Study on the Surface Acoustic Wave Sensor with Self-Assembly Imprinted Film of Calixarene Derivatives to Detect Organophosphorus Compounds

doi:10.4236/ajac.2012.39087

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American Journal of Analytical Chemistry, 2012, 3, 664-668

http://dx.doi.org/10.4236/ajac.2012.39087 Published Online September 2012 (http://www.SciRP.org/journal/ajac)

Study on the Surface Acoustic Wave Sensor with

Self-Assembly Imprinted Film of Calixarene Derivatives to

Detect Organophosphorus Compounds

Bing-Qing Cao, Qi-Bin Huang, Yong Pan

Research Institute of Chemical Defence, Beijing, China

Email: [email protected]

Received June 23, 2012; revised July 25, 2012; accepted August 7, 2012

ABSTRACT

The molecularly imprinted technology and the self-assembly technique were used together on the calixarene surface

acoustic wave (SAW) chemical sensors to detect organophosphorus compounds. 25-(thioalkyl-alkoxy)-p-tertbutylcalix[4]

arene with self-assembled monolayer character was the sensitive coating of the sensors. The sensors had a special re-

sponse to organophosphorus compounds and the response frequency shift of this sensor to organophosphorus com-

pounds in 0.1 mg/m3 was 350 Hz. The response frequency increased linearly with the increase of the concentration of

DMMP in the range from 0.1 to 0.6 mg/m3. The possible explanation of the interaction between the coatings and or-

ganophosphorus compounds was discussed.

Keywords: Calixarene; Self-Assembly; Molecular Imprinted; SAW Sensor; DMMP; Detection

1. Introduction

Nowadays, the SAW sensor technology to detect the poi-

sonous and harmful gases is a focus in the sensor field. In

1992, Larry J. Kepley [1], for the first time, published a

literature in which surface acoustic wave technique and

self-assembly technique were put together to detect the

compound Dimethyl Methylphosphonate (DMMP). The

advantages of powerful selectivity, high sensitivity, short

response time, simple membrane preparation and long usa-

ge time were reported. Because calixarenes had the in-

herent three dimensional structure and pre-organized cavi-

ties as recognition sites, studies on their self-assembly

researches were more and more valuable [2]. The particu-

lar calixarene corpus molecules were assembled on the

surface of a gum body, SiO2, gold and other metals. Then

monolayer or multilayer self-assembly system could be

formed and used in molecular recognition, chemical sen-

sors and phase transfer catalysis, enzyme mimics etc, so

it exhibited an extensive application prospect [3,4]. Der-

mody [5] made use of the SAW sensor based on self-

assembly polydiacetylene calixarene derivatives bilayer

film to detect the chlorobenzene, toluene and other aro-

matic organics; the results indicated that the upper mar-

gin functional groups of calixarenes had important con-

tributions to sensitivity and selectivity. By Schierbaum

and Weiss [6,7], termination modified thio-ether resorcin

[4] arene derivatives, a self-assembly monomolecular mem-

brane, were used to detect four chloroethylene, the sensi-

tivity of those sensors could reach nanogram grade. In

1998, Dickert [8] published an article that the molecular

imprinted polymer SAW sensor was used for checking o-

dimethyl-benzene, its detection had reached to 4.5 mg/m3

(The limit to the toxicity detection of o-dimethylbenzene

was 450 mg/m3) which displayed excellent detection effects.

Wang Cheng Heng [9] had prepared the molecular im-

printed polymer SAW sensors based on calixarene mem-

brane, which had higher sensitivity and selectivity to de-

tect the sulphur and phosphorus compound.

There were few reports about calixarenes, the Third

Generation Supramolecules, as sensitive film of the SAW

sensor in the detection of poisonous and harmful gases.

Furthermore no systematic study had been performed on

its adsorption mechanism. In this article, Isopropyl hydro-

gen methylphosphonate 1) Was used as the template mole-

cule, and 25-(thioalkyl-alkox)-p-tertbutylcalix[4]arene; 2)

Self-assembly molecular imprinted film was used as the

sensitive film in acoustic surface wave chemical sensor, to

detect the orgnaophosphorous compounds such as DMMP;

3) Diisopropyl Methyl-phosphonate (DIMP, 4) and other

interference gases. The detection limit and the selectivity

of the sensor were studied, and the influences of tempera-

ture and other factors were discussed. The structures of

several compounds were shown in Figure 1.

B.-Q. CAO ET AL. 665

OH HO

O(CH

)

S(CH

)

OCH(CH

)

COCH

OCH

25-(thioal

-p-tertbutyl -c

DMMP DIM

Isopropyl hydrogen

- methylphosphonate

kyl-alkox)

alix[4]arene

OCH(CH

)

OCH(CH

)

Figure 1. The structures of organophosphorus compounds

and 25-(thioalkyl-alkoxy)-p-tertbutylcalix[4]arene.

2. Experimental

2.1. Reagents and Apparatus

25-(Thioalkyl-alkoxyl)-p-tertbutylcalix[4]arene was synthe-

sized by our laboratory and was liquid chromatography

grade. Dimethyl Methylphosphonate (DMMP), Diisopro-

pyl Methylphosphonate (DIMP), Isopropyl hydrogen met-

hylphosphonate were reagent grade (Research Institute of

Chemical Defence, China). The other chemicals were rea-

gent grade (Beijing Chemical Reagent, Beijing, China).

For the instrumentations, a Surface Acoustic Wave dual

delay line (the centre frequency 300 MHz, the area of

delay line was 4 mm2 gold films), a Model Proteck C3100

Frequency Meter, (Korean Proteck company) was used

in this article.

2.2. Preparation of Self-Assembly Imprinted

Film of SAW Sensors

100 mL of 0.1 mmol/L 25-(thioalkyl-alkoxy)-p-tertbuty-

lcalix[4]arene self-assembly solution was preparaed, 100

mL of 5 - 10 mol/L isopropyl hydrogen methylphospho-

nate was added into the above solution, deposited for 12

hs for using later.

The surface acoustic wave dual delay line was purged

with V (sulphuric acid): V (hydrogen peroxide) = 3:1 Pi-

ranha solution to bright and clean, puffed with high pu-

rity N2 to remove surface foreign substance, in the last its

fundamental (ƒ0) frequency was measured.

The above-mentioned surface acoustic wave dual de-

lay line had been soaked in the self-assembly solution for

24 hs. After being taken out, the dual delay line was washed

to eliminate isopropyl hydrogen methylphosphonate. Its

fundamental frequency

()

′

1.26 10

and noise were measured

at the end.

The thickness of self-assembly imprinted film was es-

timated by the fact that the fundamental frequency shift

between coating and uncoating. Substrate conceptual dia-

gram was shown in Figure 2.

2.3. Appreciation of Self-Assembly Imprinted

Film of SAW Sensors

DMMP and DIMP were generated by gas dynamic gen-

erator at 28˚C. Then the response signal, response time

and recovery time to detect DMMP were obtained with

the above-mentioned sensor.

At the same condition, to verify the influence of inter-

ference gases on the SAW sensor, interference gases, which

concentrations were 100 - 1000 times more than that of

DMMP and DIMP were detected with the above-mentio-

ned sensor.

3. Results and Discussion

3.1. Evaluation of Film Thickness

Since the assembled film was prepared on SAW gold delay

line, mass deposits would result in the frequency shift of

baseline of the SAW-CA sensor, the relationship between

frequency shift and film thickness abided by following

Sauerbrey equation [10].

(1) Δ=− ×

In the Equation 1, Δf (Hz) was the frequency shift be-

tween coatings and uncoating, f0 (Hz) was fundamental

frequency of SAW sensor. h (cm) was film thickness of

self-assembly imprinted film, ρ (g/cm3) was the density

of film material. All data were calculated with the equa-

tion, the following Equation 2 was gotten.

Figure 2. Dual-delay line of surface acoustic wave chemical

sensor.

B.-Q. CAO ET AL.

666

0.657 10−

()

hf=−Δ × (2)

The frequency shift between coating and uncoating was

about 18 - 20 KHz, and the thickness of the film was about

2.5 - 3.5 nm grade approximately according to the Equa-

tion 2.

The noise frequency could be used to confirm the de-

tection limit. In certain time, the noise frequency ΔfN of

sensor was calculated with the following Equation 3:

max min

2f−

ffΔ=± (3)

where fmax was the biggest frequency and fmin was the

minimum frequency.

The experimental results indicated that the base frequ-

ency shift was 25 - 100 Hz, which was very small com-

pared with fundamental frequency. The reason was that

gold surface was coated with membrane and its surface

structure was changed into loose porous shape, the flat-

ness is smaller than that of smooth gold.

3.2. Detection of DMMP and DIMP at Different

Concentrations with SAW-MIP Sensor

Under the same experimental conditions (28˚C, RH = 70%),

the different concentrations of DMMP were detected, the

results such as the average response frequency shifts and

the response time were listed in Tables 1 and 2.

Table 1. The detection results of SAW-MIP sensor to DMMP.

Dynamic concentration/

（mg/m3） Response frequency shift/KHz Response

time/min

0.10 0.352 6.80

0.20 0.680 6.02

0.40 1.392 5.61

0.60 2.144 5.22

1.00 2.995 5.03

1.50 3.772 4.81

2.00 4.025 4.72

2.50 4.255 4.64

3.00 4.352 4.53

5.00 4.402 4.52

Table 2. The detection results of SAW-MIP sensor to DIMP.

Dynamic concentration/

（mg/m3） Response frequency shift/KHz Response

time/min

0.10 0.489 6.00

0.20 1.026 5.40

0.40 1.960 5.22

0.60 2.852 5.03

1.00 3.820 4.81

1.50 4.710 4.72

2.00 5.771 4.64

2.50 4.352 4.53

3.00 5.865 4.52

5.00 6.041 4.48

From the Table 1, we found that with decrease of

DMMP concentration, the response frequency shifts were

reduced, the response time was lengthened gradually, and

the recovery time was shortened. At high concentration,

the molecules of DMMP combined with gold quickly, so

that the time to reach balance was short and the recovery

time was longer. On the contrary, at low concentration,

since there were not so many adsorption molecules, the

response frequency was relatively weak. Although the

recovering speed was accelerated obviously, the equili-

bration needs longer time.

The SAW-MIP sensor had high sensitivity to low con-

centration DMMP and the results were shown in Figure

3. The response frequency shifts had a linear relationship

with the concentrations of DMMP at 0.1 - 0.60 mg/m3.

Even at 0.1 mg/m3, the SAW-MIP sensor still had almost

350 - 500 Hz response frequency shift, which was greater

than the 100 Hz of detection limit.

Generally, there are four kinds of adsorption models

between gas and film behavior: Henry laws, Langmuir

model, Freundlich adsorb equation and BET multilayer

adsorb model.

It had been shown in Figure 3, the detection curve as-

sumed a linear relationship at the beginning stage (0.10 -

1.00 mg/m3) and the curve was cliffier. From the linear

curve in Figure 4, the total correlation coefficient 0.98

had been obtained.

In the middle stage (1.00 - 3.00 mg/m3), the slope of

the curve was gradually with concentration, but above 5.0

mg/m3, response frequency shift no longer increased con-

spicuously. We carried on a discussion to the above-men-

tioned results by Langmuir model:

VaP

012345

(4)

In the Formula 4, θ was surface fraction of coverage of

DMMP

∆f /kHz

Concentration/（mg/m3)

Figure 3. The detection curve of DMMP at different con-

centrations (28˚C, RH = 70%).

B.-Q. CAO ET AL. 667

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Y Axis Title

X Axis Title

Linear Fit of Data1_B

()

R: 0.98335; SD: 0.27115; N: 6; P: 4.1359E−4.

Figure 4. The linear curve and the total correlation coeffi-

cient (0.10 - 1.00 mg/m3).

isothermal adsorption, a was equilibrium constant of ad-

sorption, which represented the adsorb ability of solid sur-

face, Vm was saturational adsorption quantity of DMMP,

V was practical adsorption quantity of DMMP at fractional

pressure P.

The variation amount

()

of response frequency and

adsorption quantity of imprinted sensitive film were

measured to be a direct ratio relation. When all experi-

mental data of the variety amount of response frequency

and the concentration (C) of DMMP were introduced into

the above-mentioned Formula 4, another Formula 5 would

be obtained.

ΔΔ

Δ (5)

where m

Δ was response frequency shift of saturational

adsorption, at the given conditions it was a constant.

From Formula 5, a straight line with the CFΔ

5.186FΔ=

012345

0.2

0.4

0.6

0.8

1.0

1.2

c/∆F(mg.m

-3.KHz-3)

C/(mg/m3)

to C

was gotten within range from 0.60 to 3.0 mg/m3 in Fig-

ure 5 showed:

According to the slope and intercept of the line, the

adsorption constant (a) of isothermal adsorption Lang-

muir model and the saturated frequency shift were calcu-

lated, a = 2.083, m KHz. In fact, when the

molecular imprinted film reached adsorption balance at

low concentration, the amounts of DMMP that had been

attached on film would be very small. Therefore this ad-

sorption behavior of Langmuir model on the film was

inevitable. When concentration was enhanced, the adsorp-

tion behavior of film was changed, and it could not be

described by the simple adsorption model. This result

demonstrated that the adsorption behavior became com-

paratively complicated along with the increment of DMMP

concentration. On the other hand, since the interactive com-

Figure 5. The calculation curve of parameter for langmuir

isotherm adsorption (28˚C, RH = 70%).

plexity between DMMP and the molecular imprinted film,

a simple linear relationship might not exist between the

response frequency shift and the concentration of DMMP.

The ideal molecular imprinted polymer has the imprinted

hole with appearance matching molecular size of template,

shape and functional group. Because imprinted films have

unique space structure, including the capacity of discern-

ment and 3D hole of displacement binding site, it could

be used to detect gas and high response frequency shift

was gotten in short time. It displays obvious molecular

imprinted effect. In this article Isopropyl hydrogen me-

thylphosphonate (1) was selected as the template, be-

cause its chemical structure was greatly similar to that of

DMMP, as a result, a great frequency shift was obtained

in this detection process.

3.3. Imprinted Effectiveness and

Anti-interference Experiments of the

SAW-MIP Sensors

In order to further confirming the imprinted effectiveness,

many other gases were chosen to carry on comparative

experiment. Spirits, hydrocarbon, aldehyde, ketene, aro-

matics, amines, organic acid, organophosphorus, herbosa

smoke etc, about 30 kinds of interference gases whose

concentrations were higher 100 - 1000 times than that of

DMMP were detected. The experimental results were

shown in Table 3:

It had been shown in Table 3, in general, common

organic solvents and gases did not interference with the

SAW-MIP sensors. Among them, because the structures

of organophosphorus agrochemicals were similar to DMMP,

their frequency shifted greatly, but to the imprinted effe-

ctiveness of DMMP, their responses were obviously lower

than that of DMMP at the same concentration. Moreover,

organic amines and high concentration organic acids would

also produce some influence on the examination, this might

be when the concentrations of these several compounds

B.-Q. CAO ET AL.

668

Table 3. The response of the SAW-MIP sensor to interfer-

ence gases.

Interference gas Concentration/(mg/m3) Response frequency

shift/KHz

Omethoate 1000 0.550

CH3OH 10000 0.320

CH3CH2OH 10000 0.421

HCOOH 1000 0.330

CH3COOH 1000 0.360

CH3(CH2)4COOH 1000 0.520

NH3 2000 0.521

C6H5NH2 2000 0.516

O-Anisidine 1000 0.212

C2H5OC2H5 10000 0.220

Petrdeumetherr 10000 0.510

THF 10000 0.510

n-C6H14 10000 0.130

n-C8H18 1000 0.310

CCl4 10000 0.290

HCHO 1000 0.125

CH3COCH3 10000 0.120

CH3COOC2H5 10000 0.150

C6H6 10000 0.140

C6H5CH3 1000 0.280

C6H5Cl 1000 0.113

H2O 1000 0.160

CH3CN 1000 0.190

Grass smog High 0.130

were 100 times, even higher than that of DMMP, they had

been to some extend linked or adsorbed on film surface.

Besides, when 25-(thioalkyl-alkoxy)-p-tertbutylcalix[4]

arene (2) non-imprinted film was used as SAW sensitive

film to detected toxic agents, the results indicated that

although it could be assembled into a film on Au surface

and had cavity structure, this kind of film had no especially

different 3D space structure, combining ability was small,

and had no obviously response to DMMP, which further

confirmed the imprinted effect.

4. Conclusion

In this paper, the SAW-MIP sensor to detect organophos-

phorus has been detailly studied with 25-(thioalkyl-alko-

xy)-p-tertbutylcalix[4]arene self-assembly molecular im-

printed film. Because this kind of SAW-MIP sensor has

strong selectivity, high sensitivity, great response frequency

shift and good recovery for DMMP, it was possible to be

applied to detection of the low concentration organophos-

phorus gases or quickly early-warning and it could be

widely applied in the future. Molecular imprinted tech-

nology with the self-assembly technique were used together

in calixarene surface acoustic wave chemical sensor, must

have important significance in studying on more gas sen-

sitive films and sensors

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