a novel colorimetric sensor strip for the detection of glyphosate in water.pdf

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Sensors and Actuators B 206 (2015) 357–363

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s n b

A novel colorimetric sensor strip for the detection of glyphosatein water

L.K.S. De Almeida a, S. Chigome b, N. Torto b, C.L. Frost c, B.I. Pletschke a,∗

a Department of Biochemistry and Microbiology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africab Department of Chemistry, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africac Department of Biochemistry and Microbiology, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031, South Africa

a r t i c l e i n f o

Article history:

Received 16 May 2014

Received in revised form 26 August 2014

Accepted 11 September 2014

Available online 20 September 2014

Keywords:

Colorimetric

Glyphosate

Herbicide

Nanofiber

Poly (vinyl) alcohol

Sensor

a b s t r a c t

This study presents the development of a novel first generationnanofiber based colorimetric sensor strip

for the determination of glyphosate in water. The proposed method was validated with an optical color

change of the poly (vinyl) alcohol (cd-PVA (copper doped poly (vinyl) alcohol)) nanofiber sensor strips

from blue to yellow upon the injection of the dithiocarbamic acid sample. The sensor strip demonstrated

advantageouscharacteristics including a low sample volume (30l),a rapidresponse time (∼1–3s), good

color spot stability (4 h) and a low cross-reactivity to glyphosate structural analogs, aminomethylphos-

phonic acid (AMPA) and glycine. The cd-PVA sensor strips were characterized by a practical limit of

detection of 0.1g/mland the sensor strip systemwas stable for up to 20 days at 23◦C (dark conditions).

Application of thesensorstrip to an environmentalwatersample (nopre-treatment) indicated very good

recovery of 100.9±8.7% at the mid-range (200g/ml) concentration of glyphosate, however interfering

effects were observed at a lower-range (60g/ml) concentration with a recovery of 128.2±3.1% being

observed. Interference studies confirmed the susceptibility of this system to compounds and ions com-

monly found in environmental waters; therefore pre-treatment of water samples would be required.

This system shows great potential for on-site application for high-throughput screening for glyphosate

in water.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Glyphosate is the most widely used herbicide worldwide. The

potential environmental impacts and health hazards of glyphosate

(The healthbasedvalue forglyphosate in drinking water, set by the

World Health Organizationis, 0.9g/ml [34].) have ledto increased

researchinto possible methods for detection. Several methods have

beendevelopedfor the detection of glyphosate; theseinclude HPLC

[20], capillary electrophoresis [5,6], mass spectrometry [11,14]

florescence [13] and gas chromatography [19]. Although these

methods are highly sensitive and are able to detect glyphosate at

verylow concentrations, the methods are laboriousand require the

use of highly specialized equipment. The difficulty in finding sim-

ple detection methods is due to the fact that glyphosate displays

complex behavior; it is highly soluble in water and often exists

in low concentrations [36]. However, more recently simpler spec-

trophotometric methods have been developed [16,29,33], but the

∗ Corresponding author. Tel.: +27 46 6038081.

E-mail address: [email protected] (B.I. Pletschke).

majordrawbackof these methods is the useof high samplevolumes

which limits their application.

The development of colorimetric sensor strips is of great interest

due to the potential advantages overother reported methods which

include: practicality, simplicity and visual quantification. A fully

automatedimmunosensor (based on immunocomplexcapture) has

been developed for the detection of glyphosate [10], but to the best

of our knowledge, there have been no reports on nanofiber based

colorimetric sensor strips. In comparison, reports on the develop-

ment of colorimetric sensors in thedetection of other analytes have

received wide attention. Studies using paptodes for colorimetric

sensor strip detection of zinc [30], ascorbic acid [1] and hydrazine

[2] have been reported. Ding et al. [9] developed a highly sensi-

tive and selective nanofiber based colorimetric sensor strip for the

detection of Cu2+.

The method employed for nanofiber production was electro-

spinning, which is a well established process that allows the

continuous production of nanofibers [12,15,17]. The surface matrix

chosen for the sensor strip in this study was poly (vinyl) alcohol

(PVA). PVA exhibits attractive features such as water solubility,

good chemical stability; this polymer is also non-toxic [18].

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358 L.K.S. De Almeida et al. / Sensors and Actuators B 206 (2015) 357–363

Fig. 1. The schematic representation of the cd-PVA sensor system (A). SEM micrographs are shown for pure PVA (magnification: 5315×) (B) and cd-PVA (magnification:

10,455×) (C). The nanofiber diameters of the electrospun mats were obtained using the SEM imaging platform Scandium and frequency graphs for pure PVA (D) and cd-PVA

(E) were plotted using Microsoft Excel. The nanofiber mats were electrospun under the following processing conditions: (needle tip to collector distance: 15 cm, voltage:

30 kV and flow rate: 0.5ml/h).

Our study presents the development of a first generation

nanofiber based colorimetric sensor strip for the detection of

glyphosate in water. For the purposes of our study our method

was developed based on the principle reaction mechanism demon-

strated by [16]. We propose a two step method which involves

the reaction of glyphosate to carbon disulfide, forming a dithiocar-

bamic acid intermediate (Fig. 1A), followed by sample application

onto copper doped poly (vinyl) alcohol (cd-PVA) nanofiber sensor

strips, resulting in a color change in the presence of glyphosate

(dithiocarbamic acid intermediate) (Fig. 1A).

2. Methods and materials

2.1. Chemicals

Poly (vinyl) alcohol (M w: 146,000–186,000; 99+% hydrolyzed),

aminomethyl phosphonic acid (quadropure AMPA), copper(II)

nitrate hydrate (Cu (NO3)2·H2O), carbon disulfide (anhydrous

CS2), magnesium chloride (anhydrous MgCl2) and copper (II)

sulphate (CuSO4 pentahydrate) were purchased from SIGMA.

Glycine (NH2CH2COOH), Triton®X-100 (TX-100), sodium hydrox-

ide (NaOH), calcium chloride (dry granular CaCl2), citric acid

(C6H8O7), ethylenediamine tetraacetic acid disodium salt (EDTA),

ferrous sulphate (FeSO4·7H2O), potassium chloride (KCl), sodium

chloride (NaCl), sodium carbonate (Na2CO3), sodium nitrate

(NaNO3), sodium sulfate (anhydrous Na2SO4) and zinc sulphate

(ZnSO4) were purchased from Merck. Glyphosate (purity: 99.5%)

was purchased from Supelco Analytical and manganese sulphate

(MnSO4) was purchased from Chemies Suiwes.

2.2. Synthesis of cd-PVA nanofiber sensor strips

PVA polymer (7.5%, w/v) was added to distilled water (solvent)

and the solution was subjected to reflux heating at 90 ◦C for 5h.

The solution was then cooled to 23 ◦C. Copper (in the form of cop-

per(II) nitrate, 3.35%) and 1% Triton-X100 (TX-100) was added to

the polymer solution. The copper containing PVA polymer solu-

tion was poured into a 15 ml syringe with a blunt needle attached

(inner diameter: 0.3 mm). The electrospinning process was carried

out at room temperature under the following conditions: a voltageof 30 kV, a flow rate of 0.5 ml/h and a needle tip to collector dis-

tance of 15 cm. The polymer suspension was electrospun for 10 h

and the fiber mat was collected on aluminum foil. Once the elec-

trospinning procedure was complete, the cd-PVA nanofiber mat

wasseparated from thealuminum foil and cut into 10mm×10mm

nanofiber squares.

2.3. Nanofiber partial characterization

The fiber morphology of pure PVA and cd-PVA fibers was deter-

mined using a Zeiss Evo MA 15 scanning electron microscope

(SEM). Nanofiber samples were gold sputtered in a JEOL JFC-1200

fine coater for 30 min. Images were obtained at an accelerating

voltage of 20 kV (Vega TC software, Tescan digital microscopy



L.K.S. De Almeida et al. / Sensors and Actuators B 206 (2015) 357–363 359

imaging). Fiber diameters were obtained using the SEM image

platform, Scandium. The transmission IR spectrums of pure PVA

and cd-PVA nanofibers were recorded using a Nicolet 17DSX FT-

IR spectrophotometer at room temperature in the frequency range

650–4000cm−1.

2.4. Data analysis

All data were presented as mean±SD (n = 3), unless statedotherwise. Macroscopic images were obtainedusing a SONYCyber-

shot digital camera. Quantification was achieved based on the RGB

color model. In this study digital images were imported into Adobe

Photoshop CS5.1 software, four representative areas on each test

stripwere analyzed(samplesize of 101×101averageforeacharea)

and the RGB values were retrieved. The effective intensity of the

RGB values was subsequently calculated. Three negative controls

were used in this study: no glyphosate, no carbon disulfide and no

test nanofiber test strip (blank).

2.5. Proof of concept

The experimental conditions chosen for the proof of conceptwere based on previous experimental assays conducted using the

principle reaction described in Section 1, in an un-immobilized

(free) system (data not shown). The concentration of glyphosate

chosen for this study (1000g/ml) was based on the upper limit

of the standard curve from the free system (data not shown).

Briefly, pure glyphosate (1000g/ml) was added to 2.5% (v/v) car-

bon disulfide in a 1:2.5 ratio (pH 12). A volume of 30 l of the

dithiocarbamic acid sample was then injected onto the cd-PVA

sensing strip. The experiment was carried out in duplicate. Digital

images were obtained and the effective intensity was calculated

(Section 3.2).

2.6. Effect of pH and carbon disulfide (%) concentration

The cd-PVA sensing system was optimized with respect to pH

(5–12) and carbon disulfide (0–7%) concentration.

2.7. Calibration curve

The glyphosate concentration range used for the calibration

curve was 0.1–500g/ml.

2.8. Cross reactivity of cd-PVA sensor strips

The specificity of the cd-PVA sensor strips for the structural

analogs of glyphosate; glycine (1000g/ml) and aminomethyl

phosphonic acid (AMPA, 1000g/ml), were assessed.

2.9. Reproducibility of the cd-PVA sensor strip system

The inter assay variability was investigated over eight differ-

ent cd-PVA nanofiber mats and the intra assay variability was

obtained from a total of 40 replicates. The reproducibility was

assessed at two different glyphosate concentrations (1000 and

400g/ml). Data was presented as the relative standard deviation

(%). Theaverage relative signal response (%)within nanofiber mats,

which was based on the fraction of response values obtained at

400g/ml against response values obtained at 1000g/ml (Eq.

(1)) was determined as a measure of internal consistency. The

ideal % relative response value was theoretically assumed to be

40%. Response values were defined as the effective intensity ( Ab)

of the blue color value, described in Section 3.2.

RR% = Average

Rv(400g/ml)

Rv(1000g/ml)

∗ 100 (1)

where RR is the relative signal response, Rv(400 g/ml) are the

response values at 400g/ml of glyphosate and Rv(1000 g/ml) are

the response values at 1000 g/ml of glyphosate.

2.10. Color spot stability and cd-PVA sensor strip stability

For evaluation of color spot stability30 l of the dithiocarbamic

acid intermediate (1000g/ml) was injected onto the cd-PVA sen-

sor strip and analyzed at regular intervals over an 8 h period.

Cd-PVA sensor strips were stored in the dark (covered) at 23 ◦C for

the investigation of sensor strip stability. The cd-PVA sensor strips

were assayed at 3-day intervals over 30 days.

2.11. Application of cd-PVA sensor strips to a complex matrix

Glyphosate concentrations chosen for this study were based on

the calibration curve (a mid-range concentration, 200g/ml and a

lower limit concentration of 60 g/ml). The environmental watersample was collected in glass Schott bottles from Grey Dam in the

Eastern Cape, South Africa and stored at 4 ◦C. The water sample

was filtered (Munktell filter paper, 3 HW 125 mm) for the removal

of large soil sediments. No further pretreatment strategies/pre-

concentration steps were employed in this study. Analysis was

carried out within 24 h of sampling. The water sample was spiked

with the aforementioned concentrations of glyphosate and the

recovery (%) of the cd-PVA sensor strips was investigated.

2.12. Interference study

The concentration of glyphosate used in this study was the

mid-range concentration demonstrated in the calibration curve

(200g/ml). The compounds and ions chosen for this study arecommonly found in environmental waters. Interfering compound

concentrations were based on the compliance limits for environ-

mental waters in South Africa [7] as the environmental water

sample (Section 2.11) assessed in this study was obtained from

the Eastern Cape, South Africa. Two other concentrations were

analyzed: one concentration above and one concentration below

the compliance limit. Solutions of glyphosate (200g/ml) were

prepared withthe interfering compounds and incubatedfor 15 min

at 24 ◦C before analysis. Interference was defined as the relative

error (%) and values above 5% were considered as interference.

No regulatory limits were available at the time of this study for

two compounds, namely, EDTA and citric acid, and therefore the

concentrations selected were based on previous work conducted

by [35] in South African water systems.

3. Results and discussion

3.1. Nanofiber morphology

SEM micrographs of the pure PVA (Fig. 1B) and cd-PVA (Fig. 1C)

nanofiber mats demonstrate the production of defect free (no

bead formation) heterogeneous mats, characterized by the pres-

ence of long, smooth nanofibers and flat branched fibers. The

heterogeneity of the nanofibers produced in this study may cause

a more significant impact when applying this technology at an

industrial level where the homogeneity of the nanofiber mat may

become more crucial. This is because homogenous fibers may

provide improvements in color homogeneity and purity [9]. One




electrospun cd-PVA mat was used per experiment to reduce

experimental variation.

Fiber diameter frequency plots (Fig. 1D andE) indicated a wider

distribution for pure PVA when compared to cd-PVA nanofiber

mats, with a minor reduction in the average fiber diameter size

being observed in cd-PVA (0.39m) as compared to the pure PVA

(0.43m) nanofibers. The exact reasons for the wide nanofiber

diameter distribution observed for pure PVA are not entirely clear.

The presence of varied nanofiber diameters in an electrospun mat

is a frequent occurrence, however; there is no commontheory [23]

to explain this occurrence; this is largely due to the intrinsic com-

plexity of the electrospinning process [22] and resultant nanofiber

diameter sizes are governed by several factors including polymer

type, molecularweight, concentrationand applied voltage [23]. The

wide nanofiber diameter distribution obtained for pure PVA was

most likely due to a combination of these factors. Larger nanofiber

diameters (≥800m) were attributed to the flat branchedsections

within the nanofiber mats. The results suggest that the addition of

copper to PVA polymer solutions slightly improved the resultant

nanofibers produced.

The IR spectrums for pure PVA and cd-PVA nanofibers were

assessed using Fourier transform infrared (FTIR) spectral analysis

(Supplementary Figure S1). Copper and hydroxyl group coordi-

nation was evidenced by a peak broadening and a reduction inthe vibration frequency observed in the band corresponding to

O H stretching together with a relatively large shift to a lower

wavenumber in the band corresponding to CH2 and OH groups.

Previous studies have shown evidence of copper coordination with

PVA through the coordination with the hydroxyl groups ([21,32]).

Supplementary Figure S1 related to this article can be found, in

the online version, at http://dx.doi.org/10.1016/j.snb.2014.09.039.

3.2. Proof of concept

The proof of concept for this study is shown in Fig. 2A. Data was

presented as the effective intensity ( A x) of the color values (R, G, B)

obtained from the color spots analyzed and was calculated usingEqs. (2)–(4) shown below:

Ar = − log

Rs

Rb

(2)

A g = − log

Gs

Gb

(3)

Ab = − log

BsBb

(4)

where A x are the effective intensities for red ( Ar ), green ( A g ) and

blue ( Ab). Rs, Gs and B s are the color values obtained for the test

sample. Rb, Gb and Bb are the average color values obtained for thecontrols used in this study.

An optical color change (from blue to yellow) was observed

immediately upon the injection of the dithiocarbamate sample

to the sensing strip (Fig. 2A1a and A1b) and although FTIR anal-

ysis showed evidence of copper coordination with the hydroxyl

groups of PVA, the positive signal indicated that sufficient copper

ions were still available for complex formation with theglyphosate

dithiocarbamate intermediate.No color change wasobservedin the

glyphosate and carbon disulfide controls (Fig. 2A1c and A1d). The

R (0.04±0.009) and G (0.04±0.009) values did not change signif-

icantly during this study (Fig. 2A2) and the effective intensity of

the B value (0.11±0.007) showed greater sensitivity, therefore the

effective intensity of the B value was selected as thereference color

value for the remainder of this study.

Fig. 2. The visualcolorimetricresponse(A1) and the effectivecolor intensity(A2) of

the cd-PVA sensor strips immediately after the addition of 1000 g/ml of the pure

glyphosate derivative (99.5%). 1 and 2: cd-PVA sensor strips after the addition of

the glyphosate sample (volume: 30l). Values are graphically presented as mean

values±SD (n = 2). Control reactions included: no glyphosate (3), no carbon disul-fide (4) and a no test sensor strip/blank (5). The effect of pH (5–12) (B) and carbon

disulfide concentration (0–7%)(C) on the detection of glyphosate (1000g/ml) was

evaluated. The sample volume used in this study was 30l. Values are presented

as mean values± SD (n = 3). Effective intensity was calculated against the appropri-

ate controls. The calibration curve for glyphosate (0.1–500 g/ml) (D). The sample

volume was 30l and the appropriate controls were used in this study. Values are

presented as mean values ±SD (n =3).

3.3. Effect of pH

In this study the effect of pH (5–12) was investigated and

results are illustrated in Fig. 2B. pH exhibited a strong influence on

the cd-PVA glyphosate sensing system, with color change being

visually observed (Fig. 2B) only at pH 11 and 12. This suggests that

the system is strongly dependent on pH.






Quantitative analysis (Fig. 2B) supported the visual findings.

Increasing the pH of the system caused the deprotonation of the

amine group in glyphosate andtherefore theloss of hydrogenbond-

ing with the hydrogen group [31], allowing the formation of the

dithiocarbamic acid intermediate which subsequently enabled the

formationof a metalcomplex withcoppervia thecoordinationwith

the sulfur groups. pH 12 was therefore selected as the optimum pH

value.

3.4. Effect of carbon disulfide concentration

The effect of varying carbon disulfide concentrations on the

detection of glyphosate was investigated (Fig. 2C). An increase

in the effective intensity ( Ab) (from 1% carbon disulphide) was

observed with increasing concentrations of carbon disulphide,

up to 6%, at which point the system reached a plateau. Further

addition of carbon disulfide to the system would not affect the

signal response of the cd-PVA sensing strips. Based on the results

observed, a carbon disulfide concentration of 6% was selected as

the optimum concentration for this study.

3.5. Calibration curve

The calibration curve for glyphosate (0.1–500 g/ml) is shown

in Fig. 2D.

A linear relationship (R2 = 0.96) was observed between the

concentration of glyphosate and the effective intensity values cal-

culated for the cd-PVA sensor strip. The practical detection limit

is defined as the lowest concentration that would give a visual

color alteration on the sensor strip [2]. For this study the practical

detection limit was observed at 0.1g/ml.

Colorimetric spectrophotometric studies on glyphosate detec-

tion by [16] reported a limit of detection of 1.1g/ml−1

over a glyphosate concentration range of 1.0–70g/ml. More

recently similar studies by [29] reported a Sandell sensitiv-

ity of 0.091g cm−2 over a glyphosate concentration range of

between approximately 0 and 40 g/ml. Findings by [33] afterthe spectrophotometric analysis of glyphosate indicated the low-

est quantifiable concentration at 0.084 g/ml over a glyphosate

concentration range of 0.084–21.8 g/ml. The limit of detection

obtained for our method was comparable to reported values in

literature.

3.6. Specificity studies

The results (Supplementary Table S1) indicated that AMPA and

glycine only produced 16% of the signal response observed for

glyphosate, and visual results (data not shown) indicated no clear

color change after theadditionof thetwo compounds to the sensor

strips. The cd-PVA sensor strips showed relativelya highspecificity

for the glyphosate.Supplementary Table S1 related to this article can be found, in


3.7. Reproducibility of cd-PVA sensor strips (inter-intra assay

variability)

Thereproducibility and precisionof thecd-PVA sensorstripwas

studied by assessing the inter and intra assay variability at two

different glyphosate concentrations (1000 and 400g/ml).

Findings in Table 1 indicate a higher RSD value between elec-

trospun mats (inter) in comparison to the RSD values obtained

within electrospun mats (intra). This suggests that better results

are obtained when using sensor strips from the same electrospun

mat as compared to sensor strips from different mats. This result

Table 1

The reproducibility and precision of the cd-PVA sensor strip at two different

glyphosate concentrations: 1000 and 400g/ml. Values are presented as mean

values±SD (n =3).

Variability Glyphosate concentration

(g/ml)

Relative standard

deviation, RSD (%)

Inter-assay 1000 37.1

Intra-assay 1000 13.0

Inter-assay 400 45.8

Intra-assay 400 16.0

Table 2

The recovery of glyphosate in a complex matrix. Values are presented as mean

values±SD (n =3).

Spiked concentration

(g/ml)

Recovered

concentration (g/ml)

Recovery (%)

200 201.9 ± 17.5 100.9 ± 8.7

60 76.9 ± 1.9 128.2 ± 3.1

The environmental water sample used in this study was obtained from Grey Dam,

Grahamstown, Eastern Cape, South Africa.

was expected and can possibly be explained by the heterogene-

ity observed in the cd-PVA nanofiber mats produced during theelectrospinning process, as previously mentioned. The calculated

relative signal response (%) was 39.4±0.08%; this validates inter-

nal consistency with respect to signal responses obtained within

the nanofiber mats.

3.8. Cd-PVA sensor strip color stability and cd-PVA sensor strip

stability

The color spots showed an increase in effective intensity (data

notshown) over 50min, after the initial injectionof the test sample

onto the cd-PVA sensor strips. After 50 min the color spots stabi-

lized and were stable for 4 h.

The cd-PVA sensor strip was observed to be relatively stable

(data not shown) over a 15-day period (data not shown). A sharpdecline was noted after 20 days. The poor stability of this sys-

tem after 20 days may be linked to the heterogeneous structure

of the nanofibers, poor integrity of the PVA nanofibers andpossible

instability of the copper ions within the nanofiber matrix.

Future work on the cd-PVA sensor strips should involve further

optimization with respect to electrospinning homogenous cd-PVA

nanofibers (in this study electrospinning was not conducted under

controlled environmental conditions e.g. humidity, as the relevant

equipment was not available).

3.9. Application of cd-PVA sensor strips to a complex matrix

The cd-PVA sensor strips indicated good recovery (Table 2) at a

200g/ml in the Grey Dam (100.9%±8.7) water sample. Possibleinterference effects were observed at a lower spiked glyphosate

concentration (60g/ml) in the Grey Dam sample with a recovery

of 128.2%±3.1. Interference was defined as a recovery value that

deviated ±20% outside 100% [28].

3.10. Interference study

The selectivity of thecd-PVA sensor wasstudied by assessingthe

effects of compounds commonly found in environmental waters

(Supplementary Table S2). The results demonstrated the sus-

ceptibility of the cd-PVA sensor system to compounds found in

environmental water systems (relative errors were above ±5% in

all theexperimental tests). Differentions andcompounds exhibited

varied interfering effects on the system.






Supplementary Table S2 related to this article can be found, in


Overall the findings of the interference study showed that the

cd-PVA sensor strip system was very sensitive to compounds and

ionscommonly found in environmental water systems,even at con-

centrations belowcompliance limits, therefore the pretreatment of

water samples would be a crucial requirement in the application of

the proposed method.

4. Conclusion

The ever increasing trend toward the protection of the envi-

ronment involves the increased use of non-toxic chemicals and

materials in sensor development. In the current study the derivati-

zation of glyphosate was primarily based on the principle reaction

reported by [16], which involved the use of carbon disulfide. Care-

ful handling and the appropriate disposal of this chemical would

be an important requirement when using this assay. Future studies

will explore the use of non-toxic chemicals for the derivatization

of glyphosate.

In summary, we have developed a novel first generation visual

nanofiber based colorimetric sensor strip system for the detection

of glyphosate in water. This system was based on the reaction of

glyphosate (dithiocarbamic acid intermediate) on copper doped

PVA nanofibers for a resultant color change (blue to yellow). This

system was sensitive and a practical detection limit was observed

at concentrations as low as 0.1g/ml, which was comparable to

the detection limits reported in literature for colorimetric spec-

trophotometric methods. The cd-PVA sensor strips displayed high

specificity and did not demonstrate significant cross-reactivity

with glyphosate structural analogs. Further development of the

proposed method would entail the production of homogenous

PVA nanofibers with improved mechanical stability and increased

integrity for the improvement of the reproducibility and stability

of the sensor system. The proposed method was highly sensitive

to interfering compounds; therefore the pretreatment of water

samples is crucial. The simplicity and rapid response time of this

method shows great potential for on-site applications for highthrough put screening and provides a foundation for the future

development of colorimetric sensor strips for the detection of

glyphosate.

Acknowledgements

The authors would like to thank the Water Research Commis-

sion (WRC) (Grant no. K5/1991) of South Africa for their financial

support. Conclusions drawn and opinions expressed are those of

the authors and should not be attributed to the funding body.

References

[1] A. Abbaspour, A. Khajehzadeh, A. Noori, A simple and selective sensor for thedetermination of ascorbic acid in vitamin C tablets based on paptode, Anal. Sci.24 (2008) 721–725.

[2] A. Abbaspour,E. Mirahmadi,A. Khajehzadeh,Disposable sensorfor quantitativedetermination of hydrazine in water and biological sample, Anal. Methods 2(2010) 349–353.

[5] M.G. Cikalo, D.M. Goodall, W. Matthews,Analysisof glyphosate using capillaryelectrophoresis with indirect detection, J. Chromatogr. A 745 (1996) 189–200.

[6] M.Corbera,M. Hidalgo,V. Salvado,P.P. Wieczorek, Determinationof glyphosateand aminomethylphosphonic acid in natural water using the capillary elec-trophoresis combined with enrichment step, Anal. Chim. Acta 540 (2005) 3–7.

[7] DWAF, South African Water Quality Guidelines Aquatic Ecosystems, vol. 7,Department of Water Affairs and Forestry, Pretoria, South Africa, 1996.

[9] B.Ding, Y. Si,X. Wang,J. Yu,L. Feng,G. Sun,Label-freeultrasensitivecolorimetricdetection of copper(II) ions utilizing polyaniline/polyamide-6 nano-fiber/netstrips, J. Mater. Chem. 21 (2011) 13345–13353.

[10] M.A. Gonzalez-Martinez, E.M. Brun, R. Puchades, A. Maquieira, K. Ramsey, F.Rubio,Glyphosateimmunosensor. Applicationfor waterand soilanalysis, Anal.Chem. 77 (2005) 4219–4227.

[11] Z.X.Guo,Q. Cai,Z. Yang,Determination ofglyphosate andphosphate inwater byionexhnagechromatography– inductivelycoupledplasma massspectrometrydetection, J. Chromatogr. A 1100 (2005) 160–167.

[12] M.E. Helgeson,N.J.Wagner, A correlation forthe diameter of electrospun poly-mer nanofibers, AIChE J. 53 (2007) 51–55.

[13] E.A. Hogendoorn, F.M. Ossendrijver, E. Dijkman, R.A. Baumann, Short com-munication: rapid determination of glyphosate in cereal samples by meansof pre-colummn derivatisation with 9-fluorenylmethyl chloroformate andcoupled-column liquid chromatography with fluorescence detection, J. Chro-matogr. A 833 (1999) 67–73.

[14] M. Ibanez, O.J. Pozo, J.V. Sancho, F.J. Lopez, F. Hernandez, Residue determina-

tion of glyphosate, glufosinate and aminomethylphosphonic acid in w ater andsoil samples by liquid chromatography coupled to electrospray tandem massspectrometry, J. Chromatogr. A 1081 (2005) 145–155.

[15] M. Ignatova, O. Stoilova, N. Manolova, D.G. Mita, N. Diano, C. Nicolucci, I.Rashkov, Electrospun microfibrous poly (styrene-alt-maleic anhydride)/poly(styrene-co-maleic anhydride) mats tailored for enzymatic remediation of waters polluted by endocrine disruptors, Eur. Polym. J. 45 (2009) 2494–2504.

[16] M.R. Jan, J. Shah, M. Muhammad, B. Ara, Glyphosate herbicide residue deter-mination in samples of environmental importance using spectrophotometricmethod, J. Hazard. Mater. 169 (2009) 742–745.

[17] S. Ji, Y. Li, M. Yang, Gas sensing properties of a composite composed of electrospun poly (methyl methacrylate) nanofibers and in situ polymerizedpolyaniline, Sens. Actuators B: Chem. 133 (2008) 644–649.

[18] Y.T. Jia, J. Gong, X.H. Gu, H.Y. Kim, J. Dong, X.Y. Shen, Fabrication and char-acterization of poly (vinyl alcohol)/chitosan blend nanofibers produced byelectrospinning method, Carbohydr. Polym. 67 (2007) 403–409.

[19] H. Kataoka, S. Ryu, N. Sakiyama, M. Makita, Simple and rapid determination of theherbicidesglyphosate andglufosinatein riverwater,soiland carrot samplesby gaschromatographywithflame photometricdetection, J.Chromatogr. A 726

(1996) 253–258.[20] M. Kim, J. Stripeikis, F. Inon, M. Tudino, A simplified approach to the deter-

mination of N-nitroso glyphosate in technical glyphosate using HPLC withpost-derivatization and colorimetric detection, Talanta 72 (2007) 1054–1058.

[21] J. Li, J. Suo, S. Wang, The effect of copper(II) on the thermal and mechan-ical properties of poly (vinyl alcohol)/silica hybrid, Polym. Eng. Sci. (2009),http://dx.doi.org/10.1002/pen.

[22] D. Lukás, L. Sarkar, K. Martinová, A.D. Vodsed, J. Lubasová, J. Chaloupek,P. Pokorny, P. Mikeˇ s, J. Chvojka, M. Komárek, Physical principles of elec-trospinning (electrospinning as a nano-scale technology of the twenty-firstcentury), Text. Progr. 41 (2009) 59–140.

[23] J. Malaˇ sauskiene, R. Milaˇ sius, Mathematical analysis of diameter distributionof electrospun nanofibers, Fibers Text. East. Eur. 18 (2010) 45–48.

[27] C. Raju, J.L. Rao, B.C.V. Reddy, K.V. Brahmam, Thermal and IR studies on copperdoped polyvinyl alcohol, Mater. Sci. 30 (2007) 215–218.

[28] F. Rubio, L.J. Veldhuis, B.S. Clegg, J.R. Fleeker, J.C. Hall, Comparison of directELISA and an HPLC method for glyphosate determinations in water, J. Agric.Food Chem. 51 (2003) 691–696.

[29] D.K. Sharma,A. Gupta,R. Kashyap,N. Kunar, Spectrophotometricmethod forthedetermination of glyphosate in relation to its environmental and toxicologicalanalysis, Arch. Environ. Sci. 6 (2012) 42–49.

[30] R.D. Sharma, S. Amlathe, Quantitative determinationand removal of zinc usingdisposablecolorimetricsensors: an appropriatealternativeto optodes,J. Chem.Pharm. Res. 4 (2012) 1097–1105.

[31] J. Sheals, S. Sjoberg, P. Persson, Adsorption of glyphosate on goethite: molec-ular characterization of surface complexes, Environ. Sci. Technol. 36 (2002)3090–3095.

[32] H. Tomita, Solution spinning of high-T c oxide superconductor:5. The influenceof yttrium and barium ions on the poly (vinyl alcohol)–copper(II) complex,Polymer 37 (1996) 1071–1077.

[33] C.V. Waiman, M.J. Avena, M. Garrido, B.F. Band, G.P. Zanini, A simple and rapidspectrophotometric method to quantify the herbicide glyphosate in aqueousmedia. Application to adsorption isotherms on soils goethite, Geoderma 120(2012) 154–158.

[34] WHO, Summary Statement: Glyphosate and AMPA in Drinking Water. WHOGuidelines for Drinking Water Quality, 3rd ed., World Health Organization,Geneva, 2004.

[35] V.C. Wutor, C.A. Togo, B.I. Pletschke, The effect of physio-chemical compoundson the activity of -d-galactosidase (B-GAL), a marker for enzyme indicator of microorganisms in water, Chemosphere 68 (2007) 622–627.

[36] Y. Zhu, F. Zhang, C. Tong, W. Liu, Short communication: determination of glyphosate by ion chromatography, J. Chromatogr. A 850 (1999) 297–301.

Biographies

Louise de Almeida obtained her B.Sc. (Hons) (Biotechnology) and M.Sc. (Biochem-istry) degrees at Rhodes University in 2009 and 2011, respectively. She is currentlyin the final phase of her Ph.D. studies in biochemistry and nanotechnology in Pro-fessor Brett Pletschke’s laboratory. Her research interests include nanotechnologyand nanoenzymology for the rapid detection of pesticides in water environments.She is currently employed as an environmental scientist for Debmarine Namibia.

Samuel Chigome obtained his M.Sc. in Analytical Chemistry at the University of

Botswana in 2008 and subsequently his Ph.D. in Analytical Chemistry at Rhodes


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http://localhost/var/www/apps/conversion/tmp/scratch_2/dx.doi.org/10.1002/pen





University in 2012. He was appointed as a Postdoctoral Research Fellow at RhodesUniversity in the laboratory of Professor Nelson Torto in 2012–2013. His researchinterests lie in the fabricationof electrospun nanofiberbased solidphase extractiondevices,electrospuncarbonnanofiberelectrodes formicrobial fuelcells,and electro-spun nanofiber based diagnostic probes. Samuel is currently a Senior Researcher inNatural Resources and Materials at the Botswana Institute for Technology Researchand Innovation.

Nelson Torto is a Professor of Analytical Chemistry and previously the Head of theChemistryDepartment at Rhodes University. He graduated with a B.Sc.(Hons) fromtheChemistry Schoolof Honorsof theUniversity of Manchester Instituteof Science

andTechnology (UMIST), andM.Sc.Chemistry from theUniversity of Botswana anda Ph.D. in Analytical Chemistry from the University of Lund (Sweden). His researchfocuseson theuse of nanotechnologyfor thedevelopmentof colorimetric probes fordiagnosis in biotechnology, health, water and the environment. Nelson is currentlyappointed as the Chief Executive Officer at the Botswana Institute for TechnologyResearch and Innovation.

Carminita Frost obtained a Ph.D. in Biochemistry in 2001 from the Departmentof Biochemistry and Microbiology, University of Port Elizabeth. She is currently anAssociateProfessor in Biochemistry at the Nelson Mandela Metropolitan University.Hercurrentresearch focuseson theuse ofmedicinalplantsto alleviatethe metabolicsyndrome,and studies related to the cytotoxic and genotoxiceffects of pesticidesinwater.

Brett Pletschke is currently a Professor and previous Head of Biochemistry in theDepartmentof Biochemistry and Microbiology at Rhodes University, Grahamstown,SouthAfrica. BrettreceivedhisPhD inBiochemistry in1996 atthe University ofPortElizabeth (now Nelson Mandela Metropolitan University). Prof Pletschke’s research

interestlies in understanding the phenomenon of enzyme synergy in complex envi-ronments, using lignocellulose as a suitable model substrate for the generationof a bio-economy, as well as the use of nanotechnology and enzymology for thedetection of pollutants in water (biomonitoring) and bioremediation of these toxiccompounds.

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