At a Glance
Researchers at Colorado State University have developed a digital signal generation and acquisition device that overcomes the limitations of analog EIS instrumentation. The device uses digital techniques to store multi-frequency input stimuli of various frequency ranges and utilizes state-of- the-art digital-to-analog conversion to generate the required analog stimuli. The resulting circuit can be integrated on a single chip, making it less susceptible to noise, reducing the size and cost of future EIS products. The device is well suited for a variety of mobile or in-the-field applications, such as pathogen detection, as well as in conventional benchtop systems.
The development of low cost and highly mobile detectors with digital output is active, due to ease of use and the anticipation of an Internet-of-Things connected healthcare system. Electrochemical methods of detection are inherently suitable for low cost and miniaturization and offer an attractive alternative to traditional methods for pathogen detection (e.g., polymerase chain reaction – PCR), as well as other cases since they do not require expensive equipment, personnel or specialized reagents. Electrochemical impedance spectroscopy (EIS) is an electrochemical technique with particular potential in this space.
Standard EIS employs equipment that performs a linear sweep of an analog signal through the desired frequency range. Not only is the equipment physically bulkier than the standard digital equipment of today, but the frequency range accessible to the analog equipment is limited on the low end of the frequency spectrum by the poor signal-to-noise intrinsic to this region of the spectrum. Additionally, the need to perform a linear frequency sweep slows the rate of signal acquisition. The slow rate limits the use of EIS in certain experiments and prohibits the use of certain techniques to improve signal-to-noise.
Part of the innovation lies in the sophisticated composite signal employed, which combines 32 sinusoidal signals of varying frequencies between 2 Hz and 2 kHz and incorporates an offset in order to lower the crest factor for the signal. The signal is stored digitally but delivered as a single analog composite signal. Other composite signals may be readily used.
Another aspect of the innovation lies in the onboard signal-to-noise reduction that dramatically reduces the flicker noise that is inherent to the low end of standard EIS frequency ranges. Incorporated directly into the circuit design, the result is a measurement with low end sensitivities superior to bulkier analog equipment.
Figure 1 (below) illustrates an example of the EIS platform.
Figure 1. An example of the handheld device envisioned
- Digital EIS device that is superior to conventional analog EIS instrumentation
- Reduced size of diagnostic devices
- Cost effective testing, reducing laboratory reagent, personnel, and space limitations
- Composite waveform is stored digitally and delivered as an analog signal
- Onboard signal acquisition with signal-to-noise reduction for improved sensitivity
- Excellent results from a miniaturized, low power and low cost device
- Well-suited for mobile and field applications
- Platform technology for future EIS=based pathogen detection
- Point-of-Care diagnostics
- Remote field work
- Rural medicine
Last updated: June 2023