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16 pages, 5519 KiB

Open AccessArticle

Poly(Ionic Liquid) Semi-Interpenetrating Network Multi-Responsive Hydrogels

by Alexandru Tudor, Larisa Florea, Simon Gallagher, John Burns and Dermot Diamond

Sensors 2016, 16(2), 219; https://doi.org/10.3390/s16020219 - 6 Feb 2016

Cited by 27 | Viewed by 8051

Abstract

Herein we describe poly(ionic liquid) hydrogel actuators that are capable of responding to multiple stimuli, namely temperature, ionic strength and white light irradiation. Using two starting materials, a crosslinked poly ionic liquid (PIL) and a linear poly(N-isopropylacrylamide-co-spiropyran-co-acrylic [...] Read more.

Herein we describe poly(ionic liquid) hydrogel actuators that are capable of responding to multiple stimuli, namely temperature, ionic strength and white light irradiation. Using two starting materials, a crosslinked poly ionic liquid (PIL) and a linear poly(N-isopropylacrylamide-co-spiropyran-co-acrylic acid), several semi-interpenetrating (sIPN) hydrogels were synthesised. The dimensions of hydrogels discs were measured before and after applying the stimuli, to quantify their response. Samples composed of 100% crosslinked PIL alone showed an average area reduction value of ~53% when the temperature was raised from 20 °C to 70 °C, ~24% when immersed in 1% w/w NaF salt solution and no observable photo-response. In comparison, sIPNs containing 300% w/w linear polymer showed an average area reduction of ~45% when the temperature was raised from 20 °C to 70 °C, ~36% when immersed in 1% NaF w/w salt solution and ~10% after 30 min exposure to white light irradiation, respectively. Moreover, by varying the content of the linear component, fine-control over the photo-, thermo- and salt response, swelling-deswelling rate and mechanical properties of the resulting sIPN was achieved. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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15 pages, 705 KiB

Open AccessArticle

Optical Fiber Nanotips Coated with Molecular Beacons for DNA Detection

by Ambra Giannetti, Andrea Barucci, Franco Cosi, Stefano Pelli, Sara Tombelli, Cosimo Trono and Francesco Baldini

Sensors 2015, 15(5), 9666-9680; https://doi.org/10.3390/s150509666 - 24 Apr 2015

Cited by 22 | Viewed by 7417

Abstract

Optical fiber sensors, thanks to their compactness, fast response and real-time measurements, have a large impact in the fields of life science research, drug discovery and medical diagnostics. In recent years, advances in nanotechnology have resulted in the development of nanotools, capable of [...] Read more.

Optical fiber sensors, thanks to their compactness, fast response and real-time measurements, have a large impact in the fields of life science research, drug discovery and medical diagnostics. In recent years, advances in nanotechnology have resulted in the development of nanotools, capable of entering the single cell, resulting in new nanobiosensors useful for the detection of biomolecules inside living cells. In this paper, we provide an application of a nanotip coupled with molecular beacons (MBs) for the detection of DNA. The MBs were characterized by hybridization studies with a complementary target to prove their functionality both free in solution and immobilized onto a solid support. The solid support chosen as substrate for the immobilization of the MBs was a 30 nm tapered tip of an optical fiber, fabricated by chemical etching. With this set-up promising results were obtained and a limit of detection (LOD) of 0.57 nM was reached, opening up the possibility of using the proposed nanotip to detect mRNAs inside the cytoplasm of living cells. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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14 pages, 1146 KiB

Open AccessArticle

Rationally Designing Aptamer Sequences with Reduced Affinity for Controlled Sensor Performance

by Lauren R. Schoukroun-Barnes and Ryan J. White

Sensors 2015, 15(4), 7754-7767; https://doi.org/10.3390/s150407754 - 31 Mar 2015

Cited by 14 | Viewed by 8143

Abstract

The relative ease of predicting the secondary structure of nucleic acid sequences lends itself to the design of sequences to perform desired functions. Here, we combine the utility of nucleic acid aptamers with predictable control over the secondary structure to rationally design sequences [...] Read more.

The relative ease of predicting the secondary structure of nucleic acid sequences lends itself to the design of sequences to perform desired functions. Here, we combine the utility of nucleic acid aptamers with predictable control over the secondary structure to rationally design sequences with controlled affinity towards a target analyte when employed as the recognition element in an electrochemical sensor. Specifically, we present a method to modify an existing high-gain aptamer sequence to create sequences that, when employed in an electrochemical, aptamer-based sensor, exhibit reduced affinity towards a small molecule analyte tobramycin. Sensors fabricated with the high-gain parent sequence saturate at concentrations much below the therapeutic window for tobramycin (7–18 µM). Accordingly, the rationale behind modifying this high-gain sequence to reduce binding affinity was to tune sensor performance for optimal sensitivity in the therapeutic window. Using secondary structure predictions and analysis of the NMR structure of an aminoglycoside RNA aptamer bound to tobramycin, we are able to successfully modify the aptamer sequence to tune the dissociation constants of electrochemical aptamer-based sensors between 0.17 and 3 µM. The guidelines we present represent a general strategy to lessening binding affinity of sensors employing aptamer-modified electrodes. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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22 pages, 749 KiB

Open AccessArticle

Performance and Stress Analysis of Metal Oxide Films for CMOS-Integrated Gas Sensors

by Lado Filipovic and Siegfried Selberherr

Sensors 2015, 15(4), 7206-7227; https://doi.org/10.3390/s150407206 - 25 Mar 2015

Cited by 47 | Viewed by 9541

Abstract

The integration of gas sensor components into smart phones, tablets and wrist watches will revolutionize the environmental health and safety industry by providing individuals the ability to detect harmful chemicals and pollutants in the environment using always-on hand-held or wearable devices. Metal oxide [...] Read more.

The integration of gas sensor components into smart phones, tablets and wrist watches will revolutionize the environmental health and safety industry by providing individuals the ability to detect harmful chemicals and pollutants in the environment using always-on hand-held or wearable devices. Metal oxide gas sensors rely on changes in their electrical conductance due to the interaction of the oxide with a surrounding gas. These sensors have been extensively studied in the hopes that they will provide full gas sensing functionality with CMOS integrability. The performance of several metal oxide materials, such as tin oxide (SnO_²), zinc oxide (ZnO), indium oxide (In₂O₃) and indium-tin-oxide (ITO), are studied for the detection of various harmful or toxic cases. Due to the need for these films to be heated to temperatures between 250°C and 550°C during operation in order to increase their sensing functionality, a considerable degradation of the film can result. The stress generation during thin film deposition and the thermo-mechanical stress that arises during post-deposition cooling is analyzed through simulations. A tin oxide thin film is deposited using the efficient and economical spray pyrolysis technique, which involves three steps: the atomization of the precursor solution, the transport of the aerosol droplets towards the wafer and the decomposition of the precursor at or near the substrate resulting in film growth. The details of this technique and a simulation methodology are presented. The dependence of the deposition technique on the sensor performance is also discussed. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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17 pages, 927 KiB

Open AccessArticle

Improving Atomic Force Microscopy Imaging by a Direct Inverse Asymmetric PI Hysteresis Model

by Dong Wang, Peng Yu, Feifei Wang, Ho-Yin Chan, Lei Zhou, Zaili Dong, Lianqing Liu and Wen Jung Li

Sensors 2015, 15(2), 3409-3425; https://doi.org/10.3390/s150203409 - 3 Feb 2015

Cited by 23 | Viewed by 7228

Abstract

A modified Prandtl–Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM [...] Read more.

A modified Prandtl–Ishlinskii (PI) model, referred to as a direct inverse asymmetric PI (DIAPI) model in this paper, was implemented to reduce the displacement error between a predicted model and the actual trajectory of a piezoelectric actuator which is commonly found in AFM systems. Due to the nonlinearity of the piezoelectric actuator, the standard symmetric PI model cannot precisely describe the asymmetric motion of the actuator. In order to improve the accuracy of AFM scans, two series of slope parameters were introduced in the PI model to describe both the voltage-increase-loop (trace) and voltage-decrease-loop (retrace). A feedforward controller based on the DIAPI model was implemented to compensate hysteresis. Performance of the DIAPI model and the feedforward controller were validated by scanning micro-lenses and standard silicon grating using a custom-built AFM. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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18 pages, 2269 KiB

Open AccessArticle

High Resolution Switching Mode Inductance-to-Frequency Converter with Temperature Compensation

by Vojko Matko and Miro Milanović

Sensors 2014, 14(10), 19242-19259; https://doi.org/10.3390/s141019242 - 16 Oct 2014

Cited by 22 | Viewed by 6501

Abstract

This article proposes a novel method for the temperature-compensated inductance-to-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit to achieve better temperature stability of the converter. The novelty of this method lies in the switching-mode converter, the use of [...] Read more.

This article proposes a novel method for the temperature-compensated inductance-to-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit to achieve better temperature stability of the converter. The novelty of this method lies in the switching-mode converter, the use of additionally connected impedances in parallel to the shunt capacitances of the quartz crystal, and two inductances in series to the quartz crystal. This brings a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 10 and 40 °C. The oscillator switching method and the switching impedances connected to the quartz crystal do not only compensate for the crystal’s natural temperature characteristics but also any other influences on the crystal such as ageing as well as from other oscillating circuit elements. In addition, the method also improves frequency sensitivity in inductance measurements. The experimental results show that through high temperature compensation improvement of the quartz crystal characteristics, this switching method theoretically enables a 2 pH resolution. It converts inductance to frequency in the range of 85–100 µH to 2–560 kHz. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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Review

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13 pages, 340 KiB

Open AccessReview

Microbial Biofilm as a Smart Material

by Christian Garde, Martin Welch, Jesper Ferkinghoff-Borg and Thomas Sams

Sensors 2015, 15(2), 4229-4241; https://doi.org/10.3390/s150204229 - 12 Feb 2015

Cited by 6 | Viewed by 5924

Abstract

Microbial biofilm colonies will in many cases form a smart material capable of responding to external threats dependent on their size and internal state. The microbial community accordingly switches between passive, protective, or attack modes of action. In order to decide which strategy [...] Read more.

Microbial biofilm colonies will in many cases form a smart material capable of responding to external threats dependent on their size and internal state. The microbial community accordingly switches between passive, protective, or attack modes of action. In order to decide which strategy to employ, it is essential for the biofilm community to be able to sense its own size. The sensor designed to perform this task is termed a quorum sensor, since it only permits collective behaviour once a sufficiently large assembly of microbes have been established. The generic quorum sensor construct involves two genes, one coding for the production of a diffusible signal molecule and one coding for a regulator protein dedicated to sensing the signal molecules. A positive feedback in the signal molecule production sets a well-defined condition for switching into the collective mode. The activation of the regulator involves a slow dimerization, which allows low-pass filtering of the activation of the collective mode. Here, we review and combine the model components that form the basic quorum sensor in a number of Gram-negative bacteria, e.g., Pseudomonas aeruginosa. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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Other

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9 pages, 850 KiB

Open AccessConcept Paper

Pressure and Temperature Sensors Using Two Spin Crossover Materials

by Catalin-Maricel Jureschi, Jorge Linares, Ayoub Boulmaali, Pierre Richard Dahoo, Aurelian Rotaru and Yann Garcia

Sensors 2016, 16(2), 187; https://doi.org/10.3390/s16020187 - 2 Feb 2016

Cited by 67 | Viewed by 9417

Abstract

The possibility of a new design concept for dual spin crossover based sensors for concomitant detection of both temperature and pressure is presented. It is conjectured from numerical results obtained by mean field approximation applied to a Ising-like model that using two different [...] Read more.

The possibility of a new design concept for dual spin crossover based sensors for concomitant detection of both temperature and pressure is presented. It is conjectured from numerical results obtained by mean field approximation applied to a Ising-like model that using two different spin crossover compounds containing switching molecules with weak elastic interactions it is possible to simultaneously measure P and T. When the interaction parameters are optimized, the spin transition is gradual and for each spin crossover compounds, both temperature and pressure values being identified from their optical densities. This concept offers great perspectives for smart sensing devices. Full article

(This article belongs to the Special Issue Smart Materials for Switchable Sensors)

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