A review of optical methods for ultrasensitive detection and characterization of nanoparticles in liquid media with a focus on the wide field surface plasmon microscopy

Nanomaterials in the treatment and diagnosis of rheumatoid arthritis: Advanced approaches

Rheumatoid arthritis (RA), a chronic inflammatory condition that affects persons between the ages of 20 and 40, causes synovium inflammation, cartilage loss, and joint discomfort as some of its symptoms. Diagnostic techniques for RA have traditionally been split into two main categories: imaging and serological tests. However, significant issues are associated with both of these methods. Imaging methods are costly and only helpful in people with obvious symptoms, while serological assays are time-consuming and require specialist knowledge. The drawbacks of these traditional techniques have led to the development of novel diagnostic approaches. The unique properties of nanomaterials make them well-suited as biosensors. Their compact dimensions are frequently cited for their outstanding performance, and their positive impact on the signal-to-noise ratio accounts for their capacity to detect biomarkers at low detection limits, with excellent repeatability and a robust dynamic range. In this review, we discuss the use of nanomaterials in RA theranostics. Scientists have recently synthesized, characterized, and modified nanomaterials and biomarkers commonly used to enhance RA diagnosis and therapy capabilities. We hope to provide scientists with the promising potential that nanomaterials hold for future theranostics and offer suggestions on further improving nanomaterials as biosensors, particularly for detecting autoimmune disorders.

Analytical techniques for the characterization of nanoparticles for mRNA delivery

Nanotechnology-assisted RNA delivery has gotten a tremendous boost over the last decade and made a significant impact in the development of life-changing vaccines and therapeutics. With increasing numbers of emerging lipid- and polymer-based RNA nanoparticles progressing towards the clinic, it has become apparent that the safety and efficacy of these medications depend on the comprehensive understanding of their critical quality attributes (CQAs). However, despite the rapid advancements in the field, the identification and reliable quantification of CQAs remain a significant challenge. To support these efforts, this review aims to summarize the present knowledge on CQAs based on the regulatory guidelines and to provide insights into the available analytical characterization techniques for RNA-loaded nanoparticles. In this context, routine and emerging analytical techniques are categorized and discussed, focusing on the operation principle, strengths, and potential limitations. Furthermore, the importance of complementary and orthogonal techniques for the measurement of CQAs is discussed in order to ensure the quality and consistency of analytical methods used, and address potential technique-based differences.

Switchable Polyacrylic Acid Polyelectrolyte Brushes for Surface Plasmon Resonance Applications

Imaging wide-field surface plasmon resonance (SPR) microscopy sensors based on polyacrylic acid polyelectrolyte brushes (PAA PEBs) were designed to enhance the sensitivity of nano-object detection. The switching behavior of the PAA PEBs against changes in the pH values was investigated by analyzing the chemical, morphological, optical, and electrical properties. At pH ~1, the brushes collapse on the surface with the dominance of carboxylic groups (COOH). Upon the increase in the pH to nine, the switching process completes, and the brushes swell from dissociating most of the COOH groups and converting them into COO- groups. The domination of the negatively charged COO- groups increases the electrostatic repulsion in the polymer chains and stretches the brushes. The sensitivity of the SPR sensing device was investigated using a theoretical approach, as well as experimental measurements. The signal-to-noise ratio for a Au layer increases from six to eighteen after coating with PAA PEBs. In addition, the linewidth of the recorded image decreases from six pixels to five pixels by using the Au-PAA layers, which results from the enhanced spatial resolution of the recorded images. Coating a Au-layer with PAA PEBs enhances the sensitivity of the SPR sensing device, and improves the spatial resolution of the recorded image.

The Employment of the Surface Plasmon Resonance (SPR) Microscopy Sensor for the Detection of Individual Extracellular Vesicles and Non-Biological Nanoparticles

A wide-field surface plasmon resonance (SPR) microscopy sensor employs the surface plasmon resonance phenomenon to detect individual biological and non-biological nanoparticles. This sensor enables the detection, sizing, and quantification of biological nanoparticles (bioNPs), such as extracellular vesicles (EVs), viruses, and virus-like particles. The selectivity of bioNP detection does not require biological particle labeling, and it is achieved via the functionalization of the gold sensor surface by target-bioNP-specific antibodies. In the current work, we demonstrate the ability of SPR microscopy sensors to detect, simultaneously, silica NPs that differ by four times in size. Employed silica particles are close in their refractive index to bioNPs. The literature reports the ability of SPR microscopy sensors to detect the binding of lymphocytes (around 10 μm objects) to the sensor surface. Taken together, our findings and the results reported in the literature indicate the power of SPR microscopy sensors to detect bioNPs that differ by at least two orders in size. Modifications of the optical sensor scheme, such as mounting a concave lens, help to achieve homogeneous illumination of a gold sensor chip surface. In the current work, we also characterize the improved magnification factor of the modified SPR instrument. We evaluate the effectiveness of the modified and the primary version of the SPR microscopy sensors in detecting EVs isolated via different approaches. In addition, we demonstrate the possibility of employing translation and rotation stepper motors for precise adjustments of the positions of sensor optical elements-prism and objective-in the primary version of the SPR microscopy sensor instrument, and we present an algorithm to establish effective sensor-actuator coupling.

Effects of Cascading Optical Processes: Part I: Impacts on Quantification of Sample Scattering Extinction, Intensity, and Depolarization

Light scattering is a universal matter property that is especially prominent in nanoscale or larger materials. However, the effects of scattering-based cascading optical processes on experimental quantification of sample absorption, scattering, and emission intensities, as well as scattering and emission depolarization, have not been adequately addressed. Using a series of polystyrene nanoparticles (PSNPs) of different sizes as model analytes, we present a computational and experimental study on the effects of cascading light scattering on experimental quantification of NP scattering activities (scattering cross-section or molar coefficient), intensity, and depolarization. Part II and Part III of this series of companion articles explore the effects of cascading optical processes on sample absorption and fluorescence measurements, respectively. A general theoretical model is developed on how forward scattered light complicates the general applicability of Beer's law to the experimental UV-vis spectrum of scattering samples. The correlation between the scattering intensity and PSNP concentration is highly complicated with no robust linearity even when the scatterers' concentration is very low. Such complexity arises from the combination of concentration-dependence of light scattering depolarization and the scattering inner filter effects (IFEs). Scattering depolarization increases with the PSNP scattering extinction (thereby, its concentration) but can never reach unity (isotropic) due to the polarization dependence of the scattering IFE. The insights from this study are important for understanding the strengths and limitations of various scattering-based techniques for material characterization including nanoparticle quantification. They are also foundational for quantitative mechanistic understanding on the effects of light scattering on sample absorption and fluorescence measurements.

Surface Plasmon Resonance Sensitivity Enhancement Based on Protonated Polyaniline Films Doped by Aluminum Nitrate

Complex composite films based on polyaniline (PANI) doped hydrochloric acid (HCl) incorporated with aluminum nitrate (Al(NO₃)₃) on Au-layer were designed and synthesized as a surface plasmon resonance (SPR) sensing device. The physicochemical properties of (PANI-HCl)/Al(NO₃)₃ complex composite films were studied for various Al(NO₃)₃ concentrations (0, 2, 4, 8, 16, and 32 wt.%). The refractive index of the (PANI-HCl)/Al(NO₃)₃ complex composite films increased continuously as Al(NO₃)₃ concentrations increased. The electrical conductivity values increased from 5.10 µS/cm to 10.00 µS/cm as Al(NO₃)₃ concentration increased to 32 wt.%. The sensitivity of the SPR sensing device was investigated using a theoretical approach and experimental measurements. The theoretical system of SPR measurement confirmed that increasing Al(NO₃)₃ in (PANI-HCl)/Al(NO₃)₃ complex composite films enhanced the sensitivity from about 114.5 [Deg/RIU] for Au-layer to 159.0 [Deg/RIU] for Au-((PANI-HCl)/Al(NO₃)₃ (32 wt.%)). In addition, the signal-to-noise ratio for Au-layer was 3.95, which increased after coating by (PANI-HCl)/Al(NO₃)₃ (32 wt.%) complex composite layer to 8.82. Finally, we conclude that coating Au-layer by (PANI-HCl)/Al(NO₃)₃ complex composite films enhances the sensitivity of the SPR sensing device.

Natural Products-Based Metallic Nanoparticles as Antimicrobial Agents

Natural products offer a wide range of bioactivity including antimicrobial properties. There are many reports showing the antimicrobial activities of phytochem icals from plants. However, the bioactivity is limited due to multidrug resistant properties of the microorganism and different composition of cell membrane. The antibacterial activity of the natural products is different toward Gram-negative and Gram-positive bacteria. These phenomena are caused by improper physicochemical conditions of the substance which hinder the phytochemical bioactivity against the broad range of bacteria. One of the strategies to improve the antimicrobial action is by biogenic synthesis via redox balance of the antimicrobial active substance with metal to form nanosized materials or nanoparticles (NPs). Antibiotic resistance is not relevant to NPs because the action of NPs is via direct contact with bacterial cell walls without the need of penetration into microbial cells. The NPs that have shown their effectiveness in preventing or overcoming biofilm formation such as silver-based nanoparticles (AgNPs), gold-based nanoparticles (AuNPs), platinum-based nanoparticles (PtNPs) and Zinc oxide-based nanoparticles (ZnONPs). Due to its considerably simple synthesis procedure has encouraged researchers to explore antimicrobial potency of metallic nanoparticles. Those metallic nanoparticles remarkably express synergistic effects against the microorganisms tested by affecting bacterial redox balance, thus disrupting their homeostasis. In this paper, we discuss the type of metallic nanoparticle which have been used to improve the antimicrobial activity of plant extract/constituents, preparation or synthesis process and characterisation of the plant-based metallic nanoparticles.