BIOSENSORS

1. Introduction
A biosensor is an analytical device which converts a biological response into an electrical signal.
The term biosensor is often used to cover sensor devices used in order to determine the
concentration of substances and other parameters of biological interest even where they do not
utilize a biological system directly. Biosensors function by coupling a biological sensing element
with a detector system using a transducer. The first scientifically proposed as well as successfully
commercialized biosensors were electrochemical sensors for multiple analytes. The following
statement is also defined for the biosensor, A chemical sensing device in which a biologically
derived recognition is coupled to a transducer, to allow the quantitative development of some
complex biochemical parameter
The desired biological material usually a specific enzyme is immobilized by conventional methods
such as membrane entrapment, non-covalent or covalent binding. This immobilized biological
material is in intimate contact with the transducer. The analyte binds to the biological material to
form a bound analyte which in turn produces the electronic response that can be measured. In some
instances, the analyte is converted to a product which may be associated with the release of heat,
gas, electrons or hydrogen ions. The transducer can convert the product linked changes into
electrical signals which can be amplified and measured. Biosensors can be grouped according to
their biological element or their transduction element. Biological elements include enzymes,
antibodies, micro-organisms, biological tissue, and organelles.
The advantages of biosensors include low cost, small size, quick and easy use, as well as a
sensitivity and selectivity greater than the current instruments. Biosensors have many uses in
clinical analysis, general health care monitoring. The most popular example is glucose oxidase-
based sensor used by individuals suffering from diabetes to monitor glucose levels in blood and a
pregnancy test is one of the most common used biosensors. Biosensors have found potential
applications in the industrial processing and monitoring, environmental pollution control, also in
agricultural and food industries.
In this experiment we are going to be using glucometer, blood glucose assay and pregnancy test
kits to study the basic concepts of biosensors in detail.

2. Objectives
The aim of this lab is to determine blood glucose of mammal using different methods and later
compare the two methods which are the biosensor assay and the conventional method.
Procedure
a) Blood glucose assay
To separate the plasma from the whole blood the blood sample was centrifuged at speed of
3000rpm for 5 minutes. The supernatant which is the serum was transferred to a fresh tube
and it was used to determine blood glucose concentration.
b) Blood glucose determination assay
Reagent (µL) blank Sample 1
(25:75)
Sample 2
(50:50)
Sample 3
(Undiluted
serum)
Standard
ddH2O 210 200 200 200 200
Serum - 10 10 10 -
Glucose
standard (5.5
mmol/L)
- - - - 10
Solution
(buffer)
10 10 10 10 10
Solution2
(NADP+/ATP)
10 10 10 10 10
*Hexokinase/G-
6-PDH
2 2 2 2 2
Each reagent was added according to the table above except for the enzyme * in a 96 well plates
in duplicates. The samples prepared were mixed well and the absorbance of the solutions (A1)
recorded after 3minutes, then the enzymes were added to start the reaction and absorbances
immediately taken before the 96 well plate was incubated at 37℃for 30minutes. Absorbance (A2)
of the samples was taken after 30 minutes of incubation.
Glucometer
A test strip was put into the glucometer; a drop of blood was applied on the white are of the test
strip. After the blood was drawn into the test strip the same procedure was reaped using sample
1,2 and 3. After 3 lines appear they show that enough blood has been applied to the glucometer
strip. The reading was recorded after 5 seconds countdown as it appeared on the screen after
completion of the test. After removing the test strip, the glucometer was switched by pressing and
holding the butterfly sign on the machine and results were recorded.
Pregnancy Test

3. The pregnancy test kit was unboxed to expose the absorbent pad. The pregnancy test kit was put
on a flat surface and urine was collected in a 2ml centrifuge tube. The sample was placed on the
absorbent pad using a pipette. After waiting for some minutes, the testing device had collected an
adequate amount of the urine sample. Two tests were carried out and results were recorded.
Results
Blood glucose assay Results
Column1 blank sample
a1
sample
a2
sample
a3
sample
b1
sample
b2
sample
b3
standard
0.175 0.186 0.227 0.207 0.201 0.215 0.209 0.192
0.166 0.18 0.196 0.222 0.189 0.185 0.235 0.133
average 0.1705 0.183 0.2115 0.2145 0.195 0.2 0.222 0.1625
blood glucose
concentration
2.728 2.928 3.384 3.432 3.12 3.2 3.552 2.6
Column
1
blank sample
a1
sample
a2
sample
a3
sample
b1
sample
b2
sample
b3
stand
ard
0.176 0.414 0.799 1.018 0.58 0.906 1.174 0.806
0.165 0.318 0.733 1.427 0.62 0.497 1.558 0.723
average 0.170
5
0.366 0.766 1.2225 0.6 0.7015 1.366 0.764
5
blood
glucose
concentr
ation
0.579
856
1.24473
5121
2.60510
1373
4.15761
9359
2.04054
9379
2.38574
2315
4.64565
0752
2.6
Glucometer Results
blank sample a1 sample a2 sample a3 sample b1 sample b2 sample b3 standard
error 3 Low 2.9 4 1.6 3.2 4.6 2.6
Pregnancy Test
Urine sample 1- Negative
Urine sample 2- Positive

4. Discussion
Diabetic patients are required to test their blood glucose since it is an important tool in managing
their treatment plan and preventing diabetes complications. Glucose can be tested at home with a
portable electronic device called the glucose meter that measures sugar level in a small drop of
your blood (Newman and Turner 2005).For the first part of the experiment we used conventional
method of glucose testing had more limitations as compared to glucometer. The blood assay
required more blood sample. There was poor penetration of light by the spectrophotometer
spectroscopy. It takes more time to prepare the sample and mix the reagent and a human reaction
time may occur as the reagents may start to react after the addition of the enzyme before blanking
the machine. The blood assay gives accurate results because whole blood is not used.
The second part of the experiment the glucometer tests is customized for portability since it is
small in size, sensitive, selective and uses small analyte to give results. The glucometer uses an
enzyme as a biosensor the signal is transduced an amplified and displayed on a screen for analysis.
There are major limitations of glucose meters as compared to the conventional method. Whole
blood is used for the glucometer testing hence there can be inaccurate due to metabolites found in
blood that may include results include maltose, galactose. Elevated levels of ascorbic acid can also
give a false positive. Hypoxia can also give false results when its levels are increased.
The Pregnancy Test is a rapid chromatographic immunoassay for the qualitative detection of
human chorionic gonadotropin in urine to aid in the early detection of pregnancy. Human chorionic
gonadotropin is a glycoprotein hormone produced by the developing placenta shortly after
fertilization. hCG can be detected in both urine and serum as early as 7 to 10 days after conception
and hCG levels continue to rise very rapidly (Stenman and Alfthan 2013). The appearance of hCG
in both the urine and serum soon after conception, and the rapid rise in concentration during early
gestational growth, makes it a marker for the early detection of pregnancy. The test utilizes a
combination of antibodies including a monoclonal hCG antibody to selectively detect elevated
levels of hCG. The assay is conducted by adding a urine specimen to the specimen well of the test
device and observing the formation of colored lines. The specimen migrates via capillary action
along the membrane to react with the colored conjugate (Corti, Piro et al. 1992).
For the pregnancy part of the experiment. Two samples were used urine 2 tested positive, two
distinct lines appeared meaning sample reacted the specific antibody-hCG-colored conjugate to
form a colored line at the test line region of the membrane. To serve as a procedural control, a
colored line will always appear in the control line region indicating that proper volume of specimen
has been added and membrane wicking has occurred (Mccarthy and Eapen 2015). For urine 1
which tested negative meaning only the control line appeared indicating that proper volume of
specimen has been added and membrane wicking has occurred since the test line did not show.
Absence of this colored test line suggests a negative result. For a negative result the specific
antibody-hCG-colored conjugate did not react with urine sample as no hCG hormone was detected.

5. Conclusion
The conventional method has proved to be more accurate even if it is slow. A serum has less blood
components as compared to the whole blood used by the glucometer which make the results
inaccurate. The conventional method is slow and takes a lot of time however the glucometer takes
less time and gives inaccurate. The pregnancy test has limitation, hCG Card Pregnancy test is a
qualitative test, hence, neither the quantitative value or the rate of increase in hCG can be
determined by test kit. False negative results may occur when the levels of hCG are below the
sensitivity level of the test. A number of conditions other than pregnancy, including trophoblastic
disease and certain non-trophoblastic neoplasms including testicular tumors, prostate cancer,
breast cancer, and lung cancer, cause elevated levels of hCG. It can be concluded that this test
provides a presumptive diagnosis for pregnancy. A confirmed pregnancy diagnosis should only be
made by a physician after all clinical and laboratory findings have been evaluated, therefore, the
presence of hCG in urine specimen should not be used to diagnose pregnancy unless these
conditions have been ruled out
References
Corti, A., et al. (1992). Device and method for pregnancy detection, Google Patents.
Mccarthy, D. and S. Eapen (2015). Pregnancy test device and method, Google Patents.
Newman, J. D. and A. P. Turner (2005). "Home blood glucose biosensors: a commercial
perspective." Biosensors and bioelectronics 20(12): 2435-2453.
Stenman, U.-H. and H. Alfthan (2013). "Determination of human chorionic gonadotropin." Best
Practice & Research Clinical Endocrinology & Metabolism 27(6): 783-793.