DE

JPa

b

a

ARRAA

KRAFL

1

tritbcsaciat[wi[sIan

(

h0

Sensors and Actuators B 241 (2017) 1014–1023

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l homepage: www.e lsev ier .com/ locate /snb

evelopment of arsenic(v) sensor based on Fluorescence Resonancenergy Transfer

aba Saha a, Arpan Datta Roy a, Dr. Dibyendu Dey a, Dr. Jayasree Nath b,rof. D. Bhattacharjee a, Dr. Syed Arshad Hussain a,∗

Thin Film and Nanoscience Laboratory, Department of Physics, Tripura University, Suryamaninagar 799022, Tripura, IndiaDepartment of Chemistry, Tripura University, Suryamaninagar 799022, Tripura, India

r t i c l e i n f o

rticle history:eceived 3 March 2016eceived in revised form 14 October 2016ccepted 20 October 2016

a b s t r a c t

Contamination of drinking water by arsenic is a worldwide phenomenon needing and receiving thegreatest attention in this century. In this work, a novel Fluorescence Resonance Energy Transfer (FRET)-based ratiometric sensor for detecting arsenic(v) was demonstrated. In this system, Acriflavine actedas energy donor, while Rhodamine B acted as energy acceptor. In the presence of arsenic(v) the FRET

vailable online 21 October 2016

eywords:atiometric sensorrsenic(v) sensor

efficiency increases almost linearly in the range of 0.04–0.09 mg/L. Based on these analysis a simple andhighly sensitive method for the detection of arsenic(v) has been demonstrated with the detection limit(LOD) of 10 �g/L. The applicability of the planned method has also been tested using natural lake waterwith satisfactory results.

luorescence Resonance Energy Transferaser dyes

. Introduction

Arsenic (symbol As, atomic number 33) is a group V-A, [1] heavyoxic, ubiquitous element occurring in the atmosphere, soils andocks, natural waters and organisms [2]. In terms of abundance,t ranks 20th in the earth’s crust, 14th in sea water and 12th inhe human system [2]. Volcanic eruptions, weathering reactions,iological activity are the natural sources of high arsenic con-entrations in the environment [3]. Arsenic in ground water andoil may be result of geological process or due to pollution fromnthropogenic sources such as i) the disposal of industrial wastehemicals, ii) the smelting of arsenic bearing minerals, iii) the burn-ng of fossil fuels, iv) the use of arsenical pesticides, herbicidesnd crop desiccants [4]. Organic forms of arsenic are less harmfulhan inorganic arsenic. Inorganic arsenic displays extreme toxicity4]. Of the various sources of arsenic in the environment, drinkingater probably poses the greatest threat to human health [3] and

s estimated to affect over 144 million people around the world5]. Arsenic can exist in nature in a variety of oxidation states,uch as V (arsenate), III (arsenite), 0 (arsenic), −III (arsine) [4–7].

n aqueous environment the principal forms of inorganic arsenicre arsenite (predominantly as H3AsO3) and arsenate (predomi-antly as H2AsO4

−, HAsO42−) [4,8,9]. Organic As compounds, such

∗ Corresponding author.E-mail addresses: sa h153@hotmail.com, sahussain@tripurauniv.in

S.A. Hussain).

ttp://dx.doi.org/10.1016/j.snb.2016.10.098925-4005/© 2016 Elsevier B.V. All rights reserved.

© 2016 Elsevier B.V. All rights reserved.

as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA)and trimethylarsine oxide (TMAO) are less and rarely important[4,7,10]. But about ninety percent of the total arsenic was found tobe as arsenate [11]. Also As(v) is stable under oxidizing-conditions[12]. As(v) appears as H3AsO4 at pH values below 2, whereas, in thepH range from 2 to 11 it dissociates to H2AsO4

−, HAsO42− [4,13]. The

WHO recommended guideline value of arsenic in drinking water is10 ppb [7]. However, for some countries most affected by arseniccontamination, for example, Bangladesh, India, China, Nepal, thearsenic standard has remained as 50 ppb [7,14]. The contamina-tion of drinking water supplied with naturally-occurring arsenic isa major health problem. Even low concentrations of arsenic, wheningested over a period of years, can result in a range of serioushealth issues −

(1) Skin itching to sun rays, burning and watering of eyes, weightloss, loss of appetite, weakness, melanosis, keratosis, leucome-lanosis, lethargy limited the physical activities and workingcapacities [15],

(2) Chronic respiratory, gastrointestinal symptoms of anorexia,nausea, dyspepsia, altered taste, pain in abdomen, enlargedliver and spleen and ascites [15],

(3) Large nodules are often precursors of cancer [15],(4) Bowen’s disease is a premalignant condition called intra-

epidermal carcinoma in situ, which may be noted as acomplication in chronic arsenicosis [15],

(5) Skin ulcer is a late feature of cutaneous asenicosis that may turninto malignancy [15],

J. Saha et al. / Sensors and ActuatoTa

ble

1C

omp

aris

on

of

dif

fere

nt

met

hod

s

for

the

det

erm

inat

ion

of

arse

nic

.

An

alyt

ical

Tech

niq

ue

Com

men

ts

An

alyt

ical

tool

sLO

D

(�g/

L)R

efer

ence

1.

Spec

tros

cop

yV

ery

hig

h

sen

siti

vity

Nee

ds

exp

ensi

ve

inst

rum

ents

,Ex

per

t

oper

ator

requ

ired

, in

situ

(fiel

d)

mea

sure

men

t

is

not

pos

sibl

e

in

gen

eral

In

som

e

case

s

com

ple

x

sam

ple

pre

par

atio

n

requ

ired

.

UV

–vis

-MB

74

[23]

UV

–vis

Hol

low

fibe

rex

trxn

MB

27

[24]

HPL

C-U

V

52

[25]

CE-

SDM

E-U

V

15

[26]

LC-H

G-O

3-G

PCL

0.16

[27]

ATR

-FTI

R

120

[28]

HG

-IC

P-M

S

0.00

208

[29]

FI-H

G-I

CP-

MS

0.03

21

[29]

HG

-AA

S

3.37

[30]

VM

oAs-

het

erop

olya

cid

-lu

min

olFI

-LPC

L

0.15

[31]

Surf

ace

Plas

mon

reso

nan

ce20

[32]

2.

Col

orim

etri

c

Met

hod

Mod

erat

e

sen

siti

vity

Gen

erat

es

arsi

ne

gas

S-la

yer-

fun

ctio

nal

ized

Au

NPs

.24

0

[33]

3.

Elec

troc

hem

ical

Met

hod

sH

igh

sen

siti

vity

mai

nly

use

d

for

As

(III

)

det

ecti

on. D

irec

tel

ectr

och

emic

al

det

erm

inat

ion

of

As(

v)

at

neu

tral

pH

is

alm

ost

imp

ossi

ble

as

As(

v)

is

not

elec

troa

ctiv

e

at

this

pH

.

Elec

troc

hem

ical

Ars

ine

Gen

erat

ors

1.9

[34]

An

odic

stri

pp

ing

volt

amm

etry

0.08

[35]

rs B 241 (2017) 1014–1023 1015

(6) Arsenic is a group A and category 1 human carcinogen and maycause lung cancer, skin cancer, bladder cancer, renal cancer [2].

Therefore, detection of arsenic in drinking water is of utmostimportance and has come to limelight during the last decade. Todate different kinds of chemical and physical techniques have beenused for the detection of arsenic in water [16–36]. A comparisonof some of the commonly used methods is listed in Table 1. Moreinformation about different arsenic detection techniques can befound in the review paper written by Ma et al. [37]. However, mostof these methods suffer from the large number of limitations suchas interference by a large number of ions, low/moderate sensitivity,and need heating or extraction from organic solvents, requirementof sample preservations and chemical reduction steps, which mayintroduce sample contamination [16–37]. Thus, there is a needto develop a new simple, reliable, highly sensitive method whichwould overcome the existing inadequacies in the determination oftraces amounts of arsenic.

On the other hand, Fluorescence Resonance Energy Transfer(FRET) may be a suitable method to improve the sensitivity andselectivity during sensing. FRET is the fundamental phenomenonbetween two dye molecules in which excited state energy is trans-ferred from a donor molecule to an acceptor molecule withoutemission of a photon. The transfer of energy leads to a reduction inthe donor fluorescence intensity and excited state lifetime, accom-panied with an increase in the acceptor’s emission intensity [38,39].The rate of energy transfer depends on a number of factors, includ-ing the fluorescence quantum yield of the donor in the absenceof the acceptor, the refractive index of the solution, the relativeorientation of the electric dipoles of each molecule, and the spec-tral overlap integral of the donor and acceptor [40]. If these factorschange due to the presence of any external agency then the energytransfer efficiency also changes. Therefore, it is possible to sense thepresence of external agent by observing the change in energy trans-fer efficiency [40,41]. FRET is advantageous as it measures the ratiobetween two fluorescence intensities which is independent of theexternal factors such as fluctuation of excitation source and sensorconcentration, etc. FRET observed the changes in the intensity ratioof two emission bands which is favorable in increasing the signalselectivity [42]. However, till today to the best of our knowledge,there are only few reports about the detection of As(III) using theFRET technique [21,43]. In these works FRET between CdTe quan-tum dot and Rhodamine 6G was used to sense As(III). Increase influorescence intensity of Rhodamine 6G with the As(III) concentra-tion was observed. As(III) could combine with GSH to remove theGSH from QDs and recover the efficiency of FRET [43]. But hardlyany report for the FRET based sensing of As(v) was observed.

In the present paper FRET between two dyes Acriflavine (Acf)and Rhodamine B (RhB) in the presence and absence of As(v) havebeen reported. Here Acf and RhB act as energy donor and acceptorrespectively. Both the dyes fulfill the prerequisite criteria for FRETto occur. We have already demonstrated hard water sensor [41],Ion sensor [44], pH sensor [40], DNA sensor [45,46] based on theFRET method. In this paper, in presence of As(v) the FRET efficiencyincreases almost linearly. Based on these investigation a simpleand highly sensitive method for the detection of As(v) have beendemonstrated. The proposed method has also been tested usingnatural lake water and satisfactory results were obtained.

2. Materials and methods

2.1. Materials

Both the dyes Acf, RhB as well as arsenic trioxide (As2O3) werepurchased from Sigma Chemical Co. USA and used as received.

1016 J. Saha et al. / Sensors and Actuators B 241 (2017) 1014–1023

F cencew tions

UvsT

2

p

A

inhWrfpu(

a

2

watw

3

3

s

ig. 1. (a) Fluorescence spectra of pure Acf (1), Acf + RhB (2), pure RhB (3), (b) Fluoresere done under ambient condition. Concentration of As(v) is 0.05 mg/L. Concentra

ltrapure Milli-Q water (resistivity 18.2 M�-cm) was used as sol-ent. The dyes used in our studies are cationic in nature. All thealts KCl, NaCl, MgCl2, CaCl2, and Al2(SO4)3 were purchased fromhermo Fisher Scientific India Pvt. Ltd. and used as received.

.2. Preparation of arsenic acid

Arsenic acid (H3AsO4) is prepared from arsenic trioxide (As2O3)owder as follows [47].

s2O3 + 4HNO3 + 2H2O → 2H3AsO4 + 2N2O3

Under aqueous environment arsenic acid remain as arsenateons H2AsO4

− and HAsO42−. However, monoanionic form of arse-

ate (H2AsO4−) predominates at low pH (pH < 6.9). On the other

and, arsenate dianion (HAsO42−) predominates at high pH [48].

ithin the pH range of natural water both H2AsO4− and HAsO4

2−

emain present simultaneously [49]. Arsenate ion solution at dif-erent concentrations was prepared from arsenic acid at differentH. The pH of the solutions was maintained to the designated valuesing standard buffer 1 M HCl (for low pH) and 2N NaOH solutionfor high pH).

Here, the experiments were performed at two different pH 4nd 8 as well as under ambient condition.

.3. UV–vis absorption and fluorescence spectra measurement

UV–vis absorption and fluorescence spectra of the solutionsere recorded by a Perkin Elmer Lambda-25 Spectrophotometer

nd Perkin Elmer LS-55 Fluorescence Spectrophotometer respec-ively. For fluorescence measurement the excitation wavelengthas 420 nm (close to the absorption maximum of Acf).

. Results and discussions

.1. Acf and RhB as FRET pair

The Laser dyes Acf and RhB are highly fluorescent. There existsufficient overlap between the absorption spectra of RhB and emis-

spectra of Acf + As(v) (1), Acf + RhB + As(v) (2), RhB + As(v) (3). All the measurementsof both the dyes are 10−5 M. Excitation wavelength is 420 nm.

sion spectra of Acf, which are the prerequisite condition for FRETto occur from Acf to RhB. FRET phenomenon using dyes Acf andRhB has already been studied [41,44,50]. It has been observed thatenergy transfer occurred successfully from Acf to RhB. Based on theFRET between these two dyes we have already demonstrated sev-eral sensors [41,44,50]. So, Acf and RhB are the promising materialsto use as a FRET pair for the present study.

The absorption and fluorescence maxima of Acf are located at449 and 502 nm respectively, which is assigned due to the Acfmonomers [41]. On the other hand RhB absorption spectrum pos-sesses prominent intense 0-0 band at 553 nm along with a weakhump at 520 nm which is assigned due to the 0–1 vibronic tran-sition [44]. The overlap of the emission spectra of Acf with theabsorption spectra of RhB indicates that these two fluorophore con-stitute a donor-acceptor pair of an energy transfer system. The RhBfluorescence spectrum shows a prominent band at 571 nm whichis assigned due to the RhB monomeric emission [44]. The corre-sponding absorption and emission spectra of the above results areshown in Fig. S1.

3.2. Effect of As(v) on FRET between Acf and RhB

In order to check the effect of As(v) on FRET between Acf andRhB, the concentration of Acf and RhB were optimized at 10−5 M inaqueous solution. Fig. 1(a) shows the fluorescence spectra of pureAcf, RhB and their mixture (1:1 volume ratio). In all the cases wehave measured the fluorescence with excitation wavelength fixedat 420 nm (close to the absorption maximum of Acf). It has beenobserved that with this excitation wavelength Acf shows promi-nent fluorescence, whereas RhB shows very less fluorescence. Thisindicates that, with this excitation wavelength, RhB absorbs a veryminute amount of energy. On the other hand, in case of Acf-RhBmixture, RhB fluorescence increases and Acf fluorescence decreases

compared to their pure counterpart even with this excitation wave-length. This is mainly due to the transfer of energy from Acf to RhB.There are several reports describing energy transfer between Acfand RhB [41,44,50].

J. Saha et al. / Sensors and Actuato

Table 2The values of FRET parameters in absence and presence of As(v) at ambient con-dition. Concentration of As(v) is 0.05 mg/L. FRET parameters were calculated fromspectra of Fig. 1. Concentrations of both the dyes are 10−5 M.

Concentration(mg/L)

E (%) J(�)m−1 cm−1 nm4

R0 (nm) r (nm)

wittmfwe

E

woa

mtaiaAtH

oas2tf

fliteo

cpcI(ce

dafdss

Hde(

0.00 23.50 3.12 × 1015 6.11 7.430.05 55.40 3.85 × 1015 6.33 6.10

The excitation spectra recorded with monitoring emissionavelength fixed at Acf (500 nm) and RhB (571 nm) emission max-

mum revealed that both the excitation spectra are very similar tohe absorption spectrum of Acf monomer (Fig. S2). This confirmshat in the present case the enhancement in RhB fluorescence is

ainly due to the light absorption by Acf and corresponding trans-er of a portion of the same to RhB monomer. The FRET efficiency

as found to be 23.5%, which was calculated using the followingquation [40]

= 1 − FDAFD

here FDA is the fluorescence intensity of the donor in the presencef acceptor and FD is the fluorescence intensity of the donor in thebsence of the acceptor.

Fig. 1(b) shows the fluorescence spectra of Acf, RhB and theirixture in presence of arsenic acid. Almost similar spectral fea-

ures to that of Fig. 1(a) were observed. In ambient pH range arseniccid dissociates to arsenate ion (H2AsO4

−, HAsO42−). A remarkable

ncrease in Acf fluorescence was observed in presence of arsen-te ions for pure Acf solution (curve-1). The observed increase incf fluorescence may be due to i) electrostatic attraction between

he anionic arsenate and cationic Acf [51,52] and ii) formation of-bond between the arsenate ion and the Acf molecule [53].

It is interesting to mention in this context is that increase in flu-rescence quantum yield of APSAL were occurred upon binding ofrsenate ion. This increase in fluorescence was explained due to thetrong H bonding between APSAL and arsenate ion [53]. More than0 fold enhancements in fluorescence intensity of coumarin deriva-ives were observed when coumarin interacted with As3+ salts andorm complex [54].

The most interesting thing here was that the increase in RhBuorescence in case of Acf-RhB mixture is more comparable to that

n absence of arsenate ion indicating an increase in FRET. In this casehe FRET efficiency was found to be 55.4% i.e., more than two foldnhancement in energy transfer efficiency occurred in the presencef arsenate ion.

FRET parameters during energy transfer from Acf to RhB werealculated by using Förster theory [38,39]. Details of the calculationrocedure were reported elsewhere [38–40]. The FRET parametersalculated using the spectra of Fig. 1(a) and (b) are listed in Table 2.t has been seen that significant increase in spectral overlap integralJ(�)) occurred in presence of arsenate ion. Also the dye moleculesome closer in the presence of arsenate ion. As a result, the FRETfficiency also increases from 23.5% to 55.4%.

It is relevant to mention in this context that FRET is a distanceependent phenomenon and 2–10 nm distance (between donornd acceptor) is typical for FRET to occur [41]. The energy trans-er efficiency (E) is inversely proportional to the sixth power of theistance between the donor and acceptor [40]. Also the rate con-tant and hence the FRET efficiency (E) increases with increase inpectral overlap integral [40].

In the aqueous solution of arsenic acid, both H2AsO4− and

AsO42− ions remain present simultaneously [36]. When cationic

ye Acf and RhB were added with arsenate ions in aqueous solutionlectrostatic interaction as well as H-bonding between the dyeseither Acf, RhB, or both) and the arsenate ions occurred [52–54].

rs B 241 (2017) 1014–1023 1017

As a result Acf and RhB molecules come closer in the presence ofarsenate ions. Also the orientation of the dye molecules (donor andacceptor) is affected when they are attached with the arsenate ion.This results in a change in the spectral overlap integral in the pres-ence of arsenate ions. The calculated values of FRET parameters(Table 2) revealed that spectral overlap integral (J(�)) increasesfrom 3.12 × 1015 m−1 cm−1 nm4 to 3.85 × 1015 m−1 cm−1 nm4 inpresence of arsenic acid. Also the average distance between accep-tor and donor (RhB and Acf) decreases from 7.43 nm to 6.10 nm inthe presence of arsenate ions. As a whole presence of arsenate ionprovide a favorable condition for FRET between Acf and RhB com-pared to that in aqueous solution. Scheme 1 shows the interactionbetween the arsenate ion (H2AsO4

− and HAsO42−) and the cationic

dyes in aqueous solution.

3.3. Effect of pH

pH is a very crucial factor for determining arsenate ion spe-ciation [49]. At low pH (<6.9) arsenate mono-anion (H2AsO4

−)becomes dominant. On the other hand, at higher pH dianion(HAsO4

2−) remain present in aqueous environment [49]. Accord-ingly, we have studied the effect of As(v) at different pH on energytransfer between Acf and RhB. Arsenic acid solution at different pHviz 4 and 8 were prepared.

Fig. 2(a) and (b) shows the fluorescence spectra of Acf, RhB andtheir mixture in presence of As(v) at two different pH 4 and 8respectively. Corresponding FRET parameters calculated using thespectra at these two pH are listed in Table 3. It has been observedthat energy transfer efficiency decreases at lower pH, whereas, theenergy transfer efficiency increases at higher pH compared to thesame at ambient pH.

In the previous section of this manuscript, it has been seen thatarsenate ion plays an important role in energy transfer by ini-tiating close proximity between two cationic dyes Acf and RhB.Arsenate ion brings Acf and RhB molecules closer in aqueous solu-tion through electrostatic attraction and H-bonding [51–55]. As aresult the FRET efficiency increases. However, at low pH arsenateion mainly remains as H2AsO4

− mono-anion in aqueous solu-tion. Under this condition when the dyes Acf and RhB are added,H2AsO4

− mono-anion form complex with the dyes through elec-trostatic interaction with one dye and H-bond with others. On theother hand, at higher pH, HAsO4

2− di-anion remains present inaqueous solution. The arsenate di-anion (HAsO4

2−) may bind withthe two dyes electrostatically as well as through H-bonding. There-fore, the extent of interaction at higher pH is greater. As a result,the close proximity between Acf and RhB as well as orientation andhence the spectral overlap integral is effected by resulting a changein FRET efficiency. Accordingly the distance (r) between Acf andRhB molecules decreases to 6.00 nm and also the spectral overlapintegral increases to 4.41 × 1015 m−1 cm−1 nm4 at higher pH 8.

In order to check the effect of arsenate concentration on theFRET efficiency, we have studied the FRET between Acf and RhB inpresence of varying arsenate concentration viz 40, 65 and 90 ppbat ambient condition as well as pH 4 and 8. Corresponding fluores-cence spectra were shown in Figs. S3 and S4 . The FRET parametersare listed in Table 4. From the plot of FRET efficiency as a functionof arsenate ion concentration (Fig. 3) it has been observed that theFRET efficiency increases with increase in the arsenate ion concen-tration. However, in case of lower pH the increase is very nominalwhereas at high pH as well as ambient condition significant linear

increase in FRET efficiency has occurred. This is because at pH = 8as well as under ambient condition arsenate ion remains as a mix-ture of both arsenate mono-anion (H2AsO4

−) and arsenate di-anion(HAsO4

2−). As a result, extent of induced close proximity between

1018 J. Saha et al. / Sensors and Actuators B 241 (2017) 1014–1023

Scheme 1. Probable structures of complex formation between Acf and RhB in presence of arsenate ion (a) H2AsO4− and (b) HAsO4

2− in aqueous solution.

Table 3The values of FRET parameters in presence of low (pH = 4) and high pH (pH = 8) of As(v). Concentration of As(v) is 0.05 mg/L. FRET parameters were calculated from spectraof Fig. 2. Concentrations of both the dyes are 10−5 M.

Conc. (mg/L) Low pH High pH

E (%) J(�) m−1 cm−1 nm4 R0 (nm) r (nm) E (%) J(�) m−1 cm−1 nm4 R0 (nm) r (nm)

0.050 46.10 3.71 × 1015 6.295 6.45 61.00 4.41 × 1015 6.470 6.00

J. Saha et al. / Sensors and Actuators B 241 (2017) 1014–1023 1019

F 4) (2)A .05 m

ti

3

ic[Idaosu

Fod

ig. 2. (a) Fluorescence spectra of Acf + As(v) (pH = 4) (1), Acf + RhB + As(v) (pH =

cf + RhB + As(v) (pH = 8) (2), and RhB + As(v) (pH = 8) (3). Concentration of As(v) is 0

he cationic dye pair (Acf and RhB) and arsenate ion increases withncreasing pH.

.4. Design of arsenic sensor

It is well known that arsenic contamination in drinking waters a serious health issue. Regular intake of arsenic even at very lowoncentration may cause several severe health problems to human15]. Arsenic can exist in nature in a variety of oxidation states [4–7].n aqueous environment arsenic mainly remains as arsenite (pre-ominantly as H3AsO3) and arsenate (predominantly as H2AsO4

−

nd HAsO42−) [49]. However, abundance of arsenic in natural aque-

us solution is mainly in the form of arsenate (>90%), since As(v) istable under oxidizing condition [12]. On the other hand, As(III) isnstable and converted into As(v) through oxidation [56]. Accord-

ig. 3. Variation of FRET efficiency between Acf and RhB at different concentrationf As(v) at pH = 4 & 8 as well as under ambient condition. Concentrations of both theyes are 10−5 M.

, RhB + As(v) (pH = 4) (3), and (b) Fluorescence spectra of Acf + As(v) (pH = 8) (1),g/L. Concentrations of both the dyes are 10−5 M. Excitation wavelength is 420 nm.

ingly abundance of As(III) in a natural environment is very less(<10%) [11]. It is very important to avoid arsenic contaminatedwater either for drinking or day to day use. Therefore, it is of utmostimportance to identify the arsenic contamination in drinking water,followed by a proper initiative to remove contamination.

In the present manuscript, it has been observed that the FRETefficiency between the dyes Acf and RhB is highly dependenton arsenate ion concentration in aqueous solution. Almost linearincrease in FRET efficiency was observed with increase in arsenateion concentration in aqueous solution in the range from 0.04 mg/Lto 0.09 mg/L which is equivalent to 40 to 90 ppb having linearcorrelation R2 = 0.9926. Therefore, we suggest that with proper cali-bration by observing the FRET between these two dyes it is possibleto have an idea about the arsenate concentration in aqueous solu-tion. It is relevant to mention in this context that FRET process havebeen successfully utilized to demonstrate several sensors viz hardwater sensor [41], ion sensor [44], mercury sensor, [57], Cr(III) sen-sor [58]. FRET based sensors are advantageous over conventionalfluorescence sensor as it measures the ratio of two fluorescenceintensities and are thus automatically free from environmentalperturbation [41,44,46]. We have already demonstrated the use ofFRET process in designing several sensors [41,44].

In order to have the idea about the sensitivity of the proposedsensor we have determined the limit of detection (LOD) fromthe concentration vs. FRET efficiency curve by using the formulaLOD = 3�/S, where, ‘�’ is the standard deviation of y intercept ofthe regression line, ‘s’ is the slope of the calibration curve [59]. TheLOD was found to be 10 ppb. It is important to mention that theWHO recommended guideline value of arsenic in drinking wateris 10 ppb under ambient condition. However, for some countriesmost affected by arsenic contamination, for example, Bangladesh,India, China, Nepal, the arsenic standard has remained as 50 ppb[7,14].

In the present case in designing the FRET based As(v) sensor,

As(v) concentration was varied within the range 40 to 90 ppb and adetection limit was obtained of the order of 10 ppb. Therefore theresults indicate that this sensor can be potentially used to detect

1020 J. Saha et al. / Sensors and Actuators B 241 (2017) 1014–1023

Tab

le

4FR

ET

par

amet

ers

at

dif

fere

nt

con

cen

trat

ion

of

As(

v)

(for

pH

=

4,

8

and

un

der

ambi

ent

con

dit

ion

).

The

valu

es

of

FRET

par

amet

ers

wer

e

calc

ula

ted

from

spec

tra

of

Fig.

S3

&

S4. C

once

ntr

atio

ns

of

both

the

dye

s

are

10−5

M.

Con

c.

of

As(

v)

(mg/

L)(L

ow

pH

)(a

mbi

ent

pH

)(H

igh

pH

)

E

(%)

J(�

)

m−1

cm−1

nm

4R

0(n

m)

r

(nm

)

E

(%)

J(�

)

m−1

cm−1

nm

4R

0(n

m)

r

(nm

)

E

(%)

J(�

)

(m−1

cm−1

nm

4)

R0

(nm

)

r

(nm

)

0.04

0

45.0

0

3.69

0

×

1015

6.28

9

6.49

0

53.5

5

3.83

1

×

1015

6.32

8

6.17

9

56.0

0

3.86

0

× 10

156.

330

6.08

00.

065

47.4

0

3.72

0

×

1015

6.29

8

6.40

0

61.4

3

4.41

2

×

1015

6.47

9

5.99

5

67.2

7

4.46

0 ×

1015

6.49

0

5.75

00.

090

49.9

0

3.74

0

×

1015

6.30

3

6.30

0

69.4

7

4.48

0

×

1015

6.49

6

5.66

4

76.4

9

4.58

0 ×

1015

6.52

0

5.35

0

Table 5Variation of FRET efficiency in presence and absence of salt and As(v) (ambient con-dition) (Fig. S5). Concentrations of both As(v) and salts are 0.05 mg/L. Concentrationsof both the dyes are 10−5 M.

Sample Efficiency (%) (ambient pH)

Acf + RhB + Na+ 23.47Acf + RhB + Na+ + As 55.30Acf + RhB + Ca+2 22.39Acf + RhB + Ca+2 + As 55.10Acf + RhB + Al+3 22.55Acf + RhB + Al+3 + As 55.70Acf + RhB + Mg+2 22.18Acf + RhB + Mg+2 + As 55.90Acf + RhB + K+ 22.07Acf + RhB + K+ + As 55.40Acf + RhB + water 23.50Acf + RhB + As (0.05 mg/L) 55.40

Acf + RhB + (All salts) 22.30Acf + RhB + As + (All salts) 56.30

As(v) in aqueous solution with high sensitivity with a detectionlimit of 10 ppb.

It is relevant to mention that although there are few reports ofFRET based As(III) sensor, however, hardly any report is found forFRET based As(v) sensor. From the literature survey, it is observedthat using some other techniques in few cases lower detection lim-its is achieved (Table 1). However, this limit is probably the firstattempt for designing FRET based As(v) sensor. Therefore, this strat-egy may provide a facile approach to form a FRET based ratiometricfluorescent sensor for As(v) in totally aqueous media. FRET-baseddetection method for As(v) have many remarkable advantages ashigh sensitivity and precision. Since FRET process measures theratio of two fluorescence intensities, external perturbation, noiseetc. can be eliminated automatically.

3.5. Selectivity of the sensor

In practice a good sensor should respond to a particular analyte(materials to be sensed) at a time, else the sensing process willhave erred. In the present case the change in FRET efficiency is theindication about the arsenic level in the water. Therefore, it is highlydesirable that the FRET efficiency should change due to changes inconcentration of arsenate ion in aqueous solution only.

This is because natural water contains various kinds of salts(e.g. KCl, NaCl, MgCl2, CaCl2, Al2(SO4)3 etc.). Accordingly, we havechecked the FRET between Acf and RhB in the presence of KCl, NaCl,MgCl2, CaCl2, Al2(SO4)3 etc. Interestingly, it has been observed that,in presence of these salts do not affect the FRET efficiency com-pared to that in the presence of arsenate ion in aqueous solution.Fig. 4 shows the plot of FRET efficiency between Acf and RhB in thepresence of different salts in aqueous solution. Corresponding fluo-rescence spectra’s were shown in Fig. S5. Values of FRET efficiencyare listed in Table 5. It is interesting that in the presence of As(v)(0.05 mg/L) more than two fold enhancement of FRET efficiency isobserved compared to other salts.

It is relevant to mention in this context that the FRET process ishighly sensitive to distance between the dyes as well as their ori-entation [41,44]. This attribute of FRET process allow FRET methodin using for sensing purpose [57,58,60]. In the present case the dyesAcf and RhB used as a FRET pair are cationic. Normally they repeleach other in solution [41,44]. Accordingly, FRET efficiency is verysmall [41,44]. Whereas when arsenic acid is added, the dyes Acfand RhB come closer due to electrostatic interaction or H-bonding

− 2−

formation with the arsenate anions (H2AsO4 and HAsO4 ). As aresult the FRET efficiency increases. On the other hand, in presenceof different salt viz of KCl, NaCl, MgCl2, CaCl2, Al2(SO4)3 etc. differ-ent cations are generated in aqueous solution [44]. The introduction

J. Saha et al. / Sensors and Actuators B 241 (2017) 1014–1023 1021

F s) and in presence of different salts + As(v) (yellow stacks). All measurements were doneu oncentration of both the dyes are 10–5 M. Concentration of both As(v) and different saltsa e reader is referred to the web version of this article.)

oitecieicibra

3

craw

i

wswsr

Table 6Determination of As(v) in natural lake water where As contamination were notreported. Corresponding fluorescence spectra were shown in Fig. S6, S7, S8, S9 andS10.

Sample Added (mg/L) Found (mg/L) Recovery (%) RSD (%, n = 3)

1# 0.072 0.071 98.6 0.50.124 0.121 97.5 1.20.165 0.160 96.9 1.6

2# 0.072 0.069 95.8 2.20.124 0.121 97.5 1.20.165 0.162 98.2 1.9

3# 0.072 0.070 97.2 0.70.124 0.119 95.9 2.60.165 0.161 97.5 1.3

4# 0.072 0.071 98.6 2.10.124 0.120 96.7 0.90.165 0.058 95.7 2.5

5# 0.072 0.071 98.6 1.90.124 0.118 95.1 1.3

ig. 4. FRET efficiency between Acf and RhB in presence of different salts (blue stacknder ambient condition. (Values of FRET efficiency were calculated from Fig. S5). Cre 0.05 mg/L. (For interpretation of the references to colour in this figure legend, th

f different cations (due to addition of salts) may cause an increasen the repulsion. As a result, energy transfer should decrease inhe presence of the salts according to the principle of FRET. How-ver, in the present case, the decrease is very minute as the saltoncentration is very low [41,44]. We have already demonstratedon sensor as well as hard water sensor based on the decrease innergy transfer in the presence of cations [41]. But the main points that proposed arsenic sensor is based on the increase in FRET effi-iency in presence of arsenate and there is no chance to increasen FRET efficiency in the presence of these cations. Therefore, it cane said that the selectivity of the proposed sensor is very high withespect to these salts or as a whole with respect to any other cationicnalytes.

.6. Detection of As(v) in real samples

In practical cases, lake water may contain several impuritiesompared to the deionized water or the water used in the labo-atory. Therefore, it is important to check the feasibility as well asccuracy and selectivity of the proposed sensing method with lakeater.

Accordingly, we collected two types of natural lake water-

i) Natural lake water where arsenate contamination was not diag-nosed/reported.

i) Natural lake water from arsenate prone area.

In the first category three different amounts of arsenate ionsere added with five different water samples. Then detection of the

ame was done by following our proposed technique. The resultsere listed in Table 6. Corresponding fluorescence spectra were

hown in Figs. S6–S10. The recoveries were found to be within theange 95.1%–98.6%. The results shown here are an average of three

0.165 0.059 96.3 0.8

sets of experiments for each concentration. The Relative StandardDeviations (RSD) was within the range of 0.5% to 2.6%.

Under second category the water samples were collected fromfour lakes of Tripura located in West Tripura (Jirania Block), Dhalai(Salema Block), North Tripura, (Dharmanagar Block) districts. Theseareas of Tripura, the water are highly contaminated with arsenic[61]. At first the water samples are filtered to remove extra impu-rities and then the FRET experiment was performed by using thesewater samples. From the experimental analysis, energy transfer

efficiency values were calculated and the corresponding concen-tration of As(v) has been found in the range of 52 to 69 ppb (Fig.S11). The results were listed in Table 7. These ranges of results are

1022 J. Saha et al. / Sensors and Actuato

Table 7Determination of As(v) using natural lake water from As prone area. CorrespondingFRET efficiencies and concentration of As(v) were shown in Fig. S11.

Sample Efficiency (%) Concentration found (mg/L)

1# 57.41 0.052

iA

4

bdtawetrtpaaoRb

A

tN–e

A

t

R

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

2# 59.11 0.0583# 60.96 0.0644# 62.61 0.069

n good agreement with the previously reported concentrations ofs(v) in Tripura [61].

. Conclusion

In summary, we have developed a sensitive and selective FRET-ased ratiometric sensing system between Acf and RhB for theetermination of As(v). More than two fold enhancement of energyransfer occurred (23.5%–55.4%) in presence of arsenate ions undermbient condition. Extent of increase in energy transfer efficiencyas large at high pH. At low pH, high pH as well as under ambi-

nt condition the energy transfer efficiency increases linearly withhe arsenate ion concentration in aqueous solution. Based on theesults of our investigation, we suggest that with proper calibrationhe system can be used to design As(v) sensor. Selectivity of the pro-osed sensor with respect to various salts (cations) was also testednd satisfactory results were obtained. The presented method haslso been tested using natural lake water and suitable results werebtained with good recovery, ranging between 95.1%–98.6% to theSD value within range 0.5% −2.6%. The present system has alsoeen tested with real As contaminated water.

cknowledgements

The author SAH is grateful to ‘DST’ – ‘India’ for financial supporto carry out this research work through ‘DST’ – ‘India’ project Ref.o. EMR/2014/000234. Also financial support through FIST ‘DST’

‘India’ project Ref. No. SR/FST/PSI-191/2014 has been acknowl-dged.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.snb.2016.10.098.

eferences

[1] S.J.S. Flora, Handbook of Arsenic Toxicology, Academic Press: Elsevier, 2015.[2] R. Eisler, Arsenic hazards to fish, wildlife, and invertebrates (1988).[3] P.L. Smedley, D.G. Kinniburgh, Source and behaviour of arsenic in natural

waters, British Geological Survey, U.K., Chapter 1.[4] M. Bissen, F.H. Frimmel, Arsenic—a review. Part I: occurrence toxicity,

speciation, mobility, Acta Hydrochim. Hydrobiol. 31 (2003) 9–18.[5] G. Iervolino, V. Vaiano, L. Rizzo, G. Sarno, A. Farina, D. Sannino, Removal of

arsenic fromdrinking water by photo-catalytic oxidation on MoOx/TiO2 andadsorption on �-Al2O3, J. Chem. Technol. Biotechnol. 91 (2016) 88–95.

[6] R.K. Zalups, D.J. Koropatnick, Molecular Biology and Toxicology of Metals, CRCPress, Taylor and Francis Group, 2000.

[7] T.M. Clancy, K.F. Hayes, L. Raskin, Arsenic waste management: a criticalreview of testing and disposal of arsenic-bearing solid wastes generatedduring arsenic removal from drinking water, Environ. Sci. Technol. 47 (2013)10799–10812.

[8] D. Panagiotaras, D. Nikolopoulos, Arsenic occurrence and fate in theenvironment; a geochemical perspective, J. Earth Sci. Clim. Change 6 (2015)1–9.

[9] X.-Y. Yu, T. Luo, Y. Jia, Y.-X. Zhang, J.-H. Liu, X.-J. Huan, Porous hierarchicallymicro-/nanostructured MgO: morphology control and their excellent

performance in As(III) and As(V) removal, J. Phys. Chem. C 115 (2011)22242–22250.

10] T. Yang, J.-W. Liu, C. Gu, M.-L. Chen, J.-H. Wang, Expression of arsenicregulatory protein in Escherichia coli for selective accumulation ofmethylated arsenic species, ACS Appl. Mater. Interfaces 5 (2013) 2767–2772.

[

rs B 241 (2017) 1014–1023

11] I. Rosas, R. Belmont, A. Armienta, A. Baez, Arsenic concentrations in water soil,milk and forage in Comarca Lagunera, Mexcio, Water Air Soil Poll. 112 (1999)133–149.

12] S.K. Gupta, K.Y. Chen, Arsenic removal by adsorption source, J. Water Pollut.Control Fed. 50 (1978) 493–506.

13] M. Kumaresan, P. Rivazuddin, Overview of speciation chemistry of Arsenic,Curr. Sci. 80 (2001) 837–846.

14] U.K. Chowdhury, B.K. Biswas, T.R. Chowdhury, G. Samanta, B.K. Mandal, G.C.Basu, C.R. Chanda, D. Lodh, K.C. Saha, S.K. Mukherjee, S. Roy, S. Kabir, Q.Quamruzzaman, D. Chakraborti, Groundwater arsenic contamination inBangladesh and West Bengal, India, Environ. Health Persp. 108 (2000)393–397.

15] S.C. Mukherjee, Murshidabad—one of the nine groundwater arsenic-affecteddistricts of West Bengal, India. Part II: dermatological, neurological, andobstetric findings, Clin. Toxicol. 43 (2005) 835–848.

16] C. Pasha, B. Narayana, Determination of arsenic in environmental andbiological samples using toluidine blue or safranine O by simplespectrophotometric method, Bull. Environ. Contam. Toxicol. 81 (2008) 47–51.

17] H. Kaur, R. Kumar, J.N. Babu, S. Mittal, Advances in arsenic biosensordevelopment—a comprehensive review, Biosens. Bioelectron. 63 (2015)533–554.

18] C.P. King, Determination of arsenic in natural waters using surface plasmonresonance: a low-cost analytical tool for arsenic screening, JUS SJWP 1 (2008)46–55.

19] K. Bluemlein, E.M. Krupp, J. Feldmann, Advantages and limitations of adesolvation system coupled online to HPLC-ICPqMS/ES-MS for thequantitative determination of sulfur and arsenic in arseno-peptidecomplexes, J. Anal. At. Spectrom. 24 (2009) 108–113.

20] Y. Song, G.M. Swain, Total inorganic arsenic detection in real water samplesusing anodic stripping voltammetry and a gold-coated diamond thin-filmelectrode, Anal. Chim. Acta 593 (2007) 7–12.

21] G. Tang, J. Wang, Y. Lia, X. Su, Determination of arsenic(III) based on thefluorescence resonance energy transfer between CdTe QDs and Rhodamine6G, RSC Adv. 5 (2015) 17519–17525.

22] W.-Z. Tian, W.D. Ehmann, Radiochemical neutron activation analysis forarsenic cadmium, copper and molybdenum in biological matrices, J.Radioanal. Nucl. Chem. 89 (1985) 109–122.

23] G. Hanrahan, T.K. Fan, M. Kantor, K. Clark, S. Cardenas, D.W. Guillaume, C.S.Khachikian, Design and development of an automated flow injectioninstrument for the determination of arsenic species in natural waters, Rev.Sci. Instrum. 80 (2009) 104101–104105.

24] K. Hylton, S. Mitra, A microfluidic hollow fiber membrane extractor forarsenic(V) detection, Anal. Chim. Acta 607 (2008) 45–49.

25] L. Jedynak, P. Kieronski, J. Kowalska, J. Golimowski, Speciation analysis ofarsenic by HPLC-UV in highly contaminated water samples, Chem. Anal.Warsaw 53 (2008) 557–568.

26] K. Cheng, K. Choi, J. Kim, I.H. Sung, D.S. Chung, Sensitive arsenic analysis bycarrier-mediated counter-transport single drop microextraction coupled withcapillary electrophoresis, J. Microchem. J. 106 (2013) 220–225.

27] A.D. Idowu, P.K. Dasgupta, Liquid chromatographic arsenic speciation withgas-phase chemiluminescence detection, Anal. Chem. 79 (2007) 9197–9204.

28] B. McAuley, S.E. Cabaniss, Quantitative detection of aqueous arsenic and otheroxoanions using attenuated total reflectance infrared spectroscopy utilizingiron oxide coated internal reflection elements to enhance the limits ofdetection, Anal. Chim. Acta 581 (2007) 309–317.

29] M.K. Sengupta, P.K. Dasgupta, An automated hydride generation interface toICPMS for measuring total arsenic in environmental samples, Anal. Chem. 81(2009) 9737–9743.

30] A.M. Abdel-Lateef, R.A. Mohamed, H.H. Mahmoud, Determination of arsenic(III) and (V) species in some environmental samples by atomic absorptionspectrometry, Adv. Chem. Sci. 2 (2013) 110–113.

31] A.U. Rehman, M. Yaqoob, A. Waseem, A. Nabi, Determination of arsenic(V) infreshwaters by flow injection with luminol chemiluminescence detection, Int.J. Environ. Anal. Chem. 88 (2008) 603–612.

32] C.P. King, Determination of arsenic in natural waters using surface plasmonresonance: a low-cost analytical tool for arsenic screening, J. US SJWP (2008)46–55.

33] M. Lakatos*, S. Matys, J. Raff, W. Pompe, Colorimetric As (V) detection basedon S-layer functionalized gold nanoparticles, Talanta (2015) (AcceptedManuscript).

34] H. Shen, P.K. Dasgupta, Electrochemical arsine generators for arsenicdetermination, Anal. Chem. 86 (2014) 7705–7711.

35] Yang Song, M. Greg, Development of a method for total inorganic arsenicanalysis using anodic stripping voltammetry and a Au-coated diamondthin-film electrode, Anal. Chem. 79 (2007) 2412–2420.

36] S. Kumar, G. Bhanjana, N. Dilbaghi, R. Kumar, A. Umar, Fabrication andcharacterization of highly sensitive andselective arsenic sensor based onultra-thin graphene oxide nanosheets, Sens. Actuators B Chem. (2015)(Accepted Manuscript).

37] J. Ma, M.K. Sengupta, D. Yuan, P.K. Dasgupta, Speciation and detection ofarsenic in aqueous samples: a review of recent progress in non-atomic

spectrometric methods, Anal. Chim. Acta 831 (2014) 1–23.

38] T.H. Förster, Experimentelle und theoretische Untersuchung desZwischenmolekularen übergangs von Elektrinenanregungsenergie, Z.Naturforsch. 4A (1949) 321–327.

ctuato

[

[

[

[

[

[

[

[

[[

[

[

[

[

[

[

[

[

[

[

[

[

[

Belgium (2007-08). He received Jagdish Chandra Bose Award 2008–2009, TSCST,Govt. of Tripura; Young Scientist Research Award by DAE, Govt. of India. He has

J. Saha et al. / Sensors and A

39] T.H. Förster, in: O. Sinanoglu (Ed.), Modern Quantum Chemistry, IstanbulLectures, Part III: Action of Light and Organic Crystals, Academic Press, NewYork, 1965.

40] J. Saha, A. Datta Roy, D. Dey, S. Chakraborty, D. Bhattacharjee, P.K. Paul, S.A.Hussain, Investigation of fluorescence resonance energy transfer betweenfluorescein and Rhodamine 6G, Spectrochim. Acta Mol. Biomol. Spectrosc. 149(2015) 143–149.

41] D. Dey, D. Bhattacharjee, S. Chakraborty, S.A. Hussain, Development of hardwater sensor using fluorescence resonance energy transfer, Sens. Actuators B184 (2013) 268–273.

42] S.A. Hussain, D. Dey, S. Chakraborty, J. Saha, A. Datta Roy, S. Chakraborty, P.Debnath, D. Bhattacharjee, Fluorescence resonance energy transfer (FRET)sensor, Sci. Lett. J. 4 (2015) 119.

43] B.-S. Liu, J. Gao, Z.-C. Liu, L.-N. Yu, D.-C. Yang, G.-L. Yang, Fluorescenceresonance energy transfer quenching method for determination of arsenicwith acridine orange-rhodamine B, Guangpuxue Yu Guangpu Fenxi 26 (2006)306–308.

44] D. Dey, J. Saha, A. Datta Roy, D. Bhattacharjee, S.A. Hussain, Development of anion-sensor using fluorescence resonance energy transfer, Sens. Actuators B195 (2014) 382–388.

45] D. Bhattacharjee, D. Dey, S. Chakraborty, S.A. Hussain, S. Sinha, Developmentof a DNA sensor using a molecular logic gate, J. Biol. Phys. 39 (2013) 387–394.

46] A. Datta Roy, D. Dey, J. Saha, S. Chakraborty, D. Bhattacharjee, S.A. Hussain,Development of a sensor to study the DNA conformation using molecularlogic gates: spectrochim, Acta Mol. Biomol. Spectrosc. 136 (2015) 1797–1802.

47] S. Prakash, G.D. Tuli, S.K. Basu, Adv. Inorg. Chemi. Delhi (2000).48] E. Fulladosa, J.C. Murat, M. Martıı́nez, I. Villaescusa, Effect of pH on arsenate

and arsenite toxicity to luminescent bacteria (Vibrio fischeri), Arch. Environ.Contam. Toxicol. 46 (2004) 176–182.

49] N. Chakrabarty, Arsenic Toxicity: Prevention and Treatment edited by; CRCPress: New York (2016).

50] P.D. Sahare, V.K. Sharma, D. Mohan, A.A. Rupasov, Energy transfer studies inbinary dye solution mixtures: Acriflavine + Rhodamine 6G andAcriflavine + Rhodamine B, Spectrochim. Acta Mol. Biomol. Spectrosc. 69(2008) 1257–1264.

51] S. Roy, G. Palui, A. Banerjee, The as-prepared gold cluster-based fluorescentsensor for the selective detection of AsIII ions in aqueous solution, Nanoscale 4(2012) 2734–2740.

52] H.y. Gong, D.x. Wang, Z-.t. Huang, M-.x. Wang, Recognition of anions byprotonated methylazacalixpyridines, Front. Chem. China 4 (2009) 307–312.

53] S. Lohar, A. Sahana, A. Banerjee, A. Banik, S.K. Mukhopadhyay, J.S. Matalobos,D. Das, Antipyrine based arsenate selective fluorescent probe for living cellimaging, Anal. Chem. 85 (2013) 1778–1783.

54] C.E. Vivian, T.C. Harrop, Synthesis and properties of arsenic(III)-reactivecoumarin-appended benzothiazolines: a new approach for inorganic arsenicdetection, Inorg. Chem. 52 (2013) 2323–2334.

55] S. Deng, G. Yu, S. Xie, Q. Yu, J. Huang, Y. Kuwaki, I. Masahiro, Enhancedadsorption of arsenate on the aminated fibers: sorption behavior and uptakemechanism, Langmuir 24 (2008) 10961–10967.

56] B.A. Manning, S.E. Fendorf, B. Bostick, D.L. Suarez, Arsenic(III) oxidation andArsenic(V) adsorption reactions on synthetic birnessite, Environ. Sci. Technol.

36 (2002) 976–981.

57] M. Chao, Z. Fang, W. Guangfei, W. Shuizhu, A nanoparticle-supportedfluorescence resonance energy transfer system formed via layer-by-layerapproach as a ratiometric sensor for mercury ions in water, Anal. Chim. Acta734 (2012) 69–78.

rs B 241 (2017) 1014–1023 1023

58] L. Baoxia, T. Hongliang, C. Yang, Upconversion nanoparticle-basedfluorescence resonance energy transfer assay for Cr(III) ions in urine, Anal.Chim. Acta 761 (2013) 178–185.

59] Alankar Shrivastava, Vipin B. Gupta, Methods for the determination of limit ofdetection and limit of quantitation of the analytical methods, Chron. YoungSci. 2 (2011) 21–25.

60] T. Guangchao, D. Liping, S. Xingguang, Detection of melamine based on thefluorescence resonance energy transfer between CdTe QDs and Rhodamine B,Food Chem. 141 (2013) 4060–4065.

61] S. Murcott, Arsenic Contamination in the World, An International SourceBook, IWA publishing, 2012, 132.

Biographies

Miss. Jaba Saha (M.Sc. 2012, Tripura University, India) is working as a Researchscholar in Department of Physics, Tripura University. Her major fields of interestare Fluorescence Resonance Energy Transfer in solution & ultrathin films and theirsensing applications. She has published 6 research papers in international journaland attended several scientific conferences in India.

Mr Arpan Datta Roy (M.Sc. 2013, Tripura University, India) is working as a Researchscholar in Department of Physics, Tripura University. His major fields of interestare study of biomolecules using Fluorescence Resonance Energy Transfer. He haspublished 6 research papers in international journal and attended several scientificconferences in India.

Dr. Dibyendu Dey (M.Sc. 2009, & Ph.D, 2015, Tripura University, India) is workingas a Research scholar in Department of Physics, Tripura University. His major fieldsof interest are Fluorescence Resonance Energy Transfer in solution & ultrathin films.He has published 12 research papers in international journals and attended severalscientific conferences in India.

Dr. Jayasree Nath (M.Sc. 2008, & Ph.D, 2015, Tripura University, India) is workingas a Research scholar in Department of chemistry, Tripura University. Her majorfields of interest is in surface chemistry. She has published 10 research papers ininternational journals and attended several scientific conferences in India.

Prof. D. Bhattacharjee (M.Sc., Kalyani University & Ph.D, IACS, India) is a Professorin the Department of Physics, Tripura University, India. His major fields of interestare preparation and characterization of ultra thin films by Langmuir-Blodgett & Self-assembled techniques. He visited Finland and Belgium for postdoctoral research. Hehas undertaken several research projects. He has published more than 93 researchpapers in different national and international journals and attended several scien-tific conferences in India and abroad.

Dr. S. A. Hussain (M.Sc. 2001 & Ph.D, 2007, Tripura University, India) is an AssistantProfessor in the Department of Physics, Tripura University. His major fields of inter-est are Thin Films and Nanoscience. He was a Postdoctoral Fellow of K.U. Leuven,

undertaken several research projects. He has published 83 research papers in inter-national journals and attended several scientific conferences in India and abroad.Dr. Hussain is an Editorial Board member of Elsevier journal “Applied Clay Science”.