Paper: Detecting E.Coli in water with microwave loop + antibodies & VNA - Page 1
Forum section: electronics / rf-microwave

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: September 08, 2025, 01:44:41 pm
content: Since I was playing with different loop antenna designs lately, this caught my eye.They have a loop with a capacitance gap, and a coupling loop around that, on PCB. (I link the 2nd illustration of theirs as the 1st one in there actually has a short at the SMA, hehe)The gap = capacitor is prepared with specific antibodies, and if the water has E.coli and they bind to the antobodies, it changes the dielectric properties and the resonance frequency shifts.They measure & display that on a cheap NanoVNA clone.Kind of interesting.https://www.sciencedirect.com/science/article/pii/S0956566325002088

author: SA2JON
author_rank: Newbie
timestamp: September 08, 2025, 06:49:21 pm
content: Yes looks like something you could actually make at home*. I am currently away but will have to try in a couple of months when I get home and have accesses to both a electronics lab and a biomedical.

author: Marco
author_rank: Super Contributor
timestamp: September 08, 2025, 06:58:02 pm
content: So presumably this is detecting the agglutination?Instead of coating, wouldn't it make more sense to to just bring the sample and some liquid with the antibodies together?

author: SA2JON
author_rank: Newbie
timestamp: September 08, 2025, 07:04:57 pm
content: Yes but no. Agglutination is when a antibody (most often IgM) binds to multiple antigens and create a large body of antigen/antibody particles bound to etch other.In this case we have a surface coated with an antibody and we measure the change in Z when the antibody's have bound there antigen.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 09, 2025, 06:47:44 pm
content: Check out the PI's other papers. She does a lot of cool stuff from the EE point of view.Steve

author: jpanhalt
author_rank: Super Contributor
timestamp: September 09, 2025, 07:26:39 pm
content: Are you trying to detect E. coli specifically or Enterobacteriaceae as a marker of fecal contamination? A polyvalent, E. coli-specific antibody would be quite a challenge. Why not also detect Shigella, etc.?

author: SA2JON
author_rank: Newbie
timestamp: September 15, 2025, 03:58:38 pm
content: This method I think could be generalised for most antigens. The authors have a previous paper about using the same assay for cov-19 virus.If I get the time and energy for a replication attempt I would probably use whatever antibody someone has over and can give to me for free.An interesting application would be to replace traditional POC testing devises for uHCG, cov-19, StrepA, fFOB, etc. Would it be possible to create a "coated reaction vial" for a competitive price compered to exiting tests? This method I think has the possibility for more much higher sensitivity but will require an instrument for reading(could be seen as an advantage because it reduces error).

author: LM21
author_rank: Regular Contributor
timestamp: October 07, 2025, 06:41:10 am
content: If I understand this correctly, there is a gap which has the sample. There is probably many kinds of other stray capasitances around there and they are constant. And your signal/change of Er is small. The sample should be between the plates and around it too.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 07, 2025, 09:46:49 am
content: I don't know biology, so my immediate question is, how do you knowwhatis detecting?Pretty much any material added to a small antenna will affect the RF response, but I see no specific signature (like e.g. in a NMR spectrum specific to each chemical). So, how this method can tell it is E-coli, and not something else?

author: ejeffrey
author_rank: Super Contributor
timestamp: October 07, 2025, 11:56:14 am
content: Quote from: RoGeorge on October 07, 2025, 09:46:49 amThe sensor has an antibody coating that specifically bind to e coli. That's what is meant by "functionalized" in biology. That is what does the heavy lifting, the VNA is just a convenient way to measure that junk has stuck to the sensor.