The document provides an overview of the ELISA (enzyme-linked immunosorbent assay) technique. It discusses the principle, basic procedure, materials needed, types (indirect, sandwich, competitive), advantages, disadvantages, and applications of ELISA. ELISA is a sensitive and specific quantitative immunological technique used to detect antigens, antibodies, or other proteins in biological samples. It has various applications in detecting hormones, proteins, infectious agents, and for vaccine quality control among others.

1. PRESENTED BY
S .VISWANTH REDDY
M.Pharmacy 1stYear(pharmacology)
Gokaraju rangaraju college of pharmacy
1

2. ENZYME LINKED
IMMUNOSORBENT
ASSAY
2

3. CONTENTS
ELISA
Introduction to ELISA
Principle & procedure
Materials needed
Types of ELISA
Advantages & disadvantages of ELISA
Applications
RIA
Introduction to RIA
Principle & procedure
Materials needed
Advantages & disadvantages of RIA
Instrumentation
Applications
3

4. INTRODUCTION TO ELISA
ELISA, or enzyme-linked immunosorbent assay,
are quantitative immunological procedures in
which the Ag- Ab reaction is monitored by
enzyme measurements.
The term ELISA was first used by Engvall &
Perlma in 1971.
The ELISA test, or the enzyme immunoassay
(EIA), was the first screening test commonly
employed for HIV. It has a high sensitivity.
4

5. Why known as ......?
Enzyme Linked Immunosorbent Assay
Antigen of interest is absorbed on to plastic. 1
’(.surface (‘sorbent
Antigen is recognised by specific antibody .2
’(.(‘immuno
This antibody is recognised by second antibody .3
(‘immuno’( which has enzyme attached (‘enzyme-
’(.linked
Substrate reacts with enzyme to produce product, .4
. usually coloured 5

6. BASIC PRINCIPLE OF ELISA
Use an enzyme to detect the binding of
antigen (Ag) antibody (Ab).
The enzyme converts a colorless substrate
(chromogen) to a colored product,
indicating the presence of Ag : Ab binding.
An ELISA can be used to detect either the
presence of Antigens or antibodies in a
sample depending how the test is designed.
ELISA was dveloped in 1970 and became
rapidly accepted
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7. 7

8. Materials Needed
Testing sample
Antibody (1st, 2nd) / Antigen
Polystyrene microtiter plate
Blocking buffer
Washing buffer
Substrate
Enzyme
8

9. ANTIGEN (Ag)
Any molecule that induces production of
antibodies when introduced in the body of an
animal is called antigen.
OR
 any “thing”, foreign to the immune system. e.g.
bacteria, viruses, (or their parts), pollen, etc.
Protein molecule
Carbohydrate molecule. SYMBOL FOR ANTIGEN
Microorganisms
Allergens.
Viruses Etc.
9

10. ANTIBODY ( Ab)
Antibody: proteins produced by the
immune system which help defend
against antigens
SYMBOL FOR
ANTIBODY
Y
10

11. Antibodies (Immunoglobulins)
11

12. Specimen Sample For ELISA
SERUM
CSF
SPUTUM
URINE
SEMEN
SUPERNATANT OF CULUTRE
STOOL
12

13. Enzymes Used in Elisa
Horseradish peroxidase (most commonly
used)
Alkaline Phosphatase
β-galactosidase
Lactoperoxidase
Tetra Methyl benzidine
 In case of peroxidase, the substrate hydrogen peroxide is converted
into water and o2 in the presence of electron donors . (like
diaminobenzidine or 4-chloronaphthol which themselves oxidized in
the reaction).
 Oxidation of diaminobenzidine produces dark brown color while that
of 4-chlorornaphthol yields purple color which is the basis of ELISA
13

14. ENZYME SUBSTRATE
Initially
the substrate should be colorless
After degradation by the enzyme it
should be strongly colored or fluorescent.
ENZYME SUBSTRATE CHROMOGEN STOPPING
Alkaline p-NPP p-NPP+ 1 M NaOH
Phosphatase diethandamine+Mg
Cl2
Horse radish H2O2 Tetramethylbenzidi 1 M H2SO4
Peroxidase ne + Phosphate –
Citrate buffer
Horse radish H2O2 O– 1 M HCl
Peroxidase Phenylenediamine
+ HCl
14

15. Secondary
antibody
Substrate
e
Enzym
Coloured
product
Primary
antibody
Different antigens in sample
15

16. Basic
Steps Of
Enzyme-
Linked
Immunos
orbant
Assay
16

17. TYPES OF ELISA
◦ Indirect elisa
◦ Sandwhich elisa
◦ Competetive elisa
17

18. Indirect elisa
18

19. Sandwich elisa
Antigens such as tumor markers, hormones and
serum proteins may be determined
Antigen in the sample binds with the capture antibody
on the microwell and becomes immobilized.
 The antibody of the enzyme conjugate binds with the
immobilized antigen to form a sandwich of antibody-
antigen-antibody/enzyme bound to the microwell.
Enzyme reaction product is directly proportional to
concentration of standard or analytical antigen 19

20. 20

21. ELISA SANDWICH FORMAT
YYY
Antibody
YYY
2nd antibody with enzyme
Y YYY
enzyme produces colour
Y YYY
Y
YYY
Antibody/Antigen
YYY
21

22. Competitive Elisa
 Used to determine small molecule antigens.(T3,T4,progesterone etc.)
 antibody coated microwell
 serum antigen and labelled antigen added together--competition.
 antibody-antigen-enzyme complex bound is inversely related to the concentration
of antigen present in the sample.
 The bound enzyme conjugate reacts with the chromogenic substrate added to
produce a color reaction (blue to yellow color). .
 Increased serum antigen results in reduced binding of the antigen-enzyme
conjugate with the capture antibody producing less enzyme activity and color
(yellow) formation
Substrate product concentration is inversely proportional
to the concentration of standard or test antigen added
22

23. ( to detect Ab (HIV, HCV
( to detect Ag ( Tumor Markers, Hormones
( to detect Ag ( Free Testosterone
Comparison between Indirect Sandwich & Competitive ELISA
23

24. Results
24

25. Importance of incubation step:-
During the test performance incubation
time and mentioned temperature is must
required For the proper binding between
antigen and antibody and also binding with
conjugate and color development of
substrate.
Importance of Washing :- For the removal
of any unbound Antibody/Antigen proper
washing and taping is required other wise
we get the incorrect result.
So incubation & washing is much important
for good results.
25

26. Elisa Plate
Microtitre wells 
Generally 96 
wells
Marked on one 
side alphabetically
Numerically on 
the other side
Comes with the 
kit
26

27. TEST PERFORMANCE
 Using a clean
Pipette , add 100
µL of diluted
serum sample
(Dilute the sera to
be tested 1:100 in
the sample
diluents) to each
.well
 Incubate 1 hour
.at 37°C
27

28. 28

29. ELISA PLATE READY
FOR READING
Measures the absorbance at
450nm With the help of
ELISA READER.
Calculate the absorbance
for each sample and
reference.
We used Ascent Software
for Calculation of the result
29

30. Advantages of ELISA
Reagents are relatively cheap & have a long
shelf life
ELISA is highly specific and sensitive
No radiation hazards occur during labelling
or disposal of waste.
Easy to perform and quick procedures
Equipment can be inexpensive and widely
available.
ELISA can be used to a variety of infections.
30

31. Disadvantages of ELISA
 Measurement of enzyme activity can be more
complex than measurement of activity of some
type of radioisotopes.
 Enzyme activity may be affected by plasma
constituents.
 Kits are commercially available, but not cheap
 Very specific to a particular antigen. Won’t
recognize any other antigen
 False positives/negatives possible, especially with
mutated/altered antigen
31

32. Limitations
Results may not be absolute •
Antibody must be available •
Concentration may be unclear •
False positive possible •
False negative possible •
32

33. APPLICATIONS OF ELISA
detection of Mycobacterium antibodies in tuberculosis
detection of rotavirus in feces
detection of hepatitis B markers in serum
detection of HIV antibodies in blood samples
It has also found applications in the food industry in detecting potential
eggs food allergens, such as milk, peanuts, walnuts, almonds, and
33

34. APPLICATIONS OF ELISA
1- Hormones 7- Vaccine Quality Control
2- Proteins 8- FOR GMO (Genetically modified
organism)
3- Infectious Agent ( Viral, Bacterial, 9- For Rapid Test
Parasitic, Fungal )
4- Drug Markers 10- IgG, IgM, IgA
5- Tumor Markers 11- In New Born Screening
6- Serum Proteins 12- In Clinical Research
34

35. Sensitivity of various immunoassays
35

36. Equipments for performing
the ELISA test
Pipettes
Incubator
ELISA reader
36

37. ELISA READER
(THERMOLAB SYSTEM (USA
37

38. 38

39. ]
Radioimmunoassay
39

40. INTRODUCTION
 Radioimmunoassay (RIA) is a very sensitive in vitro assay technique
used to measure concentrations of antigens (for example, hormone levels in
theblood) by use of antibodies.
 The RAST test (radioallergosorbent test) is an example of
radioimmunoassay. It is used to detect the causative allergen for
an allergy
 To perform a radioimmunoassay, a known quantity of an antigen is
made radioactive, frequently by labeling it with gamma-
radioactive isotopes of iodine attached to tyrosine.
40

41. To perform a radioimmunoassay, a known quantity of an antigen is
made radioactive, frequently by labeling it with gamma-
radioactive isotopes of iodine attached to tyrosine.
This radiolabeled antigen is then mixed with a known amount
of antibody for that antigen, and as a result, the two specifically bind to one
another.
Then, a sample of serum from a patient containing an unknown quantity of
that same antigen is added.
This causes the unlabeled (or "cold") antigen from the serum to compete
with the radiolabeled antigen ("hot") for antibody binding sites. As
theconcentration of "cold" antigen is increased, more of it binds to the
antibody, displacing the radiolabeled variant, and reducing the ratio of
antibody-bound radiolabeled antigen to free radiolabeled antigen. The
bound antigens are then separated from the unbound ones, and the
radioactivity of the free antigen remaining in the supernatant is measured
using a gamma counter.
41

42. Principle of Radioimmunoassay
Principle:Uses an immune reaction
[Antigen – Antibody reaction] to estimate
a ligand
Ag + Ag* + Ab  AgAb + Ag*Ab + Ag +
Ab*
◦ Unbound Ag* and Ag washed out
◦ Radioactivity of bound residue measured
◦ Ligand conc is inversely related to radioactivity
[Ag : ligand to be measured ; Ag* radiolabelled
ligand]
42

43. Advantages &
Disadvantages of RIA
Advantages
◦ Highly specific: Immune reactions are specific
◦ High sensitivity : Immune reactions are
sensitive
Disadvantages
◦ Radiation hazards: Uses radiolabelled reagents
◦ Requires specially trained persons
◦ Labs require special license to handle
radioactive material
◦ Requires special arrangements for
 Requisition, storage of radioactive material
 radioactive waste disposal.
43

44. Requirements for RIA
1. Preparation & characterisation
of the Antigen [Ligand to be
analysed]
2. Radiolabelling of the Antigen
3. Preparation of the Specific
Antibody
4. Development of Assay System
44

45. Preparation & Radiolabelling of
the Antigen
Antigens prepared by..
◦ Synthesis of the molecule
◦ Isolation from natural sources
Radiolabelling [Tagging procedure]
◦ 3 H 14 C 125 I are used as radioactive tags
◦ Antigens are tagged to 3 H 14 C 125
◦ Tagging should NOT affect Antigenic
specificity & Antigenic activity !
45

46. Preparation of the Specific
Antibody
Antigen injected intradermally into rabbits or
guinea pigs  antibody production
Antibodies recovered from the serum
Some ligands are not Antigenic
◦ Hormones, Steroids, Drugs  HAPTENS
◦ Eg: Gastrin, Morphine,
◦ Haptens conjugated to albumin  antigenic
46

47. Development of the Assay System
A crucial step is separation of unbound
antigens
This achieved by binding the antibodies to the
microtitre well surface [Solid phase RIA]
Antigens bound to the fixed antibodies remain
stuck to the inner surface
Decanting & washing the well removes
unbound antigens
Other techniques of separation: Centrifugation
47

48. Assay Procedure
 Add known amounts of the test sample + labelled
antigen into the microtitre wells
 Incubate  allow the reaction to reach completion
 Decant & wash contents of the well  removes all
unbound antigens
 Radioactivity remaining in the Microtitre wells
measured by a Counter [GM counter , Scintillation
counter etc]
 Intensity of radioactivity is inversely correlated with
the conc of antigens in the test sample
 Sensitive to very low conc of antigens
48

49. Antibodies: types of
labelling
,Radio-isotopes-
Enzymes -
Fluorescent
Chemi-luminescent
probes
Metal tags
49

50. Radioimmunoassay
(RIA)
 Advantages  Disadvantages
◦ Flexibility ◦ Toxicity
◦ Sensitivity ◦ Shelf life
◦ Size ◦ Disposal costs
50

51. Advantages
Radioimmunoassay is widely-used
because of its great sensitivity.
Using antibodies of high affinity, it is
possible to detect a few picograms
(10−12 g) of hormone in the tube.
The greater the specificity of the
antiserum, the greater the specificity
of the assay
51

52. limitations
 The main drawbacks to radioimmunoassay are
the expense and hazards of preparing and
handling the radioactive antigen.
 Both 125I or 131I emit gamma radiation that requires
special counting equipment
 The body concentrates iodine atoms —
radioactive or not — in the thyroid gland where
they are incorporated in thyroxine (T4).
52

53. 53

54. INSTRUMENTATION
Radiation will hit silver grains in emulsion and expose them
Expose to film
or emulsion
Isotope will emit
(radiation (usually beta
Incubate tissue with
radioactive ligand
Autoradiography
54

55. INSTRUMENTATION
55

56. REFERENCES
 Engvall E, Perlman P (1971(. "Enzyme-linked immunosorbent assay (ELISA(.
Quantitative assay of immunoglobulin G". Immunochemistry 8 (9(: 871–4.
Gofflot; El (2004(.
 Journal of Immunoassay and Immunochemistry 25 (3(: 241–58. Retrieved 13
December 2012.
Kuhar M, Yamamura HI (Jul 1976(. "Localization of cholinergic muscarinic
receptors in rat brain by light microscopic radioautography". Brain Res. 110 (2(:
229–43.
 E. Rutherford and H. Geiger (1908( "An electrical method of counting the number
of α particles from radioactive substances," Proceedings of the Royal Society
(London), Series A, vol. 81, no. 546,
 A Handbook of Radioactivity Measurements Procedures, 2nd edition: (Report No.
58), National Council on Radiation Protection and Measurements (NCRP( ,
1985 ISBN 0-913392-71-5,pages 30-31
 WWW.GOOGLE.COM/IMAGES
WWW.SLIDESHARE.NET
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57. 57

58. r r ∝ [ Ag ]
58