Turn‐On Fluorescence Sensor Based on Single‐Walled‐Carbon‐Nanohorn–Peptide Complex for the Detection of Thrombin

Proteases play a central role in several widespread diseases. Thus, there is a great need for the fast and sensitive detection of various proteolytic enzymes. Herein, we have developed a carbon nanotube (CNT)‐based protease biosensing platform that uses peptides as a fluorescence probe for the first time. Single‐walled carbon nanohorns (SWCNHs) and thrombin were used to demonstrate this detection strategy. SWCNHs can adsorb a fluorescein‐based dye (FAM)‐labeled peptide (FAM‐pep) and quench the fluorescence of FAM. In contrast, thrombin can cleave FAM‐pep on SWCNHs and recover the fluorescence of FAM, which allows the sensitive detection of thrombin. This biosensor has a high sensitivity and selectivity toward thrombin, with a detection limit of 100 pM .     

Ag‐CNT Architectures for Attomolar Dopamine Detection and 100‐Fold Fluorescence Enhancements with Cellphone‐Based Surface Plasmon‐Coupled Emission Platform

We report cellphone‐based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon‐coupled emission (SPCE) platform. To this end, silver‐coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100‐fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π–π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.     

Fluorescence Turn‐On Sensing of Lectins with Mannose‐Substituted Tetraphenylethenes Based on Aggregation‐Induced Emission

The synthesis of mannose‐substituted tetraphenylethenes (TPEs) and their aggregation‐induced emission (AIE) behavior, induced by interactions with concanavalin A (Con A), are reported. A mixture of the mannose‐TPE conjugates and Con A in a buffer solution displays an intense blue emission on agglutination within a few seconds, which serves as a “turn‐on” fluorescent sensor for lectins. The sensing is also selective: the conjugates act as a sensor for Con A, but do not sense a galactose‐binding lectin, PNA. Con A‐recognition is not affected even in the presence of other proteins in a mixture. The conjugates also exhibit high sensitivity to detect Con A. An increased sensitivity of the conjugates results if mannopyranoside substituents are linked to the TPE‐core unit with a flexible chain and/or when the number of mannose residues increases.     

Polymer‐Templated Perylene‐Probe Noncovalent Self‐Assembly: A New Strategy for Label‐Free Ultrasensitive Fluorescence Turn‐On Biosensing

A new label‐free fluorescence turn‐on strategy for highly sensitive biosensing has been developed. A negatively charged perylene probe was synthesized. Polycations could induce aggregation of the perylene probe through noncovalent interactions and the fluorescence of the probe’s monomer was efficiently quenched. Upon addition of a single‐stranded nucleic acid, competitive binding of the negatively charged nucleic acid (a polyanion) to the cationic polymer resulted in the release of a monomer and thus a turn‐on fluorescence signal was detected. Without the use of any amplification techniques, a detection limit of 2 pM DNA was obtained. Based on these results, an assay strategy for the highly sensitive detection of alkaline phosphatase (ALP) activity has been demonstrated. λ Exonuclease (λ exo) could degrade 5′‐phosphorylated single‐stranded DNA. However, when the DNA sample was treated with ALP, the phosphate functional group was removed by ALP and it could no longer be degraded by λ exo. Binding of the DNA to the perylene probe–polycation complex resulted in a turn‐on fluorescence signal, which could be used for sensing of ALP. The method is highly sensitive, a limit of detection as low as 0.02 mU mL^?1 ALP was obtained. Our method is simple, convenient, highly sensitive, and inexpensive.     

Real‐Time Fluorescence Turn‐On Detection of Alkaline Phosphatase Activity with a Novel Perylene Probe

A tetracationic perylene probe (probe 2 ) was designed and synthesized. Probe 1 was used for the real‐time fluorescence turn‐on assay of alkaline phosphatase (ALP) activity and inhibitor screening. Probe 1 monomer fluorescence could be very efficiently quenched by ATP through the formation of an ATP/probe 1 complex. ALP triggered the degradation of ATP, the breakdown of the ATP/probe 1 complex, and the recovery of the probe 1 monomer fluorescence. In the presence of an ALP inhibitor, a decrease in fluorescence recovery was observed.     

A Strategy for Dramatically Enhancing the Selectivity of Molecules Showing Aggregation‐Induced Emission towards Biomacromolecules with the Aid of Graphene Oxide

By intelligently utilizing the different interacting strengths between different moieties according to the displacement method, general biosensors with aggregation‐induced emission (AIE) characteristics for biomacromolecules without selectivity were converted to excellent, highly selective probes for one specific biomacromolecule with the aid of graphene oxide (GO) in an aqueous medium. Importantly, thanks to the different interactions between the AIE molecule and biomacromolecules, just by simply changing the AIE molecule the sensing system could detect different types of biomacromolecules, thereby providing a new approach to the development of AIE‐based sensors with high selectivity and sensitivity. More specifically, the complex of A₂HPS?HCl—a derivative of hexaphenylsilone (HPS) functionalized by two amino (A₂) groups (N(CH₂CH₃)₃)—and GO only gives an “off–on” response to DNA, with a detection limit of 2.3 μg mL^?1 toward DNA‐CT (calf thymus); interestingly, the complex of TPE‐N₂C₄ (1,2‐bis{4‐[4‐(N,N,N‐triethylammonium)butoxy]phenyl}‐1,2‐diphenylethene dibromide) and GO could only detect the presence of bovine serum albumin (BSA), whereas other biomacromolecules, including DNA, RNA, and even other proteins have very little influence.     

Water‐Soluble Fluorescent Probes for Selective Recognition of Lysine and Its Application in an Object Carry‐and‐Release System

A water‐soluble fluorescent probe PEG‐TPA‐5′ was synthesized, which shows an excellent selectivity to detect Lys in aqueous phase. An object carry‐and‐release system is established by applying PEG‐TPA‐5′ as carrier and Lys as chemical stimulating source.     

A New Signal‐On Photoelectrochemical Biosensor Based on a Graphene/Quantum‐Dot Nanocomposite Amplified by the Dual‐Quenched Effect of Bipyridinium Relay and AuNPs

A new photoelectrochemical (PEC) biosensor was developed by using carboxyl‐functionalized graphene and CdSe nanoparticles. This sensitive interface was then successfully applied to detection of thrombin based on the dual‐quenched effect of PEC nanoparticle, which relied on the electron transfer of a bipyridinium relay and energy transfer of AuNPs. After recognition with an aptamer, the PEC nanoparticle was removed and a signal‐on PEC biosensor was obtained. Moreover, the bio‐barcode technique used in the preparation of PEC nanoparticle could avoid cross‐reaction and enhances the sensitivity. Taking advantages of the various methods mentioned above, the sensitivity could be easily enhanced. In addition, in this work we also investigated graphene that was modified with different functional groups and AuNPs of different particle sizes. Under optimal conditions, a detection limit of 5.9×10^?15 M was achieved. With its simplicity, selectivity, and sensitivity, this strategy shows great promise for the fabrication of highly efficient PEC biosensors.     

Far‐Infrared‐Assisted Preparation of a Graphene–Nickel Nanoparticle Hybrid for the Enrichment of Proteins and Peptides

A new approach based on far infrared‐assisted in situ reduction was developed for the facile one‐step preparation of graphene–nickel nanoparticle hybrid by refluxing a mixture solution containing graphene oxide, nickel(II) sulfate, and hydrazine over an far‐infrared heater. The reduction time was as short as 20 min. The structure of the material was investigated by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction, energy dispersive spectroscopy, vibrating sample magnetometery, and Fourier transform infrared spectroscopy. Magnetic investigations indicate that the grapheme–nickel nanoparticle hybrid exhibits ferromagnetic behavior at room temperature. Meanwhile, the hybrid was successfully employed in the enrichment and identification of proteins and peptides in combination with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry based on its excellent magnetic responsibility, high dispersibility, large surface area, and hydrophobicity, indicating great promise for a wide range of applications.     

Uniform Decoration of Vanadium Oxide Nanocrystals on Reduced Graphene‐Oxide Balls by an Aerosol Process for Lithium‐Ion Battery Cathode Material

VO₂‐decorated reduced graphene balls were prepared by a one‐pot spray‐pyrolysis process from a colloidal spray solution of well‐dispersed graphene oxide and ammonium vanadate. The graphene–VO₂ composite powders prepared directly by spray pyrolysis had poor electrochemical properties. Therefore, the graphene–VO₂ composite powders were transformed into a reduced graphene ball (RGB)–V₂O₅ (RGB) composite by post‐treatment at 300 °C in an air atmosphere. The TEM and dot‐mapping images showed a uniform distribution of V and C components, originating from V₂O₅ and graphene, consisting the composite. The graphene content of the RGB–V₂O₅ composite, measured by thermogravimetric analysis, was approximately 5 wt %. The initial discharge and charge capacities of RGB–V₂O₅ composite were 282 and 280 mA h g^?1, respectively, and the corresponding Coulombic efficiency was approximately 100 %. On the other hand, the initial discharge and charge capacities of macroporous V₂O₅ powders were 205 and 221 mA h g^?1, respectively, and the corresponding Coulombic efficiency was approximately 93 %. The RGB–V₂O₅ composite showed a better rate performance than the macroporous V₂O₅ powders.     

A Pyridoindole‐Based Multifunctional Bioprobe: pH‐Induced Fluorescence Switching and Specific Targeting of Lipid Droplets

A versatile fluorescent probe, PITE, based on alkyl‐substituted pyridoindole (PI) and tetraphenylethylene (TE), which exhibits facile pH‐induced fluorescence switching in solution, as nanoparticles, and in the solid state, is presented. Strong fluorescence in the solid state, as well as in solution and the aggregated state, allow sensing of toxic acid vapors. Fluorescence “off–on” switching of PITE through exposure to trifluoroacetic acid and triethylamine vapor is visualized by the naked eye. A unified picture of the switchable fluorescence of PITE is obtained by comprehensive spectroscopic investigations coupled with quantum mechanical calculations. Strong fluorescence, a large Stokes shift, high photostability, and biocompatibility of PITE make it a viable probe for subcellular imaging. Extensive fluorescence microscopic studies by employing organisms including lower and higher eukaryotes reveal specific localization of PITE to lipid droplets (LDs). LDs are dynamic subcellular organelles linked to various physiological processes and human diseases. Hence, the specific detection of LDs in diverse organisms is important to biomedical research and healthcare. Isolation of LDs and subsequent colocalization studies ascertain selective targeting of LDs by the easily affordable, lipophilic bioprobe, PITE. Thus, PITE is a promising multifunctional probe for chemosensing and the selective tracking of LDs.     

Electronic Olfactory Sensor Based on A. mellifera Odorant‐Binding Protein 14 on a Reduced Graphene Oxide Field‐Effect Transistor

An olfactory biosensor based on a reduced graphene oxide (rGO) field‐effect transistor (FET), functionalized by the odorant‐binding protein 14 (OBP14) from the honey bee (Apis mellifera) has been designed for the in situ and real‐time monitoring of a broad spectrum of odorants in aqueous solutions known to be attractants for bees. The electrical measurements of the binding of all tested odorants are shown to follow the Langmuir model for ligand–receptor interactions. The results demonstrate that OBP14 is able to bind odorants even after immobilization on rGO and can discriminate between ligands binding within a range of dissociation constants from K_d=4 μM to K_d=3.3 mM . The strongest ligands, such as homovanillic acid, eugenol, and methyl vanillate all contain a hydroxy group which is apparently important for the strong interaction with the protein.     

Ultrasonic Preparation of Hierarchical Graphene‐Oxide/TiO2 Composite Microspheres for Efficient Photocatalytic Hydrogen Production

Hierarchical graphene oxide (GO)‐TiO₂ composite microspheres with different GO/TiO₂ mass ratios were successfully prepared by mixing GO and TiO₂ microspheres under ultrasonic conditions. Ultrasonication helped the GO and TiO₂ microsphere to uniformly mix on the microscale. The results showed that the GO‐TiO₂ composites that were prepared by ultrasonic mixing exhibited significantly higher hydrogen‐evolution rates than those that were synthesized by simple mechanical grinding, owing to synergetic effects, including enhanced light absorption and scattering, as well as improved interfacial charge transfer because of the excellent contact between the GO sheets and TiO₂ microspheres. In addition, GO‐TiO₂‐3 (3 wt. % GO) showed the highest hydrogen‐generation rate (305.6 μmol h^?), which was about 13 and 3.3‐times higher than those of TiO₂ microsphere and GO‐P25 (with 3 wt. % GO), respectively. Finally, a tentative mechanism for hydrogen production is proposed and supported by photoluminescence and transient photocurrent measurements. This work highlights the potential applications of GO‐TiO₂ composite microspheres in the field of clean‐energy production.     

A “Catch‐and‐Release” Protocol for Alkyne‐Tagged Molecules Based on a Resin‐Bound Cobalt Complex for Peptide Enrichment in Aqueous Media

The development of new and mild protocols for the specific enrichment of biomolecules is of significant interest from the perspective of chemical biology. A cobalt–phosphine complex immobilised on a solid‐phase resin has been found to selectively bind to a propargyl carbamate tag, that is, “catch”, under dilute aqueous conditions (pH 7) at 4 °C. Upon acidic treatment of the resulting resin‐bound alkyne–cobalt complex, the Nicholas reaction was induced to “release” the alkyne‐tagged molecule from the resin as a free amine. Model studies revealed that selective enrichment of the alkyne‐tagged molecule could be achieved with high efficiency at 4 °C. The proof‐of‐concept was applied to an alkyne‐tagged amino acid and dipeptide. Studies using an alkyne‐tagged dipeptide proved that this protocol is compatible with various amino acids bearing a range of functionalities in the side‐chain. In addition, selective enrichment and detection of an amine derived from the “catch and release” of an alkyne‐tagged dipeptide in the presence of various peptides has been accomplished under highly dilute conditions, as determined by mass spectrometry.     

The Structural Influence of Graphene Oxide on Its Fragmentation during Laser Desorption/Ionization Mass Spectrometry for Efficient Small‐Molecule Analysis

The structural influence of graphene oxide (GO) on laser desorption/ionization mass spectrometry (LDI‐MS) analysis of small molecules was systematically investigated by using size‐fractionated GO. For fractionation of GO, pH‐assisted centrifugation, sequential vacuum filtration, and sonochemical cutting processes were employed and the size‐fractionated GO was thoroughly characterized to understand their size‐dependent optochemical properties. Then, the fractionated GO was applied to the analysis of various small molecules by LDI‐MS to investigate the relationship between their optochemical properties and LDI‐MS performance. We found that large GO sheets (>0.5 μm) were more prone to fragmentation under laser irradiation during LDI‐MS analysis than small GO sheets (<0.5 μm). In this regard, the LDI‐MS analysis efficiency of various small molecules was significantly improved by using nanosized GO (NGO) as a matrix without background interference. In particular, NGO was successfully applied to the sensitive detection of hydrophobic pollutant molecules without requiring any surface‐functionalization, enrichment, and separation process. Therefore, the present study could provide important basic information and be a practical tool for the development of simple and efficient LDI‐MS platforms by using GO derivatives.