Chemical sensing with nanoparticles as optical reporters: from noble metal nanoparticles to quantum dots and upconverting nanoparticles

Recent advances in nucleic acid-functionalized metallic nanoparticles

Nucleic acid-functionalized metallic nanoparticles (N-MNPs) precisely integrate the advantageous characteristics of nucleic acids and metallic nanomaterials, offering various abilities such as resistance to enzymatic degradation, penetration of physiological barriers, controllable mobility, biomolecular recognition, programmable self-assembly, and dynamic structure-function transformation. These properties demonstrate significant potential in the field of biomedical diagnostics and therapeutics. In this review, we examine recent advancements in the construction and theranostic applications of N-MNPs. We briefly summarize the methodologies employed in the conjugation of nucleic acids with metallic nanoparticles and the formation of their superstructural assemblies. We highlight recent representative applications of N-MNPs in biomolecular diagnosis, imaging, and smart delivery of theranostic agents. We also discuss challenges currently faced in this field and provide an outlook on future development directions and application prospects.

Nanoparticle-assisted plasmonic sensors: Recent developments in clinical applications

Nanotechnology is an important science that finds a wide range of applications from energy production to industrial production processes and biomedical applications. Nanoparti-cles, which are the most frequently preferred nanomaterials that form the basis of nanotechnolo-gy, are prepared with different composition, size, shape and surface chemistry to provide new techniques in applications in many different fields. The use of nanoparticles in the preparation of plasmonic sensors has increased the interest in plasmonic sensors such as surface plasmon resonance, electrochemical sensors, surface enhanced raman scattering and colorimetric sensors due to their increased sensing capacity on sensor surfaces. Plasmonic sensors are an important option in many different fields, such as medicine, environmental agriculture and food safety, thanks to their ability to solve a multitude of challenges. Because, plasmonic sensors are defined as sensing devices with important features such as sensitive and fast detection, no need for labels, real-time analysis, portability. In this review, the information about nanoparticles and their types and working principles of plasmonic sensors is given. Then, examples in clinical applications using different plasmonic sensors prepared with plasmonic nanoparticles are discussed in detail.

Synergistic Interactions of Metals and Quantum Dots: Expanding Frontiers in Fluorescent Sensing

Fluorescent sensing technologies have emerged as powerful tools in analytical science, offering exceptional sensitivity and selectivity for detecting a wide range of analytes. Among the advanced materials driving these technologies, quantum dots (QDs) and metal nanoparticles (MNPs) stand out due to their unique optical and electronic properties. When combined, these materials exhibit synergistic interactions those significantly enhance the fluorescence signals, enable efficient quenching, and offer tunable optical properties. This review explores the various protocols involved in the development, characterization, and performance evaluation of metal-QD composites; typically, metal-enhanced fluorescence (MEF) and Förster resonance energy transfer (FRET). The applications of the materials in the domain of biomedical diagnostics, environmental monitoring, and biosensing have been highlighted. The review also discusses the current challenges and future scope in the field of metal-QD-based fluorescent sensors and their possible transformative impact on next-generation sensing technologies.

A fluorescence-based immunochromatographic assay using quantum dot-encapsulated nanoparticles for the rapid and sensitive detection of fetuin-B

Coronary artery disease (CAD) is the leading cause of death worldwide. Earlier detection of CAD improves treatment outcomes and secondary prevention. The circulating fetuin-B protein is considered to be a promising biomarker for the early detection of CAD. However, a facile and reliable clinical test for fetuin-B is still lacking. Herein, we describe a reliable fluorescent biosensor for detecting fetuin-B in plasma that combines quantum dots-doped polystyrene nanoparticles with an immunochromatographic assay strip (QNPs-ICAS). The QNPs served as detection signals in the QNPs-ICAS sensor system, which was based on a double-antibody sandwich structure. Under optimum experimental conditions, the biosensor exhibited a broad linear range of 1-200 ng mL-1 and a low detection limit of 0.299 ng mL-1. Furthermore, the proposed immunosensor demonstrated high sensitivity, satisfactory selectivity, good reproducibility, and excellent recovery. Finally, the performance and applicability of our QNPs-based ICAS system were validated in clinical samples using a commercial ELISA kit with excellent correlations (r = 0.98451, n = 116). To conclude, the proposed sensor served as a rapid, sensitive, and accurate method for detecting fetuin-B in actual clinical samples, thereby demonstrating its potential for preliminary CAD screening and diagnosis.

Nanoporous YVO4 as a luminescent host for probing molecular encapsulation

Control of phase separation of VO43- and rare earth precursors in reverse microemulsions afforded ∼35 nm YVO4 nanoparticles with functionalisable ∼7 ± 3 nm nanopores. Doping by Eu3+ allowed luminescent probing of interfacial crystallisation while xylenol orange absorption showed molecular encapsulation in particle cavities. This provides potential multifunctional systems combining UV-Vis-NIR luminescence and (photo)active molecules for optical sensing.

Responsive Sensors of Upconversion Nanoparticles

Upconversion nanoparticles are a class of luminescent materials that convert longer-wavelength near-infrared photons into visible and ultraviolet emissions. They can respond to various external stimuli, which underpins many opportunities for developing the next generation of sensing technologies. In this perspective, the unique stimuli-responsive properties of upconverting nanoparticles are introduced, and their recent implementations in sensing are summarized. Promising material development strategies for enhancing the key sensing merits, including intrinsic sensitivity, biocompatibility and modality, are identified and discussed. The outlooks on future technological developments, novel sensing concepts, and applications of nanoscale upconversion sensors are provided.

Characterising the size and shape of metallic nano-structures by their acoustic vibrations

The characterisation of metallic nano-structures is of great importance as their optical properties are strongly dependent on their size and shape. Inaccurate size or shape characterisation can result in misleading measurements in applications such as bio-imaging and sensing. Characterisation techniques such as dynamic light scattering, electron microscopy or atomic force microscopy are commonly used; however, performing sub-surface measurements (inside semi-transparent objects) or in liquid media are very challenging. Here, we use time-resolved pump-probe spectroscopy to characterise the size and shape of metallic nano-structures in a water surrounding medium by using their vibrational modes. We show that this technique can achieve size measurements with a precision of 3 nm for the largest nano-structures which are in agreement with electron microscopy images. Furthermore, we demonstrate the ability to probe individual nano-structures despite being located in the same optical point spread function (PSF). Combining the high precision and sub-optical measurements provided by this technique with the ability to insert metallic nano-structures inside biological samples might open a way to perform 3D characterisation measurements.

A Nanoparticle-Based Affinity Sensor that Identifies and Selects Highly Cytokine-Secreting Cells

We developed a universal method termed OnCELISA to detect cytokine secretion from individual cells by applying a capture technology on the cell membrane. OnCELISA uses fluorescent magnetic nanoparticles as assay reporters that enable detection on a single-cell level in microscopy and flow cytometry and fluorimetry in cell ensembles. This system is flexible and can be modified to detect different cytokines from a broad range of cytokine-secreting cells. Using OnCELISA we have been able to select and sort highly cytokine-secreting cells and identify cytokine-secreting expression profiles of different cell populations in vitro and ex vivo. We show that this system can be used for ultrasensitive monitoring of cytokines in the complex biological environment of atherosclerosis that contains multiple cell types. The ability to identify and select cell populations based on their cytokine expression characteristics is valuable in a host of applications that require the monitoring of disease progression.

Sub-20 nm Core-Shell-Shell Nanoparticles for Bright Upconversion and Enhanced Förster Resonant Energy Transfer

Upconverting nanoparticles provide valuable benefits as optical probes for bioimaging and Förster resonant energy transfer (FRET) due to their high signal-to-noise ratio, photostability, and biocompatibility; yet, making nanoparticles small yields a significant decay in brightness due to increased surface quenching. Approaches to improve the brightness of UCNPs exist but often require increased nanoparticle size. Here we present a unique core-shell-shell nanoparticle architecture for small (sub-20 nm), bright upconversion with several key features: (1) maximal sensitizer concentration in the core for high near-infrared absorption, (2) efficient energy transfer between core and interior shell for strong emission, and (3) emitter localization near the nanoparticle surface for efficient FRET. This architecture consists of β-NaYbF4 (core) @NaY0.8-xErxGd0.2F4 (interior shell) @NaY0.8Gd0.2F4 (exterior shell), where sensitizer and emitter ions are partitioned into core and interior shell, respectively. Emitter concentration is varied (x = 1, 2, 5, 10, 20, 50, and 80%) to investigate influence on single particle brightness, upconversion quantum yield, decay lifetimes, and FRET coupling. We compare these seven samples with the field-standard core-shell architecture of β-NaY0.58Gd0.2Yb0.2Er0.02F4 (core) @NaY0.8Gd0.2F4 (shell), with sensitizer and emitter ions codoped in the core. At a single particle level, the core-shell-shell design was up to 2-fold brighter than the standard core-shell design. Further, by coupling a fluorescent dye to the surface of the two different architectures, we demonstrated up to 8-fold improved emission enhancement with the core-shell-shell compared to the core-shell design. We show how, given proper consideration for emitter concentration, we can design a unique nanoparticle architecture to yield comparable or improved brightness and FRET coupling within a small volume.

Highly selective naked eye detection of vitamin B1 in the presence of other vitamins using graphene quantum dots capped gold nanoparticles

The application of Au-GQDs towards the sensitive determination of thiamine was demonstrated.

Exploring the potential of electroless and electroplated noble metal-semiconductor hybrids within bio- and environmental sensing

Over the last two decades, the rapid development and widespread application of nanomaterials has significantly influenced research in various fields, including analytical chemistry and biosensing technologies. In particular, the simple functionalization and tuning of noble metal nanoparticle (NP) surface chemistry resulted in the development of a series of novel biosensing platforms with quick read-out and enhanced capabilities towards specific analyte detection. Moreover, noble metal NPs possess a number of unique properties, viz. high surface-to-volume ratio and excellent spectral, optical, thermal, electrical and catalytic characteristics. This manuscript provides an elaborate review on galvanic noble metal NPs deposited onto semiconductor surfaces, from the preparation stage towards their application in biosensors and gas sensing. Two types of deposition approaches, viz. galvanic displacement/electroless and conventional electroplating, are introduced and compared. Furthermore, the analytical merit of hybrid nanomaterials towards the improvement of sensing abilities is highlighted. Finally, some limitations and challenges related to progress in the development and application of analytical devices based on electroless and electroplated noble metal NPs-semiconductor hybrids (NMNPsHs) in biochemical and environmental sensing are discussed.

Nitrogen-Doped Graphene Quantum Dot-Combined Sodium 10-Amino-2-methoxyundecanoate: Studies of Proinflammatory Gene Expression and Live Cell Imaging

Marine cyanobacteria are renowned for producing bioactive secondary metabolites with great structural diversity via mixed biosynthetic pathways. Lyngbya sp., a marine cyanobacterium, produces many metabolites with anti-inflammatory potentials; nevertheless, its bioactive metabolites exercising providing protection against inflammation has been deciphered inadequate. In this study, the ethanolic fraction of the Lyngbya sp. extract was purified and identified as sodium 10-amino-2-methoxyundecanoate (SAM) using Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and electron spray ionization-mass spectroscopy. SAM showed prominent inhibition of inflammation, which was analyzed by reactive oxygen species generation and nitric oxide (NO) inhibition assay. Furthermore, the anti-inflammatory potentials of SAM were evaluated in lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cell lines by fluorescence-activated cell sorting analysis, which evidenced prominent decrease in COX-2 expression (∼90%) with SAM-treated cells than the control. Subsequently, a semiquantitative real-time polymerase chain reaction analysis also revealed the downregulation of COX-2, iNOS, TNF-α, NF-κß, IL-1α, IL-1ß, IL-4, and IL-6 gene expression in SAM-treated LPS-induced RAW 264.7 cells. To further enhance the delivery of SAM into the cells, it was combined with N-doped graphene quantum dots (N-GQDs) for the anti-inflammatory potentials. It resulted in improved downregulation of COX-2, iNOS, TNF-α, NF-κß, IL-1α, IL-1ß, IL-4, and IL-6 than cells treated with SAM alone. Conclusively, N-GQDs combined with SAM have the effective therapeutic potential as an inhibitor of inflammation by modulating the expression of different cytokine genes.

Biosensing Based on Nanoparticles for Food Allergens Detection

Food allergy is one of the major health threats for sensitized individuals all over the world and, over the years, the food industry has made significant efforts and investments to offer safe foods for allergic consumers. The analysis of the concentration of food allergen residues in processing equipment, in raw materials or in the final product, provides analytical information that can be used for risk assessment as well as to ensure that food-allergic consumers get accurate and useful information to make their food choices and purchasing decisions. The development of biosensors based on nanomaterials for applications in food analysis is a challenging area of growing interest in the last years. Research in this field requires the combined efforts of experts in very different areas including food chemistry, biotechnology or materials science. However, the outcome of such collaboration can be of significant impact on the food industry as well as for consumer’s safety. These nanobiosensing devices allow the rapid, selective, sensitive, cost-effective and, in some cases, in-field, online and real-time detection of a wide range of compounds, even in complex matrices. Moreover, they can also enable the design of novel allergen detection strategies. Herein we review the main advances in the use of nanoparticles for the development of biosensors and bioassays for allergen detection, in food samples, over the past few years. Research in this area is still in its infancy in comparison, for instance, to the application of nanobiosensors for clinical analysis. However, it will be of interest for the development of new technologies that reduce the gap between laboratory research and industrial applications.

Big Potential from Small Agents: Nanoparticles for Imaging-Based Companion Diagnostics

The importance of medical imaging in the diagnosis and monitoring of cancer cannot be overstated. As personalized cancer treatments are gaining popularity, a need for more advanced imaging techniques has grown significantly. Nanoparticles are uniquely suited to fill this void, not only as imaging contrast agents but also as companion diagnostics. This review provides an overview of many ways nanoparticle imaging agents have contributed to cancer imaging, both preclinically and in the clinic, as well as charting future directions in companion diagnostics. We conclude that, while nanoparticle-based imaging agents are not without considerable scientific and developmental challenges, they enable enhanced imaging in nearly every modality, hold potential as in vivo companion diagnostics, and offer precise cancer treatment and maximize intervention efficacy.

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5-70μM, with detection limit of 3μM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

Optically Detected Degradation of NaYF4:Yb,Tm-Based Upconversion Nanoparticles in Phosphate Buffered Saline Solution

In a proof-of-concept study, we assessed different analytical and spectroscopic parameters for stability screening of differently sized β-NaYF₄:20 mol % Yb³⁺, 2 mol % Tm³⁺ upconversion nanoparticles (UCNPs) exemplarily in the bioanalytically relevant buffer phosphate buffered saline (PBS; pH 7.4) at 37 and 50 °C. This included the potentiometric determination of the amount of released fluoride ions, surface analysis with X-ray photoelectron spectroscopy (XPS), and steady-state and time-resolved fluorescence measurements. Based on these results, the luminescence lifetime of the 800 nm upconversion emission was identified as an optimum parameter for stability screening of UCNPs and changes in particle surface chemistry.

Metallic Nanobrushes Made using Ambient Droplet Sprays

An ambient solution-state method for making uniform nanobrushes composed of oriented 1D silver nanowires (NWs) with aspect ratios of 10(2) -10(4) is reported. These structures are grown over cm(2) areas on conducting surfaces. Assemblies of NWs form uniform nanobrush structures, which can capture micrometer-sized objects, such as bacteria and particulate matter. Variation in composition produces unique structures with catalytic properties.

A persistent luminescence microsphere-based probe for convenient imaging analysis of dopamine

SrMgSi₂O₆:Eu_0.01,Dy_0.02 persistent luminescence microspheres have been synthesized via a simple template method and a new probe was established based on turn-off of the persistent luminescence emission for detection and optical imaging of dopamine.

Size-exclusion chromatography of metal nanoparticles and quantum dots

This review presents an overview of size-exclusion chromatographic separation and characterization of noble metal nanoparticles (NPs) and quantum dots (QDs) over the past 25 years. The properties of NPs and QDs that originate from quantum and surface effects are size dependent; to investigate these properties, a separation technique such as size-exclusion chromatography (SEC) is often needed to obtain narrow distribution NP populations that are also separated from the unreacted starting materials. Information on the size distributions and optical properties of NPs have been obtained by coupling SEC to detection methods such as ultraviolet-visible and/or fluorescence spectroscopy. Problems associated with the sorption of NPs and QDs onto various SEC stationary phases, employing both aqueous and organic eluents, are also discussed here.

Assessing Single Upconverting Nanoparticle Luminescence by Optical Tweezers

We report on stable, long-term immobilization and localization of a single colloidal Er(3+)/Yb(3+) codoped upconverting fluorescent nanoparticle (UCNP) by optical trapping with a single infrared laser beam. Contrary to expectations, the single UCNP emission differs from that generated by an assembly of UCNPs. The experimental data reveal that the differences can be explained in terms of modulations caused by radiation-trapping, a phenomenon not considered before but that this work reveals to be of great relevance.

The advances in applying inorganic fluorescent nanomaterials for the detection of hepatocellular carcinoma and other cancers

The advances, drawbacks and application suggestions of QDs, UCNPs and CDs in HCC and other cancer detection fields are discussed.