Abstract

We demonstrate a detection method for heavy metal (HM) ions based on whispering gallery mode (WGM) lasing in a liquid crystal (LC) microdroplet biosensor. By doping with stearic acid, nematic LC 4-cyano-4’-pentylbiphenyl (5CB) microdroplets are biochemically functionalized and used as both optical microresonators and sensing elements. Typical WGM lasing emission is observed in stearic acid-doped 5CB microdroplets under a pulse laser pump. Our results show that quantitative spectral shift of WGMs can serve as a real-time indicator of the adsorption of HM ions on the microdroplet surface. The detection limit of our sensor is as low as 40 pM for Cu(II) ions, six orders of magnitude better than the exposure threshold defined by the World Health Organization. Furthermore, this sensing system has an ability to discriminate between heavy and light metal ions. We believe that this novel biosensor has great application potential for environmental monitoring and drinking water quality testing.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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2019 (3)

2018 (1)

J. Zhang, X. Su, D. Yang, and C. Luan, “Label-free liquid crystal biosensor for cecropin B detection,” Talanta 186, 60–64 (2018).
[Crossref]

2017 (3)

2016 (3)

F. Wu, Y. Wu, Z. Niu, and F. Vollmer, “Integrating a DNA Strand Displacement Reaction with a Whispering Gallery Mode Sensor for Label-Free Mercury (II) Ion Detection,” Sensors 16(8), 1197 (2016).
[Crossref]

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tunable whispering gallery modes lasing in dye-doped cholesteric liquid crystal microdroplets,” Appl. Phys. Lett. 109(23), 231906 (2016).
[Crossref]

2015 (1)

2014 (3)

D. S. Miller, X. Wang, and N. L. Abbott, “Design of Functional Materials Based on Liquid Crystalline Droplets,” Chem. Mater. 26(1), 496–506 (2014).
[Crossref]

R. Chen, V. D. Ta, and H. Sun, “Bending-Induced Bidirectional Tuning of whispering gallery mode lasing from flexible polymer fibers,” ACS Photonics 1(1), 11–16 (2014).
[Crossref]

D. Liu and C. H. Jang, “A new strategy for imaging urease activity using liquid crystal droplet patterns formed on solid surfaces,” Sens. Actuators, B 193, 770–773 (2014).
[Crossref]

2013 (5)

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

C.-H. Chen and K.-L. Yang, “A liquid crystal biosensor for detecting organophosphates through the localized pH changes induced by their hydrolytic products,” Sens. Actuators, B 181, 368–374 (2013).
[Crossref]

S. Yang, C. Wu, H. Tan, Y. Wu, S. Liao, Z. Wu, G. Shen, and R. Yu, “Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions,” Anal. Chem. 85(1), 14–18 (2013).
[Crossref]

B. Ashish, K. Neeti, and K. Himanshu, “Copper Toxicity: A Comprehensive Study,” Res. J. Recent Sci. 2, 58–67 (2013).

M. Li, H. Gou, I. Al-Ogaidi, and N. Wu, “Nanostructured Sensors for Detection of Heavy Metals: A Review,” ACS Sustainable Chem. Eng. 1(7), 713–723 (2013).
[Crossref]

2012 (2)

D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
[Crossref]

J. Lafleur, S. Senkbeil, T. G. Jensen, and J. P. Kutter, “Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants,” Lab Chip 12(22), 4651–4656 (2012).
[Crossref]

2011 (5)

X. Fan and I. M. White, “Optofluidic microsystems for chemical and biological analysis,” Nat. Photonics 5(10), 591–597 (2011).
[Crossref]

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

Q.-Z. Hu and C.-H. Jang, “Liquid crystal-based sensors for the detection of heavy metals using surface-immobilized urease,” Colloids Surf., B 88(2), 622–626 (2011).
[Crossref]

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

M. Humar and I. Muševič, “Surfactant sensing based on whispering-gallery-mode lasing in liquid-crystal microdroplets,” Opt. Express 19(21), 19836–19844 (2011).
[Crossref]

2010 (1)

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

2009 (2)

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

M. Humar, M. Ravnik, S. Pajk, and I. Musevic, “Electrically tunable liquid crystal optical microresonators,” Nat. Photonics 3(10), 595–600 (2009).
[Crossref]

2008 (3)

A. D. Price and D. K. Schwartz, “DNA hybridization-induced reorientation of liquid crystal anchoring at the nematic liquid crystal/aqueous interface,” J. Am. Chem. Soc. 130(26), 8188–8194 (2008).
[Crossref]

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
[Crossref]

F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5(7), 591–596 (2008).
[Crossref]

2007 (3)

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007).
[Crossref]

M. I. Kinsinger, B. Sun, N. L. Abbott, and D. M. Lynn, “Reversible control of ordering transitions at aqueous/liquid crystal interfaces using functional amphiphilic polymers,” Adv. Mater. 19(23), 4208–4212 (2007).
[Crossref]

J. O. Duruibe, M. O. C. Ogwuegbu, and J. N. Egwurugwu, “Heavy metal pollution and human biotoxic effects,” Int. J. Phys. Sci. 2(5), 112–118 (2007).

2006 (2)

N. H. Bings, A. Bogaerts, and J. A. C. Broekaert, “Atomic Spectroscopy,” Anal. Chem. 78(12), 3917–3946 (2006).
[Crossref]

N. M. Hanumegowda, I. M. White, and X. D. Fan, “Aqueous mercuric ion detection with microsphere optical ring resonator sensors,” Sens. Actuators, B 120(1), 207–212 (2006).
[Crossref]

2004 (1)

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
[Crossref]

2003 (4)

L. Järup, “Hazards of heavy metal contamination,” Br. Med. Bull. 68(1), 167–182 (2003).
[Crossref]

J. M. Brake, M. K. Daschner, Y. Y. Luk, and N. L. Abbott, “Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals,” Science 302(5653), 2094–2097 (2003).
[Crossref]

K. J. Vahala, “Optical microcavities,” Nature 424(6950), 839–846 (2003).
[Crossref]

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, “Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities,” Biophys. J. 85(3), 1974–1979 (2003).
[Crossref]

1997 (1)

J. Y. Hyun, G. S. Lee, T. Y. Kim, and D. J. Ahn, “Selectivity of heavy metal ions at acidic supramolecular surfaces,” Korean J. Chem. Eng. 14(6), 533–540 (1997).
[Crossref]

1986 (1)

K. E. Lorber, “Monitoring of Heavy Metals by Energy Dispersive X-ray Fluorescence Spectrometry,” Waste Manage. Res. 4(1), 3–13 (1986).
[Crossref]

1973 (1)

R. Kunkel and S. E. Manahan, “Atomic Absorption Analysis of Strong Heavy Metal Chelating Agents in Water and Waste Water,” Anal. Chem. 45(8), 1465–1468 (1973).
[Crossref]

Aas, M.

Abbasi, R.

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

Abbott, N. L.

D. S. Miller, X. Wang, and N. L. Abbott, “Design of Functional Materials Based on Liquid Crystalline Droplets,” Chem. Mater. 26(1), 496–506 (2014).
[Crossref]

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

M. I. Kinsinger, B. Sun, N. L. Abbott, and D. M. Lynn, “Reversible control of ordering transitions at aqueous/liquid crystal interfaces using functional amphiphilic polymers,” Adv. Mater. 19(23), 4208–4212 (2007).
[Crossref]

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
[Crossref]

J. M. Brake, M. K. Daschner, Y. Y. Luk, and N. L. Abbott, “Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals,” Science 302(5653), 2094–2097 (2003).
[Crossref]

Ahn, D. J.

J. Y. Hyun, G. S. Lee, T. Y. Kim, and D. J. Ahn, “Selectivity of heavy metal ions at acidic supramolecular surfaces,” Korean J. Chem. Eng. 14(6), 533–540 (1997).
[Crossref]

Al-Ogaidi, I.

M. Li, H. Gou, I. Al-Ogaidi, and N. Wu, “Nanostructured Sensors for Detection of Heavy Metals: A Review,” ACS Sustainable Chem. Eng. 1(7), 713–723 (2013).
[Crossref]

Armani, A. M.

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007).
[Crossref]

Arnold, S.

F. Vollmer and S. Arnold, “Whispering-gallery-mode biosensing: label-free detection down to single molecules,” Nat. Methods 5(7), 591–596 (2008).
[Crossref]

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, “Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities,” Biophys. J. 85(3), 1974–1979 (2003).
[Crossref]

Ashish, B.

B. Ashish, K. Neeti, and K. Himanshu, “Copper Toxicity: A Comprehensive Study,” Res. J. Recent Sci. 2, 58–67 (2013).

Ashoka, S.

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

Bell, J.

D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
[Crossref]

Bernatová, S.

Bertics, P. J.

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

Bings, N. H.

N. H. Bings, A. Bogaerts, and J. A. C. Broekaert, “Atomic Spectroscopy,” Anal. Chem. 78(12), 3917–3946 (2006).
[Crossref]

Bogaerts, A.

N. H. Bings, A. Bogaerts, and J. A. C. Broekaert, “Atomic Spectroscopy,” Anal. Chem. 78(12), 3917–3946 (2006).
[Crossref]

Brake, J. M.

J. M. Brake, M. K. Daschner, Y. Y. Luk, and N. L. Abbott, “Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals,” Science 302(5653), 2094–2097 (2003).
[Crossref]

Braun, D.

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, “Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities,” Biophys. J. 85(3), 1974–1979 (2003).
[Crossref]

Bremner, G.

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

Broekaert, J. A. C.

N. H. Bings, A. Bogaerts, and J. A. C. Broekaert, “Atomic Spectroscopy,” Anal. Chem. 78(12), 3917–3946 (2006).
[Crossref]

Caldwell, C. W.

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
[Crossref]

Carlton, R. J.

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

Chen, C.-H.

C.-H. Chen and K.-L. Yang, “A liquid crystal biosensor for detecting organophosphates through the localized pH changes induced by their hydrolytic products,” Sens. Actuators, B 181, 368–374 (2013).
[Crossref]

Chen, C.-Y.

Chen, F.-L.

Chen, J.

Chen, R.

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

R. Chen, V. D. Ta, and H. Sun, “Bending-Induced Bidirectional Tuning of whispering gallery mode lasing from flexible polymer fibers,” ACS Photonics 1(1), 11–16 (2014).
[Crossref]

Daschner, M. K.

J. M. Brake, M. K. Daschner, Y. Y. Luk, and N. L. Abbott, “Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals,” Science 302(5653), 2094–2097 (2003).
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I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
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D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
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Demir, H. V.

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

Dickson, K. A.

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
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G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Duruibe, J. O.

J. O. Duruibe, M. O. C. Ogwuegbu, and J. N. Egwurugwu, “Heavy metal pollution and human biotoxic effects,” Int. J. Phys. Sci. 2(5), 112–118 (2007).

Egwurugwu, J. N.

J. O. Duruibe, M. O. C. Ogwuegbu, and J. N. Egwurugwu, “Heavy metal pollution and human biotoxic effects,” Int. J. Phys. Sci. 2(5), 112–118 (2007).

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X. Fan and I. M. White, “Optofluidic microsystems for chemical and biological analysis,” Nat. Photonics 5(10), 591–597 (2011).
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Fan, X. D.

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
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N. M. Hanumegowda, I. M. White, and X. D. Fan, “Aqueous mercuric ion detection with microsphere optical ring resonator sensors,” Sens. Actuators, B 120(1), 207–212 (2006).
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Fan, Y.-J.

Faye, D.

D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
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G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Ferrari, M.

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Flagan, R. C.

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007).
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W. Salomons, U. Forstner, and P. Mader, Heavy Metals: Problems and Solutions (Springer, 1995).

Fort, T.

Fraser, S. E.

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007).
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M. Li, H. Gou, I. Al-Ogaidi, and N. Wu, “Nanostructured Sensors for Detection of Heavy Metals: A Review,” ACS Sustainable Chem. Eng. 1(7), 713–723 (2013).
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Hageman, K. J.

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

Hanumegowda, N. M.

N. M. Hanumegowda, I. M. White, and X. D. Fan, “Aqueous mercuric ion detection with microsphere optical ring resonator sensors,” Sens. Actuators, B 120(1), 207–212 (2006).
[Crossref]

He, T.

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

Hesht, B.

L. Novotny and B. Hesht, Principles of Nano-Optics (Cambridge University Press, ti2006)

Himanshu, K.

B. Ashish, K. Neeti, and K. Himanshu, “Copper Toxicity: A Comprehensive Study,” Res. J. Recent Sci. 2, 58–67 (2013).

Hsiao, Y.-C.

Hsu, W.-L.

Hu, Q.-Z.

Q.-Z. Hu and C.-H. Jang, “Liquid crystal-based sensors for the detection of heavy metals using surface-immobilized urease,” Colloids Surf., B 88(2), 622–626 (2011).
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M. Humar and I. Muševič, “Surfactant sensing based on whispering-gallery-mode lasing in liquid-crystal microdroplets,” Opt. Express 19(21), 19836–19844 (2011).
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M. Humar, M. Ravnik, S. Pajk, and I. Musevic, “Electrically tunable liquid crystal optical microresonators,” Nat. Photonics 3(10), 595–600 (2009).
[Crossref]

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R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
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J. Y. Hyun, G. S. Lee, T. Y. Kim, and D. J. Ahn, “Selectivity of heavy metal ions at acidic supramolecular surfaces,” Korean J. Chem. Eng. 14(6), 533–540 (1997).
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Jang, C. H.

D. Liu and C. H. Jang, “A new strategy for imaging urease activity using liquid crystal droplet patterns formed on solid surfaces,” Sens. Actuators, B 193, 770–773 (2014).
[Crossref]

Jang, C.-H.

Q.-Z. Hu and C.-H. Jang, “Liquid crystal-based sensors for the detection of heavy metals using surface-immobilized urease,” Colloids Surf., B 88(2), 622–626 (2011).
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J. Lafleur, S. Senkbeil, T. G. Jensen, and J. P. Kutter, “Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants,” Lab Chip 12(22), 4651–4656 (2012).
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Ježek, J.

Jonáš, A.

Khan, W.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
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Kim, T. Y.

J. Y. Hyun, G. S. Lee, T. Y. Kim, and D. J. Ahn, “Selectivity of heavy metal ions at acidic supramolecular surfaces,” Korean J. Chem. Eng. 14(6), 533–540 (1997).
[Crossref]

Kinsinger, M. I.

M. I. Kinsinger, B. Sun, N. L. Abbott, and D. M. Lynn, “Reversible control of ordering transitions at aqueous/liquid crystal interfaces using functional amphiphilic polymers,” Adv. Mater. 19(23), 4208–4212 (2007).
[Crossref]

Kiraz, A.

Kornfield, J. A.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

Kulkarni, R. P.

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007).
[Crossref]

Kunkel, R.

R. Kunkel and S. E. Manahan, “Atomic Absorption Analysis of Strong Heavy Metal Chelating Agents in Water and Waste Water,” Anal. Chem. 45(8), 1465–1468 (1973).
[Crossref]

Kurjib, Z.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

Kutter, J. P.

J. Lafleur, S. Senkbeil, T. G. Jensen, and J. P. Kutter, “Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants,” Lab Chip 12(22), 4651–4656 (2012).
[Crossref]

Lafleur, J.

J. Lafleur, S. Senkbeil, T. G. Jensen, and J. P. Kutter, “Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants,” Lab Chip 12(22), 4651–4656 (2012).
[Crossref]

Lee, D. Y.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

Lee, G. S.

J. Y. Hyun, G. S. Lee, T. Y. Kim, and D. J. Ahn, “Selectivity of heavy metal ions at acidic supramolecular surfaces,” Korean J. Chem. Eng. 14(6), 533–540 (1997).
[Crossref]

Lee, M.-J.

Lee, W.

Lee, Y.-H.

Lefevre, J. P.

D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
[Crossref]

Leray, I.

D. Faye, H. Zhang, J. P. Lefevre, J. Bell, J. Delaire, and I. Leray, “Mercury detection in a microfluidic device by using a molecular sensor soluble in organoaqueous solvent,” Photochem. Photobiol. Sci. 11(11), 1737–1743 (2012).
[Crossref]

Li, H.

L. Zhao, Y. Wang, Y. Yuan, Y. Liu, S. Liu, W. Sun, J. Yang, and H. Li, “Whispering gallery mode laser based on cholesteric liquid crystal microdroplets as temperature sensor,” Opt. Commun. 402, 181–185 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tapered optical fiber waveguide coupling to whispering gallery modes of liquid crystal microdroplet for thermal sensing application,” Opt. Express 25(2), 918–926 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tunable whispering gallery modes lasing in dye-doped cholesteric liquid crystal microdroplets,” Appl. Phys. Lett. 109(23), 231906 (2016).
[Crossref]

Li, M.

M. Li, H. Gou, I. Al-Ogaidi, and N. Wu, “Nanostructured Sensors for Detection of Heavy Metals: A Review,” ACS Sustainable Chem. Eng. 1(7), 713–723 (2013).
[Crossref]

Liao, S.

S. Yang, C. Wu, H. Tan, Y. Wu, S. Liao, Z. Wu, G. Shen, and R. Yu, “Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions,” Anal. Chem. 85(1), 14–18 (2013).
[Crossref]

Libchaber, A.

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, “Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities,” Biophys. J. 85(3), 1974–1979 (2003).
[Crossref]

Lin, I. H.

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

Lin, J.-D.

Liu, D.

D. Liu and C. H. Jang, “A new strategy for imaging urease activity using liquid crystal droplet patterns formed on solid surfaces,” Sens. Actuators, B 193, 770–773 (2014).
[Crossref]

Liu, S.

L. Zhao, Y. Wang, Y. Yuan, Y. Liu, S. Liu, W. Sun, J. Yang, and H. Li, “Whispering gallery mode laser based on cholesteric liquid crystal microdroplets as temperature sensor,” Opt. Commun. 402, 181–185 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tapered optical fiber waveguide coupling to whispering gallery modes of liquid crystal microdroplet for thermal sensing application,” Opt. Express 25(2), 918–926 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tunable whispering gallery modes lasing in dye-doped cholesteric liquid crystal microdroplets,” Appl. Phys. Lett. 109(23), 231906 (2016).
[Crossref]

Liu, Y.

L. Zhao, Y. Wang, Y. Yuan, Y. Liu, S. Liu, W. Sun, J. Yang, and H. Li, “Whispering gallery mode laser based on cholesteric liquid crystal microdroplets as temperature sensor,” Opt. Commun. 402, 181–185 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tapered optical fiber waveguide coupling to whispering gallery modes of liquid crystal microdroplet for thermal sensing application,” Opt. Express 25(2), 918–926 (2017).
[Crossref]

Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tunable whispering gallery modes lasing in dye-doped cholesteric liquid crystal microdroplets,” Appl. Phys. Lett. 109(23), 231906 (2016).
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K. E. Lorber, “Monitoring of Heavy Metals by Energy Dispersive X-ray Fluorescence Spectrometry,” Waste Manage. Res. 4(1), 3–13 (1986).
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Luan, C.

J. Zhang, X. Su, D. Yang, and C. Luan, “Label-free liquid crystal biosensor for cecropin B detection,” Talanta 186, 60–64 (2018).
[Crossref]

Luk, Y. Y.

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
[Crossref]

J. M. Brake, M. K. Daschner, Y. Y. Luk, and N. L. Abbott, “Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals,” Science 302(5653), 2094–2097 (2003).
[Crossref]

Lynn, D. M.

M. I. Kinsinger, B. Sun, N. L. Abbott, and D. M. Lynn, “Reversible control of ordering transitions at aqueous/liquid crystal interfaces using functional amphiphilic polymers,” Adv. Mater. 19(23), 4208–4212 (2007).
[Crossref]

Mader, P.

W. Salomons, U. Forstner, and P. Mader, Heavy Metals: Problems and Solutions (Springer, 1995).

Manahan, S. E.

R. Kunkel and S. E. Manahan, “Atomic Absorption Analysis of Strong Heavy Metal Chelating Agents in Water and Waste Water,” Anal. Chem. 45(8), 1465–1468 (1973).
[Crossref]

Miller, D. S.

D. S. Miller, X. Wang, and N. L. Abbott, “Design of Functional Materials Based on Liquid Crystalline Droplets,” Chem. Mater. 26(1), 496–506 (2014).
[Crossref]

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

Murphy, C. J.

I. H. Lin, D. S. Miller, P. J. Bertics, C. J. Murphy, J. J. De Pablo, and N. L. Abbott, “Endotoxin-induced structural transformations in liquid crystalline droplets,” Science 332(6035), 1297–1300 (2011).
[Crossref]

Musevic, I.

M. Humar, M. Ravnik, S. Pajk, and I. Musevic, “Electrically tunable liquid crystal optical microresonators,” Nat. Photonics 3(10), 595–600 (2009).
[Crossref]

Muševic, I.

Mushenheim, P. C.

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

Neeti, K.

B. Ashish, K. Neeti, and K. Himanshu, “Copper Toxicity: A Comprehensive Study,” Res. J. Recent Sci. 2, 58–67 (2013).

Niu, Z.

F. Wu, Y. Wu, Z. Niu, and F. Vollmer, “Integrating a DNA Strand Displacement Reaction with a Whispering Gallery Mode Sensor for Label-Free Mercury (II) Ion Detection,” Sensors 16(8), 1197 (2016).
[Crossref]

Novotny, L.

L. Novotny and B. Hesht, Principles of Nano-Optics (Cambridge University Press, ti2006)

Nunzi Conti, G.

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Ogwuegbu, M. O. C.

J. O. Duruibe, M. O. C. Ogwuegbu, and J. N. Egwurugwu, “Heavy metal pollution and human biotoxic effects,” Int. J. Phys. Sci. 2(5), 112–118 (2007).

Pajk, S.

M. Humar, M. Ravnik, S. Pajk, and I. Musevic, “Electrically tunable liquid crystal optical microresonators,” Nat. Photonics 3(10), 595–600 (2009).
[Crossref]

Park, S. Y.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

Peake, B. M.

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

Pilát, Z.

Price, A. D.

A. D. Price and D. K. Schwartz, “DNA hybridization-induced reorientation of liquid crystal anchoring at the nematic liquid crystal/aqueous interface,” J. Am. Chem. Soc. 130(26), 8188–8194 (2008).
[Crossref]

Raines, R. T.

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
[Crossref]

Ravnik, M.

M. Humar, M. Ravnik, S. Pajk, and I. Musevic, “Electrically tunable liquid crystal optical microresonators,” Nat. Photonics 3(10), 595–600 (2009).
[Crossref]

Reid, M. R.

S. Ashoka, B. M. Peake, G. Bremner, K. J. Hageman, and M. R. Reid, “Comparison of digestion methods for ICP-MS determination of trace elements in fish tissues,” Anal. Chim. Acta 653(2), 191–199 (2009).
[Crossref]

Righini, G. C.

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Ristic, D.

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Salomons, W.

W. Salomons, U. Forstner, and P. Mader, Heavy Metals: Problems and Solutions (Springer, 1995).

Schwartz, D. K.

A. D. Price and D. K. Schwartz, “DNA hybridization-induced reorientation of liquid crystal anchoring at the nematic liquid crystal/aqueous interface,” J. Am. Chem. Soc. 130(26), 8188–8194 (2008).
[Crossref]

Senkbeil, S.

J. Lafleur, S. Senkbeil, T. G. Jensen, and J. P. Kutter, “Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants,” Lab Chip 12(22), 4651–4656 (2012).
[Crossref]

Seo, J. M.

D. Y. Lee, J. M. Seo, W. Khan, J. A. Kornfield, Z. Kurjib, and S. Y. Park, “pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers,” Soft Matter 6(9), 1964–1970 (2010).
[Crossref]

Shen, G.

S. Yang, C. Wu, H. Tan, Y. Wu, S. Liao, Z. Wu, G. Shen, and R. Yu, “Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions,” Anal. Chem. 85(1), 14–18 (2013).
[Crossref]

Shi, H. D.

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
[Crossref]

Song, X.

Soria, S.

G. C. Righini, Y. Dumeige, P. Féron, M. Ferrari, G. Nunzi Conti, D. Ristic, and S. Soria, “Whispering gallery mode microresonators: fundamentals and applications,” Riv. Nuovo Cim. 34, 435–488 (2011).

Su, X.

J. Zhang, X. Su, D. Yang, and C. Luan, “Label-free liquid crystal biosensor for cecropin B detection,” Talanta 186, 60–64 (2018).
[Crossref]

Sun, B.

M. I. Kinsinger, B. Sun, N. L. Abbott, and D. M. Lynn, “Reversible control of ordering transitions at aqueous/liquid crystal interfaces using functional amphiphilic polymers,” Adv. Mater. 19(23), 4208–4212 (2007).
[Crossref]

Sun, H.

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

R. Chen, V. D. Ta, and H. Sun, “Bending-Induced Bidirectional Tuning of whispering gallery mode lasing from flexible polymer fibers,” ACS Photonics 1(1), 11–16 (2014).
[Crossref]

Sun, S.-H.

Sun, W.

L. Zhao, Y. Wang, Y. Yuan, Y. Liu, S. Liu, W. Sun, J. Yang, and H. Li, “Whispering gallery mode laser based on cholesteric liquid crystal microdroplets as temperature sensor,” Opt. Commun. 402, 181–185 (2017).
[Crossref]

Sutter, J. D.

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
[Crossref]

Ta, V. D.

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
[Crossref]

R. Chen, V. D. Ta, and H. Sun, “Bending-Induced Bidirectional Tuning of whispering gallery mode lasing from flexible polymer fibers,” ACS Photonics 1(1), 11–16 (2014).
[Crossref]

Tan, H.

S. Yang, C. Wu, H. Tan, Y. Wu, S. Liao, Z. Wu, G. Shen, and R. Yu, “Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions,” Anal. Chem. 85(1), 14–18 (2013).
[Crossref]

Tan, L. N.

R. J. Carlton, J. T. Hunter, D. S. Miller, R. Abbasi, P. C. Mushenheim, L. N. Tan, and N. L. Abbott, “Chemical and biological sensing using liquid crystals,” Liq. Cryst. Rev. 1(1), 29–51 (2013).
[Crossref]

Teraoka, I.

F. Vollmer, S. Arnold, D. Braun, I. Teraoka, and A. Libchaber, “Multiplexed DNA quantification by spectroscopic shift of two microsphere cavities,” Biophys. J. 85(3), 1974–1979 (2003).
[Crossref]

Tingey, M. L.

Y. Y. Luk, M. L. Tingey, K. A. Dickson, R. T. Raines, and N. L. Abbott, “Imaging the binding ability of proteins immobilized on surfaces with different orientations by using liquid crystals,” J. Am. Chem. Soc. 126(29), 9024–9032 (2004).
[Crossref]

Vahala, K. J.

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S. Yang, C. Wu, H. Tan, Y. Wu, S. Liao, Z. Wu, G. Shen, and R. Yu, “Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions,” Anal. Chem. 85(1), 14–18 (2013).
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J. Zhang, X. Su, D. Yang, and C. Luan, “Label-free liquid crystal biosensor for cecropin B detection,” Talanta 186, 60–64 (2018).
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J. Zhang, X. Su, D. Yang, and C. Luan, “Label-free liquid crystal biosensor for cecropin B detection,” Talanta 186, 60–64 (2018).
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Y. Wang, H. Li, L. Zhao, Y. Liu, S. Liu, and J. Yang, “Tapered optical fiber waveguide coupling to whispering gallery modes of liquid crystal microdroplet for thermal sensing application,” Opt. Express 25(2), 918–926 (2017).
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Biosens. Bioelectron. (1)

X. D. Fan, J. D. Sutter, I. M. White, H. Y. Zhu, H. D. Shi, and C. W. Caldwell, “Label-free quantitative DNA detection using the liquid core optical ring resonator,” Biosens. Bioelectron. 23(7), 1003–1009 (2008).
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Opt. Commun. (1)

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Sci. Rep. (1)

S. Yang, V. D. Ta, Y. Wang, R. Chen, T. He, H. V. Demir, and H. Sun, “Reconfiurable Liquid Whispering Gallery Mode Microlasers,” Sci. Rep. 6(1), 27200 (2016).
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Science (3)

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Figures (8)

Fig. 1.
Fig. 1. (a) Schematic diagram of the experimental platform. The 532 nm pump light was guided to the surface of the stearic acid-doped 5CB microdroplet via a fiber tip. A drop of aqueous solution deposited onto a polymethylmethacrylate (PMMA) substrate served as the host medium for the 5CB microdroplet. (b) Micrographs of the stearic acid-doped 5CB microdroplets with different diameters. The microdroplets were generated from the same microtube connected to a syringe pump. Scale bars 20 µm. (c) Micrograph of microdroplet excited by a fiber tip positioned correctly within its vicinity.
Fig. 2.
Fig. 2. POM images (recorded after 30 min) of 60 µm stearic acid-doped 5CB microdroplets in PBS solutions with different pH levels: (a) pH = 6.5, (b) pH = 7.5, and (c) pH = 8.5. Four independent experiments were conducted at each pH. Scale bars 20 µm.
Fig. 3.
Fig. 3. Schematic illustration of the orientational transition of stearic acid-doped 5CB microdroplets induced by changes of 5CB anchoring at the LC/aqueous solution interface: (a) without HM ions at pH = 6.5; (b) without HM ions at pH = 8.5 and (c) with HM ions at pH = 8.5.
Fig. 4.
Fig. 4. (a) Lasing emission spectra of stearic acid-doped 5CB microdroplets with diameters ranging from 40 to 60 µm. Inset: the photoluminescence images of the corresponding microlasers under excitation. Scale bar 20 µm. (b) Relationship between FSRs and 1/D. Red line is a linear fitting curve. FSRs are inversely proportional to the 5CB microdroplet diameters.
Fig. 5.
Fig. 5. (a) Wavelength shift of WGM lasing spectra of stearic acid-doped 5CB microdroplet in PBS at pH = 8.5. POM images of the corresponding droplet configurations are illustrated in insets (1) and (2). (b) Schematic illustrations of possible director configurations (first row), bright field images (second row), and polarized optical microscope images (third row) of stearic acid-doped 5CB microdroplets in PBS at pH = 8.5. The microdroplet gradually changes from a bipolar configuration to a radial configuration within 45 seconds. Scale bar 20 µm.
Fig. 6.
Fig. 6. (a) Evolution of the POM images of stearic acid-doped 5CB microdroplets incubated with 200 pM copper(II) chloride in PBS solution (pH = 8.5). Scale bar 20 µm. (b) Lasing spectra of stearic acid-doped 5CB microdroplet incubated with 200 pM copper(II) chloride in PBS solution (pH = 8.5) as a function of time. Black dots indicate the position of the WGM selected to monitor spectral shifting of the droplet lasing emission
Fig. 7.
Fig. 7. (a) Temporal dependence of WGM wavelength shift with different Cu(II) concentrations. All experiments were conducted three times. (b) Average absolute initial rates of WGM wavelength shift as a function of Cu(II) concentration.
Fig. 8.
Fig. 8. Comparison of WGM wavelength shift for various common HMs [(Hg(II), Cu(II), Cd(II) and Zn(II)] and alkaline earth metals [Mg(II) and Ca(II)] at concentrations of 400 pM. The test was performed in PBS solution with pH = 8.5.

Equations (1)

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λ 1 ( R , n 1 , n r , q , m ) = 1 2 π R n 1 [ m + 1 2 + 2 1 / 3 α ( q ) ( m + 1 2 ) 1 / 3 L ( n r 2 1 ) 1 / 2   + 3 10 2 2 / 3 α 2 ( q ) ( m + 1 2 ) 1 / 3 2 1 / 3 L ( n r 2 2 3 L 2 ) α ( q ) ( m + 1 2 ) 2 / 3 ( n r 2 1 ) 3 / 2 ]