what is the optimum dimensions for interdigitated amperometric Label-free biosensor( Length, width and separation) for detect protein bio-marker ? also what is the best chose for working electrode material and reference electrode material ? in order to get ultra-sensitive biosensor
Hello Tasneem Harahsheh ,
This is a really broad question. Which dimensions are you referring to? Length, width, separation? You may also want to specify your target. For instance, is it a molecule, nucleic acid; amino acid, enzyme, cell, etc.? What is the technique for detection? Label-free? Labelled? Hopefully the RG community can provide a more refined answer if you can be more specific.
With regards to interdigitated geometry... how are you using the device? As two individual working electrodes (for instance for redox cycling, where the current response will be inversely proportional to the diffusional distance) or are they electrically shorted together to simply form a larger working electrode? Do you perform any other electrochemical analysis with the interdigitated electrodes (such as EIS)?
For working electrodes gold, platinum and carbon are very popular. All are chemically stable. Carbon offers a very wide electrochemical 'window' with no obvious oxidative or reductive reactions. In comparison gold shows a distinctive surface oxidation starting around 600 mV vs SCE, pH 7, and of course for platinum you have the issue of oxygen reduction. Gold and platinum offer very easy attachment of bioreceptors through thiol chemistry. Carbon is very diverse and is found in many nanostructured forms. It also offers many ways to provide functionalisation.
The amperometric response of the biosensor will be related to the surface area. Nanostructured electrode surfaces are appealing because they allow for increased surface areas whilst keeping the geometric footprint of the device relatively small (important for miniaturisation). They also provide some level of physical entrapment for larger molecules whilst still permitting diffusion smaller molecules. Signal to noise (SNR) is possibly more important for most applications. Some materials may show large capacitive background currents. As an example, mesoporous carbon will have a large non-Faradaic current related to the electric double layer, especially for faster scan rates (e.g., > 25 mV.s^-1). These can mask the analytical signal.
Answering 'what is the best material for the reference electrode' is more difficult. A reference electrode is used to provide a stable reference potential to which reactions occuring at the working electrode can be compared. For development people tend to use Ag/AgCl (with sat. Cl) or SCE reference electrodes. Fabricating miniaturised reference electrodes for commercial applications presents several challenges. Often pseudo reference electrodes are used such as Ag/AgCl ink or simply platinum. See the following article for further information:
Article Microfabricated Reference Electrodes and Their Biosensing Applications
You may also find the following useful:
Article Electrochemical biosensors and nanobiosensors
Hi Tasneem Harahsheh
I beleive that Jules Lloyd Hammond has explianed the concept very well.
In my work I've used gold and platinum interdigitaded electrodes to measure the EIS. The type of electrodes I've used are 10 micron lines&gaps and 5 micron lines&gaps. The substrate size was 2.2 x 7.6 x 0.7 cm. The results that I've obtained after using these electrodes was very good comparing to the expected behaviour of our investigated materials, however I can't say these dimensions are valid for any platform.
For the amperometric detections, I've used SPCE to measure the AD of our fabricated biosensors.
The attachment has the results of our EIS and I hope you find them useful.
Cheers
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