A

Xa

b

a

ARRAA

KCMVLRC

1

oeic[tmaeiicftstsactfs

0d

Analytica Chimica Acta 650 (2009) 254–257

Contents lists available at ScienceDirect

Analytica Chimica Acta

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

light-modulated chemosensor for methanol with ratiometry and colorimetry

u Zhang a,b, Yi Chen a,∗

Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, ChinaGraduate School of Chinese Academy of Sciences, Beijing 100049, China

r t i c l e i n f o

rticle history:eceived 4 May 2009eceived in revised form 16 July 2009ccepted 23 July 2009vailable online 29 July 2009

a b s t r a c t

A light-modulated chemosensor for methanol has been developed by using a photochromic spirophenan-thoxazine as an indicator. In such a sensor, methanol can be detected easily by colorimetric recognitionwith high selectivity and anti-interference. Moreover, the concentration of indicator can be modulatedand manipulated by light, which provides a simple way for the detection of methanol in a wide range ofdetectable limit that would be useful in different detection cases.

eywords:hemosensorethanol

olatile organic compoundsight-modulation

© 2009 Elsevier B.V. All rights reserved.

atiometryolorimetry

. Introduction

Developing sensing elements for the detection of volatilerganic compounds (VOCs) is gaining interest in fields related tonvironmental applications, electronic noses, and industrial chem-cal manufacturing [1–3]. Molecular recognition of volatile organicompounds (VOCs) is challenging due to potential interference4–6]. Methanol is one of VOCs commonly found in wastewa-ers from chemical industries and oil refineries. It is known that

ethanol is toxic for the microorganisms and human beings [7–13],nd it exposure via inhalation and skin absorption may lead to toxicffects from headaches to blindness with direct digestion even lead-ng to death [14]. The detection and quality monitoring of methanols therefore obviously important for both industrial and personaloncerns [15–19]. Most of the sensors that have been developedor methanol detection are based on conductive polymers or elec-rochemical sensors [20–24], and the main shortcomings of theseensors are the need for a modulated electrical signal and poorolerance for chemical and electromagnetic disturbances. Opticalensing elements may solve some of these limitations because theyre inherently passive, immune to electromagnetic interference,

apable of responding to a wide variety of parameters and amenableo multiplexing [25–27]. Although some spectroscopy methodsor methanol detection has been reported including microwavepectroscopy [28], infrared spectra [29], fluorescence spectra [30],

∗ Corresponding author. Tel.: +86 10 8254 3595; fax: +86 10 6265 4049.E-mail address: yichencas@yahoo.com.cn (Y. Chen).

003-2670/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.aca.2009.07.058

gas chromatography [31], and others [32–34], the developmentof efficient and convenient methods for methanol detection con-tinues to be an active research area [35,36]. Herein, we reporta light-modulated methanol sensor by employing the ring-openisomer of photochromic spirophenanthoxazine (SPO) as indicator(Scheme 1). By comparison with reported sensors, the sensor pre-sented has several further merits:

(1) The sensor detects methanol with high selectivity, and no inter-ference is observed when other common VOCs exist.

(2) The performance of detection is accompanied by a colorchange from orange to colorless, which can be observed bynaked-eye.

(3) The concentration of sensor (indicator) can be modulated andmanipulated by light, which enable the detection of methanolin a wide range of detectable limit.

2. Experimental

2.1. General

1H NMR spectrum was recorded at 400 MHz with TMS as an

internal reference and CDCl3 as solvent. MS spectra were recordedwith TOF-MS spectrometer. Absorption spectra were measuredwith an absorption spectrophotometer (Hitachi U-3010). Colorationand decoloration were carried out with a UV light (power: 30 W,� = 254 nm) and a xenon lamp (500 W) as the light source withdifferent wavelength filters.

X. Zhang, Y. Chen / Analytica Chimica Acta 650 (2009) 254–257 255

So

2

sC2tiasrrcN2111(M(

2

sfs

3

3

ttlwi24atwcfsdncct

decrease in optical density of SPO were obtained with addition ofethanol (1.0%) and tetrahydrofuran (25%), respectively. In addition,primary investigation also showed that no obvious interference wasobserved when a competition experiment was conducted in which

cheme 1. Ring-open and ring-closing photoisomerization and chemical structuref indicator for methanol sensor.

.2. Materials

All chemicals for synthesis were purchased from commercialuppliers, reaction monitored by TLC silica gel plates (60F-254).olumn chromatography was performed on silica gel (Merck, 70-30 mesh). Spirophenanthoxazine (SPC) was prepared accordingo literature [37] and the details are described as follows. The start-ng material 1,3,3-trimethyl-2-methyleneindoline (0.87 g, 5 mmol)nd 9-nitroso-10-hydroxyphenanthrene (1.1 g, 5 mmol) were dis-olved into 50 ml anhydrous ethanol. The mixture was stirred undereflux for 4 h. The reaction mixture was concentrated to 5 ml undereduced pressure. Purification was carried out by flash columnhromatography with petroleum–ethyl acetate (6:1) as eluent. 1HMR (CDCl3): 8.70 (d, J = 8.1 Hz, 1H), 8.61 (t, J1 = 9.3 Hz, J2 = 9.6 Hz,H), 8.11 (d, J = 8.2 Hz 1H), 7.83 (s, 1H), 7.69 (t, J1 = 7.1 Hz, J2 = 7.0 Hz,H), 7.64 (t, J1 = 7.0 Hz, J2 = 7.1 Hz, 1H), 7.58 (t, J1 = 7.0 Hz, J2 = 7.0 Hz,H), 7.51 (t, J1 = 7.3 Hz, J2 = 7.8 Hz, 1H), 7.24 (t, J1 = 7.4 Hz, J2 = 7.6 Hz,H), 7.13 (d, J = 7.0 Hz, 1H), 6.93 (t, J1 = 7.4 Hz, J2 = 7.4 Hz, 1H), 6.61d, J = 7.7 Hz, 1H), 2.78 (s, 3H), 1.41 (s, 3H), 1.39 (s, 3H). HRMS (TOF-

S EI, m/z) [M±] calcd. for C26H22N2O: 378.1527, found: 378.1527100%).

.3. Solvents

All solvents used in the experiments were purified according totandard procedures [38], and anhydrous methanol was obtainedrom “absolute” methanol by passage through type 4A molecularieve and distilled over calcium hydride.

. Results and discussion

.1. Production of methanol sensor

A methanol sensor (SPO) was obtained by irradiating the solu-ion of spirophenanthoxazine (SPC) in dichloromethane (100 �M)o photostationary state (Scheme 1). Upon irradiation with UVight, the ring-closed isomer of spirophenanthoxazine (SPC) under-

ent photocyclization to ring-opening isomer (SPO), as presentedn Fig. 1, the absorption bands of SPC, appeared at 373, 273 and54 nm, decreased and two new absorption bands at 503 and85 nm, corresponding to the ring-opening isomer SPO, appearednd increased till the photostationary state was reached. The pho-ostationary state was reached when the solution of SPC (100 �M)as irradiated for 400 s with 254 nm light (30 W), and the photocy-

lization process was accompanied by a color change of solutionrom colorless to orange. The orange solution of SPO could betored for more than 12 h at room temperature (20 ◦C) and only 10%

ecrease in absorption (optical density) was detected. It was worthoting that the orange solution of SPO was faded slowly back toolorless SPC when the solution of SPO was stored at the dark for aouple of days, or the solution of SPO was reversed completely backo the solution of SPC with visible light irradiation (� ≥ 400 nm) in

Fig. 1. Absorption changes of SPC upon irradiation with 254 nm light in DCM(100 �M) (irradiation time: 0, 40, 80, 120, 160, 200, 240, 280, 320, 360 and 400 s).

about 10 min. The ring-opening and ring-closing photoisomeriza-tion was presented in Scheme 1.

3.2. Selectivity of sensor for methanol

Addition of methanol (MeOH) to the solution of SPO producedthe color change of solution from orange to colorless. Further inves-tigation found that the absorption bands of SPO at 503 and 485 nmdecreased and disappeared when MeOH was added. As presentedin Fig. 2, the lower detectable limit for MeOH is 173 mg. The selec-tivity of sensor was explored by monitoring the color change ofSPO with other VOCs. It is found that no significant color changewas observed (Fig. 3a) by the addition of other VOCs (acetone, ace-tonitrile, trichloromethane; ethyl acetate; diethyl ether; petroleum;hexane; ethanol; tetrahydrofuran; benzene; toluene; 2-propanol;2-butanol) in the same condition (173 mg). Further studies showedthat no marked absorption changes of SPO at 506 and 485 nmwere detected when the same amount of other VOCs were added,and as represented in Fig. 4a and b, the minimum and maximum

Fig. 2. Absorption changes of SPO (100 �M) with addition of MeOH (amount ofMeOH from top to below: 0, 23, 45, 75, 94, 118, 140, 151, 158, 165 and 173 mg).

256 X. Zhang, Y. Chen / Analytica Chimi

Fig. 3. Photographs of SPO (photostationary state) in DCM with addition of otherVOCs (a) (solvents: 173 mg. 1: without solvent; 2: methanol; 3: ethanol; 4: 2-propanol; 5: toluene; 6: diethyl ether; 7: tetrahydrofuran; 8: ethyl acetate; 9:2-butanol; 10: acetone; 11: acetonitrile; 12: trichloromethane; 13: benzene; 14: hex-ane; 15: petroleum) and with different irradiation time (b) (1: 40 s; 2: 80 s; 3: 120 s;4: 160 s; 5: 200 s; 6: 240 s; 7: 280 s; 8: 320 s; 9: 360 s; 10: 400 s; 11: SPO with additionof MeOH).

Fig. 4. Absorption changes of SPO with addition of EtOH (a) and THF (b) (amountof addition from top to below: 0, 45, 94, 140, 158 and 173 mg).

ca Acta 650 (2009) 254–257

a mixture solution containing MeOH and all above solvents wasadded to the solution of SPO in DCM.

3.3. Light-modulated ratiometric sensor for methanol

As presented in Fig. 1, the absorption of SPO was increased withUV light irradiation till the photostationary state was reached. Itsuggested that the amount (concentration) of SPO (indicator) canbe modulated by controlling irradiation time of SPC solution beforeit reached photostationary state, which enables it possible to reg-ulate the lower detectable limit of methanol. Fig. 3b showed thecolor changes of SPC in DCM (100 �M) at different irradiation time.It is found that the color of solution is more and more darken withincreasing irradiation time, and it indicates that the amount of SPO(indicator) is increased with increasing irradiation time till photo-stationary state reached. The changes of amount of SPO resulted inthe changes of lower detectable limit of MeOH. It is found that theminimum detectable limit of MeOH is 23 mg when the solution ofSPC (100 �M) was irradiated for 40 s (noting: 40 s is the least irradi-ation time, less than 40 s, no yellow color of solution was observed).The detectable limit of MeOH is increased with increase of irradi-ation time (50 mg with irradiation of solution for 80 s and 100 mgwith irradiation of solution for 160 s), and the maximum detectablelimit of MeOH is 173 mg with irradiation of SPC (100 �M) for 400 s,at that time the photostationary state was reached.

3.4. Control experiments

In order to explore the mechanism of the fading of colored SPOwith MeOH, some control experiments were carried out. First, it isfound that the color solution of SPO could not be faded to color-less by the addition of small amount of water or acid, it suggestedthat trace of water or acid did not affect sensor for MeOH detec-tion. Second, the sensor could not be used in pure water systemsince both SPC and SPO did not dissolved in water. We found how-ever that the sensor could also perform detection for MeOH evenif 50% water (v/v) was contained in MeOH, in this case the detec-tion was carried out in heterogeneous solution. Third, absorptionchange showed that MeOH causes the sensor (SPO) to go back tothe ring-closing isomer (SPC), which was further confirmed by TLCplate, where SPC and SPO appeared at the place with Rf = 0.675and 0.169 (elute: ethyl acetate/petroleum = 1:10, v/v), respectively.It is found that the spot with Rf = 0.169 disappeared and a spot withRf = 0.675 appeared when MeOH was added to sensor solution, itindicated that SPO converted back to SPC with addition of MeOHalthough the mechanism is not clear.

4. Conclusions

In summary, we have developed a light-modulated colorimet-ric methanol sensor by using ring-open isomer of photochromicspirophenanthoxazine as indicator. It has been demonstrated thatthe sensor not only has the advantages of naked-eye detection, highselectivity and anti-interference with other VOCs but also can bemodulated and manipulated for methanol detection in a wide rangeof lower detectable limit.

Acknowledgments

This work was supported by National Basic Research Program ofChina (2010CB934103) and Key Laboratory of Photochemical Con-version and Optoelectronic Materials, Technical Institute of Physicsand Chemistry, Chinese Academy of Sciences.

Chimi

R

[[[[

[

[

[

[

[

[

[

[

[

[[[[[[[[

[

[

[[

X. Zhang, Y. Chen / Analytica

eferences

[1] C. Elosua, I.R. Matias, C. Bariain, F.J. Arregui, Sensors 6 (2006) 1440–1465.[2] S.V. Patel, T.E. Mlsna, B. Fruhberger, E. Klaassen, S. Cemalovic, D.R. Baselt, Sens.

Actuators B: Chem. 96 (2003) 541–553.[3] C.K. Ho, A. Robinson, D.R. Miller, M.J. Davis, Sensors 5 (2005) 4–37.[4] M. Bezunartea, J. Estella, J.C. Echeverria, C. Elosua, C. Bariain, M. Laguna, A.

Luquin, J.J. Garrido, Sens. Actuators B 134 (2008) 966–973.[5] M. Mabrook, P. Hawkins, Sens. Actuators B: Chem. 75 (2001) 197–202.[6] J. Kondoh, S. Tabushi, Y. Matsui, S. Shiokawa, Sens. Actuators B 129 (2009)

575–580.[7] R. Von Burg, J. Appl. Toxicol. 14 (1994) 309–313.[8] T.M. Sakanashi, J.M. Rogers, S.S. Fu, L.E. Connelly, C.L. Keen, Teratology 54 (1996)

198–206.[9] A. Youssef, K. Madkour, C. Cox, B. Weiss, J. Appl. Toxicol. 12 (1992) 193–197.10] B. Bolon, F. Welsch, K.T. Morgan, Teratology 49 (1994) 497–517.11] D.M. Mellerick, H. Liu, J. Neurobiol. 60 (2004) 308–318.12] D.R. McLean, H. Jacobs, B.W. Mielke, Ann. Neurol. 8 (1980) 161–167.13] E. Skrzydlewska, M. Elas, R. Farbiszewski, A. Roszkowska, J. Appl. Toxicol. 20

(2000) 239–243.14] Methanol Toxicity, US Department of Health & Human Services, Public Health

Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA, 1992.15] Y.O. Kamatari, K. Akasaka, T. Konno, M. Kataoka, Protein Sci. 7 (1998) 681–

688.16] M.M. Guarna, G.J. Lesnicki, B.M. Tam, J. Kobinson, C.Z. Radziminski, D. Hasen-

winkle, A. Boraston, E. Jervis, R.T.A. MacGillivray, R.F.B. Turner, D.G. Kilburn,Biotechnol. Bioeng. 56 (1997) 279–286.

17] W. Zhang, L.A. Smith, B.A. Plantz, V.L. Schlegel, M.M. Meagher, Biotechnol. Prog.18 (2002) 1392–1399.

18] D. Dewez, C. Dautremepuits, P. Jeandet, G. Vernet, R. Popovic, Photochem. Pho-tobiol. 78 (2003) 420–424.

[

[

[

ca Acta 650 (2009) 254–257 257

[19] N.K. Khatri, F. Hoffmann, Biotechnol. Bioeng. 93 (2006) 871–879.20] V. Diz, M. Cassanello, R. Martin Negri, Environ. Sci. Technol. 40 (2006)

6058–6063.21] R.L. Shepherd, J.N. Barisci, W.A. Collier, A.L. Hart, Electroanalysis 14 (2002)

575–582.22] Y. Vlasov, A. Legin, A. Rdunitskaya, Anal. Bioanal. Chem. 373 (2002) 136–

146.23] C. Krantz-Rulcker, M. Stenberg, F. Winquist, I. Lunistrom, Anal. Chim. Acta 426

(2001) 217–226.24] H. Belghith, J.-L. Romette, P. Thomas, Biotechnol. Bioeng. 30 (1987) 1001–1005.25] R.A. Lieberman, Sens. Actuators B: Chem. 11 (1993) 43–55.26] K.T.V. Grattan, T. Sun, Sens. Actuators A: Phys. 82 (2000) 40–61.27] B. Lee, Opt. Fiber Technol. 9 (2003) 57–79.28] R.W. Kitchin, R.E. Willis, R.L. Cook, Anal. Chem. 53 (1981) 1190–1192.29] Z. Zhao, E.R. Malinowshi, Anal. Chem. 71 (1999) 602–608.30] N. Stevens, D.L. Akins, Sens. Actuators B 123 (2007) 59–64.31] M.C. Paraschievscu, E.G. Alley, W.T. French, R. Hernandez, K. Armbrust, Biore-

sour. Technol. 99 (2008) 5901–5905.32] H. Wang, Y. Li, Y. Chen, M. Yuan, M. Yang, W. Yuan, React. Funct. Polym. 67 (2007)

977–985.33] G. Neri, A. Bonavita, G. Rizzo, S. Galvagno, S. Capone, P. Sciiliano, Sens. Actuators

B 114 (2006) 59–64.34] P.P. Sahay, R.K. Nath, Sens. Actuators B: Chem. 134 (2008) 654–659.35] M. Bezunartea, J. Estella, J.C. Echeverra, C. Elosua, C. Bariain, M. Laguna, A.

Luguin, J.J. Garrido, Sens. Actuators B: Chem. 134 (2008) 966–973.

36] J. Judith Vijaya, L. John Kennedy, G. Sekaran, B. Jeyaraj, K.S. Nagaraja, J. Hazard.

Mater. 153 (2008) 767–774.37] J.C. Crano, R.J. Guglielmetti, Organic Photochromic and Thermochromic Com-

pounds, Plenum Press, New York, 1999.38] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals,

Pergamon press, 1966.