Antibody-Gold Nanoparticle Bioconjugates for Biosensors: Synthesis, Characterization and Selected Applications

Large gold nanoparticle release assay for attomolar detection of miRNA related to myelodysplastic neoplasms

MicroRNAs (miRNAs) hold potential as biomarkers for numerous cancer types, including myelodysplastic neoplasms (MDS). Here, we present a highly sensitive assay based on the oligonucleotide-triggered release of gold nanoparticles (AuNPs) for the detection of hsa-miR-451a with a surface plasmon resonance biosensor. The performance of the assay is in large part determined by the size and functional coating of AuNPs. Therefore, we investigate AuNPs in a size range from 43 to 170 nm, functionalized with thiol- or biotin-terminated oligonucleotides (AuNPsSdT or AuNPsBdT). Our study reveals that 103 nm AuNPsSdT are the best option to improve the assay performance due to their high colloidal stability, a release efficiency exceeding 90%, and a sensor response enhancement factor exceeding 105. We demonstrate that in conjunction with 103 nm AuNPsSdT, the AuNP release assay can detect hsa-miR-451a at levels down to 40 aM and quantify hsa-miR-451a physiological levels in human blood plasma. Moreover, we use the assay to demonstrate a significant down-regulation of hsa-miR-451a in blood plasma of MDS patients compared to healthy individuals, suggesting the potential relevance of hsa-miR-451a as a prospective MDS biomarker.

A Comparative Analysis of Optical Biosensors for Rapid Detection of SARS-CoV-2 and Influenza

Airborne pathogens, such as influenza and SARS-CoV-2, pose significant health risks. While traditional diagnostic methods have limitations, optical biosensors offer a promising solution due to their rapid, sensitive, and cost-effective nature. This review focuses on the application of optical biosensors, including colorimetry, surface plasmon resonance, surface-enhanced Raman spectroscopy, and fluorescence techniques, for the detection of influenza and SARS-CoV-2. We discuss the advantages of these techniques, such as their potential for point-of-care testing and early disease detection. By addressing the limitations of existing methods and exploring emerging technologies, optical biosensors can play a crucial role in combating the spread of airborne pathogens. This review provides a comprehensive overview of optical biosensor techniques for the detection of both SARS-CoV-2 and influenza, addressing a significant gap in the literature.

Development of crosslinker-free antibody-enzyme conjugates for immunoassays in pesticide residue detection

Immunoassays are biochemical analytical techniques based on the specific binding between antigens and antibodies. Due to their high sensitivity, rapid analysis, high throughput, cost-effectiveness, and broad applicability, immunoassays have been widely utilized across various fields. Antibody-enzyme conjugates are essential components for signal generation in immunoassays, with crosslinking chemical (crosslinker)-based methods traditionally employed for their production. However, these methods often involve hazardous reagents and complex procedures, highlighting the need for more eco-friendly alternatives. In this study, we developed a universal, crosslinker-free approach for preparing antibody-enzyme conjugates. This method eliminates the use of chemical reagents such as glutaraldehyde or periodate, as well as the intricate conjugation and purification steps typically required. Instead, gold nanoparticles (AuNPs) were employed as a versatile nanomaterial to passively adsorb horseradish peroxidase (HRP) and antibodies through a simple procedure completed within 60 minutes. The resulting conjugates were characterized using UV-vis spectroscopy, transmission electron microscopy (TEM), and zeta potential analysis. Using acetamiprid (ACE), a widely-used pesticide, as the target model, an enzyme-linked immunosorbent assay (ELISA) was developed based on the AuNP-mediated conjugates. The assay demonstrated performance comparable to that of traditional crosslinker-based methods, with an IC50 of 0.49 ng mL-1 and a limit of detection (LOD) of 0.11 ng mL-1. Recovery rates for ACE in spiked fruit samples were consistent with those obtained using liquid chromatography-mass spectrometry (LC-MS). The proposed method not only provides a reliable alternative for HRP and antibody conjugation but also advances green analytical chemistry by minimizing the use of hazardous chemicals, reducing derivative waste, and improving energy efficiency.

Towards ultrasensitive biosensors based on virus-like particles and plasmonic surface lattice resonance

Plasmonic surface lattice resonance (SLR) is a phenomenon in which individual localized surface plasmon resonances (LSPRs) excited in periodically-arranged plasmonic nanoparticles couple through the interaction with the propagating diffracted incident light. The SLR optical absorption peak is by at least one order of magnitude more intense than the LSPR one, making SLR superior for applications in which LSPR is commonly used. Recently, we have developed a route for the fabrication of spherical virus-like particles (VLPs) with plasmonic Au cores and protein coronas, where the LSPR in the cores amplifies vibrational Raman signals originating from protein-antibody interactions [ACS Synth. Biol. 12 (2023) 2320]. The particles are promising for biosensing, however, the intensity of the signals recorded in solution is not strong enough to detect antibodies at very low concentrations. Here, we show that by ordering the VLPs in periodic nanoarrays exhibiting SLR amplifies the signals by two orders of magnitude, revealing superior potential of VLP-SLR arrays in ultrasensitive biodetection.

Plasmonic Geometry-Induced Viscoelastic Biocomplex Formation with Optical Concealment, Liquid Slips, and Soundscapes in Bioassays

Plasmonic nanoparticles (NPs), typically made up of gold or silver, are widely used in point-of-care bio- and chemical sensing due to their role in enhancing detection sensitivity. Key NP properties influencing sensing performance include the material type, NP size, and geometry. While much research has focused on material and size optimization, less attention has been given to understand NP geometry effects and interactions with biomolecules involved in the bioassay. In this context, we investigate the interfacial properties of the biocomplex formed by spherical-shaped gold nanoparticles (AuNPs) and gold nanostars (AuNSts) during a sandwich assay using localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D). The chosen model to study the biocomplex specifically detects interleukin-6 (IL-6). Our results show that AuNSts, with their anisotropic shape and higher surface area, form antibody-antigen complexes more effectively than AuNPs. AuNSts also create a softer, more hydrated layer due to their complex geometry, which leads to larger liquid slips. Lastly, we showed that AuNSts avoid optical concealment at high IL-6 concentrations, unlike AuNPs, making them more reliable for detecting a wider range of concentrations. These findings highlight the importance of optimizing NP geometry for improved bio/chemical sensor performance.

Exciton-Photon Coupling Microcavity as a Selective Biosensing Platform for Nonlocal Terahertz Metamaterials

The strong-coupling microcavity between excitons and photons facilitates efficient modulation and control of light, as well as precise manipulation of photon propagation properties. This phenomenon demonstrates significant potential for diverse applications in quantum information processing, optical sensing, and nonlinear optics. The anapole, as a specific type of captured state, allows for effective control over the electromagnetic field through appropriate distributions of current and charge, generating substantial localized effects within the field. This mechanism provides a novel avenue for investigating the strong-coupling dynamics between photons and excitons in hybrid metamaterial sensing. Here, the rate of energy exchange between the excitons and the optical microcavity of the metamaterial is greater than their individual dissipation rates, resulting in significant Rabi splitting phenomena and pronounced anti-crossing behavior, ultimately forming an "ultrasensitive photoreactive region" suitable for sensing applications. Furthermore, the nonlocal metamaterial, characterized by strong light-matter coupling, can be integrated with functionalized colloidal gold and monoclonal tag antibodies to enable rapid multidimensional detection and identification of total prostate-specific antigen (tPSA) in complex environmental solutions. The proposed strong-coupling resonance microcavity plays a crucial role in the rapid evolution of nonlocal metamaterials, enhancing their applicability in molecular detection and selective recognition of fundamental light-matter interaction phenomena.

Rapid Bacterial/Viral Infections Typing Strategy Using a Portable Dual-Channel Electrochemical Biosensor Based on One-Step Assembly of Immunomagnetic Beads

Amidst multiple epidemics, a rapid, sensitive, economical, and portable infection diagnosis strategy is crucial for primary medical care, particularly through the analysis of pathogen sources to determine appropriate antibiotic use. C-reactive protein (CRP) and serum amyloid A (SAA) are host-related biomarkers, and their combined detection can effectively distinguish between bacterial and viral infections, which holds great significance for the diagnosis of unknown pathogens. In this work, a portable dual-channel electrochemical biosensor based on a one-step assembly of immunomagnetic beads was proposed for the on-site combined detection of plasma CRP and SAA, which streamlined the operation and shortened the minimum detection time to less than 3 min. The biosensor exhibited excellent linearity in the detection of 3.125-1250 ng/mL CRP and 31.25-1250 ng/mL SAA, with detection limits of 0.91 and 12 ng/mL, respectively, falling within the clinically relevant reference range. Through simulated sample tests, the biosensor effectively distinguished between bacterial infection, viral infection, and healthy plasma samples. The actual sample tests demonstrated a high correlation and comparable medical value to enzyme-linked immunosorbent assay. Overall, this proposed strategy showed potential to aid in infection diagnosis and enable rapid combined detection of multiple biomarkers.

Understanding gold nanoparticles and their attributes in ovarian cancer therapy

Ovarian cancer is one the deadliest disease wherein the survival rate is very low. Despite of advances in medical sciences, researches are still at the stage of infancy where patients are succumbing to this malignancy. Multidrug resistance, toxicity, mode of treatment related issues like catheter related complication poises a number of challenges to scientists worldwide. Novel therapy is now thus being focussed to sensitive the cells more towards the treatment. Gold nanoparticles (Au NPs), known for their high biocompatibility, and strong optical and magnetic responses, have emerged as promising agents for both the diagnosis and treatment of ovarian cancer. Owing to physical characteristics, AuNPs may be used as adjuvants in bioimaging, radiotherapy and fluorescence imaging. As a result, these characteristics substantially support AuNPs in biological domains. In addition to their therapeutic potential, Au NPs exhibit strong surface plasmon resonance (SPR) properties, enhancing imaging techniques for early detection of ovarian tumors. Furthermore, chemical properties such as Magnetic Resonance and Imaging Properties, X-ray imaging property, Two-photon or multiphoton imaging, and Optical coherence tomography (OCT) imaging properties enhance the use of Au NPs in diagnosis. This paper highlights the properties, targeting potential and diagnosis and treatment of ovarian cancer by Au NPs has been discussed.

In Situ Growth of Au NPs on Nitrogen-Doped Graphene Quantum Dots Decorated Graphene Composites for the Construction of an Electrochemical Immunosensor and Its Application in CEA Detection

Carcinoembryonic antigen (CEA) is an important tumor biomarker for the early clinical diagnosis of various cancers, and, therefore, the accurate and sensitive quantitative determination of CEA is of vital significance. In this study, we demonstrated the in situ growth of Au nanoparticles (AuNPs) on nitrogen-doped graphene quantum dots (N-GQDs) decorated reduced graphene oxide (rGO) nanocomposites by using simple drop-coating and electrochemical deposition methods. N-GQDs@rGO can be formed through the π-π stacking interaction and possesses a high specific surface area and many functional groups, providing lots of anchor sites (amino moieties in NGQDs) for the in situ electrochemical growth of AuNPs without the addition of reductants and protective agents. Such AuNPs/N-GQDs@rGO ternary nanocomposites combine the characteristics of three nanomaterials, showing a large surface area, excellent solubility, good conductivity, catalytic activity, a simple fabrication process, and notable stability, which are further used to construct a label-free electrochemical immunosensor for the determination of CEA. Under the optimized experimental conditions, the AuNPs/N-GQDs@rGO-based electrochemical immunosensor achieves a broad linear response, ranging from 1 pg/mL to 0.5 μg/mL and a low detection limit of 0.13 pg/mL. Moreover, the AuNPs/N-GQDs@rGO-based electrochemical immunosensor shows exceptional selectivity, anti-interference, and anti-fouling capabilities for the direct analysis of CEA amounts in fetal bovine serum samples, showing vast potential in the clinical screening of cancer.

Label-free localized surface plasmon resonance (LSPR) biosensor, based on Au-Ag NPs embedded in TiO2 matrix, for detection of Ochratoxin-A (OTA) in wine

Ochratoxin-A (OTA) is a widespread foodstuff contaminant with potential carcinogenic effects. Innovative sensing technologies that allow on-site and sensitive food screening can have a significant impact on food and environment safety. A novel and quantitative label-free LSPR-based biosensor was specifically designed for OTA detection, employing a portable LSPR spectroscopy sensing system for efficient on-site and cost-effective analysis. This biosensor is comprised of monoclonal anti-OTA antibodies immobilized on the surface of sputtered Au-Ag nanoparticles embedded in a TiO2 matrix. Under optimized conditions, the LSPR-based biosensor demonstrated a linear dynamic response from 0.05 to 2 ng mL-1, with an estimated limit of detection at 7 pg mL-1, using 55 μL of sample, outperforming commercial ELISA technique in relevant bioanalytical parameters. Sensitivity in OTA detection is crucial because it ensures the accurate identification of low concentrations, which is essential for preventing health risks associated to cumulative ingestion of contaminated food products. The robustness and feasibility of the presented LSPR-based biosensing was tested using spiked white wine, exhibiting a satisfactory recovery of 93 %-113 %, confirming its efficacy in a complex matrix.

Utilizing gold nanoparticles in plasmonic photothermal therapy for cancer treatment

In recent decades, significant attention has been directed towards gold nanoparticles due to their exceptional properties, capturing the interest of researchers globally. Their unique characteristics, such as localized surface plasmon resonance, high surface area to volume ratio, biocompatibility, and facile surface functionalization, render them highly suitable for diverse applications, ranging from optoelectronics and sensing to surface-enhanced spectroscopies and biomedical uses, particularly in the realm of photothermal therapy. Plasmonic photothermal therapy, an emerging biomedical technology, has garnered substantial interest for its potential in cancer treatment and management. This approach employs photothermal agents, such as gold nanoparticles, which absorb light in the near-infrared region. When these agents accumulate within cancer cells, the absorbed photon energy is converted into heat, inducing local hyperthermia. This localized effect selectively eliminates damaged cells adjacent to nanoparticles while sparing normal cells. Various shapes and sizes of gold nanoparticles have proven well-suited candidates for photothermal therapy. This paper provides an overview of the distinctive properties of gold nanoparticles. It delves into the surface functionalization techniques crucial for ensuring cancer cells' effective retention and targeting of gold nanoparticles. In this context, the present paper reviews diverse applications of gold nanoparticles with different shapes in plasmonic photothermal therapy, encompassing nanospheres, nanorods, nanoshells, nanostars, and nanocages.

Recent advances in SERS assays for detection of multiple extracellular vesicles biomarkers for cancer diagnosis

As the prevalence of cancer is escalating, there is an increased demand for early and sensitive diagnostic tools. A major challenge in early detection is the lack of specific biomarkers, and a readily accessible, sensitive and rapid detection method. To meet these challenges, cancer-derived small extracellular vesicles (sEVs) have been discovered as a new promising cancer biomarker due to the high abundance of sEVs in body fluids and their extensive cargo of biomarkers. Additionally, surface-enhanced Raman scattering (SERS) presents a sensitive, multiplexed, and rapid method that has gained attraction with recent studies showing promising results from patient samples for the multiplex detection of cancer sEVs. Various label-based SERS multiplex assays have been developed in the field of SERS including bead assays, lateral flow immunoassays, microfluidic devices, and artificial intelligence (AI)-based label-free SERS chips, targeting multiple surface proteins to ensure comprehensive multiplex diagnostics. These assays hold promise for enabling early detection, quantification, and subtyping of cancer-derived sEVs for cancer diagnostic applications. This review aims to provide a summary of the recent advances in the field of SERS multiplex assays for detection, quantification, and subtyping of sEVs to facilitate cancer diagnosis. This review further provides unique insights into the use of sEVs as a biomarker and aims to address the issues surrounding their translation from laboratories to clinics.

Sequential Growth of Quantized Peptide Brushes on Colloidal Gold

We synthesized rigid, macromolecular brushes with well-defined and quantized brush lengths on a gold nanoparticle substrate by using a macromolecular "grafting from" approach. The macromonomers used in these brushes were thiol- and maleimide-functionalized peptide coiled coil "bundlemers" that fold into discrete 4 nm × 2 nm (length × diameter) cylindrical nanoparticles. With each added peptide macromonomer layer, brush thickness increased by approximately the length of a single bundlemer nanoparticle. Due to the quantized nature of these brushes, we were able to determine grafting density and brush thickness through a simplified local surface plasmon resonance model (LSPR). The accuracy of this model is validated by dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryoTEM). The high grafting density and precise brush thickness, demonstrated by the sequential macromolecular growth of these brushes, could lead to the development of better multifunctional LSPR-based biosensors. Additionally, the LSPR model developed in this paper could be modified to describe other peptides and proteins and could prove to be a valuable tool for characterizing protein adsorption on metallic nanoparticles.

Evaluating the In Situ Effects of Whole Protein Coronas on the Biosensing of Antibody-Immobilized Nanoparticles Using Two-Color Fluorescence Nanoparticle Tracking Analysis

The formation of protein coronas around engineered nanoparticles (ENPs) in biological environments is critical in nanomedicine, as these coronas significantly influence the biological behavior of ENPs. Despite extensive research on protein coronas, understanding the in situ influence of whole (soft plus hard) protein coronas has remained challenging. In this study, we demonstrate a strategy to assess the in situ effects of whole coronas on the model biosensing of anti-IgG using IgG-conjugated gold nanoparticles (IgG-AuNPs) through fluorescence nanoparticle tracking analysis (F-NTA), which enables the selective tracking of fluorescent particles within complex media. In our approach, anti-IgG and IgG-AuNPs were labeled with distinct fluorescent dyes. The accordance in hydrodynamic diameter distributions observed at two different wavelengths verifies the successful capture of anti-IgG on the IgG-AuNPs. The counting of fluorescent anti-IgG within the size distribution allows for a quantitative assessment of biosensing efficiency. This method was applied to evaluate the effects of four protein coronas-human serum albumin, high-density lipoproteins, immunoglobulin G, and fibrinogen-as well as their mixture across varying incubation times and concentrations. The results suggest that the physical presence of whole protein coronas surrounding the IgG-AuNPs may assist the biosensing interaction in situ rather than screening it.

Promising breakthroughs in amyotrophic lateral sclerosis treatment through nanotechnology's unexplored frontier

This review explores the transformative potential of nanotechnology in the treatment and diagnosis of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder characterized by motor neuron degeneration, muscle weakness, and eventual paralysis. Nanotechnology offers innovative solutions across various domains, including targeted drug delivery, neuroprotection, gene therapy and editing, biomarker detection, advanced imaging techniques, and tissue engineering. By enhancing the precision and efficacy of therapeutic interventions, nanotechnology facilitates key advancements such as crossing the blood-brain barrier, targeting specific cell types, achieving sustained therapeutic release, and enabling combination therapies tailored to the complex pathophysiology of ALS. Despite its immense promise, the clinical translation of these approaches faces challenges, including potential cytotoxicity, biocompatibility, and regulatory compliance, which must be addressed through rigorous research and testing. This review emphasizes the application of nanotechnology in targeted drug delivery and gene therapy/editing for ALS, drawing on the author's prior work with various nanotechnological platforms to illustrate strategies for overcoming similar obstacles in drug and gene delivery. By bridging the gap between cutting-edge technology and clinical application, this article aims to highlight the vital role of nanotechnology in shaping the future of ALS treatment.

3D Printing in Biocatalysis and Biosensing: From General Concepts to Practical Applications

3D printing has matured into a versatile technique that offers researchers many different printing methods and materials with varying properties. Nowadays, 3D printing is deployed within a myriad of different applications, ranging from chemistry to biotechnology -including bioanalytics, biocatalysis or biosensing. Due to its inherent design flexibility (which enables rapid prototyping) and ease of use, 3D printing facilitates the relatively quick and easy creation of new devices with unprecedented functions.. This review article describes how 3D printing can be employed for research in the fields of biochemistry and biotechnology, and specifically for biocatalysis and biosensor applications. We survey different relevant 3D printing techniques, as well as the surface activation and functionalization of 3D-printed materials. Finally, we show how 3D printing is used for the fabrication of reaction ware and enzymatic assays in biocatalysis research, as well as for the generation of biosensors using aptamers, antibodies, and enzymes as recognition elements.

Effect of Gold Nanoparticles on Luminescence Enhancement in Antibodies for TORCH Detection

PURPOSES

To explore the optimization method and application of Au-NP-enhanced luminol--H2O2 luminescence system in TORCH (TOX, RV, CMV, HSVI, and HSVII) detection.

METHOD

4.5 × 10-5 mmol/L gold nano solution was prepared with chloroauric acid as the reducing agent and trisodium citrate as the stabilizer. After curing for 3 days, Au NPs participate in the luminal-H2O2 luminescence system to detect TORCH antibodies and establish the cut off value. SPSS 18.0 software was used to analyze the TORCH antibodies detected by the nano-gold-enhanced luminol luminescence method and TORCH kit. Additionally, its detection performance is studied.

RESULTS

The results of a paired t-test for the absorbance values of samples with and without gold nanoparticles showed that there were statistically significant differences (p < 0.001) between the two methods in the detection of TOX, RV, CMV, HSVI, and HSVII. The luminescence values with the addition of gold nanoparticles were significantly higher than those without gold nanoparticles. Using the Au NP-luminol-H2O2 chemiluminescence method, 127 serum samples were tested for TORCH antibodies. The sensitivities were 84.6%, 83.3%, 90.9%, 85.7%, and 84.6%, while the specificities were 94.7%, 96.5%, 96.6%, 97.3%, and 95.6%, respectively. The sensitivity and specificity of the chemiluminescence method enhanced by gold nanoparticles are significantly improved compared to the chemiluminescence method without enhancers.

CONCLUSIONS

Au NPs participate in the luminal-H2O2 luminescent system. The absorbance, sensitivity, and specificity of TORCH antibodies show that Au NPs can enhance the luminol-H2O2 luminescent system. Au NP-luminol-H2O2 luminescence system has broad application prospects in the detection of eugenics.

Gold Nanoparticles: Multifunctional Properties, Synthesis, and Future Prospects

Gold nanoparticles (NPs) are among the most commonly employed metal NPs in biological applications, with distinctive physicochemical features. Their extraordinary optical properties, stemming from strong localized surface plasmon resonance (LSPR), contribute to the development of novel approaches in the areas of bioimaging, biosensing, and cancer research, especially for photothermal and photodynamic therapy. The ease of functionalization with various ligands provides a novel approach to the precise delivery of these molecules to targeted areas. Gold NPs' ability to transfer heat and electricity positions them as valuable materials for advancing thermal management and electronic systems. Moreover, their inherent characteristics, such as inertness, give rise to the synthesis of novel antibacterial and antioxidant agents as they provide a biocompatible and low-toxicity approach. Chemical and physical synthesis methods are utilized to produce gold NPs. The pursuit of more ecologically sustainable and economically viable large-scale technologies, such as environmentally benign biological processes referred to as green/biological synthesis, has garnered increasing interest among global researchers. Green synthesis methods are more favorable than other synthesis techniques as they minimize the necessity for hazardous chemicals in the reduction process due to their simplicity, cost-effectiveness, energy efficiency, and biocompatibility. This article discusses the importance of gold NPs, their optical, conductivity, antibacterial, antioxidant, and anticancer properties, synthesis methods, contemporary uses, and biosafety, emphasizing the need to understand toxicology principles and green commercialization strategies.

Amyloid-β-targeting immunotherapies for Alzheimer's disease

Recent advances in clinical passive immunotherapy have provided compelling evidence that eliminating amyloid-β (Aβ) slows cognitive decline in Alzheimer's disease (AD). However, the modest benefits and side effects observed in clinical trials indicate that current immunotherapy therapy is not a panacea, highlighting the need for a deeper understanding of AD mechanisms and the significance of early intervention through optimized immunotherapy or immunoprevention. This review focuses on the centrality of Aβ pathology in AD and summarizes recent clinical progress in passive and active immunotherapies targeting Aβ, discussing their lessons and failures to inform future anti-Aβ biotherapeutics design. Various delivery strategies to optimize Aβ-targeting immunotherapies are outlined, highlighting their benefits and drawbacks in overcoming challenges such as poor stability and limited tissue accessibility of anti-Aβ biotherapeutics. Additionally, the perspectives and challenges of immunotherapy and immunoprevention targeting Aβ are concluded in the end, aiming to guide the development of next-generation anti-Aβ immunotherapeutic agents towards improved efficacy and safety.

Development of gold nanoparticle-based lateral-flow strips for NGAL protein detection in urine samples

This study focuses on enhancing the sensitivity of lateral-flow strips (LFSs) based on gold nanoparticles (AuNPs) for the detection of Neutrophil Gelatinase-Associated Lipocalin (NGAL) protein in urine samples. Several sizes of AuNP-based LFS biosensors were tested to optimize colorimetric signals for NGAL detection based on improved conjugation conditions. AuNPs of 39.8 nm diameter at pH 8 were the most sensitive for the detection of NGAL. Through systematic enhancements to the AuNP-based LFS, the study significantly improves the sensitivity, enabling the reliable detection of NGAL protein in urine samples at a level as low as 12.5 ng mL-1. These advances contribute to the refinement of diagnostic tools for the early detection of kidney injury, specifically in cases associated with the presence of NGAL protein, offering a more precise and effective screening approach.

Capped Plasmonic Gold and Silver Nanoparticles with Porphyrins for Potential Use as Anticancer Agents-A Review

Photothermal therapy (PTT) and photodynamic therapy (PDT) are potential cancer treatment methods that are minimally invasive with high specificity for malignant cells. Emerging research has concentrated on the application of metal nanoparticles encapsulated in porphyrin and their derivatives to improve the efficacy of these treatments. Gold and silver nanoparticles have distinct optical properties and biocompatibility, which makes them efficient materials for PDT and PTT. Conjugation of these nanoparticles with porphyrin derivatives increases their light absorption and singlet oxygen generation that create a synergistic effect that increases phototoxicity against cancer cells. Porphyrin encapsulation with gold or silver nanoparticles improves their solubility, stability, and targeted tumor delivery. This paper provides comprehensive review on the design, functionalization, and uses of plasmonic silver and gold nanoparticles in biomedicine and how they can be conjugated with porphyrins for synergistic therapeutic effects. Furthermore, it investigates this dual-modal therapy's potential advantages and disadvantages and offers perspectives for future prospects. The possibility of developing gold, silver, and porphyrin nanotechnology-enabled biomedicine for combination therapy is also examined.

Comparative study of optical fiber immunosensors based on traditional antibody or nanobody for detecting HER2

In this study, we present a novel biomarker detection platform employing a modified S-tapered fiber coated with gold nanoparticle/graphene oxide (GNP/GO) for quantifying human epidermal growth factor receptor-2 (HER2) concentrations, using antibodies as sensing elements. The fabrication of this device involves implementing an in-situ layer-by-layer technique coupled with a chemical adsorption step to achieve the self-assembly of GNP, GO, and antibodies on the STF surface. The detection mechanism relies on monitoring the refractive index changes induced by the adsorption of HER2 onto the immobilized antibodies. For comparative analysis, both monoclonal antibody (mAb) and the novel nanobody (Nb) were employed in constructing the STF immunosensor, referred to as the mAb immunosensor and Nb immunosensor, respectively. Spectral analysis results highlight that the Nb immunosensor exhibits twice the sensitivity of the mAb immunosensor. This enhanced sensitivity is attributed to the small size, high antigen affinity, strong specificity, and structural stability of Nb. The Nb immunosensor demonstrated an impressive detection limit of 0.001 nM for HER2, surpassing the detection limit of the mAb immunosensor. These findings underscore the potential of the proposed Nb immunosensor as a promising and sensitive tool for HER2 detection, contributing to the diagnosis and prognosis of breast cancer. Furthermore, the simplicity of production and excellent optical performance position the Nb immunosensor as a prospective real-time biosensor with minimal cytotoxicity.

Phage tailspike protein coated gold nanoparticles combined with smartphone for rapid bacterial detection and photothermal sterilization

The integration of recognition and therapeutic functions in multifunctional biosensors is of great importance in guaranteeing food security and reducing the occurrence of foodborne illness caused by foodborne pathogens. In this study, a biosensor utilizing a "sense-and-treat" approach was developed by integrating phage tailspike protein (TSP) with gold nanoparticles (AuNPs@TSP). The synthesized AuNPs@TSP showed strong binding affinity towards Salmonella typhimurium causing color changes and exhibited effective bactericidal activity when exposed to near-infrared (NIR) irradiation. This biosensor facilitated rapid colorimetric detection of S. typhimurium in 50 min, with a LOD (limit of detection) of 2.53 × 103 CFU/mL output on a smartphone APP after analyzing the red-green-blue (RGB) values from color rendering results. Furthermore, the biosensor displayed high selectivity, rapid response time, and broad applicability when tested with real samples. Moreover, the biosensor exhibited a remarkably efficient antibacterial efficacy of 100 % against S. typhimurium under 808 nm light irradiation for 6 min. This study provides a comprehensive investigation into the potential utilization of biosensors for rapid detection and eradication of foodborne pathogens in food industry.

Coordination-Driven Templated Synthesis of Hierarchically Porous Zeolitic Imidazolate Frameworks for Cascade Enzyme Cycle Amplification Coupled Immunoassay

Although hierarchically porous zeolitic imidazolate frameworks (HPZIFs) not only inherit the intrinsic architectural and chemical stabilities of their microporous counterparts but also afford open space for the efficient mass diffusion of the macromolecules involved, their rational design and construction are still challenging. Herein, HPZIFs with tailorable pore sizes ranging from 18 to 54 nm were successfully fabricated by using a newly developed soft-template-directed strategy. Our success rooted in the fact that the screened PS81-PVP44-PEO113 triblock copolymer could effectively coordinate with the metal precursor for the directed crystallization of ZIFs along surfactant assemblies. The advantages of continuous large pores and open structures in such HPZIFs were fully taken into account to serve as a bioreactor for the efficient immunoassay. The expanded large pores provided not only a significantly vast surface area to enhance the density of capture antibodies but also enough space for accommodating multiple conjugated biomolecules in one pore channel. In combination with a cascade enzyme cycle amplification strategy, a model biomarker of prostate-specific antigen (PSA) at the femtomolar level was checked with a limit of detection of 92 fM using the developed immunosensor. Specific screening on patients with prostate cancer or even benign prostatic hyperplasia was exemplified through accurately quantifying small changes of PSA concentration in clinical serum samples, prefiguring the great potential of the developed HPZIF-8 immunosensor platform for the early monitoring and diagnostics of diseases.

Rapid and High-Density Antibody Immobilization Using Electropolymerization of Pyrrole for Highly Sensitive Immunoassay

Polypyrrole (Ppy) is a biologically compatible polymer that is used as a matrix, in which drugs and enzymes can be incorporated by doping. Here, we suggest an inventive application of Ppy as a biorecognition film encapsulated with an antibody (Ab) as an alternative strategy for the on-site multistep functionalization of thiol-based self-assembled monolayers. The fabrication steps of the recognition films were followed by dropping pyrrole and Ab mixed solutions onto the electrode and obtaining a thin film by direct current electropolymerization. The efficiency of Ab immobilization was studied by using fluorescence microscopy and electrochemical (EC) methods. Finally, the Ab density was increased and immobilized in 1 min, and the sensing performance as an EC immunosensor was demonstrated using α-fetoprotein with a limit of detection of 3.13 pg/mL and sensing range from 1 pg/mL to 100 ng/mL. This study demonstrates the potential for electrochemical functionalization of biomolecules with high affinity and rapidity.

An Unconventional Immunosensor for Biomolecule Detection via Nonspecific Gold Nanoparticle-Antibody Interactions

Immunogold, that is, gold nanoparticles (AuNPs) conjugated with biomolecules such as antibodies and peptides, have been widely used to construct sandwiched immunosensors for biodetection. Two main challenges in these immunoassays are difficulties in finding and validating a suitable antibody, and the nonspecific interaction between the substrate and immunogold, which lowers the detection sensitivity and even causes false results. To avoid these issues, we took advantage of the nonspecific interaction between AuNPs and capture antibodies and proposed a new sensing mechanism. That is, after the capture of analyte targets by the capture antibodies on the substrate, AuNPs of certain chemical functionality would preferably bind to the free capture antibodies. Consequently, the amount of deposited AuNPs will inversely depend on the concentration of the analytes. As a proof-of-concept, we designed a mass-based sensor where anti-IgG antibodies were coated on a quartz crystal microbalance substrate. After IgG was introduced, tannic acid-capped AuNPs were applied to bind with the free anti-IgG antibody molecules. A frequency change (Δf) of the quartz substrate was induced by the increased mass loading. To further amplify the loading mass, an Ag enhancer solution was added, and Ag growth was catalyzed by the bound AuNPs. The Δf response showed a concentration-dependent decrease when increasing IgG concentration with a detection limit of 2.6 ng/mL. This method relies on the nonspecific interaction between AuNPs and anti-IgG antibodies to realize sensitive detection of IgG and eliminates the use of detection antibodies. The concept is an alternative to many existing immunoassay technologies.

A dual amplified gold nanoparticle-based biosensor for ultrasensitive and selective detection of fibrin

Ultrasensitive, selective, and non-invasive detection of fibrin in human serum is critical for disease diagnosis. So far, the development of high-performance and ultrasensitive biosensors maintains core challenges for biosensing. Herein, we designed a novel ribbon nanoprobe for ultrasensitive detection of fibrin. The probe contains gold nanoparticles (AuNPs) that can not only link with homing peptide Cys-Arg-Glu-Lys-Ala (CREKA) to recognize fibrin but also carry long DNA belts to form G-quadruplex-based DNAzyme, catalyzing the chemiluminescence of luminol-hydrogen peroxide (H2O2) reaction. Combined with the second amplification procedure of rolling circle amplification (RCA), the assay exhibits excellent sensitivity with a detection limit of 0.04 fmol L-1 fibrin based on the 3-sigma. Furthermore, the biosensor shows high specificity on fibrin in samples because the structure of antibody-fibrin-homing peptide was employed to double recognize fibrin. Altogether, the simple and inexpensive approach may present a great potential for reliable detection of biomarkers.

Enhancing biocatalyst performance through immobilization of lipase (Eversa® Transform 2.0) on hybrid amine-epoxy core-shell magnetic nanoparticles

Magnetic nanoparticles were functionalized with polyethylenimine (PEI) and activated with epoxy. This support was used to immobilize Lipase (Eversa® Transform 2.0) (EVS), optimization using the Taguchi method. XRF, SEM, TEM, XRD, FTIR, TGA, and VSM performed the characterizations. The optimal conditions were immobilization yield (I.Y.) of 95.04 ± 0.79 %, time of 15 h, ionic load of 95 mM, protein load of 5 mg/g, and temperature of 25 °C. The maximum loading capacity was 25 mg/g, and its stability in 60 days of storage showed a negligible loss of only 9.53 % of its activity. The biocatalyst demonstrated better stability at varying temperatures than free EVS, maintaining 28 % of its activity at 70 °C. It was feasible to esterify free fatty acids (FFA) from babassu oil with the best reaction of 97.91 % and ten cycles having an efficiency above 50 %. The esterification of produced biolubricant was confirmed by NMR, and it displayed kinematic viscosity and density of 6.052 mm2/s and 0.832 g/cm3, respectively, at 40 °C. The in-silico study showed a binding affinity of -5.8 kcal/mol between EVS and oleic acid, suggesting a stable substrate-lipase combination suitable for esterification.

Flexible nanohybrid substrates utilizing gold nanocubes/nano mica platelets with 3D lightning-rod effect for highly efficient bacterial biosensors based on surface-enhanced Raman scattering

In this study, gold nanocubes (AuNCs) were quickly synthesized using the seed-mediated growth method and reduced onto the surface of two-dimensional (2D) delaminated nano mica platelets (NMPs), enabling the development of AuNCs/NMPs nanohybrids with a 3D lightning-rod effect. First, the growth-solution amount can be changed to easily adjust the AuNCs average-particle size within a range of 30-70 nm. The use of the cationic surfactant cetyltrimethylammonium chloride as a protective agent allowed the surface of AuNCs and nanohybrids to be positively charged. Positively charged nanohybrid surfaces presented a good adsorption effect for detecting molecules with negative charges on the surface. Additionally, the NMP surfaces were rich in ionic charges and provided a large specific surface area for stabilizing the growth of AuNCs. Delaminated AuNCs/NMPs nanohybrids can generate a 3D hotspot effect through self-assembly to enhance the Raman signal. Surface-enhanced Raman scattering (SERS) is highly sensitive in detecting adenine biomolecules. Its limit of detection (LOD) and Raman enhancement factor reached 10-9 M and 3.6 × 108, respectively. Excellent reproducibility was obtained owing to the relatively regular arrangement of AuNC particles, and the relative standard deviation (RSD) was 10.7%. Finally, the surface of NMPs was modified by adding the hydrophilic poly(oxyethylene)-diamine (POE2000) and amphiphilic PIB-POE-PIB copolymer at different weight ratios. The adjustment of the surface hydrophilicity and hydrophobicity of AuNCs/NMPs nanohybrids led to better adsorption and selectivity for bacteria. AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs were further applied to the SERS detection of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli, respectively. The SERS-detection results suggest that the LOD of hydrophilic Staphylococcus aureus and hydrophobic Escherichia coli reached 92 CFU mL-1 and 1.6 × 102 CFU mL-1, respectively. The AuNCs/POE/NMPs and AuNCs/PIB-POE-PIB/NMPs nanohybrids had different hydrophilic-hydrophobic affinities, which greatly improved the selectivity and sensitivity for detecting bacteria with different hydrophilicity and hydrophobicity. Therefore, fast, highly selective, and highly sensitive SERS biological-detection results were obtained.

Development of a Paper-based Hematocrit Test and a Lateral Flow Assay to Detect Critical Fibrinogen Concentrations Using a Bottom-Up Pyramid Workflow Approach

Fibrinogen is a coagulation factor in human blood and the first one to reach critical levels in major bleeding. Hypofibrinogenemia (a too low fibrinogen concentration in blood) poses great challenges to first responders, clinicians, and healthcare providers since it represents a risk factor for exsanguination and massive transfusion requirements. Thus, the rapid assessment of the fibrinogen concentration at the point of care has gained considerable importance in preventing and managing major blood loss. However, in whole blood measurements, hematocrit variations affect the amount (volume fraction) of plasma that passes the detection zone. In an attempt to accurately determine realistic critical levels of fibrinogen (<1.5 mg/mL) in patients needing immediate treatment and medical interventions, we have developed novel diagnostic systems capable of estimating hematocrit and critical fibrinogen concentrations. A lateral flow assay (LFA) for the detection of fibrinogen has been developed by establishing a workflow employing rapid characterization methods to streamline LFA development. The integration of two detection lines enables (i) the identification of fibrinogen (first line) present in the sample and (ii) the determination of the clinically critical fibrinogen concentrations below 1.5 mg/mL (second line). Furthermore, the paper-based separation of blood cells from plasma provides a semiquantitative estimate of the hematocrit by analyzing the fractions. Initial validation of the point-of-care (PoC) hematocrit test revealed good comparability to a standard laboratory method. The developed diagnostic systems have the ability to accelerate decision-making in cases with major bleeding.

Improving Sensitivity and Reproducibility of Surface-Enhanced Raman Scattering Biochips Utilizing Magnetoplasmonic Nanoparticles and Statistical Methods

Surface-enhanced Raman scattering (SERS) technology has been widely recognized for its remarkable sensitivity in biochip development. This study presents a novel sandwich immunoassay that synergizes SERS with magnetoplasmonic nanoparticles (MPNs) to improve sensitivity. By taking advantage of the unique magnetism of these nanoparticles, we further enhance the detection sensitivity of SERS biochips through the applied magnetic field. Despite the high sensitivity, practical applications of SERS biochips are often limited by the issues of stability and reproducibility. In this study, we introduced a straightforward statistical method known as "Gaussian binning", which involves initially binning the two-dimensional Raman mapping data and subsequently applying Gaussian fitting. This approach enables a more consistent and reliable interpretation of data by reducing the variability inherent in Raman signal measurements. Based on our method, the biochip, targeting for C-reactive protein (CRP), achieves an impressive detection limit of 5.96 fg/mL, and with the application of a 3700 G magnetic field, it further enhances the detection limit by 5.7 times, reaching 1.05 fg/mL. Furthermore, this highly sensitive and magnetically tunable SERS biochip is easily designed for versatile adaptability, enabling the detection of other proteins. We believe that this innovation holds promise in enhancing the clinical applicability of SERS biochips.

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

Recent Advances in Metallic Nanostructures-assisted Biosensors for Medical Diagnosis and Therapy

The field of nanotechnology has witnessed remarkable progress in recent years, particularly in its application to medical diagnosis and therapy. Metallic nanostructures-assisted biosensors have emerged as a powerful and versatile platform, offering unprecedented opportunities for sensitive, specific, and minimally invasive diagnostic techniques, as well as innovative therapeutic interventions. These biosensors exploit the molecular interactions occurring between biomolecules, such as antibodies, enzymes, aptamers, or nucleic acids, and metallic surfaces to induce observable alterations in multiple physical attributes, encompassing electrical, optical, colorimetric, and electrochemical signals. These interactions yield measurable data concerning the existence and concentration of particular biomolecules. The inherent characteristics of metal nanostructures, such as conductivity, plasmon resonance, and catalytic activity, serve to amplify both sensitivity and specificity in these biosensors. This review provides an in-depth exploration of the latest advancements in metallic nanostructures-assisted biosensors, highlighting their transformative impact on medical science and envisioning their potential in shaping the future of personalized healthcare.

Methods gold standard in clinic millifluidics multiplexed extended gate field-effect transistor biosensor with gold nanoantennae as signal amplifiers

We present a portable multiplexed biosensor platform based on the extended gate field-effect transistor and demonstrate its amplified response thanks to gold nanoparticle-based bioconjugates introduced as a part of the immunoassay. The platform comprises a disposable chip hosting an array of 32 extended gate electrodes, a readout module based on a single transistor operating in constant charge mode, and a multiplexer to scan sensing electrodes one-by-one. Although employing only off-the-shelf electronic components, our platform achieves sensitivities comparable to fully customized nanofabricated potentiometric sensors. In particular, it reaches a detection limit of 0.2 fM for the pure molecular assay when sensing horseradish peroxidase-linked secondary antibody (∼0.4 nM reached by standard microplate methods). Furthermore, with the gold nanoparticle bioconjugation format, we demonstrate ca. 5-fold amplification of the potentiometric response compared to a pure molecular assay, at the detection limit of 13.3 fM. Finally, we elaborate on the mechanism of this amplification and propose that nanoparticle-mediated disruption of the diffusion barrier layer is the main contributor to the potentiometric signal enhancement. These results show the great potential of our portable, sensitive, and cost-efficient biosensor for multidimensional diagnostics in the clinical and laboratory settings, including e.g., serological tests or pathogen screening.

Ability of Antibodies Immobilized on Gold Nanoparticles to Bind Small Antigen Fluorescein

The analytical applications of antibodies are often associated with their immobilization on different carriers, which is accompanied by a loss of antigen-binding activity for a sufficient proportion of the bound antibodies. In contrast to data on plain carriers, minimal data are available on the properties of antibodies on the surfaces of nanoparticles. Protein antigens have been predominantly investigated, for which space restrictions do not allow them to occupy all active sites of immobilized antibodies. This study considered a low-molecular-weight compound, fluorescein, as an antigen. Spherical gold nanoparticles with five different sizes, two differently charged forms of fluorescein, and three different levels of surface coverage by immobilized antibodies were tested. For gold nanoparticles with diameters from 14 to 35.5 nm with monolayers of immobilized antibodies, the percentage of molecules capable of binding carboxyfluorescein varied from 6% to 17%. The binding of aminofluorescein was more efficient; for gold nanoparticles with an average diameter of 21 nm, the percentage of active binding sites for the immobilized antibodies reached 27% compared with 13% for the carboxyfluorescein case. A fourfold reduction in the coverage of the nanoparticles' surface compared with that of the monolayer did not lead to reliable changes in the percentage of active binding sites. The obtained data demonstrate that an antigen's binding to immobilized antibodies is limited even for small antigens and depends on the size of the nanoparticles and the electrostatic repulsion near their surface.

Characterizing a Silver Nanoparticle-Based Electrochemical Biosensor for Shiga Toxin Detection

Shiga toxins (1, 2) regularly cause outbreaks and food recalls and pose a significant health risk to the infected population. Therefore, new reliable tools are needed to rapidly detect Shiga toxin cost-effectively in food, water, and wastewater before human consumption. Enzyme immunoassay and polymerase chain reaction approaches are the gold standard detection methods for the Shiga toxin. However, these methods require expensive instruments along with expensive reagents, which makes them hard to convert into point-of-use and low-cost systems. This study introduces an electrochemical biosensing method that utilizes silver nanoparticles (AgNPs) as electrochemical tags and commercially available low-cost screen-printed carbon electrodes for detection. This study introduces the modification of reference electrodes on commercially available screen-printed carbon electrodes to detect AgNPs dissolved in nitric acid. This biosensor achieved a 2 ng/mL lowest measured concentration for Shiga toxin-1 in less than 3 h. These biosensor results also showed that the AgNP-based sensor has better linearity (for graph between peak current vs concentration) and lower standard deviation compared to gold nanoparticles (AuNP)-based electrochemical biosensors.

The application of an applied electrical potential to generate electrical fields and forces to enhance affinity biosensors

Affinity biosensors play a crucial role in clinical diagnosis, pharmaceuticals, immunology, and other areas of human health. Affinity biosensors rely on the specific binding between target analytes and biological ligands such as antibodies, nucleic acids, aptamers, or other receptors to primarily generate electrochemical or optical signals. Considerable effort has been put into improving the performance of the affinity technologies to make them more sensitive, efficient and reproducible, of the many approaches electrokinetic phenomena are a viable option. In this perspective, studies that combine electrokinetic phenomena with affinity biosensor are discussed about their promise for achieving higher sensitivity and lower detection limit.

Emerging Applications of Nanobiosensors in Pathogen Detection in Water and Food

Food and waterborne illnesses are still a major concern in health and food safety areas. Every year, almost 0.42 million and 2.2 million deaths related to food and waterborne illness are reported worldwide, respectively. In foodborne pathogens, bacteria such as Salmonella, Shiga-toxin producer Escherichia coli, Campylobacter, and Listeria monocytogenes are considered to be high-concern pathogens. High-concern waterborne pathogens are Vibrio cholerae, leptospirosis, Schistosoma mansoni, and Schistosima japonicum, among others. Despite the major efforts of food and water quality control to monitor the presence of these pathogens of concern in these kinds of sources, foodborne and waterborne illness occurrence is still high globally. For these reasons, the development of novel and faster pathogen-detection methods applicable to real-time surveillance strategies are required. Methods based on biosensor devices have emerged as novel tools for faster detection of food and water pathogens, in contrast to traditional methods that are usually time-consuming and are unsuitable for large-scale monitoring. Biosensor devices can be summarized as devices that use biochemical reactions with a biorecognition section (isolated enzymes, antibodies, tissues, genetic materials, or aptamers) to detect pathogens. In most cases, biosensors are based on the correlation of electrical, thermal, or optical signals in the presence of pathogen biomarkers. The application of nano and molecular technologies allows the identification of pathogens in a faster and high-sensibility manner, at extremely low-pathogen concentrations. In fact, the integration of gold, silver, iron, and magnetic nanoparticles (NP) in biosensors has demonstrated an improvement in their detection functionality. The present review summarizes the principal application of nanomaterials and biosensor-based devices for the detection of pathogens in food and water samples. Additionally, it highlights the improvement of biosensor devices through nanomaterials. Nanomaterials offer unique advantages for pathogen detection. The nanoscale and high specific surface area allows for more effective interaction with pathogenic agents, enhancing the sensitivity and selectivity of the biosensors. Finally, biosensors' capability to functionalize with specific molecules such as antibodies or nucleic acids facilitates the specific detection of the target pathogens.

pH and NaCl Optimisation to Improve the Stability of Gold and Silver Nanoparticles' Anti-Zearalenone Antibody Conjugates for Immunochromatographic Assay

The aim of this research is to define optimal conditions to improve the stability of gold and silver nanoparticles' anti-zearalenone antibody conjugates for their utilisation in lateral flow immunochromatographic assay (LFIA). The Turkevich-Frens method was used to synthesise gold nanoparticles (AuNPs), which were between 10 and 110 nm in diameter. Silver nanoparticles (AgNPs) with a size distribution of 2.5 to 100 nm were synthesised using sodium borohydride as a reducing agent. The onset of AuNP and AgNP aggregation occurred at 150 mM and 80 mM NaCl concentrations, respectively. Stable Au and Ag nanoparticle-antibody conjugates were achieved at 1.2 mM of K2CO3 concentration, which corresponds to the pH value of ≈7. Lastly, the highest degree of conjugation between Au and Ag nanoparticles and anti-zearalenone antibodies was at 4 and 6 µg/mL of antibody concentrations. The optimisation of the conjugation conditions can contribute to better stability of nanoparticles and their antibody conjugate and can improve the reproducibility of results of bioreporter molecules in biosensing lateral flow devices.

Goldilocks Energy Minimum: Peptide-Based Reversible Aggregation and Biosensing

Colorimetric biosensors based on gold nanoparticle (AuNP) aggregation are often challenged by matrix interference in biofluids, poor specificity, and limited utility with clinical samples. Here, we propose a peptide-driven nanoscale disassembly approach, where AuNP aggregates induced by electrostatic attractions are dissociated in response to proteolytic cleavage. Initially, citrate-coated AuNPs were assembled via a short cationic peptide (RRK) and characterized by experiments and simulations. The dissociation peptides were then used to reversibly dissociate the AuNP aggregates as a function of target protease detection, i.e., main protease (Mpro), a biomarker for severe acute respiratory syndrome coronavirus 2. The dissociation propensity depends on peptide length, hydrophilicity, charge, and ligand architecture. Finally, our dissociation strategy provides a rapid and distinct optical signal through Mpro cleavage with a detection limit of 12.3 nM in saliva. Our dissociation peptide effectively dissociates plasmonic assemblies in diverse matrices including 100% human saliva, urine, plasma, and seawater, as well as other types of plasmonic nanoparticles such as silver. Our peptide-enabled dissociation platform provides a simple, matrix-insensitive, and versatile method for protease sensing.

MnO2 nanosheets and gold nanoparticles supported electrochemical detection of circulating tumor cells

The concentration of circulating tumor cells (CTCs) in peripheral blood is strongly correlated with the progress of certain metastatic cancers. In this study, we have developed a novel and facile electrochemical biosensor for the detection of CTCs based on the use of manganese dioxide nanosheets (MnO2 NSs) and gold nanoparticles (AuNPs). Aptamer sequence of target cell is modified on the surface of AuNPs for specifical recognition. With low-speed centrifugation, numerous AuNPs@DNA can be removed from the supernatant. On the other hand, MnO2 NSs are modified on the electrode surface to capture unreacted AuNPs@DNA. The declined electrochemical signal intensity can be used to reflect the level of CTCs. This biosensor achieves a wide linear range from 10 to 104 cells mL-1 and a limit of detection as low as 3 cells mL-1. Due to the specific aptamer as the recognition element, interfering cells can be successfully distinguished and this method performs satisfactorily in clinical samples. Therefore, it has great potential to be used as a powerful tool benefiting rare cells analysis and the investigation of dynamics of cellular interactions.

Coiled-Coil-Based Biofunctionalization of 100 nm Gold Nanoparticles with the Trastuzumab Antibody for the Detection of HER2-Positive Cancer Cells

We compared different biofunctionalization strategies for immobilizing trastuzumab, an IgG targeting the HER2 biomarker, onto 100 nm spherical gold nanoparticles because of the E/K coiled-coil peptide heterodimer. First, Kcoil peptides were grafted onto the gold surface while their Ecoil partners were genetically encoded at the C-terminus of trastuzumab's Fc region, allowing for a strong and specific interaction between the antibodies and the nanoparticles. Gold nanoparticles with no Kcoil peptides on their surface were also produced to immobilize Ecoil-tagged trastuzumab antibodies via the specific adsorption of their negatively charged Ecoil tags on the positively charged gold surface. Finally, the nonspecific adsorption of wild-type trastuzumab on the gold surface was also assessed, with and without Kcoil peptides grafted on it beforehand. We developed a thorough workflow to systematically compare the immobilization strategies regarding the stability of nanoparticles, antibody coverage, and ability to specifically bind to HER2-positive breast cancer cells. All nanoparticles were highly monodisperse and retained their localized surface plasmon resonance properties after biofunctionalization. A significant increase in the amount of immobilized antibodies was observed with the two oriented coil-based strategies compared to nonspecific adsorption. Finally, all biofunctionalization strategies allowed for the detection of HER2-positive breast cancer cells, but among the investigated approaches, we recommend using the E/K coiled-coil-based strategy for gold nanoparticle biofunctionalization because it allows for the qualitative and quantitative detection of HER2-positive cells with a higher contrast compared to HER2-negative cells.

Antibacterial Activity of PVA Hydrogels Embedding Oxide Nanostructures Sensitized by Noble Metals and Ruthenium Dye

Nanostructured oxides (SiO2, TiO2) were synthesized using the sol-gel method and modified with noble metal nanoparticles (Pt, Au) and ruthenium dye to enhance light harvesting and promote the photogeneration of reactive oxygen species, namely singlet oxygen (1O2) and hydroxyl radical (•OH). The resulting nanostructures were embedded in a transparent polyvinyl alcohol (PVA) hydrogel. Morphological and structural characterization of the bare and modified oxides was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Additionally, electrokinetic potential measurements were conducted. Crystallinity data and elemental analysis of the investigated systems were obtained through X-ray diffraction and X-ray fluorescence analyses, while the chemical state of the elements was determined using XPS. The engineered materials, both as simple powders and embedded in the hydrogel, were evaluated for their ability to generate reactive oxygen species (ROS) under visible and simulated solar light irradiation to establish a correlation with their antibacterial activity against Staphylococcus aureus. The generation of singlet oxygen (1O2) by the samples under visible light exposure can be of significant importance for their potential use in biomedical applications.

Development of Nanobody-Displayed Whole-Cell Biosensors for the Colorimetric Detection of SARS-CoV-2

The accurate and effective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential to preventing the spread of infectious diseases and ensuring human health. Herein, a nanobody-displayed whole-cell biosensor was developed for colorimetric detection of SARS-CoV-2 spike proteins. Serving as bioreceptors, yeast surfaces were genetically engineered to display SARS-CoV-2 binding of llama-derived single-domain antibodies (nanobodies) with high capture efficiency, facilitating the concentration and purification of SARS-CoV-2. Gold nanoparticles (AuNPs) employed as signal transductions were functionalized with horseradish peroxidase (HRP) and anti-SARS monoclonal antibodies to enhance the detection sensitivity. In the presence of SARS-CoV-2 spike proteins, the sandwiched binding will be formed by linking engineered yeast, SARS-CoV-2 spike proteins, and reporter AuNPs. The colorimetric signal was generated by the enzymatic reaction of HRP and its corresponding colorimetric substrate/chromogen system. At the optimal conditions, the developed whole-cell biosensor enables the sensitive detection of SARS-CoV-2 spike proteins in a linear range from 0.01 to 1 μg/mL with a limit of detection (LOD) of 0.037 μg/mL (about 4 × 108 virion particles/mL). Furthermore, the whole-cell biosensor was demonstrated to detect the spike protein of different SARS-CoV-2 variants in human serum, providing new possibilities for the detection of future SARS-CoV-2 variants.

Temperature-Derived Purification of Gold Nano-Bipyramids for Colorimetric Detection of Tannic Acid

Gold nanostructures have attracted broad attention. Among various nanostructures, gold nanobipyramids have shown great potential in sensing, biomedicine, environmental protection, chemical catalysis, and optics due to their unique physical and optical properties and ease of chemical functionalization. Compared with other plasmonic nanostructures, gold nanobipyramids possess narrow optical resonances, stronger plasmonic local field enhancement, and size- and shape-dependent surface plasmon resonance. However, the synthesis and purification of homogeneous gold nanobipyramids are very challenging. The gold nanobipyramids synthesized via the commonly used seed-mediated growth method have low yields and are often coproduced with spherical nanoparticles. In this study, we reported a temperature-derived purification method for the isolation of gold bipyramids. In the presence of salt, by altering the temperature of the solution, large gold bipyramids can be separated from small spherical nanoparticles. As a result, a yield of as high as 97% gold nanobipyramids can be achieved through a single round of purification, and correspondingly, the ratio between the longitudinal surface plasmon resonance (LSPR) and transverse SPR intensity significantly increases to as high as 6.7. The purified gold nanobipyramids can be used as a colorimetric probe in the detection of tannic acid with a detection limit of 0.86 μM and a linear detection range from 1.25 to 37.5 μM.

A stable physisorbed layer of packed capture antibodies for high-performance sensing applications

Antibody physisorption at a solid interface is a very interesting phenomenon that has important effects on applications such as the development of novel biomaterials and the rational design and fabrication of high-performance biosensors. The strategy selected to immobilize biorecognition elements can determine the performance level of a device and one of the simplest approaches is physical adsorption, which is cost-effective, fast, and compatible with printing techniques as well as with green-chemistry processes. Despite its huge advantages, physisorption is very seldom adopted, as there is an ingrained belief that it does not lead to high performance because of its lack of uniformity and long-term stability, which, however, have never been systematically investigated, particularly for bilayers of capture antibodies. Herein, the homogeneity and stability of an antibody layer against SARS-CoV-2-Spike1 (S1) protein physisorbed onto a gold surface have been investigated by means of multi-parametric surface plasmon resonance (MP-SPR). A surface coverage density of capture antibodies as high as (1.50 ± 0.06) × 10¹² molecules per cm^-2 is measured, corresponding to a thickness of 12 ± 1 nm. This value is compatible with a single monolayer of homogeneously deposited antibodies. The effect of the ionic strength (i_s) of the antibody solution in controlling physisorption of the protein was thoroughly investigated, demonstrating an enhancement in surface coverage at lower ionic strength. An atomic force microscopy (AFM) investigation shows a globular structure attributed to i_s-related aggregations of antibodies. The long-term stability over two weeks of the physisorbed proteins was also assessed. High-performance sensing was proven by evaluating figures of merit, such as the limit of detection (2 nM) and the selectivity ratio between a negative control and the sensing experiment (0.04), which is the best reported performance for an SPR S1 protein assay. These figures of merit outmatch those measured with more sophisticated biofunctionalization procedures involving chemical bonding of the capture antibodies to the gold surface. The present study opens up interesting new pathways toward the achievement of a cost-effective and scalable biofunctionalization protocol, which could guarantee the prolonged stability of the biolayer and easy handling of the biosensing system.

Lateral flow immunoassays for antigens, antibodies and haptens detection

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

Application of Shear Horizontal Surface Acoustic Wave (SH-SAW) Immunosensor in Point-of-Care Diagnosis

Point-of-care testing (POCT), also known as on-site or near-patient testing, has been exploding in the last 20 years. A favorable POCT device requires minimal sample handling (e.g., finger-prick samples, but plasma for analysis), minimal sample volume (e.g., one drop of blood), and very fast results. Shear horizontal surface acoustic wave (SH-SAW) biosensors have attracted a lot of attention as one of the effective solutions to complete whole blood measurements in less than 3 min, while providing a low-cost and small-sized device. This review provides an overview of the SH-SAW biosensor system that has been successfully commercialized for medical use. Three unique features of the system are a disposable test cartridge with an SH-SAW sensor chip, a mass-produced bio-coating, and a palm-sized reader. This paper first discusses the characteristics and performance of the SH-SAW sensor system. Subsequently, the method of cross-linking biomaterials and the analysis of SH-SAW real-time signals are investigated, and the detection range and detection limit are presented.

A Direct Immunoassay Based on Surface-Enhanced Spectroscopy Using AuNP/PS-b-P2VP Nanocomposites

A biosensor was developed for directly detecting human immunoglobulin G (IgG) and adenosine triphosphate (ATP) based on stable and reproducible gold nanoparticles/polystyrene-b-poly(2-vinylpyridine) (AuNP/PS-b-P2VP) nanocomposites. The substrates were functionalized with carboxylic acid groups for the covalent binding of anti-IgG and anti-ATP and the detection of IgG and ATP (1 to 150 μg/mL). SEM images of the nanocomposite show 17 ± 2 nm AuNP clusters adsorbed over a continuous porous PS-b-P2VP thin film. UV–VIS and SERS were used to characterize each step of the substrate functionalization and the specific interaction between anti-IgG and the targeted IgG analyte. The UV–VIS results show a redshift of the LSPR band as the AuNP surface was functionalized and SERS measurements showed consistent changes in the spectral features. Principal component analysis (PCA) was used to discriminate between samples before and after the affinity tests. Moreover, the designed biosensor proved to be sensitive to different concentrations of IgG with a limit-of-detection (LOD) down to 1 μg/mL. Moreover, the selectivity to IgG was confirmed using standard solutions of IgM as a control. Finally, ATP direct immunoassay (LOD = 1 μg/mL) has demonstrated that this nanocomposite platform can be used to detect different types of biomolecules after proper functionalization.