Single-Nanoparticle-Based Nanomachining for Fabrication of a Uniform Nanochannel Sensor.

The structure of nanomaterials and nanodevices determines their functionality and applications. A single uniform nanochannel with a high aspect ratio is an attractive structure due to its unique rigid structures, easy preparation, and diverse pore structures and it holds significant promising importance in fields such as nanopore sensing and nanomanufacturing. Although the metal-nanoparticle-assistant silicon etching technique can produce uniform nanochannels, however, the fabrication of single through nanochannels remains a challenge thus far. A simple and versatile strategy is developed that allows for the retention of individual gold nanoparticle on a substrate, enabling single-nanoparticle nanomachining. This method involves three steps: the formation of a carbon protective layer on individual nanoparticles via electron-beam irradiation, selective removal of unprotected nanoparticles using a corrosive agent, and subsequent elimination of the carbon layer. This enables the fabrication of a single submillimeter-long uniform through nanochannel in the silicon wafer, which can be employed for nanopore sensing and shape-based nanoparticle distinguishing. The developed method can also facilitate single-nanoparticle studies and nanomachining for a broad application in materials science, electronics, micro/nano-optics, and catalysis.

Light-Driven Conversion of Silicon Nitride Nanopore to Nanonet for Single-Protein Trapping Analysis.

The single-molecule technique for investigation of an unlabeled protein in solution is very attractive but with great challenges. Nanopore sensing as a label-free tool can be used for collecting the structural information of individual proteins, but currently offers only limited capabilities due to the fast translocation of the target. Here, a reliable and facile method is developed to convert the silicon nitride nanopore to a stable nanonet platform for single-entity sensing by electrophoretic or electroosmotic trapping. A nanonet is fabricated based on a material reorganization process caused by electron-beam and light-irradiation treatment. Using protein molecules as a model, it is revealed that the solid-state nanonet can produce collision and trapping flipping signals of the protein, which provides more structural information than traditional nanopore sensing. More importantly, thanks to the excellent stability of the solid-state silicon nitride nanonet, it is demonstrated that the ultraviolet-light-irradiation-induced structural-change process of an individual protein can be captured. The developed nanonet supplies a robust platform for single-entity studies but is not limited to proteins.

Identification of plasmon-driven nanoparticle-coalescence-dominated growth of gold nanoplates through nanopore sensing.

The fascinating phenomenon that plasmon excitation can convert isotropic silver nanospheres to anisotropic nanoprisms has already been developed into a general synthetic technique since the discovery in 2001. However, the mechanism governing the morphology conversion is described with different reaction processes. So far, the mechanism based on redox reactions dominated anisotropic growth by plasmon-produced hot carriers is widely accepted and developed. Here, we successfully achieved plasmon-driven high yield conversion of gold nanospheres into nanoplates with iodine as the inducer. To investigate the mechanism, nanopore sensing technology is established to statistically study the intermediate species at the single-nanoparticle level. Surprisingly, the morphology conversion is proved as a hot hole-controlled coalescence-dominated growth process. This work conclusively elucidates that a controllable plasmon-driven nanoparticle-coalescence mechanism could enable the production of well-defined anisotropic metal nanostructures and suggests that the nanopore sensing could be of general use for studying the growth process of nanomaterials.

Seed-mediated growth of high yield Au nanoplates with in situ generated Au clusters through galvanic replacement.

A photochemical method is used to grow Au nanoplates in high yield from in situ generated Au cluster seeds through the galvanic replacement reaction. The morphology of nanoplates can be further controllably tuned by adjusting the pH, and enhanced morphology determined non-linear optics performances are obtained.

Double signal amplification through a functionalized nanoporous Au-Ag alloy microwire and Au nanoparticles: development of an electrochemical ˙OH sensor based on a self-assembled layer of 6-(ferrocenyl)hexanethiol.

Novel electrochemical sensors were developed based on a FcHT functionalized NPAMW and AuNPs for the analysis of ˙OH released from live cells. Self-assembled layers of FcHT can be selectively attacked by ˙OH, enabling simultaneous recognition and quantification of ˙OH, while the NPAMW and AuNPs provide a 3D multiplexed conductive structure rendering dual signal amplification.

3D nitrogen-doped graphite foam@Prussian blue: an electrochemical sensing platform for highly sensitive determination of H2O2 and glucose.

A platform is described for voltammetric sensing of hydrogen peroxide (H2O2). It is based on the use of nitrogen-doped graphite foam modified with Prussian Blue particles (PB/NGF). Graphite foam was synthesized by chemical vapor deposition, and doping with nitrogen was realized via dielectric barrier plasma discharge. PB particles were grown on the NGF through electrodeposition. SEM images of NGF verified the porous and interconnected structure of graphite foam, and XPS and Raman spectroscopy verified the successful doping with N. The performance of the PB/NGF electrode was characterized by CV and EIS which showed it to possess outstanding properties in terms of sensing H2O2. H2O2 was quantified in a range of 0.004 to 1.6 mM with a detection limit of 2.4 µM. The PB/NGF electrode also is shown to be a viable substrate for loading glucose oxidase (GOx). The GOx-functionalized electrode responds to glucose over the 0.2 to 20 mM concentration range at a potential of -50 mV (vs. Ag/AgCl), with a sensitivity of 27.48 mA M-1 cm-2 and a 0.1 M detection limit (at an S/N ratio of 3). The glucose sensor is selective, stable, and reproducible. The biosensor was successfully applied to the determination of glucose in spiked human serum samples, and this confirmed it practicability. Graphical abstract Schematic of a self-supporting amperometric glucose biosensor based on glucose oxidase and Prussian blue modified 3D nitrogen doped graphite foam.

A novel electrochemical sensor based on Cu@Ni/MWCNTs nanocomposite for simultaneous determination of guanine and adenine.

A novel electrochemical sensing platform based on combination of multi-walled carbon nanotubes and copper-nickel hybrid nanoparticles (Cu@Ni/MWCNTs) was developed for simultaneous detection of guanine (G) and adenine (A). The Ni/MWCNTs and Cu@Ni/MWCNTs nanocomposites were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical behaviors of G and A on the modified electrode were explored by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in phosphate buffer with pH 3.0. Under the optimal conditions, electrical signals were linear over the concentration ranges from 5.0 to 180µM and 8.0 to 150µM for simultaneous determination G and A with the detection limit as low as 0.35µM and 0.56µM (S/N = 3), respectively. Furthermore, linear concentration ranges in individual determination are 1.0-180µM and 2.0-150µM with detection limits of 0.17µM and 0.33µM (S/N = 3) for G and A, respectively. The sensor was successfully used to quantify G and A in real samples. The Cu@Ni/MWCNTs composite presented here can serve as a promising candidate for developing electrochemical sensor devices and plays an important role in widespread fields.

Electrochemical sensing platform based on molecularly imprinted polymer decorated N,S co-doped activated graphene for ultrasensitive and selective determination of cyclophosphamide.

A novel electrochemical sensor has been facilely fabricated by applying composite elements consisting of nitrogen and sulfur co-doped activated graphene (N,S-AGR) and molecularly imprinted polymer (MIP). N,S-AGR was synthesized by one-pot pyrogenation of a mixture of thiourea, KOH and graphene oxide, which was introduced to improve electron transfer capability and surface area of the electrode, while the electro-polymerized MIP layer afforded simultaneous recognition and quantification of cyclophosphamide (CPA) by utilizing Fe(CN)63-/4- as probe to indicate electrical signals. Under the optimal conditions, a calibration curve of current shift versus concentration of CPA was got in the range of 8×10-12-8×10-7molL-1, and the developed sensor gave a remarkably low detection limit (LOD) of 3.4×10-12mol L-1 (S/N=3). Moreover, the as-prepared sensor illustrated other good merits like stability and selectivity, and played a role in real-time therapeutic drug monitoring after CPA administration in rabbit.

Nanoporous gold leaf as a signal amplification agent for the detection of VOCs with a quartz crystal microbalance.

In this work, a novel sensing framework coupling nanoporous gold leaf (NPGL) and sensitive materials on a quartz crystal microbalance (QCM) sensor was developed for the detection of volatile organic compounds (VOCs). A bi-layer structure was established through a two-step modification process, where NPGL served as a loading platform to anchor more sensitive materials and provide a larger surface area. Sensitive materials for different target analytes (ethanol, benzene and n-heptane) were optimized, as well as the selection of the most suitable NPGL. The morphology of the bi-layer was characterized and the sensing performance, including the detection range, response time, reversibility, stability, etc., was investigated. The thermodynamics and kinetics of the gas adsorption process were studied by employing several classical models. It was found that the adsorption of the tested VOCs was more accurately represented using the Freundlich isotherm and the adsorption kinetics of these VOCs fitted well with pseudo second-order kinetics. The results of on-line monitoring demonstrated admirable sensing properties, fully indicating that the QCM sensor modified with a composite layer of sensitive material/NPGL has promising application prospects for real-time detection.