Selectivity and specificity: pros and cons in sensing

Sensing using specific and selective receptors provides two very different but complementary strategies. This Sensor Issues article will discuss the merits and challenges of specific sensors, and selective sensors based on synthetic arrays. We will examine where each has been successfully applied to a sensing challenge, and then look at how a combined approach could take elements of both to provide new sensor platforms

Nanoparticles in explosives detection – the state-of-the-art and future directions

No abstract available

Detection of explosive markers using zeolite modified gas sensors

Detection of hidden explosive devices is a key priority for security and defence personnel around the globe. Electronic noses, based on metal oxide semiconductors (MOS), are a promising technology for creating inexpensive, portable and sensitive devices for such a purpose. An array of seven MOS gas sensors was fabricated by screen printing, based on WO3 and In2O3 inks. The sensors were tested against six gases, including four explosive markers: nitromethane, DMNB (2,3-dimetheyl-2,3-dinitrobutane), 2-ethylhexanol and ammonia. The gases were successfully detected with good sensitivity and selectivity from the array. Sensitivity was improved by overlaying or admixing the oxides with two zeolites, H-ZSM-5 and TS-1, and each showed improved responses to –NO2 and –OH moieties respectively. Admixtures in particular showed promise, with excellent sensitivity and good stability to humidity. Machine learning techniques were applied to a subset of the data and could accurately classify the gases detected, even when confounding factors were introduced

Food for thought: optical sensor arrays and machine learning for the food and beverage industry

Arrays of cross-reactive sensors, combined with statistical or machine learning analysis of their multivariate outputs, have enabled the holistic analysis of complex samples in biomedicine, environmental science, and consumer products. Comparisons are frequently made to the mammalian nose or tongue and this perspective examines the role of sensing arrays in analyzing food and beverages for quality, veracity, and safety. I focus on optical sensor arrays as low-cost, easy-to-measure tools for use in the field, on the factory floor, or even by the consumer. Novel materials and approaches are highlighted and challenges in the research field are discussed, including sample processing/handling and access to significant sample sets to train and test arrays to tackle real issues in the industry. Finally, I examine whether the comparison of sensing arrays to noses and tongues is helpful in an industry defined by human taste

Plasmonic Gold Nanostars Incorporated into High-Efficiency Perovskite Solar Cells

Incorporating appropriate plasmonic nanostructures into photovoltaic (PV) systems is of great utility for enhancing photon absorption and thus improving device performance. Herein, the successful integration of plasmonic gold nanostars (AuNSs) into mesoporous TiO2 photoelectrodes for perovskite solar cells (PSCs) is reported. The PSCs fabricated with TiO2-AuNSs photoelectrodes exhibited a device efficiency of up to 17.72 %, whereas the control cells without AuNSs showed a maximum efficiency of 15.19 %. We attribute the origin of increased device performance to enhanced light absorption and suppressed charge recombination

Sensitive and specific detection of explosives in solution and vapour by surface-enhanced Raman spectroscopy on silver nanocubes

Surface-enhanced Raman spectroscopy (SERS) has been widely utilised as a sensitive analytical technique for the detection of trace levels of organic molecules. The detection of organic compounds in the gas phase is particularly challenging due to the low concentration of adsorbed molecules on the surface of the SERS substrate. This is particularly the case for explosive materials, which typically have very low vapour pressures, limiting the use of SERS for their identification. In this work, silver nanocubes (AgNCs) were developed as a highly sensitive SERS substrate with very low limit-of-detection (LOD) for explosive materials down to the femtomolar (10−15 M) range. Unlike typical gold-based nanostructures, the AgNCs were found suitable for the detection of both aromatic and aliphatic explosives, enabling detection with high specificity at low concentration. SERS studies were first carried out using a model analyte, Rhodamine-6G (Rh-6G), as a probe molecule. The SERS enhancement factor was estimated as 8.71 × 1010 in this case. Further studies involved femtomolar concentrations of 2,4-dinitrotoluene (DNT) and nanomolar concentrations of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), as well as vapour phase detection of DNT

In situ formation of low molecular weight organogelators for slick solidification

We have investigated the in situ formation of Low Molecular Weight Organogelator (LMWO) molecules in oil-on-water slicks through dual reactive precursor injection. This method alleviates the need for any carrier solvent or prior heating, therefore reducing the environmental impact of LMWOs, giving instantaneous gelation, even at low temperatures (−5 °C). We show minimal leaching from our gels into the water layer

Multichannel detection and differentiation of explosives with a quantum dot array

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform, faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each color quantum dot is functionalized with a different surface receptor via a facile ligation process. These receptors undergo nonspecific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range

Small surface, big effects, and big challenges: toward understanding enzymatic activity at the inorganic nanoparticle–substrate interface

Enzymes are important biomarkers for molecular diagnostics and targets for the action of drugs. In turn, inorganic nanoparticles (NPs) are of interest as materials for biological assays, biosensors, cellular and in vivo imaging probes, and vectors for drug delivery and theranostics. So how does an enzyme interact with a NP, and what are the outcomes of multivalent conjugation of its substrate to a NP? This invited feature article addresses the current state of the art in answering this question. Using gold nanoparticles (Au NPs) and semiconductor quantum dots (QDs) as illustrative materials, we discuss aspects of enzyme structure–function and the properties of NP interfaces and surface chemistry that determine enzyme–NP interactions. These aspects render the substrate-on-NP configurations far more complex and heterogeneous than the conventional turnover of discrete substrate molecules in bulk solution. Special attention is also given to the limitations of a standard kinetic analysis of the enzymatic turnover of these configurations, the need for a well-defined model of turnover, and whether a “hopping” model can account for behaviors such as the apparent acceleration of enzyme activity. A detailed and predictive understanding of how enzymes turn over multivalent NP-substrate conjugates will require a convergence of many concepts and tools from biochemistry, materials, and interface science. In turn, this understanding will help to enable rational, optimized, and value-added designs of NP bioconjugates for biomedical and clinical applications

Synthesis of novel multifunctional carbazole-based molecules and their thermal, electrochemical and optical properties

Two novel carbazole-based compounds 7a and 7b were synthesised as potential candidates for application in organic electronics. The materials were fully characterised by NMR spectroscopy, mass spectrometry, FTIR, thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, and absorption and emission spectroscopy. Compounds 7a and 7b, both of which were amorphous solids, were stable up to 291 °C and 307 °C, respectively. Compounds 7a and 7b show three distinctive absorption bands: high and mid energy bands due to locally excited (LE) transitions and low energy bands due to intramolecular charge transfer (ICT) transitions. In dichloromethane solutions compounds 7a and 7b gave emission maxima at 561 nm and 482 nm with quantum efficiencies of 5.4% and 97.4% ± 10%, respectively. At positive potential, compounds 7a and 7b gave two different oxidation peaks, respectively: quasi-reversible at 0.55 V and 0.71 V, and reversible at 0.84 V and 0.99 V. At negative potentials, compounds 7a and 7b only exhibited an irreversible reduction peak at −1.86 V and −1.93 V, respectively