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Time-resolved measurements of changes in the size and shape of nanobiological objects and layers are crucial to understand their properties and optimize their performance. Optical sensing is particularly attractive with high throughput and sensitivity, and label-free operation. However, most state-of-the-art solutions require intricate modeling or multiparameter measurements to disentangle conformational or thickness changes of biomolecular layers from complex interfacial refractive index variations. Here, we present a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles with spectrally separated resonance peaks. As electrodynamic simulations and model experiments show, the ruler enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes can be tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverage prior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabrication approach constitutes a generic route for multimodal nanoplasmonic optical sensing.

The temperature of nanoparticles is a critical parameter in applications that range from biology, to sensors, to photocatalysis. Yet, accurately determining the absolute temperature of nanoparticles is intrinsically difficult because traditional temperature probes likely deliver inaccurate results due to their large thermal mass compared to the nanoparticles. Here we present a hydrogen nanothermometry method that enables a noninvasive and direct measurement of absolute Pd nanoparticle temperature via the temperature dependence of the first-order phase transformation during Pd hydride formation. We apply it to accurately measure light-absorption-induced Pd nanoparticle heating at different irradiated powers with 1 °C resolution and to unravel the impact of nanoparticle density in an array on the obtained temperature. In a wider perspective, this work reports a noninvasive method for accurate temperature measurements at the nanoscale, which we predict will find application in, for example, nano-optics, nanolithography, and plasmon-mediated catalysis to distinguish thermal from electronic effects.

Food safety, particularly concerning foods contaminated by toxic chemicals, has emerged as a pervasive societal concern. The prevalence of food contaminants has spurred both scientific communities and industries to develop highly sensitive and selective sensors for rapid and precise food authentication. Noble metal nanoparticles (NPs) have garnered significant attention in this regard due to their exceptional properties, including high sensitivity, selectivity, stability, target binding affinity, and versatility for modification to detect specific contaminants. Moreover, the readout of such sensors is relatively straightforward, as their resulting color change can be observed with the naked eye. This Review aims to delve into the current strategies involving various noble metal NPs as colorimetric nanosensors in food safety monitoring applications. It begins by elucidating their working principles, encompassing localized surface plasmon resonance (LSPR), enzyme-based approaches, and other methodologies. Subsequently, the material properties of commonly utilized noble metal NPs, including those of gold, silver, palladium, platinum, and copper, are meticulously examined, providing comprehensive overviews of the benefits and drawbacks associated with each material. Furthermore, this Review summarizes the latest use cases of noble metal NPs in diverse food safety monitoring applications, ranging from the detection of heavy metal contaminants to veterinary and pesticide drug residues and foodborne pathogens. Lastly, it addresses the remaining challenges in this field and proposes feasible solutions, offering insights into future research directions. [ABSTRACT FROM AUTHOR]

Surfactants and stabilizers are always present on the surfaces of colloidal nanocrystals due to their critical function in promoting selective facet growth and since they are essential to prevent aggregate formation in solution. After synthesis, however, the presence of these molecules on the surface of a nanocrystal is problematic because they potentially significantly alter the nature of the interaction with the environment, which is critical for sensor or catalysis applications. Here, we quantitatively scrutinize this effect experimentally for the four most common stabilizers in Pd nanoparticle synthesis: cetyltrimethylammonium bromide (CTAB), tetraoctylammonium bromide (TOAB), cetyltrimethylammonium chloride (CTAC), and poly-(vinylpyrrolidone) (PVP). We use the surface-catalyzed hydrogen sorption and hydride formation reaction in Pd as a model system, due to its high relevance for hydrogen sensors. Specifically, we map in detail the (de)-hydrogenation kinetics of arrays of nanofabricated Pd nanodisks in the presence of the surfactants and benchmark it with an uncoated Pd reference. As the key results, we find that the cationic surfactants significantly decelerate the (de)-hydrogenation surface reaction, with the amplitude of deceleration mediated by the interplay between the halide-ion–Pd surface interaction strength and surfactant surface density. In contrast, a polymeric PVP coating is found to significantly accelerate hydrogen sorption. For the Pd-based hydrogen sensor application, our findings thus provide important insights for the appropriate choice of a surfactant to minimize the negative impact on hydrogen sorption kinetics and thus hydrogen detection response/recovery times. In a wider perspective, our results dramatically show how nanoparticles can attain different properties depending on what types of surfactants and stabilizers are present on their surface and how critical the quantitative understanding of their impact is for a specific application. [ABSTRACT FROM AUTHOR]