The transformation wave of bedside (PoC) medical testing is shifting from laboratories to clinical clinics, community healthcare institutions, and even households. This transformation will accelerate the speed of diagnosis, thereby speeding up patient care, improving efficacy, and reducing costs.
To achieve PoC, the first step is to use a multifunctional application optimized integrated circuit with advanced analog front-end (AFE) to connect with various biosensors for necessary data acquisition and measurement. Each IC must meet unique characteristic requirements for complex electrochemical, biological, and related measurements, including accuracy, low power consumption, and highly integrated functionality. Successful final products are characterized by excellent performance, high flexibility, and upgradability, which contribute to the realization of forward-looking platforms. These products must also be equipped with smooth and precise motion control and authentication ICs to ensure data accuracy and privacy security.
This article will explore the major transformation towards PoC and its impact on design, and then describe the widely used AFE measurement scenarios, introducing the flexible solutions that Analog Devices can provide to meet the requirements of PoC measurement, motion control, and verification.
Why do we need PoC now?
There are many factors driving the demand for PoC and sample processing, including the need for rapid medical diagnosis to improve individual health conditions. Regulatory regulations encourage or even mandate more testing. There is currently a trend of conducting PoC near clinics or homes to minimize the impact on patients, reduce costs, and save time. Therefore, such systems require the use of simple and easy-to-use yet powerful instruments and equipment to achieve these goals.
For designers of such systems, AFE、 The motion control and identity verification IC provides an intermediate interface that can directly connect patient body fluids, vital signs, and the systems required to capture, record, evaluate, and report result data from various sensors. These devices are the cornerstone of building electrochemical and optical diagnostic solutions, and require such solutions to provide measurement engines that are compatible with a variety of biosensors and chemicals, as well as a software upgradable platform.
Interface between patient vital signs and body fluids and related PoC instruments and data systems
Figure 1: Simulation and related electronic devices serve as important communication interfaces between patient vital signs and body fluids, as well as related PoC instruments and data systems. (Image source: Analog Devices)
Application oriented diversified ICs should be able to address various challenges
We can use some examples to clearly illustrate this situation:
Example 1: Optical Fluorescence Detection (FLD):
Through this technology, researchers are able to study the distribution, localization, and interactions of biological components within cells or tissues, thereby gaining a detailed understanding of cellular processes and functions that are typically unobservable by standard optical microscopes. This technique uses fluorescence induced fluorophores instead of working based on optical absorption, scattering, or reflection principles.
Fluorescent materials absorb light of specific wavelengths, exciting some of the electrons to higher energy states. When electrons return to the ground state, the fluorescent group emits light with a longer characteristic wavelength. By detecting and analyzing the emitted fluorescence, high contrast molecular level visualization of biological structures can be achieved.
The more advanced LED and photoelectric sensor system provides us with more performance and functionality. There are some ICs specifically designed for these applications, such as MAX86171 (Figure 2, top). This is an ultra-low power optical data acquisition system with transmission and reception channels. Despite its internal complexity, only a few discrete components need to be configured in applications (Figure 2, bottom).
MAX86171 multi-channel, ultra-low power, optical data acquisition system from Analog Devices (click to enlarge)
Figure 2: The MAX86171 multi-channel, ultra-low power, optical data acquisition system (top image) simplifies external wiring and the need for passive auxiliary components with its highly integrated internal functions (bottom image). (Image source: Analog Devices)
On the transmitter side, MAX86171 is equipped with 9 programmable LED driver output pins, each connected to 3 high current 8-bit LED drivers. On the receiver side, the IC is equipped with two low-noise, charge integrated front ends and ambient light cancellation (ALC) circuits, forming an optical based, highly integrated high-performance data acquisition system.
For designs that require fewer optical channels, the MAX86178ENJ+device can be used, which is an ultra-low power, clinical grade vital sign AFE that can support up to six LEDs and four photodiode inputs.
Please note that the performance indicators and priorities of medical applications are different from non-medical situations such as optical data channels. Due to the relatively low light level, the absolute background noise of the optical front-end is a key parameter, rather than the signal-to-noise ratio (SNR).
Although in the biomedical field, signal bandwidth and sampling rate are usually very low, and related parameters do not change at a rate of several kilohertz, the complex simulation characteristics of patient physiological systems and signals themselves require us to set different priorities in technical specifications. These features include high sensitivity, wide dynamic range, and low noise to successfully cope with constantly changing operating environments. In this environment, the patient's skin and internal organs will constantly move, and even slight movements can cause changes in the contact area and contact force. In addition, these characteristics are also affected by various interferences and changes, making the problem more complex.
To meet application requirements, the dynamic range of MAX86171 is between 91 and 110 decibels (dB), depending on the test layout. Its resolution is 19.5 bits, dark current noise is less than 50 picoamps (pA) (effective value), and the ambient light suppression coefficient at 120 hertz (Hz) is better than 70 dB.
Example # 2: Potentiometer, Ampere Meter, Voltammetry, and Impedance Measurement:
Nowadays, electrical engineers can proficiently measure voltage, current, impedance, and their interrelationships using various standard instruments. However, these measurements have unique requirements and limitations in chemical and biological environments, and present different scenarios:
Potentiometric method: using a potentiostat to measure the potential between two electrodes to determine the concentration of substances in a solution
Ampere meter: using a current measuring device to detect ions in a solution based on current or changes in current
Voltammetry: Applying a specific voltage curve over time to a working electrode and measuring the current generated by the system, typically using a potentiostat for measurement.
Impedance: Measuring the voltage current relationship between the skin and the body
To evaluate these parameters, an AD5940 56 ball WLCSP with a size of 3.6 × 4.2 millimeters (mm) can be used (Figure 3). This low-power AFE has multiple functions and interfaces, designed specifically for portable applications that require high-precision electrochemical technology such as ampere, volt ampere, or impedance measurements.