SERS biosensors based on cucurbituril-mediated nanoaggregates for wastewater-based epidemiology

Hierarchical self-assembly of nanoparticles (NPs) mediated by macrocyclic molecules, cucurbiturils (CBs), provides a facile method to fabricate surface-enhanced Raman spectroscopy (SERS) sensors for potential applications in biosensing and environmental monitoring. In contrast to conventional techniques for wastewater-based epidemiology (WBE), CB-NP SERS sensors offer great opportunities for on-site quantification of trace chemical and biological markers due to its high sensitivity, selectivity, reproducibility, multiplexing capability and tolerance against contamination. The working principles of the CB-Au NP nanocomposites including fabrication, sensing mechanisms and structure-property relationships are explained while the design guidelines and selected examples of CB-Au NP SERS sensors are discussed. The review concludes by highlighting recent advances in this area and exploring opportunities in the context of WBE

Quantitative SERS Detection of Uric Acid via Formation of Precise Plasmonic Nanojunctions within Aggregates of Gold Nanoparticles and Cucurbit[n]uril

This work describes a rapid and highly sensitive method for the quantitative detection of an important biomarker, uric acid (UA), via surface-enhanced Raman spectroscopy (SERS) with a low detection limit of ~0.2 μM for multiple characteristic peaks in the fingerprint region, using a modular spectrometer. This biosensing scheme is mediated by the host-guest complexation between a macrocycle, cucurbit[7]uril (CB7), and UA, and the subsequent formation of precise plasmonic nanojunctions within the self-assembled Au NP: CB7 nanoaggregates. A facile Au NP synthesis of desirable sizes for SERS substrates has also been performed based on the classical citrate-reduction approach with an option to be facilitated using a lab-built automated synthesizer. This protocol can be readily extended to multiplexed detection of biomarkers in body fluids for clinical applications

Artificial molecular and nanostructures for advanced nanomachinery

Artificial nanomachines can be broadly defined as manmade molecular and nanosystems that are capable of performing useful tasks, very often, by means of doing mechanical work at the nanoscale. Recent advances in nanoscience allow these tiny machines to be designed and made with unprecedented sophistication and complexity, showing promise in novel applications, including molecular assemblers, self-propelling nanocarriers and in vivo molecular computation. This Feature Article overviews and compares major types of nanoscale machines, including molecular machines, self-assembled nanomachines and hybrid inorganic nanomachines, to reveal common structural features and operating principles across different length scales and material systems. We will focus on systems with feature size between 1 and 100 nm, where classical laws of physics meet those of quantum mechanics, giving rise to a spectrum of exotic physiochemical properties. Concepts of nanomachines will be illustrated by selected seminal work along with state-of-the-art progress, including our own contribution, across the fields. The Article will conclude with a brief outlook of this exciting research area

SERS multiplexing of methylxanthine drug isomers via host-guest size matching and machine learning

Multiplexed detection and quantification of structurally similar drug molecules, methylxanthine MeX, incl. theobromine TBR, theophylline TPH and caffeine CAF, have been demonstrated via solution-based surface-enhanced Raman spectroscopy (SERS), achieving highly reproducible SERS signals with detection limits down to ∼50 nM for TBR and TPH, and ∼1 μM for CAF. Our SERS substrates are formed by aqueous self-assembly of gold nanoparticles (Au NPs) and supramolecular host molecules, cucurbit[n]urils (CBn, n = 7, 8). We demonstrate that the binding constants can be significantly increased using a host–guest size matching approach, which enables effective enrichment of analyte molecules in close proximity to the plasmonic hotspots. The dynamic range and the robustness of the sensing scheme can be extended using machine learning algorithms, which shows promise for potential applications in therapeutic drug monitoring, food processing, forensics and veterinary science

Cucurbituril-mediated quantum dot aggregates formed by aqueous self-assembly for sensing applications

Self-assembled nanoparticles have important applications in energy systems, optical devices and sensors, via the formation of aggregates with controlled interparticle spacing. Here we report aqueous self-assembly of rigid macrocycle cucurbit[7]uril (CB[7]) and fluorescent quantum dots (QDs), and demonstrate the potential of the system for efficient energy transfer and sensing of small molecules

Cucurbituril- mediated quantum dot aggregates formed by aqueous self- assembly for sensing applications

Self-assembled nanoparticles have important applications in energy systems, optical devices and sensors, via the formation of aggregates with controlled interparticle spacing. Here we report aqueous self-assembly of rigid macrocycle cucurbit[7]uril (CB[7]) and fluorescent quantum dots (QDs), and demonstrate the potential of the system for efficient energy transfer and sensing of small molecules

Debye screening, overscreening and specific adsorption in solutions of organic ions

Tetrabutylammonium (TBA) and tetraphenylborate (TPB) ions dissolved in dichloroethane (DCE) are widely used in electrochemistry of liquid–liquid interfaces. Unlike alkali halide solutions in water, TBA–TPB–DCE solutions feature large organic ions and a solvent with a dielectric constant almost one order of magnitude lower than that of water. This is expected to dramatically amplify the impact of ionic correlations in the properties of the solution. Here we report atomistic simulations of TBA–TPB–DCE solutions and analyze ion correlations, clustering, and charge screening effects. We target concentrations in the range of 0.01–0.25 molal (m), hence exploring concentration regimes typical for many experimental investigations. We show that the transition from monotonic to oscillatory decay of the charge density, which signals the onset of strong ion correlations, takes place in this concentration interval, leading to overscreening effects. Furthermore, we investigate the distribution and adsorption of ions at the DCE–air interface. Unlike what is observed for small inorganic ions in water at similar concentrations, we find that TPB and TBA ions accumulate near the DCE surface, resulting in significant interfacial clustering and adsorption at concentrations ∼0.25 m. TPB ions adsorb more strongly leading to free energy wells of ∼1–2 kBT. The adsorption modifies significantly the electrostatic potential of the DCE–air interface, which undergoes a shift of 0.2 V in going from pure DCE to TBA–TPB–DCE solutions at 0.25 m

Dual-triggered nanoaggregates of cucurbit[7]uril and gold nanoparticles for multi-spectroscopic quantification of creatinine in urinalysis

Plasmonic nanocomposites of cucurbit[7]uril and gold nanoparticles has been optimised and applied to rapidly detect and quantify creatinine (CRN) of clinically relevant levels in urinalysis. The in situ formation of plasmonic nanocomposites via aqueous self-assembly is mediated by a combination of the portal binding of CB7 and the electrostatic effects of CRN molecules, allowing independent spectral signatures to be extracted from the same sample solution using surface-enhanced Raman spectroscopy (SERS) and UV-Visible spectroscopy. Meanwhile the formation of host-guest complexes between CB7 and CRN allows quantification of CRN in highly diluted synthetic urine by localising CRN at or in close proximity to the plasmonic hotspots within the Au NP:CB7 nanoaggregates which enables highly reproducible SERS (within 5% error) with a sub-μM detection limit of 12.5 ng/ml (111 nM) and tolerance against the presence of proteins and other biomolecules in a complex matrix. Our nanobiosensing materials platform demonstrates the potential to be extended to other in-field applications

Pectobacterium and Dickeya: Environment to Disease Development

The soft rot Pectobacteriaceae (SRP) infect a wide range of plants worldwide and cause economic damage to crops and ornamentals but can also colonize other plants as part of their natural life cycle. They are found in a variety of environmental niches, including water, soil and insects, where they may spread to susceptible plants and cause disease. In this chapter, we look in detail at the plants colonized and infected by these pathogens and at the diseases and symptoms they cause. We also focus on where in the environment these organisms are found and their ability to survive and thrive there. Finally, we present evidence that SRP may assist the colonization of human enteric pathogens on plants, potentially implicating them in aspects of human/animal as well as plant health