Infrared photodetectors based on single-layer CVD-grown graphene and PbS quantum dots, which are fabricated by solution processing, show ultrahigh responsivities of up to 10(7) A/W under infrared light illumination. The devices fabricated on flexible plastic substrates have excellent bending stability. The photoresponse is attributed to the field-effect doping in graphene films induced by negative charges generated in the quantum dots.

Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin‐film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion‐sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge‐progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as‐fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next‐generation devices featuring wearable, deformable, printable, ultrathin, and see‐through characteristics.

1 of 41) 1603886However, despite its high absorption coefficient, [15] single-layer graphene can absorb only ≈2.3% of incident visible and infrared (IR) light due to its thinness, [16,17] which is undesirable for high performance photodetectors that require strong light absorption. Graphene's gaplessness also leads to short photocarrier lifetime in pure graphene, which is unfavorable for efficient photocurrent generation. [18][19][20] In addition to graphene, this family of materials contains an extremely large range of other 2D-layered materials that have recently attracted much research interest. [1][2][3][4][5][6][7][8] Similar to graphene, being atomically thin, these materials exhibit a wide range of unique electrical, optical, thermal, and mechanical properties that can never be seen in their three-dimensional (3D) bulk counterparts due to the dimensionality confinement effect and modulation in their band structures. [21,22] These 2D-layered materials can be metals, semiconductors, insulators, superconductors, topological insulators, or paramagnetic, diamagnetic, ferromagnetic, or anti-ferromagnetic, etc., depending on their composition and phases. [23,24] Among these materials, particular attention has been paid to 2D layered semiconductors thanks to their unique electronic [2,[24][25][26] and optoelectronic properties, [27,28] which arise from their appreciable bandgaps ranging from IR to UV and throughout the visible range.The optical and optoelectronic properties of 2D layered semiconductors are strongly dependent on their number of layers due to the quantum confinement effects in the out-of-plane direction and changes in symmetry. [29,30] This layer-dependent modulation of physical properties, such as bandgap structure, is particularly evident in the semiconducting transition metal dichalcogenides (TMDs) [2,7,29,31,32] and few-layer black phosphorus (BP). [33,34] Another effect induced by vertical quantum confinement is the increased absorption efficiency, which results from the strongly bound excitons due to the reduced thickness. [29,35,36] The atomic thickness of a 2D layered semiconductor also leads to high transparency [37] and good mechanical flexibility, [38] properties of particular interest for novel device applications such as flexible, wearable, or portable electronics. Despite their high transparency, 2D layered semiconductors can strongly interact with incident light, leading to enhanced photon absorption and electron-hole creation due to the existence of Van Hove singularities in their electronic density of states. [39] It has also been reported that 2D layered materials possess extraordinary elastic modulus and large strain (>10%) before rupture, [40][41][42][43] which allow for tuning their electronic and optical properties Following a significant number of graphene studies, other two-dimensional (2D) layered materials have attracted more and more interest for their unique structures and distinct physical properties, which has opened a window for realizing novel electronic or optoelectr...

Organic thin-film transistors (OTFTs) show promising applications in various chemical and biological sensors. The advantages of OTFT-based sensors include high sensitivity, low cost, easy fabrication, flexibility and biocompatibility. In this paper, we review the chemical sensors and biosensors based on two types of OTFTs, including organic field-effect transistors (OFETs) and organic electrochemical transistors (OECTs), mainly focusing on the papers published in the past 10 years. Various types of OTFT-based sensors, including pH, ion, glucose, DNA, enzyme, antibody-antigen, cell-based sensors, dopamine sensor, etc., are classified and described in the paper in sequence. The sensing mechanisms and the detection limits of the devices are described in details. It is expected that OTFTs may have more important applications in chemical and biological sensing with the development of organic electronics.

This work designed a novel platform for effective sensing of biomolecules by fluorescence resonance energy transfer (FRET) from quantum dots (QDs) to graphene oxide (GO). The QDs were first modified with a molecular beacon (MB) as a probe to recognize the target analyte. The strong interaction between MB and GO led to the fluorescent quenching of QDs. Upon the recognition of the target, the distance between the QDs and GO increased, and the interaction between target-bound MB and GO became weaker, which significantly hindered the FRET and, thus, increased the fluorescence of QDs. The change in fluorescent intensity produced a novel method for detection of the target. The GO-quenching approach could be used for detection of DNA sequences, with advantages such as less labor for synthesis of the MB-based fluorescent probe, high quenching efficiency and sensitivity, and good specificity. By substituting the MB with aptamer, this strategy could be conveniently extended for detection of other biomolecules, which had been demonstrated by the interaction between aptamer and protein. To the best of our knowledge, this is the first application of the FRET between QDs and GO and opens new opportunities for sensitive detection of biorecognition events.