Applications of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) transistors in chemical and biological sensors

The application of transistors based on poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) in chemical and biological sensing is reviewed. These devices offer enormous potential for facile processing of small, portable, and inexpensive sensors ideally suited for point-of-care analysis. They can be used to detect a wide range of analytes for a variety of possible applications in fields such as health care (medical diagnostics), environmental monitoring (airborne chemicals, water contamination, etc.), and food industry (smart packaging). Organic transistors are excellent candidates to act as transducers because they have the ability to translate chemical and biological signals into electronic signals with high sensitivity. Furthermore, fuctionalization of PEDOT:PSS films with a chemical or biological receptor can lead to high specificity. The advantages of using PEDOT:PSS transistors are described, and applications are presented for sensing analytes in both gaseous and aqueous environments.     

Synthesis and evaluation of nitrated poly(4-hydroxystyrene) microspheres for pH sensing

Lightly crosslinked nitrated poly(4-hydroxystyrene) microspheres were prepared for pH sensing. The first step is to prepare poly(4-acetoxystyrene) microspheres using porous glass membrane emulsification followed by suspension polymerization. The resulting microspheres have diameters between 1 and 2 μm. They hydrolyzed to poly(4-hydroxystyrene) by exposing them to base. This is followed by nitration to nitric acid. The percentage of nitrogen depends on the nitration conditions. Percentages greater than the theoretical percentage for mononitro poly(4-hydroxystyrene) can be obtained at elevated temperatures indicating partial dinitration. These microspheres were cast into hydrogel membranes for use as pH sensors. The membrane is turbid because the refractive index of the microspheres is higher than the hydrogel refractive index. At high pH, deprotonation of the hydroxyl group introduces a negative charge onto the polymer backbone causing it to swell. Swelling is accompanied by a decrease in microsphere refractive index, which is detected as a decrease in membrane turbidity.     

New CNT/poly(brilliant green) and CNT/poly(3,4-ethylenedioxythiophene) based electrochemical enzyme biosensors

A combination of the electroactive polymer poly(brilliant green) (PBG) or conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) with carbon nanotubes to obtain CNT/PBG and CNT/PEDOT modified carbon film electrodes (CFE) has been investigated as a new biosensor platform, incorporating the enzymes glucose oxidase (GOx) as test enzyme, alcohol oxidase (AlcOx) or alcohol dehydrogenase (AlcDH). The sensing parameters were optimized for all biosensors based on CNT/PBG/CFE, CNT/PEDOT/CFE platforms. Under optimized conditions, both GOx biosensors exhibited very similar sensitivities, while in the case of AlcOx and AlcDH biosensors, AlcOx/CNT/PBG/CFE was found to give a higher sensitivity and lower detection limit. The influence of dissolved O₂ on oxidase-biosensor performance was investigated and was shown to be different for each enzyme. Comparisons were made with similar reported biosensors, showing the advantages of the new biosensors, and excellent selectivity against potential interferents was successfully demonstrated. Finally, alcohol biosensors were successfully used for the determination of ethanol in alcoholic beverages.     

A highly performing electrochemical sensor for NADH based on graphite/poly(methylmethacrylate) composite electrode

A fabrication strategy for developing new electrochemical interface based on graphite/poly(methylmethacrylate) (PMMA) composite electrode for some biological molecules was proposed. The results indicated that this electrochemical sensing interface has the advantages, such as quick electron-transfer rate, avoidance of electrode fouling, highly sensitive and stable amperometric sensing for some biomolecules. Compared with carbon paste electrode, this interface would effectively minimize the over-potential and enhance the electrochemical response to some biomolecules. In order to further evaluate the high performance of this interface, the electrochemical behaviors of NADH at this sensing interface were investigated in detail.     

Multiple internal reflection poly(dimethylsiloxane) systems for optical sensing

Compact poly(dimethylsiloxane)-based (PDMS) multiple internal reflection systems which comprise self-alignment systems, lenses, microfluidic channels and mirrors have been developed for highly sensitive absorbance measurements. With the proper definition of air mirrors at both sides of the sensing region, the optical path of the light from the LED has been meaningfully lengthened without a dramatic increase of the mean flow cell volume. By recursive positioning of such air mirrors, propagating multiple internal reflection (PMIR) systems have been designed, simulated and characterized. Experimental results confirm the ray-tracing predictions and allow the determining that there are some regions of the mean flow cell volume that do not contribute to the increase of the sensitivity. The tailoring of the sensing region, following the optical path, results in a similar limit of detection (110 nM) for fluorescein diluted in phosphate buffer. Finally, a ring configuration, labelled RMIR, has also been developed. With the addition of a third air mirror, the LOD can be decreased to 41 nM with the additional advantage of a substantial decrease of the length of the sensing region. These results confirm the validity of the proposed systems for high sensitivity measurements.     

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75 kHz/%RH from 20 to 90%RH, ultrafast response (1 s and 2 s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.     

A novel fluorescent aptasensor for thrombin detection: using poly(m-phenylenediamine) rods as an effective sensing platform

In this communication, we develop a novel fluorescent aptasensor for thrombin detection with the use of poly(m-phenylenediamine) (PMPD) rods as an effective sensing platform. This aptasensor exhibits extraordinarily high sensitivity with a detection limit as low as 100 pM and excellent selectivity.     

Direct immobilization in poly(dimethylsiloxane) for DNA, protein and enzyme fluidic biochips

A new arraying method is presented based on the properties of poly(dimethylsiloxane) (PDMS) polymer to entrap beads bearing biologically active compounds. It is shown that such beads could be spotted and dried at the surface of a poly(vinyl chloride) master and subsequently transferred at the PDMS interface by direct moulding of the polymer on the mask. Moreover, the use of the PDMS-assisted-immobilization enables the development of either a low density array (100 spots) or a micro-channel biochip with a direct incorporation of the sensing element in a fluidic system for the quantitative detection of enzyme substrates, antigens and oligonucleotides, depending on the immobilized sensing element. All biochip formats were revealed by a chemiluminescent reaction detected with a charge coupled device camera.As a result, arrays of beads bearing active enzymes, antibodies and oligonucleotides were successfully obtained and enabled the achievement of biochips for the chemiluminescent detection of enzyme substrates, protein antigens and oligonucleotides sequence with detection limit of 1 μM, 1.5×10⁷ molecules and 10⁸ molecules, respectively.     

Compatibility of binary systems of poly(methyl methacrylate), poly(vinyl chloride) and poly(vinyl acetate)

The influence of the thermal treatment on the stability in time of the dispersion degree of films containing binary polymer mixtures, poly(vinyl chloride)/poly(methyl methacrylate), poly(vinyl chloride)/poly(vinyl acetate) and poly(vinyl acetate)/poly(methyl methacrylate), was studied by thermogravimetry and optical microscopy with phase contrast. The dispersion degree depends particularly on the composition of the polymer mixture and can be improved by thermal treatment at temperatures above the glass temperatures of both homopolymers. It seems that this thermal treatment yields exclusively metastable structures with a general tendency to phase separation in a short time after thermal treatment, the heterogeneity mixtures (as film) being more pronounced.     

Nanostructured latex films from poly(butyl methacrylate) latex cross-linked with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock macro-cross-linker

Biphasic polymer latexes were synthesized by a seeded swelling and polymerization method. The latexes were composed of a poly(butyl methacrylate) core and a poly(ethylene oxide) rich shell cross-linked with poly(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock diol diacrylate macro-cross-linker. Nanostructured films were obtained by annealing the biphasic polymer latexes at a temperature between the glass-transition temperatures of the core latex and the cross-linked poly(ethylene oxide) based shell. Atomic force microscope images of the latex film revealed that the poly(butyl methacrylate) core phase is confined in the poly(ethylene oxide)-rich continuous phase with the form of separate nanosized spheres.     

Sulfonated poly(pyromellitimides) and poly(naphthylimides)

A comparative synthesis of poly(imides) based on benzidine-2,2′-disulfonic acid and dianhydrides of pyromellitic and naphthalene-1,4,5,8-tetracarboxylic acids via the high-temperature polycyclocondensation in m-cresol in the presence of triethylamine has been performed for the purpose of designing proton-exchange membranes for fuel cells. The polymers are shown to be water-soluble with poly(naphthylimide) showing by a much higher hydrolytic stability than poly(pyromellitimide). To render poly(naphthylimide) insoluble in water, copoly(naphthylimide) has been synthesized using 4,4′-bis(4-aminophenoxy)diphehyl sulfone as a comonomer. Copoly(naphthylimides) combine solubility in organic solvents with insolubility in water. These polymers demonstrate high viscosity characteristics and excellent film-forming behavior. They combine excellent thermal stability and hydrolytic resistance with proton conductivity, which is higher than the proton conductivity of Nafion commercial membranes in wide temperature and relative conductivity ranges.     

Preparation of poly(fumaric acid) from poly(di-t-butyl fumarate) and poly(di-trimethylsilyl fumarate)

Polymerization conditions of di-t-butyl fumarate and di-trimethylsilyl fumarate were studied in detail. They cannot be polymerized by either anionic or coordination initiators, but radical and radiation polymerizations are successful. Characterization of poly(di-t-butyl fumarate), obtained thereby, with ¹H-NMR spectrum suggests that the backbone of the chain is stiff. From analysis of thermal properties of poly(di-t-butyl fumarate), it is found to be completely converted to poly(fumaric acid) by pyrolysis around 200°C. Poly(di-trimethylsilyl fumarate), on the other hand, can be quantitatively hydrolyzed with acid to the same polyacid, too. The preliminary measurement of the dissociation behaviors of poly(fumaric acid) was done by potentiometric titration, which shows that the titration curves of poly(fumaric acid) are different from those of poly(acrylic acid) and poly(maleic acid).     

DFT study of response mechanism and selectivity of poly(3,4-ethylenedioxythiophene) towards CO2 and SO2 as gas sensor

Structural Chemistry - To evaluate the sensing ability of poly(3,4-ethylenedioxythiophene) (PEDOT) towards CO2 and SO2 gaseous molecules, an extensive quantum mechanical study has been carried out...     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

Organic vapor sensing behaviors of carbon black/poly (lactic acid) conductive biopolymer composite

Carbon black (CB)/poly (lactic acid) (PLA) conductive biopolymer composite were fabricated by casting. A low percolation value (1.25 vol%) is achieved due to the formation of a two-dimensional conductive network in the composite. Vapor sensing behaviors of the CB/PLA conductive composite were studied. A high chemical selectivity with respect to different organic vapors and a good reproducibility to two typical solvents, ethyl acetate and ethanol, during exposure-drying runs have been demonstrated. The variations of the sensing behaviors during exposure-drying processes were associated with the evolvement of CB conductive networks. The results indicate that the Flory-Huggins interactions parameter x ₁₂, related to the solubility parameter (thermodynamic factor), molar volume (kinetic factor) and the measurement temperature, affects the vapor sensing behaviors of CB/PLA composite significantly. These results suggest CB/PLA conductive biopolymer composite can be applied as a nice vapor sensor candidate.     

Modification of capillary electrophoresis capillaries by poly(hydroxyethyl methacrylate), poly(diethylene glycol monomethacrylate) and poly(triethylene glycol monomethacrylate)

Modification of capillary electrophoresis (CE) capillaries by poly(hydroxyethyl methacrylate) (poly(HEMA), poly(diethylene glycol monomethacrylate) (poly(DEGMA) and poly(triethylene glycol monomethacrylate) (poly(TEGMA), was studied. Methods based on physical adsorption of the modifier and on its chemical binding were compared on the basis of the electroosmotic flow (EOF) reproducibility, the EOF dependence on the pH, the symmetry of the peak of positively charged tyramine, the stability of the coating and the separation of standard and milk proteins in the modified capillaries. Reproducible coatings were obtained by chemical binding of the polymers to the capillary walls and by coating with a solution of a polymer, as also demonstrated by the atomic force microscopy.     

Stereoregularity of radically polymerized poly(alkyl acrylates) and poly(trimethylsilyl acrylates) and the preparation of syndiotactic poly(methyl acrylate)

Nuclear magnetic resonance (NMR) spectroscopy was used to determine the stereoregularity of radically polymerized poly(ethyl acrylates), poly(trimethylsilyl acrylates), and poly(isopropyl acrylate-α,β-d₂). The ethyl acrylate polymers consisted of a random configuration having about 50% of isotactic diads, and their stereoregularities were independent of the polymerization temperature (40 to ?78°C). Poly(trimethylsilyl acrylates) and poly(isopropyl acrylate-α,β-d₂) prepared at low temperatures had a syndiotactic configuration. Syndiotactic poly(methyl acrylate) was derived from syndiotactic poly(trimethylsilyl acrylate). For poly(methyl acrylate), an approximate estimation of the stereoregularity by infrared spectroscopy was proposed.     

Thermogelling hydrogels of poly(ε-caprolactone-co-D,L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L-lactide) and poly(ε-caprolactone-co-L-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L-lactide) aqueous solutions

Thermogelling poly(ε-caprolactone-co-D,L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-D,L -lactide) and poly(ε-caprolactone-co-L -lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-L -lactide) triblock copolymers were synthesized through the ring-opening polymerization of ε-caprolactone and D,L -lactide or L -lactide in the presence of poly(ethylene glycol). The polymerization reaction was carried out in 1,3,5-trimethylbenzene with Sn(Oct)₂ as the catalyst at various temperatures, and the yields were about 96%. The molecular weights and polydispersities (M_w/M_n) by gel permeation chromatography were in the ranges of 5140–6750 and 1.35–1.45, respectively. The differential scanning calorimetry results showed that the melting temperatures of the poly(ε-caprolactone) components were between 30 and 40 °C. By the subtle tuning of the chemical compositions and microstructures of these triblock copolymers, the aqueous solutions underwent sol–gel transitions as the temperature increased, with the suitable lower critical solution temperature in the range of 17–28 °C at different concentrations. Transesterification in the polymerization process generated the redistribution of sequences, which remarkably affected the sol–gel transition temperature. The amphiphilic copolymers formed micelles in aqueous solutions with a diameter of 62 nm and a critical micelle concentration of about 0.032 wt % at 20 °C. Micelles aggregated as the temperature increased, leading to gel formation. The sol–gel transition was studied, with a focus on the structure–property relationship. It is expected to have potential applications in drug delivery and tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4091–4099, 2007     

Stereoblock poly(lactic acid): synthesis via solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) and poly(D-lactic acid)

Stereoblock poly(lactic acid) consisting of D- and L-lactate stereosequences can be successfully synthesized by solid-state polycondensation of a 1:1 mixture of poly(L-lactic acid) and poly(D-lactic acid). In the first step, melt-polycondensation of L- and D-lactic acids is conducted to synthesize poly(L-lactic acid) and poly(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these poly(L-lactic acid) and poly(D-lactic acid) are melt-blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt-blend is subjected to solid-state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high-molecular-weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher-molecular-weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in M(w) of stereoblock poly(lactic acid) (sb-PLA) as a function of the reaction time.     

Synthesis and characterization of methanesulfonic acid doped poly(2-chloroaniline), study of its physical properties and ammonia gas sensing application

The poly(2-chloroaniline) was prepared by in situ chemical oxidative polymerization method using ammonium thiosulphate as an oxidant and methanesulfonic acid as a dopant. The optical absorption spectra showed bands for π-π* transition of the benzenoid ring at 265 nm and at 350 nm for n-π* transition of the quinonoid ring. The broad band appeared around 550 nm was due to transition of electrons from the valance band to the conduction band, this also confirmed the good electrical conductivity of the polymer. The X-ray diffraction pattern showed characteristic diffraction peak at 2θ = 26° confirming a emeraldine salt form of the poly(2-chloroaniline). The electrical conductivity of the polymer measured by the two probe method at room temperature was 2.21×10^?3 S/cm, which was found to be thermally activated. The linear increase in conductivity with increase in the temperature suggested the electron hopping mechanism. The methanesulfonic acid doped poly(2-chloroaniline) presents a linear dependency of its electrical resistance with an increase in ammonia gas concentration (1 ppm to 300 ppm) and creates a promising sensing material for ammonia gas sensing applications.