Sensitization Strategies of Lateral Flow Immunochromatography for Gold Modified Nanomaterials in Biosensor Development

Gold nanomaterials have become very attractive nanomaterials for biomedical research due to their unique physical and chemical properties, including size dependent optical, magnetic and catalytic properties, surface plasmon resonance (SPR), biological affinity and structural suitability. The performance of biosensing and biodiagnosis can be significantly improved in sensitivity, specificity, speed, contrast, resolution and so on by utilizing multiple optical properties of different gold nanostructures. Lateral flow immunochromatographic assay (LFIA) based on gold nanoparticles (GNPs) has the advantages of simple, fast operation, stable technology, and low cost, making it one of the most widely used in vitro diagnostics (IVDs). However, the traditional colloidal gold (CG)-based LFIA can only achieve qualitative or semi-quantitative detection, and its low detection sensitivity cannot meet the current detection needs. Due to the strong dependence of the optical properties of gold nanomaterials on their shape and surface properties, gold-based nanomaterial modification has brought new possibilities to the IVDs: people have attempted to change the morphology and size of gold nanomaterials themselves or hybrid with other elements for application in LFIA. In this paper, many well-designed plasmonic gold nanostructures for further improving the sensitivity and signal output stability of LFIA have been summarized. In addition, some opportunities and challenges that gold-based LFIA may encounter at present or in the future are also mentioned in this paper. In summary, this paper will demonstrate some feasible strategies for the manufacture of potential gold-based nanobiosensors of post of care testing (POCT) for faster detection and more accurate disease diagnosis.

Photothermally sensitive gold nanocage augments the antitumor efficiency of immune checkpoint blockade in immune "cold" tumors

Introduction

Immune checkpoint blockade (ICB) has revolutionized the therapy landscape of malignancy melanoma. However, the clinical benefits from this regimen remain limited, especially in tumors lacking infiltrated T cells (known as "cold" tumors). Nanoparticle-mediated photothermal therapy (PTT) has demonstrated improved outcomes in the ablation of solid tumors by inducing immunogenic cell death (ICD) and reshaping the tumor immune microenvironment. Therefore, the combination of PTT and ICB is a promising regimen for patients with "cold" tumors.

Methods

A second near-infrared (NIR-II) light-activated gold nanocomposite AuNC@SiO2@HA with AuNC as a kernel, silica as shell, and hyaluronic acid (HA) polymer as a targeting molecule, was synthesized for PTT. The fabricated AuNC@SiO2@HA nanocomposites underwent various in vitro studies to characterize their physicochemical properties, light absorption spectra, photothermal conversion ability, cellular uptake ability, and bioactivities. The synergistic effect of AuNC@SiO2@HA-mediated PTT and anti-PD-1 immunotherapy was evaluated using a mouse model of immune "cold" melanoma. The tumor-infiltrating T cells were assessed by immunofluorescence staining and flow cytometry. Furthermore, the mechanism of AuNC@SiO2@HA-induced T-cell infiltration was investigated through immunochemistry staining of the ICD-related markers, including HSP70, CRT, and HMGB1. Finally, the safety of AuNC@SiO2@HA nanocomposites was evaluated in vivo.

Results

The AuNC@SiO2@HA nanocomposite with absorption covering 1064 nm was successfully synthesized. The nano-system can be effectively delivered into tumor cells, transform the optical energy into thermal energy upon laser irradiation, and induce tumor cell apoptosis in vitro. In an in vivo mouse melanoma model, AuNC@SiO2@HA nanocomposites significantly induced ICD and T-cell infiltration. The combination of AuNC@SiO2@HA and anti-PD-1 antibody synergistically inhibited tumor growth via stimulating robust T lymphocyte immune responses.

Discussion

The combination of AuNC@SiO2@HA-mediated PTT and anti-PD-1 immunotherapy proposed a neoteric strategy for oncotherapy, which efficiently convert the immune "cold" tumors into "hot" ones.

Photonic Lithotripsy: Near-Infrared Laser Activated Nanomaterials for Kidney Stone Comminution

Near-infrared activated nanomaterials have been reported for biomedical applications ranging from photothermal tumor destruction to biofilm eradication and energy-gated drug delivery. However, the focus so far has been on soft tissues, and little is known about energy delivery to hard tissues, which have thousand-fold higher mechanical strength. We present photonic lithotripsy with carbon and gold nanomaterials for fragmenting human kidney stones. The efficacy of stone comminution is dependent on the size and photonic properties of the nanomaterials. Surface restructuring and decomposition of calcium oxalate to calcium carbonate support the contribution of photothermal energy to stone failure. Photonic lithotripsy has several advantages over current laser lithotripsy, including low operating power, noncontact laser operation (distances of at least 10 mm), and ability to break all common stones. Our observations can inspire the development of rapid, minimally invasive techniques for kidney stone treatment and extrapolate to other hard tissues such as enamel and bone.

Gold Nanomaterials-Implemented CRISPR-Cas Systems for Biosensing

Due to their superiority in the simple design and precise targeting, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems have attracted significant interest for biosensing. On the one hand, CRISPR-Cas systems have the capacity to precisely recognize and cleave specific DNA and RNA sequences. On the other hand, CRISPR-Cas systems such as orthologs of Cas9, Cas12, and Cas13 exhibit cis-cleavage or trans-cleavage activities after recognizing the target sequence. Owing to the cleavage activities, CRISPR-Cas systems can be designed for biosensing by degrading tagged nucleic acids to produce detectable signals. To meet the requirements of point-of-care detection and versatile signal readouts, gold nanomaterials with excellent properties such as high extinction coefficients, easy surface functionalization, and biocompatibility are implemented in CRISPR-Cas-based biosensors. In combination with gold nanomaterials such as gold nanoparticles, gold nanorods, and gold nanostars, great efforts are devoted to fabricating CRISPR-Cas-based biosensors for the detection of diverse targets. This review focuses on the current advances in gold nanomaterials-implemented CRISPR-Cas-based biosensors, particularly the working mechanism and the performance of these biosensors. CRISPR-Cas systems, including CRISPR-Cas9, CRISPR-Cas12a, and CRISPR-Cas13a are discussed and highlighted. Meanwhile, prospects and challenges are also discussed in the design of biosensing strategies based on gold nanomaterials and CRISPR-Cas systems.

Gold Nanomaterials-Based Electrochemical Sensors and Biosensors for Phenolic Antioxidants Detection: Recent Advances

Antioxidants play a central role in the development and production of food, cosmetics, and pharmaceuticals, to reduce oxidative processes in the human body. Among them, phenolic antioxidants are considered even more efficient than other antioxidants. They are divided into natural and synthetic. The natural antioxidants are generally found in plants and their synthetic counterparts are generally added as preventing agents of lipid oxidation during the processing and storage of fats, oils, and lipid-containing foods: All of them can exhibit different effects on human health, which are not always beneficial. Because of their relevant bioactivity and importance in several sectors, such as agro-food, pharmaceutical, and cosmetic, it is crucial to have fast and reliable analysis Rmethods available. In this review, different examples of gold nanomaterial-based electrochemical (bio)sensors used for the rapid and selective detection of phenolic compounds are analyzed and discussed, evidencing the important role of gold nanomaterials, and including systems with or without specific recognition elements, such as biomolecules, enzymes, etc. Moreover, a selection of gold nanomaterials involved in the designing of this kind of (bio)sensor is reported and critically analyzed. Finally, advantages, limitations, and potentialities for practical applications of gold nanomaterial-based electrochemical (bio)sensors for detecting phenolic antioxidants are discussed.

Nanogold-based materials in medicine: from their origins to their future

The properties of gold-based materials have been explored for centuries in several research fields, including medicine. Multiple published production methods for gold nanoparticles (AuNPs) have shown that the physicochemical and optical properties of AuNPs depend on the production method used. These different AuNP properties have allowed exploration of their usefulness in countless distinct biomedical applications over the last few years. Here we present an extensive overview of the most commonly used AuNP production methods, the resulting distinct properties of the AuNPs and the potential application of these AuNPs in diagnostic and therapeutic approaches in biomedicine.

Gold Nanomaterials and Bone/Cartilage Tissue Engineering: Biomedical Applications and Molecular Mechanisms

Recently, as our population increasingly ages with more pressure on bone and cartilage diseases, bone/cartilage tissue engineering (TE) have emerged as a potential alternative therapeutic technique accompanied by the rapid development of materials science and engineering. The key part to fulfill the goal of reconstructing impaired or damaged tissues lies in the rational design and synthesis of therapeutic agents in TE. Gold nanomaterials, especially gold nanoparticles (AuNPs), have shown the fascinating feasibility to treat a wide variety of diseases due to their excellent characteristics such as easy synthesis, controllable size, specific surface plasmon resonance and superior biocompatibility. Therefore, the comprehensive applications of gold nanomaterials in bone and cartilage TE have attracted enormous attention. This review will focus on the biomedical applications and molecular mechanism of gold nanomaterials in bone and cartilage TE. In addition, the types and cellular uptake process of gold nanomaterials are highlighted. Finally, the current challenges and future directions are indicated.

Gold Nanomaterial Engineering for Macrophage-Mediated Inflammation and Tumor Treatment

Macrophages play an important role in the body's immune defense process. Phenotype imbalance between M1 and M2 macrophages induced by inflammation-related disorders and tumor can also be reversibly converted to treat these diseases. As exogenous substances, a large part of gold-based nanomaterials interact with macrophages once they enter the body, which provides gold nanomaterials a huge advantage to act as imaging contrasts, active substance carriers, and therapeutic agents for macrophage modulation. By cutting off macrophage recruitment, inhibiting macrophage activities, and modulating M1/M2 polarization, gold nanomaterial engineering exerts therapeutic effects on inflammation-related diseases at target sites. In this review, biological functions of macrophages in inflammation-related diseases are introduced, the effect of physicochemical factors of gold nanomaterials including size, shape, and surface chemistry is focused on the interaction between macrophages and gold nanomaterials, and the applications of gold nanomaterials are elaborated for tracking and treating these diseases by macrophages. The rational and smart engineering of gold nanomaterials allows a promising platform for macrophage-mediated inflammation and tumor imaging and treatment.

Gold Nanomaterials for Imaging-Guided Near-Infrared in vivo Cancer Therapy

In recent years, tremendous efforts have been devoted into the fields of valuable diagnosis and anticancer treatment, such as real-time imaging, photothermal, and photodynamic therapy, and drug delivery. As promising nanocarriers, gold nanomaterials have attracted widespread attention during the last two decades for cancer diagnosis and therapy due to their prominent properties. With the development of nanoscience and nanotechnology, the fascinating bio-applications of functionalized gold nanomaterials have been gradually developed from in vitro to in vivo. This mini-review emphasizes some recent advances of photothermal imaging (PTI), surface-enhanced Raman scattering (SERS) imaging, and photoacoustic imaging (PAI)-guided based on gold nanomaterials in vivo therapy in near infrared region (>800 nm). We focus on the fundamental strategies, characteristics of bio-imaging modalities involving the advantages of multiples imaging modalities for cancer treatment, and then highlight a few examples of each techniques. Finally, we discuss the perspectives and challenges in gold nanomaterial-based cancer therapy.

Nanostructured Materials Based on Noble Metals for Advanced Biological Applications

This special issue focuses on highlighting the progress of last decade regarding the new nanostructured materials based on noble metals, especially gold and silver. Innovative preparations, functionalizations, and characterizations of these nanomaterials are investigated. Moreover, biotechnological applications, and advanced uses of these compounds for environmental sensing are reported. In particular gold and silver nanomaterials are widely studied due to their high stability, amazing chemical–physical features and, for silver, marked antibacterial properties. It is also hoped that the current special issue will encourage multidisciplinary research on noble metal nanomaterials, expanding the range of potential biological applications. This must be associated with improvements in synthetic methods and with economic feasibility studies of the proposed processes, also exploring the ecotoxicological aspects.

Sub-Nanometer Thick Gold Nanosheets as Highly Efficient Catalysts

2D metal nanomaterials offer exciting prospects in terms of their properties and functions. However, the ambient aqueous synthesis of atomically-thin, 2D metallic nanomaterials represents a significant challenge. Herein, freestanding and atomically-thin gold nanosheets with a thickness of only 0.47 nm (two atomic layers thick) are synthesized via a one-step aqueous approach at 20 °C, using methyl orange as a confining agent. Owing to the high surface-area-to-volume ratio, abundance of unsaturated atoms exposed on the surface and large interfacial areas arising from their ultrathin 2D nature, the as-prepared Au nanosheets demonstrate excellent catalysis performance in the model reaction of 4-nitrophenol reduction, and remarkable peroxidase-mimicking activity, which enables a highly sensitive colorimetric sensing of H2O2 with a detection limit of 0.11 × 10-6 m. This work represents the first fabrication of freestanding 2D gold with a sub-nanometer thickness, opens up an innovative pathway toward atomically-thin metal nanomaterials that can serve as model systems for inspiring fundamental advances in materials science, and holds potential across a wide region of applications.

Gold Nanoclusters: Bridging Gold Complexes and Plasmonic Nanoparticles in Photophysical Properties

Recent advances in the determination of crystal structures and studies of optical properties of gold nanoclusters in the size range from tens to hundreds of gold atoms have started to reveal the grand evolution from gold complexes to nanoclusters and further to plasmonic nanoparticles. However, a detailed comparison of their photophysical properties is still lacking. Here, we compared the excited state behaviors of gold complexes, nanolcusters, and plasmonic nanoparticles, as well as small organic molecules by choosing four typical examples including the Au₁₀ complex, Au₂₅ nanocluster (1 nm metal core), 13 diameter Au nanoparticles, and Rhodamine B. To compare their photophysical behaviors, we performed steady-state absorption, photoluminescence, and femtosecond transient absorption spectroscopic measurements. It was found that gold nanoclusters behave somewhat like small molecules, showing both rapid internal conversion (<1 ps) and long-lived excited state lifetime (about 100 ns). Unlike the nanocluster form in which metal–metal transitions dominate, gold complexes showed significant charge transfer between metal atoms and surface ligands. Plasmonic gold nanoparticles, on the other hand, had electrons being heated and cooled (~100 ps time scale) after photo-excitation, and the relaxation was dominated by electron–electron scattering, electron–phonon coupling, and energy dissipation. In both nanoclusters and plasmonic nanoparticles, one can observe coherent oscillations of the metal core, but with different fundamental origins. Overall, this work provides some benchmarking features for organic dye molecules, organometallic complexes, metal nanoclusters, and plasmonic nanoparticles.

Multifunctional Magnetic Gold Nanomaterials for Cancer

The integration of multiple imaging and therapeutic agents into a customizable nanoplatform for accurate identification and rapid prevention of cancer is attracting great attention. Among the available theranostic nanosystems, magnetic gold nanoparticles are particularly promising as they exhibit unique physicochemical properties that can support multiple functions, including cancer diagnosis by magnetic resonance imaging, X-ray computed tomography, Raman and photoacoustic imaging, drug delivery, and plasmonic photothermal and photodynamic therapies. This review gives an overview of recent advances in the fabrication of multifunctional gold nanohybrids with magnetic and optical properties and their successful demonstration in multimodal imaging and therapy of cancer. Concerns around toxicity of these nanomaterials are also discussed in view of an imminent transition to clinical practice.

Electrochemical Deposition of Nanomaterials for Electrochemical Sensing

The most commonly used methods to electrodeposit nanomaterials on conductive supports or to obtain electrosynthesis nanomaterials are described. Au, layered double hydroxides (LDHs), metal oxides, and polymers are the classes of compounds taken into account. The electrochemical approach for the synthesis allows one to obtain nanostructures with well-defined morphologies, even without the use of a template, and of variable sizes simply by controlling the experimental synthesis conditions. In fact, parameters such as current density, applied potential (constant, pulsed or ramp) and duration of the synthesis play a key role in determining the shape and size of the resulting nanostructures. This review aims to describe the most recent applications in the field of electrochemical sensors of the considered nanomaterials and special attention is devoted to the analytical figures of merit of the devices.

Gold nanorod-encapsulated biodegradable polymeric matrix for combined photothermal and chemo-cancer therapy

PURPOSE

A biocompatible nanocomplex system co-encapsulated with gold nanorods (AuNRs) and doxorubicin (DOX) was investigated for its potentials on the combined photothermal- and chemotherapy.

MATERIALS AND METHODS

Hydrophobic AuNRs were synthesized by the hexadecyltrimethyl-ammonium bromide (CTAB)-mediated seed growth method, and then, they received two-step surface modifications of polyethylene glycol (PEG) and dodecane. The AuNR/DOX/poly(lactic-co-glycolic acid) (PLGA) nanocomplexes were prepared by emulsifying DOX, AuNR, and PLGA into aqueous polyvinyl alcohol solution by sonication. Human serum albumin (HSA) was used to coat the nanocomplexes to afford HSA/AuNR/DOX-PLGA (HADP). Size and surface potential of the HADP nanocomplexes were determined by using a Zetasizer. Cytotoxicity and cellular uptake of the HADP were analyzed by using MTT assay and flow cytometry, respectively. In vitro anticancer effects of the HADP were studied on various cancer cell lines. To assess the therapeutic efficacy, CT26 tumor-bearing mice were intravenously administered with HADP nanocomplexes and laser treatments, followed by monitoring of the tumor growth and body weight.

RESULTS

Size and surface potential of the HADP nanocomplexes were 245.8 nm and -8.6 mV, respectively. Strong photothermal effects were verified on the AuNR-loaded PLGA nanoparticles (NPs) in vitro. Rapid and repeated drug release from the HADP nanocomplexes was successfully achieved by near-infrared (NIR) irradiations. HSA significantly promoted cellular uptake of the HADP nanocomplexes to murine colon cancer cells as demonstrated by cell imaging and flow cytometric studies. By combining photothermal and chemotherapy, the HADP nanocomplexes exhibited strong synergistic anticancer effects in vitro and in vivo.

CONCLUSION

An NIR-triggered drug release system by encapsulating hydrophobic AuNR and DOX inside the PLGA NPs has been successfully prepared in this study. The HADP NPs show promising combined photothermal- and chemotherapeutic effects without inducing undesired side effects on a murine colon cancer animal model.

Plant Protein-Directed Synthesis of Luminescent Gold Nanocluster Hybrids for Tumor Imaging

Nowadays, fluorescence detection has emerged as one of the most frequently used noninvasive biosensing methods to selectively monitor biological processes within living systems. Among fluorescent nanoparticles (NPs), gold nanoclusters (AuNCs) have been intensively studied because of their intrinsic fluorescence and their endowed biocompatible surface. Herein, we selected an abundant, low-cost, and sustainable plant protein, the pea protein isolate (PPI), for its excellent biocompatibility, biodegradability, and nonallergenic character to be employed as both a reducing and stabilizing agent to facilely produce AuNCs exhibiting a strong red fluorescence. Afterward, the formed AuNCs/PPI mixture was able to self-assemble into NPs (AuNCs/PPI NPs) with the size of about 100 nm simply through a dialyzing process. Taking advantage from the protein nature of PPI, AuNCs/PPI NPs demonstrate both excellent biocompatibility and colloidal stability. Moreover, AuNCs/PPI NPs showed a great capability when employed as a bioimaging probe for both in vitro and in vivo imaging. Finally, AuNCs/PPI NPs were coated with red blood cell (RBC) membranes to improve their blood circulation property and enhance their tumor enrichment ability to meet the requirement for practical use. Results convincingly show that such super NPs (RBC-coated AuNCs/PPI NPs) were able to successfully locate tumor in vivowith an excellent imaging capability, which provides a new strategy for bioimaging with fluorescent NPs.

Structural-Engineering Rationales of Gold Nanoparticles for Cancer Theranostics

Personalized theranostics of cancer is increasingly desired, and can be realized by virtue of multifunctional nanomaterials with possible high performances. Gold nanoparticles (GNPs) are a type of especially promising candidate for cancer theranostics, because their synthesis and modification are facile, their structures and physicochemical properties are flexibly controlled, and they are also biocompatible. Especially, the localized surface plasmon resonance and multivalent coordination effects on the surface endow them with NIR light-triggered photothermal imaging and therapy, controlled drug release, and targeted drug delivery. Although the structure, properties, and theranostic application of GNPs are considerably plentiful, no expert review systematically explains the relationships among their structure, property. and application and induces the engineering rationales of GNPs for cancer theranostics. Hence, there are no clear rules to guide the facile construction of optimal GNP structures aiming at a specific theranostic application. A series of structural-engineering rationales of GNPs for cancer theranostics is proposed through digging out the deep relationships between the structure and properties of GNPs. These rationales will be inspiring for guiding the engineering of specific and advanced GNPs for personalized cancer theranostics.

Gold Nanomaterials in Consumer Cosmetics Nanoproducts: Analyses, Characterization, and Dermal Safety Assessment

Establishment of analytical methods of engineered nanomaterials in consumer products for their human and environmental risk assessment becomes urgent for both academic and industrial needs. Owing to the difficulties and challenges around nanomaterials in complex media, proper chemical separation and biological assays of nanomaterials from nanoproducts needs to be firstly developed. Herein, a facile and rapid method to separate and analyze gold nanomaterials in cosmetics is reported. Gold nanomaterials are successfully separated from different facial or eye creams and their physiochemical properties are analyzed by quantitative and qualitative state-of-the art techniques with high sensitivity or high spatial resolution. In turn, a protocol including quantification of gold by inductively coupled plasma mass spectrometry and thorough characterization of morphology, size distribution, and surface property by electron microscopes, atomic force microscope, and X-ray photoelectron spectroscope is developed. Subsequently, the preliminary toxicity assessment indicates that gold nanomaterials in cosmetic creams have no observable toxicity to human keratinocytes even after 24 h exposure up to a concentration of 200 μg mL^-1 . The environmental scanning electron microscope reveals that gold nanomaterials are mostly attached on the cell membrane. Thus, the present study provides a full analysis protocol for toxicity assessment of gold nanomaterials in consumer products (cosmetic creams).

Efficient electrochemical CO2 conversion powered by renewable energy

The catalytic conversion of CO2 into industrially relevant chemicals is one strategy for mitigating greenhouse gas emissions. Along these lines, electrochemical CO2 conversion technologies are attractive because they can operate with high reaction rates at ambient conditions. However, electrochemical systems require electricity, and CO2 conversion processes must integrate with carbon-free, renewable-energy sources to be viable on larger scales. We utilize Au25 nanoclusters as renewably powered CO2 conversion electrocatalysts with CO2 → CO reaction rates between 400 and 800 L of CO2 per gram of catalytic metal per hour and product selectivities between 80 and 95%. These performance metrics correspond to conversion rates approaching 0.8-1.6 kg of CO2 per gram of catalytic metal per hour. We also present data showing CO2 conversion rates and product selectivity strongly depend on catalyst loading. Optimized systems demonstrate stable operation and reaction turnover numbers (TONs) approaching 6 × 10(6) molCO2 molcatalyst(-1) during a multiday (36 h total hours) CO2 electrolysis experiment containing multiple start/stop cycles. TONs between 1 × 10(6) and 4 × 10(6) molCO2 molcatalyst(-1) were obtained when our system was powered by consumer-grade renewable-energy sources. Daytime photovoltaic-powered CO2 conversion was demonstrated for 12 h and we mimicked low-light or nighttime operation for 24 h with a solar-rechargeable battery. This proof-of-principle study provides some of the initial performance data necessary for assessing the scalability and technical viability of electrochemical CO2 conversion technologies. Specifically, we show the following: (1) all electrochemical CO2 conversion systems will produce a net increase in CO2 emissions if they do not integrate with renewable-energy sources, (2) catalyst loading vs activity trends can be used to tune process rates and product distributions, and (3) state-of-the-art renewable-energy technologies are sufficient to power larger-scale, tonne per day CO2 conversion systems.