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Herein the development of cellular impedance biosensors, electrochemical impedance spectroscopy, and the general principles and terms associated with the cell–electrode interface is reviewed. This family of techniques provides quantitative and sensitive information into cell responses to stimuli in real-time with high temporal resolution. The applications of cell-based impedance biosensors as a readout in cell biology is illustrated with a diverse range of examples. The current state of the field, its limitations, the possible available solutions, and the potential benefits of developing biosensors are discussed. [ABSTRACT FROM AUTHOR]

Single molecule experiments have recently attracted enormous interest. Many of these studies involve the encapsulation of a single molecule into nanoscale containers (such as vesicles, droplets and nanowells). In such cases, the single molecule encapsulation efficiency is a key parameter to consider in order to get a statistically significant quantitative information. It has been shown that such encapsulation typically follows a Poisson distribution and such theory of encapsulation has only been applied to the encapsulation of single molecules into perfectly sized monodispersed containers. However, experimentally nanocontainers are usually characterized by a size distribution, and often just a single binding pair (rather than a single molecule) is required to be encapsulated. Here the use of Poisson distribution is extended to predict the encapsulation efficiency of two different molecules in an association equilibrium. The Poisson distribution is coupled with a log-normal distribution in order to consider the effect of the container size distribution, and the effect of adsorption to the container is also considered. This theory will allow experimentalists to determine what single molecule encapsulation efficiency can be expected as a function of the experimental conditions. Two case studies, based on experimental data, are given to support the theoretical predictions. [ABSTRACT FROM AUTHOR]

Targeted drug delivery in cancer typically focuses on maximising the endocytosis of drugs into the diseased cells. However, there has been less focus on exploiting the differences in the endocytosis pathways of cancer cells versus non-cancer cells. An understanding of the endocytosis pathways in both cancer and non-cancer cells allows for the design of nanoparticles to deliver drugs to cancer cells whilst restricting healthy cells from taking up anticancer drugs, thus efficiently killing the cancer cells. Herein we compare the differences in the endocytosis pathways of cancer and healthy cells. Second, we highlight the importance of the physicochemical properties of nanoparticles (size, shape, stiffness, and surface chemistry) on cellular uptake and how they can be adjusted to selectively target the dominated endocytosis pathway of cancer cells over healthy cells and to deliver anticancer drug to the target cells. The review generates new thought in the design of cancer-selective nanoparticles based on the endocytosis pathways. [ABSTRACT FROM AUTHOR]

Nanopores are promising sensing devices that can be used for the detection of analytes at the single molecule level. It is of importance to understand and model the current response of a nanopore sensor for improving the sensitivity of the sensor, a better interpretation of the behaviours of different analytes in confined nanoscale spaces, and quantitative analysis of the properties of the targets. The current response of a nanopore sensor, usually called a resistive pulse, results from the change in nanopore resistance when an analyte translocates through the nanopore. This article reviews the theoretical models used for the calculation of the resistance of the nanopore, and the corresponding change in nanopore resistance due to a translocation event. Models focus on the resistance of the pore cavity region and the access region of the nanopore. The influence of the sizes, shapes and surface charges of the translocating species and the nanopore, as well as the trajectory that the analyte follows are also discussed. This review aims to give a general guidance to the audience for understanding the current response of a nanopore sensor and the application of this class of sensor to a broad range of species with the theoretical models. [ABSTRACT FROM AUTHOR]

Nanopore-based sensors typically work by monitoring transient pulses in conductance via current–time traces as molecules translocate through the nanopore. The unique property of being able to monitor single molecules gives nanopore sensors the potential as quantitative sensors based on the counting of single molecules. This review provides an overview of the concepts and fabrication of nanopore sensors as well as nanopore sensing with a view toward using nanopore sensors for quantitative analysis. We first introduce the classification of nanopores and highlight their applications in molecular identification with some pioneering studies. The review then shifts focus to recent strategies to extend nanopore sensors to devices that can rapidly and accurately quantify the amount of an analyte of interest. Finally, future prospects are provided and briefly discussed. The aim of this review is to aid in understanding recent advances, challenges, and prospects for nanopore sensors for quantitative analysis. [ABSTRACT FROM AUTHOR]

Nanoelectrochemistry, where electrochemical processes are controlled and investigated with nanoscale resolution, is gaining more and more attention because of the many potential applications in energy and sensing and the fact that there is much to learn about fundamental electrochemical processes when we explore them at the nanoscale. The development of instrumental methods that can explore the heterogeneity of electrochemistry occurring across an electrode surface, monitoring single molecules or many single nanoparticles on a surface simultaneously, have been pivotal in giving us new insights into nanoscale electrochemistry. Equally important has been the ability to synthesise or fabricate nanoscale entities with a high degree of control that allows us to develop nanoscale devices. Central to the latter has been the incredible advances in nanomaterial synthesis where electrode materials with atomic control over electrochemically active sites can be achieved. After introducing nanoelectrochemistry, this paper focuses on recent developments in two major application areas of nanoelectrochemistry; electrocatalysis and using single entities in sensing. Discussion of the developments in these two application fields highlights some of the advances in the fundamental understanding of nanoelectrochemical systems really driving these applications forward. Looking into our nanocrystal ball, this paper then highlights: the need to understand the impact of nanoconfinement on electrochemical processes, the need to measure many single entities, the need to develop more sophisticated ways of treating the potentially large data sets from measuring such many single entities, the need for more new methods for characterising nanoelectrochemical systems as they operate and the need for material synthesis to become more reproducible as well as possess more nanoscale control. [ABSTRACT FROM AUTHOR]

A new type of gold-coated magnetic nanoparticle with strongly magnetic zero-valent iron core–iron oxide shell were synthesized. The small size of the magnetic cores and the zero-valent iron ensured superparamagnetic behaviour and high saturation magnetization of the overall nanoparticles. The nanoparticles showed stability against magnetic aggregation and good colloidal stability, which is important for many biomedical applications. [ABSTRACT FROM AUTHOR]

Pt islands with different sizes were grown on amorphous Ni nanoparticles, allowing the tuning of the Pt–Ni interface without changing the hydrogen binding energy of the Pt sites. As a result, the HER activity of the electrocatalysts increases by decreasing the size of the Pt islands due to the greater surface area of the Pt–Ni interfaces. [ABSTRACT FROM AUTHOR]

The direct quantification of programmed death-ligand 1 (PD-L1) as a biomarker for cancer diagnosis, prognosis and treatment efficacy is an unmet clinical need. Herein, we demonstrate the first report of rapid, ultrasensitive and selective electrochemical detection of PD-L1 directly in undiluted whole blood using modified gold-coated magnetic nanoparticles as "dispersible electrodes" with an ultralow detection limit of 15 attomolar and a response time of only 15 minutes. [ABSTRACT FROM AUTHOR]

The versatile qualities of gold coated magnetic nanoparticles for both optical and electrochemical detection, as well as the separation of analytes, make them an excellent choice for ultrasensitive biosensing applications. The challenge with such nanoparticles however is that strongly magnetic nanoparticles that reach the magnet rapidly are prone to aggregation, whilst superparamagnetic nanoparticles that are stable against aggregation reach the magnet slowly. Here, we report a conglomerate nanostructure consisting of superparamagnetic nanoparticles coated with gold that provides a rapid magnetic response while exhibiting colloidal stability in solution. The performance of these gold coated magnetic nanoparticles for both bio-separation and biosensing was demonstrated for application in biosensors, dispersible electrodes for detecting microRNA and surface-enhanced Raman scattering. [ABSTRACT FROM AUTHOR]

Light-activated electrochemistry (LAE) consists of employing a focused light beam to illuminate a semiconducting area and make it electrochemically active. Here, we show how to reduce the electrochemical spatial resolution to submicron by exploiting the short lateral diffusion of charge carriers in amorphous silicon to improve the resolution of LAE by 60 times. [ABSTRACT FROM AUTHOR]

Light can be used to address electrochemical reactions on a monolithic semiconducting electrode with spatial and temporal resolution. Herein, such principle was used for the electrodeposition of Au, Ag and Cu nanoparticles on a unique silicon-based electrode. The parallel nature of the process granted manufacturing speed and platforms were applied to discriminate molecules via multi-wavelength and multivariate Raman analysis. [ABSTRACT FROM AUTHOR]

Nanoparticle tracers with small sizes and large magnetization are critical for biomedical imaging and especially for magnetic particle imaging (MPI). Small size is important for accessing future intracellular and neurological in vivo applications Here, we show <15 nm nanoparticles made of zero valent iron cores, iron oxide shells and coated with a strongly binding brush co-polymer are effective MPI tracers. The small nanoparticle cores create a hydrodynamic diameter that is half of the state-of-the-art iron oxide tracers while the strongly magnetic zero valent iron maintains similar MPI signal magnitude and resolution. [ABSTRACT FROM AUTHOR]

Herein, a glucose meter-based immunosensing platform is developed that allows the quantification of procalcitonin (PCT) in whole blood samples. PCT is a biomarker for sepsis and its early detection would improve the safety of the patient, as the diagnostic process will be easier and faster. The method employs liposomes with encapsulated glucose as a signal generation tag, which are then used in a sandwich immunoassay by conjugating an antibody to the liposome. The optimal liposomes' size and concentration of encapsulated glucose is determined experimentally to be 200 nm and 27.8 mM, respectively. Upon the addition of a surfactant (Triton X-100), the glucose is released and a signal is detected with a personal glucose meter (PGM). This signal is directly proportional to the concentration of the PCT in the sample. The dynamic range of the assay developed was 0.153–15.38 nM, and could allow the detection of PCT as low as 0.15 nM. The assay showed a high selectivity toward PCT against other proteins such as C-reactive protein and human serum albumin and good reproducibility. This assay was able to quantitatively determine the amount of PCT in whole blood samples at clinically-relevant concentrations. [ABSTRACT FROM AUTHOR]

Spatial confinement of electrochemical reactions at solid/liquid interfaces is a mature area of research, and a central theme from cell biology to analytical chemistry. Monitoring or manipulating the kinetics of a charge transfer reaction in 2D is generally achieved using scanning electrochemical microscopy or multielectrode arrays, techniques that rely on moving physical probes or on a network of electrical connections. This tutorial is introducing concepts and instruments to confine faradaic electrochemical reactions in 2D without resorting to the mechanical movement of a probe, and with the simple design of one semiconducting electrode, one electrical lead and a single-channel potentiostat. We provide a theoretical background of semiconductor electrochemistry, and describe the use of localised visible light stimuli on photoconductor/liquid and semiconductor/liquid interfaces to address electrical conductivity – hence chemical reactivity – only at one specific site defined by the experimentalist. This enables shifting of the tenet of one electrode/one wire towards one wire/many electrodes. We discuss the applications of this emerging platform in the context of surface chemistry patterning, redox imaging, chemical and biological sensing, generating chemical gradients, electrocatalysis, nanotechnology and cell biology. [ABSTRACT FROM AUTHOR]

An effective strategy for regioselective modification and directional assembly of anisotropic nanoparticles is demonstrated to explore the electric field enhancement in assembled gold nanobipyramids compared with gold nanorods. The well-defined secondary plasmonic hot spots between the coupled gold nanobipyramids exhibit the capability for single molecule detection. [ABSTRACT FROM AUTHOR]

A simple and efficient approach to produce high quality black phosphorus quantum dots (BPQDs) in a common organic solvent using a microwave technique is developed in this work. This novel approach produces a stable dispersion of crystalline BPQDs with an average lateral size of 2.95 nm and thickness of 3.59 nm. We demonstrated that the as-prepared BPQDs can be an efficient electrocatalyst for the oxygen evolution reaction (OER). Our BPQDs without any supporting catalyst exhibited an impressive electrocatalytic activity for OER with an overpotential of 450 mV at 10 mA cm−2, whilst the traditional CoOx electrocatalyst showed an overpotential of 480 mV. By integrating our BPQDs with CoOx, we achieved an outstanding electrocatalytic OER performance with an overpotential of 360 mV at 10 mA cm−2, a low Tafel slope of 58.5 mV dec−1 and excellent stability, which was even comparable to the commercial IrO2 and RuO2 systems. This work introduces a promising protocol to prepare scalable BPQDs for real-world applications including electrocatalysis. [ABSTRACT FROM AUTHOR]

Herein is reported a new type of transparent electrode, prepared by depositing a thin layer of amorphous silicon film on indium tin oxide, which enables photoswitchable electrochemistry and optical imaging to be performed simultaneously. This offers the opportunity to visualise a spatially controlled electrochemical event on an unstructured electrode surface. [ABSTRACT FROM AUTHOR]

Pentamethylcyclopentadienyl iridium(iii) complexes of bidentate carbene–triazole ligands were found to be excellent homogeneous catalysts for the hydrogen borrowing mediated coupling of alcohols with amines. The reactions are highly efficient, able to reach completion in under 6 h at 100 °C at low catalyst loadings of 0.5 mol%, and are environmentally benign, the only by-product is water. The Ir(iii) catalysts promoted C–N bond formation across a range of alcohol and amine substrates, including biologically relevant motifs. Covalent attachment to a carbon black surface generated a well-defined “hybrid” heterogeneous catalyst which gave good conversion to products in the coupling reaction of aniline with benzyl alcohol, and could be recycled with no catalyst leeching. This represents the first report of a covalently linked heterogeneous iridium catalyst on carbon used for hydrogen borrowing. Turnover numbers (TON) for the heterogeneous were found to be significantly higher than the corresponding homogeneous reaction. To elucidate the homogeneous reaction mechanism, 1H NMR studies inconjuction with deuteration experiments allowed a mechanism to be postulated. [ABSTRACT FROM AUTHOR]

A novel structure of arrays of Cu/graphene double-nanocaps was developed via a one-step low-temperature chemical vapor deposition (CVD) process. Polystyrene spheres (PSSs) are ingeniously employed as both templates and solid carbon sources. SERS measurements reveal their high sensitivity and stability due to the synergistic effect of Cu and graphene double nanocaps. [ABSTRACT FROM AUTHOR]

Solid-phase microextraction (SPME) is directly integrated with low temperature plasma ionisation mass spectrometry to rapidly detect organophosphate chemical warfare agent simulants and their hydrolysis products in chemical mixtures, including urine. In this sampling and ionization method, the fibre serves: (i) to extract molecules from their native environment, and (ii) as the ionization electrode that is used to desorb and ionize molecules directly from the SPME surface. By use of a custom fabricated SPME fibre consisting of a stainless steel needle coated with a Linde Type A (LTA) zeolitic microporous material and low temperature plasma mass spectrometry, protonated dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP) and pinacolyl methylphosphonic acid (PinMPA) can be detected at less than 100 ppb directly in water and urine. Organophosphates were not readily detected by this approach using an uncoated needle in negative control experiments. The use of the LTA coating significantly outperformed the use of a high alumina Zeolite Socony Mobil-5 (ZSM-5) coating of comparable thickness that is significantly less polar than LTA. By conditioning the LTA probe by immersion in an aqueous CuSO4 solution, the ion abundance for protonated DMMP increased by more than 300% compared to that obtained without any conditioning. Sample recovery values were between 96 and 100% for each analyte. The detection of chemical warfare agent analogues and hydrolysis products required less than 2 min per sample. A key advantage of this sampling and ionization method is that analyte ions can be directly and rapidly sampled from chemical mixtures, such as urine and seawater, without sample preparation or chromatography for sensitive detection by mass spectrometry. This ion source should prove beneficial for portable mass spectrometry applications because relatively low detection limits can be obtained without the use of compressed gases, fluid pumps, and lasers. Moreover, the ion source is compact, can be powered with a 10 V battery, and is tolerant of complex mixtures. [ABSTRACT FROM AUTHOR]

Gold coated magnetic nanoparticles (Au@MNPs) have become increasingly interesting to nanomaterial scientists due to their multifunctional properties and their potential in both analytical chemistry and nanomedicine. The past decade has seen significant progress in the synthesis and surface modification of Au@MNPs. This progress is based on advances in the preparation and characterization of iron/iron oxide nanocrystals with the required surface functional groups. In this critical review, we summarize recent developments in the methods of preparing Au@MNPs, surface functionalization and their application in analytical sensing and biomedicine. We highlight some of the remaining major challenges, as well as the lessons learnt when working with Au@MNPs. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) are attracting tremendous interest owing to their low toxicity, water dispersibility, biocompatibility, optical properties and wide applicability. Herein, CQDs with an average diameter of (4.0 ± 0.2) nm and high crystallinity were produced simply from the electrochemical oxidation of a graphite electrode in alkaline alcohols. The as-formed CQDs dispersion was colourless but the dispersion gradually changed to bright yellow when stored in ambient conditions. Based on UV-Vis absorption, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), this colour change appeared to be due to oxygenation of surface species over time. Furthermore, the CQDs were used in specific and sensitive detection of ferric ion (Fe3+) with broad linear ranges of 10–200 μM with a low limit of detection of 1.8 μM (S/N = 3). The application of the CQDs for Fe3+ detection in tap water was demonstrated and the possible mechanism was also discussed. Finally, based on their good characteristics of low cytotoxicity and excellent biocompatibility, the CQDs were successfully applied to cell imaging. [ABSTRACT FROM AUTHOR]

Pure carbon black (CB) was covalently attached to a bidentate nitrogen coordination motif with a carbon–carbon bond by spontaneous reaction with an in situ generated ligand precursor. The functionalized support was treated with [Rh(CO)2(μ-Cl)]2 to form a heterogeneous carbon-based support covalently linked to a well defined Rh(i) coordination complex. The hybrid material was characterized using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Infrared (IR) spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS). The CB-supported Rh(i) catalyst was active in both hydroamination and dihydroalkoxylation reactions achieving turnover numbers approaching 1000 and was readily recycled. The selectivity of an intramolecular dihydroalkoxylation reaction was significantly improved by covalently anchoring the catalyst to the CB surface. [ABSTRACT FROM AUTHOR]

Three series of ruthenium complexes with the general formula Ru(bpy)n(β-diketonato)3-n (bpy = 2,2'-bipyridine, n = 0, 1, 2) were prepared and investigated using cyclic voltammetry and UV-vis spectroscopy. Variation of both the number and electronic demand of the β-diketonato ligands resulted in well-defined modulation of the potential at which oxidation of the metal centre occurred. The observed potentials were shown to be in good agreement with calculated ligand electrochemical parameters. A novel ruthenium(II) complex with electrochemical behaviour similar to that of ferrocene was identified. [ABSTRACT FROM AUTHOR]

Porous silicon (PSi) rugate filters modified with alkyne-terminated monolayers were chemically patterned using a combination of photolithography of photoresist and click chemistry. Two chemical functionalities were obtained by conjugating, via click reactions, ethylene glycol moieties containing two different terminal groups to discrete areas towards the exterior of a PSi rugate filter. The patterning of biological species to the functionalized surface was demonstrated through the conjugation of fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA). Fluorescence microscopy showed selective positioning of FITC-BSA at discretely functionalized areas. Meanwhile, the optical information from precisely defined positions on the patterned surface was monitored by optical reflectivity measurements. The optical measurements revealed successful step-wise chemical functionalization followed by immobilization of gelatin. Multiplex detection of protease activity from different array elements on the patterned surface was demonstrated by monitoring the blue shifts in the reflectivity spectra resulted from the digestion of gelatin by subtilisin. Precise information from both individual elements and average population was acquired. This technique is important for the development of PSi into a microarray platform for highly parallel biosensing applications, especially for cell-based assays. [ABSTRACT FROM AUTHOR]

We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,̉-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions. [ABSTRACT FROM AUTHOR]