A High‐Performance Nitro‐Explosives Schottky Sensor Boosted by Interface Modulation

A high‐performance Schottky sensor boosted by interface modulation is fabricated for the detection of trace nitro‐explosives vapors. The interface modulation strategy results in a silicon nanowires (SiNWs) array/TiO₂/reduced graphene oxide (rGO) sensor with sensitive and selective response toward nitro‐explosives vapors. The response of the SiNWs array/TiO₂/rGO sensor toward nitro‐explosives vapors, such as 9 ppb 2,4,6‐trinitrotoluene, 4.9 ppt hexogen, and 0.25 ppq octagon, is boosted by 2.4, 7.5, and 5 times with the insertion of TiO₂. Superior selectivity is shown even compared with interfering gases of 10 ppm. Such good sensing performance can be attributed to the good sensing performance of the Schottky heterojunction‐based sensor, the Schottky barrier height modulation with the insertion of TiO₂, SiNWs array structure enhanced diffusion, and TiO₂ nanoparticles enhanced adsorption. This is believed to be the first Schottky heterojunction‐based sensor for nitro‐explosives vapors detection. This work would open a new way to develop highly sensitive and selective sensors.     

Dendrimer‐Based,High‐Luminescence Conjugated Microporous Polymer Films for Highly Sensitive and Selective Volatile Organic Compound Sensor Arrays

Conjugated microporous polymers (CMPs) are attracting increasing attention in chemical sensing due to their extended π‐conjugated framework, permanent microporous structure, and large specific surface area. However, the extremely poor solubility and processability of CMPs, as well as the serious fluorescence quenching caused by aggregation, restrict their practical applications. Herein, a high‐luminescence CMP film is constructed based on a novel dendrimer (TPETCz) featured by its central tetraphenylethylene “core” with aggregation‐induced emission effect and its highly electro‐active “branches.” High specific surface area CMP films for analyte diffusion are fabricated by a facile in situ electropolymerization method. These dendrimer‐based CMP films exhibit superior sensitivity to volatile organic compounds (VOCs). More importantly, 18 types, the most types reported, of VOC vapors are precisely distinguished by the linear discriminant analysis by establishing a 2D fluorescence sensor array based on the CMP films and the dendrimer monomer films.     

Combination of Graphene Oxide and Thiol‐Activated DNA Metallization for Sensitive Fluorescence Turn‐On Detection of Cysteine and Their Use for Logic Gate Operations

In this work, a unique, highly sensitive and selective fluorescence turn‐on approach for cysteine detection using an ensemble of graphene oxide (GO) and metallized DNA is reported. The method is based on the extraordinarily high quenching efficiency of GO and the specific interaction between cysteine and metallized DNA via robust Ag–S bonds. In the presence of GO, the dye‐labeled single‐stranded DNA shows weak fluorescence, while it exhibits a dramatic fluorescence increase upon the formation of the double helix through the “activated” metallized DNA by cysteine. In addition, the protocol shows excellent selectivity for cysteine over various other amino acids found in proteins. Importantly, by exploring GO–DNA interactions and the thiol‐mediated DNA hybridization, our sensing system can also be utilized to design the “OR” and “INHIBIT” logic gates using cysteine and DNA as inputs. To the author's knowledge, this method is the first example of combining GO and DNA metallization to fabricate a turn‐on fluorescent sensor for cysteine and logic gates.     

Emerging and Future Possible Strategies for Enhancing 1D Inorganic Nanomaterials‐Based Electrical Sensors towards Explosives Vapors Detection

Due to the necessity for maintaining homeland security and antiterrorism, a greatly growing demand exists for sensors that can detect explosives vapors. One‐dimensional inorganic nanomaterials represent one kind of the most promising materials for sensor fabrication due to the large surface‐to‐volume ratios, quantum confinement, high reaction activities, excellent electrical, optical, and chemical properties, unique anisotropic morphologies, and abundant structure tuning capabilities. All of these properties make the 1D inorganic nanomaterials ideal nanoscale building blocks in explosives vapors sensing applications. However, due to the big challenges, such as manufacturing technique with high cost and energy consumption, the difficulty of the assembling and patterning of 1D inorganic nanomaterials into functional devices, the weak repeatability for surface modification which hinder the development of sensors with high sensitivity, selectivity, low power consumption, simple structure, fast response and recovery procedures, high reliability and biocompatibility, more advanced strategies are needed for enhancing 1D‐inorganic‐nanomaterials‐based electrical sensors towards explosives vapors detection. In this article, a comprehensive review of the recent progresses on emerging and future possible strategies for enhancing 1D‐inorganic‐nanomaterials‐based electrical sensors towards explosives vapors detection is provided.     

Cationic Polyfluorenes with Phosphorescent Iridium(III) Complexes for Time‐Resolved Luminescent Biosensing and Fluorescence Lifetime Imaging

The application of a time‐resolved photoluminescence technique and fluorescence lifetime imaging microscopy for biosensing and bioimaging based on phosphorescent conjugated polyelectrolytes (PCPEs) containing Ir(III) complexes and polyfluorene units is reported. The specially designed PCPEs form 50 nm nanoparticles with blue fluorescence in aqueous solutions. Electrostatic interaction between the nanoparticles and heparin improves the energy transfer between the polyfluorene units to Ir(III) complex, which lights up the red signal for naked‐eye sensing. Good selectivity has been demonstrated for heparin sensing in aqueous solution and serum with quantification ranges of 0–70 μM and 0–5 μM, respectively. The signal‐to‐noise ratio can be further improved through time‐resolved emission spectra, especially when the detection is conducted in complicated environment, e.g., in the presence of fluorescent dyes. In addition to heparin sensing, the PCPEs have also been used for specific labeling of live KB cell membrane with high contrast using both confocal fluorescent cellular imaging and fluorescence lifetime imaging microscopies. This study provides a new perspective for designing promising CPEs for biosensing and bioimaging applications.     

Metal–Organic Polyhedra Cages Immobilized on a Plasmonic Substrate for Sensitive Detection of Trace Explosives

A novel strategy for highly sensitive detection and discrimination of explosives is developed based on the metal–organic polyhedra (MOP)‐decorated plasmonic substrate. It is found that the careful selection of the geometric and electronic characteristics of the assembly units (organic ligands and unsaturated metals sites) embedded within the MOP cage allows for the integration of multiple weak molecular interactions in a controllable fashion and thus the MOP cage can serve as an excellent receptor for selective uptake and binding of explosives. By further grafting of the MOP cage onto a plasmonic substrate with good surface‐enhanced Raman scattering enhancement factor, the resulting sensor shows a good sensing capability to various groups of ultratrace explosives, especially the challenging aliphatic nitro‐organics.     

Luminescent Graphene Oxide with a Peptide‐Quencher Complex for Optical Detection of Cell‐Secreted Proteases by a Turn‐On Response

Graphene oxide (GO) is an emerging luminescent nanomaterial with photostable and unique photoluminescence (PL) in the visible and near‐infrared region. Herein, a GO PL‐based optical biosensor consisting of a luminescent GO donor covalently linked with a peptide‐quencher complex is reported for the simple, rapid, and sensitive detection of proteases. To this end, the quenching efficiency of various candidate quenchers of GO fluorescence, such as metalloprotoporphyrins and QXL₅₇₀, are examined and their quenching mechanisms investigated. A fluorescence resonance energy transfer‐based quencher, QXL₅₇₀, is found to be much more effective for quenching the intrinsic fluorescence of GO than other charge transfer‐based quenchers. The designed GO–peptide–QXL system is then able to sensitively detect specific proteases—chymotrypsin and matrix metalloproteinase‐2—via a “turn‐on” response of quenched GO fluorescence after proteolytic cleavage of the quencher. Finally, the GO–peptide–QXL hybrid successfully detects MMP‐2 secreted from living cells—human hepatocytes HepG2—with high sensitivity.     

Molecular Engineering of “Click”‐Phospholes Towards Self‐Assembled Luminescent Soft Materials

Inspired by the self‐assembled bilayer structures of natural amphiphilic phospholipids, a new class of highly luminescent “click”‐phospholes with exocyclic alkynyl group at the phosphorus center is reported. These molecules can be easily functionalized with a self‐assembly group to generate neutral “phosphole‐lipids”. This novel approach retains the versatile reactivity of the phosphorus center, allowing further engineering of the photophysical and self‐assembly properties of the materials at a molecular level. The results of this study highlight the importance of being able to balance weak intermolecular interactions for controlling the self‐assembly properties of soft materials. Only molecules with the appropriate set of intermolecular arrangement/interactions show both organogel and liquid crystal mesophases with well‐ordered microstructures. Moreover, an efficient energy transfer of the luminescent materials is demonstrated and applied in the detection of organic solvent vapors.     

Synthesis of Poly(4‐vinylpyridine) Thin Films by Initiated Chemical Vapor Deposition (iCVD) for Selective Nanotrench‐Based Sensing of Nitroaromatics

A new nanoscale sensing concept for the detection of nitroaromatic explosives is described. The design consists of nitroaromatic‐selective polymeric layers deposited inside microfabricated trenches. As the layers are exposed to nitroaromatic vapors, they swell and contact each other to close an electrical circuit. The nitroaromatic selective polymer, poly(4‐vinylpyridine) (P4VP), is deposited in the trenches using initiated chemical vapor deposition (iCVD). P4VP is characterized for the first time as a selective layer for the absorption of nitroaromatic vapors. The Flory–Huggins equation is used to model the swelling response to nitroaromatic vapors. The Flory–Huggins interaction parameter for the P4VP–nitrobenzene system at 40 °C is 0.71 and 0.25 for P4VP–4‐nitrotoluene at 60 °C. Sensing of nitrobenzene vapors is demonstrated in a prototype device, while techniques to improve the performance of the design in terms of response time and sensitivities are described. Modeling shows that concentration and mass limits of detection of 0.95 ppb and 3 fg, respectively, can be achieved.     

Tunable Förster Resonance Energy Transfer in Colloidal Nanoparticles Composed of Polycaprolactone‐Tethered Donors and Acceptors: Enhanced Near‐Infrared Emission and Compatibility for In Vitro and In Vivo Bioimaging

A near‐infrared (NIR) fluorescent donor/acceptor (D/A) nanoplatform based on Förster resonance energy transfer is important for applications such as deep‐tissue bioimaging and sensing. However, previously reported D/A nanoparticles (NPs) often show limitations such as aggregation‐induced fluorescence quenching and poor interfacial compatibility that reduces the efficiency of the energy transfer and also leads to leaching of the small molecular fluorophores from the NP matrix. Here highly NIR‐fluorescent D/A NPs with a fluorescence quantum yield as high as 46% in the NIR region (700–850 nm) and robust optical stability are reported. The hydrophobic core of each NP is composed of donor and acceptor moieties both of which are tethered with polycaprolactone (PCL), while the hydrophilic corona is composed of poly[oligo(ethylene glycol) methyl ether methacrylate] to offer colloidal stability and “stealthy” effect in aqueous media. The PCL matrix in each colloidal NP not only offers biocompatibility and biodegradability but also minimizes the aggregation‐caused fluorescence quenching of D/A chromophores and prevents the leakage of the NIR fluorophores from the NPs. In vivo imaging using these NIR NPs in live mice shows contrast‐enhanced imaging capability and efficient tumor‐targeting through enhanced permeability and retention effect.     

Increasing Photothermal Efficacy by Simultaneous Intra‐ and Intermolecular Fluorescence Quenching

Recently, using in situ self‐assembly‐induced fluorescence quenching (i.e., intermolecular quenching denoted herein) of a photothermal agent (PTA) to enhance its photothermal efficiency has proven to be a successful photothermal therapy (PTT) strategy. But to the best of current knowledge, using simultaneous intra‐ and intermolecular fluorescence quenching of a PTA to additionally increase its photothermal efficacy has not been reported. Herein, employing a click condensation reaction and a rationally designed PTA Biotin‐Cystamine‐Cys‐Lys(Cypate)‐CBT ( 1 ), a “smart” strategy is developed of intracellular simultaneous intra‐ and intermolecular fluorescence quenching and applied it to largely increase the photothermal efficacy of the agent both in vitro and in vivo. After being internalized by biotin receptor‐overexpressing cancer cells, 1 is reduced by intracellular glutathione to initiate a CBT‐Cys condensation reaction (intramolecular quenching) and self‐assembly (intermolecular quenching) to form the nanoparticles 1‐NPs (simultaneous intra‐ and intermolecular fluorescence quenching). Experimental results indicate that 1‐NPs have higher fluorescence quenching efficiency than the control PTAs [Thiazole‐Lys(Cypate)‐Benzothiazole]₂ ( 1‐Dimer , intramolecular quenching), and nanoparticles of Cystamine‐Cys(Fmoc)‐Lys(Cypate)‐CBT ( 1‐Fmoc‐NPs , intermolecular quenching). It is envisioned that, by replacing the biotin group on 1 with other targeting warheads, the “smart” strategy is ready to increase the photothermal therapeutic efficiency of their corresponding diseases.     

High‐Fidelity Trapping of Spatial–Temporal Mitochondria with Rational Design of Aggregation‐Induced Emission Probes

High‐fidelity trapping of mitochondrial dynamic activity is critical to value cellular functions and forecast disease but lack of spatial–temporal probes. Given that commercial mitochondria probes suffering from low photostability, aggregation‐caused quenching effect, and limited signal‐to‐noise ratio from fluorescence “always on” in the process of targeting mitochondria, here, the rational design strategy of a novel aggregation‐induced emission (AIE) molecular motif and unique insight into the high‐fidelity targeting of mitochondria is reported, thereby illustrating the relationship between tailoring molecular aggregation state and mitochondrial targeting ability. This study focuses on how to exactly modulate the hydrophilicity and the aggregated state for realizing “off‐on” fluorescence, as well as matching the charge density to go across the cell membrane for mitochondrial targeting. Probe tricyano‐methylene‐pyridine (TCM‐1) exhibits an unprecedented high‐fidelity feedback on spatial–temporal mitochondrial information with several advantages such as “off‐on” near‐infrared characteristic, high targeting capacity, favorable biocompatibility, as well as excellent photostability. TCM‐1 also produces reactive oxygen species in situ for image‐guided photodynamic anticancer therapy. Through unraveling the relationship between tuning molecular aggregation behavior and organelle‐specific targeting ability, for the first time, a unique guide is provided in designing AIE‐active probes to explore the hydrophilicity and membrane potential for targeting subcellular organelles.     

Alizarin Complexone on Nanocrystalline TiO2: A Heterogeneous Approach to Anion Sensing

A novel, heterogeneous approach to “naked‐eye” colorimetric and spectrophotometric anion sensing is demonstrated, employing the molecular receptor alizarin complexone adsorbed onto a nanocrystalline, mesoporous TiO₂ film. pH buffer action intrinsic to the TiO₂ film allows dip sensing in aqueous solutions. This heterogeneous sensing system exhibits a high selectivity to F^– and CN^– anions, high sensitivity, a rapid response time, and excellent reusability.     

Protein‐Directed Metal Oxide Nanoflakes with Tandem Enzyme‐Like Characteristics: Colorimetric Glucose Sensing Based on One‐Pot Enzyme‐Free Cascade Catalysis

It is difficult and significant to realize the aim of “one‐pot” and “nonenzyme” for traditional colorimetric detection of blood glucose. The synthesis of nanomaterials with 2D morphology is also a challenge for the bovine serum albumin (BSA)‐directed method. Here, the BSA‐directed synthesis avenue for metal oxide with 2D nanomorphology is developed. MnO₂ nanoflakes (NFs) with controllable morphology can be obtained by changing the synthesis conditions. Fortunately, not only is the glucose oxidase (GOx)‐like nanozyme (MnO₂ NFs) discovered, but MnO₂ NFs also show dual enzyme activities (GOx‐like activity and peroxidase‐like activity) in similar pH range. That is to say, a “tandem nanozyme” (nanomaterial with tandem enzyme‐like characteristics) is presented here. Further, the one‐pot nonenzymatic strategy is proposed for the colorimetric detection of glucose, where the oxidation of glucose and the colorimetric detection of H₂O₂ are simultaneously conducted under the catalysis of the single nanozyme (MnO₂ NFs). The method shows high sensitivity, low limit of detection, and short detection time, due to the proximity effect and in situ reaction. The as‐synthesized 2D tandem nanozyme expands the species of nanozymes, and the proposed strategy breaks traditional colorimetric detection process, accomplishing the purposes of “one‐pot” and “nonenzyme” in the true sense.     

The Gas‐Detection Properties of Light‐Emitting Diatoms

In recent years, the porous silica structures (frustules) created by living diatoms have been studied for several nanoengineering applications based on biomimetic approaches. We focus on the gas‐sensing properties of diatoms: investigation of different species shows that the photoluminescence emission of frustules is affected by even small modifications of the surrounding gas environment, exhibiting a detection limit of few tenths of ppm in the case of nitrogen dioxide. A new understanding of this phenomenon is discussed here in terms of “static‐type” luminescence quenching through suppression of radiative states (most probably surface oxygen vacancies) induced by adsorption of gas molecules. The modeling allows the free energy of desorption to be measured by all‐optical means: the value obtained suggests that a chemisorption process is involved, in agreement with the observed absorption/desorption kinetics. The findings encourage investigation of diatoms as low‐cost biological transducers for detection of gas species.     

Intercalating Dye Harnessed Cationic Conjugated Polymer for Real‐Time Naked‐Eye Recognition of Double‐Stranded DNA in Serum

Thiazole orange (TO), an intercalating dye, is integrated into cationic poly(fluorene‐alt‐phenylene) (PFP) to develop a macromolecular multicolor probe (PFPTO) for double‐stranded DNA (dsDNA) detection. This polymer design not only takes advantage of the high affinity between TO and dsDNA to realize dsDNA recognition in biological media, but also brings into play the light‐harvesting feature of conjugated polymers to amplify the signal output of TO in situ. PFPTO differentiates dsDNA from single‐stranded DNA (ssDNA) more effectively upon excitation of the conjugated backbone relative to that upon direct excitation of TO as a result of efficient fluorescence resonance energy transfer from the polymer backbone to the intercalated TO. In the presence of dsDNA, energy transfer within PFPTO is more efficient as compared to that for free TO/PFP system, which leads to better dsDNA discriminability for PFPTO in contrast to that for TO/PFP. The distinguishable fluorescent color for PFPTO solutions in the presence of dsDNA allows naked‐eye detection of dsDNA with the assistance of a hand‐held UV lamp. The significant advantage of this macromolecular fluorescent probe is that naked‐eye detection of label‐free dsDNA can be performed in biological media in real‐time.     

A Multiresponsive Metal–Organic Framework: Direct Chemiluminescence,Photoluminescence, and Dual Tunable Sensing Applications

By incorporating an anthracene moiety into a framework, a multiresponsive luminescent metal–organic framework ( 1 ) has been synthesized, which exhibits both direct chemiluminescence (CL) and dual tunable photoluminescence. By utilizing the CL, 1 has been explored as a selective visual sensor for hydrogen peroxide. Moreover, 1 also exhibits tunable fluorescence response toward different analytes. For electron‐rich aromatics, “turn‐on” and “turn‐off” responses can be simply switched by varying the excitation wavelength. For nitroaromatics, 1 exhibits novel linear quantitative quenching response. Density functional theory (DFT) calculations and experiments have been carried out to study the unique fluorescence response. The multiple luminescence properties and dual tunable sensing response indicate that incorporating anthracene moieties into frameworks should be a promising strategy to develop unprecedented luminescent materials with remarkable sensing properties.     

Hierarchical Self‐Assembly of a Dandelion‐Like Supramolecular Polymer into Nanotubes for use as Highly Efficient Aqueous Light‐Harvesting Systems

A dandelion‐like supramolecular polymer (DSP) with a “sphere‐star‐parachute” topological structure consisting of a spherical hyperbranched core and many parachute‐like arms is constructed by the non‐covalent host–guest coupling between a cyclodextrin‐endcapped hyperbranched multi‐arm copolymer (host) and many functionalized adamantanes with each having three alkyl chain arms (guests). The obtained DSPs can further self‐assemble into nanotubes in water in a hierarchical way from vesicles to nanotubes through sequential vesicle aggregation and fusion steps. The nanotubes have a bilayer structure consisting of multiple “hydrophobic‐hyperbranched‐hydrophilic” layers. Such a structure is very useful for constructing a chlorosome‐like artificial aqueous light‐harvesting system, as demonstrated here, via the incorporation of hydrophobic 4‐(2‐hydroxyethylamino)‐7‐nitro‐2,1,3‐benzoxadiazole as donors inside the hyperbranched cores of the nanotubes and the hydrophilic Rhodamine B as the acceptors immobilized on the nanotube surfaces. This as‐prepared nanotube light harvesting system demonstrates unexpectedly high energy transfer efficiency (above 90%) in water. This extends supramolecular polymers with more complex topological structure, special self‐assembly behavior, and new functionality.     

Optical Nanoscale Pool‐on‐Surface Design for Control Sensing Recognition of Multiple Cations

General design of optical chemical nanosensors is needed to develop efficient sensing systems with high flexibility, and low capital cost for control recognition of toxic analytes. Here, we designed optical chemical nanosensors for simple, high‐speed detection of multiple toxic metal ions. The systematic design of the nanosensors was based on densely patterned chromophores with intrinsic mobility, namely, “building‐blocks” onto three‐dimensional (3D) nanoscale structures. The ability to precisely modify the nanoscale pore surfaces by using a broad range of chromophores that have different molecular sizes and characteristics enables detection of multiple toxic ions. A key feature of this building‐blocks design strategy is that the surface functionality and good adsorption characteristics of the fabricated nanosensor arrays enabled the development of “pool‐on‐surface” sensing systems in which high flux of the metal analytes across the probe molecules was achieved without significant kinetic hindrance. Such a sensing design enabled sensitive recognition of metal ions up to sub‐picomolar detection limits (～10^?11 mol dm^?3), for first time, with rapid response time within few seconds. Moreover, because these sensing pools exhibited long‐term stability, reversibility and selectivity in detecting most pollutant cations, for example, Cr(VI), Pb(II), Co(II), and Pd(II) ions, they are practical and inexpensive. The key result in our study is that the pool‐on‐surface design for optical nanosensors exhibited significant ion‐selective ability of these target ions from environmental samples and waste disposals.     

Polymeric Rulers: Distance‐Dependent Emission Behaviors of Fluorophores on Flat Gold Surfaces and Bioassay Platforms Using Plasmonic Fluorescence Enhancement

In this paper, we introduce the concept of a “polymeric ruler” for investigating distance‐dependent emission behaviors of fluorophores, namely the quenching or enhancement of fluorescence, on flat Au surfaces in the range of 5 to ～100 nm, which has not previously been easily accessible. The polymeric ruler is constructed by a highly controllable surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol)methacrylate (OEGMA), and the obtained thicknesses of the poly(OEGMA) (pOEGMA) layers range from ～5 to ～80 nm. The quenching or enhancement of fluorescence is found to be dependent upon the distance between fluorophores and the Au surface. In brief, fluorescence quenching occurs at distances within about 15 nm from the Au surface, and surface‐enhanced fluorescence is observed at tens of nanometers beyond the range of quenching with the maximum enhancement at about 40–50 nm. The obtained information on the distance‐dependent surface‐enhanced fluorescence is applied to the construction of highly sensitive bioassay platforms: the use of the 50 nm thick pOEGMA layer lowers the detection limit up to 1 pM .