hi welcome my name is ajwa very happy to have you here i've been working in medical research
for over 10 years and this is basically my open lab book i document techniques that i'm
learning techniques that i have learned and just other concepts that are of interest go ahead and
subscribe and join the study group if you find it of interest now in this video we're looking at how
a rapid antigen test also called a lateral flow test differs from the polymerase chain reaction (PCR)
test now with the polymerase chain reaction (PCR) test we are looking at genetic materials so the rna
of the virus which first gets converted to dna using reverse transcriptase and then it goes
ahead and it's amplified. this means that if you have only very low infection you can still come
up as positive using the polymerase chain reaction test. When we come to the rapid antigen test as the
name suggests it's the antigen so it's the viral protein that's being detected rather
than the viral nucleic acid and so in this this just involves a membrane several membranes that
are usually encased in a plastic case so that it's protected and you go ahead and judging by
the bands that develop on the test you decide whether you think the person... you think you're
infected or not. Let's take a look at how the bands are generated or not generated if you're negative
so you see a sample port where your sample will go in your sample is usually a swab that you
insert into your nose or into your tonsils area (throat swab) and you're going to go ahead and add a solution
to it this for interaction with the antibodies that are on the cartridge and so that's the part
where your sample that you've prepared will go thanks to the membranes that are embedded on as
part of the test the sample will migrate from the location where you place it towards the end of it
and at each step different reactions will take place so it will go closer and look at what
reactions are taking place at each step if we open the cartridge what you will find are four distinct
areas as part of the test so initially where the sample was placed is where you have the sample pad
the sample pad then migrates to an area on this that you can see it's colored like a purpley
reddy color so this area is really interesting this is the conjugation area this place has gold
particles so it turns out that gold particles that are less than 100 nanometers in size when they're
resuspended in solution usually water actually appear red and this property of gold is what's
used in this conjugation pad section of the test so the gold particles are actually negatively
charged and they're able to be conjugated to antibodies antibodies that will recognize the
viral protein the antibodies are positively charged so they can interact electrostatically
and so you are able to have on that section as a reagent a biological agent that will be able
to recognize the viral proteins downstream of the gold colloidal gold conjugation area is
your test pad and your test pad is where you're actually going to get an assessment of whether
you are positive or you are negative so that the test part area is going to have a test portion
that and if that comes up red as a band then you are positive and but it will also have a control
band and the control band is what's going to be used to check whether the test actually worked
whether the cartridge that you're using actually worked and so we're going to break each of these
components apart and discuss what's happening and then finally the last portion is your absorbent
pad and this absorbing pad is actually critical it acts in drawing the sample from the place where
you placed it right to the end so that it can go over the membrane into all the different reaction
stages and so it's actually it's like a wicking pad that draws the reagent by capillary action
to the end so this is the lateral flow mechanism that sometimes this kind of test is referred to as
so if we have a look at a sample from an infected person then when you place it it will travel along
and go to the colloidal gold conjugated antibody section so this section is interesting because
what happens is the antibody and the colloidal gold will actually move will be drawn along by
the absorbent pad to the test area so the gold particles which are red which can appear red will
actually move along with the antibodies until they get to the test area on the test area you've got
antibodies that are specific to the viral proteins but this time it doesn't move along if it finds
if there are viral proteins in the sample it will stop at the test area and as it accumulates the
gold particles accumulates because it's conjugated to the antibody and so you develop this red line
and the gold particles that are conjugated to antibodies that do not stay at that end because
as just being drawn there's always excess of the gold particle will migrate along to the control
area and there also there are antibodies but this time the antibodies are towards the antibody that
was used to recognize the viral protein so it's not an antibody that recognizes the viral protein
but an antibody that recognizes the antibody that was used to interact with the viral operation
and so you will get a van developing here this control band is necessary to confirm to validate
that your assay that the cartridge is performing as issues so you need to always have this part
coming up as red because if it doesn't that means something went wrong and things didn't work as
the issue then once again it's that absorbent pad that's really dragging everything through
into the end so that the reactions can take place now obviously if a sample did not have
viral protein thyroid proteins can be nuclear capsid they can be the envelope of the virus or
the spike protein that will be interacting with the antibody and so obviously if there wasn't any
of it then when it gets to the primary antibody that's conjugated to the colloidal gold particles
none of it will actually interact and so you're not going to get a bend but it will keep moving
along and it will that antibody will interact the secondary antibody that's at the control end and
so you will get the band coming up and that's how the lateral flow tests or rapid antigen tests work.
They're based on antibodies that are embedded on the membrane recognizing viral proteins and
interacting with them and giving you a red band thanks to the colloidal gold particles
that are conjugated to the antibodies okay so that's a quick video to explain how this
works i hope it was helpful and if it was you can go ahead and give this video a thumbs up
and i'll catch you in the next video take care keep safe follow the protocols bye