Hybrid micro-/nanogels for optical sensing and intracellular imaging

Hybrid micro-/nanogels are playing an increasing important part in a diverse range of applications, due to their tunable dimensions, large surface area, stable interior network structure, and a very short response time. We review recent advances and challenges in the developments of hybrid micro-/nanogels toward applications for optical sensing of pH, temperature, glucose, ions, and other species as well as for intracellular imaging. Due to their unique advantages, hybrid micro-/nanogels as optical probes are attracting substantial interests for continuous monitoring of chemical parameters in complex samples such as blood and bioreactor fluids, in chemical research and industry, and in food quality control. In particular, their intracellular probing ability enables the monitoring of the biochemistry and biophysics of live cells over time and space, thus contributing to the explanation of intricate biological processes and the development of novel diagnoses. Unlike most other probes, hybrid micro-/nanogels could also combine other multiple functions into a single probe. The rational design of hybrid micro-/nanogels will not only improve the probing applications as desirable, but also implement their applications in new arenas. With ongoing rapid advances in bionanotechnology, the well-designed hybrid micro-/nanogel probes will be able to provide simultaneous sensing, imaging diagnosis, and therapy toward clinical applications

Structure and vacancy distribution in copper telluride nanoparticles influence plasmonic activity in the near-infrared

Copper chalcogenides find applications in different domains including photonics, photothermal therapy and photovoltaics. CuTe nanocrystals have been proposed as an alternative to noble metal particles for plasmonics. Although it is known that deviations from stoichiometry are a prerequisite for plasmonic activity in the near-infrared, an accurate description of the material and its (optical) properties is hindered by an insufficient understanding of the atomic structure and the influence of defects, especially for materials in their nanocrystalline form. We demonstrate that the structure of Cu1.5±xTe nanocrystals can be determined using electron diffraction tomography. Real-space high-resolution electron tomography directly reveals the three-dimensional distribution of vacancies in the structure. Through first-principles density functional theory, we furthermore demonstrate that the influence of these vacancies on the optical properties of the nanocrystals is determined. Since our methodology is applicable to a variety of crystalline nanostructured materials, it is expected to provide unique insights concerning structure–property correlations

A review on radiation-induced nucleation and growth of colloidal metallic nanoparticles

This review presents an introduction to the synthesis of metallic nanoparticles by radiation-induced method, especially gamma irradiation. This method offers some benefits over the conventional methods because it provides fully reduced and highly pure nanoparticles free from by-products or chemical reducing agents, and is capable of controlling the particle size and structure. The nucleation and growth mechanism of metallic nanoparticles are also discussed. The competition between nucleation and growth process in the formation of nanoparticles can determine the size of nanoparticles which is influenced by certain parameters such as the choice of solvents and stabilizer, the precursor to stabilizer ratio, pH during synthesis, and absorbed dose

Formation of large opals via drying of wet colloidal crystals

Salgueirino-Maceira V, Rodriguez-Gonzalez B, Hellweg T, Liz-Marzan LM. Formation of large opals via drying of wet colloidal crystals. In: Australian Journal of Chemistry. Australian Journal of Chemistry. Vol 56. CSIRO Publishing; 2003: 1017-1020.The formation of opal structures with large crystalline domains is demonstrated through the formation of colloidal crystals in ethanol of surface-modified colloidal silica spheres containing small CdS nuclei, followed by controlled drying at room temperature. The high quality of the opals was characterized by scanning electron microscopy (SEM) and, more importantly, also by small-angle neutron scattering ( SANS), which allows probing of the entire sample and provides important information on the crystal structure

Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation

Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials and for sensing and optical applications. NPs can spontaneously assemble at the liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening between NPs with the addition of electrolyte or pH adjustment. The in situ modulation of nanoparticle positioning on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision

Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth

Lowering the limit of detection is key to the design of sensors needed for food safety regulations1, 2, environmental policies3, 4, 5 and the diagnosis of severe diseases6, 7, 8, 9, 10. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10−18 g ml−1 (4 × 10−20 M) in whole serum

Identification of intracellular gold nanoparticles using surface-enhanced Raman scattering

The identification of intracellular distributions of noble metal nanoparticles is of great utility for many biomedical applications. We present an effective method to distinguish intracellular from extracellular nanoparticles by selectively quenching the SERS signals from dye molecules adsorbed onto star-shaped gold nanoparticles that have not been internalized by cells