Large‐scale single‐crystalline ultrathin boron nanosheets (UBNSs, ≈10 nm) are fabricated through an effective vapor–solid process via thermal decomposition of diborane. The UBNSs have obvious advantages over thicker boron nanomaterials in many aspects. Specifically, the UBNSs demonstrate excellent field emission performances with a low turn‐on field, E to, of 3.60 V μm−1 and a good stability. Further, the dependence of (turn‐on field) E to/(threshold field) E thr and effective work function, Φ e, on temperature is investigated and the possible mechanism of temperature‐dependent field emission phenomenon has been discussed. Moreover, electronic transport in a single UBNS reveals it to be an intrinsic p‐type semiconductor behavior with carrier mobility about 1.26 × 10−1 cm2 V−1 s−1, which is the best data in reported works. Interestingly, a multiconductive mechanism coexisting phenomenon has been explored based on the study of temperature‐dependent conductivity behavior of the UBNSs. Besides, the photodetector device fabricated from single‐crystalline UBNS demonstrates good sensitivity, reliable stability, and fast response, obviously superior to other reported boron nanomaterials. Such superior electronic‐optical performances are originated from the high quality of single crystal and large specific surface area of the UBNSs, suggesting the potential applications of the UBNSs in field‐emitters, interconnects, integrated circuits, and optoelectronic devices.

We provide a novel and versatile signaling transduction strategy in the fluoroimmunoassay through regulating the interaction between graphene (Gr) and graphene quantum dots (GQDs), and demonstrate its feasibility in sensitive detection of human immunoglobulin G (IgG).

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Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: Pathogens have long presented a significant threat to human lives, and hence the rapid detection of infectious pathogens is vital for improving human health. Current detection methods lack the means to detect infectious pathogens in a simple, rapid, and reliable manner at the time and point of need. Functional nucleic acids (FNAs) have the potential to overcome these limitations by acting as key components for point-of-care (POC) biosensors due to their distinctive advantages that include high binding affinities and specificities, excellent chemical stability, ease of synthesis and modification, and compatibility with a variety of signal-amplification and signal-transduction mechanisms. This Account summarizes the work completed in our groups toward developing FNA-based biosensors for detecting bacteria. In vitro selection has led to the isolation of many RNA-cleaving fluorogenic DNAzymes (RFDs) and DNA aptamers that can recognize infectious pathogens, including Escherichia coli, Clostridium diff icile, Helicobacter pylori, and Legionella pneumophila. In most cases, a "many-against-many" approach was employed using a DNA library against a crude cellular mixture of an infectious pathogen containing diverse biomarkers as the target to isolate RFDs, with combined counter and positive selections ensuring high specificity toward the desired target. This procedure allows for the isolation of pathogen-specific FNAs without first identifying a suitable biomarker. Multiple target-specific DNA aptamers, including antiglutamate dehydrogenase (GDH) circular aptamers, anti-degraded toxin B aptamers, and anti-RNase HII aptamers, have also been isolated for the detection of bacteria such as Clostridium diff icile. The isolated FNAs have been integrated into fluorescent, colorimetric, and electrochemical biosensors using various signal transduction mechanisms. Both simple-to-use paper-based analytical devices and hand-held electrical devices with integrated FNAs have been developed for POC applications. In addition, signal-amplification strategies, including DNA catenane enabled rolling circle amplification (RCA), DNAzyme feedback RCA, and an all-DNA amplification system using a four-way junction and catalytic hairpin assembly (CHA), have been designed and applied to these systems to further increase their detection sensitivity. The use of these FNA-based biosensors to detect pathogens directly in clinical samples, such as urine, blood, and stool, has now been demonstrated with an outstanding sensitivity of as low as 10 cells per milliliter, highlighting the tremendous potential of using FNA-based sensors in clinical applications. We further describe strategies to overcome the challenges of using FNA-based biosensors in clinical applications, including strategies to improve the stability of FNAs in biological samples and prevent their nonspecific degradation from nucleases and strategies to deal with issues such as signal loss caused by nonspecific bin...