New Smartphone-based Readerless Glucose Test Strip for Prediabetes Screening

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Blood glucose measurement is a fundamental tool in the screening and management of diabetes, a chronic condition that affects over 400 million people worldwide.

It is characterized by the body’s inability to effectively regulate blood glucose levels, which can lead to a host of serious health complications, including heart disease, vision loss, and kidney failure.

Early detection of prediabetes can forestall or reverse more serious illness if healthy lifestyle adjustments or medical interventions are made in a timely manner. However, current diabetes screening methods require visits to a healthcare facility and the use of over-the-counter glucose-testing devices (glucometers), both of which are costly or inaccessible for many populations, reducing the chances of early disease detection.

To address this issue, the researchers developed GlucoScreen, a non-invasive blood glucose monitoring system that allows individuals to measure their blood glucose levels easily and accurately at home, without the need for a healthcare professional or costly equipment.

Diabetes mellitus (DM) is a complex metabolic disorder characterized by chronic hyperglycemia (high blood sugar levels). It is caused by defects in insulin secretion, insulin action, or both. Insulin is a hormone produced by the pancreas that regulates the uptake, storage, and use of glucose by cells in the body.

In diabetes, insulin deficiency or resistance leads to elevated glucose levels in the bloodstream, which can cause a wide range of health problems if left untreated. This research will explore the pathophysiology, diagnosis, and management of diabetes.

Pathophysiology:

There are two primary forms of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is an autoimmune disease in which the body’s immune system attacks and destroys the insulin-producing beta cells in the pancreas. This results in a lack of insulin production, leading to hyperglycemia. Type 1 diabetes is typically diagnosed in children and young adults and requires insulin therapy for life.

Type 2 diabetes is the most common form of diabetes and is characterized by insulin resistance, which means that the body’s cells are resistant to the effects of insulin. As a result, the pancreas produces more insulin in an attempt to compensate, but over time, the beta cells in the pancreas become exhausted and cannot keep up with the demand for insulin. This leads to high blood glucose levels, which can cause damage to various organs and tissues in the body. Type 2 diabetes is typically diagnosed in adults and is often associated with obesity and physical inactivity.

Diagnosis:

The diagnosis of diabetes is made based on fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), or glycated hemoglobin (HbA1c) levels. A fasting plasma glucose level of 126 mg/dL (7 mmol/L) or higher on two separate occasions is diagnostic of diabetes. An OGTT involves the ingestion of a glucose solution followed by measurement of plasma glucose levels after 2 hours. An OGTT result of 200 mg/dL (11.1 mmol/L) or higher is diagnostic of diabetes. HbA1c reflects average blood glucose levels over the preceding 2-3 months and a value of 6.5% or higher is diagnostic of diabetes.

Management:

The management of diabetes involves lifestyle modifications, medications, and monitoring of blood glucose levels. Lifestyle modifications include weight loss, physical activity, and dietary changes. Medications for diabetes include insulin, oral medications such as metformin, sulfonylureas, and dipeptidyl peptidase-4 (DPP-4) inhibitors. Insulin therapy is typically required for those with type 1 diabetes and may be required for those with type 2 diabetes who cannot adequately control their blood glucose levels with oral medications.

Blood glucose monitoring is an essential part of diabetes management and involves regular self-monitoring of blood glucose levels using a glucose meter. Glycemic control is the primary goal of diabetes management and is aimed at maintaining blood glucose levels within a target range to prevent long-term complications. The American Diabetes Association (ADA) recommends a target HbA1c level of less than 7% for most people with diabetes, although individualized targets may be appropriate based on factors such as age, duration of diabetes, and comorbidities.

Accessible preventive screening for diabetes and prediabetes could aid in early detection and, with lifestyle modifications, potential reversal. Current screening approaches include blood sugar measurement using laboratory testing or point-of-care (POC) devices, called portable glucose monitors (PGMs), or glucometers [64]. These procedures, while effective, are costly [23] and can require access to extra devices or testing facilities [63]. As a result, many cases remain undiagnosed and untreated, motivating the need for an accessible, low-cost way to screen individuals likely to have prediabetic conditions.

The most common blood glucose testing device is a portable glucometer, a standalone device that interfaces with an electrochemically activated test strip to provide quick blood glucose readings. Glucometers work by analyzing a small blood sample, typically from the fingertip, placed on a test strip. The test strips they use cost less than a dollar each; however, the test strips sell in batches, and the device itself averages between $20-$80 [12].

The initial cost of purchasing the glucometer setup amortizes over time to become relatively affordable for routine device users, such as those already diagnosed with diabetes who are generally required to test their blood sugar daily. However, such amortization likely does not benefit screening use cases given that screening for at-risk individuals is recommended only every three years [3].

Preventive prediabetes screening is medically and financially prudent over the long term; therefore, lowering the cost and access barriers to screening for at-risk subjects is beneficial, especially in low- and middle-income nations [47].

To respond to the need for a cost-efficient, effective, and in-home prediabetes testing approach, the researchers developed GlucoScreen, a low-cost, battery-free, stand-alone glucose testing strip readable by any smartphone that measures blood glucose without the need for an external reader.

A smartphone app guides GlucoScreen users through steps needed to perform a fasting blood sugar or glucose tolerance self-test, both of which can indicate whether they have diabetes or prediabetes[84]. Such screening can help users make informed decisions about whether to follow up and seek in-person medical care from a clinician. At-home screening also lowers the barrier to action for getting screened, thereby increasing the likelihood of more people getting screened.

GlucoScreen uses a novel means of communication from the test strip to the phone: it electronically generates touch events from the test strip through the phone’s capacitive touchscreen. This technique uses conventional glucose test strips enhanced with low-cost components. Once the smartphone processes the touchscreen events, they become available for immediate readout and storage locally or in an internet-connected health record.

This communication method between test strip and phone consumes only 10 microW of power, orders of magnitude less than conventional low-power communication approaches, which can be easily harvested from the phones’ flash. Our technique eliminates the need for batteries – which are common in other wireless communication methods, such as BLE (Bluetooth Low Energy), ZigBee, or ANT [29] – lowering costs and extending shelf life.

This research demonstrates and evaluates our touchscreen-based communication technique for blood sugar testing. Our new technique holds additional promise for building readerless assays for other electrochemical reaction-based tests, such as detecting heavy metals in water, detecting sodium in urine, and detecting malaria [66].

Phone-based biosensing for the detection of diabetes is a promising technology that has gained significant attention in recent years. The technology involves using a smartphone to detect glucose levels in bodily fluids, making it a non-invasive and convenient way to monitor blood glucose levels. There are several different technologies used in phone-based biosensing, including enzymatic and non-enzymatic methods.

Enzymatic biosensors are the most common type of glucose biosensors used for point-of-care glucose monitoring. They rely on external enzymes such as hexokinase, glucose oxidase (GOx), or glucose-1-dehydrogenase (GDH) to interact with blood and calculate glucose levels. GOx is the most commonly used enzyme due to its accessibility, affordability, and ease of storage. GOx-based assays are sold as glucose test strips that can be read by a dedicated test strip reader or a smartphone application. These devices require a drop of blood, typically from a finger prick or venous draw, for analysis. Enzyme-based biosensors are reliable and accurate, making them the gold standard for glucose testing.

Non-enzymatic biosensors include optical, microwave, electrochemical, and colorimetric methods. Optical methods such as near-infrared (NIR) and mid-infrared (MIR) spectroscopy, optical polarimetry (OP), Raman spectroscopy, the fluorescence method, and optical coherence tomography (OCT) use light to analyze the reflection or scattering of light to determine glucose concentrations.

Microwave-based techniques use radio-frequency radiation to analyze reflected signals that are affected by blood glucose fluctuations. Electrochemical methods indirectly measure blood glucose levels by measuring the correlation between biofluids and blood glucose concentration. Colorimetric methods provide a visual response proportional to glucose concentration in bodily fluids, such as saliva, sweat, or blood.

While non-enzymatic biosensors have the advantage of being non-invasive and continuous, they have a lower correlation to actual blood glucose measurements and may be impacted by skin tone, skin condition, and age. Electrochemical methods also have the drawback of low sensitivity, delayed measurement results, and a calibration requirement. Colorimetric methods can be affected by the interference of complex components found in clinical specimens, affecting their sensitivity and visual detection.

GLUCOSCREEN

In response to a growing need for scalable and cost-efficient prediabetes screening to improve public health and the lack of a low-cost and effective glucose testing solution, we propose GlucoScreen.

Concept

The GlucoScreen prototype is a fully self-contained glucose testing strip designed for low-cost, single-use blood glucose testing, transmitting glucose measurements to a smartphone that requires no additional accessories such as a dedicated reader. To take a blood glucose reading, users simply stick the GlucoScreen prototype strip to their phone and apply a small drop of their blood to the tip.

GlucoScreen calculates and displays glucose levels via a custom software application running on the phone. The blood required for testing can be drawn by a finger prick using a disposable lancet. Figure 1 shows the GlucoScreen prototype.

GlucoScreen measures blood glucose using a well-established method that is based on the oxidation of glucose by an enzyme (glucose oxidase), producing a secondary molecule (gluconic acid) that can be measured electrochemically [2] as a change in current flow. At present, our prototype strip performs the enzyme-based oxidation reaction using commercially available glucose test strips (i.e., Accu-Chek [6] and True Metrix [11]).

The output of the oxidation reaction is measured using amperometry (i.e., the detection of ions in a solution based on electric current or changes in electric current) and communicated to the smartphone via simulated taps on the touchscreen. The GlucoScreen prototype includes all components required to perform an amphoteric glucose assay and send the data to a phone.

Low-Cost and Battery-Free Operation

To maintain a low price point, we designed the GlucoScreen strip to perform only the glucose detection reaction and leveraged the phone’s resources for everything else. The strip only captures the output of the amphoteric glucose assay and sends it to the phone in real-time to process and display the results. The amperometry is performed using a custom low-power, three-electrode potentiostat on the strip, and its output is communicated to the phone via a novel communication channel—the phone’s touchscreen.

The strip communicates with the phone by periodically mimicking touch events on the phone’s touchscreen, which the phone interprets as human touch events. The amperometry output is communicated by encoding the data in the timings of these touch events using pulse width modulation (PWM). A custom application running on the phone records and decodes the touch events.

The communication phase starts from the potentiostat. The potentiostat output is fed into a voltage controlled oscillator (VCO), which controls a cascode field effect transistor (FET) output stage; this stage simulates touch on the smartphone’s touchscreen (details in Section 4). Compared to conventional low-power communication approaches – such as BLE, NFC, or ANT – our approach uses a smaller number of low-cost electrical components and requires four orders of magnitude less power [29], decreasing the strip’s overall power requirements.

The GlucoScreen prototype strip uses only 20 microW of power for continuous operation, which is easily harvested from the phone’s flash using a few photodiodes. This eliminates the need for batteries and USB components, reducing costs and extending shelf life.

Fig. 1. GlucoScreen prototype. The GlucoScreen prototype contains circuitry that lets it conduct the response signal from commercially available electrochemical blood-glucose test strips directly to the capacitive touch sensor of any smartphone via pulse-width-modulated “touch events” interpretable by any phone with a capacitive touch screen. This is done via ultra low power energy harvesting from the phone’s flash module, resulting in a novel, low-cost, self-contained blood-glucose test that obviates the need for an external reader.

Fig. 2. Step-by-step instructions for attaching the GlucoScreen prototype to a smartphone. The GlucoScreen prototype strip temporarily attaches to the phone via two adhesive contacts on the front side of the strip. Users first align the designated spot on the prototype strip (as shown in Figure 1b) with the phone’s flash. Then, they attach the strip to the back and front of the phone using the adhesive contacts. The strip features a long neck, which enables it to wrap around the phone and make adequate contact with the touchscreen.


reference link:https://dl.acm.org/doi/pdf/10.1145/3580855

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