DOI: 10.3390/s8010561. Review on Hydrogel-based pH Sensors and Microsensors

Review on Hydrogel-based pH Sensors and Microsensors

10.3390/s8010561

Crossref journal-article

MDPI AG

Sensors (1968)

Abstract

Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background of the special properties of stimuli-responsive hydrogels. Following, transducers are described which are able to convert the non-electrical changes of the physical properties of stimuli-responsive hydrogels into an electrical signal. Finally, the specific sensor properties, design rules and general conditions for sensor applications are discussed.

Bibliography

Richter, A., Paschew, G., Klatt, S., Lienig, J., Arndt, K.-F., & Adler, H.-J. P. (2008). Review on Hydrogel-based pH Sensors and Microsensors. Sensors, 8(1), 561â581.

Authors 6

Andreas Richter (first)
Georgi Paschew (additional)
Stephan Klatt (additional)
Jens Lienig (additional)
Karl-Friedrich Arndt (additional)
Hans-Jürgen P. Adler (additional)

References 90 Referenced 677

10.1007/BF02172635 / Experientia / Reversible Dehnung und Kontraktion bei Änderung der Ionisation eines Netzwerks polyvalenter Fadenmolekülionen by Kuhn (1949)
10.1038/165514a0 / Nature / Reversible dilation and contraction by changing the state of ionization of high-polymer acid networks by Kuhn (1950)
10.1007/BF02172636 / Experientia / Rapid swelling and deswelling of reversible gels of polymeric acids by ionization by Katchalsky (1949)
10.1007/BF00906477 / Monatsh. Chem. / Über Quellung von vernetzter Polymethacrylsäure by Breitenbach (1949)
10.1103/PhysRevLett.40.820 / Phys. Rev. Lett. / Collapse of gels and the critical endpoint by Tanaka (1978)
10.1126/science.218.4571.467 / Science / Collapse of gels in an electric-field by Tanaka (1982)
10.1038/346345a0 / Nature / Phase-transition in polymer gels induced by visible-light by Suzuki (1990)
10.1021/ac0343026 / Anal. Chem. / Detection of CrO42- using a hydrogel swelling microcantilever sensor by Zhang (2003)
10.1016/0032-3861(93)90160-C / Polymer / Stimuli-responsive polymers: chemical induced reversible phase separation of an aqueous solution of poly(N-isopropylacrylamide) with pendent crown ether groups by Irie (1993)
10.1039/fd9950100201 / Faraday Discuss. / Polymer gels that can recognize and recover molecules by Tanaka (1995)
10.1016/S1381-5148(02)00055-X / React. Funct. Polym. / Synthesis and characterisation of a polyacrylamide-polyacrylic acid copolymer hydrogel for environmental analysis of Cu and Cd by Li (2002)
10.1016/S0924-4247(99)00080-1 / Sens. Actuat. A / Photopatterning of thermally sensitive hydrogels useful for microactuators by Hoffmann (1999)
10.1002/masy.19991420112 / Macromol. Symp. / Photocrosslinking of thin polymer films - Materials for sensors and actuators by Kuckling (1999)
10.1002/(SICI)1099-1581(199906)10:6<345::AID-PAT885>3.0.CO;2-N / Polym. Adv. Technol. / Photocrosslinking of thin films of temperature-sensitive polymers by Kuckling (1999)
10.1038/35007047 / Nature / Functional hydrogel structures for autonomous flow control inside microfluidic channels by Beebe (2000)
10.1002/1099-1581(200008/12)11:8/12<496::AID-PAT996>3.0.CO;2-7 / Polym. Adv. Techn. / Application of sensitive hydrogels in flow control by Arndt (2000)
10.1109/JMEMS.2003.817898 / J. Microelectromech. Syst. / Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications by Richter (2003)
10.1002/masy.200450650 / Macromol. Symp. / Automatically and electronically controllable hydrogel based valves and microvalves – design and operating performance by Richter (2004)
10.1021/ac026455j / Anal. Chem. / Flow control valves for analytical microfluidic chips without mechanical parts based on thermally responsive monolithic polymers by Yu (2003)
10.1007/s10544-005-6073-z / Biomed. Microdev. / Self-actuated, thermo-responsive hydrogel valves for lab on a chip by Wang (2005)
Richter, A., and Arndt, K.F. (1999). 5th Internat. Symp. on Polym. Adv. Technol.
10.1109/JMEMS.2003.818070 / J. Microelectromech. Syst. / A hydrogel-actuated environmentally sensitive microvalve for active flow control by Baldi (2003)
10.1002/mame.200390007 / Macromol. Mater. Eng. / Temperature and pH dependent swelling behavior of poly(N-isopropylacrylamide)-copolymer and their use in flow control by Kuckling (2003)
10.1016/S0032-3861(03)00463-4 / Polymer / A microfluidic actuator based on thermoresponsive hydrogels by Harmon (2003)
10.1016/S0925-4005(01)01028-0 / Sens. Actuat. B / A disposable “intelligent mosquito” with a reversible sampling mechanism using the volume-phase transition of a gel by Suzuki (2002)
10.1109/JMEMS.2004.832190 / J. Microelectromech. Syst. / A valved responsive hydrogel microdispensing device with integrated pressure source by Eddington (2004)
10.1002/masy.200450642 / Macromol. Symp. / Adjustable low dynamic pumps based on hydrogels by Richter (2004)
10.1002/adma.200601989 / Adv. Mater. / Controlled double-sensitivity of microgels applied to electronically adjustable chemostats by Richter (2007)
10.1016/j.snb.2007.03.002 / Sens. Actuat. B / Mechanically adjustable chemostats based on stimuli-responsive polymers by Richter (2007)
Hydrogel Valves – Dead-Volume-Free Microfluidic Switches Data sheet 2007. http://www.gesim.de/upload/PDFs/Hydrogel_en.pdf.
10.1039/b210140h / Analyst / Stimulus-sensitive hydrogels and their applications in chemical (micro)analysis by Herber (2003)
10.1002/masy.200450323 / Macromol. Symp. / High response smart gels: synthesis and application by Arndt (2004)
10.1063/1.1723791 / J. Chem. Phys. / Statistical mechanics of cross-linked polymer networks I. Rubber elasticity by Flory (1943)
10.1063/1.1723792 / J. Chem. Phys. / Statistical mechanics of cross-linked polymer networks II. Swelling by Flory (1943)
10.1063/1.1750930 / J. Chem. Phys. / Solutions of long chain compounds by Huggins (1941)
10.1063/1.1750971 / J. Chem. Phys. / Thermodynamics of high polymer solutions by Flory (1941)
10.1021/ma00189a021 / Macromolecules / pH-dependent equilibrium swelling properties of hydrophobic polyelectrolyte copolymer gels by Siegel (1988)
10.1063/1.474516 / J. Chem. Phys. / Equilibrium and non-equilibrium phase transitions in copolymer polyelectrolyte hydrogels by English (1997)
Tanaka, T. (2000). Experimental Methods in Polymer Science, Academic Press Cambridge Burlington.
10.1063/1.1680734 / J. Chem. Phys. / Spectrum of light scattered from a viscoelastic gel by Tanaka (1973)
10.1063/1.437602 / J. Chem. Phys. / Kinetics of swelling of gels by Tanaka (1979)
10.1063/1.458148 / J. Chem. Phys. / Kinetics of swelling and shrinking of gels by Li (1990)
10.1016/S0966-7822(97)00024-5 / Polym. Gels Networks / A method for studying swelling kinetics based on measurement of electrical conductivity by Lesho (1997)
10.1007/s00604-003-0077-2 / Microchim. Acta / An optical chemical sensor based on swellable dicarboxylate functionalized polymer microspheres for pH copper and calcium determination by Shakhsher (2004)
10.1016/j.snb.2004.04.033 / Sens. Actuat. B / Chemical modulation of thermosensitive poly(N-isopropylacryl-amide) microsphere swelling: a new strategy for chemical sensing by Oktar (2005)
10.1016/S0925-4005(98)00238-X / Sens. Actuat. B / Integrated optical pH sensor using replicated chirped grating coupler sensor chips by Kunz (1998)
10.1039/a902183c / Anal. Comm. / An optically sensitive membrane for pH based on swellable polymer microspheres in a hydrogel by Rooney (1999)
10.1016/S0003-2670(99)00608-X / Anal. Chim. Acta / Derivatized, swellable polymer microspheres for chemical transduction by Seitz (1999)
10.1021/ac00082a021 / Anal. Chem. / Single fiber-optic pH sensor based on changes in reflection accompanying polymer swelling by Shakhsher (1994)
10.1016/S0039-9140(97)00080-5 / Talanta / A sensor for pH based on an optical reflective device coupled to the swelling of an aminated polystyrene membrane by Zhang (1997)
10.1007/BF01248239 / Microchim. Acta / Aminated polystyrene membranes for a fiber optic pH sensor based on reflectance changes accompanying polymer swelling by Zhang (1995)
10.1016/0925-4005(95)85036-8 / Sens. Actuat B / The use of metal-island-coated pH-sensitive swelling polymers for biosensor applications by Schalkhammer (1995)
10.1016/0925-4005(95)01684-8 / Sens. Actuat. B / Metal island coated polymer swelling over mirror system (MICSPOMS): a new principle for measure ionic strength by Aussenegg (1995)
10.1038/39834 / Nature / Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials by Holtz (1997)
10.1021/ja002017n / J. Am. Chem. Soc. / Photonic crystal chemical sensors: pH and ionic strength by Lee (2000)
10.1007/s00216-006-1088-8 / Anal. Bioanal. Chem. / Cation identity dependence of crown ether photonic crystal Pb2+ sensing by Yan (2007)
10.1021/ac060643i / Anal. Chem. / Fast responsive crystalline colloidal array photonic crystal glucose sensors by Alexeev (2006)
10.1021/ac020730k / Anal. Chem. / PH-sensitive holographic sensors by Marshall (2003)
10.1021/ac060416g / Anal. Chem. / Holographic lactate sensor by Sartain (2006)
10.1016/0956-5663(94)90015-9 / Biosens. Bioelectronics / An optical biosensor using a fluorescent, swelling sensing element by McCurley (1994)
10.1007/s003960050047 / Colloid Polym. Sci. / Osmotic de-swelling of polystyrene microgel particles by Saunders (1997)
10.1016/0925-4005(93)80028-A / Sens. Actuat. B / Design of a conductimetric pH microsensor swelling hydrogels by Sheppard (1993)
10.1016/0925-4005(94)01542-P / Sens. Actuat. B / Microfabricated conductimetric pH sensor by Sheppard (1995)
10.1016/j.snb.2004.01.011 / Sens. Actuat. B / Characterization of a microgravimetric sensor based on pH sensitive hydrogels by Richter (2004)
10.1109/20.706533 / IEEE Transactions on Magnetics / A remotely interogatable sensor for chemical monitoring by Stojanov (1998)
10.1088/0022-3727/32/12/308 / J. Phys. D / A magnetostatic-coupling basedremote query sensor for environmental monitoring by Grimes (1999)
10.1016/j.aca.2003.08.051 / Anal. Chimica Acta / A mass-sensitive pH sensor based on a stimuli-responsive polymer by Ruana (2003)
10.1016/0022-2860(93)80093-B / J. Mol. Structure / New directions in fiber optic chemical sensors: sensors based on polymer swelling by Seitz (1993)
McCurley, M.F., and Seitz, W.R. (1992). Swelling of a polymer membrane for use in a glucose biosensor. 487, 301–309. (10.1021/bk-1992-0487.ch024)
10.1016/S0925-4005(02)00289-7 / Sens. Actuat. B / Fiber optic Bragg grating sensor based on hydrogels for measuring salinity by Cong (2002)
10.1016/S0925-4005(03)00605-1 / Sens. Actuat. B / Demonstration of etched cladding fiber Bragg grating-based sensors with hydrogel coating by Liu (2003)
10.1016/j.trac.2005.09.006 / Trends in Analytical Chemistry / Nanomechanical biosensors: a new sensing tool by Carrascosa (2006)
10.1063/1.1514825 / Appl. Phys. Lett. / Micromechanical cantilever as an ultrasensitive pH microsensor by Bashir (2002)
10.1023/A:1025786023595 / Biomed. Microdev. / Ultrasensitive biomems sensors based on microcantilevers patterned with environmentally responsive hydrogels by Hilt (2003)
10.1081/CI-120037668 / Instrumentation Sci. Technol. / A pH sensor based on a microcantilever coated with intelligent hydrogel by Zhang (2004)
10.1021/bm0255894 / Biomacromol. / Constant-volume hydrogel osmometer: a new device concept for miniature biosensors by Han (2002)
10.1002/masy.200450645 / Macromol. Symp. / Application of sensitive hydrogels in chemical and pH sensors by Gerlach (2004)
10.1016/j.snb.2005.03.040 / Sens. Actuat. B / Chemical and pH sensors based on the swelling behavior of hydrogels by Gerlach (2005)
10.1016/j.snb.2005.10.041 / Sens. Actuat. B / Hydrogel-based piezoresistive pH sensors: design, simulation and output characteristics by Trinh (2006)
10.1016/S0925-4005(03)00121-7 / Sens. Actuat. B / A swelling hydrogel-based PCO2 sensor by Herber (2003)
10.1063/1.1773153 / J Chem. Phys. / Study of chemically induced pressure generation of hydrogels under isochoric conditions using a microfabricated device by Herber (2004)
10.1023/A:1014627029818 / Biomed. Microdev. / Hydrogel-actuated capacitive transducer for wireless biosensors by Strong (2002)
10.1002/(SICI)1521-4044(19991201)50:11/12<383::AID-APOL383>3.0.CO;2-Z / Acta Polym. / Poly(vinyl alcohol)/(poly(acrylic acid) hydrogels: FT-IR spectroscopic characterization of crosslinking reaction and work at transition point by Arndt (1999)
Kretschmer, K., Kuckling, D., and Richter, A. SPR investigations of pH dependent swelling of thin poly(vinyl alcohol)/poly(acrylic acid) layers. unpublished.
10.1063/1.470608 / J. Chem. Phys. / Hysteretic behavior and irreversibility of polymer gels by pH change by Suzuki (1995)
10.1021/ma021025g / Macromolecules / Photo-cross-linkable PNIPAAm copolymers. 2. Effects of constraint on temperature and pH-responsive hydrogel layers by Harmon (2003)
10.1021/la030217h / Langmuir / Photo-cross-linkable PNIPAAm copolymers. 4. Effects of copolymerization and cross-linking on the volume-phase transition in constrained hydrogel layers by Harmon (2003)
10.1016/j.snb.2003.12.014 / Sens. Actuat. B / Influence of phenomena of volume phase transition at the behavior of hydrogel based valves by Richter (2004)
10.1016/S0032-3861(03)00413-0 / Polymer / Photo cross-linkable poly(N-isopropylacrylamide) copolymers III: micro-fabricated temperature responsive hydrogels by Kuckling (2003)
10.1002/smll.200600590 / Small / Temperature-, pH-, and magnetic-field-sensitive hybrid microgels by Bhattacharya (2007)

Dates

Type	When
Created	16 years, 9 months ago (Dec. 1, 2008, 9:42 a.m.)
Deposited	1 year, 3 months ago (May 28, 2024, 2:07 p.m.)
Indexed	2 days, 10 hours ago (Sept. 3, 2025, 6:27 a.m.)
Issued	17 years, 7 months ago (Jan. 25, 2008)
Published	17 years, 7 months ago (Jan. 25, 2008)
Published Online	17 years, 7 months ago (Jan. 25, 2008)

Funders 0

None

BibTeX

@article{Richter_2008, title={Review on Hydrogel-based pH Sensors and Microsensors}, volume={8}, ISSN={1424-8220}, url={http://dx.doi.org/10.3390/s8010561}, DOI={10.3390/s8010561}, number={1}, journal={Sensors}, publisher={MDPI AG}, author={Richter, Andreas and Paschew, Georgi and Klatt, Stephan and Lienig, Jens and Arndt, Karl-Friedrich and Adler, Hans-Jürgen P.}, year={2008}, month=jan, pages={561–581} }

JSON

{
  "indexed": {
    "date-parts": [
      [
        2025,
        9,
        3
      ]
    ],
    "date-time": "2025-09-03T10:27:07Z",
    "timestamp": 1756895227581
  },
  "reference-count": 90,
  "publisher": "MDPI AG",
  "issue": "1",
  "license": [
    {
      "start": {
        "date-parts": [
          [
            2008,
            1,
            25
          ]
        ],
        "date-time": "2008-01-25T00:00:00Z",
        "timestamp": 1201219200000
      },
      "content-version": "vor",
      "delay-in-days": 0,
      "URL": "https://creativecommons.org/licenses/by/3.0/"
    }
  ],
  "content-domain": {
    "domain": [],
    "crossmark-restriction": false
  },
  "abstract": "<jats:p>Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background of the special properties of stimuli-responsive hydrogels. Following, transducers are described which are able to convert the non-electrical changes of the physical properties of stimuli-responsive hydrogels into an electrical signal. Finally, the specific sensor properties, design rules and general conditions for sensor applications are discussed.</jats:p>",
  "DOI": "10.3390/s8010561",
  "type": "journal-article",
  "created": {
    "date-parts": [
      [
        2008,
        12,
        1
      ]
    ],
    "date-time": "2008-12-01T14:42:49Z",
    "timestamp": 1228142569000
  },
  "page": "561-581",
  "source": "Crossref",
  "is-referenced-by-count": 677,
  "title": "Review on Hydrogel-based pH Sensors and Microsensors",
  "prefix": "10.3390",
  "volume": "8",
  "author": [
    {
      "given": "Andreas",
      "family": "Richter",
      "sequence": "first",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Institute of Electromechanical and Electronic Design, 01062 Dresden, Germany"
        }
      ]
    },
    {
      "given": "Georgi",
      "family": "Paschew",
      "sequence": "additional",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Institute of Electromechanical and Electronic Design, 01062 Dresden, Germany"
        }
      ]
    },
    {
      "given": "Stephan",
      "family": "Klatt",
      "sequence": "additional",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Institute of Electromechanical and Electronic Design, 01062 Dresden, Germany"
        }
      ]
    },
    {
      "given": "Jens",
      "family": "Lienig",
      "sequence": "additional",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Institute of Electromechanical and Electronic Design, 01062 Dresden, Germany"
        }
      ]
    },
    {
      "given": "Karl-Friedrich",
      "family": "Arndt",
      "sequence": "additional",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Physical Chemistry of Polymers, 01062 Dresden, Germany"
        }
      ]
    },
    {
      "given": "Hans-J\u00fcrgen P.",
      "family": "Adler",
      "sequence": "additional",
      "affiliation": [
        {
          "name": "Technische Universit\u00e4t Dresden, Macromolecular Chemistry and Textile Chemistry, 01062 Dresden, Germany"
        }
      ]
    }
  ],
  "member": "1968",
  "published-online": {
    "date-parts": [
      [
        2008,
        1,
        25
      ]
    ]
  },
  "reference": [
    {
      "key": "ref_1",
      "doi-asserted-by": "crossref",
      "first-page": "318",
      "DOI": "10.1007/BF02172635",
      "article-title": "Reversible Dehnung und Kontraktion bei \u00c4nderung der Ionisation eines Netzwerks polyvalenter Fadenmolek\u00fclionen",
      "volume": "5",
      "author": "Kuhn",
      "year": "1949",
      "journal-title": "Experientia"
    },
    {
      "key": "ref_2",
      "doi-asserted-by": "crossref",
      "first-page": "514",
      "DOI": "10.1038/165514a0",
      "article-title": "Reversible dilation and contraction by changing the state of ionization of high-polymer acid networks",
      "volume": "165",
      "author": "Kuhn",
      "year": "1950",
      "journal-title": "Nature"
    },
    {
      "key": "ref_3",
      "doi-asserted-by": "crossref",
      "first-page": "319",
      "DOI": "10.1007/BF02172636",
      "article-title": "Rapid swelling and deswelling of reversible gels of polymeric acids by ionization",
      "volume": "5",
      "author": "Katchalsky",
      "year": "1949",
      "journal-title": "Experientia"
    },
    {
      "key": "ref_4",
      "doi-asserted-by": "crossref",
      "first-page": "312",
      "DOI": "10.1007/BF00906477",
      "article-title": "\u00dcber Quellung von vernetzter Polymethacryls\u00e4ure",
      "volume": "80",
      "author": "Breitenbach",
      "year": "1949",
      "journal-title": "Monatsh. Chem."
    },
    {
      "key": "ref_5",
      "doi-asserted-by": "crossref",
      "first-page": "820",
      "DOI": "10.1103/PhysRevLett.40.820",
      "article-title": "Collapse of gels and the critical endpoint",
      "volume": "40",
      "author": "Tanaka",
      "year": "1978",
      "journal-title": "Phys. Rev. Lett."
    },
    {
      "key": "ref_6",
      "doi-asserted-by": "crossref",
      "first-page": "467",
      "DOI": "10.1126/science.218.4571.467",
      "article-title": "Collapse of gels in an electric-field",
      "volume": "218",
      "author": "Tanaka",
      "year": "1982",
      "journal-title": "Science"
    },
    {
      "key": "ref_7",
      "doi-asserted-by": "crossref",
      "first-page": "345",
      "DOI": "10.1038/346345a0",
      "article-title": "Phase-transition in polymer gels induced by visible-light",
      "volume": "346",
      "author": "Suzuki",
      "year": "1990",
      "journal-title": "Nature"
    },
    {
      "key": "ref_8",
      "doi-asserted-by": "crossref",
      "first-page": "4773",
      "DOI": "10.1021/ac0343026",
      "article-title": "Detection of CrO42- using a hydrogel swelling microcantilever sensor",
      "volume": "75",
      "author": "Zhang",
      "year": "2003",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_9",
      "doi-asserted-by": "crossref",
      "first-page": "4531",
      "DOI": "10.1016/0032-3861(93)90160-C",
      "article-title": "Stimuli-responsive polymers: chemical induced reversible phase separation of an aqueous solution of poly(N-isopropylacrylamide) with pendent crown ether groups",
      "volume": "34",
      "author": "Irie",
      "year": "1993",
      "journal-title": "Polymer"
    },
    {
      "key": "ref_10",
      "doi-asserted-by": "crossref",
      "first-page": "201",
      "DOI": "10.1039/fd9950100201",
      "article-title": "Polymer gels that can recognize and recover molecules",
      "volume": "101",
      "author": "Tanaka",
      "year": "1995",
      "journal-title": "Faraday Discuss."
    },
    {
      "key": "ref_11",
      "doi-asserted-by": "crossref",
      "first-page": "31",
      "DOI": "10.1016/S1381-5148(02)00055-X",
      "article-title": "Synthesis and characterisation of a polyacrylamide-polyacrylic acid copolymer hydrogel for environmental analysis of Cu and Cd",
      "volume": "52",
      "author": "Li",
      "year": "2002",
      "journal-title": "React. Funct. Polym."
    },
    {
      "key": "ref_12",
      "doi-asserted-by": "crossref",
      "first-page": "139",
      "DOI": "10.1016/S0924-4247(99)00080-1",
      "article-title": "Photopatterning of thermally sensitive hydrogels useful for microactuators",
      "volume": "77",
      "author": "Hoffmann",
      "year": "1999",
      "journal-title": "Sens. Actuat. A"
    },
    {
      "key": "ref_13",
      "doi-asserted-by": "crossref",
      "first-page": "111",
      "DOI": "10.1002/masy.19991420112",
      "article-title": "Photocrosslinking of thin polymer films - Materials for sensors and actuators",
      "volume": "142",
      "author": "Kuckling",
      "year": "1999",
      "journal-title": "Macromol. Symp."
    },
    {
      "key": "ref_14",
      "doi-asserted-by": "crossref",
      "first-page": "345",
      "DOI": "10.1002/(SICI)1099-1581(199906)10:6<345::AID-PAT885>3.0.CO;2-N",
      "article-title": "Photocrosslinking of thin films of temperature-sensitive polymers",
      "volume": "10",
      "author": "Kuckling",
      "year": "1999",
      "journal-title": "Polym. Adv. Technol."
    },
    {
      "key": "ref_15",
      "doi-asserted-by": "crossref",
      "first-page": "588",
      "DOI": "10.1038/35007047",
      "article-title": "Functional hydrogel structures for autonomous flow control inside microfluidic channels",
      "volume": "404",
      "author": "Beebe",
      "year": "2000",
      "journal-title": "Nature"
    },
    {
      "key": "ref_16",
      "doi-asserted-by": "crossref",
      "first-page": "496",
      "DOI": "10.1002/1099-1581(200008/12)11:8/12<496::AID-PAT996>3.0.CO;2-7",
      "article-title": "Application of sensitive hydrogels in flow control",
      "volume": "11",
      "author": "Arndt",
      "year": "2000",
      "journal-title": "Polym. Adv. Techn."
    },
    {
      "key": "ref_17",
      "doi-asserted-by": "crossref",
      "first-page": "748",
      "DOI": "10.1109/JMEMS.2003.817898",
      "article-title": "Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications",
      "volume": "12",
      "author": "Richter",
      "year": "2003",
      "journal-title": "J. Microelectromech. Syst."
    },
    {
      "key": "ref_18",
      "doi-asserted-by": "crossref",
      "first-page": "447",
      "DOI": "10.1002/masy.200450650",
      "article-title": "Automatically and electronically controllable hydrogel based valves and microvalves \u2013 design and operating performance",
      "volume": "210",
      "author": "Richter",
      "year": "2004",
      "journal-title": "Macromol. Symp."
    },
    {
      "key": "ref_19",
      "doi-asserted-by": "crossref",
      "first-page": "1958",
      "DOI": "10.1021/ac026455j",
      "article-title": "Flow control valves for analytical microfluidic chips without mechanical parts based on thermally responsive monolithic polymers",
      "volume": "75",
      "author": "Yu",
      "year": "2003",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_20",
      "doi-asserted-by": "crossref",
      "first-page": "313",
      "DOI": "10.1007/s10544-005-6073-z",
      "article-title": "Self-actuated, thermo-responsive hydrogel valves for lab on a chip",
      "volume": "7",
      "author": "Wang",
      "year": "2005",
      "journal-title": "Biomed. Microdev."
    },
    {
      "key": "ref_21",
      "unstructured": "Richter, A., and Arndt, K.F. (1999). 5th Internat. Symp. on Polym. Adv. Technol."
    },
    {
      "key": "ref_22",
      "doi-asserted-by": "crossref",
      "first-page": "613",
      "DOI": "10.1109/JMEMS.2003.818070",
      "article-title": "A hydrogel-actuated environmentally sensitive microvalve for active flow control",
      "volume": "12",
      "author": "Baldi",
      "year": "2003",
      "journal-title": "J. Microelectromech. Syst."
    },
    {
      "key": "ref_23",
      "doi-asserted-by": "crossref",
      "first-page": "144",
      "DOI": "10.1002/mame.200390007",
      "article-title": "Temperature and pH dependent swelling behavior of poly(N-isopropylacrylamide)-copolymer and their use in flow control",
      "volume": "288",
      "author": "Kuckling",
      "year": "2003",
      "journal-title": "Macromol. Mater. Eng."
    },
    {
      "key": "ref_24",
      "doi-asserted-by": "crossref",
      "first-page": "4547",
      "DOI": "10.1016/S0032-3861(03)00463-4",
      "article-title": "A microfluidic actuator based on thermoresponsive hydrogels",
      "volume": "44",
      "author": "Harmon",
      "year": "2003",
      "journal-title": "Polymer"
    },
    {
      "key": "ref_25",
      "doi-asserted-by": "crossref",
      "first-page": "53",
      "DOI": "10.1016/S0925-4005(01)01028-0",
      "article-title": "A disposable \u201cintelligent mosquito\u201d with a reversible sampling mechanism using the volume-phase transition of a gel",
      "volume": "83",
      "author": "Suzuki",
      "year": "2002",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_26",
      "doi-asserted-by": "crossref",
      "first-page": "586",
      "DOI": "10.1109/JMEMS.2004.832190",
      "article-title": "A valved responsive hydrogel microdispensing device with integrated pressure source",
      "volume": "13",
      "author": "Eddington",
      "year": "2004",
      "journal-title": "J. Microelectromech. Syst."
    },
    {
      "key": "ref_27",
      "doi-asserted-by": "crossref",
      "first-page": "377",
      "DOI": "10.1002/masy.200450642",
      "article-title": "Adjustable low dynamic pumps based on hydrogels",
      "volume": "210",
      "author": "Richter",
      "year": "2004",
      "journal-title": "Macromol. Symp."
    },
    {
      "key": "ref_28",
      "doi-asserted-by": "crossref",
      "first-page": "1109",
      "DOI": "10.1002/adma.200601989",
      "article-title": "Controlled double-sensitivity of microgels applied to electronically adjustable chemostats",
      "volume": "19",
      "author": "Richter",
      "year": "2007",
      "journal-title": "Adv. Mater."
    },
    {
      "key": "ref_29",
      "doi-asserted-by": "crossref",
      "first-page": "569",
      "DOI": "10.1016/j.snb.2007.03.002",
      "article-title": "Mechanically adjustable chemostats based on stimuli-responsive polymers",
      "volume": "125",
      "author": "Richter",
      "year": "2007",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_30",
      "unstructured": "Hydrogel Valves \u2013 Dead-Volume-Free Microfluidic Switches Data sheet 2007. http://www.gesim.de/upload/PDFs/Hydrogel_en.pdf."
    },
    {
      "key": "ref_31",
      "doi-asserted-by": "crossref",
      "first-page": "325",
      "DOI": "10.1039/b210140h",
      "article-title": "Stimulus-sensitive hydrogels and their applications in chemical (micro)analysis",
      "volume": "128",
      "author": "Herber",
      "year": "2003",
      "journal-title": "Analyst"
    },
    {
      "key": "ref_32",
      "doi-asserted-by": "crossref",
      "first-page": "257",
      "DOI": "10.1002/masy.200450323",
      "article-title": "High response smart gels: synthesis and application",
      "volume": "207",
      "author": "Arndt",
      "year": "2004",
      "journal-title": "Macromol. Symp."
    },
    {
      "key": "ref_33",
      "doi-asserted-by": "crossref",
      "first-page": "512",
      "DOI": "10.1063/1.1723791",
      "article-title": "Statistical mechanics of cross-linked polymer networks I. Rubber elasticity",
      "volume": "11",
      "author": "Flory",
      "year": "1943",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_34",
      "doi-asserted-by": "crossref",
      "first-page": "521",
      "DOI": "10.1063/1.1723792",
      "article-title": "Statistical mechanics of cross-linked polymer networks II. Swelling",
      "volume": "11",
      "author": "Flory",
      "year": "1943",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_35",
      "doi-asserted-by": "crossref",
      "first-page": "440",
      "DOI": "10.1063/1.1750930",
      "article-title": "Solutions of long chain compounds",
      "volume": "9",
      "author": "Huggins",
      "year": "1941",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_36",
      "doi-asserted-by": "crossref",
      "first-page": "660",
      "DOI": "10.1063/1.1750971",
      "article-title": "Thermodynamics of high polymer solutions",
      "volume": "9",
      "author": "Flory",
      "year": "1941",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_37",
      "doi-asserted-by": "crossref",
      "first-page": "3254",
      "DOI": "10.1021/ma00189a021",
      "article-title": "pH-dependent equilibrium swelling properties of hydrophobic polyelectrolyte copolymer gels",
      "volume": "21",
      "author": "Siegel",
      "year": "1988",
      "journal-title": "Macromolecules"
    },
    {
      "key": "ref_38",
      "doi-asserted-by": "crossref",
      "first-page": "1645",
      "DOI": "10.1063/1.474516",
      "article-title": "Equilibrium and non-equilibrium phase transitions in copolymer polyelectrolyte hydrogels",
      "volume": "107",
      "author": "English",
      "year": "1997",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_39",
      "unstructured": "Tanaka, T. (2000). Experimental Methods in Polymer Science, Academic Press Cambridge Burlington."
    },
    {
      "key": "ref_40",
      "doi-asserted-by": "crossref",
      "first-page": "5151",
      "DOI": "10.1063/1.1680734",
      "article-title": "Spectrum of light scattered from a viscoelastic gel",
      "volume": "59",
      "author": "Tanaka",
      "year": "1973",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_41",
      "doi-asserted-by": "crossref",
      "first-page": "1214",
      "DOI": "10.1063/1.437602",
      "article-title": "Kinetics of swelling of gels",
      "volume": "70",
      "author": "Tanaka",
      "year": "1979",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_42",
      "doi-asserted-by": "crossref",
      "first-page": "1365",
      "DOI": "10.1063/1.458148",
      "article-title": "Kinetics of swelling and shrinking of gels",
      "volume": "92",
      "author": "Li",
      "year": "1990",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_43",
      "doi-asserted-by": "crossref",
      "first-page": "503",
      "DOI": "10.1016/S0966-7822(97)00024-5",
      "article-title": "A method for studying swelling kinetics based on measurement of electrical conductivity",
      "volume": "5",
      "author": "Lesho",
      "year": "1997",
      "journal-title": "Polym. Gels Networks"
    },
    {
      "key": "ref_44",
      "doi-asserted-by": "crossref",
      "first-page": "147",
      "DOI": "10.1007/s00604-003-0077-2",
      "article-title": "An optical chemical sensor based on swellable dicarboxylate functionalized polymer microspheres for pH copper and calcium determination",
      "volume": "144",
      "author": "Shakhsher",
      "year": "2004",
      "journal-title": "Microchim. Acta"
    },
    {
      "key": "ref_45",
      "doi-asserted-by": "crossref",
      "first-page": "179",
      "DOI": "10.1016/j.snb.2004.04.033",
      "article-title": "Chemical modulation of thermosensitive poly(N-isopropylacryl-amide) microsphere swelling: a new strategy for chemical sensing",
      "volume": "104",
      "author": "Oktar",
      "year": "2005",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_46",
      "doi-asserted-by": "crossref",
      "first-page": "210",
      "DOI": "10.1016/S0925-4005(98)00238-X",
      "article-title": "Integrated optical pH sensor using replicated chirped grating coupler sensor chips",
      "volume": "50",
      "author": "Kunz",
      "year": "1998",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_47",
      "doi-asserted-by": "crossref",
      "first-page": "267",
      "DOI": "10.1039/a902183c",
      "article-title": "An optically sensitive membrane for pH based on swellable polymer microspheres in a hydrogel",
      "volume": "36",
      "author": "Rooney",
      "year": "1999",
      "journal-title": "Anal. Comm."
    },
    {
      "key": "ref_48",
      "doi-asserted-by": "crossref",
      "first-page": "55",
      "DOI": "10.1016/S0003-2670(99)00608-X",
      "article-title": "Derivatized, swellable polymer microspheres for chemical transduction",
      "volume": "400",
      "author": "Seitz",
      "year": "1999",
      "journal-title": "Anal. Chim. Acta"
    },
    {
      "key": "ref_49",
      "doi-asserted-by": "crossref",
      "first-page": "1731",
      "DOI": "10.1021/ac00082a021",
      "article-title": "Single fiber-optic pH sensor based on changes in reflection accompanying polymer swelling",
      "volume": "66",
      "author": "Shakhsher",
      "year": "1994",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_50",
      "doi-asserted-by": "crossref",
      "first-page": "1691",
      "DOI": "10.1016/S0039-9140(97)00080-5",
      "article-title": "A sensor for pH based on an optical reflective device coupled to the swelling of an aminated polystyrene membrane",
      "volume": "44",
      "author": "Zhang",
      "year": "1997",
      "journal-title": "Talanta"
    },
    {
      "key": "ref_51",
      "doi-asserted-by": "crossref",
      "first-page": "41",
      "DOI": "10.1007/BF01248239",
      "article-title": "Aminated polystyrene membranes for a fiber optic pH sensor based on reflectance changes accompanying polymer swelling",
      "volume": "121",
      "author": "Zhang",
      "year": "1995",
      "journal-title": "Microchim. Acta"
    },
    {
      "key": "ref_52",
      "doi-asserted-by": "crossref",
      "first-page": "166",
      "DOI": "10.1016/0925-4005(95)85036-8",
      "article-title": "The use of metal-island-coated pH-sensitive swelling polymers for biosensor applications",
      "volume": "24-25",
      "author": "Schalkhammer",
      "year": "1995",
      "journal-title": "Sens. Actuat B"
    },
    {
      "key": "ref_53",
      "doi-asserted-by": "crossref",
      "first-page": "204",
      "DOI": "10.1016/0925-4005(95)01684-8",
      "article-title": "Metal island coated polymer swelling over mirror system (MICSPOMS): a new principle for measure ionic strength",
      "volume": "29",
      "author": "Aussenegg",
      "year": "1995",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_54",
      "doi-asserted-by": "crossref",
      "first-page": "829",
      "DOI": "10.1038/39834",
      "article-title": "Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials",
      "volume": "389",
      "author": "Holtz",
      "year": "1997",
      "journal-title": "Nature"
    },
    {
      "key": "ref_55",
      "doi-asserted-by": "crossref",
      "first-page": "9534",
      "DOI": "10.1021/ja002017n",
      "article-title": "Photonic crystal chemical sensors: pH and ionic strength",
      "volume": "122",
      "author": "Lee",
      "year": "2000",
      "journal-title": "J. Am. Chem. Soc."
    },
    {
      "key": "ref_56",
      "doi-asserted-by": "crossref",
      "first-page": "2121",
      "DOI": "10.1007/s00216-006-1088-8",
      "article-title": "Cation identity dependence of crown ether photonic crystal Pb2+ sensing",
      "volume": "387",
      "author": "Yan",
      "year": "2007",
      "journal-title": "Anal. Bioanal. Chem."
    },
    {
      "key": "ref_57",
      "doi-asserted-by": "crossref",
      "first-page": "5149",
      "DOI": "10.1021/ac060643i",
      "article-title": "Fast responsive crystalline colloidal array photonic crystal glucose sensors",
      "volume": "78",
      "author": "Alexeev",
      "year": "2006",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_58",
      "doi-asserted-by": "crossref",
      "first-page": "4423",
      "DOI": "10.1021/ac020730k",
      "article-title": "PH-sensitive holographic sensors",
      "volume": "75",
      "author": "Marshall",
      "year": "2003",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_59",
      "doi-asserted-by": "crossref",
      "first-page": "5664",
      "DOI": "10.1021/ac060416g",
      "article-title": "Holographic lactate sensor",
      "volume": "78",
      "author": "Sartain",
      "year": "2006",
      "journal-title": "Anal. Chem."
    },
    {
      "key": "ref_60",
      "doi-asserted-by": "crossref",
      "first-page": "527",
      "DOI": "10.1016/0956-5663(94)90015-9",
      "article-title": "An optical biosensor using a fluorescent, swelling sensing element",
      "volume": "9",
      "author": "McCurley",
      "year": "1994",
      "journal-title": "Biosens. Bioelectronics"
    },
    {
      "key": "ref_61",
      "doi-asserted-by": "crossref",
      "first-page": "9",
      "DOI": "10.1007/s003960050047",
      "article-title": "Osmotic de-swelling of polystyrene microgel particles",
      "volume": "275",
      "author": "Saunders",
      "year": "1997",
      "journal-title": "Colloid Polym. Sci."
    },
    {
      "key": "ref_62",
      "doi-asserted-by": "crossref",
      "first-page": "73",
      "DOI": "10.1016/0925-4005(93)80028-A",
      "article-title": "Design of a conductimetric pH microsensor swelling hydrogels",
      "volume": "10",
      "author": "Sheppard",
      "year": "1993",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_63",
      "doi-asserted-by": "crossref",
      "first-page": "95",
      "DOI": "10.1016/0925-4005(94)01542-P",
      "article-title": "Microfabricated conductimetric pH sensor",
      "volume": "28",
      "author": "Sheppard",
      "year": "1995",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_64",
      "doi-asserted-by": "crossref",
      "first-page": "579",
      "DOI": "10.1016/j.snb.2004.01.011",
      "article-title": "Characterization of a microgravimetric sensor based on pH sensitive hydrogels",
      "volume": "99",
      "author": "Richter",
      "year": "2004",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_65",
      "doi-asserted-by": "crossref",
      "first-page": "1315",
      "DOI": "10.1109/20.706533",
      "article-title": "A remotely interogatable sensor for chemical monitoring",
      "volume": "34",
      "author": "Stojanov",
      "year": "1998",
      "journal-title": "IEEE Transactions on Magnetics"
    },
    {
      "key": "ref_66",
      "doi-asserted-by": "crossref",
      "first-page": "1329",
      "DOI": "10.1088/0022-3727/32/12/308",
      "article-title": "A magnetostatic-coupling basedremote query sensor for environmental monitoring",
      "volume": "32",
      "author": "Grimes",
      "year": "1999",
      "journal-title": "J. Phys. D"
    },
    {
      "key": "ref_67",
      "doi-asserted-by": "crossref",
      "first-page": "123",
      "DOI": "10.1016/j.aca.2003.08.051",
      "article-title": "A mass-sensitive pH sensor based on a stimuli-responsive polymer",
      "volume": "497",
      "author": "Ruana",
      "year": "2003",
      "journal-title": "Anal. Chimica Acta"
    },
    {
      "key": "ref_68",
      "doi-asserted-by": "crossref",
      "first-page": "105",
      "DOI": "10.1016/0022-2860(93)80093-B",
      "article-title": "New directions in fiber optic chemical sensors: sensors based on polymer swelling",
      "volume": "292",
      "author": "Seitz",
      "year": "1993",
      "journal-title": "J. Mol. Structure"
    },
    {
      "key": "ref_69",
      "doi-asserted-by": "crossref",
      "unstructured": "McCurley, M.F., and Seitz, W.R. (1992). Swelling of a polymer membrane for use in a glucose biosensor. 487, 301\u2013309.",
      "DOI": "10.1021/bk-1992-0487.ch024"
    },
    {
      "key": "ref_70",
      "doi-asserted-by": "crossref",
      "first-page": "487",
      "DOI": "10.1016/S0925-4005(02)00289-7",
      "article-title": "Fiber optic Bragg grating sensor based on hydrogels for measuring salinity",
      "volume": "87",
      "author": "Cong",
      "year": "2002",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_71",
      "doi-asserted-by": "crossref",
      "first-page": "468",
      "DOI": "10.1016/S0925-4005(03)00605-1",
      "article-title": "Demonstration of etched cladding fiber Bragg grating-based sensors with hydrogel coating",
      "volume": "96",
      "author": "Liu",
      "year": "2003",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_72",
      "doi-asserted-by": "crossref",
      "first-page": "196",
      "DOI": "10.1016/j.trac.2005.09.006",
      "article-title": "Nanomechanical biosensors: a new sensing tool",
      "volume": "25",
      "author": "Carrascosa",
      "year": "2006",
      "journal-title": "Trends in Analytical Chemistry"
    },
    {
      "key": "ref_73",
      "doi-asserted-by": "crossref",
      "first-page": "3091",
      "DOI": "10.1063/1.1514825",
      "article-title": "Micromechanical cantilever as an ultrasensitive pH microsensor",
      "volume": "81",
      "author": "Bashir",
      "year": "2002",
      "journal-title": "Appl. Phys. Lett."
    },
    {
      "key": "ref_74",
      "doi-asserted-by": "crossref",
      "first-page": "177",
      "DOI": "10.1023/A:1025786023595",
      "article-title": "Ultrasensitive biomems sensors based on microcantilevers patterned with environmentally responsive hydrogels",
      "volume": "5",
      "author": "Hilt",
      "year": "2003",
      "journal-title": "Biomed. Microdev."
    },
    {
      "key": "ref_75",
      "doi-asserted-by": "crossref",
      "first-page": "361",
      "DOI": "10.1081/CI-120037668",
      "article-title": "A pH sensor based on a microcantilever coated with intelligent hydrogel",
      "volume": "32",
      "author": "Zhang",
      "year": "2004",
      "journal-title": "Instrumentation Sci. Technol."
    },
    {
      "key": "ref_76",
      "doi-asserted-by": "crossref",
      "first-page": "1271",
      "DOI": "10.1021/bm0255894",
      "article-title": "Constant-volume hydrogel osmometer: a new device concept for miniature biosensors",
      "volume": "3",
      "author": "Han",
      "year": "2002",
      "journal-title": "Biomacromol."
    },
    {
      "key": "ref_77",
      "doi-asserted-by": "crossref",
      "first-page": "403",
      "DOI": "10.1002/masy.200450645",
      "article-title": "Application of sensitive hydrogels in chemical and pH sensors",
      "volume": "210",
      "author": "Gerlach",
      "year": "2004",
      "journal-title": "Macromol. Symp."
    },
    {
      "key": "ref_78",
      "doi-asserted-by": "crossref",
      "first-page": "555",
      "DOI": "10.1016/j.snb.2005.03.040",
      "article-title": "Chemical and pH sensors based on the swelling behavior of hydrogels",
      "volume": "111-112",
      "author": "Gerlach",
      "year": "2005",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_79",
      "doi-asserted-by": "crossref",
      "first-page": "17",
      "DOI": "10.1016/j.snb.2005.10.041",
      "article-title": "Hydrogel-based piezoresistive pH sensors: design, simulation and output characteristics",
      "volume": "117",
      "author": "Trinh",
      "year": "2006",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_80",
      "doi-asserted-by": "crossref",
      "first-page": "378",
      "DOI": "10.1016/S0925-4005(03)00121-7",
      "article-title": "A swelling hydrogel-based PCO2 sensor",
      "volume": "91",
      "author": "Herber",
      "year": "2003",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_81",
      "doi-asserted-by": "crossref",
      "first-page": "2746",
      "DOI": "10.1063/1.1773153",
      "article-title": "Study of chemically induced pressure generation of hydrogels under isochoric conditions using a microfabricated device",
      "volume": "121",
      "author": "Herber",
      "year": "2004",
      "journal-title": "J Chem. Phys."
    },
    {
      "key": "ref_82",
      "doi-asserted-by": "crossref",
      "first-page": "97",
      "DOI": "10.1023/A:1014627029818",
      "article-title": "Hydrogel-actuated capacitive transducer for wireless biosensors",
      "volume": "4",
      "author": "Strong",
      "year": "2002",
      "journal-title": "Biomed. Microdev."
    },
    {
      "key": "ref_83",
      "doi-asserted-by": "crossref",
      "first-page": "383",
      "DOI": "10.1002/(SICI)1521-4044(19991201)50:11/12<383::AID-APOL383>3.0.CO;2-Z",
      "article-title": "Poly(vinyl alcohol)/(poly(acrylic acid) hydrogels: FT-IR spectroscopic characterization of crosslinking reaction and work at transition point",
      "volume": "50",
      "author": "Arndt",
      "year": "1999",
      "journal-title": "Acta Polym."
    },
    {
      "key": "ref_84",
      "unstructured": "Kretschmer, K., Kuckling, D., and Richter, A. SPR investigations of pH dependent swelling of thin poly(vinyl alcohol)/poly(acrylic acid) layers. unpublished."
    },
    {
      "key": "ref_85",
      "doi-asserted-by": "crossref",
      "first-page": "4706",
      "DOI": "10.1063/1.470608",
      "article-title": "Hysteretic behavior and irreversibility of polymer gels by pH change",
      "volume": "103",
      "author": "Suzuki",
      "year": "1995",
      "journal-title": "J. Chem. Phys."
    },
    {
      "key": "ref_86",
      "doi-asserted-by": "crossref",
      "first-page": "162",
      "DOI": "10.1021/ma021025g",
      "article-title": "Photo-cross-linkable PNIPAAm copolymers. 2. Effects of constraint on temperature and pH-responsive hydrogel layers",
      "volume": "36",
      "author": "Harmon",
      "year": "2003",
      "journal-title": "Macromolecules"
    },
    {
      "key": "ref_87",
      "doi-asserted-by": "crossref",
      "first-page": "10947",
      "DOI": "10.1021/la030217h",
      "article-title": "Photo-cross-linkable PNIPAAm copolymers. 4. Effects of copolymerization and cross-linking on the volume-phase transition in constrained hydrogel layers",
      "volume": "19",
      "author": "Harmon",
      "year": "2003",
      "journal-title": "Langmuir"
    },
    {
      "key": "ref_88",
      "doi-asserted-by": "crossref",
      "first-page": "451",
      "DOI": "10.1016/j.snb.2003.12.014",
      "article-title": "Influence of phenomena of volume phase transition at the behavior of hydrogel based valves",
      "volume": "99",
      "author": "Richter",
      "year": "2004",
      "journal-title": "Sens. Actuat. B"
    },
    {
      "key": "ref_89",
      "doi-asserted-by": "crossref",
      "first-page": "4455",
      "DOI": "10.1016/S0032-3861(03)00413-0",
      "article-title": "Photo cross-linkable poly(N-isopropylacrylamide) copolymers III: micro-fabricated temperature responsive hydrogels",
      "volume": "44",
      "author": "Kuckling",
      "year": "2003",
      "journal-title": "Polymer"
    },
    {
      "key": "ref_90",
      "doi-asserted-by": "crossref",
      "first-page": "650",
      "DOI": "10.1002/smll.200600590",
      "article-title": "Temperature-, pH-, and magnetic-field-sensitive hybrid microgels",
      "volume": "4",
      "author": "Bhattacharya",
      "year": "2007",
      "journal-title": "Small"
    }
  ],
  "container-title": "Sensors",
  "original-title": [],
  "language": "en",
  "link": [
    {
      "URL": "https://www.mdpi.com/1424-8220/8/1/561/pdf",
      "content-type": "unspecified",
      "content-version": "vor",
      "intended-application": "similarity-checking"
    }
  ],
  "deposited": {
    "date-parts": [
      [
        2024,
        5,
        28
      ]
    ],
    "date-time": "2024-05-28T18:07:40Z",
    "timestamp": 1716919660000
  },
  "score": 1,
  "resource": {
    "primary": {
      "URL": "https://www.mdpi.com/1424-8220/8/1/561"
    }
  },
  "subtitle": [],
  "short-title": [],
  "issued": {
    "date-parts": [
      [
        2008,
        1,
        25
      ]
    ]
  },
  "references-count": 90,
  "journal-issue": {
    "issue": "1",
    "published-online": {
      "date-parts": [
        [
          2008,
          1
        ]
      ]
    }
  },
  "alternative-id": [
    "s8010561"
  ],
  "URL": "http://dx.doi.org/10.3390/s8010561",
  "relation": {},
  "ISSN": [
    "1424-8220"
  ],
  "subject": [],
  "container-title-short": "Sensors",
  "published": {
    "date-parts": [
      [
        2008,
        1,
        25
      ]
    ]
  }
}