Patent Application
20230349894
This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Aptamers are molecules that bind to a specific target molecule. Electrochemical aptamer sensors include an aptamer that specifically binds to an analyte of interest, and that is attached to an electrode. The aptamer has an attached redox active molecule (redox couple) which can transfer electrical charge to or from the electrode. When an analyte binds to the aptamer, the aptamer changes shape, changing the availability of a redox couple to transfer charge with the electrode. This results in a measurable change in electrical current that can be translated into a measure of the concentration of the analyte.
A major unresolved challenge for aptamers is extending the lifetime of the sensors, especially for applications where continuous operation is required, such as multiple measurements over time by the same device. Redox couples do not have infinite lifetime. Typically, the more they are used the more they degrade. The same is also true of the other materials/layers in the device, such as the blocking layer which reduces baseline current, the aptamer attachment to the electrode, the electrode material itself, and other materials/chemicals used in the sensor.
Thus, a need exists for improved device design and methods to reduce the electrochemical-induced degradations of aptamer sensor devices over time. Such an innovation could broadly advance the ability of aptamer sensors to be used in continuous or long duration sensing applications such as wearable or implantable sensors, and other types of applications.
Certain exemplary aspects of the invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take, and that these aspects are not intended to limit the scope of the invention.
Many of the drawbacks and limitations stated above can be resolved by creating novel and advanced interplays of chemicals, materials, sensors, electronics, microfluidics, algorithms, computing software, systems, and other features or designs, in a manner that affordably, effectively, conveniently, intelligently, or reliably brings sensing technology into proximity with sample fluids containing at least one analyte of interest to be measured.
In an embodiment of the invention, a sensing device for measuring an analyte is provided. The sensing device includes a sensor and a detection circuit. The sensor includes a working electrode with an aptamer and an attached redox couple to electrochemically measure the analyte. The detection circuit is operatively coupled to the sensor, and is configured to perform a partial scan of the sensor that only includes a portion of a full scan.
In an aspect of the invention, the working electrode may be one of a plurality of working electrodes configured to measure the analyte, and the detection circuit may be configured to perform the partial scan on a different subset of the plurality of working electrodes on each of at least two consecutive measurement cycles.
In another aspect of the invention, a plurality of subsets of the working electrodes may be scanned, and each subset may include at least three electrodes that are all scanned as part of a single measurement cycle.
In another aspect of the invention, the plurality of working electrodes may include at least 2, 3, 5, 10, 50, 100, 200, 500, or 1000 electrodes.
In another aspect of the invention, the partial scan may be one of a partial voltage scan, a partial current scan, or a partial frequency scan.
In another aspect of the invention, the partial scan may include providing a signal having a plurality of sampling periods to the sensor. Each sampling period may include a sampling duration, at least one set of consecutive sampling periods may be separated by a ramping period having a ramping duration, and the ramping duration may be at least 0.2%, 1.0%, 2.0%, 5.3%, 11.1%, 25.0%, 100%, 900%, or 1900% of the sampling duration.
In another aspect of the invention, the detection circuit may be further configured to partially scan the sensor a plurality of times at time intervals that are periodic, non-periodic, or random.
In another aspect of the invention, the partial scan may be one of a plurality of partial scans each associated with a measurement cycle, and the portion of the full scan provided by each partial scan may vary between measurement cycles.
In another aspect of the invention, the detection circuit may be further configured vary the portion of the full scan provided by each partial scan between measurement cycles.
In another aspect of the invention, each of the plurality of partial scans may have at least one of a starting voltage and an ending voltage, and the detection circuit may be further configured to shift at least one of the starting voltage and the ending voltage between measurement cycles.
In another aspect of the invention, the partial scan may include a first portion that generates a baseline sample range, and a second portion that generates a peak sample range.
In another aspect of the invention, the baseline sample range may only cover a portion of a baseline region, and the peak sample range may only cover a portion of a peak region generated by the full scan.
In another aspect of the invention, one or more of the peak region and the baseline region may be defined based on a slope of an output generated by the partial scan.
In another aspect of the invention, the full scan may have a voltage range of at least 0.4 volts, and the partial scan may have a voltage range of no more than 0.2 volts or 0.1 volts.
In another aspect of the invention, the first portion of the full scan range may be scanned less frequently than the second portion of the full scan range.
In another aspect of the invention, the second portion of the full scan range is scanned at least two times, five times, 10 times, 50 times, or 100 times as frequently as the first portion of the full scan range.
In another aspect of the invention, the partial scan may have a duty cycle that is less than 75%, 50%, 20%, 10%, 5%, 2%, or 1% of the full scan.
In another aspect of the invention, the partial scan may generate less than 0.75 times, 0.50 times, 0.20 times, 0.10 times, 0.05 times, 0.02 times, 0.01 times, or 0.001 times the total charge transfer generated by the full scan.
In another aspect of the invention, the partial scan may be a partial current scan having a current range that is <90%, <50%, <20%, <10%, <5% or <2% of the current range of a full current scan.
In another aspect of the invention, the partial scan may be a partial frequency scan having a frequency range that is <50%, <20%, <10%, <5%, or <2% of the frequency range of a full frequency scan.
In another embodiment of the invention, a method of measuring an analyte is provided. The method includes partially scanning the sensor that includes the working electrode having the aptamer and the attached redox couple to electrochemically measure the analyte, and partially scanning the sensor includes only providing a portion of the full scan to the sensor.
In an aspect of the invention, the working electrode may be one of the plurality of working electrodes configured to measure the analyte, and the method may further include performing the partial scan on the different subset of the plurality of working electrodes on each of the at least two consecutive measurement cycles.
In another aspect of the invention, the plurality of subsets of the working electrodes may be scanned, each subset may include at least three electrodes, and the method may further include scanning all of the at least three electrodes as part of a single measurement cycle.
In another aspect of the invention, partially scanning the sensor may include performing a partial voltage scan, a partial current scan, or a partial frequency scan.
In another aspect of the invention, partially scanning the sensor may include providing the signal having the plurality of sampling periods to the sensor. Each sampling period may have a sampling duration, at least one set of consecutive sampling periods of the plurality of sampling periods may be separated by the ramping period having the ramping duration, and the ramping duration may be at least 0.2%, 1.0%, 2.0%, 5.3%, 11.1%, 25.0%, 100%, 900%, or 1900% of the sampling duration.
In another aspect of the invention, the method may further include partially scanning the sensor a plurality of times, wherein the partial scans occur at time intervals that are periodic, non-periodic, or random.
In another aspect of the invention, each of the plurality of partial scans may be associated with a measurement cycle, and the portion of the full scan provided by each partial scan may vary between measurement cycles.
In another aspect of the invention, the partial scan may be a partial voltage scan including one or more portions of a voltage range associated with the full scan.
In another aspect of the invention, the partial voltage scan may include one or more voltage scans that cover a cumulative voltage range of less than 0.2 volts.
In another aspect of the invention, the method may further include partially scanning the sensor a plurality of times, wherein each of the plurality of partial scans is associated with a measurement cycle, and each partial scan has at least one of a starting voltage and an ending voltage that is shifted in voltage over time between measurement cycles.
In another aspect of the invention, the one or more portions of the voltage range may include at least one baseline partial scan of the baseline region, and at least one peak partial scan associated with the full scan.
In another aspect of the invention, the method may further include partially scanning the sensor a plurality of times to generate a plurality of partial scans. A first portion of the plurality of partial scans may include at least one baseline partial scan, a second portion of the plurality of partial scans may include at least one peak partial scan, and the number of partial scans in the second portion of the plurality of partial scans may be greater than the number of partial scans in the first portion of the plurality of partial scans.
In another aspect of the invention, an electrical charge may be transferred by the partial scan that generates less than half of the electrical charge transfer associated with the full scan.
In another aspect of the invention, partially scanning the sensor may include performing a partial current scan, and the partial current scan may have a duration that is less than 90% of the amount of time a full current scan would take to transfer 98% of the total charge transferred by the full scan.
In another aspect of the invention, partially scanning the sensor may include performing a partial frequency scan, and the partial frequency scan may include less than 50% of a full scanning frequency range.
In another aspect of the invention, the partial frequency scan may include at least one peak frequency for changes in signal gain.
In another aspect of the invention, the partial frequency scan may include at least one peak frequency with no signal gain.
In another aspect of the invention, partially scanning the sensor may include scanning the first portion of the full scan that generates the baseline sample range, and scanning the second portion of the full scan that generates the peak sample range.
In another embodiment of the invention, another sensing device for measuring the analyte is provided. The sensing device includes the sensor and the detection device operatively coupled to the sensor. The sensor includes a plurality of working electrodes each having an aptamer and an attached redox couple to electrochemically measure the analyte. The detection circuit is configured to perform a scan of the sensor by scanning a different subset of the plurality of working electrodes on each of at least two consecutive measurement cycles.
In another embodiment of the invention, another method of measuring an analyte is provided. The method includes scanning a first subset of the working electrodes during a first measurement cycle, and scanning a second subset of the working electrodes during a second measurement cycle that follows the first measurement cycle, wherein the first subset is different from the second subset.
The objects and advantages of the disclosed invention will be further appreciated in light of the following detailed descriptions and drawings in which:
As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, pH, size, concentration, or percentage, is meant to encompass variations of, in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods and operate the disclosed devices.
As used herein, the term “aptamer” means a molecule that undergoes a conformation change as an analyte binds to the molecule, and which satisfies the general operating principles of the sensing methods and devices as described herein. Such molecules are, e.g., natural or modified DNA, RNA, or XNA oligonucleotide sequences, spiegelmers, peptide aptamers, and affimers. Modifications may include substituting unnatural nucleic acid bases for natural bases within the aptamer sequence, replacing natural sequences with unnatural sequences, or other suitable modifications that improve sensor function. Typically, aptamers used in electrochemical sensors are tagged with a redox molecule such as methylene blue.
The devices and methods described herein encompass the use of sensors. A sensor, as used herein, is a device that is capable of measuring the concentration of a target analyte in solution. As used herein, an “analyte” may be any inorganic or organic molecule, for example: a small molecule drug, a metabolite, a hormone, a peptide, a protein, a carbohydrate, a nucleic acid, or any other composition of matter. The target analyte may comprise a drug. The drug may be of any type, for example, including drugs for the treatment of cardiac system, the treatment of the central nervous system, that modulate the immune system, that modulate the endocrine system, an antibiotic agent, a chemotherapeutic drug, or an illicit drug. The target analyte may comprise a naturally-occurring factor, for example a hormone, metabolite, growth factor, neurotransmitter, etc. The target analyte may comprise any other species of interest, for example, species such as pathogens (including pathogen induced or derived factors), nutrients, and pollutants, etc.
As used herein, the term “duty cycle” refers to the portion of a scanning signal (e.g., a voltage signal that is varied within a voltage range, a current signal that is varied within a current range, or a frequency that is varied within a frequency range) that is applied during operation of a sensor as a percentage of the “full scan”, which is the total available voltage, current, and/or frequency range typically used for operation of the sensor.
As used herein, the term “continuous sensing” may be satisfied by the device recording a plurality of readings over a period of time during which the sensing occurs. Thus, even a point-of-care testing device which provides a single data point can be considered a continuous sensing device if, for example, the test has a 15 minute duration, and the testing device operates by taking multiple data points over 15 minutes and averaging them to provide a single data measure.
One or more specific embodiments of the invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
Certain embodiments of the disclosed invention show sensors as simple individual elements. It is understood that many sensors require two or more electrodes, reference electrodes, or additional supporting technology or features that, for purposes of clarity, are not necessarily described herein. Sensors measure a characteristic of an analyte. Sensors are preferably electrical in nature, but may also include optical, chemical, mechanical, or other known sensing mechanisms. Sensors can be in duplicate, triplicate, or more, to provide improved data and readings. Sensors may provide continuous or discrete data and/or readings. Certain embodiments of the disclosed invention may show certain sub-components of sensing devices, but may omit additional sub-components needed for use of the device in various applications that are known, e.g., a battery, antenna, adhesive. These omissions may be for purposes of brevity and to focus on certain inventive aspects of the disclosed embodiments of the invention. All ranges of parameters disclosed herein include the endpoints of the ranges.
With reference to
The sensing device 100 may further include a sample volume 128 comprising a space 130 defined between the microneedle assembly 112 and the sensing layer 120, and the lumens 132. The sensing layer 120 and electrode layer 150 may form a working electrode of the sensing device 100. The sample volume 128 may be filled with a microfluidic component such as capillary channels, a hydrogel, or other suitable material, that operatively couples the fluid to the sensing layer 120. Thus, a diffusion and/or adjective flow pathway may be provided between the fluid to be sensed and the sensing layer 120. This pathway may begin at the inlets 134 to the microneedles 114 and reach the sensing layer 120. Alternative arrangements and materials may also be possible, such as using a single needle, hydrogel polymer microneedles, or other suitable means to couple the fluid to one or more sensors. Thus, embodiments of the invention are not limited to the depicted sensing device 100. In addition, a portion of sensing device 100, or even the entire sensing device 100, could be implanted into the body and perform similarly as described herein. For example, the electrode layer 150 and sensing layer 120 may be implanted inside the body on the end of an indwelling needle like those used in continuous glucose monitors.
With further reference to
Although the exemplary embodiments depicted by
With reference to
The controller 174 may comprise a computing device that includes a processor 176, a memory 178, an input/output (I/O) interface 180, and a Human Machine Interface (HMI) 182. The processor 176 may include one or more devices selected from microprocessors, micro-controllers, digital signal processors, microcomputers, central processing units, field programmable gate arrays, programmable logic devices, state machines, logic circuits, analog circuits, digital circuits, or any other devices that manipulate signals (analog or digital) based on operational instructions stored in memory 178. Memory 178 may include a single memory device or a plurality of memory devices including, but not limited to, read-only memory (ROM), random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, or data storage devices such as a hard drive, optical drive, tape drive, volatile or non-volatile solid state device, or any other device capable of storing data.
The processor 176 may operate under the control of an operating system 184 that resides in memory 178. The operating system 184 may manage computer resources so that computer program code embodied as one or more computer software applications 186 residing in memory 178 can have instructions executed by the processor 176. One or more data structures 188 may also reside in memory 178, and may be used by the processor 176, operating system 184, or application 186 to store or manipulate data.
The I/O interface 180 may provide a machine interface that operatively couples the processor 176 to other devices and systems, such as the voltage sensor 168, current sensor 170, and voltage source 172. The application 186 may thereby work cooperatively with the other devices and systems by communicating via the I/O interface 180 to provide the various features, functions, applications, processes, or modules comprising embodiments of the invention.
The HMI 182 may be operatively coupled to the processor 176 of controller 174 to allow a user to interact directly with the sensing device 156. The HMI 182 may include video or alphanumeric displays, a touch screen, a speaker, and any other suitable audio and visual indicators capable of providing data to the user. The HMI 182 may also include input devices and controls such as an alphanumeric keyboard, a pointing device, keypads, pushbuttons, control knobs, microphones, etc., capable of accepting commands or input from the user and transmitting the entered input to the processor 176.
Referring again to
In an alternative embodiment, each sequential scan may be conducted on a different electrode or subset of electrodes until they have all been used, at which point the process repeats. Sequential scanning may be advantageous because electrodes can degrade and change over time due to other factors. Thus, sequential scanning may allow for a more easily interpretable continuum of data to be recorded over time as compared to use-to-failure embodiments. In any case, sequential scans may be performed in a periodic, a non-periodic, or random manner. For example, measurement cycles may occur at predetermined intervals of time, at intervals of time having a predetermined pattern, or at random intervals of time.
In an exemplary embodiment, an electrochemical aptamer-based (EAB) sensing device may use the same type of reference and counter electrodes for all the aptamer sensor electrodes. By way of example, at least 2, 3, 5, 10, 50, 100, 200, 500, or 1000 sensor electrodes may be used in one EAB sensing device, although embodiments of the invention are not limited to any particular number of sensor electrodes. For example, if 200 electrodes are used, each individual electrode may experience 0.005 the electrochemical fatigue during a particular use period as compared to a single electrode having to support all the measurements during that use period. This method may effectively reduce the duty cycle that any one electrode must experience while sustaining the frequency of measurements needed to support continuous sensing. For example, a drug measurement that must be taken every minute for three days would require 4320 measurements in total over the measurement period. A single sensor would have to support 4320 measurements, whereas 10 sensors as taught herein would each individually only have to support around 432 such measurements. In some cases, measuring multiple electrodes simultaneously or near in time to each other can reduce measurement error, e.g., by measuring multiple sensors for each datapoint.
Embodiments of the invention may permit a subset of sensors (e.g., a subset of electrodes or sensors) to be measured at any given time to reduce measurement error or to improve the statistical validity of a measurement. The subset of sensors measured may change over time to increase the measurement lifetime of the sensing device unit. As a non-limiting example, one sensor at a time can measure a drug while the concentration of the drug is within its safe therapeutic window. However, during dosing of the drug and rapid uptake in the body, the drug concentration may be higher initially. To achieve more accurate data, three or more sensors could be used to represent each datapoint. Alternatively, one sensor could be used more often (e.g., every 5 minutes right after drug ingestion vs. every 30 minutes or every 3 hours after drug ingestion). As a result, the amount of sampling of the sensor may be reduced, thereby improving its longevity.
With reference to
In a research environment, all regions of the voltage scan range may be irrelevant because a full scan is needed to confirm the data has a proper redox peak, and because research environments do not need sensors that last for days to run experiments. In commercial applications, it is possible to monitor only the voltage sub-regions that need to be measured to continuously confirm a high quality signal. Thus, in commercial settings, partial scans may allow longer duration operation, thereby cutting costs by replacing sensors less frequently, which is also desired commercially. This increased duration may be particularly beneficial, as once nuclease degradation of the aptamers is removed by membrane protection and/or mutating the aptamer sequence, and severe sensor surface fouling is prevented, the electrochemical degradation during sampling can be the dominant degradation mechanism.
With further reference to
Current baseline sample range 292a and/or current baseline sample range 292c may also be measured in multiple ways. For example, by using an additional electrode with no redox couples, by varying the frequency of interrogation of the measurement such that the current peak sample range 292b is comparable to the current baseline sample range that would exist at that voltage where the peak 292b exists. This variable frequency technique may take advantage of the fact EAB sensors typically have a zero signal gain frequency. These examples show that the terms baseline and peak should not be narrowly limited to their exact representation shown in
The maximum voltage VMAX applied to the sensor may also be reduced to provide a partial voltage scan and improved lifetime. For example, the voltage could be scanned from VMIN or V1 to V4 in order to limit the maximum voltage applied to the device and avoid voltages that include V5 to V6 and beyond. Therefore, the controller 174 may cause the voltage source 172 to only scan up to the point where the peak current 292 is properly measured (e.g., up to V4) and not beyond. For example, a conventional scan will typically cover ˜0.4 volts or more, and with embodiments of the invention, the scan length could be less than 0.2 volts or less than 0.1 volts to capture adequate baseline and peak. Even if the baseline is partially affected by the peak, the baseline can also be predicted from the partial shape of the peak since the peak is super-imposed on the baseline.
Generally, a full voltage scan would include sufficient scanning before and after the redox peak voltage to capture baseline current values on both sides of the peak. Thus, a full voltage scan may be defined as a scan covering a voltage range that includes the redox peak and a sufficient amount of adjacent baseline where the additional current contribution from redox of the redox tag is less than 3% of the current contributed by redox of the redox tag at the peak redox tag current across the voltage range. Exemplary voltage scans that may be considered as partial scans include voltage scans having a voltage duty cycle that is less than 75%, 50%, 20%, 10%, 5%, 2%, or 1% of the full voltage scan as defined above.
A non-limiting example of a full voltage scan in one direction (negative or positive) or a net voltammogram for methylene blue is approximately 0 to −0.5 volts. In this example, the redox peak may occur from approximately −0.2 to −0.3 volts at near neutral pH and with an Ag/AgCl reference electrode. As another example, consider ferricyanide with a peak near −0.1 to −0.2 volts, or consider Nile blue with a wider redox peak spanning −0.3 to −0.5 volts.
Another way to distinguish partial voltage scans from full voltage scans may be by the total charge used to measure the sensor. For example, if a full voltage scan generates a total charge transfer of X coulombs, a voltage scan that generates less than 0.75 times, 0.50 times, 0.20 times, 0.10 times, 0.05 times, 0.02 times, 0.01 times, or even 0.001 times the total charge transfer X may be considered as a partial voltage scan. Alternately, the total charge transfer of the redox peak could be X, which may be provided by integrating the area under the redox peak curve. In this case, a voltage scan that generates less than 0.75 times, 0.50 times, 0.20 times, 0.10 times, 0.05 times, 0.02 times, 0.01 times, or even 0.001 times the total charge transfer X associated with the redox peak could be considered as a partial voltage scan.
Measurement variables such as electrochemical aptamer sensor composition, reference electrode characteristics (e.g., surface area), and environmental factors such as pH can change the position of key factors, such as current versus voltage values. Therefore, a methodology for determining key features and prediction their positions may be used to properly query sensors while minimizing oversampling that takes into account these variables. To this end, embodiments of the invention may monitor the position of baseline and peak currents over time, and adjust the partial scanning voltages such that they stay optimally aligned with these positions. For example, periodically or as needed, a full voltage scan could be performed to reveal the positions of all peaks and baselines. For example, a rising slope, apex of the peak with zero slope or alternately positive slope followed by negative slope, or falling slope of the peak could be measured to monitor peak position. Slope values may vary in a predictable way based on measurement variables. Thus, the slope values used to define boundaries between peak regions and baseline regions of a scan may be set based on the particular measurement environment being used.
By way of example,
The voltage scans may also shift predictably. To accommodate these shifts, an embodiment of the invention may automatically adjust the positions of the voltage scans over time without measurement at all, or only with intermittent measurements. For example, if the peak shifted by +2.4 mV every 60 minutes, the peak could be measured every hour to confirm the rate of peak shifting, and if the sensor was measured every 10 minutes, the peak voltage that is scanned would be automatically shifted by +0.4 mV for each 10 minutes.
Scanning signals applied to the sensor of a sensing device may include voltage scans (as described above), current scans, frequency scans, and combinations of voltage, current, and frequency scans.
Thus, embodiments of the invention may also be applied to chronocoulometric measurements. As defined herein, a full current scan may start at t=0 and end at baseline when greater than a threshold percentage (e.g., 98%) of the total charge transfer from the redox couples has occurred, or when greater than the threshold percentage of the charged to be transferred has been transferred, respectively. The threshold percentage for chronoamperometry is illustrated in
By way of explaining this frequency effect more deeply, the application of a voltage bias to the sensor interface generates electrokinetic, faradaic, mass, and charge transport phenomena that affect the output of these sensors. First, the sample electrolyte responds to voltage perturbations by dynamically aligning to their electrical fields. This effect generates double-layer charging/discharging currents in electrochemical measurements. Moreover, the voltage perturbation may cause field-induced movement actuation of the negatively charged aptamer backbone. This effect perturbs the frequency of electron transfer which, in turn, affects sensor signaling currents. Beyond field-induced modulation of the electrolyte and aptamer strands, mass transport of the redox reporter to the electrode also affects electron transfer. Furthermore, aptamer secondary structures and the thickness of the electrode-blocking monolayer and any foulants on that surface affect the currents measured, as do the standard electron transfer rate of the redox reporter and the rates of receptor-target ligand association/dissociation. All of these factors can influence the ideal measurement frequency of aptamer sensors.
Because the frequencies that provide maximal signal change can change during sensor use, a subset of frequencies may be scanned periodically to identify any frequency dependent changes.
With reference to
With reference to
The current may be sampled at two points during each cycle, e.g., once at the end of the forward voltage pulse (ifwd) and again at the end of the reverse voltage pulse (ibwd). Thus, each sample is taken immediately before the voltage direction is reversed. As a result of this current sampling technique, the contribution to the current signal resulting from capacitive (sometimes referred to as non-faradaic or charging) current is minimal. As a result of having current sampling at two different instances per square-wave cycle, two current waveforms are collected. Both have diagnostic value, and are therefore preserved. When viewed in isolation, the forward and reverse current waveforms mimic the appearance of a cyclic voltammogram (which corresponds to the anodic or cathodic halves, however, is dependent upon experimental conditions). Despite both the forward and reverse current waveforms having diagnostic worth, it is almost always the case in SWV for the potentiostat software to plot a differential current waveform derived by subtracting the reverse current waveform from the forward current waveform. This differential curve is then plotted against the applied voltage. Peaks in the differential current vs. applied voltage plot are indicative of redox processes, and the magnitudes of the peaks in this plot are used to interpret measurement of the concentration of the analyte in the sample fluid.
With respect to
Generally, to benefit from this method, the sampling voltage, sampling duration ts, and ramping duration tr of the ramping period between sampling periods must all be adequately adjusted. The ramp may be linear, sigmoidal, partially sinusoidal, or any other suitable waveform that more gradually ramps to the sampling voltage than a square wave. For a given SWV, frequencies can typically range from several Hz (ts+tr=n×100 ms) to several kHz (ts+tr=n×100 μs), and for a given SWV waveform, ts may be less than or greater than tr. Preferably, to reduce electronic sampling at the sampling voltage, ts is at least one of less than 90%, 50%, 20%, 10%, 5%, 2%, or 1% of tr. For tr to enable a more gradual ramp, tr may more generally be, but is not limited to, greater than 0.2%, 1%, 2%, 5%, 10%, 20%, 50%, 90%, 95% of the quantity tr+ts. Stated another way, and using the following equation:
where x is the fraction of each cycle attributed to the ramping duration, tr may be about 0.2%, 1.0%, 2.0%, 5.3%, 11.1%, 25.0%, 100%, 900%, or 1900% of the sample duration ts. Stated yet another way, and using the following equation:
where x is the fraction of each cycle attributed to the ramping duration, ts may be about 49.900%, 9.900%, 4.900%, 1.900%, 900%, 400%, 100%, 11.1%, or 5.3% of the sample duration ts.
An aptamer sensor lacking the features of embodiments of the invention was tested for cortisol. The aptamers were suspended on gold electrodes and protected from nuclease attack by a protecting membrane, chemicals that inhibit nucleases, or non-native base pairs on the aptamer. The aptamer had a redox couple of methylene blue to report current during duty cycles where a range of voltages was probed from 0 to −0.6 volts. The gold electrode contained a blocking layer made of a short, chained passivating species such as 6-Mercapto-1-hexanol to improve the signal to noise of the device. For this device to measure a clinically relevant concentration change without error, three sensors were needed per measurement. Measurements were taken for 2 minutes and the sensor endured 18 hours of operation before its signal degraded to 10% of its original strength, which is a point of complete failure for the device. Two days with a scan every three minutes represents 540 scans in total. This sensor's inability to achieve 24 hour use could be problematic if a user has to apply a sensing device multiple times per day.
Using principles of embodiments of the invention, the scanning voltage can be limited to 10% of the 0.6 volts scanning range, for example, from −0.1 to −0.12 volts for the baseline, −0.29 to −0.31 volts for the peak, −0.4 to −0.42 volts for another baseline, for a total of 0.06 volts of scanning which is 10% of the previous 0.6 volt scan. As a result, the device could provide 5,400 scans instead of merely 540 scans, and potentially up to 180 hours or greater than one week of use. This calculation may further depend on electrode material, surface chemistry and sample fluid conditions, but does illustrate the general impact of embodiments of the invention. The partial voltage scan can comprise one or more voltage scans having a cumulative voltage range that is less than 0.2 volts, less than 0.1 volts, or less than 0.05 volts in voltage scanned. In yet another example, a device with nine sensors, sampled in groups of three, can be measured in a serial fashion to extend the device lifetime by three times.
Another application of an embodiment of the inventions may be to reduce the duty cycle as described in
Testing fluids can vary in chemical makeup between individuals. The sensing device may degrade at differing rates dependent on an individual's sample. As another example, a sensing device in accordance with an embodiment of the invention may use serialized sensors for which a cutoff current measurement is set. Once the current decreases a given amount (e.g., 5%, 10%, or 20%), a sensor may be switched off and a new sensor activated to maintain highly accurate measurements over time given varied sensing environments.
A chronoamperometric sensor for the drug tobramycin is presented with a chronoamperometric response from 5E-6 to 1E-6 amps that takes >30 ms for a full chronoamperometric cycle. According to principles disclosed herein, the sensor may instead be measured only from 5E-6 to 2E-6 amps, which takes less than 10 ms, thereby reducing the time of sampling by a factor of three, and improving sensor longevity by as much as three times.
Software is used along with electronics to track the peak location on a voltammogram similar to that shown in
In yet another example, a cortisol aptamer sensor with a mercaptohexanol blocking layer was tested on a mechanically roughened gold rod electrode for 70 hours in serum. The duty cycle of the voltage scan for square wave voltammetry was reduced according to principles disclosed herein to 1% of its full scan value. The full scan without reduced sampling would be a square wave voltammogram with 0.035 volt amplitude performed at 400 Hz from 0.5 volts out to 0.45 volts. With reduced sampling the voltage scan was reduced from 0.4 volts to only 0.02 volts (20 times less). The signal was measured out to 70 hours with less than <10% signal loss per day after an initial 4 hour burn-in period. This is a very robust result compared to normal scanning in which the sensor would not last for more than one day.
In general, the routines executed to implement the embodiments of the invention, whether implemented as part of an operating system or a specific application, component, program, object, module or sequence of instructions, or a subset thereof, may be referred to herein as “program code.” Program code typically comprises computer-readable instructions that are resident at various times in various memory and storage devices (e.g., non-transitory storage media) in a computer and that, when read and executed by one or more processors in a computer, cause that computer to perform the operations necessary to execute operations or elements embodying the various aspects of the embodiments of the invention. Computer-readable program instructions for carrying out operations of the embodiments of the invention may be, for example, assembly language, source code, or object code written in any combination of one or more programming languages.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include both the singular and plural forms, and the terms “and” and “or” are each intended to include both alternative and conjunctive combinations, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” or “comprising,” when used in this specification, specify the presence of stated features, integers, actions, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, or groups thereof. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, “comprised of”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
While all the invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the Applicant's general inventive concept.
This application claims the benefit of Intl. App. No. PCT/US2021/051914, filed on Sep. 24, 2021 claiming the benefit of U.S. Patent Application Ser. No. 63/083,023, filed on Sep. 24, 2020, U.S. Patent Application Ser. No. 63/150,675, filed on Feb. 18, 2021, U.S. Patent Application Ser. No. 63/197,669, filed on Jun. 7, 2021, and U.S. Patent Application Ser. No. 63/215,605, filed on Jun. 28, 2021. The disclosures of each of the above applications are incorporated by reference herein in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/051914 | 9/24/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63197669 | Jun 2021 | US | |
| 63150675 | Feb 2021 | US | |
| 63083023 | Sep 2020 | US | |
| 63215605 | Jun 2021 | US |
