BeOne Science

BeOne Science and Validation

The BeOne armband is the evolution of the e-patch developped since 2016. It's been developed to measure specific biomarkers in the sweat and is going much further than giving sweat & electrolytes losses. It is able to analayze NaCl concentration over time in sweat. Belab’s proprietary Machine Learning & Artificial intelligence algorithms take several steps to extrapolate the raw data into end-user insights, understands how body adapts to exercise over time and even predict the evolution of your performance...


While our testing has primarily been conducted internally to protect our proprietary algorithm, we plan to undertake public, unbiased validation studies in the future.


This paper summarizes that vast body of intern validation work - measurement method and calibration process for switching from currents to the concentration of the measured solution. Belab has implemented A REAL BI-CHANNEL MICROFLUIDIC CONDUCTEMETER FOR A TRUE MEASURE.

It develops dynamic, two-point measurement of sweat flowing through a microfluidic channel. In the next picture, you can see the collectors.

This device can measure NaCl solutions from 0 to 130 mM. The two pairs of electrodes arranged along the microfluidic channel through which the sweat flows are stimulated with a 200kHz, 215 mV alternating current. Our findings demonstrate that the BeOne device accurately measures NaCl concentrations, achieving > 90% precision (i.e a precision of less than 2.5 mM within the range of 5 to 50 mM, and less than 8 mM within the range of 90 to 130 mM)


Sweat evaporation is a key process in regulating human body temperature. The loss of water and sodium chloride (NaCl) through sweat can vary significantly between different individuals and even for the same individual under different conditions. During prolonged and intense physical activity, especially in hot environments, excessive sweating can lead to substantial water and electrolyte imbalances, which can adversely affect physical performance.

While water loss can be estimated by measuring body weight before and after exercise, determining NaCl loss in sweat is more challenging. Traditional commercial sweat analyzers typically require stationary setups and involve collecting sweat samples using patches or microfluidic systems directly from the skin. These samples are then analyzed in a lab using techniques like ion chromatography or conductivity measurement. However, these methods have drawbacks, including contamination risks, evaporation issues, potential adhesive failures, allergic reactions, the need for expensive equipment, and specialized laboratory skills. Moreover, they do not offer real-time feedback, which is crucial for athletes to manage their hydration levels effectively.

Recent advancements in biosensor technology have paved the way for various real-time sodium measurement devices. Building on these innovations, we have developed the BeOne armband, a non-invasive device that connects to a smartphone application via Bluetooth for data display and analysis. This armband is designed to accurately measure NaCl concentrations in sweat within a range of 0 to 130 mM. It uses two sets of dual microfluidic electrodes stimulated at 200 kHz for precise detection. The primary goal of the BeOne armband is to estimate sweat flow rate by measuring conductivities between two pairs of electrodes spaced 1 cm apart. This study aims to calibrate the BeOne device for accurate NaCl concentration measurements.


Device Structure
The BeOne armband (Figure 1) integrates a sweat collector with dual pairs of electrodes to measure NaCl concentration in sweat. Each pair of electrodes is stimulated at 200 kHz with a 215 mV alternating current (AC) and sends measurements via Bluetooth to a smartphone application. The armband stimulates each pair of electrodes via separate supply circuits. In each circuit, a signal generator (AD983) measures input (Vcc) and output (Veff) currents using LTC 1698 VRMS to convert AC to direct current (DC). An analog-to-digital converter (ADC) samples these currents at 100 Hz, and an average is sent every second for concentration measurement. This is shown in figure 2.

The sweat collector, placed on the forearm, gathers sweat from a 6.25 cm2 skin surface. Sweat flows through a 1.1x0.127mm microfluidic channel with two pairs of curvilinear electrodes, each with a volume of 0.2x0.2x10 mm. The electrodes within each pair are 0.2 mm apart, and the pairs are 1 cm apart. The channel, coiled into a spiral, minimizes diffusion and turbulence. This setup ensures high measurement precision.

A Sweat-Check NaCl analyzer (WESCOR®, USA) was calibrated with NaCl control solutions (Elitech GROUP, USA). A 2 M NaCl stock solution was diluted and controlled from 5 to 130 mM, based on typical human sweat concentrations (10-90 mM). Each solution was tested in 5 BeOne microfluidic dual electrodes, stimulated with a 230 mV AC at 200 kHz. 

The BeOne armband uses a gain-based measurement technique with a voltage divider and a 401-ohm resistor to compare input and output currents: Vcc{i} and Veff{i}. The current aggregation variable, Y{i}, represents the proportion of current absorbed by the solution, calculated as:

Yi=Vcci−VeffiVcciY{i} = \frac{Vcc{i} - Veff{i}}{Vcc{i}}Yi=VcciVcci−Veffi​

The conversion from Y to NaCl concentration uses equations derived from calibration measurements.

Statistical Analysis
A linear regression determined the relationship between NaCl concentration and sweat conductivity measured by BeOne. The prediction strength was assessed via the coefficient of determination (R2) of a fourth-degree polynomial trend line.


Table 1 shows BeOne's sweat concentration measurements from 0 to 130 mM NaCl solutions. BeOne measures relative current variations Y{i} ranging from 0 to 76% with a standard deviation of less than 0.015. The relationship between conductivity and NaCl concentration is presented in Figure 4, with the following equations for electrodes 1 and 2:

C1=1395.56x4−1441.2x3+566.68x2−29.229x+0.1519C1 = 1395.56x^4 - 1441.2x^3 + 566.68x^2 - 29.229x + 0.1519C1=1395.56x4−1441.2x3+566.68x2−29.229x+0.1519C2=1234.9x4−1272.2x3+512.81x2−24.833x+0.2091

C2 = 1234.9x^4 - 1272.2x^3 + 512.81x^2 - 24.833x + 0.2091C2=1234.9x4−1272.2x3+512.81x2−24.833x+0.2091

The R2 values for these relationships are 0.9998 for electrode 1 and 0.9994 for electrode 2. Figure 5 shows the relationship between measured and solution NaCl concentrations.


The BeOne armband provides precise real-time measurements of NaCl concentration in sweat, with an accuracy of less than 2.5 mM within the 5-50 mM range and less than 8 mM within the 90-130 mM range. This accuracy aligns closely with that of the Sweat-Check analyzer for concentrations below 50 mM. Each BeOne unit will be calibrated to ensure measurement consistency. Our findings demonstrate that BeOne's dual pairs of electrodes offer accurate real-time measurements for determining NaCl concentration in sweat.


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