in that it comprises:• a silver (Ag) ohmic contact (1 ),• a 0.350 micrometer gold (Au) layer (2) as the catalyst layer of the Schottky diode metal layer,• a 20 micrometer porous silicon (PS) layer (3) as the pH-sensitive defective interface of the Schottky diode semiconductor layer,• a 550 micrometer n-type silicon (nSi) layer (4) as the substrate of the Schottky diode semiconductor layer,• a 100 micrometer indium (In) ohmic contact (5).

4. A method for producing a pH sensor according to any one of claims 1-3, characterized in that it comprises the process steps of:i. cleaning the surface oxide and organic contamination of n-type crystalline silicon using organic solvents,ii. carrying out an electrochemical etching process under illumination at a constant current density in an anodization cell in which silicon acts as the anode in a solution, while a platinum wire acts as the cathode,iii. performing the anodization process for 1-200 minutes or for 30 minutes,iv. placing an indium ohmic contact on the nSi side of the prepared porous silicon / n-type silicon (PS / nSi) structure,v. coating the porous silicon (PS) surface with metals such as gold and platinum under vacuum using the electron-beam evaporation technique, vi. placing the metal / PS / nSi diode structure with prepared contacts onto a suitable substrate,vii. coating all parts except the PS surface with wax in order to prevent unwanted interactions when operating in a liquid environment.

5. A method according to claim 4, characterized in that in step (i) of the method in question, hydrofluoric acid (HF) is used to clean the surface oxide, and acetone and isopropanol are used to remove organic contamination.

6. A method according to claim 4, characterized in that in step (ii) of the method in question, the electrochemical etching process is carried out at a constant current density of J = 1-50 mA-cm-2.

7. A method according to claim 4, characterized in that in step (ii) of the method in question, the solution mentioned comprises hydrofluoric acid and water.

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