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Utilization of gold nanoparticles to detect formalin adulteration in milk

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DOI: 10.1016/j.matpr.2020.12.233

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Utilization of gold nanoparticles to detect formalin adulteration

in milk
Mahesh Agharkar a,b, Suyog Mane a,c
a
Department of Chemistry, University of Pune, Ganeshkhind Springernature Technology and Publishing Solutions, Pune, India
b
Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007, India
c
Department of Nanotechnology, Shivaji University, Kolhapur, India

a r t i c l e i n f o a b s t r a c t

Article history: Despite the addition of formalin in milk or any food product is banned in most of the countries, its use
Available online xxxx continues because of capability to increase shelf life of food by several folds and cheap availability. An
addition of small quantity of solution of gold nanoparticles enhanced the capability of Tollen’s reagent
Keywords: and produced visible change in color due to presence of trace amount of formalin in solution. In order
Formalin to establish this new technique, various samples of milk with different quantities of formalin were pre-
Gold nanoparticles pared and color change after the reaction with gold nanoparticles suspended in Tollen’s reagent was vis-
Tollen’s reagent
ibly observed. This was also monitored by UV–Visible Spectrophotometry to confirm the formation of
Milk preservative
Gold-silver core–shell particles
gold core silver shell particles. This paper presents an easy, cost effective way to detect formalin adulter-
Milk adulteration ation in milk at very low concentrations and could be adopted in the area of quality control and can be
further modified for use in the testing of other food products.
Ó 2021 Published by Elsevier Ltd.
Second International Conference on Aspects of Materials Science and Engineering (ICAMSE 2021).

1. Introduction teration in milk even in a very minute concentration, which has to

be otherwise tested in sophisticated laboratories using expensive
Milk lasts for 48 h when stored at temperature less than 7 °C, equipment such as iso-electric focusing [7]. This technique
but its shelf life can be extended further by adding preservatives depends on the formation of gold core and silver shell particles.
[1]. Formaldehyde or formalin as it is commonly known, is the In other words, this new technique uses the principle behind the
world’s oldest and perhaps the chipset chemical used as preserva- reduction based synthesis of gold-silver core–shell nanoparticles
tive and in small amount, it is enough to increase shelf life of milk to enhance the capacity of tried and tested tollen’s reagent. While
by many folds. Formalin is extremely harmful to human body, and a silver precipitation at ppm level is invisible to the naked eye and
highly carcinogenic and its ingestion has been shown to cause cannot even be detected by UV–visible spectroscopy, a color
vomiting, abdominal pain, dizziness, and in extreme cases death change from red to yellow in case of water or pink to yellow in case
[2,3]. It is highly toxic to kidneys (nephrotoxic) [4] it forms alde- of milk is easily visible. Because it is a colloidal nanoparticle solu-
hyde compounds and fix the proteins. Formalin is an electrophile tion it is even detectable by UV–visible spectroscopy. Silver (Ag)
which means, that it can react with macromolecules such as precipitation produced as a result of reaction of Tollen’s reagent
DNA, RNA and protein and lead to the formation of reversible with aldehyde present in adulterated milk and are deposited on
adducts or irreversible cross-links [5]. Its use in any food products gold nanoparticles; thereby changing the original pink color of
has been banned all over the world but some people still continue the AuNPs solution to yellow.
to use it for same purpose. Foods known to be adulterated using
formalin include noodles, salted fish, tofu, and there is a possibility
of even chicken and beer being contaminated. Even today, formalin 2. Methodology
is used illegally as a preservative in foods, which exposes people to
formalin consumption and consequences of it [6]. 2.1. Synthesis of gold nanoparticles
This paper explains how a combination of gold nanoparticles
(AuNPs) and Tollen’s reagent can be used to detect formalin adul- Colloidal AuNPs solution was prepared as reported earlier [8,9].
Briefly, 20 ml 1  10 3 M tetrachloroauric acid was heated in a

https://doi.org/10.1016/j.matpr.2020.12.233
2214-7853/Ó 2021 Published by Elsevier Ltd.
Second International Conference on Aspects of Materials Science and Engineering (ICAMSE 2021).

Please cite this article as: M. Agharkar and S. Mane, Utilization of gold nanoparticles to detect formalin adulteration in milk, Materials Today: Proceedings,
https://doi.org/10.1016/j.matpr.2020.12.233
M. Agharkar and S. Mane Materials Today: Proceedings xxx (xxxx) xxx

conical flask for 5 min, when it started boiling, 2 ml of 0.1 M triso- UV–visible spectroscopy graphs. This approach of double experi-
dium citrate was added drop wise and solution immediately ments also confirmed the reproducibility of results also confirmed.
turned deep red. This solution was then centrifuged at 5000 rpm Firstly, we conducted the experiment directly in milk sample.
for 20 min and supernatant was discarded to remove any excess Upon drop wise with vigorous shaking of Tollen’s reagent into
trisodium citrate unreacted left in the solution. This particular the mixture of AuNPs and milk sample adulterated with formalin;
method was selected because it is eco- friendly and produces initial pink color of the solution was changed to yellow. Fig. 1 show
extremely stable spherical gold nanoparticles, which are ideal for snap shot of various concentrations of formalin adulterated milk
this purpose. from A to F, corresponding to 0 ppm, 100 ppm, 200 ppm,
This particular method was selected because it is eco-friendly 250 ppm, 500 ppm and 1000 ppm respectively as detected by
and produces extremely stable spherical AuNPs, which are ideal AuNPs enhanced Tollen’s reagent. A gradual shift from pink color
for intended purpose as stated above. of AuNPs to yellow color of gold core and silver shell (Au@Ag) par-
ticles [11] occurred. Visual results confirm that even the quantita-
tive analysis of formalin adulteration is possible with this
2.2. Preparation of Tollen’s reagent
technique.
In a control experiment without milk (Fig. 2) at 0 ppm formalin
Tollen’s reagent was prepared as reported earlier [10].
level, we observed a distinct surface plasmon resonance (SPR) band
briefly, Aqueous silver nitrate is mixed with aqueous sodium
at 525 nm (Fig. 2A) which is considered as characteristic SPR band
hydroxide. Aqueous ammonia is added drop-wise until the precip-
associated with gold nanoparticles [12,13]. As the concentration of
itated silver oxide completely dissolves. Tollens’ reagent oxidizes
formalin in the solution increased SPR band slowly manifested
an aldehyde into the corresponding carboxylic acid.
blue shift, while at 100 ppm, it exhibited SPR band at 522 nm
(Fig. 2B). At 200 ppm there was further blue shift at 512 nm
2.3. Preparation of adulterated milk samples (Fig. 2C), whereas at 250 ppm, two SPR bands were observed one
at 512 nm and another at 412 nm (Fig. 2D), indicating partially
Adulteration of milk samples (Chitale milk suppliers Pune, and/or thinly coated AuNPs by silver layer forming Au@Ag core–
India) was simulated in the laboratory at the level of 0, 100, 200, shell nanoparticles [14]. However, at 500 ppm and 1000 ppm,
250, 500 and 1000 ppm formalin (Merck). SPR bands of AuNPs completely disappeared and prominent SPR
band of AgNPs at 412 (Fig. 2E and F) respectively were observed,
2.4. Detection of formalin adulteration in milk.

To 1 ml of each milk sample was added 50 ll of AuNPs solution,

followed by vigorous shaking after which, 50 ll of Tollen’s reagent
was added to every sample, again. drop wise with vigorous shaking
However, control experiment was performed using double distilled
water instead of milk so that it could be analysed using UV–Vis
spectrophotometer. Experiment in distilled water was conducted
with the same gradual concentration increase but this time the
outcome was recorded in the form of UV–visible spectroscopy
graphs.

3. Results and discussion

Two experiments were conducted in order to verify the use of

this novel technique. First experiment was conducted with actual
milk sample and relied on visual color changes. Second experiment
was conducted in water with the same gradual concentration
increase but this time the outcome was recorded in the form of

Fig. 2. UV–Vis spectra of various concentrations of formalin adulterated water

(control) from A to F corresponding to 0 ppm, 100 ppm, 200 ppm, 250 ppm,
500 ppm and 1000 ppm respectively as detected by AuNPs enhanced Tollen’s
reagent.

Fig. 1. Snap shots of various concentrations of formalin adulterated milk from A to

F corresponding to 0 ppm, 100 ppm, 200 ppm, 250 ppm, 500 ppm and 1000 ppm Fig. 3. Schematic elaborates the mechanism of utility of gold nanoparticles and
respectively as detected by AuNPs enhanced Tollen’s reagent. Tollen’s reagent to detect formalin adulteration in milk.

2
M. Agharkar and S. Mane Materials Today: Proceedings xxx (xxxx) xxx

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Abdollah Hassanzadeh. Fabrication of interconnected plasmonic spherical
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cial interests or personal relationships that could have appeared
to influence the work reported in this paper.

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