P. Ravichandiran, Vignesh Krishnamoorthi Kaliannagounder, N. Maroli et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 257 (2021) 119776
cells. Thus, 4DBS could be employed as an efficient bioimaging probe for discriminative identification of
human cancer cells.
Ó 2021 Elsevier B.V. All rights reserved.
1
. Introduction
In humans or other life forms, metal ions play significant roles
ratiometric approach is one of the efficient methodologies with
good reliability for analyte detection. In ratiometric chemical sen-
sors, the analyte induces changes with more than one absorption
or emission band. The ratio of these bands improves the quantifi-
cation and sensitivity of the chemosensor [24]. Thus, the combina-
tion of colorimetric and ratiometric fluorescence properties leads
to development of active chemosensors for the sensing of toxic
heavy metals in the environment and in living systems.
in biological processes such as metabolism, osmotic regulation,
and cell signaling. Some alkali or alkaline earth metals such as cop-
per, iron, zinc, and sodium ions at trace levels are beneficial to liv-
ing systems [1,2]. Other heavy metals, including Hg2 , Cd , or Pd
+
2+
2+
ions, which are widely used in gold mining, coal plants, and mer-
cury lamps, are widespread in water, soil, and air and can impart
severe impacts to the environment and humans [3]. Among various
heavy metals, mercury is well-known for its high toxicity even at a
lower level, and due to the hazardous nature, its utilization is
restricted in electronic appliances by the European Union’s Restric-
tion on Hazardous Substances (RoHS) [4]. The metal ion Hg is
easily propagated and can be introduced into the human body
through respiration or absorption by skin and digestive tissues.
After accumulation of Hg2 ions at a certain level in the human
body, high binding behavior with thiol groups in proteins and
enzymes induces potential impairment of the kidneys, heart, brain,
immune system, lungs, central nervous system and other tissues
At present, the construction of effective colorimetric and ratio-
metric fluorescence chemosensor is of great need due to their sim-
plicity and easy operation [25]. Nevertheless, most of the available
chemosensors are active in the emission mode, though they do not
induce any colorimetric or ratiometric response towards specific
analytes. In addition, the higher selectivity of these chemosensors
is restricted with other alkaline earth metal ions [26,27]. Therefore,
with the essential need of the colorimetric and ratiometric fluores-
cence performance of the sensing probes in mind, we fabricated
and report the new chemosensor 4-((3-(octadecylthio)-1,4-dioxo-
1,4-dihydronaphthalen-2-yl)amino)benzenesulfonamide (4DBS)
for the colorimetric and ratiometric fluorescence detection of
2
+
+
2
+
[
5–8]. According to the U.S. Environmental Protection Agency
2
Hg in DMSO-H O (9:1, v/v) solution. The present chemosensor
2+
(
USEPA), the permissible level of Hg contamination in drinking
4DBS showed good performance in terms of high selectivity, low
detection limit (LOD), high binding constant value, and negligible
interference from other analytes. The coordination mechanism in
ꢁ1
ꢁ1
water is 2 mg L , and a maximum concentration of 5 mg L leads
to harmful effects in culture medium [9,10]. Thus, effective meth-
ods should be developed for monitoring and selective determina-
tion of Hg ions in environmental and biological samples, which
are of the highest requirement in the current circumstances.
Considering heavy metal pollution, over the past few decades,
several efficient techniques have been examined in an overall large
research effort. Of late, modern analytical techniques have often
been employed for the quantitative and qualitative determination
of heavy metals. These techniques include atomic absorption/
2
+
1
the 4DBS–Hg complex was confirmed by FT-IR and H NMR anal-
yses. Furthermore, quantum chemical calculations were performed
to support the proposed binding mechanism. Subsequent intracel-
2
+
2
+
lular detection of Hg in living cells and zebrafish larvae was per-
formed. The chemosensor 4DBS showed discriminative detection
2
+
of Hg in cancer cells that helped to distinguish human cancer
cells from normal live cells.
emission
spectrometry,
capillary
electrophoresis,
high-
performance liquid chromatography, gas chromatography, mass
spectrometry, and electrochemical methods [11–16]. These analyt-
ical techniques are comprised of several practical advantages such
as precise accuracy, high reliability, repeatability, and easy separa-
tion of selective analytes [17,18]. However, these analytical tech-
niques also have several practical drawbacks including the need
for complex instrumental operation, prolonged analysis time, uti-
lization of expensive materials, sample preparations under haz-
ardous conditions, and expensive instruments that require
sophisticated maintenance [19]. Therefore, simple and efficient
analytical techniques must be developed which allow rapid analy-
sis, high selectivity, easy operation, and economic feasibility.
Among various recent methods available for metal ion detention,
optical chemosensor have attracted wide attention among
researchers. In contrast, colorimetric and fluorescence chemosen-
sor are known to be practically more advantageous, exhibiting
real-time analysis, operational simplicity, highly reversibility, low
detection limit, qualitative/quantitative detection of specific ana-
lytes while avoiding the utilization of complex analytical or spec-
troscopic techniques [20,21]. Over the past several years,
varieties of colorimetric chemosensor have been developed that
provide low-cost direct identification of analytes based on color.
If the sensing output is a color change, this phenomenon can be
easily recognized by the naked-eye or inexpensive instruments
by a non-technical observer [22,23]. On the contrary, to overcome
the practical disadvantages of modern analytical techniques, the
2
. Experimental section
2.1. Synthesis of chemosensor 4DBS
The chemosensor 4DBS was synthesized according to our previ-
ously reported synthetic procedures with necessary modifications
Scheme 1) [28]. The preparation and the spectral analysis of com-
(
pound 3 is accessible in our earlier investigation [29]. All synthetic
procedures and the structural characterization of the chemosensor
4
DBS are briefly described in the supporting information section
(
SI) (Figs. S1 and S2).
2.2. Preparation of 4DBS and metal ion stock solutions
ꢁ3
A stock solution of 2.0 ꢂ 10 M 4DBS was prepared by mixing
ꢁ1
of 0.0122 g of 4DBS in 10 mL of DMSO. 1.0 ꢂ 10 M alkaline earth
cations, amino acids and peptides were prepared in deionized
water. Tetrabuytl ammonium salts of anions were prepared in ace-
tonitrile (CH
3
CN). From the prepared stock solutions, 25
lL 4DBS
and 50 L analytes were diluted with 4 mL of DMSO-H
l
2
O (9:1, v/
ꢁ5
v) solution to obtain a final concentration of 1.25 ꢂ 10 M and
ꢁ3
1
.25 ꢂ 10 M, respectively. The prepared solutions were investi-
gated for their binding properties at ambient temperature (RT).
2