There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.

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Supramolecular Luminescent Sensors

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high-k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum...

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics

Ammonia gas sensors: A comprehensive review.

Modern gas monitoring scenarios for medical diagnostics, environmental surveillance, industrial safety, and other applications demand new sensing capabilities. This Review provides analysis of development of new generation of gas sensors based on the multivariable response principles. Design criteria of these individual sensors involve a sensing material with multiresponse mechanisms to different gases and a multivariable transducer with independent outputs to recognize these different gas responses. These new sensors quantify individual components in mixtures, reject interferences, and offer more stable response over sensor arrays. Such performance is attractive when selectivity advantages of classic gas chromatography, ion mobility, and mass spectrometry instruments are canceled by requirements for no consumables, low power, low cost, and unobtrusive form factors for Internet of Things, Industrial Internet, and other applications. This Review is concluded with a perspective for future needs in fundament...

Multivariable Sensors for Ubiquitous Monitoring of Gases in the Era of Internet of Things and Industrial Internet

The strong and controllable chemical sensitivity of organic semiconductors (OSCs) and the amplification capability of transistors in circuits make use of OSC-based field-effect transistors compelling for chemical sensors. Analytes detected and assayed range from few-atom gas-phase molecules that may have adverse health and security implications to biomacromolecules (proteins, nucleic acids) that may be markers for physiological processes and medical conditions. This review highlights recent progress in organic field-effect transistor (OFET) chemical sensors, emphasizing advances from the past 5 years and including aspects of OSC morphology and the role of adjacent dielectrics. Design elements of the OSCs and various formats for the devices are illustrated and evaluated. Challenges associated with the present state of the art and future opportunities are also discussed.

Chemical and Biomolecule Sensing with Organic Field-Effect Transistors

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors.

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors

Understanding the sensing mechanism in organic chemical sensors is essential for improving the sensing performance such as detection limit, sensitivity, and other response/recovery time, selectivity, and reversibility for real applications. Here, we report a highly sensitive printed ammonia (NH3) gas sensor based on organic thin film transistors (OTFTs) with fluorinated difluorobenzothiadiazole-dithienosilole polymer (PDFDT). These sensors detected NH3 down to 1 ppm with high sensitivity (up to 56%) using bar-coated ultrathin (<4 nm) PDFDT layers without using any receptor additives. The sensing mechanism was confirmed by cyclic voltammetry, hydrogen/fluorine nuclear magnetic resonance, and UV/visible absorption spectroscopy. PDFDT-NH3 interactions comprise hydrogen bonds and electrostatic interactions between the PDFDT polymer backbone and NH3 gas molecules, thus lowering the highest occupied molecular orbital levels, leading to hole trapping in the OTFT sensors. Additionally, density functional theory c...

Highly Sensitive Flexible NH3 Sensors Based on Printed Organic Transistors with Fluorinated Conjugated Polymers

High-performance diketopyrrolopyrrole-based organic field-effect transistors for flexible gas sensors

We report printed flexible optoelectronic sensors composed of red organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) for detection of various biological signals in a photoplethysmograph (PPG) device. Fabricated flexible OLEDs achieved maximum luminance >1000 cd/m2 at 9 V, with peak at 640 nm. Maximum flexible OPD photosensitivity for the poly(3-hexylthiophene-2, 5-diyl) and phenyl-C61-butyric acid methyl ester (PCBM) heterojunction is $ {2} \times {10}^{{2}}$ at 0 V and 1.76 at −1 V, irradiated with 1.2 mW/cm2 at 660 nm. The diketopyrrolopyrrole thieno [3,2-b]thiophene blended with PCBM OPDs with poly (3,4-ethylenedioxythiophene):polystyrene sulfonate anode showed photosensitivity = 84 at −1 V bias to almost ${6} \times {10}^{{4}}$ at 0 V accompanied by low dark current ( ${9.5} \times {10}^{-{8}}$ A/cm2 at −1 V). PPG signals were successfully detected using the developed flexible PPG sensor and the conventional driving circuit. Human studies were conducted to evaluate the flexible PPG sensor performance in practical applications. Subject drowsiness was estimated from heart rate variability, extracted from the PPG signals, using machine learning algorithms. The flexible PPG sensor achieved 79.2% accuracy and 72.1% area under the receiver (AUC) to predict drowsiness (60-s window), which are meaningful results compared with conventional PPG sensors (83.3% accuracy and 69% AUC). Drowsiness estimation experiments using two PPG signals showed that the flexible PPG sensor achieved similar or better performance compared to conventional PPG sensors.

Flexible and Printed PPG Sensors for Estimation of Drowsiness

We demonstrate here the design, synthesis and characterization of two new chlorinated polymers, P(NDI2HD-T2CI2) and P(NDI20D-T2CI2) based on N.N-difunctionalized naphthalene diimide (NDI) and 3, 3’-dichloro-2, 2’-bithiophene (T2CI2) moieties. Our results indicate that organic thin-film transistors (OTFTs) based on these new chlorinated polymers exhibit electron mobilities approaching 0.1 cm2V−1s−1 (Ion:/off ~ 106-107), with far less ambipolarity due to their lower highest occupied molecular orbital energies, and they are more stable under deleterious high-humidity conditions (RH ~ 60%) and upon submersion in water, compared with those fabricated with the parent non-chlorinated polymers. In addition, OTFTs fabricated with the new chlorinated polymers exhibit excellent operational stabilities with <3% degradations upon bias-stress test.

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Gi-Seong Ryu

Papers

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors

Highly Sensitive Flexible NH3 Sensors Based on Printed Organic Transistors with Fluorinated Conjugated Polymers

High-performance diketopyrrolopyrrole-based organic field-effect transistors for flexible gas sensors

Flexible and Printed PPG Sensors for Estimation of Drowsiness

Naphthalene diimide-based polymeric semiconductors. Effect of chlorine incorporation and n-channel transistors operating in water