In our previous post, we explaind what is a PCB and how the PCB technology has impacted consumer electronics by enabling more compact and lighter devices.
In this post, we explain the electrochemistry evolution to date and why at Macias Sensors we are convinced that PCBs are the future of electrochemical biosensors
What is electrochemistry?
Like PCBs, electrochemistry has impacted our daily lives.
In fact, we regularly use devices that are powered by electrochemistry. The main example is batteries.
However, electrochemistry has other applications, such as water treatment or the diangostics and control of diseases.
But what is electrochemistry?
In short, electrochemistry is a science that studies the transformations between chemical en electrical energies.
Traditional electrodes for electrochemistry research
To study an electrochemical reaction you need 2 things:
- A chemical reaction, normally an oxidation or reduction
- Electrodes, these allow to monitor or cause the reaction
There are several different configurations of electrodes in electrochemistry, but the most common one is the 3 electrode cell. These electrodes work as:
- Working electrode: this electrode measures the electrochemical reaction
- Reference electrode: this electrode has a stable electrical potential and serves as a reference for the measurements.
- Counter electrode: this electrode closes the electrical circuit and enables measurements to take place
Electrochemistry evolution: Transition printed circuits
Like cabling in electronic devices, traditional electrochemical cells pose several limitations.
4 disadvantages of traditional electrochemical cells
The first and main disadvantage of traditional electrochemical cells is their size. Yes, they are versatile. And they also allow fine tuning of the experimental conditions. But they occupy a lot of space. For this reason, they are limited to specialized laboratories.
The second disadvantage is the volume they require. Since the cell and the electrodes are bulky, several mililiters of test solution are needed to make measurements. This can be prohibitive when studying reactions involving expensive reactants, like enzymes or other biological analytes.
The third disadvantage is the electrode position. In electrochemical measurements, the position and distance of the electrodes affects the results obtained. Since traditional electrochemical cells do not have fixed electrodes, this means that after each assembly, differences in results may be observed.
Finally, the fourth disadvantage is maintenance. The electrodes used in traditional electrochemical cells are very high quality and are made with precious metals such as gold or platinum. For this reason, they need to be reused. However, this also means that, to avoid contamination across experiments, these electrodes must be thoroughly cleaned and polished.
Screen-printed electrodes as a solution
As we explained above, traditional electrochemical cells pose several disadvantages. While these may be manageable for experienced personnel in a research lab, they are critical in portable applications like PoC biosensors.
The solution to these disadvantages is simple: miniaturization of electrochemical cells.
Screen-printed electrodes (SPEs) are an example of electrochemical cell miniaturisation. Fabricated by screen-printing, these printed circuits have the 3 electrodes needed for an electrochemical cell.
Thanks to ther smaller form factor, these electrodes allow the use of electrochemistry in portable applications. An example of this is the glucometer.
With SPEs, electrochemical reactions can be measure from small volumes of 50 microliters or less (depending on design). This makes electrochemistry suitable for measuring samples containing costly reagents.
Furthermore, since the electrodes are thinner and use less precious metal, SPEs tend to be single use. Which eliminates the need for maintenance.
Still, SPEs have some limitations.
While some SPEs are printed on flexible substrates, most are printed on ceramic. This is due to the high firing temperatures of precious metal inks. This limits their applicability as it makes them costly and fragile. Also, since they can only be printed on a single side, the integration of these devices in a complex electronic system is not possible.
The next step: PCB electrodes
The solution to the limitations of SPEs is to transition into PCBs.
PCB technology is significantly more versatile than SPEs, as it enables the fabrication of complex detection systems.
Thanks to the possibility of integrating circuits in multiple layers, as well as have connections across layers, PCB based electrochemistry allows the incorporation of more functionalities such as:
- resistive heaters
- temperature sensors
- heat pipes
- internal calibration chips
Furthermore, using PCB technology, it is also possible to create microfluidic circuits and flow/fill sensors. Thus, PCB based biosensors have the potential to enable fast prototyping of Lab-on-a-chip (LoC) devices.