Enhancing Electrochemical Biosensors with Electroactive Polymers
A couple of days ago, I went on this flow of research about prehistoric humans. It made my realize how much human civilization has developed. We went from living in caves, to 30 story buildings. The one important thing that we’re really lucky to have today is, medicine.
Back then, if you got on injury — you had a 90% chance of death. Today, a little wound would be fixed with a bunch bandages.
Thousands of years ago, the basic rules of life were: you live until you’re bitten by a lion or something. (which was very likely at the time). This phase lasted until, the people made its first move towards medicine. Prehistoric humans’ first interaction with medicine involves grass and clay.
After observing several different animals, they realized that animals obtained some sort of ‘special’ healing qualities just through these 2 things. It would be super weird if we used this same concept in the 21st century.
As time passed, we evolved from different substances, and obtained most medications from sources like plants. That’s until tech crashed into the party. This is the most helpful, and revolutionary equipment in all of healthcare — technology. Before, medicine was more of a guess and check. Now with technology, we have a better understanding of human biology, and can monitor biological activity within a patient at all times.
Now, the term “technology” is just the umbrella. Within that umbrella, there’s a variety of different types including — biosensors.
Biosensors (‘biological sensors’) are devices used to detect the presence or concentration of a biological analyte. An analyte is substance, in which the chemical concentration is undefined.
For example, if we had a glass full of water which has sugar dissolved in it, it could be hard to tell the amount of sugar added. To help identify this, we use particular devices.
If we took this concept, and used it for human biology — that ‘device’ would be known as biosensors.
Analytes are observed through a 4-step process:
- Molecules that recognize analytes are known a bioreceptors. Examples of bioreceptors include: DNA, antibodies, enzymes or even cells. This part of the process is called bio-recognition which involves signal generation interacting with bioreceptors and analytes
- After that, the transducer helps convert one form of energy to another, therefore converting bio-recognition event into a measurable signal. This is known as signalisation.
- Next, the electronic section of the biosensors processes the transducer signal and prepares it for display (last step). Electronic performs signal conditioning such as amplification, then are quantified for display.
- Lastly, all these signals are converted and shown through a display (normally, in a numerical form) to show the concentration of an analyte. The output signal could be shown in graphics, images, numbers are more.
But it doesn’t just end there. There are several types of biosensors that have different applications. The biosensor that I previously explained is called an ‘Electrochemical Biosensor’.
I know, it may. not have a ring to it — however, it has the potential to uncover a lot of details about an analyte’s concentration in a small amount of time. However, the only disadvantage of using this particular type is its cost.
The average price of a biosensor is between $1,000 and $10,000. However, there are several methods and materials that could be used to improve biosensors at a cheaper cost. One of the most efficient materials to use are Electroactive Polymers.
Conducting polymers have found been applied to the biomedical industry for decades now. This is mainly due to its properties being altered when electric stimulus is applied, which improves accuracy in drug delivery, tissue engineering, and more.
The properties of conducting polymers (CPs) have different changes in conductivity, oxidation state, solubility and other thermoelectric properties. However, one of its most recognized properties is its ability to undergo oxidation and reduction reactions.
- Oxidation: loss of electrons during a reaction involving increasing amounts of oxygen levels
- Reduction: gain of electrons due to the decrease in oxygen levels (opposite of oxidation)
The process of conduction for polymers, involves the removal of electrons (p-doping), which leads to a formation of a radical cation, called polaron. Normally, polaron is distributed across 3–5 quinoidal rings — which are a 6 membered carbon ring containing 2 double bonds.
Following up to that, the second electron is removed from the chain, making it a bipolaron (di-cation). The ‘spineless’ bipolarons become mobile under an electric field, developing the easy transport of a current.
The charge of the transport requires electrolytes, which provide ions to sustain polymer electroneutrality. The most important part of all of this, is the electroclyte choice, which will have a huge impact on polymer properties, and affects on electrochemical stability.
Before actually inserting polymers into biosensors, there needs to be an electrochemical analysis. Might sound a bit scary, but it’s just a specific technique that uses electrical stimulation to analyze the chemical reactivity of a solution. Based on the analysis, we can understand oxidation and reduction reactions through measuring its rates through a device called, potentiostat — which is connected to electrodes merged in electrolytes.
An example of these method includes; Amperometry
If I could describe amperometry in two words — it would be ion detector. Amperometry is basically detecting ions in a solution based on an electric current or changes of it. This technique is usually used to measure vesicle release of capacitive measurements (measures the impedance of an oscillating circuit).
In this method, an electrochemical signal is obtained and observed from changes in a current during a process of oxidation or reduction. The applied voltage that is constantly induced is applied to a polymer-modified electrode. This has been applied to glucose monitoring, and has been used for decades. By applying this concept to biosensors, and increase efficiency, with a smaller price tag.
The second step to the biosensor process involves Biorecognition Molecules.
Quick summary, bio-recognition is an element used to create a measurable signal for analysis of a targeted analyte. This is basically the key to biosensors 🔑 . An approach this could be using Antibody-Based Biorecognition.
Binding a Antibody to a CP Substrate
Antibody-Recognition: It’s kinda self explanatory, but this method specifically uses antibody/antigen biorecognition interactions. One main plus point to this method is, that the target analyte (‘antigen’), does not need to be purified prior to detection. There are several steps in a biosensor, one of which involves purification. This step is known as PCR purification — the removal of enzymes, nucleotides, primer, and other unnecessary components that don’t bind well. Some analytes that could be detected using this method includes proteins, and cytokines.
Here’s the fun part: a monolayer conducting polymer-based sensor on ITO (indium tin oxide) helps increase surface area, and sensitivity relative to ITO. Throughout the process, gold nanoparticles were produced and helped enhance conductivity while providing a binding surface for the antibody. It helped capture an analyte within a smaller time period, and provided a space/environment for it to be analyzed.
Conductive polymers have a lot to offer, and consists of distinct electrochemical activities that can be measured through techniques such as amperometry. Conductive polymers are basically superman in a molecular level. They have the ability to interact and engage with organic and inorganic materials to provide high sensitivity and selectivity — making them prime substrates for detection in biosensors.
CPs have opened doors to difference application including medical monitoring devices (glucose, etc.), diseases, and even tissue engineering. On top of that, they can have a significant impact on early detection on serious diseases, like cancer with the help of biomarker-based screening. It’s a very simple, cost-effective material can can revolutionize healthcare, and improve the way we understand science.