Blood urea nitrogen (BUN) sensors and methods of sensing urea nitrogen in biological samples

Abstract

One embodiment of a blood urea nitrogen (BUN) sensor measures urea nitrogen in a biological sample by measuring a differential voltage signal based on first and second voltage signals each representing a detected amount of carbon dioxide. The first signal represents a detected amount of carbon dioxide resulting from an enzymatic reaction of a biological sample contacting a sensor surface having a urease enzyme immobilized thereon. The second voltage signal represents a detected amount of background carbon dioxide in the biological sample. The differential voltage signal indicates an amount of urea nitrogen in the biological sample, which may be determined by appropriate correlation. Other embodiments of BUN sensors and methods of sensing BUN are also provided, as are other aspects.

Description

BLOOD UREA NITROGEN (BUN) SENSORS AND METHODS OF SENSING UREA NITROGEN IN BIOLOGICAL SAMPLES

[0001] This application claims benefit under 35 USC § 119(e) of U.S. Provisional Application No. 63 / 514,397, filed July 19, 2023. The entire contents of the above-referenced patent application are hereby expressly incorporated herein by reference. FIELD

[0002] This disclosure relates to blood urea nitrogen (BUN) sensors and methods of sensing urea nitrogen in biological samples. BACKGROUND

[0003] Urea nitrogen is a waste product found in the bloodstream of humans. It is produced by the liver from the breakdown of proteins in the human body. Urea nitrogen is normally filtered from the bloodstream by the kidneys and is removed from the body via urination. Some urea nitrogen in the bloodstream is normal.

[0004] Kidney function in humans can be evaluated by measuring the amount of urea nitrogen in the blood. The test to measure the amount of urea nitrogen is referred to as a blood urea nitrogen (BUN) test. BUN values ranging from 6 mg / dl to 24 mg / dl may be considered normal. BUN values above or below that range may indicate a disease and / or unhealthy condition (e.g., impaired kidney function, heart failure, liver failure, urinary system blockage, stress, malnutrition, dehydration, and / or excessive protein consumption).

[0005] The accuracy of conventional BUN tests, however, may be adversely affected by, e.g., potassium ions present in a blood sample, the pH level of the blood sample, and / or background ammonia present in the blood sample. Correction of these factors is needed for measurement accuracy. Such correction may add cost and complexity to a BUN sensor, and conventional BUN sensors may not be able to correct for background ammonia.

[0006] Accordingly, improved BUN sensors and methods of sensing urea nitrogen are desired. SUMMARY

[0007] In some embodiments, a sensor for measuring urea nitrogen in a biological sample is provided. The sensor includes first and second sensor components and a voltmeter. The first sensor component is operative to generate a first voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the first sensor component. The first sensor component includes a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane. The second sensor component is operative to generate a second voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the second sensor component. The second sensor component includes a second sensing membrane without any enzyme immobilized thereover. The voltmeter is coupled to receive the first and second voltage signals and is operative to output a differential voltage signal value based on the first and second voltage signals. The differential voltage signal value corresponds to an amount of urea nitrogen in the biological sample.

[0008] In some embodiments, a method of measuring urea nitrogen in a biological sample is provided. The methodincludes generating, via a first sensor component, a first voltage signal in response to the biological sample contacting the first sensor component. The first voltage signal is indicative of an amount of carbon dioxide, and the first sensor component has a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane. The method also includes generating, via a second sensor component, a second voltage signal in response to the biological sample contacting the second sensor component. The second voltage signal is indicative of an amount of carbon dioxide, and the second sensor component has a second sensing membrane without any enzyme immobilized over and in contact with the second sensing membrane. The method further includes generating, via a voltmeter, a differential voltage signal based on the first and second voltage signals, and converting, via a computer processor, a value of the differential voltage signal to a corresponding amount of urea nitrogen in the biological sample.

[0009] In some embodiments, another sensor for measuring urea nitrogen in a biological sample is provided. The sensor includes a housing and only a single electrode, wherein the single electrode is partially received in the housing. The sensor also includes a buffer solution disposed in the housing and in which the electrode is partially immersed. The sensor further includes a pH sensing membrane disposed over and in contact with the buffer solution, an electrolyte layer disposed over and in contact with the pH sensing membrane, a permeable film disposed over and in contact with the electrolyte layer, and only a single enzyme immobilized over and in contact with the permeable film. The electrode is operative to generate a voltage signal indicative of an amount of urea nitrogen in response to a biological sample contacting the enzyme.

[0010] Still other aspects, features, and advantages of this disclosure may be readily apparent from the following detailed description and illustration of a number of example embodiments and implementations, including the best mode contemplated for carrying out the invention. This disclosure may also be capable of other and different embodiments, and its several details may be modified in various respects, all without departing from the scope of the invention. For example, the BUN sensors described herein may readily be applicable to in-line fluidic flow paths in dialysis systems and / or open-heart circulation systems to monitor the kidney function of patient. More particularly, the BUN sensors described herein may be installed in a dialysis system as an in-line testing unit to monitor a patient’s nephrological function. This disclosure is intended to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims below. BRIEF DESCRIPTION OF DRAWINGS

[0011] The drawings described below are for illustrative purposes and are not necessarily drawn to scale. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. The drawings are not intended to limit the scope of the invention in any way.

[0012] FIG. 1 illustrates a side schematic view of a blood urea nitrogen (BUN) sensor configured to measure urea nitrogen in a biological sample according to embodiments provided herein.

[0013] FIG. 2 illustrates a flowchart of a method of measuring urea nitrogen in a biological sample according to embodiments provided herein.

[0014] FIG. 3 illustrates a side schematic view of another BUN sensor configured to measure urea nitrogen in a biological sample according to embodiments provided herein. DETAILED DESCRIPTION

[0015] Conventional blood urea nitrogen (BUN) sensors are typically based on an ammonium ion (NH4+) selective electrode using nonactin as an ammonium ionophore, wherein the enzyme urease is used on the electrode surface to convert blood urea in a biological sample (e.g., blood or urine) into ammonium ions, as represented in equation (1) below: CO(NH2)2+ H20 with [urease] -> 2NH3+ CO2(1) where CO(NH2)2is urea, H2O is water, 2NH3is ammonia, and CO2is carbon dioxide.

[0016] The value (or magnitude) of an electrical signal (measured in, e.g., millivolts) generated by the ammonium ion selective electrode in response to detecting ammonium ions may correspond to an amount or concentration of urea nitrogen in the biological sample. However, the measurement accuracy of such conventional BUN sensors may be adversely affected by a number of factors, including co-existing potassium ions (K+) in the biological sample. Co-existing potassium ions interfere with the nonactin-based ammonium ion selective electrode. To correct for this interference, a selectivity coefficient (or selectivity factor) has to be determined and applied to a correction algorithm.

[0017] The measurement accuracy of conventional BUN sensors may also be adversely affected by the pH level of the biological sample, which may adversely affect the urea nitrogen conversion to ammonium. To correct for this factor, a correlation between pH level and ammonia yield rate has to be developed and applied to a correction algorithm for theconventional BUN sensor. Based on such an algorithm, pH influence on BUN recovery can be corrected with an on-board pH sensor component included with the conventional BUN sensor.

[0018] The measurement accuracy of conventional BUN sensors may further be adversely affected by background ammonia in the biological sample. For example, background ammonia can be as high as 0.2 millimolar (mM) in infants and may be higher in adults with hepatitis, cirrhosis, Reye syndrome, or heart and / or kidney diseases. Such background ammonia may adversely elevate the measured urea nitrogen. Currently, no correction for background ammonia is known in conventional BUN sensors.

[0019] BUN sensors according to embodiments described herein may overcome one or more of the above-described measurement inaccuracies by measuring a CO2byproduct from a single enzymatic reaction to determine an amount (or concentration) of urea nitrogen in a biological sample (e.g., blood or urine). In one embodiment, described in more detail below, a specially-designed sensor pair may be employed to determine the amount (or concentration) of urea nitrogen in the biological sample. One sensor component of the sensor pair includes an enzyme, and the other sensor component of the sensor pair does not include an enzyme. An amount of urea nitrogen in a biological sample may be measured by the specially-designed sensor pair by measuring an electrical (voltage) signal difference between a first voltage signal generated by the sensor component modified with a urease enzyme immobilized on a sensor component surface and a second electrical signal generated by the other sensor component (which may be a standard carbon dioxide sensing component) not modified by any enzyme. A voltmeter or like electronic measuring device may be used to measure the electrical signal difference (in, e.g., millivolts). The differential voltage signal value output from the voltmeter corresponds to an amount of urea nitrogen.

[0020] In some embodiments, the amount of urea nitrogen can be determined by a computer processor executing programming instructions by accessing data stored in a non-transitory memory that may include a Nernst equation for calculating an amount of urea nitrogen based on the differential voltage signal value. Additionally or alternatively, the non-transitory memory may include a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts. In some embodiments, the correspondence may be based on Nernstian behavior. Note that BUN sensors according to embodiments described herein do not directly measure or determine carbon dioxide concentrations in the biological sample, but instead measure a difference between voltage signals indicative of detected amounts of carbon dioxide to determine an amount of urea nitrogen in the biological sample.

[0021] In another embodiment, described in more detail below, a modified Severinghaus-type pCO2(partial pressure carbon dioxide) sensor may be employed to determine an amount (or concentration) of urea nitrogen in a biological sample (e.g., blood or urine). This sensor is modified to include a single enzyme, urease, wherein a direct electrical signal measurement (not a differential electrical signal measurement) is taken and correlated to determine an amount of urea nitrogen in the biological sample.

[0022] Advantages of BUN sensors employing carbon dioxide sensing components according to embodiments described herein include no measurement interference from co-existing potassium ions in the biological sample, and no adverse measurement results caused by background ammonia in the biological sample. Another advantage of BUN sensors employing carbon dioxide sensing components according to embodiments described herein includes use of only a single enzyme to convert the urea nitrogen into ammonia and carbon dioxide. Some known BUNsensors use two enzymes (e.g., urease and carbonic anhydrase) to obtain pCO2values, where the second enzyme is used to accelerate response speed. However, use of two enzymes increases the cost and complexity of such BUN sensors.

[0023] In accordance with one or more embodiments, BUN sensors for measuring urea nitrogen in a biological sample having improved measurement accuracy will be explained in greater detail below in connection with FIGS. 1-3.

[0024] FIG. 1 illustrates a BUN sensor 100 configured to measure urea nitrogen in a biological sample according to one or more embodiments. BUN sensor 100 includes a first sensor component 102 and a second sensor component 103 each partially received in a housing 104, which is configured to receive and contain a biological sample 106, such as blood or urine, therein. The first sensor component 102 is operative to generate a first voltage signal V102 in response to detecting carbon dioxide, wherein the value (or magnitude) of the first voltage signal corresponds to an amount of carbon dioxide detected. The first sensor component 102 may include an electrode 108A coupled to a voltmeter 110. The electrode 108A may be a silver / silver chloride electrode, which advantageously has a longer service life (e.g., four weeks) and a more stable response signal than other types of electrodes, thus making it suitable for repeated-use sensor arrays. Alternatively, a platinum or gold electrode may be used. The first sensor component 102 may also include an electrolyte layer 112A partially disposed on the electrode 108A. Electrolyte layer 112A may comprise a sodium bicarbonate electrolyte in a 0.5% methyl cellulose (e.g., Methocel™) solution that forms a gel layer on the electrode 108A. A gel-like layer is easy to manufacture in miniaturized size, rendering the sensor advantageous for manufacture on electronic wafers / chips. Other electrolyte materials mayinclude PVOH (polyvinyl alcohol). The first sensor component 102 may further include a sensing membrane 114A, which may be a plasticized PVC (polyvinyl chloride) or polyurethan membrane. The first sensor component 102 may also include a urease enzyme 116 immobilized over and in contact with the sensing membrane 114A. The urease enzyme 116 is preferably a thin layer which, in some embodiments, may have a thickness ranging from 20 µm to 50 µm. Further, the urease enzyme 116 may partially or may entirely cover a surface of the sensing membrane 114A on which the urease enzyme 116 is immobilized thereon. In one exemplary embodiment, the urease enzyme 116 covers at least 75% of the sensing membrane 114A to ensure that most of the first voltage signal V102 generated at electrode 108A is caused by the enzymatic reaction of the biological sample with the urease enzyme 116.

[0025] The second sensor component 103 is operative to generate a second voltage signal V103 in response to detecting background carbon dioxide (i.e., carbon dioxide already present) in the biological sample 106, wherein the value (or magnitude) of the second voltage signal corresponds to an amount of background carbon dioxide detected. The second sensor component 103 may include an electrode 108B coupled to the voltmeter 110. The electrode 108B may also be a silver / silver chloride electrode or, alternatively, a platinum or gold electrode. The second sensor component 103 may also include a sodium bicarbonate electrolyte layer 112B partially disposed about the electrode 108B. Electrolyte layer 112B may comprise a sodium bicarbonate electrolyte in a 0.5% methyl cellulose (e.g., Methocel™) solution that forms a gel layer on the electrode 108B. Other electrolyte materials may include PVOH. The second sensor component 103 may further include a sensing membrane 114B, which may be a plasticized PVC orpolyurethan membrane, without any enzyme immobilized over and in contact with the sensing membrane 114B, as shown in FIG. 1.

[0026] The voltmeter 110 is coupled to receive the first and second voltage signals V102 and V103 from the first and second sensor components 102 and 103, respectively, and is operative to determine and output a differential voltage signal value VDIFF based on the first and second voltage signals (VDIFF = V102 – V103) that corresponds to a detected amount of urea nitrogen in the biological sample 106.

[0027] The output differential voltage signal value VDIFF of voltmeter 110 is coupled to a computer 118. In some embodiments, computer 118 may be in communication with other computers, system controllers, or other devices (of e.g., an automated diagnostic analysis system, a laboratory information system, a medical facility, etc.) either directly via wired and / or wireless connections or via a network 120 for transmitting urea nitrogen measurement results thereto and / or for receiving biological sample related information including, e.g., one or more of patient information, time and date a sample was obtained, medical facility information, tracking and routing information, and / or any other information relevant to the biological samples to be analyzed. Network 120 may be, e.g., a local area network (LAN), wide area network (WAN), or other suitable communication network, including wired and wireless networks. In some embodiments, computer 118 may be part of an automated diagnostic analysis system, a laboratory information system, a medical facility, etc.

[0028] Computer 118 may include a user interface 122, which may include a display, to enable a user to access a variety of control and status display screens and to enter commands and / or data into computer 118.

[0029] Computer 118 may also include a computer processor 118P, a non-transitory memory 118M, and programming instructions 118PI (e.g., software, programs, algorithms, and the like). Programming instructions 118PI may be stored in non-transitory memory 118M and executed by computer processor 118P. Programming instructions 118PI may additionally or alternatively be stored in another non-transitory computer readable medium. Non-transitory memory 118M may also include data 118D accessible by computer processor 118P. Data 118D may include, e.g., a Nernst equation for calculating an amount of urea nitrogen based on a differential voltage signal value. Data 118D may additionally or alternatively include a plurality of differential voltage signal values and a corresponding plurality of urea nitrogen amounts arranged in, e.g., a lookup table, database, or other suitable structure. In some embodiments, the correspondence between differential voltage signal values and urea nitrogen amounts may be based on Nernstian behavior. Non-transitory memory 118M may include other data and / or information that may be used by computer processor 118P to convert or correlate differential voltage signal values to corresponding amounts of urea nitrogen. While non-transitory memory 118M is shown internal to computer 118, all or a portion of non-transitory memory 118M may be external to and / or remote from computer 118. Computer 118 may alternatively or additionally include other processing devices / circuits (including microprocessors, A / D converters, amplifiers, filters, etc.), storage devices, transceivers, interfaces, device drivers, and / or other electronics.

[0030] Computer processor 118P executing programming instructions 118PI becomes a special purpose machine particularly suited for performing various actions, operations, analyses, and the like in accordance with the sensors and methods described herein and illustrated in theFIGS. In particular, computer processor 118P executing programming instructions 118PI is operative to, among other things, receive a differential voltage signal value (VDIFF) from voltmeter 110 and to determine an amount of urea nitrogen corresponding to the differential voltage signal value (VDIFF).

[0031] FIG. 2 illustrates a method 200 of measuring urea nitrogen in a biological sample according to one or more embodiments. At process block 202, method 200 may include generating, via a first sensor component, a first voltage signal in response to the biological sample contacting the first sensor component, wherein the first voltage signal is indicative of an amount of carbon dioxide, and the first sensor component has a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane. For example, referring to FIG. 1, the first sensor component may be first sensor component 102 having sensing membrane 114A and urease enzyme 116 immobilized over and in contact with the sensing membrane 114A, wherein first sensor component 102 generates first voltage signal V102. In response to contacting the first sensor component 102, the biological sample 106 reacts with the urease enzyme 116 to produce ammonia and carbon dioxide according to equation 1, repeated below: CO(NH2)2+ H20 with [urease] -> 2NH3+ CO2(1) Depending on the amount of urea nitrogen present in the biological sample, the total carbon dioxide concentration in the biological sample 106 may increase with enzymatically produced carbon dioxide.

[0032] At process block 204, method 200 may include generating, via a second sensor component, a second voltage signal in response to the biological sample contacting thesecond sensor component, wherein the second voltage signal is indicative of an amount of carbon dioxide, and the second sensor component has a second sensing membrane without any enzyme immobilized over and in contact with the second sensing membrane. For example, again referring to FIG. 1, the second sensor component may be second sensor component 103 having sensing membrane 114B without any enzyme immobilized over and in contact with the sensing membrane 114B, wherein second sensor component 103 generates second voltage signal V103. Background carbon dioxide in the biological sample 106 penetrates through the sensing membrane 114B into the sodium bicarbonate electrolyte layer 112B, which increases the hydrogen ion (H+) concentration in the sodium bicarbonate electrolyte layer 112B, which produces the second voltage signal (V103).

[0033] At process block 206, method 200 may include generating, via a voltmeter, a differential voltage signal based on the first and second voltage signals. For example, as shown in FIG. 1, voltmeter 110 may receive first and second voltage signals (V102 and V103) from first and second sensor components 102, 103, respectively, and may generate a differential voltage signal value (VDIFF = V102 – V103) provided to computer 118.

[0034] An amount of urea nitrogen in the biological sample relates to the value of the differential signal as follows: Higher urea nitrogen Higher CO2Larger VDIFF In some embodiments, the slope of the net signal change versus BUN concentration ranges from 30 mV to 50 mV / decade for the enzyme reaction generated signal (V102).

[0035] At process block 208, method 200 may include converting, via a computer processor, a value of the differential voltage signal to a corresponding amount of ureanitrogen in the biological sample. For example, computer processor 118P executing programming instructions 118PI of computer 118 may receive a differential voltage signal value from voltmeter 110 and convert that differential voltage signal value to a corresponding amount of urea nitrogen by accessing data 118D in non-transitory memory 118M of computer 118. Data 118D may comprise an equation, which may be a Nernstian equation in some embodiments, for calculating an amount of urea nitrogen based on a differential voltage signal value, as shown below:

[0036] Standard Nernstian equation: EMF = Constant + RT / zF *ln[M] = Constant + 2.303*RT / zF*log[M] where: [M]: ion concentration in mol / L or mmol / L; EMF: Electric Motive Force (voltage). For ISE (ion selective electrode), EMF is response signal of ion sensor; Constant: Standard signal (voltage) when concentration [M] = 1 mol / L. For ISE, it is regarded as offset; RT / zF: constant including temperature, ion charge number, etc.; EMF is proportional to the logarithm of the ion concentration; For monovalent ion, the 2.303*RT / zF = 59.2 mV / decade conc. change at temperature of 298K (25C); and For divalent ion, the 2.303*RT / zF = 29.8 mV / decade conc. change at temperature of 298K (25C).

[0037] For BUN sensor 100: BUN_1: mV(BUN) = [mV(pH) – mV(enzy)] = Offset + Slope*log[BUN]where: mV(BUN) is linearly correlated to log[BUN]; The Offset and Slope can be obtained from calibration prior to sample testing; and The recovery concentration of BUN in sample can be calculated as: ^^^^^ே^ିை^^^^௧ ^^^^ு^ି^^^^^௭௬^ିை^^^^௧^ ^^ ^^ ^^^ = 10ௌ^^^^= 10ௌ^^^^

[0038] a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts, wherein the correspondence may exhibit a Nernstian behavior (as described above) in some embodiments.

[0039] FIG. 3 illustrates another embodiment of a BUN sensor configured to measure urea nitrogen in a biological sample (e.g., blood or urine) according to one or more embodiments. BUN sensor 300 is a modified Severinghaus-type pCO2 (partial pressure carbon dioxide) sensor that measures urea nitrogen via a direct measurement of CO2 produced by a single enzymatic reaction. Sensor component 302 may include a housing 304 having only a single electrode 308, which may be a silver / silver chloride electrode. Alternatively, electrode 308 may be a platinum or gold electrode. Electrode 308 is partially immersed in a buffer solution 324 having a known pH. Buffer solution 324 may be, e.g., a sodium citrate or MES buffer solution (MES is the common name for the compound 2- ethanesulfonic acid). Bun sensor 300 may also include only a single enzyme 316 immobilized over and in contact with a permeable film 326. The single enzyme comprises urease and covers at least 75% of permeable film 326 to ensure that most of the generated voltage signal V302 at electrode 308 iscaused by the enzymatic reaction of the biological sample (not shown in FIG. 3) with the urease enzyme 316. Permeable film 326 is disposed over a sodium bicarbonate electrolyte layer 312. Permeable film 326 may be, in some embodiments, a cellulose acetate thin film or a polyurethane thin film and may have a thickness ranging from 10 µm to 30 µm. Sodium bicarbonate electrolyte layer 312 may be a thin layer having a thickness ranging from 100 µm to 500 µm after hydration in some embodiments. A pH sensing membrane 314 is disposed between the sodium bicarbonate electrolyte layer 312 and the buffer solution 324. The pH sensing membrane 314 may have a thickness ranging from 80 µm to 120 µm in some embodiments.

[0040] Electrode 308 of BUN sensor 300 may be coupled to a voltmeter 310, which is operative to receive voltage signal V302 and output a voltage signal value VBUN that corresponds to a detected amount of urea nitrogen in the biological sample applied to BUN sensor 300 (i.e., applied to the urease enzyme 316).

[0041] In some embodiments, the output of voltmeter 310 may be coupled to a computer 318, which may be configured as a special purpose machine identically or substantially similarly as computer 118 (of FIG. 1). In particular, computer 318 may include at least a processor, a non-transitory memory, programming instructions (e.g., software, programs, algorithms, and the like) stored in the non-transitory memory and executable by the processor, and data stored in the non- transitory memory that may include equations for calculating urea nitrogen amounts and / or a plurality of voltage signal values corresponding to a plurality of urea nitrogen amounts. Computer 318 is operable to receive voltage signal value VBUN from voltmeter 310 and, via execution by its processor of programming instructions stored in its non-transitory memory, convert that voltage signal value to a corresponding amount ofurea nitrogen by accessing the data stored in its non- transitory memory.

[0042] In some embodiments, computer 318 may be in communication with other computers, system controllers, or other devices (of e.g., an automated diagnostic analysis system, a laboratory information system, a medical facility, etc.) either directly via wired and / or wireless connections or via a network for transmitting urea nitrogen measurement results thereto and / or for receiving biological sample related information including, e.g., one or more of patient information, time and date a sample was obtained, medical facility information, tracking and routing information, and / or any other information relevant to the biological samples to be analyzed. The network may be, e.g., a local area network (LAN), wide area network (WAN), or other suitable communication network, including wired and wireless networks. In some embodiments, computer 318 may be part of an automated diagnostic analysis system, a laboratory information system, a medical facility, etc.

[0043] While this disclosure is susceptible to various modifications and alternative forms, specific method and apparatus embodiments have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that the particular methods and apparatus disclosed herein are not intended to limit the disclosure or the following claims.

[0044] Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

[0045] ILLUSTRATIVE EMBODIMENTS

[0046] The following provides a non-limiting list of illustrative embodiments of this disclosure:

[0047] Example Embodiment 1: A sensor for measuring urea nitrogen in a biological sample, comprising:

[0048] a first sensor component operative to generate a first voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the first sensor component, the first sensor component including a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane;

[0049] a second sensor component operative to generate a second voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the second sensor component, the second sensor component including a second sensing membrane without any enzyme immobilized thereover; and

[0050] a voltmeter operatively coupled to receive the first and second voltage signals and operative to output a differential voltage signal value based on the first and second voltage signals, the differential voltage signal value corresponding to an amount of urea nitrogen in the biological sample.

[0051] Example Embodiment 2: The sensor of Example Embodiment 1, further comprising a computer processor operatively coupled to the voltmeter, the computer processor operatively coupled to a non-transitory memory comprising programming instructions executable on the computer processor and comprising data for correlating differential voltage signal values with respective amounts of urea nitrogen; wherein the computer processor executing the programming instructions is operative to receive a value for the differential voltage signal from the voltmeter and determinethe amount of urea nitrogen corresponding to the differential voltage signal value.

[0052] Example Embodiment 3: The sensor of any one of Example Embodiments 1 or 2, wherein the data comprises a Nernst equation for calculating the amount of urea nitrogen based on the differential voltage signal value or comprises a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts via a Nernstian behavior.

[0053] Example Embodiment 4: The sensor of any one of Example Embodiments 1-3, further comprising a housing that includes the first and second sensor components each partially received therein, wherein the housing is operative to receive and contain the biological sample therein.

[0054] Example Embodiment 5: The sensor of any one of Example Embodiments 1-4, wherein:

[0055] the first sensor component further comprises a first silver / silver chloride electrode coupled to the voltmeter; and

[0056] the second sensor component further comprises a second silver / silver chloride electrode coupled to the voltmeter.

[0057] Example Embodiment 6: The sensor of any one of Example Embodiments 1-5, wherein:

[0058] the first sensor component further comprises a first electrode and a first sodium bicarbonate electrolyte layer disposed about a portion of the first electrode; and

[0059] the second sensor component further comprises a second electrode and a second sodium bicarbonate electrolyte layer disposed about a portion of the second electrode.

[0060] Example Embodiment 7: The sensor of any one of Example Embodiments 1-6, wherein the biological sample comprises blood or urine.

[0061] Example Embodiment 8: A method of measuring urea nitrogen in a biological sample, the method comprising:

[0062] generating, via a first sensor component, a first voltage signal in response to the biological sample contacting the first sensor component, the first voltage signal indicative of a first amount of carbon dioxide, the first sensor component having a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane;

[0063] generating, via a second sensor component, a second voltage signal in response to the biological sample contacting the second sensor component, the second voltage signal indicative of a second amount of carbon dioxide, the second sensor component having a second sensing membrane without any enzyme immobilized over and in contact with the second sensing membrane;

[0064] generating, via a voltmeter, a differential voltage signal based on the first and second voltage signals; and

[0065] converting, via a computer processor, a value of the differential voltage signal to a corresponding amount of urea nitrogen in the biological sample.

[0066] Example Embodiment 9: The method of any one of Example Embodiments 1-8, wherein the converting further comprises converting, via the computer processor, the value of the differential voltage signal to the corresponding amount of urea nitrogen in the biological sample based on data stored in a non-transitory memory accessible by the computer processor, the data including a Nernst equation for calculating the corresponding amount of urea nitrogen based on the value ofthe differential voltage signal or including a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts via a Nernstian behavior.

[0067] Example Embodiment 10: The method of any one of Example Embodiments 1-9, wherein:

[0068] the first sensor component further comprises a first silver / silver chloride electrode coupled to the voltmeter; and

[0069] the second sensor component further comprises a second silver / silver chloride electrode coupled to the voltmeter.

[0070] Example Embodiment 11: The method of any one of Example Embodiments 1-10, wherein:

[0071] the first sensor component further comprises a first electrode and a first sodium bicarbonate electrolyte layer disposed about a portion of the first electrode; and

[0072] the second sensor component further comprises a second electrode and a second sodium bicarbonate electrolyte layer disposed about a portion of the second electrode.

[0073] Example Embodiment 12: The method of any one of Example Embodiments 1-11, wherein the biological sample comprises blood or urine.

[0074] Example Embodiment 13: A sensor for measuring urea nitrogen in a biological sample, comprising:

[0075] a housing;

[0076] only a single electrode, the single electrode partially received in the housing;

[0077] a buffer solution disposed in the housing and in which the electrode is partially immersed;

[0078] a pH sensing membrane disposed over and in contact with the buffer solution;

[0079] an electrolyte layer disposed over and in contact with the pH sensing membrane;

[0080] a permeable film disposed over and in contact with the electrolyte layer; and

[0081] only a single enzyme immobilized over and in contact with the permeable film; wherein:

[0082] the electrode is operative to generate a voltage signal indicative of an amount of urea nitrogen in response to the biological sample contacting the enzyme.

[0083] Example Embodiment 14: The sensor of any one of Example Embodiments 1-13, further comprising a voltmeter operatively coupled to the electrode, the voltmeter operative to output a voltage value based on the voltage signal.

[0084] Example Embodiment 15: The sensor of any one of Example Embodiments 1-14, further comprising a computer operatively coupled to the voltmeter and operative to convert the voltage value to the amount of urea nitrogen.

[0085] Example Embodiment 16: The sensor of any one of Example Embodiments 1-15, wherein the electrode comprises a silver / silver chloride electrode.

[0086] Example Embodiment 17: The sensor of any one of Example Embodiments 1-16, wherein the buffer solution comprises a sodium citrate or MES buffer solution.

[0087] Example Embodiment 18: The sensor of any one of Example Embodiments 1-17, wherein the electrolyte layer comprises a sodium bicarbonate electrolyte layer.

[0088] Example Embodiment 19: The sensor of any one of Example Embodiments 1-18, wherein the single enzyme comprises urease.

[0089] Example Embodiment 20: The sensor of any one of Example Embodiments 1-19, wherein the urease enzyme covers at least 75% of the permeable film.

Claims

CLAIMS What is claimed is:

1. A sensor for measuring urea nitrogen in a biological sample, comprising: a first sensor component operative to generate a first voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the first sensor component, the first sensor component including a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane; a second sensor component operative to generate a second voltage signal indicative of an amount of carbon dioxide detected in response to the biological sample contacting the second sensor component, the second sensor component including a second sensing membrane without any enzyme immobilized thereover; and a voltmeter operatively coupled to receive the first and second voltage signals and operative to output a differential voltage signal value based on the first and second voltage signals, the differential voltage signal value corresponding to an amount of urea nitrogen in the biological sample.

2. The sensor of claim 1, further comprising a computer processor operatively coupled to the voltmeter, the computer processor operatively coupled to a non-transitory memory comprising programming instructions executable on the computer processor and comprising data for correlating differential voltage signal values with respective amounts of urea nitrogen; wherein the computer processor executing the programming instructions is operative to receive a value for the differential voltage signal from the voltmeter anddetermine the amount of urea nitrogen corresponding to the differential voltage signal value.

3. The sensor of claim 2, wherein the data comprises a Nernst equation for calculating the amount of urea nitrogen based on the differential voltage signal value or comprises a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts via a Nernstian behavior.

4. The sensor of claim 1, further comprising a housing that includes the first and second sensor components each partially received therein, wherein the housing is operative to receive and contain the biological sample therein.

5. The sensor of claim 1, wherein: the first sensor component further comprises a first silver / silver chloride electrode coupled to the voltmeter; and the second sensor component further comprises a second silver / silver chloride electrode coupled to the voltmeter.

6. The sensor of claim 1, wherein: the first sensor component further comprises a first electrode and a first sodium bicarbonate electrolyte layer disposed about a portion of the first electrode; and the second sensor component further comprises a second electrode and a second sodium bicarbonate electrolyte layer disposed about a portion of the second electrode.

7. The sensor of claim 1, wherein the biological sample comprises blood or urine.

8. A method of measuring urea nitrogen in a biological sample, the method comprising:generating, via a first sensor component, a first voltage signal in response to the biological sample contacting the first sensor component, the first voltage signal indicative of a first amount of carbon dioxide, the first sensor component having a first sensing membrane and a urease enzyme immobilized over and in contact with the first sensing membrane; generating, via a second sensor component, a second voltage signal in response to the biological sample contacting the second sensor component, the second voltage signal indicative of a second amount of carbon dioxide, the second sensor component having a second sensing membrane without any enzyme immobilized over and in contact with the second sensing membrane; generating, via a voltmeter, a differential voltage signal based on the first and second voltage signals; and converting, via a computer processor, a value of the differential voltage signal to a corresponding amount of urea nitrogen in the biological sample.

9. The method of claim 8, wherein the converting further comprises converting, via the computer processor, the value of the differential voltage signal to the corresponding amount of urea nitrogen in the biological sample based on data stored in a non-transitory memory accessible by the computer processor, the data including a Nernst equation for calculating the corresponding amount of urea nitrogen based on the value of the differential voltage signal or including a plurality of differential voltage signal values corresponding to a plurality of urea nitrogen amounts via a Nernstian behavior.

10. The method of claim 8, wherein: the first sensor component further comprises a first silver / silver chloride electrode coupled to the voltmeter; andthe second sensor component further comprises a second silver / silver chloride electrode coupled to the voltmeter.

11. The method of claim 8, wherein: the first sensor component further comprises a first electrode and a first sodium bicarbonate electrolyte layer disposed about a portion of the first electrode; and the second sensor component further comprises a second electrode and a second sodium bicarbonate electrolyte layer disposed about a portion of the second electrode.

12. The method of claim 8, wherein the biological sample comprises blood or urine.

13. A sensor for measuring urea nitrogen in a biological sample, comprising: a housing; only a single electrode, the single electrode partially received in the housing; a buffer solution disposed in the housing and in which the electrode is partially immersed; a pH sensing membrane disposed over and in contact with the buffer solution; an electrolyte layer disposed over and in contact with the pH sensing membrane; a permeable film disposed over and in contact with the electrolyte layer; and only a single enzyme immobilized over and in contact with the permeable film; wherein: the electrode is operative to generate a voltage signal indicative of an amount of urea nitrogen in response to the biological sample contacting the enzyme.

14. The sensor of claim 13, further comprising a voltmeter operatively coupled to the electrode, the voltmeter operative to output a voltage value based on the voltage signal.

15. The sensor of claim 14, further comprising a computer operatively coupled to the voltmeter and operative to convert the voltage value to the amount of urea nitrogen.

16. The sensor of claim 13, wherein the electrode comprises a silver / silver chloride electrode.

17. The sensor of claim 13, wherein the buffer solution comprises a sodium citrate or MES buffer solution.

18. The sensor of claim 13, wherein the electrolyte layer comprises a sodium bicarbonate electrolyte layer.

19. The sensor of claim 13, wherein the single enzyme comprises urease.

20. The sensor of claim 19, wherein the urease enzyme covers at least 75% of the permeable film.

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